Assessing the seasonality of foliar nutrient concentrations in woody plants

Seasonal variations in foliar nutrient concentrations are an important strategy of plants to adapt to different climates and availabilities of soil nutrients. Gaps in our knowledge, however, remain in both the seasonality of the concentrations of multiple nutrients in plant leaves and their spatial pattern on a large scale. We compiled data on foliar concentrations of nine essential nutrients (N, P, K, Ca, Mg, Fe, Mn, Zn, and Cu) in woody plants in China and evaluated the characteristics and latitudinal patterns of their seasonal variability (i.e., seasonality). Foliar concentrations of mobile nutrients (N, P, K, and Zn) in deciduous broadleaf woody plants decreased significantly during the growing season, but nonmobile nutrients (Ca and Mn) continued to accumulate. In contrast, the foliar nutrient concentrations in evergreen broadleaves and conifers generally showed no significant seasonal trend. The seasonality of foliar nutrient concentration was weaker for the nutrients with higher foliar concentrations, supporting the hypothesis of seasonal stability of high-demand nutrients. The seasonality of foliar nutrient concentration was stronger for deciduous than evergreen plants, while the effect of plant phylogeny was not statistically significant. The seasonality of foliar N and P concentrations increased with latitude in the deciduous broadleaf woody plants, but evergreen plants showed no significant latitudinal trend. The spatial patterns of seasonality for foliar N and P concentrations were significantly explained by climate and foliar habit. These findings improve our understanding of the seasonality of plant foliar concentrations of multiple nutrients as a strategy to adapt to varying climatic conditions.