作 者 ：孙守家,孟平,张劲松,黄辉,万贤崇*
期 刊 ：生态学报 2010年 30卷 14期 页码：3718~3726
Keywords:Juglans regia, Vigna radiata, agroforestry system, isotope, water source,
摘 要 ：通过对比核桃枝条和绿豆茎内δD值差异来分析核桃和绿豆水分来源和利用。结果表明，核桃-绿豆农林复合系统的根系在表层土壤（0—30 cm）中交叉存在，生态位重叠。旱季中表层土壤含水量与δD值之间存在显著的负相关关系（R2=0.77，P=0.02），雨季相关关系不显著（R2=0.03，P=0.73）。δD值分析表明，旱季中核桃利用深层土壤（30—80cm）水分占总水分来源的51%以上，雨季中则主要利用浅层土壤水分，间作绿豆和单作绿豆主要利用表层土壤水分。雨季中表层土壤水分能同时满足核桃和绿豆生长需要，但复合系统中光能竞争导致间作绿豆光合速率显著地低于单作绿豆。旱季间作绿豆0—20 cm土壤水分含量、凌晨叶片水势和光合速率明显高于单作绿豆，显示间作绿豆体内水分状况好于单作绿豆。线性模型分析结果显示间作绿豆体内约有1.58%—5.39%的水分来核桃夜晚水力提升，表明复合系统在旱季一定程度上缓冲季节性水分胁迫对农作物生长的影响。
Abstract:Water is a primary resource limiting terrestrial biological activity, particularly in arid and semi-arid regions. In this study, a temporal and spatial variation of water status in soil and Juglans regia and Vigna radiata during spring and summer in an agroforestry system in the rocky mountainous area of north China (a semi-arid region) was traced by analyzing the difference of hydrogen isotope. Root dynamics of the two species were measured in both dry and wet seasons. Variation in δD of was compared to detect the water sources and use. Results showed that 61.61% of J regia roots co-existed with total roots of V radiate in shallow soil (0—30 cm depth). There was a significant difference of shallow soil water content and the δD value between dry and wet season. A significantly inverse correlation (R2=0.77，P=0.02) was found between soil water content and δD value in dry season but not （R2=0.03，P=0.73）in wet season. Analyses of δD value showed that 38.39% of the total roots, distributed in the deep soil layers (30-80 cm depth), absorbed over 51% of the total water from the soil in dry season. The shallow soil provided all water in the monocropped V radiate, whereas around 1.58% to 5.39% water in the intercropped V radiate was derived from the deep soil. In wet season, around 63.52% to 78.99% water of J regia and all water of V radiate were extracted from the shallow soil, which reflected that the shallow soil was able to synchronously meet the water need for J regia and V radiate when the shallow soil had sufficient moisture. However, photosynthetic rate of the intercropped V radiate was significant (P<0.05) lower than that of the monocropped due to light competition in the agroforestry system. In dry season, predawn leaf water potential and photosynthetic rate of V radiate, as well as the water content in 0-20 cm soil layers, in the intercropping field were significant higher than those in the monocropping field. The δD data also suggested approximately 1.58% to 5.39% water in the intercropped V radiate was derived from the hydraulic lift by J regia at night. In general, the intercropped V radiate presented better water status and hence higher assimilation rate than the monocropped V radiate in dry season likely due to water lift by J regia and relative higher moisture in understory of J regia. However, the intercropped V radiate lost a certain photosynthetic capacity in wet season due to being partially shaded by J regia. Therefore, the intercropped V radiate was able to avoid harsh drought stress in dry season at the expenses of photosynthetic capacity in wet season. On the other hand, the intercropped V radiate did not competed with J regia for water resources largely due to their differential distribution of root systems. In dry season, J regia was able to extract water from the deep soil layers while the V radiate mainly depended on water from the shallow soil. In wet season water was not the limitation resource for the plant growth.
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