To investigate species’ resource competition strategies with traits of the leaf economics spectrum across contrasting environments and to examine the effects of nutrient additions on the ranking of species based on their leaf economics spectrum in an alpine grassland on the Qinghai-Tibetan Plateau, five leaf traits (LDMC: leaf dry matter content, SLA: specific leaf area, LC: leaf carbon concentration, LN: leaf nitrogen concentration and LP: leaf phosphorus concentration) were measured for 10 plant common species in all plots. The results showed that N addition significantly increased LN by 9.4% and P addition significantly increased LP by 81.8%. There were significant interactions between N addition and P addition on SLA and LDMC, which increased SLA by 15.3% and decreased LDMC by 10.1%. In addition, there were species-specific responses of leaf traits across multivariate trait space to nutrient additions. The variation in species responses to NP addition significantly changed the species ranking based on the leaf economics spectrum. These results showed that co-occurring species followed a conservative strategy in the infertile environment and an exploitative strategy in the fertilized ones by increasing SLA and leaf nitrogen and phosphorus concentrations. Different species responses to NP addition caused a new species distribution based on the leaf economics spectrum. These results suggest that, before using leaf traits to predict responses of community structure and ecosystem functioning to nitrogen and phosphorus additions, it is necessary to take the species-specific responses into consideration.

Seasonal freezing and thawing process occurs in the non-growing season in the alpine grassland on the Tibetan Plateau. However, it is still unclear that how warming would affect this process in the alpine zone. From October 2013 to April 2014, the research used minirhizotron directily and soil temperature indirectly to investigate the effects of warming on the freezing and thawing process. The results showed that, warming significently increased soil temperature at the depths of 5, 10 and 20 cm, and soil temperatue in the winter warming plots was 0.01-0.18^oC higher than that in the annual warming plots. Wamrming significantly decreased the depth of soil frozen layer in the frozen period and thawing period of winter spring, but had no effect on the the depth of soil frozen layer in the thawing period of fall-winter. It is due to warming-induced redution on soil miosture. Warming significantly reduced lasting days of frozen period and increased lasting days thawing period of winter-spring, and did not affect the lasting days of freezing period of fall-winter. Effects of winter warming on frozen soil depths and lasting days were much greater than annual warming. The reults suggest that the enhanced freezing and thawing circles with a warming trend may subsequently affect soil carbon (C) and nitrogen (N) in this region.