Effects Of Light Intercept Of Tree Canopy On Grain Yield And Quality Of Wheat In Almond(amygdalus Communis L.)/Winter Wheat(triticum Aestivum L.) Intercropping

Agro-forestry intercropping is the main pattern of agricultural production in southern Xinjiang.The area of wheat intercropping with fruit tree is more than 3.33×10⁵ hm² in Hetian,Kashgar and Kirgiz Autonomous Prefecture of Kizilsu in southern Xinjiang.With the increase of the tree age,especial in full fruiting period,the low light stress which caused by light intercept of tree canopy became the main reason for the sharp reduction of winter wheat yield and the change of nutrient quality,which seriously restricted the healthy and sustainable development of the intercropping pattern.Therefore,it is of great significance to optimizing the fruit tree-grain crop intercropping pattern and guiding the research on the supporting cultivation and regulation approaches in the intercropping pattern,by clarify the effect and its physiological mechanism on wheat grain yield and the quality formation which caused by light intercept of fruit tree canopy,in the intercropping mode.In this study,Xindong 20（Triticum aestivum L.,var.Xindong 20）,the main winter wheat cultivar in South Xinjiang,was taken as the research object.In the almond（Amygdalus communis L.）-winter wheat intercropping system,Delayed open-central shape（DC）,Open-center shape（OC）,High stem-shape（HS）and Semicircle small-canopy shape（SC）4 tree structures which are widely used in production and have great differences in tree structure indexes were taken as the treatment:From jointing stage to maturity stage of wheat,the environmental indexes,yield formation index,nutrient quality indexes,photosynthetic characteristics,grouting characteristics of different intercropping areas（Zone1-Zone3）and monoculture wheat（CK）were studied,and the changes of endogenous hormone content and key enzyme activity of starch synthesis in grain during the grouting process were studied.The physiological mechanism of canopy light interception on wheat yield and nutrient quality formation under intercropping model was further discussed.The results are as follows:1.Under the intercropping system of Almond-winter wheat,the light intensity above intercropping wheat canopy SC>OC>HS>DC,and decreased 47.03%,68.21%,70.09%and 82.43%,respectively,compared with CK in the grain filling stage;the PAR in the intercropping area decreased rapidly in about15 days from the jointing stage（April 9）to the heading stage（April 23）,during which the PAR in the whole intercropping area decreased nearly 60%.PAR intensity was affected by both tree from and distance between wheat intercropping areas and tree trunks.The influence range of PAR daily average value（fluorescence to the grain filling stage）of the almond canopy to the intercropping area was 1.50 times of tree height,1.70 times of crown height and 1.38 times of crown breadth.2.Canopy interception of light had a great influence on the spectral composition above intercropping wheat canopy.The reduction degree of blue-violet light,yellow-green lightand red-orange light is greater than the total radiation,while reduction degree of UV,near-infrared and far-infrared is lower than the total radiation.Thus,the light composition above intercropping wheat canopy changed significantly.The ratio of‘near-IR/far-IR light’and‘red-orange light/far-IR’can be used as a light quality evaluation index.Light quality,temperature,humidity,and other indicators have a high correlation with PAR,and the changes of environmental indicators in each treatment and region are affected by canopy light interception.3.The influence of tree from on the yield of intercropping wheat is quite different.Compared with CK,the yield of intercropping SC>OC>HS>DC decreased by 18.24%,35.43%,33.00%and 63.68%（data in2017）,which is significantly lower than the decrease degree of PAR.The 1000-grain weight was closely related to the light intensity at the grain filling stage.The effective panicles per unit area were highly related to PAR daily mean value at the jointing stage and the ratio of"red light/far-red light"at the booting stage.The panicle grain number were highly related to daily mean PAR strength from booting stage to flowering stage.4.Compared to the monocropping,in the grain of intercropping winter wheat,the content of amylose increased,the ratio of amylose/amylopectin increased,and the ratio of amylose/amylopectin was negatively correlated with PAR daily mean value and light intensity index of different sunlight bands.The content of albumin decreased,the content of gliadin increased.Albumin was positively correlated with"red-orange light/far-IR"and"near-IR/far-IR",while gliadin was negatively correlated with the 2 light quality parameters.The content of total amino acids,essential amino acids and he first limiting amino acid（Lysine）increased,and the score of amino acids increased.5.Intercropping caused the change of flag leaf photosynthetic system activity,from flowering to filling stage the photosynthetic capacity of flag leaf decreased,the chlorophyll and soluble protein content decreased,the maximum net photosynthetic rate decreased,and the actual photosynthetic efficiency of photosystem II（ФSPⅡ）decreased.Under the light shade level,there was a significant compensation phenomenon of canopy apparent photosynthetic（CAP）.There was a significant positive correlation between the maximum photosynthetic rate of flag leaf in the heading to grain-filling stage,CAP in grain-filling stage,1000-grain weight and yield.6.In the almond-winter wheat intercropping system,the correlation between 1000-grain weight and the average grain-filling rate（V）,the maximum grain-filling rate（Vmax）,the effective grain-filling duration（Se）,the increased grain quality during the effective filling duration（Ws）and the average filling rate during the effective grain-filling duration（Vs）were significantly positive correlation.The V,Vmax,Se,Ws and Vs were significantly or very significantly positively correlated with the PAR daily average value;the Ws and the Se were significantly or very significantly positively correlated with the pre-grain-filling period.7.Intercropping cause the content of ABA and GA₃ increased,IAA and ZT decreased;IAA was positively correlated with light intensity and‘red light/far-IR at the grain-filling stage,ZT was positively correlated with PAR intensity at the grain-filling stage,ABA and GA₃ were negatively correlated with light intensity at the grain-filling stage;the activity of AGPase and GBSS in wheat grain increased,the activity of SSS decreased;AGPaseand GBSSactivity was negatively correlated with light intensity in the grain-filling stage,SSS activity was mainly affected by light quality composition.8.The grain filling parameters were regulated by endogenous hormones.V,Vmax and Vs were negative regulation by GA₃.Se,Ws and W were positively regulated by the peak content of ZT.The grain-filling characteristic parameters were closely related to the activity of AGPase and SSS,W,V,Vmax,Se and Ws were all significantly positively correlated with the peak activity of SSS during grain filling.V and Vmax were negatively correlated with the peak activity of AGPase.Se,Ws and Vs showed significant or extremely significant positive correlation with peak and mean activity of AGPase.9.In the process of grain filling,the activities of main hormones and enzymes had little effect on the total starch content,but had a greater effect on the proportion of amylose and amylopectin.The amylose content was negatively regulated to IAA,ZT content and SSS enzyme activity,while the amylopectin content was negatively regulated to ABA content,the peak content GA₃ and AGPase enzyme activity.Grain albumin,globulin content and glutenin/gliadin ratio,were positively regulated by the content of IAA and ZT,alcohol soluble protein content ere negative regulation by mean content of ZT.In conclusion,in the system of almond-winter wheat intercropping system,the PAR in the intercropping area decreased rapidly in about 15 days from the jointing stage to the heading stage,the illumination condition of the intercropping area was seriously affected by canopy shading during heading stage to maturity stage of wheat.The influence range of light was 1.50,1.70 and 1.38 times of tree height,crown height and crown breadth.Wheat population has strong adaptability to light level of shade,useing tree from which with small canopy size or transform the tree from which with large canopy size,all of them can effectively mitigating the effects of light intercept by tree canopy on wheat yield.Light intercept by tree canopy reduced PAR intensity and the R/FR ratio,thus inhibiting the photosynthetic capacity of wheat,reductions in amount of photosynthetic assimilates after anthesis and it contribution to grain yield,reduce the grain filling rate,shortened the valid continual filling time.Finally,cause the grain yield decreased significantly.The content of ZT,IAA and the activity of SSS decreased,while the content of GA3,ABA and activity of AGPase increased.This resulted in the increase of amylose/amylopectin ratio,the decrease of glutenin/prolamin ratio,the increase of amino acid content,the increase of amino acid score.