不同龄阶梭梭根区土壤水分时空变化特征

Spatio-temporal variations of soil moisture in the root zone of Haloxylon ammodendron at different life stages

土壤水是荒漠植被发育最主要的制约因子。不仅影响植物的生长和发育,还限制着植被的种类、数量和分布。梭梭作为北方荒漠区重要的固沙植物,研究梭梭林地土壤水分动态对其植被生存或恢复以及群落稳定性维持具有重要意义。鉴于少有学者研究过不同龄阶梭梭根区的土壤含水率差异,于2014年2月至2014年11月,采用中子仪法和烘干法对0—400 cm沙层土壤含水率进行了原位观测,分析了不同龄阶梭梭根区土壤水分的时空变化规律。结果表明:(1)梭梭根区土壤水分时间变化可分为4个阶段:2月下旬—3月下旬是土壤水分快速补给期,4月上旬—5月下旬是土壤水分均衡期,6月上旬—10月下旬是土壤水分耗损期,11月上旬—次年2月中旬是土壤水分稳定期;(2)梭梭根区0—50 cm土层,受降雨、融雪水入渗补给和蒸发的影响较大,土壤水分变异系数较大且随深度增加迅速减小,50 cm以下土层变异系数较小且随深度变化微小;(3)不同龄阶梭梭根区剖面平均土壤含水率全年与春、夏、秋季均表现为:枯树>成熟梭梭>中龄梭梭>裸地;(4)随距梭梭树干距离的增大(0—5 m范围内),土壤含水率整体呈减小趋势;降雨前后,梭梭根区浅层(0—10 cm)土壤含水率增量大于裸地土壤含水率增量。

Soil water, as a major factor limiting vegetation in deserts, does not only affect the survival and growth of plants, but also the species abundance and distribution. To research the spatiotemporal variations of soil moisture content in root zone is vital for understanding the recovery, maintenance and the stability of plant communities in deserts. In the Gurbantunggut desert in northwestern China, Haloxylon ammodendron as the dominant species plays an important role in dune stabilization. However, little is known about the effects o[ plant life stage on the variations of soil moisture content in the root zone for Haloxylon ammodendron. In our study, soil water dynamics were monitored for eight typical Haloxylon ammodendrons individuals in an inter-dune low land at the southern edge of Gurbantunggut Desert, each with a soil moisture monitoring point 20--30 cm away from the stem base. Another two points were set in the inter-shrub bare soil. In addition, 16 points were positioned two individuals with 10 meters away from each other. Thus there were totally 26 points. From February 2014 to November 2014, in-situ observations for soil moisture within 0--400 cm soil were performed by neutron probe method in combination with oven-drying method to explore the spatiotemporal variations of soil moisture in the root zone of Haloxylon ammodendron individuals at different life stages. Results show that （ 1 ） the annual variation of soil water underwent 4 periods, i.e., recharging period （from later February to early March）, equilibrium period （from early April to late May）, discharging period （from early June to late October）, and stable period （from early November to middle February of the following year） ; （2） soil water dynamics differed within profiles, with a higher coefficient of variation that decreases rapidly with depth in the top 50 cm soil layer, and a relatively constant coefficient for 50--dO0 cm soil layers; （3） the averaged soil moisture content at different life stages in spring, summer, fall, as well as in the whole year displayed a pattern in order of dead individual 〉 adult individulal 〉 young individual 〉 bare soil; （4） soil moisture decreased gradually with the increasing distance to the Haloxylon ammodendron base stem within 5 meters; and （5） following rainfall events, the soil moisture content in 10 cm soil increased more in the root zone than in the bare soil.