沉水植物茎叶微界面特性研究进展

沉水植物茎叶-水界面是浅水湖泊的重要界面之一,对湖泊生物地球化学循环和水环境质量具有重要影响。富营养化水体中,大量的附着物常富集在沉水植物茎叶表面,形成了特殊的生物-水微界面。对该微界面特性进行深入研究,有助于揭示沉水植物在微环境层面对富营养化水体中物质循环的调控过程和机制。沉水植物茎叶微界面具有促进水体养分转化、改变环境因子及可溶性物质的空间分布,增加物质运输的阻力和距离、降低植物光合作用、调控重金属等生态功能;微界面结构及环境因子受水体营养盐浓度、沉水植物种类及生长阶段等因素的影响。对微界面结构功能的主要研究方法进行了分析总结,并对沉水植物茎叶微界面的研究前沿进行了展望。

Research advances in and perspectives on characteristics of the micro-boundary layer around leaves and stems of submerged macrophytes

Submerged macrophytes constitute an important component of shallow aquatic ecosystems. They provide most of the accessible surface area, constant survival substrates, and available nutrients for periphyton, which remains attached to the stem and leaf surfaces of submerged macrophytes and forms a special bio-water boundary layer. As one of the most important interfaces in shallow lakes, the submerged macrophyte-water boundary layer plays roles in macrophyte growth, biogeochemical cycling, water environment maintenance, and ecological regulation. The present study summarizes the research advancements regarding characteristics of the micro-boundary layer (MBL) around leaves and stems of submerged macrophytes. The ecological functions, biotic and environmental factors, and research methods are identified and reviewed. Perspectives for the focus of future research on MBL around submerged macrophytes are raised.The MBL around submerged macrophytes has important ecological functions. The dense periphyton in MBL exerts negative effects on photosynthesis in submerged macrophytes, creates a barrier hindering the transport of dissolved substances, such as O₂, and leads to the degradation and even disappearance of submerged macrophytes in eutrophic waters. The plant stress derived from pollutants may be alleviated because of the periphytic barrier in the MBL. The epiphytic bacteria in the MBL can be of considerable importance for nutrient transformation and cycling in eutrophic ecosystems. Periphyton is an assemblage of algae, bacteria, fungi, protozoan, inorganic matter, and organic detritus that remains attached to submerged macrophyte surfaces where significant spatio-temporal variations exist in the MBL. The heterogeneity of micro-environmental parameters is the key factor shaping the MBL around submerged macrophytes, given the complex constituents, changing spatial structure, and fluctuation of oxidation-reduction status within this microcosm. At the spatial heterogeneity, in the vertical direction of stem and leaf surfaces, O₂ concentration and pH in the MBL increase markedly with decreasing distance to the surface of leaves and stems and peak at the surface. The trend of the oxidation-reduction potential (ORP) is reverse.Plant species and growing stages are biotic factors that affect the MBL, and nutrients load, light intensity, flow velocity, and habitat are the major environmental factors. The growth stages of macrophytes create large fluctuations and dynamics in O₂, pH, ORP, and soluble substrates at the surface of stems and leaves by changing the thickness of the diffusive boundary layer around the macrophyte. O₂ concentration and pH in the MBL around the leaves and stems of submerged macrophytes increase when macrophytes begin the rapid growing stage, which is accompanied by gradually increasing spatial differentiation. O₂ concentration and pH in the MBL around the leaves and stems reach peaks at the stable growth stage, and increase slightly or decline when the periphyton layer begins the declining stage. However, the ORP shows the opposite trend to that of O₂, and pH. MBL is mainly affected synergistically by plant physiological and periphyton characteristics during the life cycle of macrophytes. Environmental factors affect the MBL via periphyton composition, periphyton mass, and macrophytes growth. Scanning electron microscopy, high spatial resolution of microsensors, microchemical analysis, molecular biology techniques, and isotope tracer techniques are applicable approaches for the study of the characteristics of MBL; however, they have not yet been comprehensively utilization. To further investigate the leaf and stem MBL, we must focus on establishing standard methods and models of the MBL structure and functions to verify the modulation processes and mechanism of the MBL on the biogeochemical cycling in eutrophicated waters. Long-term ecological research under controlled conditions is required.