Heritable Changes in Physiological Gas Exchange Traits in Response to Long-Term, Moderate Free-Air Carbon Dioxide...

Atmospheric carbon dioxide ([CO₂]) concentrations significantly alter developmental plant traits with potentially far-reaching consequences for ecosystem function and productivity. However, contemporary evolutionary responses among extant plant species that coincide with modern, anthropogenically driven [CO₂] rise have rarely been demonstrated among field-grown plant populations. Here we present findings from a long-term, free-air carbon dioxide enrichment (FACE) study in a seminatural European grassland ecosystem in which we observe a differential capacity among plant species to acclimate intrinsic water-use efficiencies (WUEs) in response to prolonged multigenerational exposure to elevated [CO₂] concentrations. In a reciprocal swap trial, using controlled environment growth chambers, we germinated seeds from six of the most dominant plant species at the FACE site [Arrhenatherum elatius (L.), Trisetum flavescens (L.), Holcus lanatus (L.), Geranium pratense (L.), Sanguisorba officinalis (L.), and Plantago lanceolata (L.)]. We found that long-term exposure to elevated [CO₂] strongly influenced the dynamic control of WUE_i in the first filial generations (F₁) of all species as well as an unequal ability to adapt to changes in the [CO₂] of the growth environment among those species. Furthermore, despite trait-environment relationships of this nature often being considered evidence for local adaptation in plants, we demonstrate that the ability to increase WUE_i does not necessarily translate to an ecological advantage in diverse species mixtures.