Sorgoleone production enhances mycorrhizal association and reduces soil nitrification in sorghum

Abstract

The control of nitrogen (N) flows via nitrates leaching and nitrous oxide emission is crucial for a safe environment. Some plants have shown abilities to suppress soil nitrification by releasing biological inhibitors, such as sorgoleone in sorghum. We hypothesized that the N uptake capacity of plants partly influences soil nitrification, and so do the intensity of the arbuscular mycorrhizal fungi (AMF)-sorghum symbiosis. Therefore, this study clarified the relationships between sorghum biological nitrification inhibition levels and AMF and fungi abundances in rhizosphere soils and sorghum roots by qPCR. The varieties 296B, IS32234, and IS20205, which release low (L-sorg), medium (M-sorg), and high (H-sorg) sorgoleone, respectively, were grown in φ 12 cm × 1 m pipes. Including a control without plant, they received 0 and 120 kg N ha−1 as ammonium sulfate solution. Samples were collected from 0 to 10, 10–30, and 30–80 cm soil layers. AMF and fungi populations at 31 days were significantly higher in H-sorg followed by M-sorg soils. The application of 120 kg N ha−1 (70 days) substantially increased AMF’s abundance in the 0–10 cm horizon. This result reveals that N-rich environments favor AMF expression. The AMF increase was more marked in the H-sorg and M-sorg soils, indicating that the levels of sorgoleone released may also influence the AMF symbiosis. Although H-sorg harbored more endophytic fungi, we did not observe any difference in root AMF colonization. The higher sorgoleone varieties showed higher plant biomass and N amounts, reflecting better N absorption and assimilation. The study reveals that sorgoleone, which confers sorghum its nitrification inhibition ability, also strengthens the sorghum-AMF symbiosis, N uptake and reduces the ammonia pool subjected to nitrification, and possibly the loss of nitrogen.