| Temperature of a plant organ is an integrative index to its physiological activities and the adaptation to the environments,thus being a usful parameter for crop breeding.Up to now,little attempt has been made to elucidate the compound effect of ecological and physiological factors on the surface temperature of a plant organ such as the rice spikelet.In this study,typical japonica rice cultivars with contrasting canopy features were used as testing materials,pot and field experiments were performed for two years.Temperatures of flag leaf,superior and inferior spikelets and their diurnal change through development were precisely measured by an accurate hand-held infrared thermometer,with the aims to explore the spatial-temporal variations in panicle temperature as well as its response to environmental condictions created by sowing date and nitrogen treatments.The main conclusions are as follows:1.The temporal and spatial variations of leaf and panicle temperature.Using Wuyujing3,Ningjing 8 and Wuyunjing 7,three typical japonica rice cultivars,the diurnal variation of leaves,superior and inferior spikelets temperature during different grain-filling periods were accurately measured by infrared thermometers.In this study,organ temperature is expressed as temperature difference(TD)between it and its ambient environment.The results showed that(1)The leaf and panicle temperature showed a significant diurnal variation.The plant temperature of the three cultivars all began to rise from sunrise,reached the highest temperature at 9 or 12 o ’clock,then began to decline,reached the lowest temperature at sunset,and then rose slightly.(2)There were significant differences in temperature between leaf and panicle.Leaf temperature was lower than panicle temperature in daytime,but higher than panicle temperature at night.The temperature of superior spikelets was higher in daytime than that of inferior spikelets,but there was no significant difference between them at night.(3)Along with the grain-filling process,the diurnal variation of leaf and panicle temperature still obvious,but the differences between leaf and panicle temperature and superior and inferior spikelets temperature change owing to the different cultivars.In the early and middle stages of grain filling,the difference between leaf and panicle temperature of Ningjing 8 and Wuyunjing 7 is greater than that in the late stages of grain filling.In the early and middle stages of grain filling,the difference between superior and inferior spikelets temperature of Ningjing 8 and Wuyujing 3 is greater than that in the late stages of grain filling.2.The physiological and ecological mechanism of temperature difference between superior and inferior spikelets.Plant temperature was influenced by two parts: physiological effect and environmental effect.The reference plants test were set to estimate the environmental effects of temperature difference of different parts in rice panicles.It was found that the panicle temperature difference was mainly affected by the physiological metabolic activities(physiological effects),but less by the environmental effects.The diurnal variation of starch and sucrose contents in leaves,grains and bracts was analyzed.It was found that the contents of sucrose and starch in leaves and bracts showed an obvious diurnal variation trend,but there was no obvious trend in grains,indicating that bracts were also an important source organ.The contents of sucrose and starch in bracts of inferior spikelets were significantly lower than those of superior spikelets at the early stage of grain filling,indicating that the inactivity of photosynthetic carbon metabolism in bracts of inferior spikelets was one of the physiological reasons for insufficient grain filling and lower temperature in inferior spikelets.3.The response of plant temperature to sowing date treatment.Sowing date regulation test was set to study the response of plant temperature to light-thermo pattern.32 mutants with significant differences in growth and development characteristics were used as materials.Three sowing date treatments were set: early sowing,suitable sowing and delayed sowing treatment.The results showed that(1)The light-thermo pattern difference caused by sowing date had a significant effect on plant temperature.Under different sowing date treatments,leaf temperature was significantly higher than air temperature,and the temperature difference between them increased significantly in the early stage of grain filling,and the increase of leaf temperature difference was the least under suitable sowing date treatments.The temperature of panicle was significantly higher than that of leaf at the early stage of grain filling.With the advance of grain filling process,the temperature of leaf was gradually higher than that of panicle.The temperature difference between panicle and leaf was significantly increased by sowing in advance treatment,while the temperature difference between panicle and leaf was significantly reduced by sowing in delay treatment.The temperature of the superior spikelets was significantly higher than that of the inferior spikelets,and the temperature difference between the superior and the inferior spikelets was the largest in the suitable sowing treatment and gradually decreased with the advance of grain filling process.(2)The response of plant temperature to environmental conditions showed significant genotypic differences.In terms of leaf temperature difference,cultivars such as DW145 were sensitive to light-thermo pattern,while cultivars such as DW035 were insensitive.In the temperature difference between panicle and leaf,cultivars such as DW018 were sensitive,while cultivars such as DW033 were insensitive.In terms of temperature difference between superior and inferior spikelets,cultivars such as DW044 were sensitive,while cultivars such as DW123 were insensitive.4.The response of plant temperature to nitrogen fertilization modes.In this experiment,22 representative japonica rice cultivars in southern China were used as materials,three nitrogen fertilization modes treatments were set: base/topdressing,5/5;base/topdressing,10/0;no nitrogen fertilization.The results showed that(1)Nitrogen fertilization modes treatment also had a significant effect on plant temperature,especially the temperature difference between superior and inferior spikelets.Under different nitrogen fertilization modes treatments,leaf temperature was significantly lower than air temperature,and temperature difference between leaf and air at mature stage was significantly greater than that at grain filling stage.No nitrogen fertilizer treatment could significantly reduce temperature difference between leaf and air at grain-filling stage and significantly increase temperature difference between leaf and air at maturity stage.Panicle temperature was significantly lower than leaf temperature,and the difference between them increased significantly at the grain filling stage and had no significant difference lately.The temperature of the superior spikelets was significantly higher than that of the inferior spikelets,and the temperature difference between the superior and inferior spikelets was significantly reduced by not applying nitrogen fertilizer.(2)The response of plant temperature to environmental conditions showed significant genotypic differences.In terms of leaf temperature difference,Ningjing 3 and other cultivars were sensitive to nitrogen fertilization modes treatment,while Zhendao 18 and other cultivars were insensitive.In terms of temperature difference between panicle and leaf,Ningjing 8 and other cultivars were sensitive,while Yanjjing 10 and other cultivars were insensitive.In the temperature difference between superior and inferior spikelets,Zhendao 16 and other cultivars were sensitive,while Zhendao 11 and other cultivars were insensitive.In summary,using the deactivated plants as reference,we successfully dissected the compound effect of environmental and physiological factors on TD between superior and inferior spikelets.The results showed that the position within the panicle had a relatively smaller influence on the TD,while the physiological activities had a larger effect.In addition,the pattern of TD within rice panicle is conserved across contrasting environments,such as different light-thermo patterns and nitrogen fertilization modes.Our findings highlight the physiological significance of spikelet temperature and enlarges our knowledge of the ecophysiological mechanism underlying CT,thus has relevance to crop breeding. |
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