Objectives The interactions between microbial phosphorus (P) mobilization and root traits govern crop yield. Investigating the impacts of straw addition on dynamics of microbial abundance and microbial P mobilization as well as root traits is important to reveal the mechanism of high crop P-use efficiency underlying root-microbe interaction.
Methods Tomato (Solanum lycopersicum) field experiment was conducted under addition (+straw) and no addition of straw (–straw) conditions. At 15, 30, and 45 days of transplanting, the shoot biomass, P content and root morphological traits of tomato were analyzed. The abundance of soil bacteria and fungi with phosphate-solubilizing abilities and the microbial biomass P and Olsen-P content were determined at the same time.
Results The shoot P content of tomato under +straw was lower than those under –straw at 45 days of transplanting, and the P content in the aboveground part of tomato (leaves, stems, and fruits) were 21.8% higher at maturing stage. Straw addition increased abundance of bacteria and phosphate-solubilizing microbes encoding phoD, phoC and pqqC genes, and raised microbial P content in soil. At 15 days of transplanting, tomato under +straw had smaller root/shoot ratio, lower root tissue density, larger specific root length, and root traits were significantly correlated with soil Olsen-P. +Straw decreased tomato root elongation during 15–30 days of transplanting. During 30–45 days after transplanting, the abundant phosphorus-solubilizing microorganisms and the release of microbial P promoted soil P bioavailability and increased growth of thin roots with large specific length.
Conclusions The proliferation of microbes caused slow growth of tomato roots initially after straw addition, whereas P mobilization mediated by the decline in microbial biomass P and phosphate-solubilizing functional microorganisms promoted rapid elongation of fine roots at the late stage. Straw return stimulated microbial P mobilization coupling with efficient root P-acquisition strategies increased crop P uptake in tomato at maturity.