Enhanced tea quality driven by improved aggregate structure and stability:A case study from leguminous green manure intercropping

Intensive tea cultivation often leads to soil degradation via acidification and fertility decline, thereby threatening plantation sustainability. Although legume intercropping is widely recognized as a beneficial management practice, the integrated mechanisms by which it simultaneously improves soil structure and tea quality remain insufficiently quantified. Here, we examined the effects of five tea–legume intercropping systems—CK (tea monoculture), TM (tea–mung bean), TMA (tea–mung bean/Chinese milk vetch), TS (tea–soybean), and TSA (tea–soybean/Chinese milk vetch)—on soil chemical properties, aggregate architecture, and tea quality. Intercropping, particularly TS and TSA, significantly alleviated soil acidification ( p < 0.05) and enhanced soil fertility, increasing soil organic carbon (SOC) and total nitrogen (TN) by more than 25% ( p < 0.05). Notably, TMA produced the highest inorganic N content. Intercropping also substantially improved soil physical structure: TMA most strongly increased the proportion of large macroaggregates (> 2 mm) by 107.52% and their contributions to soil C (CR) and N (NR) pools by > 120% ( p < 0.05), while aggregate stability indices (MWD, GMD, R 0.25 ) were maximally improved by 57.47%, 48.91%, and 32.60%, respectively ( p < 0.05). Consequently, tea quality was markedly enhanced. Theanine content increased by 28.56% under TSA and 26.91% under TMA, whereas EGCG content peaked under TMA with a 27.63% increase ( p < 0.05). Mechanistic modeling revealed a nutrient-pathway differentiation: theanine accumulation was strongly driven by soil and large-macroaggregate nitrogen, whereas EGCG formation was primarily associated with soil and large-macroaggregate carbon. Both compounds were positively associated with aggregate stability ( p < 0.05). Overall, this study demonstrates that legume intercropping synergistically enhances tea quality by improving soil aggregate structure, increasing C and N sequestration, and differentially regulating nutrient supply pathways, thereby providing a scientific basis for sustainable tea plantation management.