半干旱黄土丘陵区不同人工植被恢复土壤水分的相对亏缺

土壤水分是制约半干旱黄土丘陵区植被恢复和生态建设的关键因子。而缺乏科学指导的人工植被恢复会加剧土壤水分耗竭，造成土壤水分亏缺，从而严重阻碍该区生态系统恢复和脆弱生境的有效改善。本研究以典型半干旱黄土丘陵区甘肃定西龙滩流域为例，对比不同植被恢复模式下土壤储水状况，并通过构建土壤水分相对亏缺指数CSWDI（Compared Soil Water Deficit Index）和样地土壤水分相对亏缺指数PCSWDI（Plot Compared Soil Water Deficit Index）进行定量化分析与评价，发现各人工植被均存在不同程度的土壤水分亏缺。其中，柠条、油松、山杏林地PCSWDI分别达到0.65、0.62、0.62，土壤水分亏缺严重，尤其是100 cm以下土层；山毛桃林地和苜蓿草地PCSWDI分别为0.38和0.17，在100—200 cm土层有一定程度的水分亏缺，但相对较轻；侧柏林地土壤水分的亏缺主要集中在20—100 cm这一层次，100 cm以下则随深度增加而降低；0—200 cm土层内，杨树林地、撂荒草地和马铃薯农地无显著水分亏缺，且在0—100 cm内土壤水分有一定的补充。CSWDI和PCSWDI能有效反映不同层次和样地土壤水分相对亏缺状况，可用于同一地区不同植被恢复模式土壤水分响应的定量化分析与评估。

Soilwater deficit under different artificial vegetation restoration in the semi-arid hilly region of the Loess Plateau

Because of the semi-arid climate and water scarcity in China's Loess Plateau, soil water, the effective water source for plant growth, has become a key limiting factor in vegetation restoration and ecological reconstruction in the region. However, these activities without an appropriate scientific guidance may result in excessive water consumption and soil water deficit in different soil layers, which in turn restrict significantly the local ecological restoration and environmental enhancement. Quantitative evaluation of soil water deficit and its profile distribution based on local rainfall and soil water condition is the premise and foundation for proper vegetation restoration and sustainable ecological development in the Loess Plateau, and therefore is one of the top research priorities at present with both theatrical and practical significance. In this study, we selected a typical semi-arid loess hilly catchment located in the Dingxi city of Gansu province, China, to quantify the response of soil water deficit to different artificial vegetation restoration practices. Soil water under different vegetation covers including Platycladus orientalis, Armeniaca sibirica, Pinus tabulaeformis, Caragana korshinskii, Amygdalus davidiana, Medicago sativa, Populus simonii, Solanum Tuberosum, as well as abandoned land and natural grassland were analyzed based on filed sampling and laboratory test. For comparison purpose, the background soil water content was set to the value of natural grassland covered by local climax community for a long period. Next, the Compared Soil Water Deficit Index (CSWDI) and Plot Compared Soil Water Deficit Index (PCSWDI) were calculated and analyzed to quantify soil water deficit degree and its profile distribution with different vegetation types. The comparison result shows that soil water deficit appeared in all lands with artificial vegetation covers with a different degree except Populus simonii forestland and Solanum tuberosum farmland. In addition, it was found that all artificial vegetation covers had low available soil water storage. PCSWDI of Caragana korshinskii, Pinus tabulaeformis, and Armeniaca sibirica forestland was 0.65, 0.62 and 0.62, respectively. These three vegetation types have led to a serious deep soil desiccation especially in soil layers from 100 to 200 cm. This soil water deficit may last for a long time period due to the fact that water is hardly recharged below 100 cm by rainfall in this area. Soil water deficit was also found in Amygdalus davidiana shrubland and Medicago sativa grassland mostly in soil layers between 100 and 200 cm. However, soil water conditions were favorable compared to those in Caragana korshinskii, Pinus tabulaeformis and Armeniaca sibirica forestland. Soil water deficit in Platycladus orientalis forestland was found mainly in soil layers from 20 to 100 cm. Meanwhile, soil water content increased in the layers below 100 cm with a decreasing CSWDI. No significant soil water deficit was detected in Populus simonii forestland, abandoned grassland, and Solanum tuberosum farmland in top 200 cm soil layers. The results showed that soil water in these lands could be quickly replenished, especially the top 100 cm soil layers. Results of this study also indicated that the CSWDI and PCSWDI were capable of reflecting conditions of soil water deficit in different soil layers and plots. They could be used as quantitative indices for soil water deficit analysis under different vegetation covers. The results of this study suggested that for sustainable artificial vegetation restoration in the semi-arid loess hilly area, proper artificial vegetation types should be selected based on rainfall and soil water conditions. In addition, optimal control of density and productivity of vegetation community and adoption of effective management practices must be employed.