Effects of straw addition on soil microbes-root morphology governing phosphorus-acquisition of Solanum lycopersicum

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.