Shifts in plant resource use strategies across climate and soil gradients in dryland steppe communities

Background and aims: Despite being Earth’s largest biome and a key contributor to global energy budgets, arid regions (or drylands) are critically understudied relative to mesic ecosystems. Here we clarify how dryland species vary in their functional traits across environmental gradients. Methods: We measured nine traits reflecting resource use for 68 species inhabiting dryland steppe communities across northwestern China. We tested predictions from various theoretical frameworks including the leaf economics spectrum, leaf energy balance theory and least-cost optimality theory. Results: Species on drier or sunnier sites had smaller leaves with higher LMA, higher leaf nitrogen concentration per area (N_area), and a greater drawdown of CO₂ during photosynthesis (i.e., lower C_i:C_a) suggesting higher photosynthetic water use efficiency. Leaf nitrogen per mass and plant height (typically < 1.4 m for all species) did not vary with climate or with soil properties. Trait-trait relationships showed little patterning in relation to climate or soil. Traits of forbs were more strongly influenced by environmental properties than those of the shrubs, trees, or grasses sampled. Conclusion: We investigated variation in plant traits that influence carbon economy, water use and competitive interactions, and found that in dry and low fertility environments, dryland steppe species exhibited a mixture of resource acquisitive (e.g. high N_area) and conservative leaf traits (e.g. high LMA). Our results demonstrate the utility of applying multiple theoretical frameworks to better understand variation in resource use strategies among co-occurring species.