Dual-chamber measurements of δ13C of soil-respired CO2 partitioned using a field-based three end-member model

The contribution of old soil C (SOM) to total soil respiration (R_S) in forest has been a crucial topic in global change research, but remains uncertain. Isotopic methods, such as natural variations in carbon isotope composition (δ¹³C) of soil respiration, are more frequently being applied, and show promise in separating heterotrophic and autotrophic contributions to R_S. However, natural and artificial modification of δ¹³C_Rs can cause isotopic disequilibria in the soil-atmosphere system generating a mismatch between what is usually measured and what process-based models will predict. Here we report the partitioning of the soil surface CO₂ flux in a warm Mediterranean forest into components derived from root, litter/humus, and SOM sources using a new, three end-member mixing model, and compare this with the conventional partitioning into autotrophic and heterotrophic components. The three end-member mixing model takes into account both the discrimination during CO₂ respiration/decomposition of the three components, as well as the fractions of their CO₂ fluxes integrated over the total soil profile mass. In addition, we used a novel dual-chamber technique to ensure that δ¹³C_Rs was subjected to minimal artefacts during measurement.We observed that by using measured soil surface CO₂ concentrations as a baseline level for the dual-chamber operation, it was possible to achieve and monitor the necessary conservation of the soil CO₂ steady-state diffusion conditions during the measurements, without using permanent collars inserted deeply into the soil. When R_S (8.64 g CO₂ m² d⁻¹) was partitioned into two components, the mean autotrophic and heterotrophic respiration was 56 and 44%, respectively. When R_S was partitioned using the three-way model, however, roots, litter/humus, and SOM contributed 30, 33, and 37% of the total flux. Our results confirm that to improve the estimates of the partitioning method, it is important to distinguish the fractional contribution of the long-term SOM-derived flux from younger and more labile sources.     

Origin of positive δC of emitted CO2 from soils after application of biogas residues

Bioenergy production from renewable organic material is known to be a clean energy source and therefore its use is currently much promoted in many countries. Biogas by-products also called biogas residues (BGR) are rich in partially stable organic carbon and can be used as an organic fertilizer for crop production. However so far, many environmental issues relevant when BGR are applied to agricultural land (soil C sequestration, increased denitrification and nutrient leaching) still have to be studied. Therefore a field experiment was set up to investigate the degradation of BGR and its impact on the decomposition of native soil organic matter based on a natural abundance stable isotope approach. Maize, a C₄ plant has been used as bioenergy crop, therefore the δ¹³C of total C in BGR was −16.0‰_PDB and soil organic matter was mostly derived from C₃ plant based detritus, SOM thus showed a δ¹³C of −28.4‰_PDB. Immediately after BGR application, soil-emitted CO₂ showed unexpectedly high δ¹³C of up to +23.6‰_PDB, which has never been reported earlier. A subsequent laboratory scale experiment confirmed the positive δ¹³C of soil-emitted CO₂ after BGR addition and showed that obviously, the added BGR led to a consumption of dissolved inorganic C in soils. Additionally, it was observed that the δ¹³C of CO₂ driven from inorganic C of BGR (BGR-IC) by acid treatment was +35.6‰_PDB. Therefore, we suggest that also under field conditions the transformation of BGR-IC into CO₂ contributed largely to CO₂ emissions in addition to the decomposition of organic matter, which affected both the amount and the carbon isotope signature of emitted CO₂ in the initial period after BGR application. Positive δ¹³C of inorganic C contained in BGR was attributed to processes with strong fractionation of C isotopes during anaerobic fermentation in the biogas formation process.     

Abiotic drivers and their interactive effect on the flux and carbon isotope (C and δC) composition of peat-respired CO2

Feedbacks to global warming may cause terrestrial ecosystems to add to anthropogenic CO₂ emissions, thus exacerbating climate change. The contribution that soil respiration makes to these terrestrial emissions, particularly from carbon-rich soils such as peatlands, is of significant importance and its response to changing climatic conditions is of considerable debate. We collected intact soil cores from an upland blanket bog situated within the northern Pennines, England, UK and investigated the individual and interactive effects of three primary controls on soil organic matter decomposition: (i) temperature (5, 10 and 15 °C); (ii) moisture (50 and 100% field capacity – FC); and (iii) substrate quality, using increasing depth from the surface (0–10, 10–20 and 20–30 cm) as an analogue for increased recalcitrance of soil organic material. Statistical analysis of the results showed that temperature, moisture and substrate quality all significantly affected rates of peat decomposition. Q₁₀ values indicated that the temperature sensitivity of older/more recalcitrant soil organic matter significantly increased (relative to more labile peat) under reduced soil moisture (50% FC) conditions, but not under 100% FC, suggesting that soil microorganisms decomposing the more recalcitrant soil material preferred more aerated conditions. Radiocarbon analyses revealed that soil decomposers were able to respire older, more recalcitrant soil organic matter and that the source of the material (deduced from the δ¹³C analyses) subject to decomposition, changed depending on depth in the peat profile.     

Application of NaHCO3/ DTPA Extractant-ICP Spectrometry Technique in Soil Test for Availability of Nutrients and Heavy Metals

Soil test for availability of nutrients and heavy metals is extensively served as a means for the evaluations of soil fertility, and environmental effects and phytotoxicity of pollutants in soils, and for the fertilizer recommendation in agricultural and environmental sciences. Therefore, great attention has been paid to the measurement of elemental availability in soil test.     

Is yield enhancement by CO2 enrichment greater in genotypes with a higher capacity for nitrogen fixation?

Yield responsiveness to elevated CO₂ concentration [CO₂] was previously found to be greater when nitrogen (N) was supplied in adequate amounts; however, it remains unclear whether genotypic differences in N₂-fixing capacity affect yield responsiveness in soybean. We tested the hypothesis that yield responsiveness to elevated [CO₂] in soybean is greater in a genotype with a higher capacity for N₂ fixation. We used three near-isogenic genotypes with contrasting nodulation capacities: super-nodulating, normally nodulating and non-nodulating genotypes. Plants were subjected to two levels of [CO₂] (ambient or elevated: ambient + 200 μmol mol⁻¹) and two temperature regimes (low or high: low + ca. 4-5 °C) using temperature gradient chambers. The super-nodulating genotype exhibited a higher N content in leaves, regardless of [CO₂] and temperature. Photosynthetic rates were enhanced by CO₂ enrichment at earlier growth stages, but not at later growth stages, regardless of genotype. This photosynthetic acclimation was reflected in biomass production in all the genotypes examined. Yield responsiveness to elevated [CO₂] was greater in the nodulating genotypes than in the non-nodulating genotype, but the genotypic differences were obscured between the normally nodulating and super-nodulating genotype, thus our hypothesis was not fully verified.     

Controls on soil carbon accumulation during woody plant encroachment: Evidence from physical fractionation, soil respiration, and δC of respired CO2

Woody plant encroachment into grasslands and savannas is a globally extensive land-cover change that alters biogeochemical processes and frequently results in soil organic carbon (SOC) accrual. We used soil physical fractionation, soil respiration kinetics, and the isotopic composition of soil respiration to investigate microbial degradation of accrued SOC in sandy loam soils along a chronosequence of C₃woody plant encroachment into a C₄-dominated grassland in southern Texas. Our previous work in this system demonstrated significant changes in the chemistry and abundance of lignin and aliphatic biopolymers within particulate soil fractions during the first 40 yrs of woody plant encroachment, indicating selective accrual of purportedly more recalcitrant plant chemicals. However, during the long-term soil laboratory incubation presented herein, a greater proportion of SOC was mineralized in soils from older woody stands (34-86 yrs) than in soils from younger woody stands (14-23 yrs) and grasslands, providing no evidence for greater biochemical recalcitrance as a controlling mechanism for SOC accrual. In addition, δ¹³C values of respired CO₂ indicate that the mineralized SOC was predominately of C₃ origin from all woody stands along the chronosequence, and that respired CO₂ was primarily derived from the free light fraction (density <1.0 g/cm³) and macroaggregate-sized soil fraction. Our data suggested that the location of SOC among soil fractions was more important than plant polymer chemistry in determining SOC turnover rates during incubation. Surprisingly, estimates of the size and turnover rate of the active SOC pool based on respiratory kinetics did not increase with woody encroachment, and the turnover rate of the slower SOC pool decreased, again supporting the notion that increases in biochemically recalcitrant biopolymers did not hinder decomposition in the lab. These data indicate environmental conditions that may allow for C accrual in the field were alleviated during the controlled incubation. Therefore, C accrual in these sandy loam soils following woody encroachment should not be assumed stable, and this factor should be taken into account when considering responses of SOC to climate change or when making management decisions regarding land cover impacts on SOC.     

Comparison of a dual‐inlet gas isotope ratio mass spectrometry system and an automated single‐inlet mass spectrometry system for δ13C analysis

Abstract

A dual‐inlet isotope ratio mass spectrometer (VG‐SIRA 12, Isotech, Middlewich, England) using sealed‐glass combustion sample preparation and an automated single‐inlet isotope ratio mass spectrometry system (RoboPrep Sample Converter interfaced with a TracerMass Stable Isotope Detector, Europa Scientific, Crewe, England) were compared for δ¹³C analysis. Two hundred twenty four samples of plant and animal tissue were analyzed for S¹³C using the two systems. Delta ¹³C values obtained from the two instruments were highly correlated (r²=0.986, P=0.0001). The slope of the relationship was not different from one nor was the Y‐intercept different from zero (Y=‐0.2 + 1.0X; P=0.86 and P=0.28 for the slope and Y‐intercept, respectively). In addition, samples from two complete experiments were run on both mass spectrometery systems and statistical analyses performed. In both experiments, differences between treatments were detectable using the RoboPrep system that were not detectable using the SIRA 12 system. In all cases mean δ¹³C values were comparable between the two systems, and coefficients of variation were low; well within acceptable experimental limits.     

高低应答CO2水稻品种苗期根系对高C环境的响应

本文利用水培试验和琼脂板培养试验研究了高CO₂条件下产量响应存在显著差异的两个水稻品种：II优084(高响应)和武运粳23(低响应),在幼苗期根系形态对高C的响应差异。水培试验结果表明,在幼苗时期,高应答品种II优084在低氮条件下地上部生物量在高CO₂下增加28.5%,根系干物质量对高CO₂响应显著,增幅为28.5%,而其不定根数目没有显著增加,对干物质量响应贡献较大的为总根长。II优084的总根长在高CO₂下增幅为26.3%,不同根粗的根长均有高响应。低应答品种武运粳23低氮下地上部和根系响应不显著,而在正常氮和高氮下则不同。正常氮条件下,地上部对高CO₂响应不显著,而根系生物量在高CO₂下显著增加76.0%,不定根数目增加25.8%,同时总根长增加45.0%,不同根粗的根长均有高响应,II优084则没有显著响应。在高氮条件下,武运粳23地上部生物量在高CO₂下增加35.5%,根系生物量增加80.3%,不定根数目增加38.5%,根系平均直径增加16.7%,总根长无响应,而II优084生物量在高氮下无显著差异。同时,武运粳23在正常氮和高氮下的根系表面积和体积对高CO₂响应也较II优084显著。琼脂板培养试验的结果与水培结果一致,武运粳23根系形态对高浓度蔗糖的响应普遍高于II优084。试验结果说明品种对高C环境的响应特征不随培养条件的变化而变化。与植株生长后期不同,在幼苗期正常氮条件下低应答品种武运粳23的根系生物量和各形态指标对高C的响应明显高于II优084,说明水稻苗期生长响应参数与后期产量响应参数不一定一致,可能是由于苗期生长高响应的品种在营养生长期旺长,反而不利于后期生殖生长,从而导致后期产量的低响应。     

大气CO2 浓度升高对绿豆生长及C、N 吸收的影响

研究大气CO₂ 浓度升高对绿豆生长及C、N 吸收的影响, 有助于了解未来气候变化下绿豆养分平衡的变化。利用FACE (Free Air CO₂ Enrichment)系统在大田条件下研究了CO₂ 浓度升高对绿豆生物量及C、N 吸收的影响。结果表明: 大气CO₂ 浓度升高使绿豆叶、茎、荚、根、地上部分生物量、总生物量及根冠比增加。各发育期地上部分含N 量下降10.39%~21.06%, 含C 量增加0.41%~1.13%, C/N 增加12.23%~26.68%; 籽粒中N、C 含量及C/N 无显著变化。植株地上部分吸N 量和吸C 量分别增加1.99%~50.87%和14.43%~92.69%。未来大气CO₂ 浓度升高条件下, 绿豆将通过生物量的增加固定更多的C, 并增加对N 素的吸收, 未来的绿豆生产应考虑增加土壤的施肥水平以保证其养分供应。     

Impacts of prescribed burnings on litter production,nitrogen concentration, δ13C and δ15N in a suburban eucalypt natural forest of subtropical Australia

Purposes

Prescribed burning is projected to be adopted more frequently with intensifying climate change; thus, a long-term study is necessary to understand the burning impacts on forest productivity and carbon (C) and nitrogen (N) cycling. Litter fall production rate can be used to indicate burning impacts on forest productivity, whereas N concentration, and C and N isotope composition (δ¹³C and δ¹⁵N) can be used to infer burning impacts on C and N cycling in plant-soil system.

Materials and methods

In this study, the impacts of low-intensity prescribed burning on litter production, N concentration, and C and N isotope compositions were continuously investigated for 6 years at five study sites in a natural eucalypt forest of subtropical Australia.

Results and discussion

Higher leaf litter production rate, N concentration and δ¹⁵N, and lower δ¹³C could be seen shortly after prescribed burning. The higher leaf litter N concentration and lower δ¹³C were likely due to the ease of competition for soil N and moisture from understory vegetation in the short term by prescribed burning. Leaf δ¹⁵N and N concentration were closely correlated, and seasonal changes in leaf litter production rate, δ¹³C and δ¹⁵N were observed. Burning season and related severity might determine the suppression degree of understory vegetation. Time since fire (TSF) was a significant impact factor influencing the litter fall production rate, N concentration, δ¹³C and δ¹⁵N of leaf litter fall for a decade following prescribed burning. However, monthly rainfall and temperature were less consistent in their impacts.

Conclusions

Nitrogen limitation was enhanced by prescribed burning through the removal of litter and understory vegetation in the N poor forest and might be responsible for the long-term burning impacts. Low-intensity prescribed burning might have a long-lasting impact on forest litter productivity in nutrient poor forests in subtropical Australia.

     

开放式空气CO2浓度升高对水稻土壤可溶性C、N和P的影响

采用 FACE (Free air carbon dioxide enrichment)技术,研究了不同 N 施肥水平下,大气 CO2浓度升高对水稻/小麦轮作中水稻土壤可溶性 C、N、P 的影响。结果表明,CO2浓度升高使土壤表层可溶性 C 含量增加,土壤 5 ~ 15 cm 的可溶性 C 含量倾向于降低,增加 N 肥施用(常规 N 处理)更易于使土壤可溶性 C 含量降低。CO2浓度升高使水稻土壤中的可溶性 N 含量降低,在低 N 处理和土壤表层降低幅度较大,N 肥施用仍有提高的余地。CO2浓度升高使水稻成熟期土壤可溶性 P 含量增加,但是常规N 处理下会降低水稻生长前期和土壤表层的可溶性 P,增加 N 肥施用有利于水稻对 P 的吸收。     

Effects of Soil Texture and CaCO3 on Turnover of Organic Material in Chao Soils

Decomposition experiments of ^14C-labelled sickle alfalfa in chao soils of different texture and these soils after removal of CaCO3 were carried out under field and laboratory conditions respectively.The amount of residual ^14C in,or ^14CO2 evolved from,the soils at intervals after the beginning of devomposition were measured and the distribution of native and labelled C between particle size fractions isolated from these soils was edtermined.Results showed that contents of both labelled (^14C) and non-labelled (^12C) carbon decreased with increasing particle size.The enrichment factor for ^14C was higher than that for ^12C in the clay fraction,the reverse being true for the silt enrichment factors.The effect of soil texture on the decomposition of plant material could not be observed in chao soils when the clay content was lower than 270g kg^-1,while it became obvious once CaCO3 was removed was correlated from these soils.The decomposition rate of plant material in the soil from which the native CaCO3 Was removed was correlated significantly to both the clay content of the soil and the application rate of CaCO3.A preliminary correction equation describing the effect of clay and CaCO3 on the decomposition of organic material in chao soil was derived from the results obtained.     

Assessment of enzymatic methods in the δ18O value determination of the L-tyrosine p-hydroxy group for proof of illegal meat and bone meal feeding to cattle

The δ(18)O value of the p-hydroxy group of L-tyrosine depends on the biosynthesis by plants or animals, respectively. In animal proteins it reflects the diet and is therefore an absolute indicator for illegal feeding with meat and bone meal. The aim of this investigation was to perform the positional (18)O determination on L-tyrosine via a one-step enzymatic degradation. Proteins from plants, herbivores, omnivores, and carnivores were characterized by their δ(13)C, δ(15)N, and δ(18)O values, the latter for normalizing the positional δ(18)O values. Their L-tyrosine was degraded by tyrosine phenol lyase to phenol, analyzed as (2,4,6)-tribromophenol. Degradation by tyrosine decarboxylase yielded tyramine. The δ(18)O values of both analytes corresponded to the trophic levels of their sources but were not identical, probably due to an isotope effect on the tyrosine phenol lyase reaction. Availability of the enzyme, easy control of the reaction, and isolation of the analyte are in favor of tyrosine decarboxylase degradation as a routine method.     

Effect of cycloheximide on N2O and NO3– production in a forest and an agricultural soil

The present work aims at evaluating the effect of cycloheximide at concentrations of between 0.5 and 5mgg^–1 on N₂O and NO₃ ^– production in two slightly alkaline soils, sampled from deciduous woodland and arable cultivation. In the first experiment, peptone was used as the “inducing substrate” for heterotrophic activity, and soil was incubated with cycloheximide (at different concentrations) and/or acetylene (1mll^–1) to block induced eukaryotic protein synthesis and ammonia monooxygenase activity, respectively. Peptone addition stimulated N₂O and NO₃ ^– production significantly in woodland soil, whereas arable soil showed no significant N₂O emissions and low NO₃ ^– production. Low cycloheximide concentrations drastically reduced N₂O emissions in woodland soil, suggesting a potential role of fungi in N₂O emissions. However, acetylene was equally effective in blocking N₂O emissions and part of NO₃ ^– production, so that a possible role of ammonia monooxygenase in an organic-inorganic pathway of N nitrification in fungal metabolism can be hypothesized. A second experiment was carried out on the woodland soil to check if low cycloheximide concentrations had non-target biocidal effects on soil microorganisms. Attention was focused on the range of concentrations which had reduced N₂O emission in the woodland soil. The results suggested that at concentrations of cycloheximide between 0.5 and 2mgg^–1 any biocidal effect on microbial biomass was negligible in the first 48h; therefore only selective inhibition of protein synthesis could be expected. The whole nitrifier population seemed to be particularly sensitive to cycloheximide concentrations higher than 2.5mgg^–1. Received: 4 July 1997     

Evaluation of press mud cake as a source of nitrogen and phosphorus for rice–wheat cropping system in the Indo-Gangetic plains of India

Press mud cake (PMC) is an important organic source available for land application in India. Adequate information regarding availability of nitrogen and phosphorous contained in PMC to rice–wheat (RW) cropping system is lacking. In field experiments conducted for 4 years to study the effect of PMC application to rice as N and P source in RW system, application of 60 kg N ha⁻¹ along with PMC (5 t ha⁻¹) produced grain yield of rice similar to that obtained with the 120 kg N ha⁻¹ in unamended plots. In the following wheat, the residual effects of PMC applied to preceding rice were equal to 40 kg N and 13 kg P ha⁻¹. Immobilization of soil and fertilizer N immediately after the application of PMC was observed in laboratory incubation. The net amount of N mineralized from the PMC ranged from 16% at 30 days to 43% at 60 days after incubation. Available P content in the soil amended with PMC increased by about 60% over the unamended control within 10 days of its application. The P balance for the no-PMC treatment receiving recommended dose of 26 kg P ha⁻¹ year⁻¹ was −13.5 kg P ha⁻¹ year⁻¹. The P balance was positive (+42.3 to 53.5 kg P ha⁻¹ year⁻¹) when PMC was applied to rice. Application of PMC increased total N, organic carbon, and available P contents in the soil.     

Adsorption Kinetics of Pb2+ and Cu2+ on Variable Charge Soils and Minerals: Ⅱ. Equations for Describing Experimental Data

Different mathematical methods,including linearization,differential,integration and nonlinear least squares approximation (Newton-Marquardt method),were used to fit different kinetic equations,such as zero-order,first-order (i.e.membrane diffusion),second-order,parabolic-diffusion,Elovich,two-constant equations,to the experimental data of Pb^2 and Cu^2 adsorption on variable charge soils and kaolinite.Assuming each M^2 occupied two adsorption sites,two more equations,the so-caled surface second-order equation and third-order equation were derived and compared with the above equations according to the fitting results,which showed that the second-order equation and surface second-order equation,being one equation in different expressions under some conditions,were better than the other equations in describing the Pb^2 and Cu^2 adsorption kinetics,and the latter was the best.     

Is burial of wheat straw in ditches a way to reduce CH4 emissions from rice cultivation?

Burial of wheat straw in ditches and incorporation of wheat straw are the two main ways of returning wheat straw prior to rice cultivation in China. To examine the effect of burying wheat straw in ditches on CH₄ emissions from rice cultivation, a field experiment was conducted at Yixing, Jiangsu, China in 2004. CH₄ flux was measured using a closed-chamber technique in three treatments (CK, no wheat straw application; WI, evenly incorporating 3.75 t ha⁻¹ wheat straw into the 0.1 m topsoil; WD, burying 3.75 t ha⁻¹ wheat straw in 0.14-m deep by 0.25-m wide ditches). Seasonal CH₄ emissions ranged from 49.7 to 218.4 kg CH₄ ha⁻¹. The application of wheat straw in these two ways significantly increased CH₄ emissions by 4.0-fold and 4.4-fold, respectively ( P  < 0.05). Although CH₄ flux from the non-ditch area in the WD treatment was as low as that in the CK treatment, it was counter-balanced by extremely high CH₄ flux from the ditch, which was approximately 6.0-fold as much as that from WI, leading to comparability between treatments WI and WD in total CH₄ emissions ( P  > 0.05). No significant difference was observed between the three treatments in grain yield ( P  > 0.05). The results indicated that burial of wheat straw in ditches is not a way to reduce CH₄ emission from rice cultivation.     

Variability in pattern and hydrogen isotope composition (δ2H) of long-chain n-alkanes of surface soils and its relations to climate and vegetation characteristics: A meta-analysis

The average chain length (ACL), carbon preference index (CPI), and hydrogen isotope composition (δ²H) of long-chain n-alkanes in sediments have been used to retrieve information about the paleoclimate. Despite their importance as in-between media from leaves to sediments, n-alkanes of surface soils have not been systematically analyzed at large scale. Such an investigation of the spatial variation of n-alkane properties in soil and their dependence on climatic and botanic (e.g., vegetation type) factors could provide a rationale for a better estimation of the past environment. We synthesized the patterns and δ²H of long-chain n-alkanes in soil (δ²H^n-alkanes) with regard to vegetation types (cropland, grassland, shrubland, and woodland) and environmental factors using data from peer-reviewed papers. Our results showed that the ACL and CPI of soil C₂₇–C₃₃ n-alkanes were not suitable indicators for differentiating vegetation types at large scale; instead, ACL significantly correlated with water conditions such as mean annual precipitation (MAP) and Palmer drought severity index (PDSI), and CPI significantly correlated with temperature without significant influence of vegetation type. The variation (i.e., standard deviation) of fractionation between the δ²H values in annual precipitation and in soil n-alkanes (ε_rain-soil) was smaller than that reported in leaves; therefore, soils were better suited to quantifying the general growing conditions of plants at a certain site. The fractionation ε_rain-soil correlated with climatic conditions as described by the PDSI and relative humidity (RH). This correlation agreed with the change in leaf water enrichment with changing RH taken from the literature and was independent of the vegetation type at large scale. This meta-analysis may provide useful information for the variations of the patterns and δ²H_n-alkanes values in surface soils.     

Effects of a ‘one film for 2 years’ system on the grain yield,water use efficiency and cost-benefit balance in dryland spring maize (Zea mays L.) on the Loess Plateau,China

‘One film for 2 years’ (PM2) has been proposed as a practice to control the residual film pollution; however, its effects on grain-yield, water-use-efficiency and cost-benefit balance in dryland spring maize production have still not been systematically explored. In this study, we compared the performance of PM2 with the annual film replacement treatment (PM1) and no mulch treatment (CK) on the Loess Plateau in 2015–2016. Our results indicated the following: (1) PM2 was effective at improving the topsoil moisture (0–20 cm) at sowing time and at seedling stage, but there was no significant influence on soil water storage, seasonal average soil moisture or evapotranspiration; (2) PM2 induced significantly higher cumulative soil temperatures compared to CK, and there was no significant difference between PM2 and PM1; (3) no significant differences were identified in grain-yield and water-use-efficiency between PM1 and PM2, and compared to CK, they improved by 16.3% and 15.5%, respectively; (4) because of lower cost of plastic film, tillage, film laying and remove in PM2, economic profits improved by 21% and 70% compared to PM1 and CK. This research suggested that PM2 was effective at alleviating the spring drought and was beneficial in reducing poverty traps in dryland.     

Use of pyrolysis/GC–MS combined with thermal analysis to monitor C and N changes in soil organic matter from a Mediterranean fire affected forest

In Mediterranean ecosystems, forest fires are a common phenomenon. They involve the transformation of vegetation and litter, leaving charred residues and so influencing the carbon cycle by changing (a) the amounts of soil organic matter and (b) the proportions within it of pools with differing stability. In addition to affecting C cycles, fires also affect the amounts of N within soil organic matter, and its availability.