# Bacillus aryabhattai and silicon modulate soil biological activity and performance of Mimosa caesalpiniifolia under water deficit

## TL;DR

This study shows that using Bacillus aryabhattai and silicon can improve the growth and soil health of Mimosa caesalpiniifolia seedlings under drought conditions.

## Contribution

The novel contribution is demonstrating the synergistic effects of Bacillus aryabhattai and silicon on plant performance and soil biology under water deficit.

## Key findings

- Combined B. aryabhattai and silicon treatment increased chlorophyll and carotenoid content regardless of water level.
- Soil enzymatic activities increased up to 600% with B. aryabhattai and silicon under drought conditions.
- B. aryabhattai and silicon improved water use efficiency and soil respiration under drought.

## Abstract

Mimosa caesalpiniifolia is a native legume commonly used in agroforestry systems, degraded land recovery, and timber production in semiarid regions. Although this species is naturally hardy, its seedlings are highly sensitive to water deficit during early growth stages, limiting their establishment under drought conditions. This study investigated the effects of Bacillus aryabhattai inoculation and silicon (Si) application on seedling growth, physiological performance, and soil microbial and enzymatic activity under two water regimes (50% and 100% water level) and four treatments (control, B. aryabhattai, Si, and B. aryabhattai + Si), in a greenhouse experiment. Seedlings under 100% water level showed significantly higher shoot and root biomass, leaf number, root length, plant height, and seedling quality indices. Chlorophyll and carotenoid contents increased in combined B. aryabhattai + Si treatments, independent of water level. Water use efficiency improved under drought conditions (50%). Soil basal respiration rose by ~ 87% and 75% with B. aryabhattai and B. aryabhattai + Si at 50% water level, respectively. Enzymatic activities (arylsulfatase, β-glucosidase, phosphatases, urease) increased up to 600% with B. aryabhattai + Si compared to control. Si concentration was highest in shoots with B. aryabhattai at 100% water level, and in roots with B. aryabhattai + Si at 50% water level. Soil Si concentration peaked in the Si-only treatment at 100% water level. These findings demonstrate the synergistic potential of B. aryabhattai and Si to enhance drought tolerance and soil biological quality in M. caesalpiniifolia seedlings, supporting sustainable restoration in semiarid ecosystems.