东印度洋束毛藻固氮作用及其对新生产力贡献的研究

Trichodesmium is the major N2-fixing cyanobacteria. its nitrogen fixation rate during its bloom was 42 Tg N yr-1 in global scale. The annual input of new Nitrogen into the tropical North Atlantic of was at least 1.6 × 1012 mol N by Trichodesmium N2 fixation alone. N2 fixation by Trichodesmium is of greater quantitative significance in supporting oceanic production. we will intend to carry out the investigation and research on Trichodesmium nitrogen fixation in the eastern Indian Ocean carrying the the Indian Ocean Research Cruise of National Natural Science Fund Committee. The species of Trichodesmium will be identified , and colonies, filaments, cells abundances will be counted in net samples and standard aqueous layer samples collected in the field by fluorescent microscope. The features of spatial and temporal variation and diurnal vertical variation will be revealed. Nitrogen fixation rate of Trichodesmium was measured by acetylene reduction assay. The correlation between environment factors with growth, N2 fixation rate of Trichodesmium will be analyzed in the culture experiment. The amount of nitrogen fixation and input of new nitrogen will be calculated on the base of Trichodesmium biomass in survey area. We will evaluate the contribution of nitrogen fixation to new nitrogen, determine its impacts on ecosystems and biogeochemical processes in the eastern Indian Ocean.

在海洋生态系统中束毛藻是主要的固氮蓝藻，据估计在水华期束毛藻全球固氮速率可达到42 Tg N yr-1，在大西洋北部热带海域，每年束毛藻固氮可提供1.6 × 1012 mol N新生氮。束毛藻固氮作用对是海洋系统的初级生产力具有重要贡献。本项目拟搭载国家基金委印度洋航次，开展东印度洋束毛藻调查与固氮作用研究，通过现场拖网和标准水层采集样品，室内荧光显微镜观察物种组成和计数藻团、藻丝体、细胞丰度，归纳东印度洋束毛藻物种和丰度的时空变化规律，以其昼夜垂直变化特征。采用乙炔还原法现场测定束毛藻固氮速率。通过室内培养实验，分析不同环境因子对束毛藻生长与固氮速率的相关性。结合调查区域束毛藻生物量，计算其固氮量和对新生氮的贡献量，评价束毛藻固氮作用对东印度洋新生产力的贡献，了解束毛藻固氮作用在东印度洋生态系统中的地位，以及在地球生物化学过程中的作用。

本项目搭乘国家基金委印度洋航次，现场采集生物样品，结合现场环境因子数据，获得印度洋蓝藻束毛藻物种组成、丰度及分布的时空变化特征，以现场培养实验为基础，计算了该区域束毛藻固氮速率。研究结果表明，东印度洋蓝藻类群是主要是束毛藻和胞内植生藻，共鉴定出3种束毛藻，分别为红海束毛藻（Trichodesmium erythraeum）、汉氏束毛藻（Trichodesmium hildebrandtii）以及铁氏束毛藻（Trichodesmium thiebaultii），其中铁氏束毛藻是优势物种，平均丰度为29.6235×103 cells/m3。胞内植生藻大部分与硅藻共生。而与硅藻共生的胞内植生藻中，以与笔尖根管藻（Rhizosolenia styliformis）及钝根管藻半棘变型（Rhizosolenia hebetata f. semispina）共生居多。在东印度洋白天时蓝藻固氮速率在0.015-0.681μmolN/L/h之间，夜间时固氮速率在0.026-0.640μmolN/L/h之间，白天和黑夜的固氮速率相差不大。但是白天和夜晚固氮蓝藻优势物种存在差异，白天以>10μm固氮蓝藻为主，而夜晚以单细胞蓝藻为主。从地区分布上来看，赤道附近站位的固氮速率明显要高于孟加拉湾和近岸站位的固氮速率。