Dynamics of root–microbe interactions governing crop phosphorus acquisition after straw amendment

Abstract

Phosphorus (P) mobilization by microorganisms influences root morphological and exudation traits related to crop nutrient acquisition. However, the dynamics of root P acquisition strategies in response to P immobilization followed by release that accompany microbial growth and decay remain unclear. We evaluated root–microbe interactions governing P uptake by Brassica chinensis and Solanum lycopersicum grown for 56 days in low-P (10 mg P kg−1) and high-P (100 mg P kg−1) soil with or without straw addition. Straw addition increased the growth of bacteria and fungi (including microorganisms harbouring the phoD, phoC and pqqC genes) and enhanced the microbial P pool. The high microbial abundance 29 days after straw addition was associated with short roots and weak carboxylate exudation in B. chinensis and S. lycopersicum regardless of P fertilization. Phosphate-solubilizing microbes harbouring the phoD, phoC and pqqC genes together with microbial P release increased plant-available soil P, influencing variation in root P-acquisition strategies between the species. The high level of CaCl2-extractable P due to P release upon microbial decay and phosphate-solubilizing microorganisms was associated with short roots and weak carboxylate exudation in B. chinensis, but underpinned crop nutrient acquisition in low-P soil amended with straw after day 40. S. lycopersicum increased root elongation in response to mobilization of microbial P after day 44. The long roots coupled with the increased P availability due to microbial P release elicited large P acquisition by S. lycopersicum in straw-amended, low-P soil. By contrast, microbial abundance and microbially mediated P availability had little influence on root P-acquisition strategies in B. chinensis and S. lycopersicum in high-P, straw-amended soil. This study highlighted the importance of temporally varying root–microbe interactions in influencing crop P acquisition in low-P, straw-amended soil.