黄河三角洲贝壳堤优势灌木水分生态位研究

As global warming proceeds, sea levels are predicted to continue rising driven by both thermal expansion of ocean water and melt water from the polar ice caps. At the end of the 21st century, global sea level rise will reach 18~59cm. During the past 30 years, China's coastal sea level rose by an average rate of 2.6mm/year, higher than the global sea level rise. Coastal ecosystems occurring at the terrestrial interface of land and sea will be among the first ecosystems threatened by sea-level rise. As such, it becomes increasingly important to decipher the present role of ocean water in coastal ecosystems in order to assess the coming effects of sea-level rise scenarios..Soil hydrology is known to be an important environmental variable that affects the distribution, water relations and survivorship of vegetation in coastal ecosystems. Sea-level rise will alter the soil hydrology of coastal ecosystems. However, clear links between soil hydrologic conditions, the distribution of vegetation and the physiology of vegetation on coastal ecosystems have yet to be established..Basing on environmental gradients produced by the diminishing influence of the ocean, we will test whether symbiotic abilities and water niche differentiations of three interacting shrub species (Tamarix chinensis L., Periploca sepium Bge., Ziziphus jujuba var. spinosa Hu) from an arid chenier ecosystem in the Yellow River Delta are more related to differences in root distribution pattern, water stress or salinity tolerance. Water stress and salinity tolerance of 3 dominant shrub species will be explored by conducting physiology measurements, including sap osmolality, stomatal conductance, photosynthesis rate, plants water potential, sap water Na+/K+ ratio, and chemical signaling/regulation. Parallel soil analyses will also be conducted that including electrical conductivity, humidity, bulk density, porosity, salinity and water isotopes. Stable isotopes are used to trace the path of different water sources to investigate the differences in water source utilization among 3 chenier shrub species. δD and δ18O values within stem water will be measured concurrently with physiology measurements and soil analyses during the wet and dry season and from 3 areas proximal and distal to the ocean. Species composition will also be examined in connection with distance from the coast, depth to water table, soil water content, soil salinity and groundwater salinity..This study will demonstrate the water niche differentiation mechanism and the ecological consequences of water hydraulic lift. And the effects of sea level rise on plant community structure will also be discussed. Though this study focuses on coastal chenier ecosystem and dominant plant species of the Yellow River Delta it has implications for coastal ecosystems threatened by sea level rise across the globe.

全球变化导致海平面上升，将显著改变海岸带土壤水文特征，而使海岸带植物水分关系发生变化，进而改变海岸带植物群落动态。然而，海岸带植物水分利用策略机理还有待于进一步深入研究。以黄河三角洲贝壳堤植物群落3种优势灌木为研究对象，根据由海洋到内陆海水影响逐渐减弱形成的生态环境梯度，同步观测土壤理化性状和植物抗逆生理生态指标。稳定同位素技术和传统方法相结合，定量计算植物对各种水源利用比例及水分提升的比例；基于生态位分化及生态位互补理论，结合植物抗逆生理生态指标，探讨植物水分生态位分化机理和水分提升作用的生态学意义，揭示植物对有限水资源合理分配的内在机制和植物共生机理，预测海平面上升导致的海岸带植物群落变化，为海平面变化后海岸带植被的保护和恢复提供一定的理论指导。

在黄河三角洲海岸带生态系统中水资源的可利用性是影响植物生长和分布的关键生态因子之一。在调查分析黄河三角洲贝壳堤岛的植被群落类型、地带性分布特征及其关键影响因子基础上，选取柽柳、杠柳、酸枣3种优势灌木群落为研究对象，测定分析灌木木质部水及土壤水、地下水氧稳定同位素动态特征，揭示灌木水分利用机制。定量计算3种灌木的水分生态位宽度及重叠度，初步阐明3种灌木对水分胁迫的适应机制及种间共生特征。.黄河三角洲贝壳堤岛有种子植物56种，隶属于20科52属；有灌丛和草甸2个植被型，杠柳、酸枣和柽柳为灌丛优势种。植被呈现较为典型的地带性分布特征，土壤因子、地质地貌等是决定地带性分布的关键因素。. 大雨（20.4mm）使灌丛表层土壤水（0-60cm）和灌木木质部水的δ18O值显著降低，而小雨（3.0mm、6.6mm）对表层土壤水δ18O值没有显著影响，大雨和小雨对深层土壤水（60-100cm）及地下水均没有显著影响。大雨对表层土壤水（0-60cm）和灌木木质部水的δ18O值的影响一般在雨后第3天开始减弱，第6天恢复到降雨前水平。大雨后3种灌木对雨水的利用比例为柽柳（30.5%~66.6%）＞滩脊地势较低处酸枣（40.1%~56.1%）＞杠柳（23.9%~28.0%）＞滩脊地势较高处酸枣（0.2%~1.9%）。无降雨时，高潮线附近柽柳主要利用表层土壤水以避免盐分胁迫，滩脊柽柳则以深层土壤水和地下水为主；滩脊地势较低处酸枣以深层土壤水为主，对地下水也有一定程度利用；滩脊地势较高处酸枣以深层土壤水为主；杠柳从各个土壤层吸收水分。. 3种灌木的水分生态位宽度依次为酸枣＞杠柳＞柽柳。在土壤水分匮乏时，滩脊共生的柽柳与酸枣水分生态位重叠度较小，表明物种间的生态位产生分化以减少种间竞争。在降雨补充土壤水后（9月采样时段），3种灌木的生态位宽度显著增加以获取更多水资源，且滩脊共生的柽柳与酸枣出现了较大的生态位重叠度，体现了植物对有限水资源的高效利用。滩脊柽柳较大的生态位宽度和高潮线柽柳较小的生态位宽度体现了柽柳较强的生态位调节能力，说明在盐旱胁迫生境中柽柳具有更强的适应性。在低盐生境中，杠柳较大的水分生态位宽度体现了较强的干旱生境适应能力。以上研究结果将为分析和预测海平面上升、海岸侵蚀等环境变化引起的群落潜在演替趋势提供一定理论支撑。