Effects Of Nitrogen Application And Different Maize (Zea Mays L.)/Alfalfa (Medicago Sativa L.) Intercropping Patterns On Photosynthetic Characteristics And Root Morphology Of Maize In The Agro-pastoral Transitional Zone Of Northeast China

Nitrogen（N）is one of the important sources of plant nutrients,and non-leguminous plants use nitrogen fertilizer to meet their growth needs.However,excessive application of nitrogen fertilizer not only hindered the development of agriculture in China by reducing the optimal utilization of nitrogen fertilizer for crops,but also caused environmental pollution.Roots are closely related to the absorption of water and N uptake in crops.Maize（Zea mays L.）is the main food and feed crop in the world.Alfalfa（Medicago sativa L.）is a high-quality perennial legume forage.Therefore,it is of great importance to study the interaction between photosynthetic characteristics and root morphological characteristics to determine whether intercropped maize has higher nutrient uptake than single maize,and is also of great significance to the sustainable development of ecological environment security of food and animal husbandry in the agro-pastoral transitional zone of Northeast China.Intercropping of maize and alfalfa were studied at Jilin Songnen Grassland Ecosystem National Observation and Research Station of Northeast Normal University in a split-plot design with four replications in 2018.The main plots include two nitrogen levels and subplots include five cropping patterns.Two nitrogen levels include N0（no nitrogen fertilizer addition）and N1（nitrogen fertilizer addition）.Four cropping patterns include MM（monoculture maize）,IMA23（two rows of maize intercropping with six rows of alfalfa,spacing of 30 cm）,IMA42（four rows of maize intercropping with six rows of alfalfa,spacing of 20 cm）,IMA43（four rows of maize intercropping with six rows of alfalfa,spacing of 30 cm）.This experiment mainly studied the effects of nitrogen application and maize/alfalfa intercropping system on maize yield,root morphology,photosynthesis and their correlation,and the main results were as follows:（1）Under N application condition,the yield of maize IMA23 was significantly reduced by14%in intercropping compared with monoculture,while the yield of maize IMA43 was increased by 4%with N fertilizer application.（2）Among all cropping modes,nitrogen application had the greatest effect on root morphology parameters of IMA42,which was 18%lower than that of monoculture maize,while nitrogen application only increased the crown root volume and number of IMA43 by 3%compared with that of monoculture maize.The response of soil water content（SWC）in maize and alfalfa intercropping system to nitrogen application rate decreased slightly in 2018.The highest soil moisture content of IMA43 increased by 4%in September and the lowest soil moisture content of IMA23 decreased by 22%in October compared to monoculture maize.（3）In terms of photosynthetic indices under N application,the photosynthetic rate of maize after maize/alfalfa intercropping was 30%higher than that of monoculture maize,noted for IMA42.Stomatal conductance increases by 35%and decreases by 3%in IMA42 and IMA23.The IMA23 showed a 15%reduction in intercellular CO₂concentration.The transpiration rate of IMA42 and IMA23 increased by 18%and decreased by 6%,respectively.The leaf-air vapor pressure deficit increased by 1%in IMA23 and decreased by 8%in IMA42.The leaf temperature of IMA23 increased by 3%,while that of IMA43 decreased by 3%;IMA42 showed the most significant increase in soil relative moisture,increasing by 6%.Compared with monoculture maize,intercepted maize photo-synthetically active radiation increased up to 3%,noted for IMA42,while IMA23 decreased by 2%.（4）Regression analysis showed that photosynthetic rate was significantly correlated with maize crown root volume and root length,while there was no significant correlation between photosynthetic rate and crown root number,crown root dry weight and crown root surface area under N application.In conclusion,in maize/alfalfa intercropping system affects maize photosynthesis through changes in crown root volume and root length.The yield and root morphological parameters of monoculture maize were the highest among different planting patterns,and maize growth and nutrient uptake were not improved after maize/alfalfa intercropping.