Leaf litter of a dominant cushion plant shifts nitrogen mineralization to immobilization at high but not low temperature in an alpine meadow

We evaluated the effects of temperature and addition of leaf litter of Androsace tapete MaximWe-a dominant cushion plant species of alpine meadows on the Tibetan Plateau-on carbon (C) and nitrogen (N) mineralization, microbial biomass C (MBC) and N (MBN). A laboratory incubation experiment with and without cushion plant litter addition was conducted for 112 days at three temperature regimes (-1, 5 and 11 A degrees C). C and net N mineralization were simultaneously measured during the incubation period. C and N mineralization were affected by interactions between litter addition and temperature. Litter addition increased C mineralization and MBN but shifted N mineralization to immobilization at higher temperature. The positive relationship between net N mineralization and MBC and MBN was shifted to a negative one through cushion plant litter addition. Cushion plant litter also changed the relationship between C mineralization and net N mineralization from insignificantly positive to significantly negative. These findings indicate that low temperature in winter could be important for alpine plants because low temperature can increase net N mineralization and supply plants with available N for their growth in the early growing season. During the growing season, climate warming-either directly through a temperature effect or indirectly through triggering increased cushion plant litter production-might lead to stronger competition for N between alpine plants and microorganisms.