Climate Seasonality Mediates Global Patterns of Foliar Carbon and Nitrogen Isotopes

Frequent extreme climate events have significantly affected plant intrinsic water-use efficiency (iWUE) and forest nitrogen (N) availability. Understanding the coupling between climate seasonality and plant water, carbon, and nitrogen may provide insights into how plants respond to climate change. Here, we integrated ?C-13 and d(15)N in woody plant leaves as a probe to elucidate the iWUE and N availability patterns of plants under global change and found that woody plants from sites with high climate seasonality, especially precipitation seasonality, tend to have improved iWUE and N availability compared with those with low seasonality. Specifically, high potential evapotranspiration, solar radiation, vapor pressure deficit, and low precipitation during the growth season are the driving factors. The intra-annual and annual climate explained 43% and 49% of ?C-13 and 40% and 53% of d(15)N, respectively, suggesting that the intra-annual climate is at least as important as the annual climate. These results suggest that not only the direction (decrease vs. increase) of decadal climate should be counted but also the abnormal fluctuation of intra-annual should be considered. Climate seasonality is a more suitable ecological filter for determining plant distribution across terrestrial ecosystems.