Over the last 200 million years, apparent shifts in atmospheric carbon dioxide (CO2) and climatic conditions occurred coincident with the evolution and diversification of plants and their traits, including traits that jointly regulate the fluxes of carbon and water through leaves. In turn, those traits are key mediators of plant functions like growth and transpiration, which determine how plants shape ecosystem functions and feedbacks to climate change. Yet, despite an abundance of experimental studies of elevated CO2 and warming on plant growth and physiology, few such studies focus on the effects of climate change on traits that most directly shape a plant’s ability to trade water for carbon, including anatomical features of leaf stomata and xylem, and physiological and morphological traits that shape plant drought tolerance. Here, we explore the response of such traits to factorial combinations of elevated CO2 and temperature in an intact, mixedgrass prairie in North America. We focus on 5 of the most common species in that ecosystem, including a C4 grass (Bouteloua gracilis), a C3 grass (Pascopyrum smithii), a C3 sedge (Carex duriuscula), and two C3 forbs (Artemisia frigida, Sphaeralcea coccinea).
Results/Conclusions
Effects of elevated CO2 and warming were relatively small to negligible for all measured traits, including: the fraction of leaf area comprised of stomata, dimensions of leaf xylem and veins, leaf dry matter content (LDMC), leaf turgor loss point, and pre-dawn leaf water potential. The responses of these traits to experimental treatments were also species specific. For example, elevated CO2 reduced the fraction of leaf area comprised of stomata for the C4 grass (by ~30%), but for other species, this treatment and warming had minimal effects on allocation of leaf area to stomata. All three graminoids had less negative turgor loss points under elevated CO2 (i.e., lower leaf-level ‘drought-tolerance’), with the strongest reduction for the C4 grass, but leaf turgor loss point was not responsive to the treatments for the two forbs. In ambient conditions and across all treatments, the 5 species had substantially and consistently different values for each measured trait. For this widespread grassland plant community, the effects of climate change on traits that regulate fluxes of water and carbon through plants will likely be driven by shifts in plant community composition (e.g., relative abundance of different species), with a smaller contribution of intraspecific shifts in trait values.