High nighttime humidity and dissolved organic carbon content support rapid decomposition of standing litter in a semi-arid landscape

1. Litter in arid and semi-arid ecosystems usually exhibits a prolonged standing dead phase after senescence; however, we know little about the ways in which abiotic and microbial processes affect standing litter decomposition. 2. We conducted a 26-month (in situ) decomposition experiment in a steppe to investigate the potential mechanisms governing the decomposition of standing litter, and a 192-day laboratory incubation experiment to further explore the impacts of the standing dead stage on the subsequent litter decomposition and soil organic carbon formation after the litter falls to the soil surface. 3. Compared with soil surface litter, standing litter has higher dissolved organic carbon (DOC) content. Standing litter also experienced higher nighttime relative humidity on its surface, which enhanced litter moisture content. The higher DOC concentration, combined with the greater nighttime moisture content, stimulated more microbial activity in standing litter. The decomposition rat...