内蒙古温带草地土壤有机碳组分含量和分解速率的空间格局及其影响因素

Spatial patterns and determinants of soil organic ca rbon component contents and decomposition rate in temperate grasslands of Nei Mongol,China

草地是陆地生态系统的重要组成部分,在陆地碳循环中发挥着重要作用。然而,目前地球系统模型对草地土壤碳动态的预测仍存在较大不确定性,其主要原因是对土壤有机碳组分含量和分解速率的空间格局及其影响因素的认识尚不充分。该研究基于在内蒙古温带草地开展的样带调查,按土壤颗粒的粒径大小进行土壤分级,并通过室内培养方法测定土壤碳分解速率,在此基础上进一步利用方差分解探究气候、土壤、植物和矿物4类因素对内蒙古温带草地表层土壤有机碳组分含量和分解速率影响的相对重要性。结果显示:(1)土壤有机碳及其组分含量呈现自西南向东北增加的空间格局,草甸草原中整土及不同组分碳含量最大,典型草原次之,荒漠草原最小;而有机碳标准化的碳分解速率呈现相反的趋势。(2)气候和矿物是驱动土壤有机碳组分含量空间变异的主要因素,且两者在不同组分中的相对重要性存在差异,即随土壤粒径减小,矿物的相对重要性逐渐增加。(3)碳分解速率受矿物、土壤和气候因素共同影响。上述结果表明不同土壤碳组分含量和碳分解速率空间变异的影响因素存在差异,矿物因素对细颗粒组分的影响尤为重要,意味着地球系统模型中应考虑矿物因素在不同碳组分中的作用,从而更准确地预测全球变化背景下的草地土壤碳动态。

Aims Grassland is an important component of terrestrial ecosystems around the world and plays an important role in terrestrial carbon cycling.However,large uncertainties still exist in predictions of soil organic carbon(SOC)dynamics in grassland ecosystems using earth system models,partly due to an inadequate understanding of the spatial patterns and drivers of soil carbon components and the rate of decomposition.In this study,we explored the determinants of the contents of total SOC and its components as well as the rate of soil carbon decomposition in the topsoil of temperate grasslands of Nei Mongol.Methods Soil samples at depths of 0-10 cm were collected during July to August 2015 from field sites on the Nei Mongol Plateau.We measured the contents of total SOC and its partitioning in three soil aggregate size-classes,and the decomposition rate based on laboratory incubation.In addition,we acquired a suite of explanatory factors including climatic,edaphic,vegetation,and mineral variables.Variance partitioning analyses were then used to investigate the relative importance of the four factors in affecting the contents of total SOC,aggregate-classified carbon fractions and soil carbon decomposition rate.Important findings The contents of total SOC and three carbon fractions displayed an increasing trend from southwest to northeast of the study area,while soil carbon decomposition rate(standardized by SOC)showed a reverse trend.The carbon contents in bulk soil and different aggregate fractions are highest in the meadow steppe,followed by the typical steppe and the desert steppe;whereas soil carbon decomposition rate(standardized by SOC)was highest in the desert steppe,followed by the typical steppe and the meadow steppe.The spatial variations of carbon contents in the three soil aggregate fractions were mainly driven by climatic and mineral factors,with finer soil particles attaching greater relative importance in the effect by the mineral factor.The soil carbon decomposition rate(standardized by SOC)was affected by mineral,edaphic,and climatic factors.These findings highlight the importance of considering the differential influences by minerals in different soil aggregate carbon fractions,particularly the silt-and clay-associated carbon in the Earth system models,so as to improve the accuracy in the prediction of SOC dynamics in grassland ecosystems under changing environment.