植物功能群去除对高寒草甸群落结构、多样性及生产力的影响

Abstract

群落中物种的丧失在干扰下普遍存在，但对生态系统过程和功能的影响仍存在较大不确定性。选取青藏高原东缘典型高寒草甸为对象，开展优势植物功能群的梯度去除试验，以模拟长期过牧干扰下物种的损失。经过连续两个生长季的功能群去除，我们对群落的物种组成、结构、多样性和生物量等特征进行了分析，探讨了上述指标的响应过程和机制。研究结果表明：（1）功能群的去除降低了群落高度，增加了物种均匀度，并显著影响了禾草、杂草优势比以及功能群多样性和优势度；（2）同时，去除操作显著减小了凋落物量与禾草生物量，并显著影响了群落地上生物量；（3）进一步分析还发现，禾草、莎草和杂草功能群之间存在显著的竞争关系，群落生产力主要取决于禾草功能群并随物种均匀度的增大而显著减小。上述结果表明，禾草在高寒草甸群落中占据竞争优势地位，植物功能群的损失主要通过改变种间竞争关系、引起有机物质丢失影响群落过程和功能。;Impacts of biodiversity loss on ecosystem dynamics and functioning have aroused considerable attention and controversies. Loss of plant species is common in natural assembled community, whereas the response of ecosystem process remains unclearly. The continuous overgrazing of livestock has resulted significant plant species loss, like palatable grass and sedge species in alpine meadow on the Qinghai-Tibet plateau. In this study, we conducted a plant removal experiment to simulate the species loss along retrogressive succession gradient of alpine meadow resulting from long term overgrazing. A typical alpine meadow located on the eastern edge of the plateau was selected as the object to conduct the removal manipulation. The study site was fenced in April 2014 after the long term moderate winter grazing of yaks to exclude grazing of herbivores. Six removal treatments including: remove no plant species, remove Grass, remove Grass and Sedge, remove all species, randomly remove 25% of community aboveground biomass, and randomly remove 50% of community aboveground biomass. In middle July 2014 and 2015, we removed aboveground part of specific plant species individuals in 1 m×1 m plots. In late July 2016, the community coverage, height, species composition, diversity indices and biomass were investigated based on 0.5 m×0.5 m quadrats to detect response of alpine meadow to the removal experiment. The results showed that (1) removal of plant functional group (PFG) decreased the weighted-average height of community, but had no significant effect on the cumulative coverage of community. (2) Removal manipulation significantly influenced the summed dominance ratio (SDR) of Grass and Forb group, while no significant for Sedge group. (3) Removal of PFG increased the species evenness, and significantly influenced PFG diversity and dominance, whereas showed no significant effects for other diversity indices. (4) Removal of PFG reduced the litter biomass and Grass biomass. Only the removal of all plant reduced the community aboveground biomass. (5) In addition, further analysis showed that the community aboveground biomass was mainly depending on the Grass group, and decreased significantly with the increase of species evenness. And significantly competitive relationships were found among Grass, Sedge and Forb groups. The results showed that Grass species in the alpine meadow community have the greatest competitive advantage, the loss of plant species could change the community properties by means of influencing the inter-specific competitive relationships and significant plant biomass loss. The successive long-term monitoring on the response of community functioning to plant species loss should be strengthened.