Response of Root-Exuded Organic Acids in Irrigated Rice to Different Water Management Practices

Abstract

Knowledge of the composition and volume of root-exuded organic substances is crucial for understanding the biochemical processes in the rhizosphere. The present study was undertaken to quantify organic acids from the roots of drought-tolerant and non-drought-tolerant rice cultivars (DTR and NDTR) and their response to irrigation during different growth periods. Alternating wetting and moderate drying with 4 cm water layer of flood irrigation until the soil water potential reaches −15 kilopascal (kPa) (WMD) significantly enhanced succinic, maleic, citric, malic, oxalic, tartaric, and total organic acids in the two rice cultivars during the trial by 80.59–86.68, 31.62–58.55, 16.55–43.00, 17.89–25.66, 13.68–29.70, 12.40–16.05, and 17.34–21.24%, respectively. Alternate wetting and severe drying with 4 cm water layer of irrigation until the soil water potential reached −30 kPa (WSD) notably decreased formation of maleic, citric, malic, oxalic, tartaric, and total organic acids in the two rice cultivars during the experiment by 5.19–25.15, 13.96–29.92, 20.81–34.88, 32.20–42.51, 12.79–24.66, and 6.67–24.22%, respectively. Acetic acid output between CF (continuous flooding with a 3–4 cm water layer) and WMD treatments in pads with two rice cultivars did not differ. The WSD treatment increased acetic acid exudation by 16.93–25.99% in two rice cultivars during the experiment. The high content of acetic and total organic acids in DTR should be responsible for the smaller loss of total organic acids in the WSD treatment and the high drought tolerance capacity. The results contribute to valuable background knowledge for exploring the role of root exudates in soil-plant relationships.