Leaf nitrogen and phosphorus concentration and the empirical regulations in dominant woody plants of shrublands across southern China

Aims Understanding the changes in N and P concentration in plant organs along the environmental gradients can provide meaningful information to reveal the underline mechanisms for the geochemical cycles and adaptation strategies of plants to the changing environment. In this paper, we aimed to answer: (1) How did the N and P concentration in leaves of evergreen and deciduous woody plants change along the environmental gradients? (2) What were the main factors regulating the N and P concentration in leaves of woody plants in the shrublands across southern China?
Methods Using a stratified random sampling method, we sampled 193 dominant woody plants in 462 sites of 12 provinces in southern China. Leaf samples of dominant woody plants, including 91 evergreen and 102 deciduous shrubs, and soil samples at each site were collected. N and P concentration of the leaves and soils were measured after lapping and sieving. Kruskal-Wallis and Nemenyi tests were applied to quantify the difference among the organs and life-forms. For each life-form, the binary linear regression was used to estimate the relationships between leaf log N] and log P] concentration and mean annual air temperature (MAT), mean annual precipitation (MAP) and log soil total N], P]. The effects of climate, soil and plant life-form on leaf chemical traits were modeled through the general linear models (GLMs) and F-tests.
Important findings 1) The geometric means of leaf N and P concentrations of the dominant woody plants were 16.57 mg·g^-1 and 1.02 mg·g^-1, respectively. The N and P concentration in leaves (17.91 mg·g^-1, 1.14 mg·g^-1) of deciduous woody plants was higher than those of evergreen woody plants (15.19 mg·g^-1, 0.89 mg·g^-1). The dependent of leaf P concentration on environmental (climate and soil) appeared more variable than N concentration. 2) Leaf N and P in evergreen woody plants decreased with MAT and but increased with MAP, whereas those in deciduous woody plants showed opposite trends. With increase in MAP, leaf P concentration decreased for both evergreen and deciduous woody plants. 3) Soil N concentration had no significant effect on both evergreen and deciduous woody plants. However, leaf P concentration of the tow increased significantly with soil P concentration. (4) GLMs showed that plant growth form explained 7.6% and 14.4% of variation in leaf N and P, respectively. MAP and soil P concentration contributed 0.8% and 16.4% of the variation in leaf P, respectively. These results suggested that leaf N was mainly influenced by plant growth form, while leaf P concentration was driven by soil, plant life-form, and climate at our study sites.