| 论文摘要： |
Excess nitrogen (N) loading is one of the main factors causing eutrophication. Biological N fixation (BNF), as a main contributor to N loading, plays a critical role in the N cycle. The N-2 fixation rate (N(2)fix) is regulated by many factors and is usually higher under conditions of N deficiency. Most studies have focused on the regulation of factors that influence the N(2)fix in specific aquatic ecosystems or artificial conditions, while fewer have focused on large scale such as the latitudinal distribution of N(2)fix. To understand the regulation of the N(2)fix in latitudinal zones, the key factors, and the underlying mechanism, we compared the N(2)fix in 27 lakes located in different latitudinal zones and analyzed the main regulators. The results showed that (1) heterocyst density (D-Het) and the N(2)fix were highest in low-temperate lakes and were 2.5-2.7 and 11.6-22.1 times greater than in high-temperate lakes and tropical lakes, respectively, in the 99th quantile; (2) D-Het increased and then decreased with increasing latitude and radiation, and peaked at 30.28 degrees N and 2300 J/cm/d; (3) D-Het was positively correlated with temperature and increased slightly with increasing temperature; (4) N(2)fix increased and then decreased with increasing latitude, temperature and radiation, and peaked at 38.8 degrees N, 24.21 degrees C and 2120 J/cm/d. The results suggest that BNF could be regulated by larger scale factors, e.g., temperature and radiation in latitudinal scale. Compared with high-temperate lakes and tropical lakes, low-temperate lakes may face more difficulties in controlling eutrophication due to the potentially higher N loading from BNF under similar nutrient and morphometric conditions. |
