Quantifying the feedback between rice architecture, physiology and microclimate under current and future CO2 conditions

To assess the micrometeorological consequences of rice variety choices in relation to rising CO2 associated to climate change, we quantified the interplay between rice architecture, physiology, and microclimate in current (385 mu mol mol(-1)) and future (580 mu mol mol(-1)) CO2 microenvironments. Two rice varieties contrasting in canopy structure and physiology were grown embedded in irrigated rice paddies, under elevated CO2 (using a Free-Air CO2 Enrichment facility) and ambient CO2 conditions. The high-yielding indica variety Takanari is more photosynthetically active and characterized by a more open canopy than a commonly cultivated variety Koshihikari. Our results show a strong diurnal interplay between solar angle, canopy structure, plant physiology, and the overlying atmosphere. Plant architecture was identified as a strong determinant of the relation between plant physiology and microclimate that in turn affects the surface forcing to the overlying atmosphere. Takanari was able to maintain lower canopy temperature both in current and future CO2 owing to the greater atmospheric mixing and stomatal conductance than Koshihikari. In the perspective of food security, a shift to such a higher-yielding variety would have consequences on the regional surface energy balance, which subsequently might alter regional weather.