UV radiation and decomposer biodiversity co-drive responses of litter decomposition to nitrogen enrichment in a Tibetan alpine steppe

Abstract:

The decomposition of dead organic matter is a key process of biogeochemical cycling in terrestrial ecosystems. However, the relative importance of biotic and abiotic factors regulating the responses of litter decomposition to nitrogen (N) enrichment remain unclear. Here, we conducted a two-year (2015-2016) field experiment to examines the changes of decomposition rate of four types litter and the related regulating factors along a manipulative N gradient in a Tibetan alpine steppe. We observed that the decomposition rate of Stipa purpurea, Carex stenophylloides, Potentilla multifida and litter mixture decreased under N enrichment. We also found that the changes of the decomposition rate were positively associated with the canopy light transfer. The decreased canopy light transfer due to N-induced increase in plant height and leaf area would decelerate litter decomposition rate by inhibiting photodegradation. UV irradiation manipulative experiment further confirms this finding, UV radiation is an important factor regulating litter decomposition in this alpine steppe. Meanwhile, litter decomposition rate was also positively correlated with soil bacterial diversity. N-induced decrease in soil bacterial diversity may weaken the facilitative interactions among microbial decomposers, thus potentially decreasing litter decomposition rate. These results show that N-induced decline in canopy light transfer and decomposer biodiversity co-drive litter decomposition in alpine steppe. These findings suggest that both biotic and abiotic factors should be considered for better predicting response of ecosystem carbon cycle to exogenous N inputs.