Conclusions
Our work documents the water-carbon trade-off response to long-term experimental manipulation for tree species common to the boreal-temperate ecotone in North America. Empirically quantifying those responses across a large number of species in a relatively realistic experimental context contributes to our understanding of whether and how stomatal behavior is expected to vary across species and their hierarchical affiliations (e.g., climate of origin or phylogeny) in response to climate change. In particular, we found thatg1 was reduced in response to growth conditions that caused a decline of soil VWC (i.e., rainfall removal and warming). We also showed that there was a large variation among species intrinsicg1 ; however, their responses to reduced rainfall and warming did not depend on species identity or grouping. Our study also provides additional evidence that soil moisture will govern plants’ response to future climate change: when soil moisture is abundant plants use it to facilitate greater carbon assimilation, but when soil water is limited plants will have diminished carbon assimilation but more efficient water use.