The Impact of Reduced Nitrogen Fertilizer Application and AMF Inoculation on Nitrogen Utilization in Intercropped Areca catechu and Vanilla planifolia

Areca (Areca catechu L.) is an important economic crop in tropical regions, but excessive nitrogen application leads to low nitrogen fertilizer utilization efficiency (approximately 30%) and groundwater pollution. Vanilla (Vanilla planifolia Andrews) is a high-value spice plant that can be intercropped with areca to enhance land use efficiency. 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 results showed that nitrogen reduction significantly inhibited chlorophyll content (decreased by 46.21%), net photosynthesis (decreased by 71.13%), and transpiration rate (decreased by 44.34%) of vanilla orchid without inoc of AMF, but had little effect on the photosynthesis of areca. Inoculation with AMF, notably Funneliformis mosseae, alleviated the adverse effects of reduced nitrogen on vanilla orchids. The net photosynthesis increased by 76.23%, and the intercellular CO2 concentration rose by 69.48%, both of which were significantly enhanced. 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 (increased by 38.86% in vanilla) and nitrate reductase (increased by 53.77% in areca), promoting soil mineral nutrient activation and nitrogen metabolism. Studies have shown that nitrogen reduction combined with AMF inoculation can significantly improve the nitrogen use efficiency of the areca and vanilla intercropping system, alleviate environmental pressure, reveal its synergistic mechanism in the tropical intercropping system, and provide a theoretical basis for sustainable agriculture in tropical regions.