Abstract
The factors regulating potential acquisition of sulphur (S)-containing amino acids by plant roots from the rhizosphere remain poorly understood. Using radio tracer (C-14 and S-35), we studied the competition for two S-containing amino acids (i.e., cysteine (Cys) and methionine (Met)) within 24 hours (h), by the rhizosphere microbial community and maize plants (Zea mays L.). Our results showed that the capture of Cys and Met by the maize plants was much lower, with only <10% of the added amino acid-C-14 or S-35 captured by the plant, compared to the rhizosphere microbial community (76.9%) on average. We suggest that this could be a result of relatively high availability of inorganic N and S in soil solution, the lack of transmembrane for amino acids on maize root cells, as well as the rapid turnover of Cys and Met by soil microbes in the rhizosphere. The addition of inorganic S, significantly reduced plant capture of Cys and Met-C-14 by maize plants in the rhizosphere but had little effect on the capture of Cys and Met-S-35 (p<0.05). Overall, our results imply that (1) Cys and Met are available carbon (C), nitrogen (N) and S sources for maize plants, potentially contributing to total plant N and S demand under certain conditions; (2) Utilization of Cys and Met by maize roots in the rhizosphere is independent of inorganic S availability; (3) Increased amino acid concentration led to higher capture by both plants and soil microbes, but had little effect on the competition success on either side.
