Elevated carbon dioxide and temperature imparted intrinsic drought tolerance in aerobic rice system through enhanced exopolysaccharide production and rhizospheric activation

Abstract

Elevation in atmospheric carbon dioxide (CO2) concentration and temperature coupled with moisture stress is anticipated by most of the climate change prediction models (IPCC, 2014). Climate change results in atmospheric warming that trigger water stress to rice and could influence soil health, functioning and biological activities. Therefore, it is required to quantify indicative parameters like soil-exopolysaccharides which indicates greater water holding capacity of soil and imparted drought tolerance to rice. Carbon pools and related soil enzymes are also indicative of soil health status. We designed one field study in open top chambers (OTCs) to assess the impact of elevated CO2, temperature and deficit moisture stress on rice. There were two replicated CO2 enrichment treatment in OTCs, namely, ambient CO2 (394 ± 20 ppm and ambient temperature; a-CO2) and elevated CO2 (550 ± 20 ppm) with temperature (2 °C ± 0.3 more than ambient; e-CO2T). Three aerobic rice (grown in saturated soil moisture condition) cultivars (CR-143-2-2, APO and CR Dhan 201) were grown in separate blocks in each OTCs with adequate nutrient level and water stress (−40 kPa). Total soil and colloidal exopolysaccharides (EPSs), soil labile carbon (C) pools, soil enzymes (dehydrogenase, Fluorescein diacetate and β-glucosidase) and plant enzymes (catalase, peroxidase and super oxide dismutase) were measured as indicators of the soil health, functioning and intrinsic drought tolerance to the system. Total soil EPS (29%), colloidal EPS (37%), microbial biomass C (30%), readily mineralizable C (29%), dehydrogenase (15%), FDA (38%), and β-glucosidase (13%) activities were significantly higher under elevated CO2 and temperature (e-CO2T) to that of ambient condition (a-CO2). The total and colloidal EPS, soil labile C pools and soil enzymatic activities were found higher at panicle initiation (PI) and grain filling (GF) stage than other physiological growth stages of rice. On the other hand, plant stress enzymes like catalase, peroxidise and superoxide dismutase (SOD) were decreased under e-CO2T by 24, 20 and 32%, respectively, as compared to a-CO2. All these indicated e-CO2T could impart additional intrinsic drought tolerance to tropical aerobic rice system (aerobic rice cultivars grown with adequate nutrient supply) in future climate change scenario.