Data_Sheet_1_Modulation of Litter Decomposition by the Soil Microbial Food Web Under Influence of Land Use Change.docx

Soil microbial communities modulate soil organic matter (SOM) dynamics by catalyzing litter decomposition. However, our understanding of how litter-derived carbon (C) flows through the microbial portion of the soil food web is far from comprehensive. This information is necessary to facilitate reliable predictions of soil C cycling and sequestration in response to a changing environment such as land use change in the form of agricultural abandonment. To examine the flow of litter-derived C through the soil microbial food web and it’s response to land use change, we carried out an incubation experiment with soils from six fields; three recently abandoned and three long term abandoned fields. In these soils, the fate of 13C-labeled plant litter was followed by analyzing phospholipid fatty acids (PLFA) over a period of 56 days. The litter-amended soils were sampled over time to measure 13CO2 and mineral N dynamics. Microbial 13C-incorporation patterns revealed a clear succession of microbial groups during litter decomposition. Fungi were first to incorporate 13C-label, followed by G− bacteria, G+ bacteria, actinomycetes and micro-fauna. The order in which various microbial groups responded to litter decomposition was similar across all the fields examined, with no clear distinction between recent and long-term abandoned soils. Although the microbial biomass was initially higher in long-term abandoned soils, the net amount of 13C-labeled litter that was incorporated by the soil microbial community was ultimately comparable between recent and long-term abandoned fields. In relative terms, this means there was a higher efficiency of litter-derived 13C-incorporation in recent abandoned soil microbial communities compared to long-term abandoned soils, most likely due to a net shift from SOM-derived C toward root-derived C input in the soil microbial food web following land-abandonment.

土壤微生物群落通过催化枯落物分解调控土壤有机质（SOM）动态。然而，目前我们对枯落物来源碳（C）如何在土壤食物网的微生物组分中流动的认知仍远未全面。这一认知对于精准预测环境变化（如以农田撂荒形式发生的土地利用变化）下的土壤碳循环与固存过程至关重要。为探究枯落物来源碳在土壤微生物食物网中的流动路径及其对土地利用变化的响应，我们采集了6块样地的土壤开展培养试验：其中3块为近期撂荒样地，3块为长期撂荒样地。本研究以13C标记植物枯落物对土壤进行添加后，在56天的培养周期内通过分析磷脂脂肪酸（PLFA）示踪微生物群落对13C的利用情况。同时，我们定期对添加枯落物的土壤进行采样，以测定13CO₂释放与矿质氮动态。微生物13C同化模式显示，枯落物分解过程中微生物类群呈现明确的演替顺序：真菌最先同化13C标记物，随后依次为革兰氏阴性菌（G− bacteria）、革兰氏阳性菌（G+ bacteria）、放线菌与微型动物。所有供试样地的微生物类群响应枯落物分解的顺序均保持一致，近期撂荒与长期撂荒土壤之间未出现显著差异。尽管长期撂荒土壤的微生物生物量初始值更高，但最终土壤微生物群落同化的13C标记枯落物净总量在两类样地间基本相当。相对而言，近期撂荒土壤的微生物群落对枯落物来源13C的同化效率更高，这一现象极有可能源于土地撂荒后土壤微生物食物网从依赖土壤有机质来源碳向依赖根系来源碳输入的净转变。