龙须菜(Gracilaria lemaneiformis)在营养限制胁迫后对NH_4-N的超补偿吸收研究

NH_4-N OVER-COMPENSATORY UPTAKE OF GRACILARIA LEMANEIFORMIS UNDER THE STRESS OF NUTRIENTS DEFICIENCY

采用营养限制胁迫处理的方法,研究龙须菜对NH4N的超补偿吸收现象。龙须菜在低营养限制胁迫(饥饿)下培养10天后,恢复营养盐培养3天,测定其对NH4N吸收速率。N吸收实验结果表明,对NH4N(采用靛酚蓝分光光度法测定)表现出较强的超补偿吸收能力。与持续正常培养的对照组和持续受高浓度营养盐胁迫的处理组比较,各组在培养第一天时对NH4N的吸收速率差异明显,饥饿处理组最高为17.73μmol/(g·h),对照组最高为12.25μmol/(g·h),高营养盐处理组最高只有6.12μmol/(g·h)。随着培养时间的推移,对照组与处理组之间的差异逐渐减小,培养到第三天时吸收速率趋于一致。而各组对NO3N(采用锌镉还原萘乙二胺分光光度法测定)的吸收速率都很小,最高为饥饿处理组只有1.49μmol/(g·h),说明龙须菜优先选择吸收NH4N。实验结束后称重发现对照组、饥饿处理组和饱和组生长率(SGR)分别为5.85%、5.44%、5.02%,ANOVA方差分析表明,三者存在显著差异(P=0.0046<0.05),证实大型海藻也存在超补偿生长的现象。

Over-compensatory growth is a common phenomenon in some higher animals and plants. Research on compensatory growth has covered ruminant animal, aquatic animal, higher plant and micro-algae. However, a few were done on macro-algae compensatory growth and ammonium over-compensatory uptake. In this paper, Gracilaria lemaneiformis was used as experimental material for the study of NH_4-N over-compensatory uptake under laboratory conditions. G.lemaneiformis was thoroughly cleaned, free of epibiotics carefully removed, and cultured in beakers in an illuminating incubator under 22℃, 4500lx, L:D 14/10, 30 salinity and pH 8.0. The experiments included two periods. Firstly, G.lemaneiformis was cultured for 10 days under the condition of nutrients stress, i.e. nutrients deficiency and nutrients enrichment (PES culture medium), with fresh water one as the control. Secondly, the nutrients stress was lifted; the treated and the control were simultaneously cultured for another 3 days under the same nutrients supply with daily medium change. The experiments were done in 450ml beakers with 1.2g G.lemaneiformis and 400ml PES medium, and the concentration of NH_4-N, NO_3-N, PO_4-P, was 100, 280, and 72μmol/L respectively. Triplicate were set for each group. During the experiment, the NH_4-N, NO_3-N uptake rate were measured periodically. After subject to the nutrients deficiency, G.lemaneiformis showed a strong ability of NH_4-N uptake. The uptake rate of NH_4-N of the starved group, the control group and the fed group, was 17.73, 12.25, and 6.12μmol/(g·h), respectively. The starved had the highest uptake rate of NH_4-N but its highest uptake rate of NO_3-N was only 1.49μmol/ (g·h), much smaller than that of NH_4-N, indicating that G.lemaneiformis assimilated NH_4-N first. As a result, the concentration of NO_3-N in the beakers was 3 times higher of the NH_4-N. As the culture time proceeded, difference between the treated and the control decreased gradually and finally were equivalent. The special growth rate (SGR) in the group of the starved, the control and the fed was 5.85%, 5.44% , and 5.02% respectively. The difference of the growth rate between the treated and the control was significant (P=0.0046<0.05). After 10 days of nutrients deficiency, there was a short phase of rapid NH_4-N uptake demonstrating over-compensatory growth. Thus, NH_4-N over-compensatory uptake of G.lemaneiformis could be used as guidance for cultivation. Moreover, G.lemaneiformis have very high productivity and ability of absorbing large quantities of N. It is believed that G.lemaneiformis cultivation in large scale is a good solution to eutrophication in coastal waters.