Increased organic fertilizer significantly increases leaf nitrogen and phosphorus but not carbon content in a tropical tea plantation

Carbon (C), nitrogen (N), and phosphorus (P) are essential elements for plant growth and metabolism, with their stoichiometry playing a pivotal role in ecosystem functioning. In tea plantations, fertilization strongly influences the balance of these elements. However, the effects of organic fertilizers on the leaf C, N, and P contents and their stoichiometry in tropical tea plants remain poorly understood. In this study, we examined the impact of organic fertilizer on the leaf C, N, and P contents and their ratios of Camellia sinensis var. assamica (CSA) and Camellia sinensis var. sinensis (CSS) in Hainan, China. Our findings indicated that organic fertilizer significantly increased leaf N and P contents but had no effect on leaf C content. Additionally, organic fertilizer significantly decreased leaf C: N ratio of CSA and CSS, as well as leaf C: P ratio of CSA, but significantly increased leaf N: P ratio of CSS. Soil organic carbon (SOC), total N, and total P also increased, while their stoichiometric ratios decreased in CSA but not CSS. In the unfertilized tea plantation, leaf C, N, and P contents and their stoichiometry of CSA and CSS were significantly correlated with soil NO₃^--N, whereas they were significantly correlated with soil NH₄⁺-N in the fertilized tea plantation. Our results suggest that the differential responses of leaf C, N, and P contents of CSA and CSS to organic fertilizer might be attributed to the distinct leaf physiological characteristics of these two tea plant species.