Global CO_2 rise leads to reduced maximum stomatal conductance in Florida vegetation

摘要

A principle response of C3 plants to increasing concentrations of atmospheric CO_2 (CO_2) is to reduce transpirational water loss by decreasing stomatal conductance (g_s) and simultaneously increase assimilation rates. Via this adaptation, vegetation has the ability to alter hydrology and climate. Therefore, it is important to determine the adaptation of vegetation to the expected anthropogenic rise in CO_2. Short-term stomatal opening-closing responses of vegetation to increasing CO_2 are described by free-air carbon enrichments growth experiments, and evolutionary adaptations are known from the geological record. However, to date the effects of decadal to centennial CO_2 perturbations on stomatal conductance are still largely unknown. Here we reconstruct a 34% (±12%) reduction in maximum stomatal conductance (g_(smax)) per 100 ppm CO_2 increase as a result of the adaptation in stomatal density (D) and pore size at maximal stomatal opening (a_(max)) of nine common species from Florida over the past 150 y. The species-specific g_(smax) values are determined by different evolutionary development, whereby the angiosperms sampled generally have numerous small stomata and high g_(smax), and the conifers and fern have few large stomata and lower g_(smax). Although angiosperms and conifers use different D and a_(max) adaptation strategies, our data show a coherent response in g_(smax) to CO_2 rise of the past century. Understanding these adaptations of C3 plants to rising CO_2 after decadal to centennial environmental changes is essential for quantification of plant physiological forcing at time-scales relevant for global warming, and they are likely to continue until the limits of their phenotypic plasticity are reached.