植物钙化响应水体氮、磷升高的生理机制与生态意义

The recover and re-establishment of submerged vegetation is very important for the control and restoration of eutrophical water body and has key role in maintenance of clear-water stable state in shallow lakes. Charophyte plants are important submerged macrophyte. Calcified charophyte species are pioneer groups in re-establishment of vegetation and calcified Potamogeton plants dominated meso-eutrophic shallow water lake. However, the studies on the correlation between plants calcification and the nutrient of water body were always by neglected. Therefore, the responses of calcified plants in physical mechanism to the increases of N and P in water body and its significance are very essential. Based on the results of previous studies, we choose calcified charophyte species and potamogeton species as the objects, focus on calcification and utilization of dissolve inorganic carbon of calcified plants, investigate the effect of the increase of N and P in water body on plants calcification, analyze the correlation between plant calcification and utilization of N nutrient and its mechanism, explore the contribution of calcification to the cycle of P. In all, we try to make clear the role of calcification in the acclimation of Chara plants to eutrophication process. Furthermore, we try to give an explanation to the dominance of calcified potamogeton species in meso-eutrophic lakes.

恢复和重建以沉水植物为主的水生植被，是控制和修复富营养化水体的关键。钙化轮藻是沉水植被修复的先锋类群，且钙化的眼子菜属植物是中-富营养水体的优势类群，但植物钙化与水体氮、磷升高的关联一直被忽略。因此钙化植物的钙化对水体氮、磷升高的响应机制与意义是亟需系统探讨的科学问题。本项目在前期青年基金的研究基础上，拟以钙化轮藻和眼子菜为研究对象，以植物钙化和无机碳利用为切入点，通过野外调查和室内研究，系统研究水体氮、磷升高对植物钙化、生长和分布的影响及其影响的生理机制，重点研究植物钙化影响无机氮（NO3-N和NH4-N）利用的生理机制，评估植物钙化对水体P循环的贡献，为钙化轮藻作为沉水植物修复先锋类群提供选种依据，并为钙化眼子菜中-富营养化水体的优势地位提供理论依据。

为了弄清植物钙化响应水体氮磷升高的生理机制和生态意义，本研究首先开展了南水北调东线沿线重要湖泊（洪泽湖和南四湖）和云贵高原不同营养水平湖泊（泸沽湖、洱海 、抚仙湖和滇池）沉水植物的钙化调查、湖泊优势种非优势种的氮磷计量学比较研究。然后通过一系列控制实验研究植物钙化对水体氮磷升高的响应及其生理机制。实验首先探讨了轮藻钙化与无机碳限制的关系，结果发现普生轮藻钙化与植物对无极碳的利用线性相关，普生轮藻钙化的首要限制因子是水体的HCO3-碱度。随后通过实验比较穗状狐尾藻、伊乐藻和金鱼藻响应无机氮组成和氨氮胁迫的差异，结果表明氨氮添加可显著提高植物组织内游离氨基酸（FAA）的含量，植物体内可溶性糖含量（SC）存在显著的种间差异，但氨氮胁迫时SC/FAA的差异主要源于氮源形态组成（56%），体内FAA、SC含量高的植物在富营养水体中更有优势；相比较金鱼藻，菹草通过钙化降低溶液△pH,提高SC/FAA来缓解氨氮胁迫的毒性，从而表现出同等氨氮胁迫水平下更高的耐受性。沉水植物去除水体中的磷主要有 3 种途径：植物利用、吸附和沉淀作用，但通过钙磷共沉淀进入湖泊底泥中的这一部分磷才是植物从水体真正去除的磷。水培条件下，钙离子添加可显著促进水体磷的下降，菹草通过提高吸附性磷（H2O-P）和钙磷(HCl-P)含量增强磷的富集,而金鱼藻显著升高了灰分中有机磷(NaOH-P)的含量,这表明水体磷升高背景下, 菹草具有更强的形成CaCO3-P共沉淀的能力,具备竞争优势；微宇宙实验中，磷添加提高菹草沉积物NaOH-P（Fe/Al-P）从而使沉积物TP升高，钙添加促进金鱼藻沉积物HCI-P含量升高，但NaOH-P（Fe/Al-P）下降导致TP降低；两种植物均可通过吸收、吸附和共沉淀将上覆水（包括间隙水）中的磷富集到植物体，随着时间变化，植物富集磷的主要途径发生变化，菹草主要体现在钙磷共沉淀和吸附作用，而金鱼藻表现微吸收和钙磷共沉淀；由于更强的钙磷共沉淀（Ca-P）能力，与气生的粉绿狐尾藻相比，菹草在高磷水平下对水体磷的实际去除能力更大。