| Shanxi Province is located in the mid latitude continental climate area,with large temperature difference between day and night and abundant light and heat resources,which is one of the important production areas of Apple planting industry in China.In recent years,the apple industry in Shanxi Province has been expanding,and apple has become the first large fruit in Shanxi Province.Fruit farmers in some areas have embarked on the road of poverty alleviation and prosperity through the apple industry.However,Shanxi Province is located in the Loess Plateau.It is dry and rainless all the year round.The distribution of rainfall is uneven in time and space.The contradiction between water supply and agricultural production is serious,which seriously affects the development of Apple planting.For this reason,Professor Sun Xihuan proposed the water storage pit irrigation method,which has the characteristics of water conservation and low field engineering technical requirements.Transpiration is an important physiological process of plants.Transpiration of fruit trees is an important basis for the establishment of orchard irrigation system,and canopy conductance is an important parameter for the simulation of orchard transpiration.It is of great significance to explore the change law of canopy conductance for the analysis of material and energy exchange between orchard ecosystem and atmosphere.In this paper,11-year-old dwarf Red Fuji Changfu No.2 was used as the test material.Under the field test conditions,the upper and lower limits of irrigation were different(water storage pit irrigation T1:80% and 60% of the field water capacity;water storage pit irrigation T2:100% and 80% of the field water capacity;water storage pit irrigation T3:100% and 60% of the field water capacity;surface irrigation CK: 100%and 60% of the field water capacity)The variation characteristics of canopy conductance in different time scales and its response to influencing factors were studied.The purpose is to provide theoretical basis for improving the accuracy of transpiration simulation of fruit trees.The main conclusions are as follows:1.Distribution of soil moisture in different irrigation upper and lower limits of water storage pit(1)The gradient of soil moisture was well controlled and kept within the range of designed soil moisture.Under the same irrigation upper and lower limits,the average water content of soil in the whole growth period of CK treatment was close to that of T3 treatment,but the irrigation amount in the whole growth period of CK treatment was 1.33 times that of T3 treatment.(2)The vertical distribution law of soil moisture in each treatment is similar,which is the first increase and then decrease along the depth direction.The maximum value of soil moisture in T1 and T3 treatment mainly appears in the depth of 80 cm,the maximum value of soil moisture in T2 treatment mainly appears in the depth of 100 cm,and the maximum value of soil moisture in CK treatment mainly appears in the depth of40 cm.2.Diurnal variation characteristics of canopy conductance(1)The canopy conductance of each treatment showed a single peak change trend in typical sunny days in different months.The canopy conductance began to increase from 7:00 to 7:30 in the morning,reached the peak value from 10:00 to 12:00 in the morning,and then began to decline.The slope in the rising stage was steeper,the slope in the declining stage was slower,and the trend in the declining stage was fluctuating.(2)Increasing the upper and lower limits of irrigation under water storage pit irrigation can significantly improve the canopy conductance of fruit trees.Under different irrigation modes,the canopy conductance under water storage pit irrigation is significantly higher than that under surface irrigation.3.Response of diurnal variation of canopy conductance to influencing factors(1)Under the condition of full irrigation,the canopy conductance was positively correlated with solar radiation,atmospheric temperature and saturated water vapor pressure difference,and negatively correlatedwith air relative humidity.Meteorological factors have a significant effect on canopy conductance.(2)The regression analysis of canopy conductance and meteorological factors shows that the relationship between canopy conductance and solar radiation is logarithmic function,and the regression relationship between canopy conductance and relative humidity,air temperature and saturated water vapor pressure difference has asymmetric response.(3)The correlation analysis of photosynthetic factors and canopy conductance showed that transpiration rate,net photosynthetic rate,stomatal conductance,leaf temperature were positively correlated with canopy conductance,and intercellular carbon dioxide concentration was negatively correlated with canopy conductance.Leaf surface temperature and intercellular carbon dioxide concentration had a greater impact on canopy conductance,while net photosynthetic rate had a smaller impact.The linear regression equations of canopy conductance and main photosynthetic factors were established by stepwise regression analysis,and the judgment coefficients were all above 0.8.4.Seasonal variation of canopy conductance and its response to influencing factors(1)Under the condition of full irrigation of water storage pit,the change rule of canopy conductance in the growth period increased first and then decreased,and the canopy conductance in the whole growth period from the middle of June to the middle of September was larger.(2)The relationship between canopy conductance and solar radiation is a quadratic function,the relationship between canopy conductance and air relative humidity is an exponential function,the relationship between canopy conductance and air temperature is a linear relationship,and the relationship between canopy conductance and saturated water vapor pressure difference is an exponential function.On the scale of seasonal variation of canopy conductance,the order of the influence of meteorological factors is: relative humidity > saturated vapor pressure difference > solar radiation > air temperature,which shows that on the scale of seasonal variation,the air moisture condition has a greatinfluence on canopy conductance.(3)Through regression analysis and correlation analysis,the effects of soil moisture conditions on canopy conductance were studied.Under T2 treatment,the response relationship between soil moisture and canopy conductance was poor,the linear correlation coefficient was 0.149,and the fitted quadratic function judgment coefficient was 0.2380.The canopy conductance of the other treatments responded well to the soil moisture conditions,and the judgment coefficients were all above 0.4814.5.Study on the model of canopy conductanceThe coefficient of linear model is 0.704,the maximum relative error is 51.8%,the minimum relative error is 0.9%,and the average relative error is 18.3%.The coefficient of Jarvis model is 0.845,the maximum relative error is 30.2%,the minimum relative error is 0.3%,and the average relative error is 13.7%.By comparing the error values of the decision coefficients of the linear model and Jarvis model,it is found that Jarvis model has a better prediction effect. |
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