Effects of carbon on microbe-root interaction mediating P acquisition by vegetable crops

  Objectives  Carbon (C) underpins microbial metabolism. Thus, it is critical to understand the microbe-root interaction associated with high P use efficiency. This study investigated the influence of C on microbial mediated P availability and its role in modifying root morphological and exudation traits.

  Methods  A pot experiment with glucose addition was conducted to investigate the effects of microbial mediated P availability (microbial biomass P and Olsen-P) on root morphological (root biomass, root/shoot ratio, root length, diameter, specific length and tissue density) and exudation traits (acid phosphatase, citrate, and malate) governing P acquisition by Brassica chinensis at day 7 and 21.

  Results  At 7 days after addition, glucose increased microbial biomass P while decreasing soil Olsen-P. When roots in glucose and no-glucose soils were compared, root biomass and root/shoot ratio increased, while total root length decreased by 33%. Furthermore, root diameter increased by 37%, while specific root length decreased by 46%. When glucose amended soil was compared to no-glucose soil, the rhizosphere citrate content increased by 106%. Microbial biomass P decreased from the 7th to the 21st day after glucose addition, and soil Olsen-P increased, eliciting higher Olsen-P in glucose soil than no-glucose soil on the 21st day after addition. In parallel with the variation in microbial biomass P and Olsen-P, Brassica chinensis proliferated rapidly, increased root length by 31%, but decreased rhizosphere exudation of acid phosphatase and citrate in the former compared to the no-glucose soil. On days 7 and 21, there was no difference in the shoot P content of Brassica chinensis in the glucose and no-glucose treatments.

  Conclusions  Glucose addition increased microbial biomass P but decreased soil Olsen-P content, resulting in strong citrate exudation to meet crop P demand on day 7. However, at day 21, microbial biomass P decreased, increasing soil P availability and stimulating rapid root elongation. To summarize, microbial biomass P turnover and efficient root P-acquisition strategies determine crop P use efficiency.