Effects Of Air Temperature Raise And Soil Water Deficit On Photosynthetic-transpiration Relationship And Grain Yield In Winter Wheat(Triticum Aestivum L.)

Climate change is one of the main challenges limiting the sustainable development of global agricultural production.The extreme weather caused by climate change,such as high temperatures and drought,has a substantial influence on the water-carbon cycle of the farmland ecosystem,especially on the coupled relationship between photosynthesis and transpiration.Therefore,it is crucial to systematically investigate the water-carbon coupling mechanism at the leaf scale for clarifying the water-carbon coupling behavior and its impact on farmland productivity.Winter wheat(Triticum aestivum L.)is an important grain crop and its growth and development are closely related to meteorological conditions.This study focused on winter wheat,the experiment was conducted with lysimeters at the Xinxiang Comprehensive Experimental Station of the Chinese Academy of Agricultural Sciences from 2020 to 2022.The two-year experiment consisted of two factors,i.e.,temperature(raising by 1.5℃ and 0℃)and water(irrigation rate of sufficient and deficit water supply was 45 and 33 mm,respectively).The effects of air temperature raise and soil water deficit on crop growth and development,the coupled relationship between photosynthesis and transpiration,and the grain yield of winter wheat were investigated.The main results were as follows:(1)Air temperature raise and water deficit affected the fluorescence parameters and key photosynthetic enzyme activities of winter wheat leaves.Whether warming or non-warming,the water deficit decreased the maximum photochemical efficiency(Fv/Fm)of winter wheat leaves.Under the condition of air temperature raise,the water deficit increased the actual photosynthetic efficiency(Y(II))and photochemical quenching(q P)of winter wheat.Under the condition of non-warming,the water deficit decreased both Y(II)and q P of winter wheat.In addition,the water deficit increased the activity of Rubisco in winter wheat leaves under the same temperature.Under the same water condition,air temperature raise promoted the Rubisco activity in winter wheat leaves.(2)Air temperature raise and water deficit significantly affected crop growth,photosynthesis,and grain yield of winter wheat.The increased temperature and water deficit shorten the wheat growth duration,decreased the leaf area index,and reduced wheat biomass.Under the condition of sufficient water supply,the temperature raise increased the net photosynthetic rate and transpiration rate of winter wheat leaves,but under the condition of water deficit,the results were on the contrary.Under the warming and non-warming conditions,the grain yield of winter wheat in the water deficit treatment was 8.9% and 12.4%(P<0.05)lower than that in the sufficient water supply treatment,respectively.Under the full water supply and water deficit treatments,the grain yield under the warming treatment was 4.4% and 1.3%(P<0.05)lower than that under the non-warming treatment,respectively.Increasing temperature tended to decrease wheat yield,but adequate water supply could improve the grain yield of winter wheat and reduce the adverse impact of temperature raise on wheat yield.(3)Air temperature raise and water deficit decreased the stomatal density and stomatal conductance of winter wheat leaves,resulting in a decoupling effect of photosynthesis and transpiration rate.Under the condition of the same air temperature,the water deficit decreased the stomatal density.Under the condition of increasing temperature and water deficit,the stomatal conductance of wheat leaves was decreased.Ball-Berry and Penman-Monteith models were used to simulate the photosynthetic rate and transpiration rate.The poor performance of the Ball-Berry model and the Penman-Monteith model was obtained under the condition of non-warming and water deficit and the condition of warming and water deficit.The slope of the relationship between photosynthetic and transpiration rate in the non-warming and water deficit treatment,the warming and sufficient water supply treatment,and the warming and water deficit treatment was lower than that in the full water supply treatment without temperature raise.The results indicated that the simultaneous occurrence of air temperature raise and water deficit resulted in the decoupling of the relationship between photosynthetic rate and transpiration rate.