Alteration of soil organic matter pools and aggregation in semi‐arid steppe topsoils as driven by organic matter input
Alteration of soil organic matter pools and aggregation in semi‐arid steppe topsoils as driven by organic matter input
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DOI：
10.1111/j.1365-2389.2008.01104.x
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发表时间：
2009-04
影响因子：
4.2
通讯作者：
M. Steffens;A. Kölbl;I. Kögel‐Knabner
中科院分区：
文献类型：
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作者：
M. Steffens;A. Kölbl;I. Kögel‐Knabner
放牧是影响草地土壤有机碳储量和团聚体稳定性的重要因素之一。本研究的主要目的是分析放牧后有机质输入增加对土壤有机碳组分的质量和数量及其对团聚体形成、稳定性和碳固存的贡献。对不同放牧强度（连续放牧= Cg，冬季放牧= Wg， 1999年以来未放牧= Ug99, 1979年以来未放牧= Ug79）下不同有机质输入的沙质草原表层土进行了集料粒度、密度和粒度分异及集料稳定性测量。有机质的大量输入导致粗粒级（ASC）中有机碳含量的增加，尤其是轻粒级（LF）。我们发现放牧没有引起土壤有机质（SOM）的变化。SOM质量（13C固体核磁共振光谱，中性糖分析）在不同放牧强度之间具有可比性，但未放牧的地块在所有馏分中分解的SOM略多。我们发现Ug79的放射性碳浓度普遍高于Cg。与Cg相比，Ug79的骨料稳定性（抗超声）更大。放牧区凋落物投入增加了LF数量，加速了SOM的周转，导致粗团聚体的形成和稳定。放射性碳浓度的增加表明，有机-矿物结合的转变速度更快，但该池的OC含量没有变化。总而言之，额外的凋落物输入被隔离在中间低碳池中，而有机-矿物质关联的长期池似乎接近饱和。我们的结论是，草原生态系统的管理变化并不一定会增加碳固存，它们作为碳汇的假定潜力必须受到质疑。
Grazing is one of the most important factors that may reduce soil organic carbon (SOC) stocks and subsequently aggregate stability in grassland soils. The central aim of this study was to analyse the quality and quantity of SOC fractions and their contribution to aggregate formation, stability and carbon sequestration, as affected by increased inputs of organic matter after grazing exclusion. We applied a combined aggregate size, density and particle size fractionation procedure and aggregate stability measurements to sandy steppe topsoils with different organic matter inputs from different grazing intensities (continuously grazed = Cg, winter grazing = Wg, ungrazed since 1999 = Ug99, ungrazed since 1979 = Ug79). Greater inputs of organic matter led to larger amounts of OC in coarse aggregate size classes (ASC) and especially in light fractions (LF). We found no grazing‐induced changes of soil organic matter (SOM) quantity in fine ASC and mineral fractions. SOM quality (13C solid‐state NMR spectroscopy, neutral sugar analysis) was comparable between different grazing intensities, but ungrazed plots had slightly more decomposed SOM across all fractions. We found generally greater radiocarbon concentrations in Ug79 compared with Cg. Aggregate stability, analysed as resistance to sonication, was greater in Ug79 compared with Cg. Larger litter inputs in grazing exclosures increased LF quantity, led to faster SOM turnover and resulted in the formation and stabilization of coarse aggregates. Organo‐mineral associations turned over faster as indicated by increased radiocarbon concentrations, but the OC content of this pool did not change. To summarize, additional litter inputs were sequestered in the intermediate LF pool and the long‐term pool of organo‐mineral associations appears to be close to saturation. We conclude that management changes in steppe ecosystems do not necessarily increase carbon sequestration and their assumed potential to act as carbon sinks has to be questioned.