Spatial heterogeneity of soil phosphorus influencing bacterial functional adaptations in alkaline calcareous soils

TL;DR

This study explores how soil bacteria adapt to low phosphorus levels in alkaline soils and how these adaptations can improve crop growth with less fertilizer.

Contribution

The study reveals how spatial phosphorus heterogeneity shapes bacterial adaptations and their impact on plant growth in alkaline soils.

Findings

Low-P soil PSB secrete more organic acids but less indole acetic acid compared to high-P soils.

LPSB inoculation significantly improves wheat biomass, yield, and phosphorus use efficiency.

PSB can reduce fertilizer dependency by achieving similar yields with 70% phosphate fertilization.

Abstract

To enhance sustainable soil fertility and efficient phosphorus (P) management, phosphate-solubilizing bacteria (PSB) play a central role in solubilizing soil mineral phosphorus by releasing organic acids and acidifying micro-niches. Thus far, the influence of spatial P heterogeneity on bacterial eco-physiological adaptations to P-limited, alkaline soils remains poorly understood. This study examined how soil edaphic factors vary across major wheat-growing regions, assessing their influence on the abundance and functional properties of culturable PSB. Soil available P was the strongest predictor of culturable bacterial abundance, with a threshold of P < 6.3 mg kg–1 dry soil driving major variations. At low P levels, organic matter played a key role, while at higher P levels, potassium (K ≥ 123) and pH further shaped bacterial abundance. Low-P soil PSB (LPSB) secreted elevated levels of organic acids such as malic, succinic, gibberellic and citric acid, but low levels of indole acetic acid. A clear trade-off was observed between P solubilization and growth-related traits: LPSB invested more in acquiring resources (e.g., producing siderophores and organic acids) and less in synthesizing phytohormones. A net house study showed that LPSB contribute to plant growth. Plants with 70% phosphate fertilization (P70) and PSB inoculation reached the yield levels comparable to those with 100% fertilization without the PSB, indicating the potential of PSB to reduce dependency on fertilizers. This was associated with a significant increase in wheat biomass (24.3%), yield (28.53%) and P use efficiency (31.66%) by LPSB inoculation compared to the control P70. Our findings emphasize the importance of microbial functional plasticity in enhancing P use efficiency in P-limited soil, offering a basis for developing climate-smart bioformulations to improve sustainable crop productivity.

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