黄土丘陵区不同恢复年限人工刺槐林土壤水分时空动态及其时间稳定性

Spatiotemporal dynamics and temporal stability of soil moisture at black locust plantations with different restoration years on hilly region of the loess plateau,China

以空间代时间的方法研究不同恢复年限对人工刺槐林土壤水分时空动态及其时间稳定性的影响,对于了解人工刺槐林在生态恢复过程中的土壤水分动态特征具有重要意义。基于长期定位观测,选取黄土丘陵沟壑区15、20、30、35 a等4个恢复年限人工刺槐林,自2014年5月至2018年10月每年生长季(5-10月)开展土壤水分自动观测。研究结果如下:(1)不同恢复年限刺槐林土壤水分差异显著,刺槐林土壤储水量随恢复年限增加呈现先增加后降低的趋势,排序依次为30 a(184.9 mm)>20 a(184.6 mm)>35 a(150.8 mm)>15 a(128.8 mm);不同恢复年限刺槐林土壤水分的时空分布特征差异明显,土壤水分变异性随土层增加而降低,但不随恢复年限而有规律的变化;土壤水分主要受到降水以及植被生长的影响,其变异性的时空格局也说明随土壤深度增加土壤水分的稳定性随之增加;(2)通过相对差分分析不同恢复年限刺槐林土壤水分时间稳定性,确定15、20、30、35 a的代表深度分别为80、100、80、150cm土层,都属于与100cm相近的土壤深度;(3)Spearman秩相关分析显示,上土层与下土层的土壤水分的时间稳定性特征差异明显;(4)线性回归与纳什系数结果表明通过相对差分与时间稳定性指数得到土壤水分代表深度的结果是可接受的,其中15 a恢复年限刺槐林的结果最好,决定系数R2和纳什系数NSE分别可达0.91和0.82,但总体结果仍存在误差,在区域土壤水分模拟时需考虑这一不确定性。(5)灰色关联分析表明,土壤质地(砂粒),土壤总氮、土壤容重、土壤有机碳、土壤总孔隙度以及坡度是不同恢复年限刺槐林土壤水分时间稳定性主要影响因素。

Black locust(Robinia pseudoacacia)are widespread across the Loess Plateau of China.It′s of great importance for understanding the variation of soil water in black locust plantations under restoration to study dynamic of soil water in black locust plantations with different restoration years and it′s temporal stability by the substitution of space for time with restoration time going.Based on long⁃term in⁃situ observation of soil moisture in growing season from May 2014 to October 2018,relative difference and Spearman rank correlation analysis were used to study the temporal stability of soil water in 15 a,20 a,30 a and 35 a black locust plantations.Results showed that(1)the soil water storage of black locust plantations with different restoration years was significantly different,the soil water storage increased first and then decreased,with the increase of restoration years,and the order was 30 a(184.9 mm)>20 a(184.6 mm)>35 a(150.8 mm)>15 a(128.8 mm).As soil depth deepened,soil water decreased with the increase of soil depths,but does not change regularly with restoration years;results indicates that soil moisture is mainly affected by precipitation and vegetation growth,and its spatiotemporal distribution patterns of variability(CV,Coefficient of Variation)also indicates that stability of soil moisture increased with soil depth increasing accordingly;(2)Temporal stability of soil moisture was established by relative difference analysis and index of temporal stability at black locust plantations with different restoration years,the representative depths of 15 a,20 a,30 a and 35 a were 80 cm,100 cm,80 cm and 150 cm soil depth,respectively,which were all close to 100 cm soil depth;(3)Spearman rank correlation analysis shows that the upper and lower soil layers have their own time stability pattern;(4)The results of linear regression and Nash⁃coefficient show that it is acceptable to obtain the representative depth of soil water by relative difference and index of temporal stability,but there are some uncertainties remained,which should be taken into account in the further region soil water simulation study.(5)Results of Grey relational analysis shows that soil texture(Sandy),soil total nitrogen(STN),soil bulk density(BD),soil organic carbon(SOC),soil total porosity(STP)and slope degree are the major influencing factors on time stability of soil moisture at different restoration years which indicates that the spatiotemporal dynamics of soil moisture are influenced by heterogeneity of environmental factors.The results may provide theoretical reference and scientific basis for further ecological civilization construction in the Yellow River Basin.