关键词: 氮沉降, 磷限制, 叶片磷组分, 化学计量特征, 宏基因组

Abstract: Aim Phosphorus (P) is the primary limiting nutrient for the productivity of forest ecosystems. However, increasing nitrogen (N) deposition may lead to P limitation, and the mechanisms by which plants maintain P supply under P limiting conditions remain unclear. Methods This study focused on Indocalamus tessellatus, a dominant understory species in subtropical forests, and conducted a simulated N deposition experiment. Three N addition levels were set: control (CT, 0 kg N·ha−1·yr−1), low N (LN, 40 kg N·ha−1·yr−1), and high N (HN, 80 kg·N·ha−1·yr−1). During the fifth and sixth experimental years, surface soil and I. tessellatus leaves were sampled to determine leaf P fractions, soil physicochemical properties, phosphatase activity, microbial biomass, and P cycling functional genes. These measurements aimed to elucidate the effects of N addition on plant nutrient limitation status and their adaptive strategies. Important findings The results showed that, compared with the control, low N treatment significantly reduced leaf P content and increased the N to P ratio. Simultaneously, low N treatment significantly increased the content and allocation proportion of metabolic P in leaves, while significantly decreasing the content of inorganic P and lipid P. Although high N treatment had no significant effect on leaf stoichiometric characteristics, it significantly reduced leaf nucleic acid P content and increased the microbial biomass N to P ratio as well as the abundance of soil P cycling functional genes (e.g., ugpA and phnF). In summary, low N addition induced P limitation in I. tessellatus. To adapt to P deficiency caused by low N addition, the plant optimized the allocation of non metabolic P fractions toward metabolic P in the leaves. Under high N addition, the allocation of leaf P fractions and enhanced microbial metabolic activity may be important reasons for the less pronounced P limitation in I. tessellatus. These findings deepen our understanding of how understory plants in subtropical forests adapt to N induced P limitation, and provide a theoretical reference for nutrient management of subtropical forests in response to N deposition.

Key words: Nitrogen deposition, Phosphorus limitation, Leaf phosphorus fractions, Stoichiometric characteristics, Metagenome