水分和光照条件对核桃-黄豆农林复合系统中黄豆光合作用和生长的影响

Effects of Water and Light Conditions on Photosynthesis and Growth of Soybean in Walnut-Soybean Agroforestry System

【目的】研究核桃-黄豆农林复合系统中不同种植位置间作作物在不同水分、光照条件下的水分利用和碳代谢,为更好了解种间相互作用对植物生长的影响提供参考。【方法】2017年,在太行山南麓低山丘陵区核桃-黄豆农林复合系统中,测定不同种植位置黄豆在旱季(7月中旬)和雨季(8月下旬)的土壤含水量、凌晨和正午水势、正午茎秆导水损失率(PLC)、株高和基径、生物量以及根、茎、叶的非结构性碳(NSC)含量。【结果】1)在旱季,随着与核桃树距离的增加,土壤含水量降低,黄豆凌晨和正午水势下降,正午茎秆PLC上升,距核桃树1.5和2.5 m的黄豆光合速率和气孔导度较大,距核桃树0.6 m和单作的黄豆光合速率偏低,但总体上间作和单作的黄豆气体交换没有显著差异。旱季生物量、根冠比和NSC随着与核桃树距离增加而增大。2)在雨季,除距核桃树0.6 m处土壤含水量偏低外,其余位置均无显著性差异,土壤含水量比旱季高60%以上。不同种植位置黄豆凌晨水势没有显著性差异,但单作黄豆正午水势更低,茎秆PLC较间作黄豆严重。光合速率、气孔导度、生物量、NSC含量、根冠比均随着与核桃树距离增加而增大。根、茎、叶NSC含量均显著高于旱季,主要由淀粉储藏增加引起。【结论】在旱季,不同种植位置黄豆水分状况均受一定程度的干旱影响,复合系统中间作黄豆水分状况好于单作,但旱季水分胁迫没有显著影响光合作用和生长;遮荫的影响覆盖了水分状况改善的作用。在雨季,复合系统中黄豆主要受遮荫影响,距离树木越远生长情况越好。在研究年份水分不是主要限制因子的情况下,间作互利作用未体现,而复合系统中的光能竞争会导致间作黄豆生长量明显下降。

【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.