Leaf size variations in four ground-floor bryophytes and their environmental drivers across the forests of the eastern Qinghai-Tibet Plateau

Variations in leaf size and its responses to environmental variables will improve our understanding of how different species adapt to regional climate changes. Bryophytes usually form dominant ground-floor cover in temperate and boreal forests and could be used as indicators of the forest types. However, interspecific and intraspecific variations in leaf size of bryophytes and their relationships with environmental variables remain poorly understood. We sampled four ground-floor bryophytes, i.e., Abietinella abietina, Rhytidium rugosum, Thuidium assimile, and T. cymbifolium, across the forests of the eastern Qinghai-Tibet Plateau (QTP), measured the leaf length (LL), leaf width (LW), and leaf area (LA) of each species, and estimated the relative amounts of interspecific (BTV), intraspecific trait variation (ITV), and environmental factors to the total trait variance. Hierarchical partitioning analysis was used to evaluate the individual effects of environmental factors on leaf size variations in each species. The trait-environment relationships were analyzed using a simple linear model. The coefficient of variation of LA, LL, and LW ranged from 18.29% to 64.04%, from 11.42% to 37.91%, and from 11.71% to 36.44%, respectively. For the three leaf size traits, BTV was greater than ITV and climate had stronger explanatory power than soil and microhabitat. The leaf size of A. abietina was primarily dominated by climate and positively correlated with temperature seasonality. The leaf size of R. rugosum and T. assimile were controlled by soil and increased with the increasing soil organic carbon. Bryophyte cover determined the leaf size of T. cymbifolium and they were positively related. The results suggested that the leaf size of three species would tend to be smaller under global warming of the QTP. The findings provided valuable evidence in variations of bryophyte leaf size and new insights into the plants’ responses to global climate change.