摘要
海岸带是海洋环境中受人类活动影响最大、生物地球化学循环最为活跃的地区。这一地区氮的生物地球化学循环包括 :生物固氮、有机氮的氨化、氮的硝化、反硝化等 4个主要过程。概括性地介绍了有关这四个过程的发生机制、环境影响因素及研究方法等方面的研究动态、进展、存在的科学问题与今后的研究方向。过去十几年来 ,固氮主要集中在对束毛藻属的研究上 ,其间有两个重要发现 ,一是生物固氮在海洋氮循环中的作用远比人们以前的想象要重要得多 ;二是蓝细菌已经在海洋中存在了 2 0亿年 ,它们有可能调节大气中的 CO2 ,进而影响全球气候。由于有机物的结构千差万别 ,含氮有机物的氨化过程可能是一个简单的矿化反应 ,也有可能是一系列复杂的代谢过程 ,在水解酶的作用下含氮有机物降解为下一级化合物。硝化过程分两步进行 ,氨的硝化为反硝化细菌提供了重要的硝酸盐来源 ,通常采用同位素方法来研究硝化过程。发生在沉积物中的反硝化过程是氮循环的关键步骤 ,反硝化过程一方面减少了海水中初级生产者可利用的氮 ,另一方面产生了终结产物 N2 和 N2 O,而 N2 O是一种温室气体 。
The biogeochemical cycling of nitrogen is a significant factor influencing global climatic change. It is a complex process involving interactions between the atmosphere, seawater, sediments, and microorganisms. Nitrogen cycling is particularly active in estuarine and coastal zones, regions where human activities can impact on the natural process. There are four major processes in biogeochemical cycling: nitrification fixation;organic nitrogen ammonification;nitrification, and denitrification. The mechanisms and physico-chemical factors regulating the four major processes will be reviewed, along with an outline of the active research directions in this field. Recent research on nitrogen fixation has highlighted the role of Trichodesmium. Biological nitrogen fixation is a more important process than previously understood and may have an influence on the capacity of the oceans to sequester carbon. The nitrogen fixation rates of cyanobacterial mats can range from 0.8 to 76 g N /(m·a). Usually, the contribution of cyanobacterial nitrogen fixation in estuaries is relatively small, but in tropical coastal marine lagoons, it may account for a significant proportion of the total annual nitrogen inputs. This research suggests that available organic carbon is probably the main factor limiting the nitrogen fixing potential in oligotrophic marine environments. The addition of carbon compounds such as glucose, polysaccharides, xylan or alginate can stimulate nitrogen fixation activity. Depending on the structural complexity of the organic matter, ammonification can be either a simple mineralization reaction or a complex series of metabolic steps involving a number of hydrolytic enzymes during which N-containing polymers are broken down to their soluble sub-units. The ammonification rates for coastal sediments reported is ranged from 7 to 644 (mg N/(m^2·d),) and is controlled by temperature, oxygen penetration into the sediment, the nature and concentration of organic matter and the physiological characteristics of microbial
出处
《生态学报》
CAS
CSCD
北大核心
2004年第12期2907-2914,共8页
Acta Ecologica Sinica
基金
中国科学院知识创新工程重要方向资助项目 ( KZCX3 -SW-2 14 )
广东省自然科学基金资助项目 ( 0 3 2 62 2 )
中国科学院南海海洋研究所知识创新工程前沿领域资助项目 ( LYQY2 0 0 3 0 3)~~
关键词
海岸带
固氮
氨化
硝化
反硝化
生物地球化学
coastal zone
biological nitrogen fixation
ammonification
nitrification
denitrification
biogeochemistry
