Abstract:

Objective: Agroforestry system has been widely used,because it can improve the utilization rate of natural resources. Regulation of inter-specific relationships in agroforestry system is an important way to ensure high yield and efficiency of this system,and water and light are the core contents of the regulation. In this study,the water use and carbon metabolism of intercropping crops in an agroforestry system under different water conditions were investigated,in order to better understand the effects of interspecific interactions on plant growth. Method: In 2017, soybeans were sownat different locations from walnut trees in the walnut-soybean agroforestry system in the southern foothills of Taihang Mountains.The soil moisture content,predawn and mid-day water potential,mid-day stem percentage loss of conductivity (PLC),plant height and basal diameter,biomass,and nonstructural carbohydrate (NSC) content of root,stem and leaf of soybean plants were measured in dry (mid-July)and rainy season(late August). Result: 1) In dry season,with the increase of distance from walnut tree,the surface soil moisture content decreased,the predawn and mid-day water potential of soybean plants decreased,and the mid-day stem PLC increased. The photosynthetic rate and stomatal conductance of soybean plants at 1.5 m and 2.5 m away from walnut tree were higher,while the photosynthetic rate of soybean plants at 0.6 m away from walnut tree and mono-cropped soybean plants was lower.However,there in general was no significant difference in gas exchange between intercropped and mono-cropped soybean. Biomass,root-shoot ratio and NSC increased with the increase of distance from walnut trees. 2) In rainy season,except for at 0.6 m away from walnut tree where the soil moisture content was low,there was no significant difference in the soil moisture content over other locations. The soil moisture content in the rainy season was more than 60% higher than that in the dry season. In rainy season,there was no significant difference in the predawn water potential of soybean plants at different locations,but the midday water potential in monoculture was lower,and the PLC was more severe than thosein intercropped soybean. Photosynthetic rate,stomatal conductance,biomass,NSC content and root-shoot ratio all increased with the increase of the distance from walnut tree. The NSC content of root,stem and leaf in the rainy season was significantly higher than that in the dry season,which was mainly caused by the increase of starch storage. Conclusion: In the dry season,the water situation of soybean atdifferent locations is affected by drought,and the water situation of soybean in the agroforestry system is better than that of mono-culture.However,the degree of water imbalance in the dry season doesnot significantly affect photosynthesis and growth,because the effects of shading overshadow the effects of water status. In the rainy season,soybeans in the agroforestry system are mainly affected by shading,so the farther away from the trees,the better the growth. Under the condition that water is not the limiting factorin the study year,the mutual benefit of intercropping could not be shown.In contrast,light energy competition in the agroforestry system would lead to obvious decrease of soybean growth.

Key words: walnut-soybean agrforestry system, planting location, water status, photosynthesis, growth, nonstructural carbohydrate (NSC)