物种组成对高寒草甸植被冠层降雨截留容量的影响

高寒草甸退化减少地上生物量、叶面积指数(LAI),因而减少冠层降雨截留容量(S)。但是,未有研究评价物种组成改变对S的影响。用水浸泡法和水量平衡法研究青藏高原高寒草甸3个不同退化阶段下(未退化、轻度退化、中度退化)的S变化规律,并评价物种组成改变对S的影响。结果表明:高寒草甸退化显著减少S(P<0.05)。在未退化、轻度退化、中度退化的高寒草甸,水浸泡法测得的S分别为0.612 mm,0.289 mm 和0.217 mm;水量平衡法测得的S分别为0.979 mm,0.493 mm 和0.419 mm。物种组成改变对S的影响表现为:随着高寒草甸的3个不同退化阶段,S减少的幅度先大于后小于LAI减少的幅度。原因是:(1)在未退化的草甸,鹅绒委陵菜(Potentilla arserina)的叶面积占有显著优势,占总叶面积的31.18%;在轻度退化的草甸,禾本科植物(Graminoid)的叶面积占有显著优势,占总叶面积的44.41%,而鹅绒委陵菜是稀有种,仅占总叶面积的3.76%;在中度退化的草甸,鹅绒委陵菜的叶面积占有显著优势,占总叶面积的19.91%;(2)鹅绒委陵菜的叶单位面积吸附水量(S_L)是禾本科植物的大约2.5倍。

Effects of species composition on canopy rainfall storage capacity in an alpine meadow, China

Canopy rainfall storage capacity (S) strongly affects the rainfall interception (I) processes and is therefore a parameter that is required in rainfall interception models. Most investigations of rainfall interception loss concentrate on forests, while a paucity of information is available for alpine meadow interception. Previous studies suggest that meadow degradation leads to reduced aboveground biomass, leaf area index (LAI) and subsequent reduction in S. However, the effect of changes in species composition on S is poorly understood. In this paper, we estimted herbaceous S along three different stages of alpine meadow degeneration (non-degraded, lightly degraded and moderately degraded) in the Qinghai-Tibetan Plateau, China, and evaluated the effect of changes in species composition on S. The water soakage method and the water budget balance method using rain simulations were used to estimate S. While evaluating the effect of changes in species composition on S, K-means clustering was used to objectively classify all the species into four groups with the greatest possible differences of specific storage capacity per unit one-sided leaf area (S_L) between their average values and the minimum variance within each group. We found that alpine meadow degeneration significantly reduced S (P<0.05). In non-degraded, lightly degraded and moderately degraded alpine meadows, S estimated using the water soakage method were 0.612 mm, 0.289 mm, 0.217 mm, respectively; S estimated using the water budget balance method were 0.979 mm, 0.493 mm, 0.419 mm, respectively. This implies the importance of considering the evaporation(E)during rainfall in evaluating the eco-hydrological significance of significant reduction in S during meadow degeneration. The effect of changes in species composition on S was highlighted by the fact that the reduction in S was firstly more than and then less than the proportional reduction in LAI along the three different stages of alpine meadow degradation. This could be explained by the following: (1) In non-degraded meadow, Potentilla arserina was the dominant species, accounting for 31.18% of the total leaf area; in lightly degraded meadow, graminoid plants were the dominant species, accounting for 44.41% of the total leaf area, while Potentilla arserina was a rare species with a leaf area of only 3.76%; in moderately degraded meadow, Potentilla arserina was the dominant species with a leaf area of 19.91%, respectively; (2) S_L of Potentilla arserina was approximately 2.5 times greater than that of graminoid plants. We concluded that the difference of S_L among different species and the magnitude of change in each species leaf area relative to the total leaf area during meadow degeneration together determined the effect of changes in species composition on S. The larger the difference of S_L among different species and the magnitude of change in species leaf area relative to the total leaf area are, the larger the effect of changes in species composition on S will be.