雅江河谷防沙治沙工程近地表特性——林下植被特性、生物结皮及土壤养分变化特征

采用对比分析和时空互代法，从植被配置模式（杨树+砂生槐、砂生槐、花棒、藏沙蒿）、工程年限（6，10，30a）2个方面，研究了雅鲁藏布江（简称雅江）河谷防沙治沙生态工程实施过程中林下植被特性、地表生物结皮及土壤养分等变化特征.结果表明，工程年限为10a的乔灌（杨树+砂生槐）、灌木（砂生槐、花棒）型样地较草本（藏沙蒿）更有利于提高林下植物多样性，且杨树+砂生槐样地的林下植被地上生物量、枯落物量、地下生物量、土壤有机质、全氮与全磷含量均显著高于其他3种样地.藏沙蒿样地的生物结皮最为发育，花棒样地次之，杨树+砂生槐样地无结皮.随年限延长，杨树+砂生槐样地林下植物多样性、枯落物量、地下生物量、土壤有机质、全氮及全磷含量呈增加趋势，生物结皮仅在6a样地中有发育；砂生槐样地地上生物量、地下生物量、生物结皮逐渐增加，但植物多样性、全氮含量呈下降趋势，枯落物量、有机碳及全氮含量呈先增加后减小规律.不同配置模式中，杨树+砂生槐乔灌型样地各项指标综合表现最佳，并随工程年限延长，对促进河谷沙地植被演替、提高植被生产力、提升沙地肥力等作用愈强.建议该区防沙治沙工程中应推广杨树+砂生槐乔灌型模式为主.

Variation characteristics of vegetation characteristics,biological crusts and soil nutrients under the main vegetation configuration modes in the process of sand control in the Yarlung Zangbo River valley

In order to understand the impact of ecological project for sand control on the vegetation, biological crusts and soil characteristics of the middle reaches of the Yarlung Zangbo River valley. The characteristics of understory vegetation, surface biological crusts, and soil fertility properties during the implementation of the project with different vegetation configuration modes and ages were analyzed. 4 modes which restoration ages were approximately 10 years were selected, including Populus+Sophora moorcroftiana (YS+SSH), Sophora moorcroftiana (SSH), Hedysarum scoparium (HB) and Artemisia wellbyi (ZSH). Because of the most widely implemented of YS+SSH and SSH, three ages were studied (i.e. 6, 10 and 30 years old). The results showed that:The arbor+shrub (YS+SSH) and shrub (SSH and HB) plots with 10 years were more conducive to increasing species diversity than the herb (ZSH). The above-ground biomass, litter volume, underground biomass, soil organic matter, total nitrogen and total phosphorus content of the YS+SSH plot were significantly higher than the other three plots. The biological crusts of the ZSH plot were the most developed, followed by the HB plots, and the YS+SSH plot had no crust. The species diversity index, litter storage, underground biomass, soil organic matter, total nitrogen and total phosphorus content of the YS+SSH plot increased with the increase of years, but the biological crust was only in 6 years. The aboveground biomass, underground biomass, and biological crusts of the SSH plot gradually increased with the increasing of years, but the species diversity index and total nitrogen content showed a downward trend. The litter storage, organic carbon and total nitrogen content increased first and then decreased. Among the different modes, the YS+SSH plot had the best comprehensive near-surface characteristics. With the increasing of the project years, it had stronger effects on promoting the succession of vegetation on the sandy land in this area, increasing the productivity of the vegetation, and enhancing the fertility of the sandy land. Therefore, it is suggested that the vegetation configuration mode of arbor+shrub(YS+SSH) should be promoted in the ecological project for sand control in this area.