Warming and elevated CO2 alter the suberin chemistry in roots of photosynthetically divergent grass species

A majority of soil carbon (C) is either directly or indirectly derived from fine roots, yet roots remain the least understood component of the terrestrial carbon cycle. The decomposability of fine roots and their potential to contribute to soil C is partly regulated by their tissue chemical composition. Roots rely heavily on heteropolymers such as suberins, lignins and tannins to adapt to various environmental pressures and to maximize their resource uptake functions. Since the chemical construction of roots is partly shaped by their immediate biotic/abiotic soil environments, global changes that perturb soil resource availability and plant growth could potentially alter root chemistry, and hence the decomposability of roots. However, the effect of global change on the quantity and composition of root heteropolymers are seldom investigated. We examined the effects of elevated CO2 and warming on the quantity and composition of suberin in roots of Bouteloua gracilis (C4) and Hesperostipa comata (C3) grass species at the Prairie Heating and CO2 Enrichment (PHACE) experiment at Wyoming, USA. Roots of B. gracilis exposed to elevated CO2 and warming had higher abundances of suberin and lignin than those exposed to ambient climate treatments. In addition to changes in their abundance, roots exposed to warming and elevated CO2 had higher omega-hydroxy acids compared to plants grown under ambient conditions. The suberin content and composition in roots of H. comata was less responsive to climate treatments. In H. comata, alpha,omega-dioic acids increased with the main effect of elevated CO2, whereas the total quantity of suberin exhibited an increasing trend with the main effect of warming and elevated CO2. The increase in suberin content and altered composition could lower root decomposition rates with implications for root-derived soil carbon under global change. Our study also suggests that the climate change induced alterations in species composition will further mediate potential suberin contributions to soil carbon pools.