黄土高原不同植被类型区人工林地深层土壤干燥化效应

Effects of deep soil desiccation on artificial forestlands in different vegetation zones on the Loess Plateau of China

人工林地土壤干燥化正在日益严重的威胁着黄土高原人工植被建设成效。在黄土高原3个植被类型区广泛观测苹果、刺槐、油松、辽东栎、狼牙刺、沙棘和柠条等23种不同立地和树龄林地深层土壤湿度基础上,比较和分析了各类林地土壤含水量、土壤湿度剖面分布和土壤干燥化强度,定量评价了各类林地深层土壤干燥化效应。研究结果表明：（1）23种林地0～1000 cm土层土壤湿度、土壤贮水量和土壤有效含水量平均值依次为10.84%、1409.8 mm和446.6 mm,明显低于荒草地土壤湿度和当地土壤稳定湿度值,各类林地平均土壤水分过耗量超过500 mm,每年多消耗土壤水分36.8 mm。林地土壤水分过耗量和耗水速度以中部半干旱森林草原区最高,南部半湿润森林区相对较低。林地土壤干燥化速度为：柠条和狼牙刺林地〉油松林地〉刺槐和沙棘林地〉苹果园地和辽东栎林地;（2）除林龄较短的苹果、沙棘和柠条林地外,各类林地在300 cm以下深层土壤湿度明显低于荒草地土壤湿度和土壤稳定湿度值,林地深层土壤湿度表现为阳坡低于阴坡、坡地低于平地,最大耗水深度接近或超过1000 cm。随林龄增长,林地深层土壤湿度逐渐降低,土壤干层逐渐加深和加厚;（3）23种林地土壤干燥化指数平均值为51.6%,达到中度（偏重）干燥化强度,林地土壤干层厚度达到或超过800 cm,随着降水量从半湿润区向半干旱偏旱区趋势性减少,林地土壤干燥化强度趋于强化,土壤干层厚度趋于增加。土壤干燥化强度和土壤干层厚度表现为：油松、辽东栎、狼牙刺和柠条林地〉刺槐林地〉苹果和沙棘林地。

Soil desiccation on artificial forestlands is increasingly threatening the achievements and effects of artificial vegetation constructions of the loess plateau. Based on widely observations of deep soil moisture on 23 kinds of tree and shrub forestlands, which included apple tree （Malus domestica Borkh）, black locust tree （Robinia pseudoacia） , Chinese pine tree （Pinus tabulaeformis Cart. ）, Manchurian oak tree （Quercus liaotungensis）, David＇s mountain laurel shrub （ Sophora viciifolia）, seabuekthorn shrub （ Hippophae rhammoides ） and littleleaf peashrub （ Caragana microphylla ）, at different growth locations and in different growth ages on 3 vegetation zones of the Loess Plateau, soil water amounts, soil water distributions and soil desiccation intensities on various forestlands were compared and analyzed, effects of soil desiccation of different forestlands were quantitatively assessed. The results show as following： （A） Average soil moistures, soil water storages and available soil water storages in 0 - 1000 cm soil layers of 23 forestlands were 10.84% , 1409.8mm and 446.6mm respectively, which were obviously lower than local natural grasslands and soil stable moisture, and soil water overuse amounts was higher than 500mm and annual soil water overuse was 36.8mm. Soil water overuse amounts and speeds on middle semi-arid forest-steppe zone was the highest one and south semi-humid forest zone was the lowest one in 3 vegetation zones. Sequences of soil desiccation speeds of forestlands from high to slow were littleleaf peashrub and David＇s mountain laurel shrub, Chinese pine tree, black locust tree and seabuckthorn shrub, apple tree and Manchurian oak tree. （B） Except young apple tree, seabuckthorn shrub and littleleaf peashrub land, soil moistures beneath 300 cm soil layers on all other forestlands were obviously lower than natural grasslands and local soil stable moisture, and soil moisture of south slope forestlands were lower than north slope forestlands, and slope forestlands were lower than that highlands. Maximum soil water use depth of forestlands were close to or over 1000 cm. soil moistures on deep soil layers of forestlands decreased and thickness of desiccated soil layers increased as forest growth age increased. （C） Average soil desiccation index of 23 forestlands was 51.6%, soil desiccation intensity was medium desiccated （prone to serious desiccated）. Thicknesses of desiccated soil layers on forestlands reached or passed 800 cm, and soil desiccation intensities strengthened and thicknesses of desiccated soil layers deepened as rainfall decreased from south semi-humid zone to north semi-arid prone drought zone. Sequences of soil desiccation intensities and desiccated soil layer thicknesses of forestlands from high to low were Chinese pine tree, Manchurian oak tree and littleleaf peashrub firstly, black locust tree secondly, apple tree and seabuckthorn shrub lastly.