The effect of pika grazing on Stipa purpurea is amplified by warming but alleviated by increased precipitation in an alpine grassland

摘要

Climate warming may cause alpine grassland degradation by decreasing plant growth and increasing pika grazing, although the concurrent precipitation change may further confound the plant and pika responses to warming. We aim to investigate the interactive effect of changes in temperature, precipitation and pika herbivory on plant growth. A 2-year field manipulation experiment of 2 degrees C warming and 15-30% increased precipitation was conducted in an alpine grassland ecosystem. During the growing season, warming significantly reduced plant height growth of the two dominant species Stipa purpurea and Kobresia macrantha, whereas increased precipitation and its interactions with warming stimulated plant height growth. Regarding the widespread species S. purpurea, warming significantly increased the frequency, consumption, and intensity of pika herbivory, whereas increased precipitation significantly reduced pika herbivory intensity, resulting in a net positive effect of increased precipitation and its interactions with warming and pika herbivory on plant growth. However, the pika grazing on K. macrantha varied little with warming and precipitation change. There was generally a much larger effect of pika grazing on S. Purpurea than on K. macrantha, which corresponded to higher specific leaf area and nitrogen content in S. purpurea than in K. macrantha. The diet selection of pika may explain why the sensitivity of pika herbivory to warming and precipitation change differed between the two dominant plant species. Our data suggest that the effect of pika grazing on Stipa plants is amplified by climatic warming, and such a negative effect could be alleviated by increased precipitation.