Alternate partial root-zone drip fertigation (ADF) is a combination of alternating irrigation and drip fertigation,with the potential to save water and increase nitrogen (N) fertilizer efficiency.A 2-year greenhouse e...Alternate partial root-zone drip fertigation (ADF) is a combination of alternating irrigation and drip fertigation,with the potential to save water and increase nitrogen (N) fertilizer efficiency.A 2-year greenhouse experiment was conducted to evaluate the effect of different fertigation frequencies on the distribution of soil moisture and nutrients and tomato yield under ADF.The treatments included three ADF frequencies with intervals of 3 days (F3),6 days (F6) and 12 days (F12),and conventional drip fertigation as a control (CK),which was fertilized once every 6 days.For the ADF treatments,two drip tapes were placed 10 cm away on each side of the tomato row,and alternate drip irrigation was realized using a manual valve on the distribution tapes.For the CK treatment,a drip tape was located close to the roots of the tomato plants.The total N application rate of all treatments was 180 kg ha^(-1).The total irrigation amounts applied to the CK treatment were450.6 and 446.1 mm in 2019 and 2020,respectively;and the irrigation amounts applied to the ADF treatments were 60%of those of the CK treatment.The F3 treatment resulted in water and N being distributed mainly in the 0–40-cm soil layer with less water and N being distributed in the 40–60-cm soil layer.The F6 treatment led to 21.0 and 29.0%higher 2-year average concentration of mineral N in the 0–20 and 20–40-cm soil layer,respectively and a 23.0%lower N concentration in the 40–60-cm soil layer than in the CK treatment.The 2-year average tomato yields of the F3,F6,F12,and CK treatments were 107.5,102.6,87.2,and 98.7 t ha^(-1),respectively.The tomato yield of F3 was significantly higher (23.3%) than that in the F12 treatment,whereas there was no significant difference between the F3 and F6 treatment.The F6 treatment resulted in yield similar to the CK treatment,indicating that ADF could maintain tomato yield with a 40%saving in water use.Based on the distribution of water and N,and tomato yield,a fertigation frequency of 6 days under ADF should be considered as a water-saving strategy for greenhouse tomato production.展开更多
Determining soil N mineralization response to soil temperature and moisture changes is challenging in the field due to complicated effects from other factors. In the laboratory, N mineralization is highly dependent on...Determining soil N mineralization response to soil temperature and moisture changes is challenging in the field due to complicated effects from other factors. In the laboratory, N mineralization is highly dependent on temperature, moisture and sample size. In this study, a laboratory incubation experiment was carefully designed and conducted under controlled conditions to examine the effects of soil temperature and moisture on soil N mineralization using soil samples obtained from the Stipa krylovii grassland in Inner Mongolia, China. Five temperature(i.e. 9℃, 14℃, 22℃, 30℃ and 40℃) and five moisture levels(i.e. 20%, 40%, 60%, 80% and 100% WHC, where WHC is the soil water holding capacity) were included in a full-factorial design. During the 71-day incubation period, microbial biomass carbon(MBC), ammonium nitrogen(NH4 ^+-N) and nitrate nitrogen(NO3^--N) were measured approximately every 18 days; soil basal respiration for qCO2 index was measured once every 2 days(once a week near the end of the incubation period). The results showed that the mineral N production and net N mineralization rates were positively correlated with temperature; the strongest correlation was observed for temperatures between 30℃ and 40℃. The relationships between moisture levels and both the mineral N production and net N mineralization rates were quadratic. The interaction between soil temperature and moisture was significant on N mineralization, i.e. increasing temperatures(moisture) enhanced the sensitivity of N mineralization to moisture(temperature). Our results also showed a positive correlation between the net nitrification rate and temperature, while the correlation between the NH4 ^+-N content and temperature was insignificant. The net nitrification rate was negatively correlated with high NH4 ^+-N contents at 80%–100% WHC, suggesting an active denitrification in moist conditions. Moreover, qCO2 index was positively correlated with temperature, especially at 80% WHC. With a low net nitrification rate and high soil basal respiration rate, it was likely that the denitrification concealed the microbial gross mineralization activity; therefore, active soil N mineralization occurred in 60%–80% WHC conditions.展开更多
The increasing demand for fresh sweet maize (Zea mays L. saccharata) in southern China has prioritized the need to find solutions to the environmental pollution caused by its continuous production and high inputs of...The increasing demand for fresh sweet maize (Zea mays L. saccharata) in southern China has prioritized the need to find solutions to the environmental pollution caused by its continuous production and high inputs of chemical nitrogen fertilizers. A promising method for improving crop production and environmental conditions is to intercrop sweet maize with legumes. Here, a three-year field experiment was conducted to assess the influence of four different cropping systems (sole sweet maize (SS), sole soybean (SB), two rows sweet maize-three rows soybean (S2B3) intercropping, and two rows sweet maize-four rows soybean (S2B4) intercropping), together with two rates of N fertilizer application (300 and 360 kg N ha-1) on grain yield, residual soil mineral N, and soil N2O emissions in southern China. Results showed that in most case, inter- cropping achieved yield advantages (total land equivalent ratio (TLER=0.87-1.25) was above one). Moreover, intercropping resulted in 39.8% less soil mineral N than SS at the time of crop harvest, averaged over six seasons (spring and autumn in each of the three years of the field experiment). Generally, intercropping and reduced-N application (300 kg N ha-1) produced lower cumulative soil N20 and yield-scaled soil N20 emissions than SS and conventionaI-N application (360 kg N ha-l), respectively. $2B4 intercropping with reduced-N rate (300 kg N ha-~) showed the lowest cumulative soil N20 (mean value=0.61 kg ha-1) and yield-scaled soil N20 (mean value=0.04 kg t-1) emissions. Overall, intercropping with reduced-N rate maintained sweet maize production, while also reducing environmental impacts. The system of S2B4 intercropping with reduced-N rate may be the most sustainable and environmentally friendly cropping system.展开更多
We investigated the effect of forest thinning on soil nitrogen mineralization, nitrification and transformation in a Cryptomeria japoni-ca plantation at high elevation to provide basic data for forest manage-ment. We ...We investigated the effect of forest thinning on soil nitrogen mineralization, nitrification and transformation in a Cryptomeria japoni-ca plantation at high elevation to provide basic data for forest manage-ment. We chose four study plots for control, light, medium and heavy thinning treatment, and three sub-plots for buried bag studies at similar elevations in each treatment plot to measure the net N mineralization and nitrification rates in situ. The contents of soil inorganic N (ammonium and nitrate) were similar between treatments, but all varied with season, reaching maxima in September 2003 and 2004. The seasonal maximum net Nmin rates after four treatments were 0.182, 0.246, 0.303 and 0.560 mg?kg-1?d-1 in 2003, and 0.242,0.258,0.411 and 0.671 mg?kg-1?d-1in 2004, respectively. These estimates are approximate with the lower annual rates of N mineralization for this region. Forest thinning can enhance net N mineralization and microbial biomass carbon. The percentage of annual rates of Nmin for different levels of forest thinning compared with the control plot were 13.4%, 59.8%and 154.2%in 2003, and 0.1%, 58.8%and 157.7%in 2004 for light, medium, and heavy thinning, respectively. These differences were related to soil moisture, temperature, precipita-tion, and soil and vegetation types. Well-planned multi-site comparisons, both located within Taiwan and the East-Asia region, could greatly im-prove our knowledge of regional patterns in nitrogen cycling.展开更多
Forest soil carbon (C) is an important compo- nent of the global C cycle. However, the mechanism by which tree species influence soil organic C (SOC) pool composition and mineralization is poorly understood. To un...Forest soil carbon (C) is an important compo- nent of the global C cycle. However, the mechanism by which tree species influence soil organic C (SOC) pool composition and mineralization is poorly understood. To understand the effect of tree species on soil C cycling, we assessed total, labile, and recalcitrant SOC pools, SOC chemical composition by 13C nuclear magnetic resonance spectroscopy, and SOC mineralization in four monoculture plantations. Labile and recalcitrant SOC pools in surface (0-10 cm) and deep (40-60 cm) soils in the four forests contained similar content. In contrast, these SOC pools exhibited differences in the subsurface soil (from 10 to 20 cm and from 20 to 40 cm). The alkyl C and O-alkyl C intensities of SOC were higher in Schima superba and Michelia macclurei forests than in Cunninghamia lanceolata and Pinus massoniana forests. In surface soil, S. superba and M. macclurei forests exhibited higher SOC mineralization rates than did P. massoniana and C.lanceolata forests. The slope of the straight line between C60 and labile SOC was steeper than that between C60 and total SOC. Our results suggest that roots affected the composition of SOC pools. Labile SOC pools also affected SOC mineralization to a greater extent than total SOC pools.展开更多
In order to understand the effects of increasing atmospheric nitrogen (N) deposition on the subtropical bamboo ecosystem, a nearly six-year field experiment was conducted in a Pleioblastus amarus plantation in the r...In order to understand the effects of increasing atmospheric nitrogen (N) deposition on the subtropical bamboo ecosystem, a nearly six-year field experiment was conducted in a Pleioblastus amarus plantation in the rainy region of SW China, near the western edge of Sichuan Basin. Four N treatment levels---control (no N added), low- N (50 kg N ha-1 a-l), medium-N (150 kg N ha-1 a-l), and high-N (300 kg N ha-1 a-1)--were applied monthly in the P. amarus plantation starting in November 2007. In June 2012, we collected intact soil cores in the bamboo plantation and conducted a 30-day laboratory incubation experiment. The results showed that the soil N net miner- alization rate was 0.96 4- 0.10 mg N kg-1 day-1, under control treatment. N additions stimulated the soil N net mineralization, and the high-N treatment significantly increased the soil N net mineralization rate compared with the control. Moreover, the soil N net mineralization rate was significantly and positively correlated with the fine root biomass, the soil microbial biomass nitrogen content and the soil initial inorganic N content, respectively,whereas it was negatively correlated with the soil pH value. There were no significant relationships between the soil N net mineralization rate and the soil total nitrogen (TN) content and the soil total organic carbon content and the soil C/N ratio and the soil microbial biomass carbon con- tent, respectively. These results suggest that N additions would improve the mineral N availability in the topsoil of the P. amarus plantation through the effects of N additions on soil chemical and physical characteristics and fine-root biomass.展开更多
The fluxes of masses and the nutrients Ca,Mg,K,N,P and S were determined in the litterfall of two adjacent forest ecosystems of Hungarian oak(Quercus frainetto L.)and European beech(Fagus sylvatica L.)in a mountainous...The fluxes of masses and the nutrients Ca,Mg,K,N,P and S were determined in the litterfall of two adjacent forest ecosystems of Hungarian oak(Quercus frainetto L.)and European beech(Fagus sylvatica L.)in a mountainous area of northeastern Greece in 2010–2015.The foliar litterfall for both species reached about 70%of the total litterfall,and was significantly higher from the other two fractions(woody and rest litterfall).The fluxes of masses and nutrients were compared between ecosystems for each fraction separately.Only one significant statistical difference was found,that of K in the woody litterfall.In addition,the stocks of masses and nutrients were calculated in the forest floors and mineral soils of the two ecosystems.Likewise,the stocks of nutrients in the forest floors and mineral soils were compared between ecosystems.In the L horizon of the forest floors,statistical differences,as a result of species effect,were found for the stocks of Ca and N.In the FH horizons,the masses and all the nutrient stocks differed significantly,as the beech plot had much higher quantities of organic matter and nutrients.These higher quantities were probably due to low soil temperatures(microclimate)and high acidity in the beech plot(species effect)that slowed down decomposition.In the mineral soils,the propagation of random error derived from random errors of the individual soil layers was an important factor in the statistical comparisons.Because of the soil acidity in the beech plot,the stocks of exchangeable base cations were significantly higher in the oak plot,whereas the other nutrient stocks did not differ.展开更多
[Objectives]This study was conducted to understand the process of soil nitrogen mineralization in Eucalyptus plantations,and to identify the characteristics of soil nitrogen mineralization with different litter inputs...[Objectives]This study was conducted to understand the process of soil nitrogen mineralization in Eucalyptus plantations,and to identify the characteristics of soil nitrogen mineralization with different litter inputs.[Methods]With the soil of the Eucalyptus plantation in Fusui County,Guangxi as the research object,the soil nitrogen mineralization of the Eucalyptus plantation under different litter treatments(removing litter,adding litter and retaining litter)was studied by PVC tube closed-top in-situ incubation.[Results]①After 1 year of litter treatment,the inorganic nitrogen(NH_(4)^(+)-N+NO_(3)^(-)-N)in the soil of different treatments ranked as adding litter(20.15 mg/kg)>retaining litter(16.02 mg/kg)>removing litter(11.60) mg/kg),and the differences reached a significant level(P<0.05).②After 30 d of in-situ incubation,there were significant differences in soil nitrate nitrogen content before and after incubation in the three treatments(removing litter,adding litter,and retaining litter)before and after incubation(P<0.05),but no significant differences were observed in soil ammonium nitrogen content(P>0.05).Soil nitrate nitrogen contents increased from 1.47,2.01 and 1.72 mg/kg before incubation to 3.66,6.73 and 5.02 mg/kg,respectively,and soil ammonium nitrogen content increased from 11.60,20.15 and 16.02 mg/kg before incubation to 13.65,21.54 and 17.18 mg/kg,respectively.The net nitrogen mineralization quantities of the three treatments were 4.24,6.11 and 4.46 mg/kg,respectively,and the net nitrogen mineralization rates from large to small were adding litter[0.180 mg/(kg·d)]>retaining litter[0.141 mg/(kg·d)]>removing litter[0.125 mg/(kg·d)].Therefore,both removal and addition of litter affected the soil nitrogen input and nitrogen mineralization rate of the Eucalyptus plantation,thereby affecting soil nitrogen availability and the ability of soil to maintain plant-available nitrogen.[Conclusions]This study provides a theoretical basis for nutrient management in Eucalyptus plantations,especially nitrogen nutrient management.展开更多
Soil N transformations using the polyvinyl chloride (PVC) closed-top tube in situ incubation method were studied in Nanchang urban forests of the mid-subtropical region of China in different months of 2007. Four plo...Soil N transformations using the polyvinyl chloride (PVC) closed-top tube in situ incubation method were studied in Nanchang urban forests of the mid-subtropical region of China in different months of 2007. Four plots of 20 m × 20 m were established in four different plant communities that represented typical successional stages of forest development including shrubs, coniferous forest, mixed forest and broad- leaved forest. Average concentrations of soil NH4^+-N from January to December were not different among the four plant communities. The concentrations of soil NO3^--N and mineral N, and the annual rotes of ammonification, nitrification and net N-mineralization under the early successional shrub community and coniferous forest were generally lower than that of the late successional mixed and broad-leaved forests (p〈0.05). Similar differences among the plant communities were also shown in the relative nitrification index (NH4^+-N/NO3^--N) and relative nitrification intensity (nitrification rate/net N-mineralization rate). The annual net N-mineralization rate was increased from younger to older plant communities, from 15.1 and 41.4 kg.ha^-1.a^-1 under the shrubs and coniferous forest communities to 98.0 and 112.9 kg.ha^-1.a^-1 under the mixed and broad-leaved forests, respectively. Moreover, the high annual nitrification rates (50-70 kg.ha^-1.a^-1) and its end product, NO3-N (2.4-3.8 mg·kg^-1), under older plant communities could increase the potential risk of N loss. Additionally, the temporal patterns of the different soil N variables mentioned above varied with different plant community due to the combined affects of natural biological processes associated with forest maturation and urbanization. Our results indicated that urban forests are moving towards a state of"N saturation" (extremely niUification rate and NO3^--N content) as they mature.展开更多
Soil organic carbon (SOC) retaining capacities of epipedon (EP), subsoil (SS) and soil cover (SC) as a whole, are soil type specific. Depending on individual and sites characteristics, the generalized humus status ind...Soil organic carbon (SOC) retaining capacities of epipedon (EP), subsoil (SS) and soil cover (SC) as a whole, are soil type specific. Depending on individual and sites characteristics, the generalized humus status indices of soil types (EP and SC thickness and SOC stocks) may vary. Land use and land use change primarily influence the properties and fabric of the EP, but the humus status (SOC concentration and stock, fabric of horizons) of the SS remains practically unchangeable. The mean mineral soils SOC stocks, EP quality and SOC distribution in soil profiles depend mainly on the water regime, mineral composition (texture, calcareousness), development of eluvial processes and the land use peculiarities of soils. The mean area weighted SC SOC stock of Estonian mineral soils is 99.9 Mg ha–1, thereby the mean hydromorphic soils SOC retention capacity considerably exceeds the SOC retention capacity of automorphic soils (means are accordingly 127.5 and 78.9 Mg ha–1). The sustainable management of SOC is based on adequate information about actual SOC stocks and theoretically established or optimal humus status levels of soil types. The aggregate of SOC retained in the mineral soils of Estonia (3,235,100 ha) amounts to 323 ± 46 Tg (1 Tg = 1012 g). Approximately 42% of this is sequestered into stabilized humus, 40% into instable raw-humous material and 18% into forest (grassland) floor and shallow peat layers.展开更多
The potassium-releasing characteristics of a bacterium from different minerals were studied through pure culture and soil column experiments. The results showed that the strain NBT of tested strains had the highest po...The potassium-releasing characteristics of a bacterium from different minerals were studied through pure culture and soil column experiments. The results showed that the strain NBT of tested strains had the highest potassium-releasing capacity. It released 35.2 mg/L after 7days of pure culture incubation at 28@, 31.8% - 1203.7% more than other tested strains. Potassium released from the minerals was obviously affected by pH, aerobic condition, soil and mineral properties. The strain NBT had a much higher potential to release potassium in the pH 6.5-8.0 than other pHs. Living cell inoculation resulted in an increase of 84.8% -127.9% compared with that of the dead cell inoculation. More aerobic condition produced more K than a less aerobic one. The potassium-releasing order was as follows: illite>feldspar>muscovite. Soil column experiment showed that the bacterial number increased from (2.6 - 3.0) × 106/g to (6.8 - 7.4) × 107/g. Soil available potassium content increased by 31.2 - 33.6mg/kg in yellow-brown soil and 21.7mg/kg in paddy soil, when inoculated with the strain NBT, 290.6% and 185.5% increment of the dead cell inoculation soils respectively.展开更多
The Brazil nut tree(Bertholletia excelsa) is a frequent component of agroforestry systems in the Amazon because of its adaptation to nutrient-poor upland soils and multiple uses.We investigated the aboveground bioma...The Brazil nut tree(Bertholletia excelsa) is a frequent component of agroforestry systems in the Amazon because of its adaptation to nutrient-poor upland soils and multiple uses.We investigated the aboveground biomass production(kg dry weight),nutrient uptake and requirements(N,P,Ca,Mg,K) of Brazil nut trees of different sizes grown under agroforestry conditions and fertilized at different levels.Eight of 70 experimental trees with different size were harvested and stem,branches and leaves were separated.Nutrient contents were determined for three trees of varying size.Average tree growth was fast,but variability was high,suggesting considerable potential for the improvement of this economically important species.The trees responded to increased levels of fertilizer and lime with significantly increased foliar nutrient contents and growth,probably because of the improved availability of Mg and Ca for which the species seems to have a relatively high demand.In contrast to Brazil nut trees grown in forest or dense plantations,the agroforestry trees invested a substantial part of their biomass and nutrients in large branches and developed spreading crowns.To improve stem form,reduce competition with associated crops for light and recycle nutrients,regular pruning of lower branches or planting arrangements that favor self-pruning are recommended.These measures would also increase the recycling of Ca and Mg,large quantities of which are contained in the branches.展开更多
Field surveys indicate lateral variation in peat humification levels (von Post) in dominantly occurring fibric,fibric to hemic,sapric and hemie to sapric peats across a gradient from the margin towards the centre of...Field surveys indicate lateral variation in peat humification levels (von Post) in dominantly occurring fibric,fibric to hemic,sapric and hemie to sapric peats across a gradient from the margin towards the centre of tropical lowland peat domes.Cement-peat stabilisation can be enhanced by adding mineral soil fillers (silt,clays and fine sands) obtained from Quaternary floodplain deposits and residual soil (weathered schist).The unconfined compressive strength (UCS) of the stabilised cement-mineral soil fifler-peat mix increases with the increased addition of selected mineral soil filler.Lateral variation in the stabilised peat strength (UCS) in the top 0 to 0.5 m layer was found from the margin towards the centre of the tropical lowland peat dome.The variations in the UCS of stabilised tropical lowland peats along a gradient from the periphery towards the centre of the peat dome are most likely caused by a combination of factors due to variations in the mineral soil or ash content of the peat and horizontal zonation or lateral variation in the dominant species of the plant assemblages (due to successive vegetation zonation of the peat swamp forest from the periphery towards the centre of the tropical lowland peat dome).展开更多
Production of cut flowers is very prevalent in Iran. Carnation is most famous for its use as a cut flower. This study was carried out in the research greenhouse of Islamic Azad University, Isfahan (Khorasgan) Branch, ...Production of cut flowers is very prevalent in Iran. Carnation is most famous for its use as a cut flower. This study was carried out in the research greenhouse of Islamic Azad University, Isfahan (Khorasgan) Branch, to explore the effect of different growing media on some vegetative and reproductive traits of carnation. The experimental design was randomized complete, using 50% perlite and different growing media including: mineral soil and coco peat in 6 proportions (50% coco peat, 10% soil + 40% coco peat, 20% soil + 30% coco peat, 30% soil + 20% coco peat, 40% soil + 10% coco peat, 50% soil). During growth period, irrigation rate, humidity and temperature were similar. The growth characteristics of carnation were determined at the end of growth period. The results indicated that although there were no significant differences between studied growing substrates in chlorophyll a, b. Statistical analysis showed fresh weight of flower was far greater in coco peat 10% + soil 40% and soil 50% compared to other growing media. Fresh and dry weight of root and shoot in soil 50% were higher than other growing media. The results showed that highest concentration of Fe and Zn was observed in coco peat 40% + soil 10%. The concentration of Mn in coco peat 10% + soil 40% was higher than other growing media. The results showed that the highest Ca concentration was observed in soil 50% and the lowest concentration of this element was obtained in coco peat 50%. According to the obtained results, mineral soil can be used as a suitable alternative to cocopeat for cultivation and growth of carnation in greenhouse.展开更多
Soil nitrogen mineralization(Nmin)is a key process that converts organic N into mineral N that controls soil N availability to plants.However,regional assessments of soil Nmin in cropland and its affecting factors are...Soil nitrogen mineralization(Nmin)is a key process that converts organic N into mineral N that controls soil N availability to plants.However,regional assessments of soil Nmin in cropland and its affecting factors are lacking,especially in relation to variation in elevation.In this study,a 4-week incubation experiment was implemented to measure net soil Nmin rate,gross nitrification(Nit)rate and corresponding soil abiotic properties in five field soils(A-C,maize;D,flue-cured tobacco;and E,vegetables;with elevation decreasing from A to E)from different altitudes in a typical intensive agricultural area in Dali City,Yunnan Province,China.The results showed that soil Nmin rate ranged from 0.10 to 0.17 mg·kg^(-1)·d^(-1)N,with the highest value observed in field E,followed by fields D,C,B,and A,which indicated that soil Nmin and Nit rates varied between fields,decreasing with elevation.The soil Nit rate ranged from 434.2 to 827.1μg·kg^(-1)·h^(-1)N,with the highest value determined in field D,followed by those in fields E,C,B,and A.The rates of soil Nmin and Nit were positively correlated with several key soil parameters,including total soil N,dissolved organic carbon and dissolved inorganic N across all fields,which indicated that soil variables regulated soil Nmin and Nit in cropland fields.In addition,a strong positive relationship was observed between soil Nmin and Nit.These findings provide a greater understanding of the response of soil Nmin among cropland fields related to spatial variation.It is suggested that the soil Nmin from cropland should be considered in the evaluation of the N transformations at the regional scale.展开更多
Afforestation effectively improved soil microbial communities and significantly increased soil nitro-gen mineralization rate(Rm).Soil microorganisms drive Rm by regulating soil N-cycling genes.Soil nitrification genes...Afforestation effectively improved soil microbial communities and significantly increased soil nitro-gen mineralization rate(Rm).Soil microorganisms drive Rm by regulating soil N-cycling genes.Soil nitrification genes had a major effect on soil Rm than denitrification genes after afforestation.Assessing the function of forest ecosystems requires an understanding of the mechanism of soil nitrogen mineralization.However,it remains unclear how soil N-cycling genes drive soil nitrogen mineralization during afforestation.In this study,we collected soil samples from a chrono-sequence of 14,20,30,and 45 years of Robinia pseudoacacia L.(RP14,RP20,RP30,and RP45)with a sloped farmland(FL)as a control.Through metagenomic sequencing analysis,we found significant changes in the diversity and composition of soil microbial communities involved in N-cycling along the afforestation time series,with afforestation effectively increasing the diversity(both alpha and beta diversity)of soil microbial communities.We conducted indoor culture experiments and analyzed correlations,which revealed a significant increase in both soil nitrification rate(Rn)and soil nitrogen mineralization rate(Rm)with increasing stand age.Furthermore,we found a strong correlation between soil Rm and soil microbial diversity(both alpha and beta diversity)and with the abundance of soil N-cycling genes.Partial least squares path modeling(PLS-PM)analysis showed that nitrification genes(narH,narY,nxrB,narG,narZ,nxrA,hao,pmoC-amoC)and denitrification genes(norB,nosZ,nirK)had a greater direct effect on soil Rm compared to their effect on soil microbial communities.Our results reveal the relationships between soil nitrogen mineralization rate and soil microbial communities and between the mineralization rate and functional genes involved in N-cycling,in the context of Robinia pseudoacacia L.restoration on the Loess Plateau.This study enriches the understanding of the effects of microorganisms on soil nitrogen mineralization rate during afforestation and provides a new theoretical basis for evaluating soil nitrogen mineralization mechanisms during forest succession.展开更多
基金supported by the National Natural Science Foundation of China(51809189)the Shanxi Province Key Laboratory of Soil Environment and Nutrient Resources,China(2019002)。
文摘Alternate partial root-zone drip fertigation (ADF) is a combination of alternating irrigation and drip fertigation,with the potential to save water and increase nitrogen (N) fertilizer efficiency.A 2-year greenhouse experiment was conducted to evaluate the effect of different fertigation frequencies on the distribution of soil moisture and nutrients and tomato yield under ADF.The treatments included three ADF frequencies with intervals of 3 days (F3),6 days (F6) and 12 days (F12),and conventional drip fertigation as a control (CK),which was fertilized once every 6 days.For the ADF treatments,two drip tapes were placed 10 cm away on each side of the tomato row,and alternate drip irrigation was realized using a manual valve on the distribution tapes.For the CK treatment,a drip tape was located close to the roots of the tomato plants.The total N application rate of all treatments was 180 kg ha^(-1).The total irrigation amounts applied to the CK treatment were450.6 and 446.1 mm in 2019 and 2020,respectively;and the irrigation amounts applied to the ADF treatments were 60%of those of the CK treatment.The F3 treatment resulted in water and N being distributed mainly in the 0–40-cm soil layer with less water and N being distributed in the 40–60-cm soil layer.The F6 treatment led to 21.0 and 29.0%higher 2-year average concentration of mineral N in the 0–20 and 20–40-cm soil layer,respectively and a 23.0%lower N concentration in the 40–60-cm soil layer than in the CK treatment.The 2-year average tomato yields of the F3,F6,F12,and CK treatments were 107.5,102.6,87.2,and 98.7 t ha^(-1),respectively.The tomato yield of F3 was significantly higher (23.3%) than that in the F12 treatment,whereas there was no significant difference between the F3 and F6 treatment.The F6 treatment resulted in yield similar to the CK treatment,indicating that ADF could maintain tomato yield with a 40%saving in water use.Based on the distribution of water and N,and tomato yield,a fertigation frequency of 6 days under ADF should be considered as a water-saving strategy for greenhouse tomato production.
基金funded by the National Natural Science Foundation of China (31270500, 31240002)the Strategic Priority Research Program of Chinese Academy of Sciences (XDA05 050602)+1 种基金the Open Research Fund of the Key Laboratory of Vegetation Restoration and Management of Degraded Ecosystems, Chinese Academy of Sciencesthe support of the Duolun Restoration Ecology Research Station, which is part of the Institute of Botany, Chinese Academy of Sciences, for providing access to the sampling site
文摘Determining soil N mineralization response to soil temperature and moisture changes is challenging in the field due to complicated effects from other factors. In the laboratory, N mineralization is highly dependent on temperature, moisture and sample size. In this study, a laboratory incubation experiment was carefully designed and conducted under controlled conditions to examine the effects of soil temperature and moisture on soil N mineralization using soil samples obtained from the Stipa krylovii grassland in Inner Mongolia, China. Five temperature(i.e. 9℃, 14℃, 22℃, 30℃ and 40℃) and five moisture levels(i.e. 20%, 40%, 60%, 80% and 100% WHC, where WHC is the soil water holding capacity) were included in a full-factorial design. During the 71-day incubation period, microbial biomass carbon(MBC), ammonium nitrogen(NH4 ^+-N) and nitrate nitrogen(NO3^--N) were measured approximately every 18 days; soil basal respiration for qCO2 index was measured once every 2 days(once a week near the end of the incubation period). The results showed that the mineral N production and net N mineralization rates were positively correlated with temperature; the strongest correlation was observed for temperatures between 30℃ and 40℃. The relationships between moisture levels and both the mineral N production and net N mineralization rates were quadratic. The interaction between soil temperature and moisture was significant on N mineralization, i.e. increasing temperatures(moisture) enhanced the sensitivity of N mineralization to moisture(temperature). Our results also showed a positive correlation between the net nitrification rate and temperature, while the correlation between the NH4 ^+-N content and temperature was insignificant. The net nitrification rate was negatively correlated with high NH4 ^+-N contents at 80%–100% WHC, suggesting an active denitrification in moist conditions. Moreover, qCO2 index was positively correlated with temperature, especially at 80% WHC. With a low net nitrification rate and high soil basal respiration rate, it was likely that the denitrification concealed the microbial gross mineralization activity; therefore, active soil N mineralization occurred in 60%–80% WHC conditions.
基金supported by the Key Technologies R&D Program of China during the 12th Five-year Plan period(2012BAD14B16-04)the Science and Technology Development Program of Guangdong,China(2012A020100003 and 2015B090903077)
文摘The increasing demand for fresh sweet maize (Zea mays L. saccharata) in southern China has prioritized the need to find solutions to the environmental pollution caused by its continuous production and high inputs of chemical nitrogen fertilizers. A promising method for improving crop production and environmental conditions is to intercrop sweet maize with legumes. Here, a three-year field experiment was conducted to assess the influence of four different cropping systems (sole sweet maize (SS), sole soybean (SB), two rows sweet maize-three rows soybean (S2B3) intercropping, and two rows sweet maize-four rows soybean (S2B4) intercropping), together with two rates of N fertilizer application (300 and 360 kg N ha-1) on grain yield, residual soil mineral N, and soil N2O emissions in southern China. Results showed that in most case, inter- cropping achieved yield advantages (total land equivalent ratio (TLER=0.87-1.25) was above one). Moreover, intercropping resulted in 39.8% less soil mineral N than SS at the time of crop harvest, averaged over six seasons (spring and autumn in each of the three years of the field experiment). Generally, intercropping and reduced-N application (300 kg N ha-1) produced lower cumulative soil N20 and yield-scaled soil N20 emissions than SS and conventionaI-N application (360 kg N ha-l), respectively. $2B4 intercropping with reduced-N rate (300 kg N ha-~) showed the lowest cumulative soil N20 (mean value=0.61 kg ha-1) and yield-scaled soil N20 (mean value=0.04 kg t-1) emissions. Overall, intercropping with reduced-N rate maintained sweet maize production, while also reducing environmental impacts. The system of S2B4 intercropping with reduced-N rate may be the most sustainable and environmentally friendly cropping system.
基金supported by Strategic Priority Research Program of the Chinese Academy of Sciences(XDA05070303)
文摘We investigated the effect of forest thinning on soil nitrogen mineralization, nitrification and transformation in a Cryptomeria japoni-ca plantation at high elevation to provide basic data for forest manage-ment. We chose four study plots for control, light, medium and heavy thinning treatment, and three sub-plots for buried bag studies at similar elevations in each treatment plot to measure the net N mineralization and nitrification rates in situ. The contents of soil inorganic N (ammonium and nitrate) were similar between treatments, but all varied with season, reaching maxima in September 2003 and 2004. The seasonal maximum net Nmin rates after four treatments were 0.182, 0.246, 0.303 and 0.560 mg?kg-1?d-1 in 2003, and 0.242,0.258,0.411 and 0.671 mg?kg-1?d-1in 2004, respectively. These estimates are approximate with the lower annual rates of N mineralization for this region. Forest thinning can enhance net N mineralization and microbial biomass carbon. The percentage of annual rates of Nmin for different levels of forest thinning compared with the control plot were 13.4%, 59.8%and 154.2%in 2003, and 0.1%, 58.8%and 157.7%in 2004 for light, medium, and heavy thinning, respectively. These differences were related to soil moisture, temperature, precipita-tion, and soil and vegetation types. Well-planned multi-site comparisons, both located within Taiwan and the East-Asia region, could greatly im-prove our knowledge of regional patterns in nitrogen cycling.
基金supported by the National Natural Science Foundation of China(Grant No.31570466)the National Basic Research Program of China(Grant no.2012CB416905)
文摘Forest soil carbon (C) is an important compo- nent of the global C cycle. However, the mechanism by which tree species influence soil organic C (SOC) pool composition and mineralization is poorly understood. To understand the effect of tree species on soil C cycling, we assessed total, labile, and recalcitrant SOC pools, SOC chemical composition by 13C nuclear magnetic resonance spectroscopy, and SOC mineralization in four monoculture plantations. Labile and recalcitrant SOC pools in surface (0-10 cm) and deep (40-60 cm) soils in the four forests contained similar content. In contrast, these SOC pools exhibited differences in the subsurface soil (from 10 to 20 cm and from 20 to 40 cm). The alkyl C and O-alkyl C intensities of SOC were higher in Schima superba and Michelia macclurei forests than in Cunninghamia lanceolata and Pinus massoniana forests. In surface soil, S. superba and M. macclurei forests exhibited higher SOC mineralization rates than did P. massoniana and C.lanceolata forests. The slope of the straight line between C60 and labile SOC was steeper than that between C60 and total SOC. Our results suggest that roots affected the composition of SOC pools. Labile SOC pools also affected SOC mineralization to a greater extent than total SOC pools.
基金supported by the National Natural Science Foundation of China(No.31300522)Specialized Research Fund for the Doctoral Program of Higher Education of China(No.20125103120018)
文摘In order to understand the effects of increasing atmospheric nitrogen (N) deposition on the subtropical bamboo ecosystem, a nearly six-year field experiment was conducted in a Pleioblastus amarus plantation in the rainy region of SW China, near the western edge of Sichuan Basin. Four N treatment levels---control (no N added), low- N (50 kg N ha-1 a-l), medium-N (150 kg N ha-1 a-l), and high-N (300 kg N ha-1 a-1)--were applied monthly in the P. amarus plantation starting in November 2007. In June 2012, we collected intact soil cores in the bamboo plantation and conducted a 30-day laboratory incubation experiment. The results showed that the soil N net miner- alization rate was 0.96 4- 0.10 mg N kg-1 day-1, under control treatment. N additions stimulated the soil N net mineralization, and the high-N treatment significantly increased the soil N net mineralization rate compared with the control. Moreover, the soil N net mineralization rate was significantly and positively correlated with the fine root biomass, the soil microbial biomass nitrogen content and the soil initial inorganic N content, respectively,whereas it was negatively correlated with the soil pH value. There were no significant relationships between the soil N net mineralization rate and the soil total nitrogen (TN) content and the soil total organic carbon content and the soil C/N ratio and the soil microbial biomass carbon con- tent, respectively. These results suggest that N additions would improve the mineral N availability in the topsoil of the P. amarus plantation through the effects of N additions on soil chemical and physical characteristics and fine-root biomass.
基金financially supported by the Programme of "Effects of Atmospheric Pollutants on Forest Ecosystems" from the Ministry of Agriculture and Foodthe Greek Ministry of Environmentthe European Commission
文摘The fluxes of masses and the nutrients Ca,Mg,K,N,P and S were determined in the litterfall of two adjacent forest ecosystems of Hungarian oak(Quercus frainetto L.)and European beech(Fagus sylvatica L.)in a mountainous area of northeastern Greece in 2010–2015.The foliar litterfall for both species reached about 70%of the total litterfall,and was significantly higher from the other two fractions(woody and rest litterfall).The fluxes of masses and nutrients were compared between ecosystems for each fraction separately.Only one significant statistical difference was found,that of K in the woody litterfall.In addition,the stocks of masses and nutrients were calculated in the forest floors and mineral soils of the two ecosystems.Likewise,the stocks of nutrients in the forest floors and mineral soils were compared between ecosystems.In the L horizon of the forest floors,statistical differences,as a result of species effect,were found for the stocks of Ca and N.In the FH horizons,the masses and all the nutrient stocks differed significantly,as the beech plot had much higher quantities of organic matter and nutrients.These higher quantities were probably due to low soil temperatures(microclimate)and high acidity in the beech plot(species effect)that slowed down decomposition.In the mineral soils,the propagation of random error derived from random errors of the individual soil layers was an important factor in the statistical comparisons.Because of the soil acidity in the beech plot,the stocks of exchangeable base cations were significantly higher in the oak plot,whereas the other nutrient stocks did not differ.
基金Supported by National Natural Science Foundation of China(31760201,31560206,31160152)Guangxi Innovation-driven Development Project(GK AA17204087-11)。
文摘[Objectives]This study was conducted to understand the process of soil nitrogen mineralization in Eucalyptus plantations,and to identify the characteristics of soil nitrogen mineralization with different litter inputs.[Methods]With the soil of the Eucalyptus plantation in Fusui County,Guangxi as the research object,the soil nitrogen mineralization of the Eucalyptus plantation under different litter treatments(removing litter,adding litter and retaining litter)was studied by PVC tube closed-top in-situ incubation.[Results]①After 1 year of litter treatment,the inorganic nitrogen(NH_(4)^(+)-N+NO_(3)^(-)-N)in the soil of different treatments ranked as adding litter(20.15 mg/kg)>retaining litter(16.02 mg/kg)>removing litter(11.60) mg/kg),and the differences reached a significant level(P<0.05).②After 30 d of in-situ incubation,there were significant differences in soil nitrate nitrogen content before and after incubation in the three treatments(removing litter,adding litter,and retaining litter)before and after incubation(P<0.05),but no significant differences were observed in soil ammonium nitrogen content(P>0.05).Soil nitrate nitrogen contents increased from 1.47,2.01 and 1.72 mg/kg before incubation to 3.66,6.73 and 5.02 mg/kg,respectively,and soil ammonium nitrogen content increased from 11.60,20.15 and 16.02 mg/kg before incubation to 13.65,21.54 and 17.18 mg/kg,respectively.The net nitrogen mineralization quantities of the three treatments were 4.24,6.11 and 4.46 mg/kg,respectively,and the net nitrogen mineralization rates from large to small were adding litter[0.180 mg/(kg·d)]>retaining litter[0.141 mg/(kg·d)]>removing litter[0.125 mg/(kg·d)].Therefore,both removal and addition of litter affected the soil nitrogen input and nitrogen mineralization rate of the Eucalyptus plantation,thereby affecting soil nitrogen availability and the ability of soil to maintain plant-available nitrogen.[Conclusions]This study provides a theoretical basis for nutrient management in Eucalyptus plantations,especially nitrogen nutrient management.
基金supported by grants from the National Natural Science Foundation of China (Nos. 30960311 &30600473)
文摘Soil N transformations using the polyvinyl chloride (PVC) closed-top tube in situ incubation method were studied in Nanchang urban forests of the mid-subtropical region of China in different months of 2007. Four plots of 20 m × 20 m were established in four different plant communities that represented typical successional stages of forest development including shrubs, coniferous forest, mixed forest and broad- leaved forest. Average concentrations of soil NH4^+-N from January to December were not different among the four plant communities. The concentrations of soil NO3^--N and mineral N, and the annual rotes of ammonification, nitrification and net N-mineralization under the early successional shrub community and coniferous forest were generally lower than that of the late successional mixed and broad-leaved forests (p〈0.05). Similar differences among the plant communities were also shown in the relative nitrification index (NH4^+-N/NO3^--N) and relative nitrification intensity (nitrification rate/net N-mineralization rate). The annual net N-mineralization rate was increased from younger to older plant communities, from 15.1 and 41.4 kg.ha^-1.a^-1 under the shrubs and coniferous forest communities to 98.0 and 112.9 kg.ha^-1.a^-1 under the mixed and broad-leaved forests, respectively. Moreover, the high annual nitrification rates (50-70 kg.ha^-1.a^-1) and its end product, NO3-N (2.4-3.8 mg·kg^-1), under older plant communities could increase the potential risk of N loss. Additionally, the temporal patterns of the different soil N variables mentioned above varied with different plant community due to the combined affects of natural biological processes associated with forest maturation and urbanization. Our results indicated that urban forests are moving towards a state of"N saturation" (extremely niUification rate and NO3^--N content) as they mature.
基金Funding for the research was provided by the Estonian Ministry of Education and Research(Project No.0172613AGML03).
文摘Soil organic carbon (SOC) retaining capacities of epipedon (EP), subsoil (SS) and soil cover (SC) as a whole, are soil type specific. Depending on individual and sites characteristics, the generalized humus status indices of soil types (EP and SC thickness and SOC stocks) may vary. Land use and land use change primarily influence the properties and fabric of the EP, but the humus status (SOC concentration and stock, fabric of horizons) of the SS remains practically unchangeable. The mean mineral soils SOC stocks, EP quality and SOC distribution in soil profiles depend mainly on the water regime, mineral composition (texture, calcareousness), development of eluvial processes and the land use peculiarities of soils. The mean area weighted SC SOC stock of Estonian mineral soils is 99.9 Mg ha–1, thereby the mean hydromorphic soils SOC retention capacity considerably exceeds the SOC retention capacity of automorphic soils (means are accordingly 127.5 and 78.9 Mg ha–1). The sustainable management of SOC is based on adequate information about actual SOC stocks and theoretically established or optimal humus status levels of soil types. The aggregate of SOC retained in the mineral soils of Estonia (3,235,100 ha) amounts to 323 ± 46 Tg (1 Tg = 1012 g). Approximately 42% of this is sequestered into stabilized humus, 40% into instable raw-humous material and 18% into forest (grassland) floor and shallow peat layers.
文摘The potassium-releasing characteristics of a bacterium from different minerals were studied through pure culture and soil column experiments. The results showed that the strain NBT of tested strains had the highest potassium-releasing capacity. It released 35.2 mg/L after 7days of pure culture incubation at 28@, 31.8% - 1203.7% more than other tested strains. Potassium released from the minerals was obviously affected by pH, aerobic condition, soil and mineral properties. The strain NBT had a much higher potential to release potassium in the pH 6.5-8.0 than other pHs. Living cell inoculation resulted in an increase of 84.8% -127.9% compared with that of the dead cell inoculation. More aerobic condition produced more K than a less aerobic one. The potassium-releasing order was as follows: illite>feldspar>muscovite. Soil column experiment showed that the bacterial number increased from (2.6 - 3.0) × 106/g to (6.8 - 7.4) × 107/g. Soil available potassium content increased by 31.2 - 33.6mg/kg in yellow-brown soil and 21.7mg/kg in paddy soil, when inoculated with the strain NBT, 290.6% and 185.5% increment of the dead cell inoculation soils respectively.
基金funded by the German Ministry of Education and Research(BMBF)the Brazilian Conselho National de Desenvolvimento Científico e Tecnológico(CNPq)
文摘The Brazil nut tree(Bertholletia excelsa) is a frequent component of agroforestry systems in the Amazon because of its adaptation to nutrient-poor upland soils and multiple uses.We investigated the aboveground biomass production(kg dry weight),nutrient uptake and requirements(N,P,Ca,Mg,K) of Brazil nut trees of different sizes grown under agroforestry conditions and fertilized at different levels.Eight of 70 experimental trees with different size were harvested and stem,branches and leaves were separated.Nutrient contents were determined for three trees of varying size.Average tree growth was fast,but variability was high,suggesting considerable potential for the improvement of this economically important species.The trees responded to increased levels of fertilizer and lime with significantly increased foliar nutrient contents and growth,probably because of the improved availability of Mg and Ca for which the species seems to have a relatively high demand.In contrast to Brazil nut trees grown in forest or dense plantations,the agroforestry trees invested a substantial part of their biomass and nutrients in large branches and developed spreading crowns.To improve stem form,reduce competition with associated crops for light and recycle nutrients,regular pruning of lower branches or planting arrangements that favor self-pruning are recommended.These measures would also increase the recycling of Ca and Mg,large quantities of which are contained in the branches.
基金the IPPP grant PV018-2011A for financial support from the University of Malaya
文摘Field surveys indicate lateral variation in peat humification levels (von Post) in dominantly occurring fibric,fibric to hemic,sapric and hemie to sapric peats across a gradient from the margin towards the centre of tropical lowland peat domes.Cement-peat stabilisation can be enhanced by adding mineral soil fillers (silt,clays and fine sands) obtained from Quaternary floodplain deposits and residual soil (weathered schist).The unconfined compressive strength (UCS) of the stabilised cement-mineral soil fifler-peat mix increases with the increased addition of selected mineral soil filler.Lateral variation in the stabilised peat strength (UCS) in the top 0 to 0.5 m layer was found from the margin towards the centre of the tropical lowland peat dome.The variations in the UCS of stabilised tropical lowland peats along a gradient from the periphery towards the centre of the peat dome are most likely caused by a combination of factors due to variations in the mineral soil or ash content of the peat and horizontal zonation or lateral variation in the dominant species of the plant assemblages (due to successive vegetation zonation of the peat swamp forest from the periphery towards the centre of the tropical lowland peat dome).
文摘Production of cut flowers is very prevalent in Iran. Carnation is most famous for its use as a cut flower. This study was carried out in the research greenhouse of Islamic Azad University, Isfahan (Khorasgan) Branch, to explore the effect of different growing media on some vegetative and reproductive traits of carnation. The experimental design was randomized complete, using 50% perlite and different growing media including: mineral soil and coco peat in 6 proportions (50% coco peat, 10% soil + 40% coco peat, 20% soil + 30% coco peat, 30% soil + 20% coco peat, 40% soil + 10% coco peat, 50% soil). During growth period, irrigation rate, humidity and temperature were similar. The growth characteristics of carnation were determined at the end of growth period. The results indicated that although there were no significant differences between studied growing substrates in chlorophyll a, b. Statistical analysis showed fresh weight of flower was far greater in coco peat 10% + soil 40% and soil 50% compared to other growing media. Fresh and dry weight of root and shoot in soil 50% were higher than other growing media. The results showed that highest concentration of Fe and Zn was observed in coco peat 40% + soil 10%. The concentration of Mn in coco peat 10% + soil 40% was higher than other growing media. The results showed that the highest Ca concentration was observed in soil 50% and the lowest concentration of this element was obtained in coco peat 50%. According to the obtained results, mineral soil can be used as a suitable alternative to cocopeat for cultivation and growth of carnation in greenhouse.
基金founded by China Postdoctoral Science Foundation(2021M703131)National Key Research and Development Program(2019YFD1100503).
文摘Soil nitrogen mineralization(Nmin)is a key process that converts organic N into mineral N that controls soil N availability to plants.However,regional assessments of soil Nmin in cropland and its affecting factors are lacking,especially in relation to variation in elevation.In this study,a 4-week incubation experiment was implemented to measure net soil Nmin rate,gross nitrification(Nit)rate and corresponding soil abiotic properties in five field soils(A-C,maize;D,flue-cured tobacco;and E,vegetables;with elevation decreasing from A to E)from different altitudes in a typical intensive agricultural area in Dali City,Yunnan Province,China.The results showed that soil Nmin rate ranged from 0.10 to 0.17 mg·kg^(-1)·d^(-1)N,with the highest value observed in field E,followed by fields D,C,B,and A,which indicated that soil Nmin and Nit rates varied between fields,decreasing with elevation.The soil Nit rate ranged from 434.2 to 827.1μg·kg^(-1)·h^(-1)N,with the highest value determined in field D,followed by those in fields E,C,B,and A.The rates of soil Nmin and Nit were positively correlated with several key soil parameters,including total soil N,dissolved organic carbon and dissolved inorganic N across all fields,which indicated that soil variables regulated soil Nmin and Nit in cropland fields.In addition,a strong positive relationship was observed between soil Nmin and Nit.These findings provide a greater understanding of the response of soil Nmin among cropland fields related to spatial variation.It is suggested that the soil Nmin from cropland should be considered in the evaluation of the N transformations at the regional scale.
基金supported by the National Natural Science Foundation of China(No.41907031)the China Postdoctoral Science Foundation(No.2021T140565)the China Postdoctoral Science Foundation(No.2019M650276).
文摘Afforestation effectively improved soil microbial communities and significantly increased soil nitro-gen mineralization rate(Rm).Soil microorganisms drive Rm by regulating soil N-cycling genes.Soil nitrification genes had a major effect on soil Rm than denitrification genes after afforestation.Assessing the function of forest ecosystems requires an understanding of the mechanism of soil nitrogen mineralization.However,it remains unclear how soil N-cycling genes drive soil nitrogen mineralization during afforestation.In this study,we collected soil samples from a chrono-sequence of 14,20,30,and 45 years of Robinia pseudoacacia L.(RP14,RP20,RP30,and RP45)with a sloped farmland(FL)as a control.Through metagenomic sequencing analysis,we found significant changes in the diversity and composition of soil microbial communities involved in N-cycling along the afforestation time series,with afforestation effectively increasing the diversity(both alpha and beta diversity)of soil microbial communities.We conducted indoor culture experiments and analyzed correlations,which revealed a significant increase in both soil nitrification rate(Rn)and soil nitrogen mineralization rate(Rm)with increasing stand age.Furthermore,we found a strong correlation between soil Rm and soil microbial diversity(both alpha and beta diversity)and with the abundance of soil N-cycling genes.Partial least squares path modeling(PLS-PM)analysis showed that nitrification genes(narH,narY,nxrB,narG,narZ,nxrA,hao,pmoC-amoC)and denitrification genes(norB,nosZ,nirK)had a greater direct effect on soil Rm compared to their effect on soil microbial communities.Our results reveal the relationships between soil nitrogen mineralization rate and soil microbial communities and between the mineralization rate and functional genes involved in N-cycling,in the context of Robinia pseudoacacia L.restoration on the Loess Plateau.This study enriches the understanding of the effects of microorganisms on soil nitrogen mineralization rate during afforestation and provides a new theoretical basis for evaluating soil nitrogen mineralization mechanisms during forest succession.