# Legume cover under Camellia oleifera forests enhances understory biomass carbon storage and soil CO2 flux but declines soil inorganic carbon storage on a karst steep slope

## TL;DR

Using legumes under Camellia forests boosts plant and root carbon storage but reduces soil inorganic carbon and increases CO2 emissions.

## Contribution

This study first demonstrates a trade-off between aboveground vegetation and soil inorganic carbon storage under legume cover.

## Key findings

- Legume cover increases understory vegetation and root biomass carbon storage.
- Legume cover reduces soil inorganic carbon storage and increases soil CO2 flux.
- Alfalfa cover enhances microbial community stability but increases global warming potential.

## Abstract

Legume cover is a widely used and useful soil management strategy in orchards across the world. However, it remains unclear how the alfalfa cover affects vegetation and soil carbon storage, soil greenhouse gas fluxes, and global warming potential in Camellia oleifera forests. Furthermore, the understory vegetation, soil physicochemical properties, and microorganisms as potential drivers of vegetation and soil carbon storage, soil greenhouse gas fluxes, and global warming potential remain unexplored.

This study determined vegetation and soil carbon storage, soil greenhouse gas fluxes, and global warming potential under legume cover and non-cropping cover and explored the potential drivers on a karst steep slope.

The results showed that cropping cover under Camellia oleifera forests elevated understory vegetation aboveground and vegetation root biomass carbon storage (p = 0.0002) and reduced soil N2O flux (p = 0.0210), but reduced soil inorganic carbon storage (p = 0.0003) and enhanced soil CO2 flux (p = 0.0002) and global warming potential (p = 0.0002). In addition, cropping cover not only increased understory vegetation species richness (p = 0.0104), aboveground biomass (p = 0.0002), and vegetation root biomass (p = 0.0009) but also decreased soil microbial carbon (p = 0.0360) and phosphorus limitation (p = 0.0104) and enhanced soil organic carbon decomposition (p = 0.0043). Moreover, cropping cover shifted microbial community assembly processes and life-history strategies and enhanced soil bacterial community stability (p = 0.0000) and soil bacterial and fungal network stability. A trade-off existed between understory vegetation aboveground (Spearman r = −0.69, p = 0.0030) and vegetation root biomass carbon storage (Spearman r = −0.62, p = 0.0099) and soil inorganic carbon storage.

Alfalfa cover is recommended for improved understory vegetation aboveground and vegetation root biomass carbon storage, soil physicochemical properties, and soil microbial community stability and network stability, whereas it may not be recommended due to increased soil CO₂ flux and global warming potential, as well as reduced soil inorganic carbon storage. This study first demonstrated the trade-off between understory vegetation aboveground and vegetation root biomass carbon storage and soil inorganic carbon storage, and this trade-off should be carefully considered when conducting multi-storage management.