Study On Leaf Trait And Radiation Use Of Alfalfa/Spring Wheat Intercropping System Under Irrigation

The Hexi corridor area where there are abundant land,light resources and excellent irrigation condition,is an important area for agriculture and animal husbandry in China.Spring wheat（Triticum aestivum）and alfalfa（Medicago sativa）are the main food and forage crops in the area.Long-term monoculture accelerates soil nutrient depletion,leads to soil degradation and secondary salinization,thus posing a great threat to efficient and sustainable agricultural and animal husbandry production.Intercropping of spring wheat with alfalfa is an important way to improve the sustainable use of land.On the one hand,cereal-grass intercropping increases forage production on the basis of ensuring food production,which can promote the development of animal husbandry.On the other hand,the addition of leguminous crop can improve soil fertility and quality,which is in line with the concept of sustainable development and has great significance for environmental protection.In addition,irrigation is an important measure to ensure high and stable crop yields in the region,but the response of the cereal-grass intercropping system to irrigation is not clear.Leaf trait can well reflect the adaptation of plants to environmental changes,but the variability and regulation mechanism of leaf trait under intercropping are still unclear.In view of these,this research conducted a two-year field experiment in the Hexi corridor area of Gansu Province from 2021 to 2022.Two spring wheat-alfalfa strip intercropping were evaluated:12 rows of spring wheat and 4 rows of alfalfa（12W4A）per strip and 8 rows of spring wheat and 4 rows of alfalfa（8W4A）per strip.Sole spring wheat（SW）and sole alfalfa（SA）were used as control.There were four irrigation treatments,including 450(I₄₅₀),360(I₃₆₀),270(I₂₇₀)and 180 mm(I₁₈₀).The effect of intercropping ratio on crop leaf traits and radiation use efficiency were discussed under irrigation,aiming to provide a reference for the construction of suitable cereal and grass planting patterns and the optimization of irrigation management in this area.The main results are as follows:1)Intercropping increased the structural trait of alfalfa leaf and decreased the structural trait of spring wheat flag leaf.Intercropping increased leaf width and area of alfalfa at the second cut,while changes of flag leaf thickness,length,width and area of spring wheat showed SW>12W4A>8W4A.The effect of irrigation on leaf structural trait was different between species,with the increase of irrigation amount,leaf length,width and area of alfalfa increased significantly,and leaf thickness,mass per unit area and dry matter content decreased significantly.Flag leaf thickness of spring wheat increased,and flag leaf length,width and area showed a trend of first increasing and then decreasing,and the maximum values all appeared under I₃₆₀,while flag leaf mass per unit area and dry matter content showed a decreasing trend.2)Intercropping enhanced radiation use efficiency of alfalfa while reducing radiation use efficiency of spring wheat,and a higher proportion of spring wheat improved radiation use efficiency.Radiation use efficiency of intercropped alfalfa was higher than that of monocultured alfalfa,and the overall radiation use efficiency in2021 was 12W4A>8W4A>SA.Leaf area index,radiation interception amount and radiation use efficiency of spring wheat were SW>12W4A>8W4A.The effect of irrigation on radiation use efficiency was different between species,with the increase of irrigation amount,leaf area index,radiation interception amount and radiation use efficiency of alfalfa increased,while leaf area index,radiation interception amount and radiation use efficiency under sole spring wheat showed a trend of first increasing and then decreasing,and the maximum value appeared at I₃₆₀.3)Intercropping enhanced the photosynthetic characteristics of alfalfa but decreased the photosynthetic characteristics of spring wheat and a higher proportion of spring wheat increased photosynthetic characteristics of the intercrops.Net photosynthetic rate,stomatal conductance and intercellular CO₂concentration of intercropped alfalfa were higher than those of monocultured alfalfa,while limitation to stomata changed adversely.Changes of net photosynthetic rate,stomatal conductance,instantaneous water use efficiency,leaf nitrogen concentration and chlorophyll contents of spring wheat flag leaf were SW>12W4A>8W4A.The effect of irrigation on photosynthetic gas exchange characteristics was different between species,with the increase of irrigation amount,net photosynthetic rate,stomatal conductance and transpiration rate of alfalfa leaf increased significantly,while intercellular CO₂concentration,instantaneous water use efficiency,leaf nitrogen concentration and chlorophyll content decreased.Net photosynthetic rate,stomatal conductance and transpiration rate of spring wheat flag leaf first increased and then decreased,peaking at I₃₆₀,while intercellular CO₂concentration,instantaneous water use efficiency,leaf nitrogen concentration and chlorophyll content showed a decreasing trend.In summary,for the alfalfa/spring wheat intercropping system in the Hexi corridor area,alfalfa and spring wheat under 12W4A and I₃₆₀had good leaf structural trait,photosynthesis and radiation utilization,which are conducive to crop growth.Therefore,it is recommended that 12W4A of alfalfa/spring wheat intercropping and I₃₆₀level of irrigation management be implemented in this area.