# Biochar regulates putative keystone microbial taxa to drive phosphorus cycling and increase availability in urban greenspace soils

## TL;DR

Biochar improves soil quality in urban green spaces by increasing phosphorus availability through direct and microbial mechanisms.

## Contribution

This study identifies specific microbial taxa and genes regulated by biochar that drive phosphorus cycling in urban soils.

## Key findings

- Biochar application increased available and total phosphorus content in soil.
- Biochar regulates keystone microbial taxa and genes involved in phosphorus cycling.
- Microbial co-occurrence and PLS-PM models confirm biochar's role in enhancing phosphorus availability.

## Abstract

The quality of soil in urban green spaces often deteriorates due to poor design practices, insufficient maintenance, and environmental pressures associated with urbanization. Although biochar, as an effective soil additive, can significantly improve the soil quality in greenspace, it significantly influences the phosphorus (P) cycling processes through functional regulation of microbial community; however, further analysis is essential to validate this mechanism. Therefore, this study reported pot experiments using Euonymus kiautschovicus, a typical urban greenspace plant, followed by metagenomic analysis for investigating microbial-driven P cycle mechanisms. Four treatment groups were established according to the dosage of biochar, including 0% (CK), 4% (BC4), 8% (BC8), and 12% (BC12). Biochar application significantly increased soil available P (AP) and total P (TP) content, with BC12 demonstrating maximum AP and TP content of 21.79 mg kg−1 and 0.62 g kg−1, respectively. On the one hand, biochar serves as a direct source of P. On the other hand, it enhances AP by regulating P-cycling functional microorganisms. Random forest model identified phnP, phoA, relA, ppnK, pstA, phnD, and pstS as the putative keystone genes regulating soil P cycling. Microbial co-occurrence network analysis and partial least squares path modeling (PLS-PM) demonstrated that the biochar application improved soil AP by regulating putative keystone microbial taxa (Modules 1 and 2) involved in P cycling. This study elucidates the microbial mechanisms underlying biochar-mediated P cycling in greenspace soils, providing a scientific basis for biochar application for improved soil quality in urban greenspace.

Scientific illustration showing how corn stover converts to biochar at five hundred degrees Celsius, increasing soil phosphorus available to Euonymus kiautschovicus via both direct and microbially mediated pathways, with functional gene modules, a correlation heat map, and urban and plant elements depicted.