氮饥饿细基江蓠繁枝变型和孔石莼氨氮的吸收动力学特征

以氮饥饿海藻为材料,采用多瓶法和干扰法相结合的技术,测定两种海藻在不同起始浓度下不同时间间隔内的NH₄+吸收率,对不同阶段的吸收率进行非线性回归分析,结果表明它们均符合饱和吸收动力学特征.最大吸收率和半饱和常数均随着吸收时间的延长而降低.在整个吸收过程中,吸收曲线的初始斜率变化不大,这表明在低浓度下的吸收率不受短时间快吸收的影响而保持相对的稳定.同时两种海藻相比,在相应时间内的吸收动力学参数不同,孔石莼的最大吸收率、半饱和常数和初始斜率均大于细基江蓠繁枝变型.处于氮饥饿状态的两种海藻对NH₄+-N的吸收存在以下3个时相:(1)起始短期的快吸收阶段;(2)内部营养盐浓度控制的吸收阶段;(3)外界营养盐浓度控制的吸收阶段.

Nature of NH4+ uptake kinetics of Gracilaria tenuistipitata var. liui and Ulva pertusa.

Nonlinear time courses of NH₄+ depletion from the mediumimply that the rate limiting step for ammonium uptake changes over time.NH₄+ uptake by the starved macroalgae Gracilaria tenuistipitata var.liui and Ulva pertusa were studied from the depletion of NH₄+ after single additions of NH₄+ to cultures.The experiments were carried out by the combination of two different experimental setups——the "multiple flask" and the "perturbation" technologies.Uptake rate was nonlinear with time and decreased in V_m as incubation time increased (i.e., V_max0~15, V_max15~30, V_max30~60, V_max90~120 and V_max120~240).The corresponding maximum uptake rates, the half saturation constants and the V_max/K_s (a) ratios (the affinity for ammonium uptake at low substrate concentrations) in U.pertusa were all higher than those of in G.tenuistipitata.Three distinct succeeding phases of NH₄+ uptake were identified: (1) Surge uptake phase, (2) internally controlled uptake phase, and (3) externally controlled uptake phase.The nature of NH₄+ uptake rate of decline is species specific and may be due to feedback inhibition from the filling of an internal pool.