Divergence and conservative of stomatal conductance in coexisting species in response to climatic stress in Tibetan Plateau

Convergence of eco-physiological function in harsh habitats due to environmental filtering is well-known, however, some evidence of eco-physiological divergence in coexisting species also exists. Experimental data to verify whether divergence of eco-physiological function in coexisting species increases with increasing environmental stress remain limited. Here, we measured bulk leaf oxygen isotope and functional traits along a climatic stress gradient in a grassland in Tibetan Plateau where drought, excess radiation, and temperature increased from east to west. Enrichment (Δ 18 O) in bulk leaf oxygen isotope was used as proxy for time-integrated gs. We found that the leaf water use (Δ 18 O and leaf area [LA]) spectrum was independent of the leaf economic spectrum, indicating that coexisting species shifted from high nitrogen use efficiency (high ratio of leaf carbon to nitrogen) and water loss (high LA) in low-stress habitats to high photosynthetic capacity (high leaf nitrogen) and low water loss (low gs) in high-stress habitats. As the stress intensity of climate increases, higher mean and maximum and lower skewness (varying from positive to negative values) of Δ 18 O in coexisting species confirmed that the abundance of water-saving species increased to cope with climatic stress, while the greater standard deviation and kurtosis further indicated that climatic stress drove the divergence in gs in coexisting species. This study revealed that coexisting species adopt more diversified water use strategies and the abundance of water-saving species increases to cope with climatic stress, regardless of decreases in overall species abundance.