Stable carbon isotope used to estimate water use efficiency can effectively indicate seasonal variation in leaf stoichiometry

Estimates of seasonal variation in plant stoichiometry and water use efficiency (WUE) are critical for predicting the time courses of carbon and water fluxes. However, the relationship between seasonal stoichiometry and WUE, and their relationship with climatic factors remains unclear. The carbon isotope composition has been widely used to evaluate the WUE. We hypothesized that WUE is closely related to seasonal variation in plant stoichiometry, and then stable carbon isotope can be used to indicate the variation in future models. For this study, we investigated seasonal changes in WUE and 14 elements (C, N, P, S, K, Na, Ca, Mg, Al, Fe, Mn, Zn, Cu, and Ba) of Quercus variabilis in a warm temperate forest, Central China. The WUE gradually reduced from late spring until leaf senescence in fall. Leaf C and N initially increased and then decreased. Leaf P, S, and K generally decreased, whereas Ca, Ba, Al and Fe gradually accumulated throughout the growing season. Leaf C:N, C:P, and N:P were lowest in early season, and then typically increased. As expected, WUE was positively correlated with N, P, S, K, and Mg, while negatively with C, Ca, Al, and Fe as well as C:N, C:P, and N:P. WUE increased with higher temperatures but had no relationship with precipitation. Leaf N, P, S, and K increased, while C:N, C:P, and N:P decreased with higher temperatures. Our results suggested that seasonal stoichiometry and WUE was closely coupled with plant growth, and temperature may be the main dynamic driver of water and nutrients in forest ecosystems. As WUE was estimated by carbon isotope composition, our findings provide new insights toward integrating carbon isotope with Earth system models.