# Effect of Dryland-to-Paddy Conversion on Soil Aggregate Phosphorus Fractions and Microbial Functional Diversity in a Typical Black Soil Region of the Sanjiang Plain

## TL;DR

Converting drylands to paddy fields in the Sanjiang Plain changes soil phosphorus fractions and microbial diversity, with implications for soil health and nutrient cycling.

## Contribution

The study reveals how dryland-to-paddy conversion alters phosphorus fractions and microbial communities in black soil, identifying key functional genes involved.

## Key findings

- Dryland-to-paddy conversion increased soil organic carbon and electrical conductivity, and improved aggregate stability.
- The conversion shifted phosphorus fractions from NaOH-Po to NaOH-Pi and HCl-Pi, with macroaggregates storing most of the increased total phosphorus.
- Microbial community changes included increased Bradyrhizobium and Pseudomonas, and decreased Streptomyces and Mesorhizobium.

## Abstract

The Sanjiang Plain is a key black soil agricultural zone in Northeast China. The conversion of dry-lands (DL) to paddy fields (PF) alters soil aggregate phosphorus (P) fractions and microbial diversity, yet the underlying mechanisms are unclear. This study compared DL and PF (converted from DL) soils. The results showed that electrical conductivity (EC) and soil organic carbon (SOC) increased significantly after the dryland-to-paddy conversion (p < 0.05). The proportions of macroaggregates and microaggregates increased, while the silt+clay fraction declined (p < 0.05), indicating enhanced aggregate stability. Soil total P increased by 16.04%, of which 83.81%, was attributed to macroaggregate-associated P. The dominant P fractions shifted from NaOH-Po to NaOH-Pi and HCl-Pi. The land-use change also markedly altered the soil microbial community structure, leading to increased abundances of Bradyrhizobium and Pseudomonas and decreased abundances of Streptomyces and Mesorhizobium, collectively driving the transformation of P fractions. The key functional genes identified were gcd, phoD, and phnA. However, this study did not capture the temporal dynamics of P forms and microbial community structure across different stages of land-use conversion. Future research should track these dynamics throughout the conversion process to clarify the mechanisms of P evolution.