Terrace-Mediated Nutrient Redistribution Enhances Nitrogen Assimilation and Amino Acid Accumulation in Tea Plantations Across Hillslope Positions

Terracing is widely used for soil conservation in hilly tea plantations, yet its influence on tea quality formation across landscape positions remains insufficiently understood. This study compared terraced and sloping tea gardens at summit, midslope, and footslope positions in a subtropical tea-growing region of Hunan Province, China. Soil nutrients, leaf nitrogen (LeafN) status, nitrogen-assimilation enzyme activities, chlorophyll characteristics, and amino acid profiles were evaluated to explore the ecological links between terrace management and tea quality formation. Terracing significantly increased soil organic matter (SOM) and total nitrogen (TN), exhibiting peak increases of 18.1% and 32.8%, respectively, at the midslope position. These soil nutrient improvements significantly altered leaf carbon-nitrogen balance, resulting in lower leaf C/N ratios, a 49.3% increase in chlorophyll content, and a marked enrichment of total free amino acids (particularly glutamic acid and arginine) at the midslope position. While sloping gardens showed a conventional decline in fertility and quality from footslope to summit, terraced gardens exhibited a distinct midslope optimum. Redundancy analysis indicated that TN accounted for a substantial proportion of variation in tea quality indicators. These patterns are primarily driven by terrace-mediated nutrient redistribution and improved hillslope drainage conditions at the midslope position. Overall, the findings suggest that terracing may modify hillslope nutrient redistribution patterns and contribute to optimized nitrogen utilization and tea quality stability in mountainous tea-growing systems.