Effects of distance from a tree line on photosynthetic characteristics and yield of wheat in a jujube tree/wheat agroforestry system

Abstract

Planting trees near crops can diversify the landscape, provide pollinators for crops, and allow predators to control insect pests. However, trees can also compete with crops for light, water, and nutrients. Field experiment at the Shihezi Oasis in northern Xinjiang Province assessed the effects of distance on photosynthetic characteristics and yield of wheat in a jujube tree (Zizyphus jujuba Mill.)/wheat (Triticum aestivum L.) agroforestry system. The experiment used two treatments: a control of sole-cropped wheat (D0) and a jujube tree/wheat agroforestry system. The agroforestry system included the different distances of 90, 110, and 130 cm (D1, D2, and D3, respectively) between the wheat and the jujube trees. Photosynthetic characteristics, leaf area index (LAI), the number of stems, and yield components of wheat were determined. The net photosynthetic rate (Pn) and the stomatal conductance (Gs) of the D0, D2, and D3 during the filling stage were significantly higher than the D1. No significant difference in transpiration rate (Tr) and intercellular CO2 concentration (Ci) was noted between sole-cropped wheat and agroforestry system. From the tillering to ripening stages, significant differences were observed in stem, tiller number, and dry matter accumulation per plant, and in LAI, which ranked D0 > D3 > D2 > D1. D0 and D3 plants had significantly higher numbers of spikes, grains per spike, and weight of thousand grains than D1 and D2 plants. The crop yield was ranked as D0 > D3 > D2 > D1, with significant differences among D0, D1, D2, and D3. In conclusion, wheat yield increased as the distance from jujube trees increased in this jujube tree/wheat intercropping system.