Response of Thai rice varieties under elevated CO2 concentrations

Plant height and tiller number will be measured and counted starting at 30 DAS and will be determined every week until maximum tillering stage, while plant height will be determined until maturity stage. Biomass at maximum tillering and harvesting stages by harvesting both shoot and root parts. Plant parts will be dried separately at 60°C until constant weight is obtained. The root-shoot ratio and the total plant biomass will be calculated from these components. The heading date will be determined by counting the stems and panicle numbers per plant to calculate the heading rate. Heading date will be determined from samples that will be allowed to produce yield at the end of the treatment. The heading date will be defined as the day on which the mean heading rate reached 50% for each treatment. The number of spikelets per panicle of the main tiller will be counted to determine the number and weight of filled and unfilled spikelets and the percentage of spikelet fertility. The weight of 1000 grains per plant will also be determined. At both maximum tillering and harvesting stages, the leaf area will be determined using leaf area meter (LiCor3100, Li-Cor Inc., USA). Leaf dry weight will be determined by drying the leaves at 60°C until constant weight is obtained and record the weight. Leaf mass per area will be determined as the ratio of leaf weight and leaf area. The chlorophyll content will be optically measured using chlorophyll meter (SPAD-502, Minolta).