Plant roots alter microbial functional genes supporting litter decomposition

Decomposition of soil organic carbon is central to the global carbon cycle and profoundly affected by plant roots. While root “priming” of decomposition has been extensively investigated, it is not known how plants alter the molecular ecology of soil microbial decomposers. We disentangled the effects of Avena fatua, a common annual grass, on 13C-labeled root litter decomposition and quantified multiple genetic characteristics of soil bacterial and fungal communities. In our study, plants consistently suppressed rates of litter decomposition. Plant uptake N may cause soil microbes under N limitation and reduce their activities. Microbes from planted soils had relatively more genes coding for low molecular weight compound degradation enzymes, while those from unplanted had more macromolecule degradation genes. Higher abundances of “water stress” genes in planted soils suggested plant-induced water stress for microbes. We used a quantitative model to integrate our extensive data set; it indicated that the multiple soil environmental and microbial mechanisms involved in litter decomposition all acted through changing the functional gene profiles of microbial decomposers living near plant roots.