2000−2020年藏北高寒草地水源涵养功能变化及影响因素分析

藏北地区平均海拔4500 m以上,被称为“世界屋脊上的屋脊”,同时也是青藏高原生态安全屏障的主体,但在全球气候变化和人类活动的双重影响下,藏北高寒草地生态系统变化明显,部分区域出现退化趋势。2009年我国开始实施了《西藏生态安全屏障保护与建设工程》(以下简称工程),旨在恢复和保育高原的生态系统及其服务功能。而水源涵养是藏北高寒草地生态系统最为重要的服务功能之一,工程实施以来,藏北草地的水源涵养功能如何变化、生态工程的效益如何?本文基于InVEST模型评估了2000–2020年生态工程前后藏北草地水源涵养功能的变化,量化了气候变化和人类活动在其中的贡献率。结果表明:(1)藏北各类型草地的水源涵养能力虽然差异较大,但工程实施后水源涵养的功能均出现了明显的变化,产水量比工程实施前增加10.07%,水源涵养服务上升8.86%。其中高寒草甸区的水源涵养变化速率增长最大,由工程前的–1.84 mm yr^(–1)转变为工程后的2.24 mm yr^(–1);其次是高寒荒漠草原和高寒草原,在工程的影响下水源涵养功能下降的速率明显减缓。(2)气候变化仍是藏北草地水源涵养功能的主要影响因素,但生态工程对藏北各类高寒草地水源涵养功能变化的作用明显,在高寒草甸、高寒草原、高寒荒漠草原区分别达到了13.99%、8.75%、3.71%,有效地促进了藏北草地的水源涵养功能的改善。

Effects of Enclosure on Plant and Soil Nutrients in Different Types of Alpine Grassland

Enclosure is one of the most widely used management tools for degraded alpine grassland on the northern Tibetan Plateau, but the responses of different types of grassland to enclosure may vary, and research on these responses can provide a scientific basis for improving ecological conservation. This study took one site for each of three grassland types(alpine meadow, alpine steppe and alpine desert) on the northern Tibetan Plateau as examples, and explored the effects of enclosure on plant and soil nutrients by comparing differences in plant community biomass, leaf-soil nutrient content and their stoichiometry between samples from inside and outside the fence. The results showed that enclosure can significantly increase all aboveground biomass in these three grassland types, but it only increased the 10–20 cm underground biomass in the alpine desert. Enclosure also significantly increased the leaf nutrient content of the dominant plants and contents of total nitrogen(N), total potassium(K), and organic carbon(C) in 10–20 cm soil in alpine desert, thus changing the stoichiometry between C, N and P(phosphorus). However, enclosure significantly increased only the N content of dominant plant leaves in alpine steppe, while other nutrients and stoichiometries of both plant leaves and soil did not show significant differences in alpine meadow and alpine steppe. These results suggested that enclosure has differential effects on these three types of alpine grasslands on the northern Tibetan Plateau, and the alpine desert showed the most active ecological conservation in the responses of its soil and plant nutrients.

The Facilitation of Restoration by Cushion Plant Androsace tapete in a Degraded Alpine Grassland

The cushion plant Androsace tapete is an endemic species that is widely distributed in the Qinghai-Tibetan Plateau, and also predominant in the alpine grassland that is locally degraded due to overgrazing and other reasons. As an ecosystem engineer cushion plant, its ability to facilitate the restoration of degraded alpine grassland was studied in a degraded alpine grassland at an elevation of 4500 m on the southern slope of the Nyainqentanglha Mountains in Damxung. The species diversity, soil nutrients and water content underneath and outside the cushion plant A. tapete were investigated. The results showed that soil nutrients underneath the A. tapete cushion were significantly increased by about 16%-48% compared to outside the cushion, of which the organic matter and total N were increased by 16.2% and 18.9% respectively, and the soil water content was increased about 12%. The index of species diversity of richness(S), Shannon-Wiener’s H and Simpson’s D all increased with the coverage of cushion plant A. tapete. Our results suggested that this cushion plant can facilitate restoration of the degraded alpine grassland by modifying the local soil environment and increasing the community diversity, so it should be conserved for the restoration of degraded alpine grasslands on the Qinghai-Tibetan Plateau.