半干旱黄土区成熟柠条林地土壤水分利用及平衡特征

选择半干旱黄土区流域尺度不同地形条件下成熟柠条林作为研究对象,并以荒坡草地作为对照,在2009—2011年生长季节对0—210cm土壤含水量进行连续观测,开展了剖面土壤水分变异、动态平衡及影响因素研究。结果显示:土壤水分平均值:30—130cm对照>北坡>东坡>南坡,150—210cm南坡(上、中坡位)>对照>北坡>东坡,南坡和北坡样地上坡位>中坡位>下坡位。土壤水分的季节变化表现为9月﹥8月﹥7月,5、6、10月份最低;不同地形条件下,柠条林地土壤水分极差值和变异系数并没呈现出规律性变化,在垂直尺度上,柠条林地土壤水分极差值和变异系数曲线在0—50cm表现比较活跃,70—210cm则相对稳定;在连续干旱年份土壤储水量并没有连续的降低和亏缺,在第1个欠水年亏缺比较严重,第2个欠水年盈亏量基本平衡,而第3个欠水年则略有盈余。研究认为:小流域尺度下的地形条件差异造成了土壤水分规律性变化,但在特定植被生长发育状态和剖面尺度下,植被因子将会成为土壤水分动态变化的主控因子。柠条林发育至成熟阶段,土壤水分补偿与消减将会保持平衡状态。土壤水分与植被生长的相互关系一方面表现出一定的时间差,另一方面植被对土壤水分也具有一定的适应性。这是因为土壤含水率高促进植物生长,植物生长势增强会进一步加大对土壤水分的消耗,土壤水分含量不足则会抑制植物生长,植物生长势减弱会进一步降低对土壤水分的消耗。

Soil water use and balance characteristics in mature forest land profile of Caragana korshinskii in Semiarid Loess Area

Compared with sparse native grassland (CK), soil water content and exchange range, as well as balance characteristics were investigated in the soil depth of 0-210 cm with 20 cm interval in mature Caragana korshinskii shrublands located in different topographic locations in a typical semi-arid loess watershed during growing seasons in 2009-2011. Soil water content ranged from high to low as CK, north, east and south slope in the depth of 30-130 cm, while as upper and middle position of south slope, CK, north and east slope in the depth of 150-210 cm, as well as upper, middle and lower position in south and north slope. Seasonal soil water declined in sequence of September, August, July, May, June and October. No regular change of soil water range value and variation coefficient was found under different terrain conditions. However, soil water range value and variation coefficient is active in the depth of 0-50cm, while relatively stable in the depth of 70-210 cm in vertical scales. No continuous soil water deficit was found in the drought years in succession, which serious soil water deficit was found in the first drought year, profit and loss balance in the second drought year, and slightly surplus in the third drought year. Obviously, terrain condition difference influenced soil water variation in a small watershed scale. But in a particular type of vegetation, plant factor would be key factor influencing soil water movement in the stable soil layer. The resplendent and consumption of soil water kept a balance status in mature Caragana korshinskii shrubland in this study. Results indicated that the response of vegetation growth was later than the soil moisture deficit (about one year), and vegetation growth can adapt to the soil water condition. This was mainly because relatively high soil water content in initial period can promote the vegetation growth conditions due to high available soil water resource. However, the relatively good growth conditions of Canagana korshinskii plants would consume more soil water than initial period and lead more soil water consumption. On the other hand, low available soil water would inevitable limit the vegetation growth and lead relatively lower soil water consumption.