土层厚度对刺槐旱季水分状况和生长的影响

Effects of soil thickness on dry-season water relations and growth in Robinia pseudoacacia

该研究测定了旱季和雨季刺槐(Robinia pseudoacacia)林不同土层厚度的土壤含水量,刺槐的树高、胸径、小枝凌晨水势、叶片碳稳定同位素组成(δ13C)、叶面积、比叶重和气体交换指标;分析了刺槐旱季和雨季的水分状况和土层厚度之间的关系;通过刺槐对季节性干旱胁迫的反应,估计华北石质山区不同土层厚度土壤水分对刺槐的承载能力;并求证近年来该地区刺槐衰败和水分因素的关系。结果显示:随着土层厚度减小,旱季土壤含水量下降、凌晨小枝水势降低;气孔导度和最大光合速率都减小,而瞬时水分利用效率增加,雨季上述指标无显著性差异,旱季土壤含水量只有雨季的60%左右。随着土层变薄,刺槐叶片δ13C增高,叶面积减小,比叶重增加;刺槐树高和胸径减小。以上结果表明:刺槐在不同季节下的水分状况综合反映土壤的供水能力,土层浅薄导致土壤水分承载力不足,致使刺槐在旱季受到较严重的水分胁迫,这可能是刺槐出现衰败的重要原因。

Aims Our main purposes were to explore effects of soil thickness on the soil water carrying capacity of black locust （Robinia pseudoacacia） forests and to investigate the role of soil moisture in causing decline of black locust forests in regions of northern China in recent years. Methods We measured soil moisture, pre-dawn twig water potential and gas exchange of black locust in the dry season and wet season. We also measured stable carbon isotope ratio （dl3C） of leaf, leaf morphology and growth of black locust. Combined with the differential response in the dry season and wet season, we analyzed the relationship between water status of black locust and the soil thickness. Important findings In the dry season, the twig predawn water potential and soil moisture significantly declined with decreased soil thickness, and the net photosynthetic rate and stomatal conductance of black locust also decreased. But there were no significant differences in these indexes in the wet season. Average soil moisture in the dry season was only 60% that in the wet season. With decrease in soil thickness, δ^13C increased, area of leaf decreased and leaf mass per area increased. As a result, tree height and diameter at breast height significantly decreased with decrease in soil thickness. Results revealed that the water status of black locust in the different seasons strongly reflected water supply capacity of the soil, and that thin soil thickness was the main cause for the decline of black locust forests due to low carrying capacity of vegetation caused by inadequate water storage in the dry season.