Abstract:

Species diversity–productivity relationships in natural ecosystems have been well documented in the literature. However, biotic and abiotic factors that determine their relationships are still poorly understood, especially under future climate change scenarios.

Randomized block factorial experiments were performed in three meadows along an elevational gradient on Yulong Mountain, China, where open-top chambers and urea fertilizer manipulations were used to simulate warming and nitrogen addition, respectively. Besides species diversity, we measured functional diversity based on five traits: plant height, specific leaf area and leaf carbon, nitrogen and phosphorus contents. Several abiotic factors relating to climate (air temperature and precipitation) and soil chemistry (pH, organic carbon concentration, total nitrogen concentration and phosphorus concentration) were also measured. Generalized linear mixed-effect models were used to investigate the responses of species diversity and productivity to elevation, warming, nitrogen addition and their interactions. The effects of biotic and abiotic factors on the direction and magnitude of their relationship were also assessed.

Species diversity decreased with increasing elevation and declined under warming at mid-elevation, while productivity decreased with increasing elevation. Functional richness, maximum air temperature, soil pH and their interactions showed strong but negative influences on the species diversity–productivity relationship; the relationship shifted from positive to neutral and then to slightly negative as these sources of variation increased. Our study highlights the negative effects of short-term warming on species diversity and emphasizes the importance of both biotic and abiotic drivers of species diversity–productivity relationships in mountain meadow communities.

Key words: climate warming, elevation, functional traits, nitrogen addition, plant community composition, soil pH, Yulong Mountain