Effects of fruit tree canopy shading on grain filling of intercropping winter wheat

Fruit tree-wheat intercropping system is the main agricultural production pattern in sou-thern Xinjiang. In this study, almond (Amygdalus communis)-winter wheat (Xindong 20 (Triticum aestivum, var. Xindong 20) intercropping system was used as the research object. Four tree forms of delayed open-central shape (DC), open-center shape (OC), high stem-shape (HS), and semicircle small-canopy shape (SC) and three intercropping distances (wheat intercropping area respectively 1.5, 2.5 and 3.5 m from the tree trunk) were set to create tree canopy shading treatments, with monoculture wheat as the control. The environmental factors and the grain filling characteristic of winter wheat under different treatment conditions were measured, and the correlation between grain filling characteristics and 1000-grain weight and environmental factors was established to provide information for selecting the best management standards and optimizing the intercropping system. The results showed that under the almond tree-winter wheat intercropping system, the PAR, red/far-red light (R/FR), and temperature above the wheat canopy were significantly decreased due to canopy shading, resulting in a significant increase in humidity. The degree of variation was affected by tree form and distance. The PAR decrease degree of the four treatments was DC＞OC/HS＞SC, except for HS. The PAR decrease of the other tree form treatments was 1.5 m＞2.5 m＞3.5 m. The PAR decrease was distributed in the range of 35.5%-86.6%. A cubic polynomial equation represented the grain filling process, and the specific property of grain filling and 1000-grain weight was assessed using the correlation analysis. The decrease in the 1000-grain weight in the intercropping system was closely associated with the decreases in average grain-filling rate (V), maximum grain-filling rate (V_max), effective grain-filling duration (S_e), and effective grain-filling duration (V_s). The shortening of S_e and the reduction in the grain filling rate were related with the reduction in the PAR incidence above the wheat canopy. In the fruit tree-winter wheat intercropping system, the reduction of PAR, dry matter accumulation after flowering, and S_e were reduced by tree canopy shading consequently for the decrease in the 1000-grain weight of the intercropping wheat. When the distance between the intercropping area and the tree trunk was greater than 75% of tree height, and shading intensity was less than 35.5% of the natural light intensity, the intercropping with the almond tree could increase the 1000-grain weight of wheat by increasing the effective grain-filling duration.