三峡水库消落带植被高程梯度分异及其对生境胁迫的响应

三峡水库蓄水运行形成的极端生境胁迫深刻改变了消落带植被结构和功能。在消落带横向断面高程梯度上，植被生境具有典型的空间异质性。选取三峡水库典型自然恢复消落带，通过野外调查和室内分析，揭示了消落带自然演替植被的群落构成、物种多样性和生物量随高程梯度的分异特征，系统分析了极端淹水、侵蚀-沉积、土壤环境等生境胁迫类型对消落带植被高程梯度分异的影响。结果表明：①研究消落带适生植被以草本为主，共有15科25种23属，其中禾本科种类较多，但单属单种、单优群落现象明显；一年生和多年生草本分别占52%和48%，且一年生草本多在消落带上部定居，多年生草本主要在消落带下部聚集。②物种多样性指数与高程呈正相关趋势，在145-150m范围内较低，在160-170m范围内较高。③植被生物量为199.68-1211.2g/m²，总体呈现随高程增加而显著增加的趋势；受多种生境因子的复合胁迫影响，生物量随高程存在局部波动。④水库水位变动形成淹水时长、出露时令、淹水强度等是影响消落带植被生物量高程梯度分异的主导因子；侵蚀/沉积过程改变土层厚度、根层土壤持水能力和肥力条件，对植被生长产生重要影响；土壤水分和氮是植被生长的限制性因子。因此，优势生境适宜性物种选育、土壤基质保育和植被格局功能优化是三峡水库消落带植被恢复和生态功能重建的重要任务。

Vegetation differentiation along elevation gradient in the water level fluctuation zone of the Three Gorges Reservoir and its response to habitat stressing

The extreme habitat stressing generated by the Three Gorges Reservoir''s impoundment has profoundly altered the structure and function of vegetation in the water level fluctuation zone. Along the elevation gradient laterally, the habitat of riparian vegetation exhibited typically spatial heterogeneity. Combined with field investigation and laboratory analysis, this study revealed the divergence characteristics of community composition, species diversity, and biomass of natural successional vegetation along elevation gradient in a typical natural recovery water level fluctuation zone of the Three Gorges Reservoir. Additionally, the effects of habitat stressing including extreme flooding, soil erosion-sediment deposition, and soil properties on vegetation spatial distribution pattern were systematically explored with correlation analysis and principal component analysis. Major obtained findings were as follows:(1)the adaptive vegetation existing in the study area was primarily herbaceous, consisting of 25 species and 23 genera in 15 families, with Gramineae dominating. But the phenomenon of single genus, single species, and single superior community, on the other hand, was obvious. Annual and perennial herbs made up 52% and 48% of the total, respectively. Meanwhile, the former was prone to congregate in the high-elevation of the water level fluctuation zone, whilst the latter tended to gather in the low-elevation of the water level fluctuation zone. (2)The species diversity index appeared a positive coupling trend with elevation, with its lowest value appearing in 145-150m and the maximum value occurring in 160-170m. (3)The riparian vegetation biomass varied from 199.68g/m² to 1211.2g/m², showing a significant increment trend with increasing elevation in general. Nevertheless, there were slight fluctuations in vegetation biomass due to the synergistic effect of compound habitat stressing. (4)The relationship between vegetation biomass and habitat stressing was identified via the fusion of qualitative and quantitative analysis. The results illustrated that the differences of inundation duration, emergence time, and inundation intensity derived from seasonal water level fluctuation by reservoir operation were the dominant factors that influenced the spatial distribution of vegetation biomass with elevation gradient. Erosion-deposition processes altered soil layer thickness, water holding capacity, and fertility conditions, all of which had important effects on vegetation development. Soil moisture and nitrogen, the essential soil properties affecting material and energy cycles among vegetation and soil, were restrictive factors for vegetation growth in the water level fluctuation zone. In summary, the dominant habitat suitability species selection, soil substrates conservation and vegetation patterns optimization are critical tasks for vegetation restoration and ecological function reconstruction of the degraded water level fluctuation zone in Three Gorges Reservoir.