| To study how air temperature and relative humidity (RH), genotypes, organ age and agronomic practice affect organs temperature and spikelet fertility of rice, we conducted a series of experiment in the field and plant growth chambers by measuring organs temperature, spikelet fertility and microclimate of rice. In addition, we investigated the effect of agronomic practices on TD and canopy temperature to assess the role of agronomic practices in enhancing the resistance of rice to avoid heat injury. The main results of the study are listed below(1) The panicle, leaf temperatures were affected by air temperature, air humidity, plant type and age of organs of rice. Under similar conditions of air humidity, the organ temperature was lower in the low air temperature than in the high air temperature. At the same air temperature, the organ temperature increased when the air humidity was high. The organ temperature was also affected by the plant type of the varieties. Under similar climatic conditions, the organ temperature of erect panicle varieties was lower than that of curved panicle varieties. Cultivars with panicle above the flag leaf showed lower organs temperature than cultivars with panicle below the flag leaf. After heading, there were significant differences between organ temperatures at different stages of rice growth, the more mature the organs, the higher the organ temperature.(2) The spikelet fertility, seed setting rate and 1000 grain weight were significantly affected by air temperature and humidity at heading stage of rice. Cultivars grown at a region with lower RH and higher temperature had higher spikelet fertility, seed setting rate and 1000 grain weight than those in higher RH under the similar air temperature during heading. Under ambient temperature of 28-35℃conditions, panicle temperature and spikelets fertility, seed setting rate showed a significant negative correlation. The lower temperature of rice organs during grain filling stage were positively correlated with spikelet fertility, seed setting rate and 1000 grain weight. Thus, it was suggested that temperature of panicle and leaf may be a potential methodology for screening physiologically superior lines in rice breeding programs. The differences in panicle and leaf temperature, and spikelet fertility of different cultivars were related with photosynthesis and chlorophyll content, the conductivity of the soak solutio and MDA, soluble sugar content and amino proline content, ABA and GA, and the expression of heat shock proteins. These differences could be the potential reasons for differences in heat resistance among the rice cultivars.(3) Panicle fertilizer application rate (PFAR) had a significant effect on organs and canopy temperature. Increasing PFAR resulted in the higher panicle number, LAI, plant high and specific leaf weight. It was also observed that air temperature, humidity, light intensity and content of CO2 were also affected by different PFAR treatments, medium PFAR was proved to be best for microclimate within rice population. Besides, there were felicitous leaf area index, length of second leaf, photosynthetic rate, transpiration and lower canopy temperature at medium PFAR. The temperature of plant organs was significantly affected by PFAR, the more the PFAR, the lower the temperature of panicle and leaf. This study clearly showed that medium PFAR has a significant effect on the temperature of plant organs and canopy, and also enhance the resistance to heat stress.(4) Row-spacing treatments has a significant effect on organ temperature. The panicle number, LAI, specific leaf weight and the yield of medium row-spacing treatments (30 cm×13.3 cm) was the highest, while the lowest values were observed under narrow row-spacing was the lowest with a significant difference at 0.05 level. Medium row-spacing treatments significantly diminished internode length and enhanced internode thickness, wall thickness, the number of vascular bundles, and lodging resistance at the 0.05 level compared to wide row-spacing and medium row-spacing. Significant differences were also observed in the CO2content, light intensity, air temperature and humidity among different row-spacing. These findings clearly showed that the medium row-spacing resulted in ideal microclimate and lower organs temperature reduced chances of heat injury and enhanced heat resistance.(5) Water stress has a significant effect on organ and canopy temperature. Increasing water stress caused increase in organs and canopy temperature. The lowest grain yield was observed under higher water stress treatment (W3). Lower seed setting rate and 1000 grain weight were the reasons for lowest yield of W3. Water stress significantly influenced physiological characteristics of flag leaf, soluble sugar content, amino proline content, CAT and POD activity of flag leaf and these values were the maximum under W2 treatment. In addition, water stress has a significant effect on chlorophyll content, photosynthetic rate (Pn), transpiration rate (Tr) and stomata conductance (Cs), W2 were highest. Significant differences existed in air temperature, humidity, light intensity and content of CO2 among different water stress, there was ideal microclimate within population of rice with W2. These results clearly revealed that the water stress treatment significantly influenced plant organs and canopy temperature increased risk of heat injury and ultimately caused reduction in yield.
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