Response of dominant and common species flowering phenology to nitrogen addition in an alpine meadow

Timely flowering is one of the most important life history strategies for plants species, while global changes, such as nitrogen deposition, increasingly influence the process of flowering phenology. Based on in situ experiments with different concentrations of nitrogen addition, we studied the first flowering date and flowering duration in an alpine meadow of eastern Qinghai-Tibet Plateau, to evaluate effect of nitrogen addition on the flowering phenology. The results showed that: 1) Nitrogen addition significantly delayed the first flowering date for grasses species under the low nitrogen (LN) and high nitrogen (HN) addition level (P < 0.01), and significantly shortened the flowering duration under the high nitrogen addition level (P < 0.05). Nitrogen addition significantly extended flowering duration for all forbs species (LN: P < 0.05; HN: P < 0.01), and high nitrogen addition significantly advanced first flowering date for the forbs species (P < 0.05). 2) We identified a significant negative correlation between the first flowering date and flowering duration for the investigated species (P < 0.05). 3) The richness of flowering species decreased with nitrogen addition; for example, the numbers of flowering species decreased by 29% under low nitrogen level and 49% under high nitrogen level. These findings indicated that nitrogen addition plays an important role in regulating plant flowering phenology in alpine meadow. In summary, our study suggested that nitrogen addition had a species-specific impact on flowering phenology of the plants, which might further influence community composition, structure and function in the alpine meadow.