元江干热河谷海拔梯度植物群落组成及多样性格局

Composition and diversity pattern of plant community with elevational gradient in Yuanjiang dry-hot valley

关键词:  萨王纳植被, 干热河谷, α-多样性, β-多样性, 海拔梯度, 植被恢复

Key words:  savanna vegetation, dry-hot valley, α-diversity, β-diversity, elevational gradient, vegetation restoration

摘要:

尽管中国西南干热河谷塑造了植被外貌与非洲稀树草原相似的景观,但与其不同的是,该区域河谷的深切以及山脉对气流的阻挡形成的垂直地貌和气候类型,更容易引起土地退化、物种流失和植物群落异质性。然而,先前研究较少关注该区域植物群落物种组成及多样性的垂直分布格局及主要调控因子。该研究以元江国家级自然保护区(元江干热河谷)为对象,通过调查450 m(低海拔)、850 m(中海拔)、1 250 m(中高海拔)和1 650 m(高海拔)的土壤营养、气象因子和物种组成,计算物种重要值、α-多样性和β-多样性,探索其随海拔梯度的变化规律。结果表明:(1)低海拔土壤有机碳和硝态氮显著大于其他海拔。(2)不同海拔物种组成和物种重要值差异显著,高海拔的物种多样性较高,而低海拔的物种多度较高。(3)α-多样性中,Shannon-Wiener多样性指数和Pielou均匀度指数随海拔升高而增加,而乔木物种的Simpson优势度指数在低海拔达到最大; β-多样性中,处于相邻海拔群落的Jaccard相似性指数和Sorenson相似性指数随着海拔升高呈上升趋势,而非相邻海拔梯度群落的Jaccard相似性指数和Sorenson相似性指数较相邻海拔梯度呈下降趋势。(4)CCA表明土壤含水量、温度、土壤有机质、铵态氮和硝态氮是影响海拔梯度物种组成差异的主要因子。该研究证实了干热河谷植物群落的多样性、相似性和稳定性随海拔升高而增加,未来区域植物群落恢复及其对干旱的响应和适应研究需考虑群落在空间上异质性,并针对性地制定不同的保护和恢复措施。

Abstract:

Although dry-hot valleys in Southwest China have shaped a landscape with a vegetation appearance similar to that of African savannas, they are different from the African savannas because of the vertical geomorphology and climate type formed by the depth of river valley and the blocking of air flow by mountains in this region, which are more prone to land degradation, species loss and plant community heterogeneity. However, previous studies have paid little attention to the vertical distribution pattern and main regulatory factors of plant community species composition and diversity. In this study, the soil nutrients, meteorological factors and species composition of 450 m(low elevation, LE), 850 m(middle elevation, ME), 1 250 m(middle-high elevation, M-HE)and 1 650 m(high elevation, HE)were investigated in Yuanjiang National Nature Reserve(Yuanjiang dry-hot valley ), and the species important values, α-diversity and β-diversity were calculated to explore their changes with the elevation gradients. The results were as follows:(1)Soil organic carbon(SOC)and nitrous nitrogen(NO₃^--N)at LE were significantly higher than those at other elevations.(2)The species composition and species importance value of different elevations were significantly different.(3)The species diversity of HE was high, while the species abundance of LE was high. In α-diversity, Shannon-Wiener diversity index and Pielou evenness index increased with elevation, while Simpson dominance index of tree species reached its maximum at LE. In β-diversity Jaccard and Sorenson similarity indexes of communities in adjacent elevations increased with the elevations, but those of communities in non-adjacent elevations decreased with the elevations to compare with adjacent elevations.(4)CCA showed that SWC, SOM, NO₃^--N and NH₄⁺-N were the main factors affecting species differences at different elevations. It is concluded that the diversity, similarity and stability of plant communities in the hot-dry valley increased with the increasing of elevation, and the future research on the restoration of plant communities and their response and adaptation to drought should consider the spatial heterogeneity of the community, and different protection and restoration measures also should be formulated accordingly in this region.