Responses Of Stomatal Conductance To CO₂ Concentration And Temperature Increase In Different Rank Of Rice Leaves

The rise of CO2 concentration and temperature are the main characteristics of global change.The changes in CO2 and temperature have a direct effect on the stomatal conductance of crop leaves,which will affect photosynthesis and transpiration of crops,and affect crop yield and water use efficiency.Is stomatal conductance of crop leaf adaptable to CO2 concentration and temperature like photosynthesis?CO2 concentration and temperature increase will promote the senescence of crops.What is the difference between the stomatal conductance of leaves at different leaf positions and the increase of CO2 concentration and temperature?This is the two scientific problem that directly affects the accuracy of crop population photosynthesis and transpiration.In response to these two problems,In this study,the experiment using the platform of TFACE(Free Air CO2 enrichment and Increase temperature),located in Changshu,(31°35’5.64"N,120°55’6.69"E),a vice(Oryza sativa L.)cultivar Changyou 5 as the experimental materials,researched the influence of stomatal conductance on leaf position when CO2 concentration and temperature increased.The experiment has 4 processes,each processing 3 repetitions,CK、Free Air CO2 enrichment 500ppm(C)、Free Air CO2 enrichment and Increase temperature 500ppm+2℃(CT)、Increase temperature+2℃(T).The gas exchange data of leaves with different leaf positions at different growth stages were determined by LI-6400 photosynthesis system.According to the experimental data,the effects of the increase of CO2 concentration and temperature on the stomatal conductance,transpiration rate,Ci/Ca and nitrogen content of leaves in different leaf positions of rice were quantitatively analyzed,and the stomatal conductance model of BWB was calibrated and tested by using the test data.On this basis,the experiment data of CO2 concentration and temperature rise treatment and BWB stomatal conductance model simulation analysis were combined to evaluate the simulated effect of BWB model on the stomatal conductance of different rice Ieaf positions under the condition of CO2 concentration and temperature rise.The main results are as follows:(1)The increase of CO2 concentration(C)significantly decreased the transpiration rate(17.8%)of the second top leaves in the jointing stage of rice at the saturated light,as well as the stomatal conductance(50.6%and 57.3%)and transpiration rate(28.3%and 44.2%)of the third top leaves at the heading stag and the flag leaves at the filling stages.Temperature increased(T)significantly increased stomatal conductance(42%)of the flag leaves at jointing stage,but significantly decreased stomatal conductance(32.4%)and transpiration rate(16.8%)of the third top leaves at heading stage.The increase of CO2 concentration and temperature(CT)significantly increased the transpiration rate(49.6%)of the flag leaves at the jointing stage,but significantly decreased the stomatal conductance(28.1%and 41.1%)and transpiration rate(18.8%and 31.4%)of the third top leaves at the heading stage and the flag leaves at the filling stages.(2)CO2 concentration and temperature increased adaptability to stomatal conductance of rice leaves.The adaptive response of the stomatal conductance to the increase of CO2 concentration increased with the increase of the leaf position,but the adaptive response to the increase of temperature decreased with the increase of the leaf position.The stomatal conductance of the third top leaves at the jointing stage,the third top leaves at the heading stage and the flag leaves leaf at the filling stage had an adaptive response to the increase of the temperature of the concentration of CO2.The ratio of the above adaptive response may be reduced with the increase of the leaf position with the increase of the CO2 concentration,and the ratio of the decrease of photosynthesis rate decreases with the increase of the Ieaf position.The ratio of the increase of CO2 to the increase of photosynthetic rate decreased with the increase of leaf position,and the ratio of the decrease of photosynthetic rate decreased with the increase of leaf position,which was caused by the increase of the ratio of nitrogen accumulation in leaves with the increase of leaf position.The increase of CO2 concentration and temperature had no effect on the Ci/Ca of leaves in different leaf positions of rice,and further showed that the stomatal conductance of different leaf bits of rice was coupled with the photosynthesis rate under the increase of CO2 concentration and the increase of temperature.(3)The stomatal conductance model(BWB model)underestimated the stomatal conductance of the flag leaves at the jointing stage and the third top leaves at the heading stage,which underestimated the stomatal conductance of 17%and 12%,respectively.However,the stomatal conductance of the third top leaves at the jointing stage and the flag leaves and the third top leaves at the filling stage were overestimated by 18%,28%,and 15%,respectively.The BWB model would underestimate the temperature increase and CO2 concentration and temperature,and simultaneously increase the stomatal conductance of the flag leaves leaf at the jointing stage and the third top leaves at filling stage of the rice,and overestimate 33-34%.(4)The stomatal conductance model(BWB model)simulated the stomatal conductance of the remaining leaf positions with the parameters of the flag leaves leaf,and simulated the stomatal conductance of the second top leaves in the flag leaves leaf.The control treatment underestimated 16%in the jointing stage,and the temperature and the increase of CO2 concentration and temperature were 23%and 21%respectively.For the simulation of the stomatal conductance of the third top leaves,the control treatment underestimated 22%at the jointing stage and 59%over the filling period;the increase of CO2 concentration was 56%over the filling period,and the treatment at the jointing stage,the filling period and the heading period were 17%,26%and 91%respectively,and the concentration and temperature of the treatment at the same time were over estimated at 20%at the heading stage.In this study,field experiments were conducted to quantify the responses of CO2 and temperature to stomatal conductance at different leaf positions in rice at different growth stages.The results have laid a foundation for further improvement of the existing vane stomatal conductance model and accurate estimation of CO2 and temperature increase for photosynthesis and transpiration of crop populations.