Diverse and divergent influences of phenology on herbaceous aboveground biomass across the Tibetan Plateau alpine grasslands

Abstract

Indirect influences of phenology on productivity (e.g., phenology-functional traits-productivity) could exist due to close associations between phenology and plant functional traits, which may further result in the divergent responses of vegetation biomass to phenology among plant functional groups (PFGs). Here, we introduced functional traits (i.e., plant height and growth rate) to analyse the influences of phenology on aboveground biomass (AGB) of two symbiotic PFGs based on 19-year in-situ observational data for plant phenology at 7 sites across the Tibetan Plateau alpine grasslands. The vegetative growth phase (VGP) and reproductive growth phase (RGP) were calculated according to the observed green-up date, first flowering date and first fruit-ripening date. The commonality analysis and structural equation modelling were applied to explore the paths and degrees of phenological influence on AGB. The results showed that the phenological influences on herbaceous AGB included both direct (“phenology-AGB”) and indirect paths (“phenology-functional traits-AGB”) and differed between two PFGs. Phenological metrics, especially VGP, were the key factors driving the adjustment (path coefficients |w| = 0.19 – 0.67), although maximum plant height (Hmax) contributed to the most to the AGB (|w| = 0.78). Specifically, the grasses had two indirect phenological influence paths on AGB, while the sedges had multiple direct and indirect influence paths. Comparing the differences in phenology and functional traits between two PFGs, our study implied that grasses may tend to preferentially adjust vegetative (stem) growth via phenology, while sedges may tend to preferentially adjust root and reproductive growth via phenology, which could be relevant to the differences in the synthesis, accumulation, allocation, and decomposition of organic matter in diverse organs and the growth and reproduction strategies, competition and symbiosis of different PFGs.