南沙群岛海域夏季营养盐对浮游植物生长的限制

Effects of nutrient on phytoplankton growth in the waters of the Nansha Islands in summer

为探讨氮和磷对浮游植物生长的限制作用，2013年夏季在南沙群岛海域西南大陆架S1站（9°30′N, 109°30′E）和曾母暗沙附近S2站（4°30′N, 109°30′E）进行了添加N、P营养盐的现场加富实验。结果显示：加富N和N＋P后，叶绿素a（Chl-a）含量显著增长（P〈0.05），其中，S1站点叶绿素a从初始的0.05 mg·m^-3分别达到0.29和0.80 mg·m^-3；S2站点叶绿素a从初始的0.09 mg·m^-3则分别达到0.79和1.02 mg·m^-3，说明添加N或N＋P可以促进浮游植物增长。在加富P后，2个站点的叶绿素a浓度均未显著增加，说明单独添加磷不能促进浮游植物的增长。限制因子分析表明，S1站点的浮游植物生长具N限制，而S2站点浮游植物生长的首要限制元素为N，其次为P。水体中N/P范围为5～25时最适应浮游植物生长。相关性分析结果表明，N/P值与Chl-a浓度和浮游植物的生长速度（R）无显著相关性，表明该2个站点水体的N/P值不能单独控制浮游植物的生长。

To investigate the effects of nitrogen （N） and phosphorus （P） on the growth of phytoplankton, an enrichment incubation experiment was carried out in the waters of Nansha Islands in summer of 2013. Two experimental sites, S1 （9°30′N, 109°30′E） and S2 （4°30′N, 109°30′E）, were in the southwest continental shelf and near the James shoal area, respectively. The results showed that the chlorophyll-a increased significantly （P〈0.05） after addition of single N or mixed N and P. The chlorophyll-a concentration increased from 0.05 mg·m-3 to 0.29 and 0.80 mg·m^-3 at S1 site, and from 0.09 mg·m^-3 to 0.79 and 1.02 mg·m^-3 at S2 site after addition of single N and mixed N and P, respectively. However, the enrichment of P did not promote the phytoplankton growth because the chlorophyll-a concentration showed no significant increase by adding single P at both sites. The N concentration was found to be the limitation factor of phytoplankton growth at S1, but both N and P concentrations were at S2. Moreover, the most adaptable N/P ratio for phytoplankton growth should be between 5 and 25. The results of correlation analysis showed there was no significant relationship between the N/P ratio and the concentration or the growth rate of chlorophyll-a, suggesting that the N/P ratio would not influence the phytoplankton growth in the waters of Nansha Islands in summer.