铁对浮游植物吸收营养盐的围隔实验初步研究

IRON IMPACT ON PHYTOPLANKTON NUTRIENTS UPTAKE IN MESOCOSM

利用围隔实验初步研究了铁的加入对浮游植物吸收营养盐的影响。结果表明,春季向黄海天然水体中进行单纯的DIN和PO4-P加富并不能明显地促进浮游植物的生长(M2与M1相比),在营养盐加富的条件下铁的加入则能够对浮游植物的生长起到明显地促进作用(M3、M4与M2相比);铁的加入能够明显提高浮游植物对DIN和PO4-P的吸收利用率。加铁围隔M3和M4中浮游植物对DIN的吸收利用率分别为59%和45%,分别比M2提高了9倍和6.5倍;对PO4-P的吸收利用率分别为88%和86%,均比M2提高了3.2倍。M3和M4中浮游植物对氮的平均吸收速率分别是M1的2倍和M2的1.5倍;对磷的平均吸收速率以M3中最高,达到了其他围隔袋的2倍之多。铁的加入能够提高浮游植物对氮的平均吸收速率;对于磷来说,低浓度(10-2μmol/L)添加铁似乎对其吸收速率无甚影响,但是添加10-1μmol/L的铁能够明显的促进浮游植物对磷的吸收速率。铁的加入能够明显降低浮游植物体内的氮磷比,且这种响应非常敏感。

A research on possible iron effect on phytoplankton uptake of nutrients was conducted in mesocosm placed in the Yellow Sea （35.6°N, 122.3′E） in the condition same to the ambient natural ocean. The experimental device was attached at the rear of R/V Dongfanghong2 from March 24 to April 3, 2005, during which water samples for measurement of dissolved oxygen （DO）, dissolved inorganic nutrients （PO4-P, NO3-N, SiO3-Si, NH4-N and NO2-N）, particulate nitrogen （PN）, particulate phosphorus （PP）, and chlorophyll-a were collected at 8：00 and 18：00 daily in four units from M1 to M4 （M1 was the blank without adding anything and M2 was the blank having nutrients added） in different nutrient concentrations. Samples then were treated and measured against standard procedures for determination on the utilization of DIN and PO4-P by phytoplankton, average uptake rates of DIN and PO4-P, and ratios of DIN/P and PN/PP in the mesocosm water and phytoplankton. The results show that, the growth of phytoplankton was not enhanced significantly by adding DIN and PO4-P only into the natural Yellow Sea water （compared with M1 and M2）. However, in the case of nutrients satiation （M2）, adding nanomoler iron promoted obviously the phytoplankton growth and nutrient utilization： the DIN utilization in units M3 and M4 was boosted up by 59% and 45%, which was 9 and 6.5 times of the control unit M2, respectively. Similarly, the utilization of PO4-P in units M3 and M4 was 88% and 86%, respectively, over 3 times of the control. The average DIN uptake rate in units M3 and M4 was twice over that of M1, and 1.5 times over M2, and the average uptake rate of PO4-P in M3 approximately doubled those of other units. Therefore, adding iron enhanced the uptake of N. In terms of P uptake, adding high concentration of iron at 0.1 μmol/L clearly improved the P uptake, Therefore, adding Fe into the water can effectively reduce the N/P ratio in the phytoplankton cells in a very sensitive way.