光照和营养盐磷对微型及微微型浮游植物生长的影响

Effect of irradiance and phosphate on growth of nanophytoplankton and picophytoplankton

2004年9月,在长江口及邻近水域通过在培养水体中添加不同量的磷酸盐和改变光照强度进行现场受控培养实验,对光照和营养盐磷耦合培养作用下浮游植物生长及对磷营养盐的吸收变化进行了研究,结果表明：高光照条件下（100﹪自然光照）,磷酸盐浓度在高磷水平（0.60μmol/L）培养水体中下降速率明显比中磷（0.41μmol/L）、低磷水平（0.25μmol/L）快,浮游植物生长存在着显著的磷限制性,微型浮游植物（nanophytoplankton,简称Nano,2～20μm）在高磷水平下的生长明显得到促进,聚球藻（Synechococcus sp.,简称Syn,＜2μm）密度在培养初期有小幅度增加,而微微型真核浮游植物（picoeukaryote,简称Euk,＜2μm）在低磷水平下生长较快;在低光照条件下（50﹪自然光照）,磷酸盐浓度在高磷水平培养水体中的下降是受到抑制的,Nano和Syn也都更宜在中磷水平培养水体中生长,Euk在高磷水平下的生长也是受到抑制的,且在中磷水平培养水体中,三类浮游植物的生长周期都得到延长;无光照暗环境培养条件下磷酸盐浓度在不同磷水平下始终保持着增加趋势,三类浮游植物也都无法生长,磷酸盐浓度随培养时间呈线性增加趋势,浮游植物细胞密度则呈指数下降趋势,且磷酸盐的添加对其本身的释放速率和浮游植物衰减速率都没有影响.

In situ incubation experiments were conducted to investigate the phosphate uptake and growth variations of nano- and pico-phytoplankton controlled by the coupling between different phosphorus concentrations and different levels of irradiances in Changjiang estuary and its adjacent sea. By comparing the nutrient concentrations in incubation bottles at fixed intervals and the species numbers of both nanophytoplankton and picophytoplankton, the results were as follows： The uptake rates of phosphate increased distinctly at a high phosphate level （0.60μmol/L） under high irradiance （100 % natural irradiance）, which showed that the growth of phytoplankton was strongly phosphate-limited. The cell densities of nanophytoplankton and Synechococcus sp. also increased obviously. Moreover, picoeukphytoplankton seemed to be adapted to a low phosphate level （0.25 μmol/L）, which reflected that growth of different phytoplankton species had different adaptation to phosphate level. It was also possible that there was nutrient competition between nanophytoplankton and picoeukphytoplankton, when nanophytoplankton grown and became dominate species at a high phosphate level the growth of picoeukphytoplankton could be limited. Therefore, the larger phytoplankton species was in favor of a high phosphate level in the maximum turbidity zone of the Changjiang estuary. Under low irradiance （50% of nature irradiance）, phosphate uptake was restrained at high phosphate levels and the growth of both nanophytoplankton and synechococcus sp. was also limited. Moreover, they grew well at intermediate phosphate levels （0.41 μmol/L） and picoeukphytoplankton grew well at a low phosphate levels. In fact, there was no such environment with a low irradiance and a low phosphate levels in the maximum turbidity zone, so that phytoplankton bloom hardly occurred there. In addition, the results also showed that the growth periods of all three kinds of phytoplankton at intermediate phosphate levels were prolonged obviously, suggesting that the limitation of phytoplankton growth mainly reflected its growth period changes. Without irradiance, the addition of phosphate didn＇ t affect the release rates of phosphate with lineal increase and the growth rates of phytoplankton with exponential decrease, which showed that phosphate regeneration was faster in day than in night and the irradiance was a significant factor to affect phosphorous biogeochemical cycle in the Changjiang estuary.