REU: Biotic Regulation of Soil Organic Matter Accumulation and Loss in Subtropical Agroecosystems

这项拟议的研究将集中在美国东南部温暖潮湿的农业生态系统中土壤有机碳和氮的动态机制，那里高度风化的Ultisols给土壤有机质(SOM)管理带来了独特的问题。对山前土壤有机质动态的研究表明，在常规耕作条件下，土壤有机质迅速流失，而在养护管理下，土壤有机质流失减少甚至逆转。这些格局似乎随着土壤质地、景观位置和管理实践的不同而不同。研究人员假设，土壤生物群的活动通过对水稳性团聚体的影响，在调节土壤有机质的周转和稳定方面发挥着重要作用。目的是研究植物根、腐生真菌、微型节肢动物和蚯蚓对水稳性土壤团聚体中C和N的周转和稳定的调节作用，以及对SOM堆积和退化生态系统中植物凋落物向土壤库和植物生物量转化的调节作用。具体地说，该项目将量化每一种生物操作对以下方面的影响：1)颗粒物OM分解和生物丰度2)团聚体的形成和稳定3)相关团聚体和土壤颗粒、主动-无保护、主动保护、被动和土壤溶液有机C和N的池和4)使用C-13和N-15示踪剂的池之间的转移速率。调查人员在之前的赠款和机构支持以及设施上取得了很高的成效，足以运行该项目。

The proposed research will focus on mechanisms of soil organic carbon and nitrogen dynamics in agroecosystems in the warm, humid southeastern U.S. where highly weathered Ultisols present unique problems for soil organic matter (SOM) management. Studies of OM dynamics in Piedmont soils have shown rapid losses of SOM under conventional cultivation and reduced or even reversed SOM losses under conservation management. These patterns appear to vary with soil texture, landscape position and management practices. The investigators hypothesize that the activities of soil biota are important in regulating the turnover and stabilization of SOM through their effects on water-stable aggregates. The objectives are to investigate the regulatory role of plant roots, saprophytic fungi, microarthropods and earthworms on turnover and stabilization of C and N in water-stable soil aggregates, and on transformations of C and N from plant litter to soil pools and plant biomass in SOM aggrading and degrading ecosystems. Specifically, the project will quantify the effects of each biotic manipulation on: 1) particulate OM decomposition and biotic abundances 2) aggregate formation and stabilization 3) aggregate associated and bulk soil pools of particulate, active- unprotected, active-protected, passive and soil solution organic C and N and 4) transfer rates between pools using C-13 and N-15 tracers. The investigators have been very productive on their previous grants and institutional support and facilities are more than adequate for running the project.