三江平原沼泽湿地4种优势植物空间格局对不同水位环境的响应

Responses in spatial pattern of four dominant species to different water level environments in a freshwater marsh in the Sanjiang Plain

水文过程是沼泽湿地最基本的生态过程,理解物种空间格局形成机制及其种群特征随水位环境变化的规律对于科学指导沼泽湿地植被恢复具有重要意义。本研究分别选择三江平原季节性积水与常年积水沼泽,应用点格局方法中的完全空间随机模型、泊松聚块模型和嵌套双聚块模型分析了毛薹草(Carex lasiocarpa)、漂筏薹草(C.pseudocuraica)、狭叶甜茅(Glyceria spiculosa)、小叶章(Deyeuxia angustifolia)4个主要优势植物种群的空间格局,并测定了不同水位环境条件下的种群密度和个体大小特征。结果表明:在沼泽湿地中,4个优势种群在0-200 cm的尺度范围内都偏离了完全随机模型,表现为集体性聚集分布特征,且聚集距离主要集中在0-50 cm之间。随着水位的升高,毛薹草种群密度、个体生物量、株高和基径都呈显著增大趋势,但其聚集强度变弱;而小叶章种群密度和个体大小则显著降低,其聚集强度增大;漂筏薹草和狭叶甜茅种群密度、个体大小和聚集强度变化并不显著。在季节性积水区,4个物种在小尺度上均偏离了泊松聚块模型,符合嵌套双聚块模型,即在大聚块中分布较高密度的小聚块。但是,在常年积水区,仅毛薹草、漂筏薹草和狭叶甜茅3个物种符合嵌套双聚块模型,而小叶章种群则符合泊松聚块模型,说明在高水位胁迫下小叶章种群空间格局的大聚块中不存在较高密度的小聚块。综上所述,水位环境胁迫主要通过影响繁殖分配、种内竞争、易化作用以及个体大小变异等生物学过程共同决定着三江平原淡水沼泽湿地植物种群的斑块化分布特征,不同零模型可以帮助解释种群空间分布格局的形成机制。

Aims:Instability of hydrological regimes is one of the most basic ecological processes in wetlands.Our objective is to determine how changing water level environments impacts the spatial patterns of marsh plants in the freshwater wetlands in the Sanjiang Plain,Northeast China.Methods:We analyzed the spatial distribution patterns of populations for four dominant species(Carex lasiocarpa,C.pseudocuraica,Glyceria spiculosa,Deyeuxia angustifolia)in the seasonal inundated(SI)marsh and perennial inundated(PI)marsh in the Ecological Experiment Station of Mire Wetland in the Sanjiang Plain.We utilized a small-scale point pattern analysis based on three null models,including:complete spatial randomness process(CSR),Poisson cluster process(Neyman-Scott process,NS),and nested double-cluster process(DC).We then tested the population density and individual size characteristics of each species.Results:Regardless of water level conditions,the four main dominant species were completely diverged from the CSR model,and the aggregation distance was primarily focused on 0-50 cm scale.These results indicate that there is a stronger aggregation in small scales for these marsh plants species,but the aggregated intensity was expressed in differences among water level environments.With the rising water level,the population density,individual aboveground biomass,plant height,and stem base diameter of C.lasiocarpa exhibited a significantly increasing trend,but its aggregated intensity became weaker.By contrast,these individual size parameters of D.angustifolia exhibited a dramatically decreasing trend,whereas its aggregated intensity increases.In addition,the changes in individual sizes and aggregated intensity of the other two species(i.e.,C.pseudocuraica and G.spiculosa)were not significant.In seasonal inundated(SI)marsh,the four main dominant species were diverged from the NS model in small-scales,but their spatial distributions fit better with the DC model at 0-200 cm scale,indicating that there is a series of clustered patterns under slight flood stress.In the perennial inundated(PI)marsh,the spatial patterns of three species(i.e.,C.lasiocarpa,C.pseudocuraica and G.spiculosa)also fit better with the DC model at 0-200 cm scale.However,the spatial patterns of D.angustifolia fit well with the NS model,implying the small-scale clustering disappeared with the intensification of flooding stress.Conclusion:Hydrologic regimes may determine the patch patterns of marsh plants in the Sanjiang Plain,primarily via variations in reproductive allocation,intraspecific competitions,facilitation effect and individual sizes.The application of the various null models could help explain the formation mechanisms of the population spatial distribution patterns more efficiently.