Long-Term Impact of Soil Management on Microbial Biomass C, N and P in Rice-Based Cropping System

A 12-year field experiment was conducted to investigate the effect of different tillage methods and fertil- ization systems on microbial biomass C, N and P of a gray fluvo-aguic soil in rice-based cropping system. Five fertilization treatments were designed under conventional tillage (CT) or no tillage (NT) system: no fertilizer (CK); chemical fertilizer only (CF); combining chemical fertilizer with pig manure (PM); combining chemical fertilizer with crop straw (CS) and fallow (F). The results showed that biomass C, N and P were enriched in the surface layer of no-tilled soil, whereas they distributed relatively evenly in the tilled soil, which might result from enrichment of crop residue, organic manure and mineral fertilizer, and surficial development of root systems under NT. Under the cultivation system, NT had slightly greater biomass C, N and P at 0～5 cm depth, significantly less biomass C, N and P at 5～15 cm depth, less microbial biomass C, N and equivalent biomass P at 15 ～30 cm depth as compared to CT, indicating that tillage was beneficial for the multiplica tion of organisms in the plowed layer of soil. Under the fallow system, biomass C, N and P in the surface layer were significantly greater for NT than CT while their differences between the two tillage methods were negligible in the deeper layers. In the surface layer, biomass C, N and P in the soils amended with organic manure combined with mineral fertilizers were significantly greater than those of the treatments only with mineral fertilizers and the control. Soils without fertilizer had the least biomass nutrient contents among the five fertilization treatments. Obviously, the long-term application of organic manure could maintain the higher activity of microorganisms in soils. The amounts of biomass C, N and P in the fallowed soils varied with the tillage methods; they were much greater under NT than under CT, especially in the surface layer, suggesting that the frequent plowing could decrease the content of organic matter in the surface layer of the fallowed soil.

Changes of Soil Microbial Biomass C and P During Wheat Growth After Application of Fertilizers

A pot experiment was carried out with a clay loam in a green house. The results showed that soil microbial biomass C increased with the application of organic manure at the beginning of the experiment and then gradually decreased with declining of the temperature. The soil biomass C increased at the tillering stage when the temperature gradually increased, and rose to the highest value at the anthesis stage, being about 554.9-794.4 mg C kg-1. The application of organic manure resulted in the highest increase in biomass C among the fertilization treatments while that of ammonium sulphate gave the lowest. At the harvest time the soil biomass C decreased to the presowing level. Like the soil biomass C the amount of biomass P was increased by the incorporation of organic manure and was the highest among the treatments, with the values of the check and ammonium sulphate treatments being the lowest. Meanwhile, the changing patterns of the C/P ratio of soil microbial biomass at stages of wheat growth are also described.

Effect of heat-disturbance on microbial biomass carbon and microbial respiration in Chinese fir(Cunninghamia lanceolata) forest soils

Prescribed fire has now become the usual management practice in the Chinese fir （Cunninghamia lanceolata （Lamb.） Hook.） plantation in southern China. Heat generated during fire may affect carbon （C） dynam- ics in soils. We investigated the microbial biomass C （MBC） and microbial respiration in two Chinese fir forest soils （one is not exposed to fire for the past 88 years, and the other is recently exposed to prescribed fire） after soil heating （100 and 200 ℃） under three moisture regimes [25, 50 and 75 % of water holding capacity （WHC）]. For both soils, significant reduction in MBC with increasing heating temperature was found. Soils without exposing to fire previously had significantly greater MBC concentra- tion than the fire-exposed soils when heated at 100 or 200 ℃. Lower soil water content resulted in higher MBC concentrations in both soils. In contrast, both soils had the highest soil microbial respiration rate at 50 % WHC. Soils without exposing to fire previously had the greatest microbial respiration rates at 200 ℃, while the fire-ex- posed soils when heated at 100 ℃ had greatest microbialrespiration rates. During 14-days post-heat incubation, soil MBC in both soils was greatest after heating at 200 ℃ and 25 % WHC. However, soil previously exposed to fire had the lowest CO2 evolution when incubated at 25 % WHC.

Responses of microbial activities and soil physical-chemical properties to the successional process of biological soil crusts in the Gurbantunggut Desert,Xinjiang

Biological soil crusts （BSCs） are capable of modifying nutrient availability to favor the establishment of biogeochemical cycles. Microbial activities serve as critical roles for both carbon and nutrient transformation in BSCs. However, little is known about microbial activities and physical-chemical properties of BSCs in the Gurbantunggut Desert, Xinjiang, China. In the present research, a sampling line with 1-m wide and 20-m long was set up in each of five typical interdune areas selected randomly in the Gurbantunggut Desert. Within each sampling line, samples of bare sand sheet, algal crusts, lichen crusts and moss crusts were randomly collected at the depth of 0-2 cm. Varia- tions of microalgal biomass, microbial biomass, enzyme activities and soil physical-chemical properties in different succession of BSCs were analyzed. The relationships between microalgal biomass, microbial biomass, enzymatic activities and soil physical-chemical properties were explored by stepwise regression. Our results indicate that micro- algal biomass, microbial biomass and most of enzyme activities increased as the BSCs developed and their highest values occurred in lichen or moss crusts. Except for total K, the contents of most soil nutrients （organic C, total N, total P, available N, available P and available K） were the lowest in the bare sand sheet and significantly increased with the BSCs development, reaching their highest values in moss crusts. However, pH values significantly decreased as the BSCs developed. Significant and positive correlations were observed between chlorophyll a and microbial biomass C. Total P and N were positively associated with chlorophyll a and microbial biomass C, whereas there was a significant and negative correlation between microbial biomass and available P. The growth of cyanobacteria and microorganism contributed C and N in the soil, which offered substrates for enzyme activities thus increasing enzyme activities. Probably, improvement in enzyme activities increased soil fertility and promoted the growth of cyanobacteria, eukary- otic algae and heterotrophic microorganism, with the accelerating succession of BSCs. The present research found that microalgal-microbial biomass and enzyme activities played important roles on the contents of nutrients in the successional stages of BSCs and helped us to understand developmental mechanism in the succession of BSCs.

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.

Microbial Biomass Carbon and Total Organic Carbon of Soils as Affected by Rubber Cultivation

Soil samples were collected from different rubber fields in twenty-five plotsselected randomly in the Experimental Farm of the Chinese Academy of Tropical Agriculture Scienceslocated in Hainan, China, to analyse the ecological effect of rubber cultivation. The results showedthat in the tropical rubber farm, soil microbial biomass C (MBC) and total organic C (TOC) wererelatively low in the content but highly correlated with each other. After rubber tapping, soil MBCof mature rubber fields decreased significantly, by 55.5 percent. compared with immature rubberfields. Soil TOC also decreased but the difference was not significant. Ratios of MBC to TOCdecreased significantly. The decreasing trend of MBC stopped at about ten years of rubbercultivation. After this period, soil MBC increased relatively while soil TOC still kept indecreasing. Soil MBC changes could be measured to predict the tendency of soil organic matterchanges due to management practices in a tropical rubber farm several years before the changes insoil TOC become detectable.

Effects of a decade of organic fertilizer substitution on vegetable yield and soil phosphorus pools, phosphatase activities, and the microbial community in a greenhouse vegetable production system

Partial substitution of chemical fertilizers by organic amendments is adopted widely for promoting the availability of soil phosphorus(P)in agricultural production.However,few studies have comprehensively evaluated the effects of longterm organic substitution on soil P availability and microbial activity in greenhouse vegetable fields.A 10-year(2009–2019)field experiment was carried out to investigate the impacts of organic fertilizer substitution on soil P pools,phosphatase activities and the microbial community,and identify factors that regulate these soil P transformation characteristics.Four treatments included 100%chemical N fertilizer(4 CN),50%substitution of chemical N by manure(2 CN+2 MN),straw(2 CN+2 SN),and combined manure with straw(2 CN+1 MN+1 SN).Compared with the 4 CN treatment,organic substitution treatments increased celery and tomato yields by 6.9-13.8%and 8.6-18.1%,respectively,with the highest yields being in the 2 CN+1 MN+1 SN treatment.After 10 years of fertilization,organic substitution treatments reduced total P and inorganic P accumulation,increased the concentrations of available P,organic P,and microbial biomass P,and promoted phosphatase activities(alkaline and acid phosphomonoesterase,phosphodiesterase,and phytase)and microbial growth in comparison with the 4 CN treatment.Further,organic substitution treatments significantly increased soil C/P,and the partial least squares path model(PLS-PM)revealed that the soil C/P ratio directly and significantly affected phosphatase activities and the microbial biomass and positively influenced soil P pools and vegetable yield.Partial least squares(PLS)regression demonstrated that arbuscular mycorrhizal fungi positively affected phosphatase activities.Our results suggest that organic fertilizer substitution can promote soil P transformation and availability.Combining manure with straw was more effective than applying these materials separately for developing sustainable P management practices.

Effects of Lanthanum on Microbial Biomass Carbon and Nitrogen in Red Soil

The result of soil. culture experiment shows that lanthanum has inhibitory effect on the microbial biomass C and N in red soil, and the inhibition is strengthened with increasing concentration of La. The result of rice pot culture experiment shows that low concentration of La has slight stimulative effect on the microbial biomass C and N in red soil, but its high concentration has inhibitory effect and the inhibition is strengthened with increasing concentration of La. Soil microbial biomass is an important indicator for evaluating rare earths-polluted soil. It is assumed that the critical La concentration is 100 mg.kg(-1) at which red soil tends to be polluted.

The Importance of Three Protozoa in Corn Straw Decomposition and Nutrient Transformation

Three typical soil protozoa of Bodo edax, Colpoda cucullus and Amoeba proteus were inoculated into the soil amended with corn straw. The soils were then incubated at 25℃ for 60 days. It was found that the protozoa, particularly Bodo edax, significantly reduced soil microbial biomass C. However, the decomposition of corn straw was accelerated by the protozoa. Colpoda cucullus significantly enhanced soil available P content, but Amoeba proteus decreased soil available P content. Colpoda cucullus and Bodo edax did not obviously influence NH4+-N and NO3--N contents. In contrast, Amoeba proteus significantly increased both NH4+-N and NO3--N contents.

Plant Biomass, Primary Production and Mineral Cycling of a Mixed Oak Forest in Linnebjer, Sweden

Plant biomass, primary production and mineral cycling were studied in a mixed deciduous forest (Quercus robur L., Tilia cordata L. and Corylus avellana L.) in southern Sweden. Plant biomass amount above and below ground was 201 and 37 t&middotha-1, respectively. Primary production above and below ground was an estimated 13.3 and 2.3 t&middotha-1, respectively. Carbon was the dominant element in the forest ecosystem, comprising 133 t&middotha-1. Other major elements were: N > Ca > K > Si > Mg > S > Mn > P > Fe and Na (range 1123 to 18 kg&middotha-1), followed by some trace elements. Yearly litterfall restored 6.0 t&middotha-1 organic matter or 2.3 t&middotha-1 carbon. Approximately 45% decomposed and returned to the soil during the year. Monitoring of other elements revealed that the ecosystem received inputs through dry and wet deposition, in particular 34.4 kg&middotha-1 S and 9.4 kg&middotha-1 of N yearly as throughfall. Determination of yearly biomass increase showed that the oak forest ecosystem was still in an aggradation or accumulation phase.

Soil and microbial C:N:P stoichiometries play vital roles in regulating P transformation in agricultural ecosystems:A review

Stoichiometry plays a crucial role in biogeochemical cycles and can modulate soil nutrient availability and functions. In agricultural ecosystems,phosphorus(P) fertilizers(organic or chemical) are often applied to achieve high crop yields. However, P is readily fixed by soil particles, leading to low P use efficiency. Therefore, understanding the role of carbon:nitrogen:P stoichiometries of soil and microorganisms in soil P transformation is of great significance for P management in agriculture. This paper provides a comprehensive review of the recent research on stoichiometry effect on soil P transformation in agricultural ecosystems. Soil microorganisms play an important role in the transformation of soil non-labile inorganic P to microbial biomass P by regulating microbial biomass stoichiometry. They also mobilize soil unavailable organic P into available P by changing ecoenzyme stoichiometry. Organic materials, such as manure and straw, play an important role in promoting the transformation of insoluble P into available P as well. Additionally, periphytic biofilms can reduce P loss from rice field ecosystems. Agricultural stoichiometries are different from those of natural ecosystems and thereby should receive more attention due to the influences of anthropogenic factors. Therefore, it is necessary to conduct further stoichiometry research on the soil biochemical mechanisms underlying P transformation in agricultural ecosystems. In conclusion, understanding stoichiometry impact on soil P transformation is crucial for P management in agricultural ecosystems.

Soil Aggregates, Organic Matter, and Labile C and N Fractions after 37 Years of N, P and K Applications to an Irrigated Subtropical Soil under Maize-Wheat Rotation

Abstract： Physical, chemical and biological soil properties in surface （0-5 cm） and subsurface soil （5-15 cm） were determined in a field experiment conducted with seven treatments consisted of different combinations of fertilizer N （0, 100 and 200 kg N ha^-1）, P （0, 22 and 44 kg P2O5 ha^-1） and K （0, 41 and 82 kg K2O ha^-1） applied both to summer-grown maize （Zea mays L.） and winter-grown wheat （Triticum aestivum L.） crops continuously for 37 years under irrigated subtropical conditions. Application of N, P and K significantly increased water stable aggregates and had profound effects in increasing the mean weight diameter as well as the formation of macro-aggregates, which were highest in both surface （81%） and subsurface （74%） soil layers with application of 100 kg N ＋ 22 kg P2O5 ＋ 41 kg K2O ha^-1 （N100P22K41）. The N100P22K41 treatment also enhanced total organic C （TOC） from 4.4 g kg^-1 in no-NPK control to 4.8 g kg^-1in surface layer and from 3.3 to 4.1 g kg1 in subsurface layer leading to the 20% higher TOC stocks in 0-15 cm soil. The labile C and N fractions such as water soluble C, particulate and light fraction organic matter, potentially mineralizable N and microbial biomass were also highest under the optimized balanced application of N100P22K41. Relatively higher increase in all labile fractions of C and N as proportion of TOC and total N, respectively suggested that these are potential indicators to reflect changes in management practices long before changes in TOC and TN are detectable. These results demonstrated that optimized balanced application of N, P and K is crucial for improving soil health ensuring long-term sustainability of farming systems in semiarid subtropical soils.

Soil Carbon Sequestration,Water Use Efficiency(WUE) and Biological Nitrogen Fixation(BNF) Under Conservation Agriculture in Rain-fed Dry Area of North-west Pakistan

Land degradation,unbalanced nutrition,change in climate and its extreme variability are the factors affecting the sustainability of agriculture and food security.In North-west Pakistan,more than 50%of the cultivated area is rain-fed and the crop productivity is low.Conservation agriculture reduces greenhouse gas emissions by enhancing soil carbon sequestration and then improved soil fertility,WUE and crop productivity.A field experiment

Cycling of Carbon and Other Elements in a Beech Forest Hestehave, Jutland, Denmark, in the Past 50 Years

Plant biomass, primary production and mineral cycling in the beech forest (Fagus sylvatica L.), Hestehave in Jutland, Denmark were studied over a 50-year period. The role of the forest as a carbon sink was also assessed. Aboveground tree biomass was 226 t·ha-1 in 1970 and after a 50-year 539 t·ha-1 in 2014, an unexpected increase with 313 t·ha-1. Annual production at those two points in time was 13.4 and 20.5 t·ha-1, respectively. It was apparent that the tree biomass was still acting as a sink for carbon, which was the dominant element in the aboveground parts. The concentration of other elements (N > K > Mg > P > S > Na > Mn > Zn > Fe > Cu) ranged from 495 to 0.4 kg·ha-1. Annual litterfall restored 3.2 t·ha-1 to the soil as organic matter or 1.6 t·ha-1 as carbon. Over the year 53% of the litterfall was decomposed. A pH decrease of 0.95 units in the soil was observed between 1968 and 1993. This was attributed to fallout from a neighbouring thermal heating station affecting sulfur deposition and increasing soil acidification. After 1993, when filters were fitted in the heating station, the pH decrease in the soil was smaller, only 0.09 pH-units up to 2011. The increased tree growth is an additional, likely explanation for the observed soil acidification. Deposition of the growth-limiting element nitrogen increased during later years and is now, most likely around 20 kg·ha-1 per annum, which may partly contribute to the increased production.

Elevated CO_(2) increases shoot growth but not root growth and C:N:P stoichiometry of Suaeda aralocaspica plants

The purpose of the current study was to investigate the eco-physiological responses,in terms of growth and C:N:P stoichiometry of plants cultured from dimorphic seeds of a single-cell C4 annual Suaeda aralocaspica(Bunge)Freitag and Schütze under elevated CO_(2).A climatic chamber experiment was conducted to examine the effects of ambient(720μg/L)and CO_(2)-enriched(1440μg/L)treatments on these responses in S.aralocaspica at vegetative and reproductive stages in 2012.Result showed that elevated CO_(2) significantly increased shoot dry weight,but decreased N:P ratio at both growth stages.Plants grown from dimorphic seeds did not exhibit significant differences in growth and C:N:P stoichiometric characteristics.The transition from vegetation to reproductive stage significantly increased shoot:root ratio,N and P contents,but decreased C:N,C:P and N:P ratios,and did not affect shoot dry weight.Moreover,our results indicate that the changes in N:P and C:N ratios between ambient and elevated CO_(2) are mainly caused by the decrease of N content under elevated CO_(2).These results provide an insight into nutritional metabolism of single-cell C4 plants under climate change.

Effect of land use on microbial biomass－C, －N and －P in red soils

Eleven red soils varying in land use and fertility status were used to examine the effect of land use on microbial biomass C, N and P. Microbial biomass C in the red soils ranged from about 68 mg C/kg to 225 mg C/kg, which is generally lower than that reported from other types of soil, probably because of low organic matter and high acidity in the red soils. Land use had considerable effects on the amounts of soil C mic . The C mic was the lowest in eroded fallow land, followed by woodland, tea garden, citrus grove and fallow grassland, and the highest in vegetable and paddy fields. There was significant correlation between C mic and organic matter content, suggesting that the influence of land use on C mic is mainly related to the input and accumulation of organic matter. Microbial biomass N in the soils ranged from 12.1 Nmg/kg to 31.7 Nmg/kg and was also affected by land use. The change of N mic with land use was similar to that of C mic . The microbial C/N ratio ranged from 5.2 to 9.9 and averaged 7.6. The N mic was significantly correlated with soil total N and available N. Microbial biomass P in the soils ranged from 4.5 mg P/kg to 52.3 mg P/kg. The microbial C/P ratio was in the range of 4-23. The P mic was relatively less affected by land use due to differences in fertilization practices for various land use systems.

Effect of Long-Term Straw Incorporation on SoilMicrobial Biomass and C and N Dynamics

A study was performed on the long-term effect of straw incorporation on soil microbial biomass C contents, C and N dynamics in both Rothamsted and Woburn soils. The results showed that for both soils,the microbial biomass C contents were significantly different among all the treatments, and followed the sequence in treatments of straw chopped and incorporated into 10 cm (CI10) > straw burnt and incorporated into 10 cm (BI10) > straw chopped and incorporated into 20 cm (CI20) > straw burnt and incorporated into 20 cm (BI20). Laboratory incubation of soils showed that the cumulative CO2 evolution was closely related to the soil microbial biomass C content. Carbon dioxide evolution rates (CO2-C, μg (g d) -1 ) decreased rapidly in the first two weeks’ incubation, then decreased more slowly. The initial K2SO4-extractable NH4-N and NO3-N contents were low and similar in all the treatments, and all increased gradually with the incubation time. However, net N immobilization was observed in chopped treatments for Rothamsted soils during the first 4 weeks. Nevertheless, more N mineralization occurred in neatment CI10 than any other treatment at the end of incubation for both soils. The Woburn soils could more easily suffer from the leaching of nitrate because the soils were more permeable and more N was mineralized during the incubation compared to the Rothamsted soils.

Responses of Soil Microbial Activity and Biomass to Salinity After Repeated Additions of Plant Residues

Microbial adaptation to salinity can be achieved through synthesis of organic osmolytes,which requires high amounts of energy;however,a single addition of plant residues can only temporarily improve energy supply to soil microbes.Therefore,a laboratory incubation experiment was conducted to evaluate the responses of soil microbes to increasing salinity with repeated additions of plant residues using a loamy sand soil with an electrical conductivity in saturated paste extract(EC_e) of 0.6 dS m^(-1).The soil was kept non-saline or salinized by adding different amounts of NaCl to achieve EC_e of 12.5,25.0 and 50.0 dS m^(-1).The non-saline soil and the saline soils were amended with finely ground pea residues at two rates equivalent to 3.9 and 7.8 g C kg^(-1) soil on days 0,15 and29.The soils receiving no residues were included as a control.Cumulative respiration per g C added over 2 weeks after each residue addition was always greater at 3.9 than 7.8 g C kg^(-1) soil and higher in the non-saline soil than in the saline soils.In the saline soils,the cumulative respiration per g C added was higher after the second and third additions than after the first addition except with3.9 g C kg^(-1) at EC_e of 50 dS m^(_1).Though with the same amount of C added(7.8 g C kg^(-1)),salinity reduced soil respiration to a lesser extent when 3.9 g C kg^(-1) was added twice compared to a single addition of 7.8 g C kg^(-1).After the third residue addition,the microbial biomass C concentration was significantly lower in the soils with EC_e of 25 and 50 dS m^(_1) than in the non-saline soil at3.9 g C kg^(-1),but only in the soil with EC_e of 50 dS m^(-1) at 7.8 g C kg^(-1).We concluded that repeated residue additions increased the adaptation of soil microbial community to salinity,which was likely due to high C availability providing microbes with the energy needed for synthesis of organic osmolytes.

Effect of intensity and duration of freezing on soil microbial biomass,extractable C and N pools,and N2O and CO2 emissions from forest soils in cold temperate region

Freezing can increase the emissions of carbon dioxide （CO2） and nitrous oxide （N2O） and the release of labile car- bon （C） and nitrogen （N） pools into the soil. However, there is limited knowledge about how both emissions respond differ- ently to soil freezing and their relationships to soil properties. We evaluated the effect of intensity and duration of freezing on the emissions of CO2 and N2O, net N mineralization, microbial biomass, and extractable C and N pools in soils from a mature broadleaf and Korean pine mixed forest and an adjacent secondary white birch forest in northeastern China. These soils had different contents of microbial biomass and bulk density. Intact soil cores of 0-5 cm and 5-10 cm depth sampled from the two temperate forest floors were subjected to -8, -18, and -80℃ freezing treatments for a short （10 d） and long （145 d） duration, and then respectively incubated at 10~C for 21 d. Soil cores, incubated at 10℃ for 21 d without a pretreatment of freezing, served as control. Emissions of N20 and COz after thaw varied with forest type, soil depth, and freezing treatment. The differ- ence could be induced by the soil water-filled pore space （WFPS） during incubation and availability of substrates for N20 and CO2 production, which are released by freezing. A maximum N2O emission following thawing of frozen soils was observed at approximately 80% WFPS, whereas CO2 emission from soils after thaw significantly increased with increasing WFPS. The soil dissolved organic C just after freezing treatment and CO2 emission increased with increase of freezing duration, which paralleled with a decrease in soil microbial biomass C. The cumulative net N mineralization and net ammonification after freezing treatment as well as N2O emission were significantly affected by freezing temperature. The N2O emission was nega- tively correlated to soil pH and bulk density, but positively correlated to soil KzSO4-extractable NO3 -N content and net am- monification. The CO2 emission was positively correlated to the cumulative net N mineralization and net ammonification. From the above results, it can be reasonably concluded that for a wide range of freezing temperature and freezing duration, N2O and CO2 emissions after thaw were associated mainly with the changes in soil net N mineralization and the availability of substrate liberated by freezing as well as other soil properties that influence porosity.

Land use effects on the dynamics of soil C,N and microbes in the water-wind erosion crisscross region of the northern Loess Plateau,China

The water-wind erosion crisscross region of the northern Loess Plateau in China is under constant pressure from severe erosion due to its windy and dry climate and intensive human activities. Identifying sustainable land use patterns is key to maintaining ecosystem sustainability in the area. Our aim was to appraise the impacts of different land use regimes on the dynamics of soil total organic C(TOC), total N(TN), and microbes in a typical watershed in the northern Loess Plateau to identify suitable land use types that can maintain soil fertility and sustainability. A field experiment was performed in Liudaogou watershed in Shenmu City, Shaanxi Province, China, where the dynamics of soil TOC and TN, microbial biomass C and N, microbial respiration, and net N mineralization in six typical land use types, dam land, rainfed slope land, deciduous broadleaf forest, evergreen coniferous forest, shrubland, and grassland,were measured in three different growing seasons. Land use type and season significantly affected TOC, TN, and the dynamics of microbial biomass and activity. As the most anthropogenically disturbed land use pattern, dam land was an optimal land use pattern for TOC sequestration due to its higher TOC and TN, but lower microbial activity. Soil TOC, TN, and microbial properties demonstrated a decreasing trend after natural grassland was converted to shrubland,forest, and rainfed slope land. Shrubland with exotic N-fixing Korshinsk peashrub(Caragana korshinskii Kom.) can maintain TOC, TN, and microbial properties similar to those in grassland. Soil TOC, NH_(4+)^(-)N, TN, moisture, and extractable C were the principal indexes for soil microbial biomass and activity and explained 88.90% of the total variance. Thus, grassland was the optimal land use pattern in the water-wind erosion crisscross region of the northern Loess Plateau to maintain ecosystem stability and sustainability.