Seasonal dynamics of root exudation in Schima wallichii in tropical and sub-tropical forests of Mizoram, Northeast India

Root exudation plays an important role in regulating carbon and nitrogen fluxes in the rhizosphere. However, the interplay between seasonal climatic and spatial edaphic constraints remains poorly understood across climatic zones. This study aims to investigate the dynamics of root exudation in Schima wallichii across two distinct climatic zones (Tropical and Subtropical) in Mizoram, Northeast India. We examined various soil physicochemical parameters, microbial biomass stoichiometry, and carbon and nitrogen exudation rates using Redundancy Analysis (RDA) and a Structural Equation Model (SEM). Results indicated that differences across climatic zones had a more pronounced effect than seasonal variation (pre- and post-monsoon). The tropical climatic zone is characterised by high acidity, and total nitrogen (TN) showed higher carbon and nitrogen exudation rates than the sub-tropical climatic zone. RDA revealed that pH and TN are the primary drivers of rhizospheric flux predictions. Furthermore, SEM analysis revealed that soil pH acts as a pervasive negative regulator, inducing S. Wallichii to release more carbon to detoxify toxic substances in the rhizosphere. Observation of distinct negative feedback indicated that high soil TN suppressed soil microbial biomass nitrogen but upregulated nitrogen exudation by S. wallichii to overcome microbial nutrient limitation. The ternary plot revealed that tropical microbial communities exhibit high stoichiometric plasticity, whereas subtropical communities maintain homeostasis. This finding revealed that S. wallichii physiologically decouples exudation to sustain microbial activity under pedoclimatic stress.