沉水植物茎叶微界面调控重金属生物富集机制研究

Background.Various kinds of substances in water, including organic matter, silt, zoogloea, algae, microorganisms etc., often cumulate on the leaf and stem surface in submerged macrophytes. A micro-interface is therefore established which varies in its composition, structure and thickness depending on the actual environmental properties. It provides organic material for bacteria thus plays an important role in micro-interfacial processes. The subsequent heterogeneous oxidation-reduction microenvironment within this micro-interface proves to exert fundamentally regulatory effects on nitrogen transformative processes such as ammonification, denitrification and anammox. However, the role of the micro-interface in heavy metal bioaccumulation has not been determined yet..Strategies.The composition of this micro-interface, its responses to micro-environmental changes and its role in regulating heavy metal bioaccumulation constitute the fundamental horizon for better understanding the feature of submerged macrophytes in water management and ecological remediation. The present project adopts comprehensively the microcosmic and macroscopic analysis, and in situ and control experimental approaches, to proceed an intensive study on the mechanisms regulating heavy metal bioaccumulation by the shoot-water micro-interface in submerged macrophytes..Material and methods.Three macrophyte species, Vallisneria asiatica, Potamogeton crispus and Myriophyllum spicatum are chosen for their dominance and abundance in regional aqua-ecosystems. Their responses to Cd, Cu and Zn are to be studied both in situ and under control condition in greenhouse. Micro-chemical analysis technique is applying to characterize the substance composition and spatio-temporal changes of the micro-interface as well as the dynamics of heavy metal adsorption. High-resolution microelectrode technique is applying to measure the micro-environmental factors including dissolved oxygen, pH and oxidation-reduction potential to determine their effects on heavy metal bioaccumulation processes. Scanning electron microscope, stable isotope and mass spectrometry techniques are applying to realize the composition and structure of the micro-interface under various eutrophic levels, and to quantify the internal heavy metal distribution under different photosynthetic intensities..Aims of the project.This study aims therefore at 1) revealing whether the shoot-water micro-interface may hinder or facilitate the heavy metal bioaccumulation in shoots of submerged macrophytes, 2) elucidating the influence of substance composition and structural changes of the micro-interface on heavy metal bioaccumulation processes, and 3) dissecting the regulatory mechanisms of photosynthesis and respiration on heavy metal accumulation via shoot in submerged macrophytes. The putative results suppose to provide primarily scientific fundamental to ecological remediation of heavy metal-affected waters.

沉水植物茎叶表面附着水体中各种物质形成茎叶-水微界面，产生的氧化-还原异质环境是水中氮素转化机制的重要基础，其对茎叶吸收富集水体重金属污染物过程的调节机制尚待探讨。本项目拟综合运用微观与宏观分析、原位与实验模拟相结合的方法，对沉水植物茎叶微界面调节水体重金属富集机制进行深入研究。通过微量化学分析技术测定典型沉水植物茎叶微界面物质组成结构、时空变化特征与重金属吸附动态；利用高分辨率微电极技术测定茎叶微界面溶解氧、pH、氧化还原电位等环境因子，分析其对重金属吸收时空动态的影响；通过扫描电镜、同位素示踪、质谱分析技术，测定不同水体富营养化水平及不同光合及呼吸作用强度时茎叶重金属富集规律。辨明微界面在重金属经茎叶进入植物体过程中的促进或阻碍作用，揭示微界面组成和结构差异对重金属进入沉水植物茎叶的影响，探讨水体富营养化、植物光合及呼吸作用调控茎叶重金属元素富集的机制，为水体生态修复提供科学支撑。

背景：沉水植物茎叶表面附着水体中各种物质形成茎叶-水微界面，产生的氧化-还原异质环境是水中氮素转化机制的重要基础，其对茎叶吸收富集水体重金属污染物过程的调节机制尚待探讨。.主要研究内容：（1）沉水植物茎叶微界面组成和结构特征。包括不同富营养化程度下沉水植物茎叶微界面的物质组成和显微结构；沉水植物不同生长阶段茎叶微界面组成与结构变化规律；（2）微界面环境因子表征及其对重金属胁迫的响应。利用微电极技术，测定典型沉水植物茎-叶微界面DO、pH、Eh等环境因子，分析不同生长阶段重金属处理下，微界面主要环境因子变化规律；沉水植物微界面重金属胁迫下生长变化与生理胁迫响应；（3）茎叶微界面对典型沉水植物茎叶重金属富集的影响。测定典型沉水植物茎叶微界面对3种重金属元素（Cu、Cd、Zn）在茎、叶及微界面中的累积动态；测定胁迫下沉水植物吸收水体营养盐动态，阐明光合作用对微界面调控茎叶重金属富集过程的影响；（4）流域重金属富集特征及生态风险评价。以射阳河流域为研究区，选取7种代表性重金属元素，综合利用沉积学、地统计学等多种研究手段，探究沉积物重金属浓度空间分布与来源，了解研究区域重金属污染历史，评价重金属污染程度与生态风险，以及其与人为诱导的土地利用/土地覆盖变化的关系。.主要结果及意义：沉水植物微界面结构复杂，异质性大，具明显的时空变化特征，附着生物具反硝化作用活性，生态意义重大。水体营养盐负荷、底质状况、光照是影响沉水植物微界面结构的主要环境因子。不同沉水植物茎叶微界面结构存在差异，同时，生长阶段对茎叶微界面结构有明显的影响。重金属对萌芽期的植株微界面的环境因子分布影响较大，对衰亡期影响次之，成熟期影响最小。微界面附着物叶绿素含量在重金属处理下呈上升趋势，与植物相反，对金属进入植物体内具有促进作用。流域尺度上，人类源是区域重金属浓度升高的主要因素。高覆盖度的草林地可削减流域内重金属污染。