Effect of Different Irrigation Methods on Dissolved Organic Carbon and Microbial Biomass Carbon in the Greenhouse Soil

The objective of this study was to investigate the contents and distribution of dissolved organic carbon （DOC） and microbial biomass carbon （MBC） at 0-100 cm soil depth under three irrigation treatments, viz., subsurface, drip and furrow irrigation in the greenhouse soil. The soil samples were collected at different depths （0-100 cm）, and the contents of soil total organic carbon （TOC）, DOC and MBC were analysed. The experiment was conducted for 10 yr, during which period the application of fertilizers and crop management practices were kept identical. The results showed that the contents of TOC, DOC and MBC were significantly affected by different irrigation regimes, decreased with the increase of soil depth. TOC at 0-10 and 80-100 cm soil depths followed the order of furrow irrigation 〉 subsurface irrigation 〉 drip irrigation, whereas at the depth of 10-80 cm followed the order of subsurface irrigation 〉 furrow irrigation 〉 drip irrigation. DOC and MBC contents at 0-100 cm soil depths followed the order of furrow irrigation 〉 drip irrigation 〉 subsurface irrigation, and drip irrigation 〉 furrow irrigation 〉 subsurface irrigation, respectively. The ratios of DOC and MBC to TOC accounted for 4.98-12.87% and 1.48-2.82%, respectively, which were the highest in the drip irrigation treatment, followed were in the furrow irrigation treatment, and the lowest in subsurface irrigation treatment. There were significant positive correlations among the contents of DOC, MBC and TOC in all irrigation treatments. The furrow irrigation facilitated the accumulation of TOC and DOC, while drip irrigation increased the MBC. The content of TOC and the ratios of DOC to TOC were the lowest in subsurface irrigation treatment.

Seasonal variation in soil microbial biomass carbon and nitrogen in an artificial sand-binding vegetation area in Shapotou, northern China

In this study, seasonal variation characteristics of surface soil microbial biomass carbon （MBC） and soil microbial biomass nitrogen （MBN） of an artificial vegetation area located in Shapotou for different time periods were studied using the chloroform fumigation method, and the results were compared with those of near-natural vegetation areas and mobile dunes. Results showed that the MBC and MBN levels in the 0-5 cm soil layer were higher in autumn than in summer and spring. As the prolongation of vegetation restoration raised the MBC and MBN levels in summer and autumn, no clear variation was found in spring. However, the MBC and MBN in 5-20 cm had no obvious seasonal variation. During summer and autumn, the variation trend of MBC and MBN in the vertical direction was shown to be 0-5 〉 5-10 〉 10-20 cm in the vegetation area, while for mobile dunes, the MBC and MBN levels increased as the depth increased. The natural vegetation area was shown to possess the highest MBC and MBN levels, and yet mobile dunes have the lowest MBC and MBN levels. MBC and MBN levels in artificial sand-binding vegetation increased with the prolongation of vegetation restoration, indicating that the succession of sand-binding vegetation will result in the ac- cumulation of soil carbon and nitrogen, as well as the restoration of soil fertility.

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.

Influence of Salt Content on Soil Microbial Biomass Carbon

Soil salinization has become a global issue. Saline and alkaline arable land was taken as research object in this paper and four salt gradients were set(S1: 0.1%; S2:0. 5%; S3:0.9%; S4:1.3%). Through the addition of different substrates( CK: no addition of substrate; N: addition of nitrogen source; C: addition of glucose,C + N: addition of glucose and nitrogen source) to soil,it analyzed the influence of salt content on the soil microbial biomass carbon( SMBC) for the purpose of surveying the response mechanism of soil carbon turnover to salt stress. Results indicated that after addition of different substrates,the SMBC in high salt content(S3 and S4) is obviously lower than that in low salt content( S1 and S2). The decline rate of S3 and S4 is 5. 4% and 14. 2% for no addition of substrate; the decline rate is 9.0% and 24.0% for addition of nitrogen source; the decline rate is 11.5% and 28.0% for addition of carbon source; the decline rate is 19.5% and 39.5% for addition of carbon source + nitrogen source. Compared with no addition of substrates,addition of nitrogen source could not increase the SMBC. Addition of carbon source and carbon + nitrogen can significantly increase the SMBC,and the increase in low salt content soil( 80.0%- 81.0% and 58.0%- 59.0%) is obviously higher than high salt content soil( 52.0%- 69.0%and 34.0%- 50.0%). Generally,when the soil salt content is low( 0.5%),the influence of different substrate treatment is little on the SMBC,and increasing the soil salt content can obviously reduce the SMBC.

Effects of Different Land Cover Types on Soil Microbial Biomass Carbon and Nitrogen in the Lower Reaches of Niyang River

[Objectives]To comprehensively and deeply explore the effects of different land cover types in the lower reaches of Niyang River on soil microbial biomass carbon and nitrogen,and to provide a scientific basis for the rational use and sustainable management of land resources in this area.[Methods]Taking the 3 types of land cover(cultivated land,grass land and forest land)in the lower reaches of Niyang River in Tibet as the research object,the contents,distribution characteristics and relationships of soil organic carbon,organic nitrogen,microbial biomass carbon,microbial biomass nitrogen and readily oxidizable organic carbon,and their relationships were studied in 0-10,10-20,20-40,40-60,and 60-100 cm soil depth.[Results]The soil organic carbon content of forest land was higher than that of grass land and cultivated land;the vertical change trend of soil organic carbon content decreased with the increase of depth(P<0.05),and it was mainly concentrated in the soil with a depth of 0-20 cm.The soil organic carbon content was significantly different among forest land,grass land and cultivated land(P<0.05),but there was no significant difference between cultivated land and grass land(P>0.05).The soil organic nitrogen content was significantly different among cultivated land,grass land,and forest land(P<0.05),but there was no significant difference between grass land and forest land(P>0.05).The readily oxidizable organic carbon,microbial biomass carbon and nitrogen in forest land were higher than that in cultivated land and grass land.The change trend of soil readily oxidizable organic carbon,microbial biomass carbon and microbial biomass nitrogen was similar to the change of soil organic carbon content,showing a significant positive correlation.In addition to being subject to land cover,soil microbial biomass carbon and nitrogen content were also subject to the interaction of factors such as soil temperature,humidity,pH and vegetation types.[Conclusions]Changes in land cover significantly affect soil organic carbon and nitrogen,readily oxidizable organic carbon,microbial biomass carbon and nitrogen content.

Seasonality and moisture regime control soil respiration, enzyme activities, and soil microbial biomass carbon in a semi-arid forest of Delhi, India

Soil respiration,soil enzymes,and microbial biomass are important in carbon cycling in the terrestrial ecosystem which is generally limited by environmental factors and soil carbon availability.Hence,we tried to assess the factors affecting the functional aspects of these processes in a semi-arid climate.We monitored soil respiration(surface)using a portable infrared gas analyzer(Q-Box SR1LP Soil Respiration Package,Qubit Systems,Canada)equipped with a soil respiration chamber(Model:G 180).Soil respiration was measured at midday during each season throughout the study period.Soil enzymatic activities and microbial biomass carbon(MBC)were analyzed following the standard protocol for a year during peak time in four seasons at 0-10 cm and 10-20 cm depth.Soil respiration shows significant variation with highest in monsoon(3.31μmol CO2 m−2 s^(−1))and lowest in winter(0.57μmol CO2 m^(−2) s^(−1)).Similarly,β-glucosidase,dehydrogenase,and phenol oxidase activity ranged from 11.15 to 212.59μg PNP g^(−1) DW h^(−1),0.11 to 16.47μg TPF g^(−1) DW h^(−1),and 4102.95 to 10187.55μmol ABTS+g^(−1) DW min^(−1),respectively.MBC ranged from 17.08 to 484.5μgCg^(−1).Besides,soil respiration,soil enzymes(exceptβ-glucosidase),and MBC were significantly correlated with soil moisture.Seasonality,optimum moisture and temperature played a significant role in determining variations in soil microbiological processes(exceptβ-glucosidase activity);the carbon cycling in the study area is assisted by enzyme activity;dehydrogenase and phenol oxidase played a significant role in soil respiration;hence,this landscape is sensitive to environmental changes.

Changes in Organic Carbon Index of Grey Desert Soil in Northwest China After Long-Term Fertilization

Soil organic carbon （SOC）, soil microbial biomass carbon （SMBC） and SMBC quotient （SMBC/SOC, qSMBC） are key indexes of soil biological fertility because of the relationship to soil nutrition supply capacity. Yet it remains unknown how these three indexes change, which limits our understanding about how soil respond to different fertilization practices. Based on a 22-yr （1990-2011） long-term fertilization experiment in northwest China, we investigated the dynamics of SMBC and qSMBC during the growing period of winter wheat, the relationships between the SMBC, qSMBC, soil organic carbon （SOC） concentrations, the carbon input and grain yield of wheat as well. Fertilization treatments were 1） nonfertilization （control）; 2） chemical nitrogen plus phosphate plus potassium （NPK）; 3） NPK plus animal manure （NPKM）; 4） double NPKM （hNPKM） and 5） NPK plus straw （NPKS）. Results showed that the SMBC and qSMBC were significantly different among returning, jointing, flowering and harvest stages of wheat under long-term fertilization. And the largest values were observed in the flowering stage. Values for SMBC and qSMBC ranged from 37.5 to 106.0 mg kg1 and 0.41 to 0.61%, respectively. The mean value rank of SMBC during the whole growing period of wheat was hNPKM〉NPK_M〉NPKS〉CK〉NPK. But there were no statistically significant differences between hNPKM and NPKM, or between CK and NPK. The order for qSMBC was NPKS〉NPKM〉CK〉hNPKM〉NPK. These results indicated that NPKS significantly increased the ratio of SMBC to SOC, i.e., qSMBC, compared with NPK fertilizer or other two NPKM fertilizations. Significant linear relationships were observed between the annual carbon input and SOC （P〈0.01） or SMBC （P〈0.05）, and between the relative grain yield of wheat and the SOC content as well （P〈0.05）. But the qSMBC was not correlated with the annual carbon input. It is thus obvious that the combination of manure, straw with mineral fertilizer may be benefit to increase SOC and improve soil quality than using only mineral fertilizer.

Long-term effects of gravel―sand mulch on soil organic carbon and nitrogen in the Loess Plateau of northwestern China

Gravel-sand mulch has been used for centuries to conserve water in the Loess Plateau of north- western China. In this study, we assessed the influence of long-term （1996-2012） gravel-sand mulching of cultiv- ated soils on total organic carbon （TOC）, light fraction organic carbon （LFOC）, microbial biomass carbon （MBC）, total organic nitrogen （TON）, particulate organic carbon （POC）, mineral-associated organic carbon （MOC）, perma- nganate-oxidizable carbon （KMnO4-C）, and non-KMnO4-C at 0-60 cm depths. Mulching durations were 7, 11 and 16 years, with a non-mulched control. Compared to the control, there was no significant and consistently positive effect of the mulch on TOC, POC, MOC, KMnO4-C and non-KMnO4-C before 11 years of mulching, and these organic C fractions generally decreased significantly by 16 years. LFOC, TON and MBC to at a 0-20 cm depth in- creased with increasing mulching duration until 11 years, and then these fractions decreased significantly between 11 and 16 years, reaching values comparable to or lower than those in the control. KMnO4-C was most strongly correlated with the labile soil C fractions. Our findings suggest that although gravel-sand mulch may conserve soil moisture, it may also lead to long-term decreases in labile soil organic C fractions and total organic N in the study area. The addition of manure or composted manure would be a good choice to reverse the soil deterioration that occurs after 11 years by increasing the inputs of organic matter.

Impacts of low-intensity prescribed fire on microbial and chemical soil properties in a Quercus frainetto forest

Prescribed fire is a common economical and effective forestry practice, and therefore it is important to understand the effects of fire on soil properties for better soil management. We investigated the impacts of low-intensity prescribed fire on the microbial and chemical properties of the top soil in a Hungarian oak(Quercus frainetto Ten.) forest. The research focused on microbial soil parameters(microbial soil respiration(RSM), soil microbial biomass carbon(Cmic) and metabolic quotient(qCO2) and chemical topsoil properties(soil acidity(pH),electrical conductivity(EC), carbon(C), nitrogen(N), C/N ratio and exchangeable cations). Mean annual comparisons show significant differences in four parameters(C/N ratio,soil pH, Cmic and qCO2) while monthly comparisons do not reveal any significant differences. Soil pH increased slightly in the burned plots and had a significantly positive correlation with exchangeable cations Mg, Ca, Mn and K.The mean annual C/N ratio was significantly higher in the burned plots(28.5:1) than in the control plots(27.0:1). The mean annual Cmic(0.6 mg g-1) was significantly lower although qCO2(2.5 lg CO2–C mg Cmic h-1) was significantly higher, likely resulting from the microbial response to fire-induced environmental stress. Low-intensity prescribed fire caused very short-lived changes. The annual mean values of C/N ratio, pH, Cmic and qCO2showed significant differences.

Effects of Caragana microphylla plantations on organic carbon sequestration in total and labile soil organic carbon fractions in the Horqin Sandy Land, northern China

Afforestation is conducive to soil carbon（C） sequestration in semi-arid regions. However, little is known about the effects of afforestation on sequestrations of total and labile soil organic carbon（SOC） fractions in semi-arid sandy lands. In the present study, we examined the effects of Caragana microphylla Lam. plantations with different ages（12-and 25-year-old） on sequestrations of total SOC as well as labile SOC fractions such as light fraction organic carbon（LFOC） and microbial biomass carbon（MBC）. The analyzed samples were taken from soil depths of 0–5 and 5–15 cm under two shrub-related scenarios： under shrubs and between shrubs with moving sand dunes as control sites in the Horqin Sandy Land of northern China. The results showed that the concentrations and storages of total SOC at soil depths of 0–5 and 5–15 cm were higher in 12-and 25-year-old C. microphylla plantations than in moving sand dunes（i.e., control sites）, with the highest value observed under shrubs in 25-year-old C. microphylla plantations. Furthermore, the concentrations and storages of LFOC and MBC showed similar patterns with those of total SOC at the same soil depth. The 12-year-old C. microphylla plantations had higher percentages of LFOC concentration to SOC concentration and MBC concentration to SOC concentration than the 25-year-old C. microphylla plantations and moving sand dunes at both soil depths. A significant positive correlation existed among SOC, LFOC, and MBC, implying that restoring the total and labile SOC fractions is possible by afforestation with C. microphylla shrubs in the Horqin Sandy Land. At soil depth of 0–15 cm, the accumulation rate of total SOC under shrubs was higher in young C. microphylla plantations（18.53 g C/（m^2·a）; 0–12 years） than in old C. microphylla plantations（16.24 g C/（m^2·a）; 12–25 years）, and the accumulation rates of LFOC and MBC under shrubs and between shrubs were also higher in young C. microphylla plantations than in old C. microphylla plantations. It can be concluded that the establishment of C. microphylla in the Horqin Sandy Land may be a good mitigation strategy for SOC sequestration in the surface soils.

Land use effects on soil organic carbon, nitrogen and salinity in saline-alkaline wetland

Land-use and soil management affects soil organic carbon （SOC） pools, nitrogen, salinity and the depth distribution. The objective of this study was to estimate land-use effects on the distribution of SOC, labile fractions C, nitrogen （N） and salinity in saline-alkaline wetlands in the middle reaches of the Heihe River Basin. Three land-use types were selected： intact saline-alkaline meadow wetland, artificial shrubbery （planting Tamarix） and farmland （cultivated for 18 years） of soils previously under meadow wetland. SOC, easily oxidized carbon, microbial biomass carbon, total N, NO3--N and salinity concentrations were measured. The results show that SOC and labile fraction carbon contents decreased significantly with increasing soil depth in the three land-use wetlands. The labile fraction carbon contents in the topsoil （0-20cm） in cultivated soils were significantly higher than that in intact meadow wetland and artificial shrubbery soil. The aboveground biomass and soil permeability were the primary influencing factors on the contents of SOC and the labile carbon in the intact meadow wetland and artificial shrubbery soil, however, the farming practice was a factor in cultivated soil. Agricultural measures can effectively reduce the salinity contents; however, it caused a significant increase of NO 3--N concentrations which posed a threat to groundwater quality in the study area.

How Physical Disturbance and Nitrogen Addition Affect the Soil Carbon Decomposition?

The decomposition of soil organic carbon(SOC)plays a critical role in regulating atmospheric CO_(2)concentrations and climate dynamics.However,the mechanisms and factors controlling SOC decomposition are still not fully understood.Here,we conducted a 60 days incubation experiment to test the effects of physical disturbance and nitrogen(N)addition on SOC decomposition.N addition increased the concentration of NO3-by 51%in the soil,but had little effect on the concentration of NH4+.N addition inhibited SOC decomposition,but such an effect differed between disturbed and undisturbed soils.In disturbed and undisturbed soils,application of N decreased SOC decomposition by 37%and 15%,respectively.One possible explanation is that extra N input suppressed microbial N mining and/or increased the stability of soil organic matter by promoting the formation of soil aggregates and incorporating part of the inorganic N into organic matter,and consequently decreased microbial mineralization of soil organic matter.Physical disturbance intensified the inhibition of N on SOC decomposition,likely because physical disturbance allowed the added N to be better exposed to soil microbes and consequently increased the availability of added N.We conclude that physical disturbance and N play important roles in modulating the stability of SOC.

Changes in the activities of key enzymes and the abundance of functional genes involved in nitrogen transformation in rice rhizosphere soil under different aerated conditions

Soil microorganisms play important roles in nitrogen transformation. The aim of this study was to characterize changes in the activity of nitrogen transformation enzymes and the abundance of nitrogen function genes in rhizosphere soil aerated using three different methods(continuous flooding(CF), continuous flooding and aeration(CFA), and alternate wetting and drying(AWD)). The abundances of amoA ammonia-oxidizing archaea(AOA) and ammonia-oxidizing bacteria(AOB), nirS, nirK, and nifH genes, and the activities of urease, protease, ammonia oxidase, nitrate reductase, and nitrite reductase were measured at the tillering(S1), heading(S2), and ripening(S3) stages. We analyzed the relationships of the aforementioned microbial activity indices, in addition to soil microbial biomass carbon(MBC) and soil microbial biomass nitrogen(MBN), with the concentration of soil nitrate and ammonium nitrogen. The abundance of nitrogen function genes and the activities of nitrogen invertase in rice rhizosphere soil were higher at S2 compared with S1 and S3 in all treatments. AWD and CFA increased the abundance of amoA and nifH genes, and the activities of urease, protease, and ammonia oxidase, and decreased the abundance of nirS and nirK genes and the activities of nitrate reductase and nitrite reductase, with the effect of AWD being particularly strong. During the entire growth period, the mean abundances of the AOA amoA, AOB amoA, and nifH genes were 2.9, 5.8, and 3.0 higher in the AWD treatment than in the CF treatment, respectively, and the activities of urease, protease, and ammonia oxidase were 1.1, 0.5, and 0.7 higher in the AWD treatment than in the CF treatment, respectively. The abundances of the nirS and nirK genes, and the activities of nitrate reductase and nitrite reductase were 73.6, 84.8, 10.3 and 36.5% lower in the AWD treatment than in the CF treatment, respectively. The abundances of the AOA amoA, AOB amoA, and nifH genes were significantly and positively correlated with the activities of urease, protease, and ammonia oxidase, and the abundances of the nirS and nirK genes were significantly positively correlated with the activities of nitrate reductase. All the above indicators were positively correlated with soil MBC and MBN. In sum, microbial activity related to nitrogen transformation in rice rhizosphere soil was highest at S2. Aeration can effectively increase the activity of most nitrogen-converting microorganisms and MBN, and thus promote soil nitrogen transformation.

Effects of soil salinity on rhizosphere soil microbes in transgenic Bt cotton fields

With increased cultivation of transgenic Bacillus thuringiensis （Bt） cotton in the saline alkaline soil of China, assessments of transgenic crop biosafety have focused on the effects of soil salinity on rhizosphere microbes and Bt protein residues. In 2013 and 2014, investigations were conducted on the rhizosphere microbial biomass, soil enzyme activities and Bt protein contents of the soil under transgenic Bt cotton （variety GK19） and its parental non-transgenic cotton （Simian 3） cultivated at various salinity levels （1.15, 6.00 and 11.46 dS m-1）. Under soil salinity stress, trace amounts of Bt proteins were ob- served in the Bt cotton GK19 rhizosphere soil, although the protein content increased with cotton growth and increased soil salinity levels. The populations of slight halophilic bacteria, phosphate solubilizing bacteria, ammonifying bacteria, nitrifying bacteria and denitrifying bacteria decreased with increased soil salinity in the Bt and non-Bt cotton rhizosphere soil, and the microbial biomass carbon, microbial respiration and soil catalase, urease and alkaline phosphatase activity also decreased. Correlation analyses showed that the increased Bt protein content in the Bt cotton rhizosphere soil may have been caused by the slower decomposition of soil microorganisms, which suggests that salinity was the main factor influencing the relevant activities of the soil microorganisms and indicates that Bt proteins had no clear adverse effects on the soil microorganisms. The results of this study may provide a theoretical basis for risk assessments of genetically modified cotton in saline alkaline soil.

In-Field Corn Residue Management for Bioenergy Use: Potential Effects on Selected Soil Health Parameters

In the U.S. biofuel industry is using corn (Zea mays L.) residue mix (CRM) consisting of corncob and stover for cellulosic ethanol and biogas production. The field storage method left different depths of CRM on the field after its removal, where negative effects on plant growth were observed. The objective of this study is to evaluate the CRM effect on selected soil health indicators. The field study conducted with four different depths of CRM, two tillage systems (no-till (NT) and chisel plow (CP), and three nitrogen (N) rates (0, 180, and 270 kg⋅N⋅ha−1) in a randomized complete block design with split-split arrangements in three replications in a continuous corn system from 2010 to 2012 at the Agronomy Research Farm at Iowa State University. The findings of this study showed a negative effect on soil organic carbon (SOC) change across all treatments at 0 - 15 cm (−0.35 to −0.03 Mg⋅ha−1⋅yr−1), while at 15 - 30 cm there was an increase in SOC rate (0.13 to 0.40 Mg⋅ha−1⋅yr−1) after 2-yr. In addition, soil aggregate-associated C of macro-aggregates decreased by 8%, while micro-aggregates increased by 2%. Soil microbial biomass carbon (MBC) across tillage and N rates for 2.5 & 7.5 CRM treatments increased by 14% in June to July 2011, while in 2012 increased by 9%. However, at the 15 cm soil depth, soil bulk density (ρb), soil penetration resistance (SPR), and soil pH showed no significant differences among CRM treatments. The findings of this study showed that in-field CRM management can affect certain soil health parameters in the short term.

Variation of Ecostoichiometric Ratios of Soil Microbes in Zhoushan Forest Park

Taking surrounding woodland soils of Cedrus deodara(Roxb.)G.Don,Prunus ceraifera cv.Pissardii,Ginkgo biloba L.and Ligustrum lucidum in Zhoushan Forest Park of Henan Province as the research objects,the physicochemical properties of sample plots were investigated,and the contents of soil microbial biomass carbon,nitrogen,phosphorus and total soil nutrients were determined.The results showed that the carbon-nitrogen ratios and carbon–phosphorus ratios were 8.0-11.4 and 17.1-25.3,respectively;the percentages of carbon,nitrogen and phosphorus in soil organic carbon(SOC),total nitrogen(TN)and total phosphorus(TP)were 2.84%-5.1%,2.69%-4.44%and 2.19%-5.62%,respectively.The carbon–nitrogen ratio and carbon-phosphorus ratio of P.ceraifera,G.biloba and L.lucidum forests were signifi cantly lower than that of C.deodara forest(P<0.05).The MBC/SOC,MBN/TN and MBP/TP ratios of G.biloba forest were the highest,which had signifi cant difference with those of other tree species(P<0.05).The contents of carbon,nitrogen and phosphorus were extremely or signifi cantly correlated with SOC,TN,TP,tree species and human disturbance,but had no correlation with soil pH,slope,slope direction,etc.Tree species and human disturbance also significantly affected the physical and chemical properties closely related to soil microbial biomass.

Drying-rewetting cycles reduce bacterial diversity and carbon loss in soil on the Loess Plateau of China

With global climate change, soil drying-rewetting(DRW) events have intensified and occurred frequently on the Loess Plateau of China. However, the extent to which the DRW cycles with different wetting intensities and cycle numbers alter microbial community and respiration is barely understood. Here,indoor DRW one and four cycles treatments were implemented on soil samples obtained from the Loess Plateau, involving increase of soil moisture from10% water-holding capacity(WHC) to 60% and 90% WHC(i.e., 10%–60% and 10%–90% WHC, respectively). Constant soil moistures of 10%, 60%,and 90% WHC were used as the controls. The results showed that bacterial diversity and richness decreased and those of fungi remained unchanged under DRW treatments compared to the controls. Under all moisture levels, Actinobacteriota and Ascomycota were the most dominant bacterial and fungal phyla,respectively. The bacterial network was more complex than that of fungi, indicating that bacteria had a greater potential for interaction and niche sharing under DRW treatments. The pulse of respiration rate declined as the DRW cycle increased under 10%–60% WHC, but remained similar for different cycles under 10%–90% WHC. Moreover, the DRW treatments reduced the overall carbon loss, and the direct carbon release under 10%–60% WHC was larger than that under 10%–90% WHC. The cumulative CO_(2) emissions after four DRW cycles were significantly positively correlated with microbial biomass carbon and negatively correlated with fungal richness(Chao 1).