Organic Carbon Turnover Research Articles

Relating microbial community structure to functioning in forest soil organic carbon transformation and turnover.

Forest soils store vast amounts of terrestrial carbon, but we are still limited in mechanistic understanding on how soil organic carbon (SOC) stabilization or turnover is controlled by biotic and abiotic factors in forest ecosystems. We used phospholipid fatty acids (PLFAs) as biomarker to study soil microbial community structure and measured activities of five extracellular enzymes involved in the degradation of cellulose (i.e., β-1,4-glucosidase and cellobiohydrolase), chitin (i.e., β-1,4-N-acetylglucosaminidase), and lignin (i.e., phenol oxidase and peroxidase) as indicators of soil microbial functioning in carbon transformation or turnover across varying biotic and abiotic conditions in a typical temperate forest ecosystem in central China. Redundancy analysis (RDA) was performed to determine the interrelationship between individual PFLAs and biotic and abiotic site factors as well as the linkage between soil microbial structure and function. Path analysis was further conducted to examine the controls of site factors on soil microbial community structure and the regulatory pathway of changes in SOC relating to microbial community structure and function. We found that soil microbial community structure is strongly influenced by water, temperature, SOC, fine root mass, clay content, and C/N ratio in soils and that the relative abundance of Gram-negative bacteria, saprophytic fungi, and actinomycetes explained most of the variations in the specific activities of soil enzymes involved in SOC transformation or turnover. The abundance of soil bacterial communities is strongly linked with the extracellular enzymes involved in carbon transformation, whereas the abundance of saprophytic fungi is associated with activities of extracellular enzymes driving carbon oxidation. Findings in this study demonstrate the complex interactions and linkage among plant traits, microenvironment, and soil physiochemical properties in affecting SOC via microbial regulations.

Bacteria and fungi respond differently to multifactorial climate change in a temperate heathland, traced with 13C-glycine and FACE CO2.

It is vital to understand responses of soil microorganisms to predicted climate changes, as these directly control soil carbon (C) dynamics. The rate of turnover of soil organic carbon is mediated by soil microorganisms whose activity may be affected by climate change. After one year of multifactorial climate change treatments, at an undisturbed temperate heathland, soil microbial community dynamics were investigated by injection of a very small concentration (5.12 µg C g−1 soil) of 13C-labeled glycine (13C2, 99 atom %) to soils in situ. Plots were treated with elevated temperature (+1°C, T), summer drought (D) and elevated atmospheric carbon dioxide (510 ppm [CO2]), as well as combined treatments (TD, TCO2, DCO2 and TDCO2). The 13C enrichment of respired CO2 and of phospholipid fatty acids (PLFAs) was determined after 24 h. 13C-glycine incorporation into the biomarker PLFAs for specific microbial groups (Gram positive bacteria, Gram negative bacteria, actinobacteria and fungi) was quantified using gas chromatography-combustion-stable isotope ratio mass spectrometry (GC-C-IRMS).Gram positive bacteria opportunistically utilized the freshly added glycine substrate, i.e. incorporated 13C in all treatments, whereas fungi had minor or no glycine derived 13C-enrichment, hence slowly reacting to a new substrate. The effects of elevated CO2 did suggest increased direct incorporation of glycine in microbial biomass, in particular in G+ bacteria, in an ecosystem subjected to elevated CO2. Warming decreased the concentration of PLFAs in general. The FACE CO2 was 13C-depleted (δ13C = 12.2‰) compared to ambient (δ13C = ∼−8‰), and this enabled observation of the integrated longer term responses of soil microorganisms to the FACE over one year. All together, the bacterial (and not fungal) utilization of glycine indicates substrate preference and resource partitioning in the microbial community, and therefore suggests a diversified response pattern to future changes in substrate availability and climatic factors.

Short-term effects of tillage practices on soil organic carbon turnover assessed by δ13C abundance in particle-size fractions of black soils from northeast China.

The combination of isotope trace technique and SOC fractionation allows a better understanding of SOC dynamics. A five-year tillage experiment consisting of no-tillage (NT) and mouldboard plough (MP) was used to study the changes in particle-size SOC fractions and corresponding δ 13C natural abundance to assess SOC turnover in the 0–20 cm layer of black soils under tillage practices. Compared to the initial level, total SOC tended to be stratified but showed a slight increase in the entire plough layer under short-term NT. MP had no significant impacts on SOC at any depth. Because of significant increases in coarse particulate organic carbon (POC) and decreases in fine POC, total POC did not remarkably decrease under NT and MP. A distinct increase in silt plus clay OC occurred in NT plots, but not in MP plots. However, the δ 13C abundances of both coarse and fine POC increased, while those of silt plus clay OC remained almost the same under NT. The C derived from C3 plants was mainly associated with fine particles and much less with coarse particles. These results suggested that short-term NT and MP preferentially enhanced the turnover of POC, which was considerably faster than that of silt plus clay OC.

Possible effect of soil organic carbon on its own turnover: A negative feedback

Soil carbon (C) sequestration plays an important role in mitigating climate change; therefore, it is essential to understand the mechanisms underlying soil organic carbon (SOC) turnover and dynamics. The humification coefficient of input organic materials (h) and the SOC decomposition rate (k) together control the SOC turnover, and they have been well known to be affected by factors including climatic factors, organic material qualities, soil characteristics, and anthropogenic activities. However, the SOC content changes over time, and thus far, whether the SOC content is an inherent factor has not been understood clearly. By using a new mathematical method, we found that SOC is possibly able to regulate its own turnover through a negative feedback: h decreases and k increases simultaneously with an increase in the SOC content. This feedback is caused by a series of chemical, biological, and physical mechanisms. We suggest that the response of the SOC pool to climate change is a function of the C input level to soil, temperature, and negative feedback of the SOC turnover; in addition, organic materials should be applied in priority to soils with low SOC content to enhance the soil C sequestration.

Long-term organic carbon turnover rates in natural and semi-natural topsoils

We combined published and new radiocarbon and ancillary data for uncultivated topsoils (typically 15 cm depth), to make two databases, one for the United Kingdom (133 sites), and one global (114 sites). Forest topsoils are significantly higher in radiocarbon than non-forest soils, indicating greater enrichment with “bomb carbon” and therefore faster C turnover, if steady-state conditions are assumed. Steady-state modelling, taking into account variations in atmospheric 14CO2, including the effects of 20th century nuclear weapons testing and radioactive decay, was used to quantify soil carbon turnover rates. Application of a model with variable slow (20 year mean residence time, MRT) and passive (1,000 year MRT) carbon pools partitioned the topsoil C approximately equally, on average, between the two pools when the entire data set was considered. However, the mean slow:passive ratio of 0.65:0.35 for forest soil was highly significantly different (p < 0.001) from the 0.40:0.60 ratio for non-forest soils. Values of the slow and passive fractions were normally distributed, but the non-forest fractions showed greater variation, with approximately twice the relative standard deviations of the forest values. Assuming a litter input of 500 g C m−2 a−1, average global C fluxes (g C m−2 a−1) of forest soils are estimated to be 298 (through a fast pool of MRT 1 year), 200 (slow pool) and 2.0 (passive pool), while for non-forest soils, respective average fluxes of 347, 150 and 3.3 g C m−2 a−1 are obtained. The results highlight the widespread global phenomenon of topsoil C heterogeneity, and indicate key differences between forest and non-forest soils relevant for understanding and managing soil C.

Community genomic analyses constrain the distribution of metabolic traits across the Chloroflexi phylum and indicate roles in sediment carbon cycling.

BackgroundSediments are massive reservoirs of carbon compounds and host a large fraction of microbial life. Microorganisms within terrestrial aquifer sediments control buried organic carbon turnover, degrade organic contaminants, and impact drinking water quality. Recent 16S rRNA gene profiling indicates that members of the bacterial phylum Chloroflexi are common in sediment. Only the role of the class Dehalococcoidia, which degrade halogenated solvents, is well understood. Genomic sampling is available for only six of the approximate 30 Chloroflexi classes, so little is known about the phylogenetic distribution of reductive dehalogenation or about the broader metabolic characteristics of Chloroflexi in sediment.ResultsWe used metagenomics to directly evaluate the metabolic potential and diversity of Chloroflexi in aquifer sediments. We sampled genomic sequence from 86 Chloroflexi representing 15 distinct lineages, including members of eight classes previously characterized only by 16S rRNA sequences. Unlike in the Dehalococcoidia, genes for organohalide respiration are rare within the Chloroflexi genomes sampled here. Near-complete genomes were reconstructed for three Chloroflexi. One, a member of an unsequenced lineage in the Anaerolinea, is an aerobe with the potential for respiring diverse carbon compounds. The others represent two genomically unsampled classes sibling to the Dehalococcoidia, and are anaerobes likely involved in sugar and plant-derived-compound degradation to acetate. Both fix CO2 via the Wood-Ljungdahl pathway, a pathway not previously documented in Chloroflexi. The genomes each encode unique traits apparently acquired from Archaea, including mechanisms of motility and ATP synthesis.ConclusionsChloroflexi in the aquifer sediments are abundant and highly diverse. Genomic analyses provide new evolutionary boundaries for obligate organohalide respiration. We expand the potential roles of Chloroflexi in sediment carbon cycling beyond organohalide respiration to include respiration of sugars, fermentation, CO2 fixation, and acetogenesis with ATP formation by substrate-level phosphorylation.

Soil microbial diversity patterns of a lowland spring environment

The Po river plain lowland springs represent unique paradigms of managed environments. Their current locations used to be swamps that were drained 6-7 centuries ago, and they have been in constant use ever since. Our aims were to identify the effects of land use on the microbial communities of these soils, look for associated diversity drivers, and assess the applicability of ecology theories with respect to identified patterns. We screened the microbial diversity across a land use transect via high-throughput sequencing of partial 16S rrRNA gene amplicons. Land use had a major effect on soil properties and microbial community structures. Total organic carbon and pH were major diversity drivers for Bacteria, and pH was important for Archaea. We identified the potential contribution of soil amendments to the indigenous microbial communities, and also gained insights into potential roles of taxa in the organic carbon turnover. Verrucomicrobia coincided with the higher values of the recalcitrant organic carbon. Actinobacteria and Acidobacteria correlated with the more labile organic carbon. Finally, the higher diversity found in the soils less enzymatically active and relatively poorer in nutrients, may be explained to an extent by niche-based theories such as the resource heterogeneity hypothesis and Connell's intermediate disturbance hypothesis.

Turnover and availability of soil organic carbon under differentMediterranean land‐uses as estimated by13Cnatural abundance

SummarySoil organic matter (SOM) is an important factor in ecosystem stability and productivity. This is especially the case for Mediterranean soils suffering from the impact of human degradation as well as harsh climatic conditions. We used the carbon (C) exchange resulting fromC3‐C4andC4‐C3vegetation change under field conditions combined with incubations under controlled conditions to evaluate the turnover and availability of soil organicCunder different land‐uses. The 40‐year succession ofHyparrenia hirtaL. (C4photosynthesis) after more than 85 years of olive tree (Olea europaeaL.;C3photosynthesis) growth led to the exchange of 54% of soil organic C fromC3toC4forms. In contrast, 21 years of vine (Vitis viniferaL.) growing afterH. hirtadecreased the organic C content to 57%. Considering this exchange and decrease as well as the periods after the land‐use changes, we calculated the mean residence time (MRT) of soil C of different ages. TheMRTof C under grassland dominated byH. hirtawas about 19 years, but was 180 years under the vineyard. The rates of C accumulation under theH. hirtagrassland were about 0.36 Mg C ha−1 year−1. In contrast, the rates ofClosses after conversion from natural grassland to a vineyard were 1.8 times greater and amounted to 0.65 Mg C ha−1 year−1. We conclude that changes of land use from naturalMediterranean grassland to a vineyard lead to very largeClosses that cannot be compensated for over the same periods.

Turnover of organic carbon and nitrogen in soil assessed from δ13C and δ15N changes under pasture and cropping practices and estimates of greenhouse gas emissions

The continuing clearance of native vegetation for pasture, and especially cropping, is a concern due to declines in soil organic C (SOC) and N, deteriorating soil health, and adverse environment impact such as increased emissions of major greenhouse gases (CO2, N2O and CH4). There is a need to quantify the rates of SOC and N budget changes, and the impact on greenhouse gas emissions from land use change in semi-arid subtropical regions where such data are scarce, so as to assist in developing appropriate management practices. We quantified the turnover rate of SOC from changes in δ13C following the conversion of C3 native vegetation to C4 perennial pasture and mixed C3/C4 cereal cropping (wheat/sorghum), as well as δ15N changes following the conversion of legume native vegetation to non-legume systems over 23years. Perennial pasture (Cenchrus ciliaris cv. Biloela) maintained SOC but lost total N by more than 20% in the top 0–0.3m depth of soil, resulting in reduced animal productivity from the grazed pasture. Annual cropping depleted both SOC and total soil N by 34% and 38%, respectively, and resulted in decreasing cereal crop yields. Most of these losses of SOC and total N occurred from the >250μm fraction of soil. Moreover, this fraction had almost a magnitude higher turnover rates than the 250–53μm and <53μm fractions. Loss of SOC during the cropping period contributed two-orders of magnitude more CO2-e to the atmosphere than the pasture system. Even then, the pasture system is not considered as a benchmark of agricultural sustainability because of its decreasing productivity in this semi-arid subtropical environment. Introduction of legumes (for N2 fixation) into perennial pastures may arrest the productivity decline of this system. Restoration of SOC in the cropped system will require land use change to perennial ecosystems such as legume–grass pastures or native vegetation.

Carbon release from Sphagnum peat during thawing in a montane area in China

Soil thawing may affect the turnover of soil organic carbon (C) and the release of C to the atmosphere. Little is known about C release during thawing in the Great Hing'an Mountains, China. Through the incubations, we studied the emissions of CO2 and CH4 during thawing from the Sphagnum moss layer to the permafrost layer under aerobic and anaerobic conditions. Carbon was released quickly during thawing under different conditions. The Sphagnum moss layer produced more CO2 than the other layers. However, there was little CH4 release during thawing in the Sphagnum moss layer and burst of CH4 emissions in the peat and permafrost soils. These bursts include stored CH4 in the frozen samples and productions from microbial activity. The temperature sensitivity during thawing decreased across the freezing point in the Sphagnum moss layer, did not change greatly in the root layer, and increased greatly in the peat and permafrost layers. Changes in soil substrates and enzyme activities may affect C release during thawing.

Modification of the RothC model for simulations of soil organic C dynamics in dryland regions

The Rothamsted Carbon Model (RothC), models the turnover of soil organic carbon (C) in non-waterlogged topsoils. It requires only easily obtainable inputs, and has been widely and successfully used in many regions of the world. However, it has been shown to have limitations when used to predict soil C dynamics in semiarid areas, where unrealistically high C inputs have been required to obtain good simulations. Soils of semiarid regions, highly vulnerable to soil C depletion, could represent a sink of C and become economically valuable in the C credit market. Hence, we introduced modifications to RothC with the aim of improving the prediction of soil C dynamics for semiarid regions.Modifications made were: i) the minimum value of the rate modifying factor for moisture was changed from 0.2 to 0.15 and 0.10 (indicated with the suffix 20, 15 and 10, respectively, in the name of the model); ii) the maximum soil moisture deficit was increased and the hydrological constants (field capacity, wilting point and hygroscopic water) were calculated using pedotransfer function by van Genuchten (1980) (RothC20, RothC15, and RothC10); and iii) soils that were bare were allowed to dry out more than in the current version of RothC (RothC_N, RothC20_N, RothC15_N, and RothC10_N).The modifications were tested on data from six experiments: five sites from semiarid regions and one from a temperate region.The modifications made in this study, which essentially reduce decomposition rate in soil, improved the model's performance for dry regions, especially when the rotation included a fallow. The model now requires more realistic C inputs to the soil, and one additional input (silt) that is normally measured with clay. These modifications do not impair the performance of the model under temperate conditions and so represent a broadening in the capability of the RothC model. Among all the various models compared, for simulation of SOC turnover we suggest the use of RothC10_N for dry regions as a part of global scale modelling.

Influence of exogenous calcium carbonate and rice straw on active organic carbon of Karst soils

To elucidate the features of active organic carbon in Karst soils in the turnover of soil organic carbon,14C–labeled straw and 14C–labeled calcium carbonate were respectively added to each of the terra fusca,rendzina and zonal red soil of Huanjiang Guangxi for a 100 d incubation test.Soils with no addition were regarded as CK.Results showed that 14C–labeled straw exhibited obviously higher influence on 14C–MBC,14C–DOC in the three soils,compared to 14C–labeled calcium carbonate(P0.05).After 5 d of incubation,total MBC(microbial biomass carbon) reached the peak in the three soils added with 14C–labeled straw or 14C–labeled calcium carbonate,and the MBC in red soils was 231.7,273.0 mg/kg,were respectively 70.2% and 100.5% higher than that in the CK;the MBC in terra fusca was 288.1,307.7 mg/kg,were respectively 23.0% and 31.3% higher than that in the CK while MBC in rendzina was 683.7,787.2 mg/kg,were respectively 4.5% and 20.3% higher than that in the CK;DOC(dissolved organic carbon) in the three soils also reached the maximum.The MBC in rendzina was obviously higher than that in terra fusca and red soil,but the DOC in red soil was obviously higher in terra fusca,rendzina(P0.05).Exogenous 14C–labeled matters could promote the increase of soil active organic carbon and in the same condition,rendzina and terra fusca are more likely to accumulate organic carbon,compared to red soil.

Projections of changes in grassland soil organic carbon under climate change are relatively insensitive to methods of model initialization

SummaryModel initialization in soil organic carbon (SOC) turnover models has often been described as a crucial step in making future projections. Model initialization by the spin‐up of pools of SOC (model equilibrium run) has been questioned, because equilibrium has to be assumed. Measured SOC pools are independent of model assumptions and are thought to reflect better real site conditions. It has been suggested that model initialization with measured SOC fractions could provide an advantage over model spin‐up of SOC pools. In this study we tested this suggestion in relatively undisturbed native grasslands in Australia. We tested the Rothamsted SOC turnover model (RothC) under climate change at 12 sites with three different initialization methods, viz. model initialization with (i) spin‐up of model pools with inert organic matter (IOM) pool size calculated from a regression equation, (ii) spin‐up of model pools with measured IOM and (iii) all pools estimated from measured fractions. Averaged over the sites and initialization methods, maximum absolute variations (absolute differences in projected SOC stocks expressed as a percentage of initial 2008 SOC stocks) as well as averaged absolute variations throughout the projection period were very small (2.2 and 1.6%, respectively). Averaged across the sites, there were no significant differences in projected grassland SOC stocks under climate change after 93 years of simulation with model initialization by different methods and averaged absolute variation was only 1.6% across initialization methods. These findings suggest that in a relatively undisturbed land‐use system such as native grassland, projections of SOC under climate change are relatively insensitive to the model initialization method.

Soil aggregate fraction-based 14C analysis and its application in the study of soil organic carbon turnover under forests of different ages

There still exist uncertainties in the trend, magnitude and efficiency of carbon sequestration with regard to the changes in soil organic carbon (SOC) pools after afforestation. In this study, SOC turnover times of the meadow steppe and planted forests at Saihanba Forest Station of Hebei Province, China are estimated by means of the radiocarbon (14C) method. Our results show that the SOC turnover times can be as long as from 70 to 250 years. After planting the Pinus sylvestri var. mongolica in the Leymus chinensis meadow steppe, the turnover times of organic carbon in both bulk samples and soil aggregate fractions of the topsoils are decreased with an increase of the stand age. Such a lowering of the turnover time would cause an increase in soil CO2 flux, implying that afforestation of grassland may reduce the capacity of topsoil to sequestrate organic carbon. Combined stable isotope and 14C analyses on soil aggregate fractions suggest that there are different responses to afforestation of grassland between young and old carbon pools in topsoils. In the young and middle-age planted forests, the proportion of CO2 emission from the older soil carbon pool shows an increasing trend. But in the mature planted forest, its proportion tends to decline, indicating that the stand age may influence the soil carbon sequestration mechanism. The CO2 emission from the topsoils estimated using the 14C method is relatively low compared to those by other methods and may be caused by the partial isolation of the young carbon component from the soil aggregates. For more accurate estimation of CO2 flux, future studies should therefore employ improved methodology for more effective separation of different soil carbon components before isotope analyses.

盐分和底物对黄河三角洲区土壤有机碳分解与转化的影响

PDF HTML阅读 XML下载 导出引用 引用提醒 盐分和底物对黄河三角洲区土壤有机碳分解与转化的影响 DOI: 10.5846/stxb201206290914 作者: 作者单位: 滨州学院山东省黄河三角洲生态环境重点实验室 作者简介: 通讯作者: 中图分类号: 基金项目: 国家自然科学基金项目（41101220，41101277）；山东省优秀中青年科学家奖励基金项目（BS2011HZ001）；山东省高校科研发展计划项目（J13LE58）；滨州学院国家级大学生创新训练计划项目（201210449127）；滨州学院博士基金项目（2008Y05） Effects of salinity and exogenous substrates on the decomposition and transformation of soil organic carbon in the Yellow River Delta Author: Affiliation: Shangdong Key laboratory of Eco-enviromental Science for Yellow River Delta, Binzhou University, Binzhou 256603, Shandong, China Fund Project: 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:土壤盐碱化能抑制微生物活性，影响土壤有机碳的分解与转化。以黄河三角洲盐碱耕地为研究对象，采用室内恒温培养法，设置3个NaCl盐分梯度（S1：0.1%；S2：0.5%；S3：0.9%），通过在土壤中添加不同底物（CK：不添加底物；N：添加氮；C：添加碳；C+N：添加碳+氮），研究该土壤释放CO2-C量、土壤微生物生物量碳（SMBC）、土壤微生物呼吸商（qCO2）及溶解性有机碳（DOC）对盐分和底物的响应。结果表明：在45 d的培养期内，CK、N处理中S1盐分土壤释放CO2-C量最高，S2和S3明显低于S1，降低幅度分别为18.3%-23.7%和24.3%-39.8%。C、C+N处理中3个盐分土壤释放CO2-C量差异较小，特别是在C+N处理中，3个盐分土壤释放CO2-C差异不显著。4个底物处理中，SMBC均在S1和S2盐分中含量较高，S3盐分最低。与CK相比，N处理并不能提高SMBC含量，C、C+N处理可明显提高SMBC，但S1和S2盐分土壤提高的幅度（80.4%-80.5%、58.0%-58.7%）明显高于S3（68.9%、49.7%）。4个底物处理中，qCO2均在S1盐分土壤中最高，C、C+N处理可明显提高qCO2。CK、N处理中3个盐分土壤DOC差异不显著，C、C+N处理中S3盐分土壤DOC较高。说明在无碳源输入条件下，增加盐分含量能明显抑制土壤释放CO2量。添加碳源后，盐分含量对土壤释放CO2的影响变小。微生物对碳源和盐分胁迫的响应较快，添加碳源能明显提高微生物数量及其活性。但较高盐分（含盐量 > 0.5%）可明显降低土壤微生物活性及对外源碳的利用率，导致较高盐分SMBC及qCO2较低而DOC较高。 Abstract:In the Yellow River Delta, nearly 50 percent of soils are saline and alkaline. Soil salinization can suppress microbial activity and thus affect the decomposition and transformation of soil organic carbon, while little information was found about the effects of salinity and exogenous C and N amendment on the decomposition and transformation of soil organic carbon in this area. A laboratory experiment was conducted to investigate the effects of soil salinity and exogenous substances on the turnover of organic carbon under conditions with 25℃ and 60% water holding capacity over 45 days. Three levels of salinity (S1: 0.1%; S2: 0.5%; S3: 0.9%) using NaCl (w/w) were imposed in the saline-alkaline cultivated soil in Yellow River Delta. Soil was amended with or without C (750 mg/kg) or inorganic N (30 mg/kg) as glucose or NH4Cl, and 4 treatments were established, including (Control: no substrates addition, N: NH4Cl addition, C: glucose addition, C+N: glucose and NH4Cl addition). The CO2-C emission, soil microbial biomass carbon (SMBC), dissolved organic carbon (DOC) and calculation of the respiratory quotient(qCO2)were determined. Without glucose addition, the cumulative amount of CO2-C emission was highest in S1 during the incubation, and it was decreased by 18.3%-23.7% and 24.3%-39.8% in S2 and S3 compared with S1, respectively. After glucose addition, the cumulative amount of CO2-C emission little changed among the three salinity soils, and especially it was no significant difference between the three salinity soils in C+N treatment. SMBC was higher in S1 and S2 than that in S3 under the four treatments with substrates addition. Addition of NH4Cl had no significant effect, but addition of glucose significantly increased SMBC, and SMBC increased by 80.4%-80.5% or 58.0%-58.7% in S1 and S2 in C or C+N treatment, and only 68.9% or 49.7% in S3. The qCO2 was significant higher in S1 than that in S2 and S3, and it was significantly improved with glucose addition. Compare with the control, DOC reminded unchanged in the N treatment, but it increased in S3 with glucose addition. It was suggested that the CO2 emission could be depressed with the increase of soil salinity without C addition, and soil salinity had little influence on CO2 emission after C addition. Microorganism was more sensitive to exogenous carbon and soil salinity. The size and the activity of microbial biomass would be improved with C addition, but higher salinity (>0.5%) could depress the microbial activity and the utilization of exogenous carbon, resulting in higher SMBC and qCO2 and lower DOC in higher salinity soil. 参考文献 相似文献 引证文献

Distribution of organic carbon and nitrogen in soil aggregates of aspen (Populus simonii Carr.) woodlands in the semi-arid Loess Plateau of China

The distribution and turnover of organic carbon (OC) and nitrogen (N) associated with aggregates in soils is critical for understanding the behaviour of C and N in soils. We collected soil samples from aspen (Populus simonii Carr.) woodland in the semi-arid Loess Plateau of China to investigate the distribution of aggregate-associated OC and N. The distribution of aggregates and aggregate-associated OC and N were measured, and OC and N stocks in each aggregate fraction were calculated. Across the sites and soil depths, microaggregates and the silt + clay fraction dominated the distribution of soil aggregates, which varied with site. Organic C and N accumulated mainly in the macro- and micro-aggregate fractions in loamy soils but in the silt + clay fractions in sandy soils. The OC and N stocks in the bulk soil of aspen woodland were determined by the OC and N stocks associated with silt + clay fraction. The results of this study indicate that soil texture may play an important role in assessing the distributions of soil OC and N in both bulk soils and aggregate size fractions in aspen woodland, especially in semi-arid regions. Furthermore, the establishment of aspen woodland would result in greater accumulation of OC and N in loam soils than in sandy soils.

Quantification of Sedimentary Organic Carbon Storage and Turnover of Tidal Mangrove Stands in Southern China Based on Carbon Isotopic Measurements

Mangrove ecosystems are highly productive and play an important role in tropical and global coastal carbon (C) budgets. However, sedimentary organic carbon (SOC) storage and turnover in mangrove forests are still poorly understood. Based on C isotopic measurements of sediment cores of 2 mangrove stands in southern China, SOC density was 431.77 Mg ha−1 at site 1 (a Aegiceras corniculatum-dominated high tidal stand) and 243.65 Mg ha−1 in site 2 (a Bruguiera gymnorrhiza + Kandelia candel-dominated middle tidal stand). SOC δ13C values at both mangrove sites ranged from -29.4% to −26.0%. SOC δ13C was enriched with depth at 20–50 cm at site 1, which possibly resulted from preferential microbial decomposition. SOC δ13C at site 2 experienced frequent tidal flushing, and presented relatively stable values with depth. A bomb-14C-based SOC turnover model indicated that turnover times of SOC at 20–50 cm at site 1 were 4.44–26.04 yr. Modern C input from abundant roots might account for the very short SOC turnover times at these subsurface layers. As a result, our study suggested that tidal processes had a great influence on SOC storage and turnover in mangrove forests.

Natural organic matter quantification in the waters of a semiarid freshwater wetland (Tablas de Daimiel, Spain)

Dissolved organic matter (DOM) concentrations have been measured in the waters of a semiarid freshwater wetland, the Tablas de Daimiel, Spain, when the system-characterised by variable hydroperiodicity conditions, was completely flooded (February 2011). Fluxes of DOM from the wetland soils to the overlying waters were measured by using a passive diffusion sampler (peeper). Not only dissolved organic carbon (DOC) concentrations were measured but refractory organic matter (ROM, usually known as humic substances) was also quantified using a novel voltammetric method. Fluorescence spectra were recorded to help in selecting the appropriate standard for ROM quantification, test the homogeneity of DOM in the waters and get an indication of their source. The results obtained show a 7-fold increase in measured ROM concentrations from the Gigüela River to the outlet, which points to a net exportation of ROM from the wetland and to the existence of an internal source of ROM in the system, probably diffusion from the wetland soils. This hypothesis is confirmed by the flux of ROM from the soils to the water column measured with the peeper and by the common fluorescence characteristics of column and interstitial waters. The smaller increase in DOC concentrations along the wetland, in spite of the higher DOC fluxes from soils, suggests that there is significant turnover of organic carbon (OC) in the water column. The system acts as a major carbon sink but, when flooded, exports OC as DOM.

Modeling topsoil carbon sequestration in two contrasting crop production to set-aside conversions with RothC – Calibration issues and uncertainty analysis

Model simulations of soil organic carbon turnover in agricultural fields have inherent uncertainties due to input data, initial conditions, and model parameters. The RothC model was used in a Monte Carlo based framework to assess the uniqueness of solution in carbon sequestration simulations. The model was applied to crop production to set-aside conversions in Iowa (sandy clay-loam soil, humid-continental climate) and Greece (clay-loam soil, Mediterranean). The model was initialized and calibrated with particulate organic carbon data obtained by physical fractionation. The calibrated values for the Iowa grassland were 5.05tCha−1, 0.34y−1, and 0.27y−1 for plant litter input and decomposition rate constants for resistant plant material (RPM) and humus, respectively, while for the Greek shrubland these were 3.79tCha−1, 0.21y−1, and 0.0041y−1, correspondingly. The model sensitivity analysis revealed that for both sites, predicted soil organic carbon content was most sensitive to the total plant litter input and the RPM rate. The Iowa soil was projected to sequester 17.5tCha−1 and the Greek soil 54tCha−1 over 100 years and the projected uncertainty was 65.6% and 70.8%, respectively. We propose this methodology to assess the factors affecting carbon sequestration in agricultural soils and quantify the uncertainties.

Microbial responses to carbon and nitrogen supplementation in an Antarctic dry valley soil

AbstractThe soils of the McMurdo Dry Valleys are exposed to extremely dry and cold conditions. Nevertheless, they contain active biological communities that contribute to the biogeochemical processes. We have used ester-linked fatty acid (ELFA) analysis to investigate the effects of additions of carbon and nitrogen in glucose and ammonium chloride, respectively, on the soil microbial community in a field experiment lasting three years in the Garwood Valley. In the control treatment, the total ELFA concentration was small by comparison with temperate soils, but very large when expressed relative to the soil organic carbon concentration, indicating efficient conversion of soil organic carbon into microbial biomass and rapid turnover of soil organic carbon. The ELFA concentrations increased significantly in response to carbon additions, indicating that carbon supply was the main constraint to microbial activity. The large ELFA concentrations relative to soil organic carbon and the increases in ELFA response to organic carbon addition are both interpreted as evidence for the soil microbial community containing organisms with efficient scavenging mechanisms for carbon. The diversity of the ELFA profiles declined in response to organic carbon addition, suggesting the responses were driven by a portion of the community increasing in dominance whilst others declined.