Effects of Co-Application of Biochar and Nitrogen Fertilizer on Soil Properties and Microbial Communities in Tea Plantation

Soil acidification reduces the abundance and activity of beneficial microorganisms, impairs tea plant growth, and ultimately leads to a decline in tea quality. Maintaining healthy soil is critical for sustainable tea agriculture. However, the interactive effect of biochar and nitrogen fertilizer on the microbial community structure and function in acidic tea plantation soils remains unclear. This study was designed to explore whether the co-application of biochar and fertilizer could enhance soil properties and maintain microbial health in tea plantations. Three treatments were set up through a controlled pot experiment: no fertilizer or biochar application (B 0 N 0 ), fertilizer without biochar (B 0 N 1 ), and biochar with fertilizer (B 1 N 1 ). High-throughput sequencing technology was used to investigate the characteristics of soil microbial communities in tea plantations. Biochar amendment increased soil pH by 0.8 units, organic matter and total nitrogen by 13.5% and 21.4%, and reduced NH 4 + -N and NO 3 − -N leaching by 10.8% and 12.9%, respectively. It also modulated microbial community structure, enhanced the abundance of nitrogen-cycling genes (e.g., narB , nirK , nosZ ), and influenced nitrogen availability through adsorption. Nitrate was identified as the main factor shaping microbial communities under fertilization. These results highlight the potential of biochar as a sustainable amendment to improve soil health and nitrogen retention in tea cultivation systems. Further field studies are warranted to validate its efficacy in enhancing tea productivity and reducing environmental nitrogen losses under real-world conditions.