Historical analysis of mangrove leaf traits throughout the 19th and 20th centuries reveals differential responses to increases in atmospheric CO₂

Aim To reconstruct the historic response of two dominant mangrove species to increases in atmospheric CO 2 over the past two centuries. Location I ndo‐ P acific. Methods We use a novel approach to assess plant responses to rising atmospheric CO 2 concentrations by measuring leaf traits of herbarium specimens of two dominant and widespread mangrove species. Results Leaf traits were correlated with atmospheric CO 2 concentration and latitude, but not with rainfall or the multidecadal multivariate E l N iño– S outhern O scillation index. R hizophora stylosa and A vicennia marina exhibited significant differences in their response to elevated CO 2 . Increases in atmospheric CO 2 concentrations over the past 165 years have led to a corresponding rise in photosynthetic carbon gain by the widespread mangrove A . marina , but not by R . stylosa. Main conclusions CO 2 fixation is at the heart of plant energy acquisition, global primary productivity and CO 2 sequestration. Given that atmospheric CO 2 concentrations have been rapidly rising for the past two centuries, surprisingly few datasets have examined the long‐term response of trees to rising CO 2 . Our results suggest changes to interspecific interactions, nutrient cycling and carbon sequestration in these globally significant forests are expected as CO 2 concentrations continue to increase.