低盐在短时间内对绿潮浒苔(Ulva prolifera)氮磷吸收的动态影响

THE IMPACT OF A SHORT LOWERED SALINITY ON NUTRIENT UPTAKE BY GREEN TIDE-FORMING ALGA ULVA PROLIFERA

我国黄海出现的绿潮发源于黄海南部苏北辐射沙洲紫菜养殖区,苏北沙洲区濒临的沿岸河网众多,来自沿岸径流的淡水携带大量氮磷等营养盐间歇性入海,导致海水的富营养化并伴随着盐度的周期性波动。本研究通过模拟实验研究低盐度(15和5)对浒苔吸收氮盐(NO_3~–-N和NH_4^+-N)和磷盐(PO_4^(3–)-P)的影响,主要发现:与盐度30相比,在低盐度(15和5)时,浒苔对NO_3~–-N的1h最大吸收速率(V_(max))和亲和力(V_(max)/Ks)分别提高280%和350%左右,半饱和常数(Ks)下降15%左右,并能够维持对NO_3~–-N的高效吸收(24h);盐度15和5时,浒苔对NH_4^+-N的1h最大吸收速率(V_(max))分别提高40%和200%,亲和力(V_(max)/Ks)分别提高20%和180%, Ks分别提高15%和30%,但是盐度降低对NH_4^+-N的长效吸收产生负面影响,甚至在盐度5条件下出现吸收高浓度NH_4^+-N后再释放的现象;与盐度30相似,盐度15条件下浒苔能够快速吸收PO_4^(3–)-P,而盐度5则导致藻细胞内的PO_4^(3–)-P在早期阶段快速流失,并在后期不能有效吸收PO_4^(3–)-P。本实验的结果表明,降低盐度有利于浒苔对氮源的快速吸收,在盐度15下浒苔能够实现对硝酸盐和磷盐的高效吸收。

Green tides in the Yellow Sea were found originated in the Pyropia cultivation region of Subei Shoal,northern Jiangsu,China,where many coastal rivers flood into the sea and bring a short and large amount of nutrients including nitrogen and phosphorus.We studied the dynamic change in the uptake of nitrate,ammonium,and phosphate by green tide-forming alga Ulva prolifera under a short and low salinity impact.Three salinity levels at 30,15,and 5 were simulated.The maximum uptake rate(Vmax),the half-saturation constant Ks,and the affinity(Vmax/Ks)were used.The results show that,compared those of salinity 30,those of low salinities at 15 and 5 showed considerable enhancement in terms of nutrient absorption and affinity.For examples,the maximum uptake rate and the affinity to NO3–-N at salinities 15 and 5 in 1h enhanced about 280%and 350%,respectively,and the half-saturation constant decreased by about 15%,which resulted in a continuous efficient uptake of nitrate in 24h.At salinities 15 and 5,the maximum uptake rate of NH4+-N increased by 40%and 200%,the affinity increased by 20%and 180%,and the half-saturation constant(Ks)increased by 15%and 30%,respectively.However,the short lowered salinity resulted in an absorption delay of a long period,and at salinity 5,the U.prolifera thalli could even take high-concentration NH4+-N first and then release it.At salinity 15,U.prolifera could quickly uptake phosphate(PO4 3–-P),which is very similar to that at salinity 30,while at salinity 5,the algae could release phosphate from cells at the early growth stage,causing the inability of absorbing phosphate in later growth stages.Therefore,a lower salinity could benefit U.prolifera for quick uptake of nitrogen sources.Specifically,at salinity 15,the algae could absorb both NO3–-N and PO4 3–-P in high efficiency in response to a suddenly reduced salinity.