亚热带湖滨沙地典型下垫面土壤水分变化

亚热带湖滨沙化作为南方荒漠化的一种典型类型,阐明沙化土壤水分变化规律对该地区植被恢复与重建具有重要指示意义。研究于2013年2月至2014年2月对鄱阳湖多宝湖滨沙地的土壤水分动态进行了监测,分析了不同覆被条件下沙地土壤水分在年内及极端气候条件下的动态特征。结果如下:(1)湖滨沙地土壤水分在梅雨和伏旱时期差异显著。在梅雨期及其前后,土壤水分主要受降水控制,各下垫面土壤平均含水量相对较高(0.063 cm~3/cm~3),且差异较小;而在伏旱及其后期,覆盖条件的差异起关键作用,湿地松样地的土壤平均含水量均低于0.035 cm~3/cm~3。(2)持续高温干旱天气下,浅层10cm土壤含水量迅速降低,之后维持在极低水平(0.01 cm~3/cm~3);随着深度增加,不同样地土壤含水量差异将会增强。(3)在多雨季节,17年生湿地松能有效增加土壤表层的持水能力;在干旱季节,湿地松对降水的截留及吸附作用强烈地影响土壤水分的补给量及补偿深度,当降水强度较低时,17年生湿地松样地的浅层土壤水分难以获得补给。因此,在亚热带沙地进行湿地松种植时,应增大初植密度,并且对于植株过高的湿地松林,也应采取适当措施降低其密度,以抵御愈加频发的极端干旱事件带来的风险,促使沙化地区发生持续的正向演替。

Effects of vegetation coverage on soil moisture: Evidence from subtropical lakeside sandy lands in South China

Lakeside desertification is a common type of desertification in South China. Soil moisture dynamics of lakeside sandy land have important implications for regional vegetation restoration and reconstruction. Using soil moisture data from the Duobao Sand Hills of Poyang Lake recorded from February 2013 to February 2014, we investigated soil moisture dynamics under different vegetation coverage and extreme weather conditions. We found that (1) soil moisture levels of lakeside sandy land in the rainy season were significantly different from the levels in the drought season. Soil moisture, mainly affected by precipitation, was maintained at a higher level ( > 0.063 cm³/cm³) and was less sensitive to the type of underlying surface in the rainy season. However, different types of vegetation cover affected soil moisture differently. Soil moisture in the presence of Pinus elliottii was relatively low ( < 0.035 cm³/cm³) during the drought period. (2) Under high temperatures and drought conditions, shallow-soil moisture of desertified lands dropped rapidly at first, then remained exceptionally low ( < 0.01 cm³/cm³). With the increase in soil depth, the differences in soil moisture among soils with Pinus elliottii, Vitex trifolia Linn., or bare sandy lands became more significant. (3) 17-year-old Pinus elliottii effectively increased the water-holding capacity of the soil surface during the rainy season. However, due to water absorption and obstruction of rainfall, Pinus elliottii affected groundwater recharge during the drought period in terms of the amount of water and soil depth. Therefore, the shallow-soil water of a 17-year-old Pinus elliottii stand is difficult to recharge when precipitation intensity is low. Based on our findings, we suggest to increasing the initial planting density of Pinus elliottii then decreasing mature Pinus elliottii density in subtropical sandy land in South China to neutralize the effects of more frequent extreme droughts and to induce continuous positive succession in desertified areas.