Phosphorus deficiency in soils with red color: Insights from the interactions between minerals and microorganisms

Abstract

Phosphorus (P) deficiency limits agricultural productivity in many tropical and subtropical soils. The aim of this study was to investigate the influences of typical mineral components and microorganisms on P availability in soil. Three representative soil minerals, i.e., montmorillonite (Mt), calcium carbonate (Cal) and goethite (Gt) were incubated with phosphate-solubilizing fungus (PSF, Aspergillus niger) and apatite (the dominant P source on Earth) in soil. In the control treatment, the fungus promoted phosphate dissolution and P release (from < 1 to 370.40 mg kg−1), primarily via secreting oxalic acid. Mt addition promoted fungal respiration and up-regulated oxaloacetate acetylhydrolase (regulating organic acid secretion, based on RNA sequencing analysis). However, strong adsorption of organic acids by Mt finally caused decline of P availability (from ~ 400 to 24 mg kg−1). Cal addition decreased fungal counts (down to < 5% of the value for the control treatment). Additionally, the consumption of organic acids (by Cal dissolution) further reduced P release. Gt stimulated fungal respiration, whereas its toxicity significantly decreased fungal abundance. Moreover, Gt demonstrated the maximal P adsorption capacity, i.e., 1.266 mg g−1. Therefore, Gt demonstrated evident negativity on P release. Despite the strong sorption of organic acids, Mt showed high potential to promote P release in the long-term due to the enhanced fungal bioactivity. Our results hence indicated that different minerals had totally distinct effects on P release, which should be addressed when investigating biogeochemistry in soil.