WARMING EFFECTS ON PLANT GROWTH, SOIL NUTRIENTS, MICROBIAL BIOMASS AND SOIL ENZYMES ACTIVITIES OF TWO ALPINE MEADOWS IN TIBETAN PLATEAU

The aim of this study was to assess initial effects of warming on the plant growth, soil nutrient contents, microbial biomass and enzyme activities of two most widespread ecosystem types: swamp meadow (deep soil, high water content) and alpine meadow (poor soil, low water content), in the hinterland of the Qinghai-Tibet Plateau (altitude 4600-4800 m a.s.l.) The temperature of air and upper soil layer was passively enhanced using open-top chambers (OTCs) (50 cm high with 60 cm at opening and constructed of 6 mm thick translucent synthetic glass) from 2006 to 2008. The use of OTCs clearly raised temperature and decreased soil moisture. In warmed plots, monthly mean air temperature was increased by 2.10 degrees C and 2.28 degrees C, soil moisture of 20 cm soil layer was decreased by 2.5% and 3.9% in alpine meadow and swamp meadow, respectively. Plant biomass significantly increased by 31% in alpine meadow and 67% in swamp meadow. Warming also affected soil microbial biomass C and N at both meadows. In swamp meadow, warming caused the decrease of soil organic carbon and total nitrogen in 0-5 cm layer and an increase in 5-20 cm. While in alpine meadow, these soil parameters increased in 0-5 cm layer and decreased in 5-20 cm layer. The effects of warming on enzyme activities differed depending on the enzyme and the meadow ecosystem. In general, enzyme activities were higher in the upper soil layers (0-5 cm) than in the lower soil layers (5-20 cm). The experiment results exhibited that warming improved the soil biochemical and microbiological conditions in high-mountain meadows, at least in the short term.