Optimizing nitrogen management for young rubber plantations: gradients effects on nutrient partitioning and root structural adaptation

Yongfa Zhang^*DongQi JinXuehua LuoChunmei ZhaoXinxin XueChangqi RenXiaoshuang WuYu WangJingmin ZhangWei Luo^*Wenbin Wang^*

• Rubber Research Institute, Chinese Academy of Tropical Agricultural Sciences, Danzhou, China

Efficient nitrogen (N) management is crucial for the sustainable cultivation of rubber tree (Hevea brasiliensis) seedlings. This study aimed to determine the effects of low (CK, 32.4 g tree–1), medium (MN, 64.8 g tree–1), and high (HN, 97.2 g tree–1) nitrogen application on plant growth, chlorophyll content, nitrogen allocation, and root architecture in young rubber trees. Results indicate that MN application optimized plant performance. The MN treatment yields the highest sustained chlorophyll a+b content, peaking 60 days post-fertilization, and the lowest chlorophyll a/b ratio, which suggests a potentially more efficient configuration of the photosynthetic apparatus. Notably, MN treatment demonstrates superior nitrogen fertilizer utilization, as evidenced by significantly higher nitrogen derived from fertilizer (Ndff) values in leaves across various growth stages and in most organs (roots, stems, bark) during dormancy. Consistently, MN application results in the highest whole-plant biomass (846.88 g/plant) and total nitrogen accumulation (13.79 g/plant), with a marked increase in allocation to structural components (main stem, branches). The treatment of MN promotes the development of a more vigorous fine root system during dormancy, as evidenced by significantly greater root length, diameter, surface area, and volume, correlating positively with root N content and Ndff. Correlation analysis revealed significant positive associations between fine root N content/Ndff and root architectural traits, indicating a synergistic relationship between root development and nitrogen uptake efficiency. Consequently, while HN application provides a transient boost in chlorophyll a, it is associated with lower nitrogen uptake efficiency (ANdff and %Ndff) and increased dependence on soil nitrogen (%Ndfs), leading to reduced biomass and N accumulation. This pattern of inefficiency under high nitrogen inputs underscores suboptimal fertilizer use and suggests a greater potential for environmental nitrogen losses. Therefore, medium nitrogen application emerges as the most effective strategy for enhancing seedling growth and nitrogen use efficiency in young rubber tree seedlings.