Response to water stress of soil enzymes and root exudates from drought and non-drought tolerant corn hybrids at different growth stages

Song, F., Han, X., Zhu, X. and Herbert, S. J. 2012. Response to water stress of soil enzymes and root exudates from drought and non-drought tolerant corn hybrids at different growth stages. Can. J. Soil Sci 92: 501-507. Drought tolerant corn hybrids (Zen mays L.) are an excellent model to evaluate the effect of water stress on rhizosphere functions. The purpose of this study was to investigate the influences of water stress on soil pH, enzyme activities, and root exudates from corn. Two corn hybrids, Baidan 9 (drought tolerant) and Baidan 31 (non-drought tolerant) were grown in soil-filled pots for pH and enzyme assays and in hydroponics culture for root exudate analysis. Water stress was imposed at four growth stages: seedling, elongation, tasseling and grain-filling stages. Soil pH was lower in the rhizosphere than bulk soil, but was not affected by water deficiency. Water stress increased protease activity at the seedling stage, but reduced its activities at other stages compared to the control. A significant positive correlation was observed between pH and alkaline phosphatase activity under water stress. Compared to Baidan 31, the rhizosphere of drought-tolerant Baidan 9 had greater protease and catalase activities at all growth stages, greater alkaline phosphatase, lower acid phosphatase and greater invertase activities at elongation, tasseling and filling stages. Osmotic stress increased the organic acid concentration (malic, lactic, acetic, succinic, citric and maleic acids) in root exudates of Baidan 9 and Baidan 31; as well there was a greater fumaric acid concentration in Baidan 31 under osmotic stress than without stress. The increased soil enzyme activities and organic acids exuded from the rhizosphere of plants under water stress might contribute to drought tolerance in corn hybrids.