Effects of desert plant communities on soil enzyme activities and soil organic carbon in the proluvial fan in the eastern foothills of the Helan Mountain in Ningxia,China

It is of great significance to study the effects of desert plants on soil enzyme activities and soil organic carbon(SOC)for maintaining the stability of the desert ecosystem.In this study,we studied the responses of soil enzyme activities and SOC fractions(particulate organic carbon(POC)and mineral-associated organic carbon(MAOC))to five typical desert plant communities(Convolvulus tragacanthoides,Ephedra rhytidosperma,Stipa breviflora,Stipa tianschanica var.gobica,and Salsola laricifolia communities)in the proluvial fan in the eastern foothills of the Helan Mountain in Ningxia Hui Autonomous Region,China.We recorded the plant community information mainly including the plant coverage and herb and shrub species,and obtained the aboveground biomass and plant species diversity through sample surveys in late July 2023.Soil samples were also collected at depths of 0–10 cm(topsoil)and 10–20 cm(subsoil)to determine the soil physicochemical properties and enzyme activities.The results showed that the plant coverage and aboveground biomass of S.laricifolia community were significantly higher than those of C.tragacanthoides,S.breviflora,and S.tianschanica var.gobica communities(P<0.05).Soil enzyme activities varied among different plant communities.In the topsoil,the enzyme activities of alkaline phosphatase(ALP)andβ-1,4-glucosidas(βG)were significantly higher in E.rhytidosperma and S.tianschanica var.gobica communities than in other plant communities(P<0.05).The topsoil had higher POC and MAOC contents than the subsoil.Specifically,the content of POC in the topsoil was 18.17%–42.73%higher than that in the subsoil.The structural equation model(SEM)indicated that plant species diversity,soil pH,and soil water content(SWC)were the main factors influencing POC and MAOC.The soil pH inhibited the formation of POC and promoted the formation of MAOC.Conversely,SWC stimulated POC production and hindered MAOC formation.Our study aimed to gain insight into the effects of desert plant communities on soil enzyme activities and SOC fractions,as well as the drivers of SOC fractions in the proluvial fan in the eastern foothills of the Helan Mountain and other desert ecosystems.

Soil Organic Carbon Stock and Soil Quality under Four Major Agroecosystems in the Eastern Flank of Mount Bambouto (West-Cameroon)

Assessing soil organic carbon stock (SOCS) and soil quality (SQ) helps design better agricultural practices to improve environmental sustainability and productivity. The purpose of the study is to assess SOCS and soil quality SQ in the main agroecosystems (AES) of the eastern flank of Mount Bambouto (West, Cameroon). Using multiple statistics tests and principal component analysis (PCA), SOCS and Soil Quality Index (SQI) were computed for each AES. SOCS and SQI were computed based on soil chemical properties and analysis of variance. Topsoil samples (0 - 30 cm) were collected in a different AES and analyzed in the laboratory. The four AES identified and selected are cultivated land (CL), forest areas (FA), mixed areas (MA), and bush areas (BA). Further, multiple comparison tests were used to compare soils from different AES. PCA was used to select the most appropriate indicators that control SOCS and SQ. Several soil properties showed high to very high coefficient of variation within the AES. Organic matter (OM) was significantly high in FA. SOCS and SQ differ significantly (p = 0.000) between the AES. The study further indicates that the main variables controlling SQ within the eastern flank of Mount Bambouto are OM, pHw, N, C/N, and CEC. While the main soil parameters controlling SOCS are OM, OC, BD, C/N, S, and pHKCl.

Effect of fire disturbance on active organic carbon of Larix gmelinii forest soil in Northeastern China

Active organic carbon in soil has high biological activity and plays an important role in forest soil ecosystem structure and function. Fire is an important disturbance factor in many forest ecosystems and occurs frequently over forested soils. However, little is known about its impact on soil active organic carbon (SAOC), which is important to the global carbon cycle. To investigate this issue, we studied the active organic carbon in soils in the Larix gmelinii forests of the Da Xing'an Mountains (Greater Xing'an Mountains) in Northeastern China, which had been burned by high-intensity wildfire in two different years (2002 and 2008). Soil samples were collected monthly during the 2011 growing season from over 12 sample plots in burned and unburned soils and then analyzed to examine the dynamics of SAOC. Our results showed that active organic carbon content changed greatly after fire disturbance in relation to the amount of time elapsed since the fire. There were significant differences in microbial biomass carbon, dissolved organic carbon, light fraction organic carbon, particulate organic carbon between burned and unburned sample plots in 2002 and 2008 (p < 0.05). The correlations between active organic carbon and environmental factors such as water content, pH value and temperature of soils, and correlations between each carbon component changed after fire disturbance, also in relation to time since the fire. The seasonal dynamics of SAOC in all of the sample plots changed after fire disturbance; peak values appeared during the growing season. In plots burned in 2002 and 2008, the magnitude and occurrence time of peak values differed. Our findings provide basic data regarding the impact of fire disturbance on boreal forest soil-carbon cycling, carbon-balance mechanisms, and carbon contributions of forest ecosystem after wildfire disturbance.

Effects of Different Land Use Types on Soil Organic Carbon and Carbon Management Index in Karst Area

[Objective] The aim was to reveal changes of soil organic matter fraction and their corresponding carbon management indexes as affected by different land use types.[Method]Soil organic carbon,active soil organic carbon and soil carbon management index（CMI）of different land use types in Guilin Maocun karst area were studied.Sampling with field investigation and laboratory testing was carried out.Heavy potassium chromate method was adopted to determine soil organic matter.333 mmol/L KMnO4 oxidation method was used to determine active organic carbon.[Result]With active soil organic matter increasing,the differences of CMI between different land use types were bigger.The CMI value of different land uses was shrubforest paddy fielddry farmland.The statistical analysis showed that labile organic matter was related with major soil properties at a significant level.[Conclusion]Labile organic matter could be used to reveal the influence of different land use types on soil organic matter and carbon management index in karst area.

Predicting dynamics of soil organic carbon mineralization with a double exponential model in different forest belts of China

The dynamics of soil organic carbon （SOC） was analyzed by using laboratory incubation and double exponential model that mineralizable SOC was separated into active carbon pools and slow carbon pools in forest soils derived from Changbai and Qilian Mountain areas. By analyzing and fitting the CO2 evolved rates with SOC mineralization, the results showed that active carbon pools accounted tor 1.0% to 8.5% of SOC with an average of mean resistant times （MRTs） for 24 days, and slow carbon pools accounted for 91% to 99% of SOC with an average of MRTs for 179 years. The sizes and MRTs of slow carbon pools showed that SOC in Qilian Mountain sites was more difficult to decompose than that in Changbai Mountain sites. By analyzing the effects of temperature, soil clay content and elevation on SOC mineralization, results indicated that mineralization of SOC was directly related to temperature and that content of accumulated SOC and size of slow carbon pools from Changbai Mountain and Qilian Mountain sites increased linearly with increasing clay content, respectively, which showed temperature and clay content could make greater effect on mineralization of SOC.

Impacts of Rice Field Winter Planting on Soil Organic Carbon and Carbon Management Index

To tackle with the problem of prevailing farmland abandonment in winter,5 treatments includes Chinese milk vetch-double cropping rice(CRR),rape-double cropping rice(RRR),garlic-double cropping rice(GRR),winter crop multiple cropping rotation(ROT),winter fallow control(WRR)were set up.By measuring soil total organic carbon,active organic carbon and its components and calculating the soil carbon pool management index in 0~15 cm and 15~30 cm soil layers in the early and late rice ripening stage.The effects of different winter planting patterns on the changes of soil organic carbon and carbon pool management index were discussed.In order to provide theoretical basis for the optimization and adjustment of winter planting pattern of double cropping rice field in the middle reaches of Yangtze River.The results showed that soil total organic carbon,active organic carbon and its components in different winter cropping patterns were increased,and ROT and CRR treatments were more beneficial to the accumulation of soil total organic carbon,active organic carbon and its components as well as the improvement of soil carbon pool management index,which should be preferred in the adjustment of cropping patterns.

Natural vegetation restoration of Liaodong oak(Quercus liaotungensis Koidz.) forests rapidly increased the content and ratio of inert carbon in soil macroaggregates

The lack of clarity of how natural vegetation restoration influences soil organic carbon(SOC) content and SOC components in soil aggregate fractions limits the understanding of SOC sequestration and turnover in forest ecosystems.The aim of this study was to explore how natural vegetation restoration affects the SOC content and ratio of SOC components in soil macroaggregates(>250 μm), microaggregates(53–250 μm), and silt and clay(<53 μm) fractions in 30-, 60-, 90-and 120-year-old Liaodong oak(Quercus liaotungensis Koidz.) forests, Shaanxi, China in 2015.And the associated effects of biomasses of leaf litter and different sizes of roots(0–0.5, 0.5–1.0, 1.0–2.0 and >2.0 mm diameter) on SOC components were studied too.Results showed that the contents of high activated carbon(HAC), activated carbon(AC) and inert carbon(IC) in the macroaggregates, microaggregates and silt and clay fractions increased with restoration ages.Moreover, IC content in the microaggregates in topsoil(0–20 cm) rapidly increased;peaking in the 90-year-old restored forest, and was 5.74 times higher than AC content.In deep soil(20–80 cm), IC content was 3.58 times that of AC content.Biomasses of 0.5–1.0 mm diameter roots and leaf litter affected the content of aggregate fractions in topsoil, while the biomass of >2.0 mm diameter roots affected the content of aggregate fractions in deep soil.Across the soil profiles, macroaggregates had the highest capacity for HAC sequestration.The effects of restoration ages on soil aggregate fractions and SOC content were less in deep soil than in topsoil.In conclusion, natural vegetation restoration of Liaodong oak forests improved the contents of SOC, especially IC within topsoil and deep soil.The influence of IC on aggregate stability was greater than the other SOC components, and the aggregate stability was significantly affected by the biomasses of litter, 0.5–1.0 mm diameter roots in topsoil and >2.0 mm diameter roots in deep soil.Natural vegetation restoration of Liaodong oak forests promoted SOC sequestration by soil macroaggregates.

Effects of continuous nitrogen addition on microbial properties and soil organic matter in a Larix gmelinii plantation in China

Continuous increases in anthropogenic nitrogen（N） deposition are likely to change soil microbial properties, and ultimately to affect soil carbon（C） storage.Temperate plantation forests play key roles in C sequestration, yet mechanisms underlying the influences of N deposition on soil organic matter accumulation are poorly understood. This study assessed the effect of N addition on soil microbial properties and soil organic matter distribution in a larch（Larix gmelinii） plantation. In a 9-year experiment in the plantation, N was applied at100 kg N ha-1 a-1 to study the effects on soil C and N mineralization, microbial biomass, enzyme activity, and C and N in soil organic matter density fractions, and organic matter chemistry. The results showed that N addition had no influence on C and N contents in whole soil. However,soil C in different fractions responded to N addition differently. Soil C in light fractions did not change with N addition, while soil C in heavy fractions increased significantly. These results suggested that more soil C in heavy fractions was stabilized in the N-treated soils. However,microbial biomass C and N and phenol oxidase activity decreased in the N-treated soils and thus soil C increased in heavy fractions. Although N addition reduced microbial biomass and phenol oxidase activity, it had little effect on soil C mineralization, hydrolytic enzyme activities, d13 C value in soil and C–H stretch, carboxylates and amides, and C–O stretch in soil organic matter chemistry measured by Fourier transform infrared spectra. We conclude that N addition（1） altered microbial biomass and activity without affecting soil C in light fractions and（2） resulted in an increase in soil C in heavy fractions and that this increase was controlled by phenol oxidase activity and soil N availability.

Bentonite-humic acid improves soil organic carbon,microbial biomass,enzyme activities and grain quality in a sandy soil cropped to maize(Zea mays L.) in a semi-arid region

A bentonite-humic acid(B-HA) mixture added to degraded soils may improve soil physical and hydraulic properties, due to effects such as improved soil structure and increased water and nutrient retention, but its effect on soil physicochemical and biological properties, and grain quality is largely unknown. The effect of B-HA, added at 30 Mg ha^(-1), was studied at 1,3, 5 and 7 years after its addition to a degraded sandy soil in a semi-arid region of China. The addition of B-HA significantly increased water-filled pore space and soil organic carbon, especially at 3 to 5 years after its soil addition to the soil. Amending the sandy soil with B-HA also increased the content of microbial biomass(MB)-carbon,-nitrogen and-phosphorus, and the activities of urease, invertase, catalase and alkaline phosphatase. The significant effect of maize(Zea mays L.) growth stage on soil MB and enzyme activities accounted for 58 and 84% of their total variation, respectively. In comparison, B-HA accounted for 8% of the total variability for each of the same two variables. B-HA significantly enhanced soil properties and the uptake of N and P by maize in semi-arid areas. The use of B-HA product would be an effective management strategy to reclaim degraded sandy soils and foster sustainable agriculture production in northeast China and regions of the world with similar soils and climate.

Microbial community structure and functional metabolic diversity are associated with organic carbon availability in an agricultural soil

Exploration of soil environmental characteristics governing soil microbial community structure and activity may improve our understanding of biogeochemical processes and soil quality. The impact of soil environmental characteristics especially organic carbon availability after 15-yr different organic and inorganic fertilizer inputs on soil bacterial community structure and functional metabolic diversity of soil microbial communities were evaluated in a 15-yr fertilizer experiment in Changping County, Beijing, China. The experiment was a wheat-maize rotation system which was established in 1991 including four different fertilizer treatments. These treatments included： a non-amended control（CK）, a commonly used application rate of inorganic fertilizer treatment（NPK）; a commonly used application rate of inorganic fertilizer with swine manure incorporated treatment（NPKM）, and a commonly used application rate of inorganic fertilizer with maize straw incorporated treatment（NPKS）. Denaturing gradient gel electrophoresis（DGGE） of the 16 S r RNA gene was used to determine the bacterial community structure and single carbon source utilization profiles were determined to characterize the microbial community functional metabolic diversity of different fertilizer treatments using Biolog Eco plates. The results indicated that long-term fertilized treatments significantly increased soil bacterial community structure compared to CK. The use of inorganic fertilizer with organic amendments incorporated for long term（NPKM, NPKS） significantly promoted soil bacterial structure than the application of inorganic fertilizer only（NPK）, and NPKM treatment was the most important driver for increases in the soil microbial community richness（S） and structural diversity（H）. Overall utilization of carbon sources by soil microbial communities（average well color development, AWCD） and microbial substrate utilization diversity and evenness indices（H＇ and E） indicated that long-term inorganic fertilizer with organic amendments incorporated（NPKM, NPKS） could significantly stimulate soil microbial metabolic activity and functional diversity relative to CK, while no differences of them were found between NPKS and NPK treatments. Principal component analysis（PCA） based on carbon source utilization profiles also showed significant separation of soil microbial community under long-term fertilization regimes and NPKM treatment was significantly separated from the other three treatments primarily according to the higher microbial utilization of carbohydrates, carboxylic acids, polymers, phenolic compounds, and amino acid, while higher utilization of amines/amides differed soil microbial community in NPKS treatment from those in the other three treatments. Redundancy analysis（RDA） indicated that soil organic carbon（SOC） availability, especially soil microbial biomass carbon（Cmic） and Cmic/SOC ratio are the key factors of soil environmental characteristics contributing to the increase of both soil microbial community structure and functional metabolic diversity in the long-term fertilization trial. Our results showed that long-term inorganic fertilizer and swine manure application could significantly improve soil bacterial community structure and soil microbial metabolic activity through the increases in SOC availability, which could provide insights into the sustainable management of China＇s soil resource.

Effects of Carbon and Nitrogen Additions on Soil Microbial Biomass Carbon and Enzyme Activities Under Rice Straw Returning

The effects of different amounts of carbon and nitrogen sources on the soil microbial biomass carbon,dissolved organic carbon and related enzyme activities were studied by the simulation experiment of rice straw returning to the field,and the mechanism of the decomposition of rice straw returning to the field was discussed.Completely randomized experiment of the two factors of the three levels was designed,and a total of nine treatments of indoor soil incubation tests were conducted.Full amount of rice straw was applied to the soil in this simulation experiment and different amounts of brown sugar and urea were added in the three levels of 0(no carbon source and nitrogen source),1(low levels of carbon and nitrogen sources)and 2(high levels of carbon and nitrogen sources),respectively.The results showed that the addition of different amounts of carbon and nitrogen sources to the rice straw could increase the soil carbon content.Compared with T0N0,the microbial biomass carbon of T2N2 was increased significantly by 170.48%;the dissolved organic carbon content of T1N2 was significantly increased by 58.14%and the free humic acid carbon contents of T0N2,T1N1 and T2N0 were significantly increased by 56.16%and 45.55%and 47.80%,respectively;however,there were no significant differences among those of treatments at later incubation periods.The addition of different carbon and nitrogen sources could promote the soil enzyme activities.During the incubation period,all of the soil enzyme activities of adding sugar and urea were higher than those of T0N0 treatment.Therefore,the addition of different amounts of carbon and nitrogen sources to rice straw returning could improve soil microbial biomass carbon content,dissolved organic carbon and soil enzyme activities.

The establishment and development of Haloxylon ammodendron promotes salt accumulation in surface soil of arid sandy land

Haloxylon ammodendron, a representative C_4 succulent xerophyte and salt-secreting plant, is widely used in vegetation reestablishment programs to stabilize shifting sand, and is one of the dominant shrubs in the shelter belt used to control desertification in the desert-oasis ecotone in northwestern China. In this study, we collected soil samples in an age sequence of 0-, 2-, 5-, 13-, 16-, 31-, and 39-year-old H. ammodendron plantations to assess the effects of the shrub on soil fertility and salinity. Results show that SOC and total N concentrations increased significantly with increasing plantation age and increased 5.95-(in the interspaces) to 9.05-fold(under the canopy) and 6.15-to 8.46-fold at the 0-5 cm depth at the 39-year-old plantation compared with non-vegetated sandy land. Simultaneously, H. ammodendron establishment and development resulted in significant salt accumulation in the surface layer. On average, total soil salt content at the 0-5 cm and 5-20 cm depth increased 16.8-fold and 4.4-fold, respectively, compared with non-vegetated sandy land. The increase of total salt derived mostly from the accumulation of SO_4^(2-), Ca^(2+) and Na^+ with H. ammodendron development. The accumulation in salinity was more significant than the increase in fertility, suggesting that improved soil fertility did not limit the impact of salinization. The adverse effect of salt accumulation may result in H. ammodendron plantation degradation and impact community stability in the long run.

Soil macroaggregates and organic-matter content regulate microbial communities and enzymatic activity in a Chinese Mollisol

The formation and turnover of macroaggregates are critical processes influencing the dynamics and stabilization of soil organic carbon(SOC).Soil aggregate size distribution is directly related to the makeup and activity of microbial communities.We incubated soils managed for>30 years as restored grassland(GL),farmland(FL)and bare fallow(BF)for 60 days using both intact and reduced aggregate size distributions(intact aggregate distribution(IAD)<6 mm;reduced aggregate distribution(RAD)<1 mm),in treatments with added glucose,alanine or inorganic N,to reveal activity and microbial community structure as a function of aggregate size and makeup.Over a 60-day incubation period,the highest phospholipid fatty acid(PLFA)abundance was on day 7 for bacteria and fungi,on day 15 for actinomycete.The majority of the variation in enzymatic activities was likely related to PLFA abundance.GL had higher microbial abundance and enzyme activity.Mechanically reducing macroaggregates(>0.25 mm)by 34.7%in GL soil with no substrate additions increased the abundance of PLFAs(average increase of 15.7%)and activities of β-glucosidase(increase of 17.4%)and N-acetyl-β-glucosaminidase(increase of 7.6%).The addition of C substrates increased PLFA abundance in FL and BF by averages of 18.8 and 33.4%,respectively,but not in GL soil.The results show that the effect of habitat destruction on microorganisms depends on the soil aggregates,due to a release of bioavailable C,and the addition of substrates for soils with limited nutrient availability.The protection of SOC is promoted by larger size soil aggregate structures that are important to different aggregate size classes in affecting soil C stabilization and microbial community structure and activity.

Fauna-associated Changes in Chemical and Biochemical Properties of Soil

Objective To study the impacts of abundance of woodlice, termites, and mites on some functional aspects of soil in order to elucidate the specific role of soil fauna in improving soil fertility in desert. Methods Fauna-rich sites were selected as experimental sites and adjacent areas were taken as control, Soil samples were collected from both sites. Soil respiration was measured at both sites. The soil samples were sent to laboratory, their chemical and biochemical properties were analyzed. Results Woodlice showed 25% decrease in organic carbon and organic matter as compared to control site. Whereas termites and mites showed 58% and 16% decrease in organic carbon and organic matter. In contrast, available nitrogen （nitrate and ammonical both） and phosphorus exhibited 2-fold and 1.2-fold increase, respectively. Soil respiration and dehydrogenase activity at the sites rich in woodlice, termites and mites produced 2.5-, 3.5- and 2-fold increases, respectively as compared to their control values. Fauna-associated increase in these biological parameters clearly reflected fauna-induced microbial activity in soil. Maximum decrease in organic carbon and increase in nitrate-nitrogen and ammonical-nitrogen, available phosphorus, soil respiration and dehydrogenase activity were produced by termites and minimum by mites reflecting termite as an efficient soil improver in desert environment. Conclusion The soil fauna-associated changes in chemical （organic carbon, nitrate-nitrogen, ammonical-nitrogen, phosphorus） and biochemical （soil respiration, dehydrogenase activity） properties of soil improve soil health and help in conservation of desert pedoecosystem.

Effect of scots pine forest management on soil properties and carabid beetle occurrence under post-fire environmental conditions——a case study from Central Europe

Background: Fires have a fundamental impact on phytocoenoses and, depending on the size of the fire, can have a positive or negative effect. The role of fires in the formation of the species composition of plants, restoration of stands and changes in soil properties is well studied. However, the long-term relationship between forest management methods, soil properties and epigeic entomofauna assemblages in post-fire areas is still not clear. The effects of Scots pine stand management methods on biochemical soil properties and ground beetle assemblages in the largest post-fire area in Central Europe after the second World were investigated. The study was conducted in the Rudy Raciborskie Forest district in southern Poland. The soil properties and epigeic beetle community structure were analysed. The research covered areas with natural and artificial pine regeneration, which were subjected to various care treatments.Results: The tendency for higher accumulations of organic matter in the soil of stands that underwent natural regeneration was proven. The stimulating role of soil organic carbon on the activity of dehydrogenases in the soil of naturally renewed areas with silvicultural treatment(NRAT) was noted. Regardless of the manner of stand regeneration, the activity of β-glucosidase was higher in the areas in which breeding treatments were practised.Furthermore, managed forest stands presented a higher abundance of carabid beetles than stands without treatment practices. Thirteen epigeic beetle species from the families Geotrupidae, Carabidae, Curculionidae,Cerambycidae and Silphidae were captured, with beetles from the first two families being the most numerous. Rare epigeal carabid species in the fauna of Poland and Europe, such as Carabus glabratus(Paykull) and Carabus auronitens Fabr., found appropriate habitat conditions for survival in the post-fire areas. Compared with the other areas, in the NRAT area, there were better stand and soil properties and more features conducive to epigeic entomofaunal occurrences. The highest post-fire content of polycyclic aromatic hydrocarbons was recorded in the soils of the sites that underwent artificial regeneration. The results suggest that preparing the soil before the introduction of new vegetation affects the amount of aromatic hydrocarbons(PAHs).Conclusions: The better performance of the NRAT stand draws attention to the positive aspects of the use of natural regeneration, both from ecological and economic perspectives. The effects of forest management on the amount of soil organic matter after fires have been proven. The natural regeneration of stands was conducive to the accumulation of organic matter. The enzymatic activity of soils is influenced by the renewal method and forest management strategy. The NRAT area was characterized by the highest number of carabid species.

去除凋落物和草毡层对寒温带典型森林土壤活性有机碳的短期影响

[目的]探究去除凋落物和草毡层对寒温带森林土壤活性有机碳的影响,为我国寒温带森林土壤碳循环的研究提供科学参考。[方法]以大兴安岭北部3种典型森林(白桦林、樟子松林和兴安落叶松林)为研究对象,在3种林型中设置对照、去除凋落物、去除草毡层以及去除凋落物和草毡层4种处理,于2021年9月对各处理不同土层(0—10 cm和10—20 cm)土壤进行取样,研究其土壤活性有机碳组分及其影响因子。[结果]在0—10 cm土层,与对照相比,去除凋落物后土壤可溶性有机碳和易氧化有机碳含量在白桦林和樟子松林中无显著变化,而在兴安落叶松林中显著降低了25.49%和39.40%;土壤微生物量碳含量在白桦林和兴安落叶松林中显著降低了19.26%和18.86%,而在樟子松林中无显著变化。去除草毡层后土壤可溶性有机碳和易氧化有机碳含量在白桦林和樟子松林中显著降低了16.08%,60.69%和17.38%,17.33%,而在兴安落叶松林中的变化不显著;土壤微生物量碳含量在3种林型中显著降低了19.47%~42.02%。同时去除凋落物和草毡层后3种林型土壤微生物量碳和易氧化有机碳含量极显著降低了22.03%~27.01%和52.22%~57.01%;土壤可溶性有机碳含量降低了11.25%~22.18%,其中白桦林和樟子松林达显著水平;在10—20 cm土层,不同去除处理对3种林型土壤可溶性有机碳和微生物量碳含量均无显著影响,白桦林和樟子松林土壤易氧化有机碳含量分别在去除草毡层以及同时去除凋落物和草毡层后显著降低,而兴安落叶松林土壤易氧化有机碳含量无明显变化。3种林型土壤活性有机碳各组分与土壤总有机碳、全氮、含水量呈显著正相关,与土壤pH则呈显著负相关。[结论]去除凋落物和草毡层降低了土壤活性有机碳含量,凋落物和草毡层的存在有利于土壤活性有机碳的形成与累积。

高寒草地退化对土壤碳氮磷及酶活性的影响

【目的】土壤碳氮磷元素是支撑高寒草地生态系统的关键,高寒草甸退化会改变土壤养分含量及分布规律,明确高寒草甸退化对土壤关键养分碳氮磷含量及其与酶活性之间相关性的影响可为退化高寒草甸的恢复提供理论依据。【方法】以东祁连山围封草地(FG)为对照,对轻度(LD)、中度(MD)和重度(SD)退化高寒草甸土壤有机碳、全氮、有效氮、全磷、有效磷含量,以及土壤碳氮磷转化相关的过氧化氢酶、脲酶、碱性磷酸酶活性进行研究。【结果】相比FG,退化基本导致高寒草甸土壤的有机碳含量升高,SD 0~10 cm土层有机碳含量最高,为82.1 g/kg;退化导致过氧化氢酶活性表现出下降的趋势,围封草地20~30 cm土层的过氧化氢酶活性最高,为23.35 mg/g,LD 10~20 cm土层的过氧化氢酶活性最低,为20.90 mg/g。退化导致土壤全氮含量降低,有效氮含量和脲酶活性显著升高,SD草地有效氮含量和脲酶活性均最高,分别为649 mg/k和3.47 mg/g,脲酶活性在FG和SD随土层加深而升高,但在MD和SD随土层加深而降低。4种类型草地全磷的变化范围为0.18~0.22 g/kg,退化对0~10 cm土层的全磷含量没有显著影响,而使0~10 cm土层,LD和MD的有效磷含量分别增加了152%和60%,而SD降低了32%,0~30 cm土层碱性磷酸酶活性升高,变化范围为0.52~0.62 mg/g。相关性分析表明,围封草地土壤有机碳与过氧化氢酶活性呈显著负相关,而轻度和重度退化未表现出有相关性;围封草地土壤全氮、有效氮含量与脲酶活性均没有相关性,而轻度和中度退化高寒草甸的脲酶活性与土壤有效氮含量存在显著正相关性;围封草地的土壤全磷、有效磷含量与碱性磷酸酶活性均成呈显著正相关,而退化草地未表现出明显的相关性。【结论】高寒草甸退化后改变了其关键养分与其相关酶活性之间的相关性,重度退化高寒草甸恢复中应考虑土壤磷素的投入。

水稻土微生物群落、酶活性及理化性质对有机肥、石灰连续施用的响应

【目的】探究水稻土微生物群落、酶活性及理化性质对有机肥、石灰连续施用的响应规律,为培育健康水稻土提供理论依据。【方法】于2014年冬季,选取湘东双季稻区典型酸紫泥田,分别进行了连续施用鸡粪发酵商品有机肥、生石灰的大田试验。每年早、晚稻翻耕前各撒施一次有机肥、石灰,施用量均为2.25 t/hm^(2),分别以不施有机肥、石灰的处理为对照。在处理后第3年(2017年)和第7年(2021年)晚稻黄熟期,采集表层(0—15 cm)混合土壤样品,测定土壤微生物磷脂脂肪酸(PLFAs)含量、酶活性及理化性质,筛选指示性强、响应敏感的土壤指标。基于土壤理化性质与生物学性质间的相互关系,构建结构方程模型,解析土壤PLFAs含量与酶活性对有机肥、石灰处理的响应机理。【结果】与对照相比,有机肥连施3年后,土壤革兰氏阴性菌(G^(-))PLFAs含量提高23%,革兰氏阳性菌/革兰氏阴性菌值(G^(+)/G^(-))因而降低29%;连施7年后,总PLFAs、细菌、革兰氏阳性菌(G^(+))和放线菌PLFAs含量分别提高16%、13%、28%和38%,腐生真菌PLFAs含量降低19%,而G^(-)菌PLFAs含量、G^(+)/G^(-)均与对照无显著差异。石灰连施3年后,土壤微生物类群PLFAs含量平均降低30%,连施7年后,平均降幅增至36%。有机肥施用3年后,土壤脲酶活性提高了29%;施用7年后,土壤过氧化氢酶、蔗糖酶和脲酶活性分别显著提高了63%、82%和39%。连施石灰3年,脲酶活性显著提高25%,连续施用7年则显著降低39%,对其他酶活性无显著影响。有机肥连施3、7年,土壤通气孔隙度分别增加了14%、33%,有机质总量分别增加了12%、7%,3个活性有机碳组分平均分别提高29%、69%;pH和碱解氮、有效磷、速效钾含量无显著变化;连续施用石灰3、7年,土壤pH分别提高0.6、0.6个单位,而通气孔隙度分别显著降低了47%、28%,总有机质和易氧化有机碳含量无显著变化,细颗粒有机碳含量分别提高了24%、9%,粗颗粒有机碳含量分别提高了100%、21%,施用石灰3年对速效养分含量无显著影响,施用石灰7年土壤碱解氮含量显著降低而有效磷含量显著增加。土壤物理、化学、生物学指标对连续施用有机肥的响应比值以正值为主,对连续施用石灰的响应比值以负值为主,土壤生物、化学指标对连续施用有机肥7年的响应比值较3年趋向更高正值,而对施用石灰趋向更高负值,达到17%~149%。结构方程分析结果表明,连续施用有机肥主要通过增加粗颗粒有机碳含量提升土壤易氧化有机碳,提升微生物总PLFAs含量和脲酶活性,而随着石灰累积用量的增加,降低土壤通气孔隙度、粗颗粒有机碳和碱解氮含量,降低土壤微生物总PLFAs、脲酶活性。【结论】长期连续施用有机肥可持续改善土壤通气性,增加有机质积累,提高土壤物理、化学和生物学性质,短期施用石灰有利于改善土壤物理、化学和生物学性状,但长期连续施用则降低石灰的正向效果。粗颗粒有机碳对土壤生物和化学性状响应有机肥、石灰连续施用的影响最为关键,具有预测土壤健康的潜能。

连云港耕地土壤有机碳时空分异及影响因素

为了揭示连云港耕地土壤有机碳(SOC)的时空分布特征及影响因素,选取连云港市耕地土壤作为研究对象,采取表层(0~20cm)土壤及深层(150~200 cm)土壤样品,进行了SOC、总氮(TN)及总磷(TP)的测试。结果表明:2004年SOC含量在中等级分布频率最高,2019年SOC含量在中、中上、高、极高4个等级上均广泛分布。近15 a(2004-2019年)耕地浅表SOC含量增加了0.57个百分点,有机碳密度增加了1.34 kg·m^(-2),SOC储量增加了1.36 Tg,平均固碳速率为7.26×10~4kg·km^(-2)·a^(-1)。不同类型土壤固碳速率差异较大,平均固碳速率表现为灰潮土>滨海盐土>砂姜黑土>棕潮土>棕壤>粗骨土。不同用地类型土壤的SOC含量差异大,平均固碳速率为水田>旱地>水浇地。近15 a研究区土壤C:N:P(SOC:TN:TP)稍有提高,说明SOC含量空间异质性稍有提高,研究区土壤C:N:P数值与江西耕地土壤等相比明显偏低,表明土壤微生物对SOC矿化分解速率较快,研究区耕地土壤环境不利于碳的储存。

化肥减量配施有机肥对花生土壤有机碳及其组分的影响

为了探究化肥减量配施两种不同黄腐酸钾有机肥对土壤有机碳(SOC)及其组分的影响,采取盆栽试验模拟大田花生种植,以不施肥、纯施化肥为对照,设置100%化肥配施100%有机肥、75%化肥配施25%有机肥、50%化肥配施50%有机肥、25%化肥配施75%有机肥和施用100%有机肥处理,探讨了SOC、可溶性有机碳(DOC)、微生物生物量碳(MBC)、易氧化有机碳(LOC)和惰性有机碳(ROC)在花生不同生育期内的含量特征。结果表明:化肥减量配施有机肥各处理SOC及其组分含量在花生各生育期均表现为:花针期显著高于结荚期和成熟期,其中DOC和MBC含量结荚期显著高于成熟期(P<0.05);各处理SOC及其组分含量均表现为:25%化肥配施75%生化黄腐酸钾处理显著高于不施肥、单施化肥和单施有机肥处理,50%化肥配施50%矿源黄腐酸钾处理显著高于不施肥、单施化肥和单施有机肥处理;其中花针期25%化肥配施75%生化黄腐酸钾处理SOC、DOC、MBC、LOC和ROC含量分别为133.0 g/kg、284.4 mg/kg、269.7 mg/kg、30.76 g/kg和111.2 g/kg,50%化肥配施50%矿源黄腐酸钾处理SOC、DOC、MBC、LOC和ROC含量分别为130.9 g/kg、250.5 mg/kg、251.7 mg/kg、29.86 g/kg和110.8 g/kg。综上,化肥减量配施生化黄腐酸钾对SOC及其组分含量的影响整体优于配施矿源黄腐酸钾,化肥减量配施黄腐酸钾花针期含量显著高于结荚期和成熟期(P<0.05),其中25%化肥配施75%生化黄腐酸钾处理对提升SOC及其组分含量效果最佳。