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

Soil Organic Carbon Sequestration Potential in Nectarine Orchards under Different Reclamation Systems

The Red Soil Hilly Region in South China, where there is a high capacity of carbon(C), and the land use and vegetation cover change greatly, is an important ecological area in the world, and has an important impact on the global carbon cycle and the seasonal fluctuation of atmospheric CO_2. To better evaluate the effects of reclamation systems in orchards converted from grasslands on soil carbon sequestration, we investigated soil organic carbon(SOC) content and stable C isotope(δ^(13)C)composition in three nectarine orchards at Yuchi Experimental Station in South China. Compared with the sloping clean tillage orchard and terraced clean tillage orchard, SOC content in the terraced orchard with grass cover was increased by 14.90% to 38.49%, and 7.40% to 15.33%, respectively. During the 14 years after orchard establishment, the soil organic matter sources influenced both δ^(13)C distribution with depth and carbon replacement. SOC turnover of the upper soil layer in the terraced orchard with grass cover(a mean 63.05% of replacement in the 20 cm after 14 years) was 1.59 and 1.41 times larger than that of the sloping clean tillage orchard and terraced clean tillage orchard under subtropical conditions, respectively. The equilibrium value of soil organic carbon in the three treatments ranged from 16.067 to 25.608 g/kg under the experimental conditions. The equilibrium value of soil organic carbon in the surface layer under grass cover was 54.801 t/hm^2, and the carbon sequestration potential was 24.695 1 t/hm^2.

Effects of Vegetation Restoration Age on Soil C:N:P Stoichiometry in Yellow River Delta Coastal Wetland of China

Vegetation restoration can alter carbon(C),nitrogen(N),and phosphorus(P)cycles in coastal wetlands affecting C:N:P stoichiometry.However,the effects of restoration age on soil C:N:P stoichiometry are unclear.In this study,we examined the re-sponses of soil C,N,and P contents and their stoichiometric ratios to vegetation restoration age,focusing on below-ground processes and their relationships to aboveground vegetation community characteristics.We conducted an analysis of temporal gradients based on the'space for time'method to synthesize the effects of restoration age on soil C:N:P stoichiometry in the Yellow River Delta wetland of China.The findings suggest that the combined effects of restoration age and soil depth create complex patterns of shifting soil C:N:P stoichiometry.Specifically,restoration age significantly increased all topsoil C:N:P stoichiometries,except for soil total phosphorus(TP)and the C:N ratio,and slightly affected subsoil C:N:P stoichiometry.The effects of restoration age on the soil C:N ratio was well constrained owing to the coupled relationship between soil organic carbon(SOC)and total nitrogen(TN)contents,while soil TP con-tent was closely related to changes in plant species diversity.Importantly,we found that the topsoil C:N:P stoichiometry was signific-antly affected by plant species diversity,whereas the subsoil C:N:P stoichiometry was more easily regulated by pH and electric con-ductivity(EC).Overall,this study shows that vegetation restoration age elevated SOC and N contents and alleviated N limitation,which is useful for further assessing soil C:N:P stoichiometry in coastal restoration wetlands.

Impact on Soil Organic C and Total Soil N from Cool- and Warm-Season Legumes Used in a Green Manure-Forage Cropping System

Annual forage legumes are important components of livestock production systems in East Texas and the southeastern US. Forage legumes contribute nitrogen (N) to cropping systems through biological N fixation, and their seasonal biomass production can be managed to complement forage grasses. Our research objectives were to evaluate both warm- and cool-season annual forage legumes as green manure for biomass, N content, ability to enhance soil organic carbon (SOC) and soil N, and impact on post season forage grass crops. Nine warm-season forage legumes (WSL) were spring planted and incorporated as green manure in the fall. Forage rye (Secale cereale L.) was planted following the incorporation of WSL treatments. Eight cool-season forage legumes (CSL) were fall planted in previously fallow plots and incorporated as green manure in late spring. Sorghum-sudangrass (Sorghum bicolor x Sorghum bicolor var. sudanense) was planted over all treatments in early summer after forage rye harvest and incorporation of CSL treatments. Sorghum-sudangrass was harvested in June, August and September, and treatments were evaluated for dry matter and N concentration. Soil cores were taken from each plot, split into depths of 0 to 15, 15 to 30 and 30 to 60 cm, and soil C and N were measured using combustion analysis. Nylon mesh bags containing plant samples were buried at 15 cm and used to evaluate decomposition rate of above ground legume biomass, including change in C and N concentrations. Mungbean (Vigna radiata L. [Wilczek]) had the highest shoot biomass yield (6.24 t DM ha-1) and contributed the most total N (167 kg∙ha-1) and total C (3043 kg∙ha-1) of the WSL tested. Decomposition rate of WSL biomass was rapid in the first 10 weeks and very slow afterward. Winter pea (Pisum sativum L. spp. sativum), arrow leaf clover (Trifolium vesiculosum Savi.), and crimson clover (Trifolium incarnatum L.) were the most productive CSL in this trial. Austrian winter pea produced 8.41 t DM ha-1 with a total N yield of 319 kg N ha-1 and total C production of 3835 kg C ha-1. The WSL treatments had only small effects on rye forage yield and N concentration, possibly due to mineralization of N from a large SOC pool already in place. The CSL treatments also had only minimal effects on sorghum-sudangrass forage production. Winter pea, arrow leaf and crimson clover were productive cool season legumes and could be useful as green manure crops. Mungbean and cowpea (Vigna unguiculata [L.] Walp.) were highly productive warm season legumes but may include more production risk in green manure systems due to soil moisture competition.

Growing Cover Crops to Improve Biomass Accumulation and Carbon Sequestration: A Phytotron Study

Cover crop system has shown a potential approach to improving carbon sequestration and environmental quality. Six of each winter and summer cover crops were subsequently grown in two soils, Krome gravelly loam soil (KGL), and Quincy fine sandy soil (QFS), in phytotrons at 3 temperatures (10/20, 15/25, 25/30oC for winter/summer cover crops) to investigate their contributions for carbon (C) sequestration. Among winter cover crops, the highest and the lowest amounts of C accumulated were by bellbean (Vicia faba L.), 597 g/m2 and white clover (Trifolium repens), 149 g/m2, respectively, in the QFS soil. Among summer cover crops, sunn hemp (Crotalaria juncea L.) accumulated the largest quantity of C (481 g/m2), while that by castorbean (Ricinus communis) was 102 g/m2 at 30oC in the KGL soil. The mean net C remained in the residues following the 127 d decomposition were 187 g/m2 of C (73% of the total) and 91 g/m2 (52% of the total) for the winter and summer cover crops, respectively. Following a whole cycle of winter and summer cover crops grown, the mean soil organic C (SOC) increased by 13.8 and 39.1% in the KGL and QFS soil, respectively, compared to the respective soils before. The results suggest that triticale, ryegrass, and bellbean are the promising winter cover crops in the QFS soil, while sunn hemp, velvetbean (Mucuna pruriens), and sorghum sudangrass (Sorghum bicolor ×S. bicolor) are recommended summer cover crops for both soils under favorable temperatures.

Effect of Reducing Chemical Fertilizer on Rice Yield,Output Value,Content of Soil Carbon and Nitrogen after Utilizing the Milk Vetch

A located field experiment was carried out to study the effects of different amount of chemical fertilizer usage on rice yield,economic benefits of rice,soil carbon（C） and total nitrogen（TN） under ploughing back of Chinese milk vetch for 5consecutive years.Six treatments were included in the experiment,they are CK（unfertilized）,CF（100% chemical fertilizer with the amount of N,P2O5,K2 O being150,75,120 kg/hm^2respectively）,A1（22 500 kg/hm^2 Chinese milk vetch and 100%chemical fertilizer）,A2（Chinese milk vetch and 80% nitrogen and potassium fertilizer and 100% phosphate fertilizer）,A3（Chinese milk vetch and 60% nitrogen and potassium fertilizer and 100% phosphate fertilizer）,A4（Chinese milk vetch and 40% nitrogen and potassium fertilizer and 100% phosphate fertilizer）.The results were as follows：application of fertilizer could increase the yield of rice,while Chinese milk vetch combined with fertilizer application had a much more increase effect in rice yield.Under the condition of milk vetch application with 22 500 kg/hm^2,the early rice yield of the treatment A1 was significantly increased by 7.7% compared with that of CF.And the yield of treatment A3 was basically identical to or slight increase in comparison with that of CF.Decreasing amount of fertilizers cloud improve output value of rice in the case of the utilization of Chinese milk vetch.The treatment A1 increased output value of rice by 5.92% in comparison of CF,and treatment A2 was by 4.08% in the next.Treatment A4 showed much better effect in increasing soil organic carbon and total nitrogen in the paddy soil than those of treatments applying mineral fertilizer only.There was a significant reduction on soil organic carbon and TN in treatment A2 in comparison with that of CF.In general,amount of application of milk vetch with 22 500 kg/hm^2 could replace chemical fertilizer partially,it also could improve rice yield,decrease the production cost,and raise the utilization efficiency of nutrients.

Preliminary Analysis on Abnormal Granularity Layers of Soil Profile and the Response of Relative Factors in Loess Plateau

[Objective] The paper was to analyze organic carbon content （SOC）, granularity, total nitrogen content （TN）, carbon-nitrogen ratio （C/N）, calcium carbonate content （CaCO3） of 1cm soil profiles in returning forest in Zhifanggou watershed of Ansai County in Loess Plateau, so as to study the changes of physical and chemical properties in abnormal layer of soil reflected with granularity, as well as the physical and chemical responses of soil. [Method] Three quadrats with the size of 10 m×10 m were randomly selected in three sampling plots in Loess Plateau, three profiles in upper, middle and lower slope were excavated, and the samples were collected with interval of 10 cm; the surface layer with the depth of 0-10 cm was divided into two layers of 0-5 and 5-10 cm for sampling, respectively. Eleven samples were collected in each profile with a total of 99 samples. Its organic carbon content, granularity, total nitrogen content, carbon-nitrogen ratio and CaCO3 content were analyzed. [Result] The soil profiles in three sampling sites contained five characteristic layers, including a1, b1, b2, c1 and c2, the content of soil granule with particle size less than 0.02 mm decreased, and those with particle size 0.02 mm increased, the organic carbon content and C/N value （a1, b1, b2, c2） increased, but the increase trend of CaCO3 content was not obvious. [Conclusion] The study shows that the characteristic soil layer is commonly existed in loess region, especially the eroded loess region, which should be paid attention in the research fields of modern soil science and ecology.

Land-use induced changes in topsoil organic carbon stock of paddy fields using MODIS and TM/ETM analysis:A case study of Wujiang County,China

Topsoil soil organic carbon (SOC) that plays an important role in mitigating atmospheric carbon dioxide (CO_2) buildup is greatly affected by human activities.To evaluate the influence of land-use changes on SOC stocks in paddy soils,a new algorithm was developed by integrating MODIS (moderate resolution imaging spectral-radiometer) and TM/ETM data for timely monitoring the land-use change in Wujiang County.Thereafter,the land-use class-maps derived from MODIS and TM/ETM analyses were further used to estima...

Effect of N and P addition on soil organic C potential mineralization in forest soils in South China

Atmospheric nitrogen deposition is at a high level in some forests of South China. The effects of addition of exogenous N and P on soil organic carbon mineralization were studied to address: (1) if the atmospheric N deposition promotes soil C storage through decreasing mineralization; (2) if the soil available P is a limitation to organic carbon mineralization. Soils (0–10 cm) was sampled from monsoon evergreen broad-leaved forest (MEBF), coniferous and broad-leaved mixed forest (CBMF), and Pinus massoniana...

Degradation induces changes in the soil C:N:P stoichiometry of alpine steppe on the Tibetan Plateau

Due to the Tibetan Plateau’s unique high altitude and low temperature climate conditions,the region’s alpine steppe ecosystem is highly fragile and is suffering from severe degradation under the stress of increasing population,overgrazing,and climate change.The soil stoichiometry,a crucial part of ecological stoichiometry,provides a fundamental approach for understanding ecosystem processes by examining the relative proportions and balance of the three elements.Understanding the impact of degradation on the soil stoichiometry is vital for conservation and management in the alpine steppe on the Tibetan Plateau.This study aims to examine the response of soil stoichiometry to degradation and explore the underlying biotic and abiotic mechanisms in the alpine steppe.We conducted a field survey in a sequent degraded alpine steppe with seven levels inNorthern Tibet.The plant species,aboveground biomass,and physical and chemical soil properties such as the moisture content,temperature,pH,compactness,total carbon(C),total nitrogen(N),and total phosphorus(P)were measured and recorded.The results showed that the contents of soil C/N,C/P,and N/P consistently decreased along intensifying degradation gradients.Using regression analysis and a structural equation model(SEM),we found that the C/N,C/P,and N/P ratios were positively affected by the soil compactness,soil moisture content and species richness of graminoids but negatively affected by soil pH and the proportion of aboveground biomass of forbs.The soil temperature had a negative effect on the C/N ratio but showed positive effect on the C/P and N/P ratios.The current study shows that degradation-induced changes in abiotic and biotic conditions such as soil warming and drying,which accelerated the soil organic carbon mineralization,as well as the increase in the proportion of forbs,whichwere difficult to decompose and input less organic carbon into soil,resulted in the decreases in soil C/N,C/P,and N/P contents to a great extent.Our results provide a sound basis for sustainable conservation and management of the alpine steppe.

Effect of Simulated Acid Rain on Potential Carbon and Nitrogen Mineralization in Forest Soils

Acid rain is a serious environmental problem worldwide. In this study, a pot experiment using forest soils planted with the seedlings of four woody species was performed with weekly treatments of pH 4.40, 4.00, 3.52, and 3.05 simulated acid rain (SAR) for 42 months compared to a control of pH 5.00 lake water. The cumulative amounts of C and N mineralization in the five treated soils were determined after incubation at 25 ℃ for 65 d to examine the effects of SAR treatments. For all five treatments, cumulative CO2-C production ranged from 20.24 to 27.81 mg kg-1 dry soil, net production of available N from 17.37 to 48.95 mg kg-1 dry soil, and net production of NO-3 -N from 9.09 to 46.23 mg kg-1 dry soil. SAR treatments generally enhanced the emission of CO2-C from the soils; however, SAR with pH 3.05 inhibited the emission. SAR treatments decreased the net production of available N and NO3-N. The cumulative CH4 and N2O productions from the soils increased with increasing amount of simulated acid rain. The cumulative CO2-C production and the net production of available N of the soil under Acmena acuminatissima were significantly higher (P ≤ 0.05) than those under Schima superba and Cryptocarya concinna. The mineralization of soil organic C was related to the contents of soil organic C and N, but was not related to soil pH. However, the overall effect of acid rain on the storage of soil organic matter and the cycling of important nutrients depended on the amount of acid deposition and the types of forests.

Changes in Soil C and N Contents and Mineralization Across a Cultivation Chronosequence of Paddy Fields in Subtropical China

Dynamics of soil organic matter in a cultivation chronosequence of paddy fields were studied in subtropical China.Mineralization of soil organic matter was determined by measuring CO2 evolution from soil during 20 days of laboratoryincubation. In the first 30 years of cultivation, soil organic C and N contents increased rapidly. After 30 years, 0-10 cmsoil contained 19.6 g kg-1 organic C and 1.62 g kg-1 total N, with the corresponding values of 18.1 g kg-1 and 1.50g kg-1 for 10-20 cm, and then remained stable even after 80 years of rice cultivation. During 20 days incubation themineralization rates of organic C and N in surface soil (0-10 cm) ranged from 2.2% to 3.3% and from 2.8% to 6.7%,respectively, of organic C and total N contents. Biologically active C size generally increased with increasing soil organicC and N contents. Soil dissolved organic C decreased after cultivation of wasteland to 10 years paddy field and thenincreased. Soil microbial biomass C increased with number of years under cultivation, while soil microbial biomass Nincreased during the first 30 years of cultivation and then stabilized. After 30 years of cultivation surface soil (0-10 cm)contained 332.8 mg kg-1 of microbial biomass C and 23.85 mg kg-1 of microbial biomass N, which were 111% and 47%higher than those in soil cultivated for 3 years. It was suggested that surface soil with 30 years of rice cultivation insubtropical China would have attained a steady state of organic C content, being about 19 g kg-1.

Profile Distribution and Storage of Soil Organic Carbon in an Aquic BrownSoil as Affected by Land Use

Many attempts have been made to estimate the soil organic carbon (SOC) storage under different land uses, especiallyfrom the conversion of forest land or grassland into cultivated field, but limited reports were found on the estimation ofthis storage after cultivated field converted into woodland or grassland, especially in small scales. This study is aimed toinvestigate the dynamics of SOC concentration, its storage and carbon /nitrogen (C/N) ratio in an aquic brown soil at theShenyang Experimental Station of Ecology, Chinese Academy of Sciences under four land use patterns over 14 years. Thefour land use patterns were paddy field (PF), maize field (MF), fallow field (FF) and woodland (WL). In each pedon at 0-150cm depth, soil samples were collected from ten layers. The results showed that the profile distribution of SOC was differentunder different land uses, indicating the effect of land use on SOC. Soil organic carbon was significantly related with soiltotal N, and the correlation was slightly closer in nature ecosystems (with R2=0.990 and P<0.001 in both WL and FF, n=30)than in agroecosystems (with R2=0.976 and P<0.001 in PF, and R2=0.980 and P<0.001 in MF, n=30). The C/N ratio in theprofiles decreased generally with depth under the four land use patterns, and was comparatively higher in WL and lowerin PF. The C/N ratio of the FF was closer to that in the same soil depths of MF than to that of PF. Within 100 cm depth, theannual sequestration of SOC was 4.25, 2.87, and 4.48 t ha-1 more in WL than in PF, MF and FF, the annual SOC increasingrate being 6.15, 3.26, and 5.09 % higher, respectively. As a result, the SOC storage was significantly greater in WL than inany of the other three land use patterns, P=0.001, 0.008, and 0.008 as compared with PF, MF, and FF, respectively, whilethere was no significant difference among the other three land uses. It is suggested that woodland has the potential tomake a significant contribution to C storage and environmental quality.

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.

Change of soil productivity in three different soils after long-term field fertilization treatments

Soil productivity(SP) without external fertilization influence is an important indicator for the capacity of a soil to support crop yield.However,there have been difficulties in estimating values of SPs for soils after various long-term field treatments because the treatment without external fertilization is used but is depleted in soil nutrients,leading to erroneous estimation.The objectives of this study were to estimate the change of SP across different cropping seasons using pot experiments,and to evaluate the steady SP value(which is defined by the basal contribution of soil itself to crop yield) after various longterm fertilization treatments in soils at different geographical locations.The pot experiments were conducted in Jinxian of Jiangxi Province with paddy soil,Zhengzhou of Henan Province with fluvo-aquic soil,and Gongzhuling of Jilin Province with black soils,China.Soils were collected after long-term field fertilization treatments of no fertilizer(control;CK-F),chemical fertilizer(NPK-F),and combined chemical fertilizer with manure(NPKM-F).The soils received either no fertilizer(F0) or chemical fertilizer(F1) for 3-6 cropping seasons in pots,which include CK-P(control;no fertilizer from long-term field experiments for pot experiments),NPK-P(chemical fertilizer from long-term field experiments for pot experiments),and NPKM-P(combined chemical and organic fertilizers from long-term field experiments for pot experiments).The yield data were used to calculate SP values.The initial SP values were high,but decreased rapidly until a relatively steady SP was achieved at or after about three cropping seasons for paddy and fluvo-aquic soils.The steady SP values in the third cropping season from CK-P,NPK-P,and NPKM-P treatments were 37.7,44.1,and 50.0% in the paddy soil,34.2,38.1,and 50.0% in the fluvo-aquic soil,with the highest value observed in the NPKM-P treatment for all soils.However,further research is required in the black soils to incorporate more than three cropping seasons.The partial least squares path mode(PLS-PM) showed that total N(nitrogen) and C/N ratio(the ratio of soil organic carbon and total N) had positive effects on the steady SP for all three soils.These findings confirm the significance of the incorporation of manure for attaining high soil productivity.Regulation of the soil C/N ratio was the other main factor for steady SP through fertilization management.

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.

黑河中游荒漠绿洲过渡带典型固沙植物根区土壤C、N、P化学计量特征

【目的】土壤C、N、P化学计量特征可表征土壤养分供应能力和储量变化,是反映土壤养分循环及其肥力水平的关键指标。固沙植物以灌木和半灌木为主,在抑制荒漠化和维持绿洲生态安全方面扮演着重要的角色。分析固沙植物根区的土壤C、N、P化学计量特征,探究其养分含量变化规律,可为维持荒漠绿洲过渡带的稳定性和今后的防风固沙工程实践提供科学方案和必要参考。【方法】以黑河中游荒漠绿洲过渡带3种典型固沙植物梭梭、泡泡刺和沙拐枣为研究对象,测定固沙植物根区不同土层深度土壤中的有机碳(SOC)、全氮(STN)和全磷(STP)指标,分析3种固沙植物根区土壤C、N、P化学计量特征及影响因素。【结果】3种典型固沙植物根区SOC含量均在60~80cm土层出现峰值,STN、STP含量的峰值均出现在表层土壤;SOC含量随土层深度的增加先增大后减小,STN和STP随土层深度的增大而减小;在研究区特定的环境条件下,植物类型对土壤C、N、P含量及其化学计量特征有显著影响,梭梭根区的土壤养分含量较其他两种植物更高;3种典型固沙植物根区各理化性质指标之间的相关系数总体表现为梭梭>泡泡刺>沙拐枣。【结论】黑河中游荒漠绿洲过渡带梭梭、泡泡刺和沙拐枣根区土壤C、N、P含量具有显著差异(P<0.05),梭梭的保肥能力及其环境适应性较其他两种植物更强。

Carbon and Nitrogen Transformations in Surface Soils Under Ermans Birch and Dark Coniferous Forests

Soil samples were taken from an Ermans birch （Betula ermanii）-dark coniferous forest （Picea jezoensis and Abies nephrolepis） ecotone growing on volcanic ejecta in the northern slope of Changbai Mountains of Northeast China, to compare soil carbon （C） and nitrogen （N） transformations in the two forests. The soil type is Umbri-Gelic Cambosols in Chinese Soil Taxonomy. Soil samples were incubated aerobically at 20℃ and field capacity of 700 g kg^-1 over a period of 27 weeks. The amount of soil microbial biomass and net N mineralization were higher in the Ermans birch than the dark coniferous forest （P 〈 0.05）, whereas the cumulative C mineralization （as CO2 emission） in the dark coniferous forest exceeded that in the Ermans birch （P 〈 0.05）. Release of the cumulative dissolved organic C and dissolved organic N were greater in the Ermans birch than the dark coniferous forest （P 〈 0.05）. The results suggested that differences of forest types could result in considerable change in soil C and N transformations.

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.

Responses of plant community to the linkages in plant-soil C:N:P stoichiometry during secondary succession of abandoned farmlands,China

Succession is one of the central themes of ecology;however,the relationship between aboveground plant communities and underground soils during secondary succession remains unclear.In this study,we investigated the composition of plant community,plant-soil C:N:P stoichiometry and their relationships during secondary succession after the abandonment of farmlands for 0,10,20,30,40 and 50 a in China,2016.Results showed that the composition of plant communities was most diverse in the farmlands after secondary succession for 20 and 50 a.Soil organic carbon and total nitrogen contents slightly decreased after secondary succession for 30 a,but both were significantly higher than those of control farmland(31.21%-139.10%and 24.24%-121.21%,respectively).Moreover,C:N ratios of soil and microbe greatly contributed to the changes in plant community composition during secondary succession of abandoned farmlands,explaining 35.70%of the total variation.Particularly,soil C:N ratio was significantly and positively related with the Shannon-Wiener index.This study provides the evidence of synchronous evolution between plant community and soil during secondary succession and C:N ratio is an important linkage between them.