The Impact of Reduced Nitrogen Fertilizer Application and Arbuscular mycorrhizal fungi Inoculation on Nitrogen Utilization in Intercropped Areca catechu L. and Vanilla planifolia Andrews

Areca (<i>Areca catechu</i> L.) is an important economic crop in tropical regions, but excessive nitrogen application leads to low nitrogen fertilizer utilization efficiency (approximately 30%). Vanilla (<i>Vanilla planifolia</i> Andrews) can be intercropped with areca to enhance land use efficiency. However, the impact of combined nitrogen reduction and <i>Arbuscular mycorrhizal fungi</i> (AMF) inoculation on the intercropping system of areca and vanilla remains unclear. This study examined the impact of nitrogen reduction (at levels of conventional fertilization, a 30% reduction and a 60% reduction) and the inoculation of AMF on the photosynthetic characteristics, physiological metabolism, and nitrogen utilization within an areca and vanilla intercropping system, employing a two-factor experimental design. The nitrogen reduction significantly inhibited SPAD value (chlorophyll content) (decreased by 46.21%), net photosynthesis (P_n) (decreased by 71.13%), and transpiration rate (T_r) (decreased by 44.34%) of vanilla without inoculation of AMF, but had little effect on the photosynthesis of areca. Inoculation with AMF, notably <i>Funneliformis mosseae</i>, alleviated the adverse effects of reduced nitrogen on vanilla. The net photosynthesis and intercellular CO₂ concentration (C_i) significantly increased by 76.23% and 69.48%, respectively. Additionally, the nitrogen uptake efficiency of the areca was improved, with root vitality increasing by 39.96%. Additionally, AMF enhanced the activities of acid phosphatase (ACP) (increased by 38.86% in vanilla) and nitrate reductase (NR) (increased by 53.77% in areca), promoting soil mineral nutrient activation and nitrogen metabolism. The nitrogen reduction combined with AMF inoculation can improve the nitrogen use efficiency of the areca and vanilla intercropping system, revealing its synergistic mechanism in the tropical intercropping system.