The overall decomposition of the spring-detached litter is faster than the autumn-detached litter in a steppe ecosystem

Abstract

In the grasslands, a large proportion of plant shoots senesces into standing dead materials in autumn and stays over the winter period instead of becoming detached litter immediately. However, the information on the decomposition of plant standing dead materials during the winter period and its impacts on their subsequent decomposition after littering in coming spring remain unavailable. We conducted a two-year experiment in Inner Mongolia to compare the decomposition process of the litters detached in autumn versus that detached in spring of two dominant plant Leymus chinensis and Stipa grandis. Throughout the whole decomposition period, the autumn litter was directly positioned upon the soil surface, while the spring litter suspended as standing dead for the first 7 months of winter before being detached. We found that the overall decomposition rate of spring litter was faster than the autumn litter over the experimental period. The decomposition rate was correlated positively with the N content, but negatively with the C/N ratio, lignin concentration and lignin/N ratio in litters. The spring litter showed a sharp decrease in lignin remaining during the standing-dead stage, while the autumn litter did not, which suggests an important role of photodegradation in the breakdown of lignin over the winter period that facilitates the litter decomposition in subsequent stages. These findings highlight the difference in the decomposition rates of the litters detached in autumn versus in spring, and suggest to incorporate the effects of the standing-dead stage in calculating or modeling the nutrient turnover rates in semi-arid steppe ecosystems.