# Nano-biochar–nano-calcium oxide synergies enhance yellow-brown soil health and tea productivity via microbial, enzymatic, and genetic pathways

## TL;DR

Combining nano-biochar and nano-calcium oxide improves soil health and tea productivity under drought by boosting microbial activity, enzyme levels, and gene expression.

## Contribution

The study reveals novel synergistic effects of nano-biochar and nano-calcium oxide on soil and tea plant traits under drought stress.

## Key findings

- Combined nBC and nCaO increased soil pH, organic matter, and nutrient availability under drought.
- Soil enzymes and N-C-P cycling genes like phoD, phoC, and narG were significantly upregulated.
- Tea quality traits like caffeine and polyphenol content improved with the combined treatment.

## Abstract

Tea (Camellia sinensis L. O. Kuntze) is an important economic crop widely cultivated in tropical and sub-tropical regions, where drought stress often limits its growth and productivity. Soil application of nano-biochar (nBC) and nano-calcium oxide (nCaO) offers a promising approach for enhancing soil health, tea quality, and yield. A pot experiment was executed to explore the synergistic effects of nBC and nCaO on soil enzymatic and microbial activities, N-P-C cycling genes, and the quality and yield of tea seedlings under drought stress. The results showed that, under drought stress, the combined application of nBC and nCaO significantly improved the soil physico-chemical and microbial properties viz. an increase in soil pH (23.29%), soil organic matter (53.18%), soil total carbon (30.56%), available N (63.12%), available P (140.85%), available K (32.92%), microbial biomass carbon (9.90%) and microbial biomass N (8.23%) compared with the control. This may have been due to manifold increase in the expression levels of N-C-P cycling genes such as phoD (5.2-fold), phoC (7.0-fold), narG (3.4-fold) and GH31 (1.8-fold) and relatively higher abundance of archaeal and bacterial communities. Soil urease, acid-phosphatase, nitrate reductase, β-glucosidase, catalase, phosphomonoesterase, and N-acetyl-β-d-glucosaminidase enzyme values were 48.32, 13.34, 100.00, 43.37, 612.5, 61.30, and 43.65% higher, respectively, in soils amended with both nBC and nCaO than in the control under drought stress. Furthermore, co-application of nBC and nCaO significantly enhanced tea quality traits such as caffeine (5.89%), polyphenol (12.24%), total catechins (11.00%) and amino acid (16.17%), as well as yield parameters including plant height (10.43%), leaf area (97.55%) and 10-bud weight (42.53%) relative to the control. Overall, the combined application of nBC and nCaO substantially improved soil enzymatic and microbial activities, as well as tea quality and yield traits, under drought stress.

Illustration showing how the addition of biochar and calcium (nBC + Ca) to soil improves plant nutrient availability, soil enzymes, and microbial activity, leading to increased gene expression, enhanced plant height and yield, and improved leaf quality traits such as higher caffeine, polyphenol, and catechin content. Bar graphs and a correlation matrix are included to represent data on plant growth, gene expression, and enzyme interactions.