围封对蒙古荒漠草原和高山草原植物群落组成及稳定性的影响

基于蒙古国两种典型草地生态系统类型(荒漠草原和高山草原),采取围封和放牧两种处理方式,对2013-2018年这两种草地类型的群落盖度进行系统分析。按植物分类学法,将群落内的所有物种划分为五大功能群--杂草类、蒿类、豆科、禾本科和莎草科,采用Gordon稳定性方法评估围封对群落稳定性的影响。结果表明:1)围封显著增加荒漠草原杂草类植物覆盖度,减少蒿类和禾本科植物覆盖度,年际间无明显的变化规律,而对于高山草原,围封对不同功能群盖度无显著影响;2)围封增加荒漠草原的群落稳定性,而对高山草原无明显影响;3)群落稳定性与优势种盖度占群落的比例呈显著的正相关关系,荒漠草原的优势种占比高于高山草原,导致荒漠草原的群落稳定性更好。根据上述结果,建议在对草地进行围封管理前,应充分考虑当地的环境条件及围封对植物群落及生态系统的潜在影响,同时辅以休牧、轮牧或季节性放牧等措施,才能真正提高草原生态系统服务的使用价值。

Community phylogenetic structure of grasslands and its relationship with environmental factors on the Mongolian Plateau

The community assembly rules and species coexistence have always been interested by ecologists. The community phylogenetic structure is the consequence of the interaction process between the organisms and the abiotic environment and has been used to explain the relative impact of abiotic and biotic factors on species co-existence. In recent years, grassland degradation and biodiversity loss have become increasingly severe on the Mongolian Plateau, while the drivers for these changes are not clearly explored, especially whether climate change is a main factor is debated in academia. In this study, we examined the phylogenetic structure of grassland communities along five transects of climate aridity on the Mongolian Plateau, and analyzed their relations with environmental factors, with the aims to understand the formation mechanism of the grassland communities and the role of climatic factors. We surveyed grassland communities at 81 sites along the five transects, and calculated their net relatedness index(NRI) at two different quadrat scales(small scale of 1 m2 and large scale of 5 m2) to characterize the community phylogenetic structure and analyze its relationship with the key 11 environmental factors. We also calculated the generalized UniFrac distance(GUniFrac) among the grassland communities to quantify the influence of spatial distance and environmental distance on the phylogenetic β diversity. The results indicated that plant community survey using the large scale quadrat contained sufficient species to represent community compositions. The community phylogenetic structure of grasslands was significantly overdispersed at both the small and large scales, and the degree of overdispersion was greater at the large scale than at the small scale, suggesting that competitive exclusion instead of habitat filtering played a major role in determination of community composition. Altitude was the main factor affecting the community phylogenetic structure, whereas climatic factors, such as precipitation and temperature, had limited influence. The principal component analysis of the 11 environmental factors revealed that 94.04% of their variation was accounted by the first four principal components. Moreover only 14.29% and 23.26% of the variation in community phylogenetic structure were explained by the first four principal components at the small and large scales, respectively. Phylogenetic β diversity was slightly significantly correlated with both spatial distance and environmental distance, however, environmental distance had a less explanatory power than spatial distance, indicating a limited environmental effect on the community phylogenetic structure of grasslands on the Mongolian Plateau. In view of the limited effect of climatic factors on the community phylogenetic structure of grasslands, climate change may have a smaller impact on grassland degradation than previously thought.

植物功能群在调控气候和土壤因子对蒙古高原草原群落物种丰富度和生物量影响中的作用

植物功能群组成主要受环境因素驱动,同时植物功能群组成也是影响草地生物多样性和生产力的主要因素之一。因此,理解植物功能群在调控环境因素对生态系统功能和生物多样性影响中可能发挥的作用至关重要。通过对蒙古高原草原65个样点的植物生物量和物种丰富度的调查,将157种多年生草本植物分为两种植物功能群(即禾草和杂类草)。通过随机森林模型和普通最小二乘回归,确定与植物功能群物种丰富度和地上生物量显著相关的环境因素(即干燥度、土壤总氮和pH),并利用结构方程模型探讨筛选出的环境因素与群落物种丰富度和生物量间的关系,以及植物功能群在驱动这种关系中发挥的作用。干燥度与禾草、杂类草以及整个群落的地上生物量和物种丰富度均呈显著的单峰关系。所有的物种丰富度和生物量指标均与土壤总氮和pH值显著相关。禾草在维持蒙古高原草原生态系统群落生物量中起着关键作用,并受气候因素的直接影响。而杂类草物种丰富度决定了群落总丰富度,并受到土壤因素直接的调控。因此,群落组成在调控环境因素对群落生物量和植物多样性的影响中起着关键作用。