Crop growth limitation set by low water temperature stress in rice

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Low temperature of irrigation water can affect rice (Oryza saliva L.) growth by limiting various processes, which differ with the growth stages, but a synthetic understanding is still limited. The objective of this study was to determine the effect of low water temperature on growth, development and yield during three growth periods under field conditions. The treatment was conducted during the vegetative, the reproductive and grain-filling periods, In the temperatures range from 16 to 25ﾟC, cool water decreased grain yield most severely during the reproductive period by limiting spikelet fertility with a more than five-fold difference between cultivars at 19ﾟC, but the crop growth rate (CGR) was least damaged. The varietal difference in spikelet fertility was not associated with CGR, photosynthetic rates, and anther length. Root pruning at panicle formation and at booting also did not alter spikelet density. The largest influence on CGR occurred in the vegetative period. While leaf area and radiation interception were markedly reduced, radiation use efficiency was relatively unaffected. A cultivar with high ability of leaf expansion showed higher CGR under cool water temperatures. The effect on the photosynthetic rates was relatively small (5-15 %) when averaged over the treatment period, but the response to the water temperature changed substantially during the treatment for the vegetative and the reproductive growth periods, with a large reduction in the first half and the recovery in the second half. These changes were largely attributable to the response of the stomatal conductance to the water temperature, possibly via changes in the water status of the plants. Cool water also reduced crop N accumulation by limiting both N accumulation per unit biomass increase and leaf area production per unit N increase, but the latter had the comparative importance in CGR reduction due to low water temperatures.