Energy budget and transpiration characteristics of rice grown under elevated co2 and high temperature conditions as determined by remotely sensed canopy temperatures

Abstract

The effects of elevated CO2 concentration and high temperatures on transpiration and gaseous diffusive resistances of rice canopy were investigated. Akihikari and IR36 cultivars were grown under two CO2 concentrations ([CO2], 365 and 700 μL L-1) × three temperatures (29.8, 30.4 and 32.5°C on average over the experimental period), created by two Temperature Gradient Chambers. From 2 August (panicle initiation) to 22 August (booting), measurements were made of dry and wet bulb temperatures, canopy surface temperatures (Tc) and net radiation along with evapotranspiration (E) measurements by microlysimeters. Aerodynamic resistance (ra), obtained from the measured E and microclimate data, showed a fairly constant value (11.7 s m-1)- Then, ra, Tc and microclimates data were substituted into energy budget equations to obtain E and canopy resistance (rc). In all plots, calculated E was in good agreement with measurement by lysimeters, and rc reached minimum values (rcjnm) at solar radiation above 500 W m-2. Elevated [CO2] at the lowest temperature plot increased rm by 40-49% and Tc by 1.4-1.6°C and it reduced E by 14-16% of those under ambient CO2 conditions. With the rising growth temperature, these effects of elevated [CO2] drastically decreased. The observed r, responses to temperature and [CO2] seemed to have reflected a long-term acclimation of rice to these environments. These results indicate that anticipated global warming significantly reduces the advantageous effects of elevated [CO2] on plant water use.