Water level modulates the soil microbial response to elevated tropospheric ozone in wheat

Abstract

Water level modulates the tropospheric ozone impact on the plant, although the extent to which this effect is transferred to the soil microbiota is unknown. We investigate whether water availability can alter the microbial response to elevated ozone concentrations in an ozone-sensitive wheat variety. An open-top chamber trial was set up with four ozone levels (Pre-industrial; Ambient; Ambient+20 ppb; Ambient+40 ppb) and two irrigation levels (stress and optimum). The rhizosphere fraction of the soil (0-5 cm) showed higher sensitivity to ozone and irrigation level than the bulk fraction. Ambient air was the least sensitive treatment, and Ambient+20 was the most sensitive to irrigation. Regardless of the irrigation level, Ambient and Ambient+40 air showed contrasting microbiological characteristics. Water stress alters the intermediate behaviour of Ambient+20 by increasing its metabolic quotient. Pre-industrial air tended to behave like Ambient+20 at both irrigation levels (lower qMic and higher qCO₂), so changes in ozone with respect to Ambient lead to lower efficiency of C use. Irrigation modulates the effect of ozone on soil microbiota.