微型浮游动物摄食实验——稀释法中浮游植物负生长的可能原因分析

Negative phytoplankton growth rates in dilution experiments and the possible causes

稀释法(dilution technique)是研究微型浮游动物摄食和浮游植物生长的常用方法之一,负值浮游植物生长率是稀释实验中常见的现象。分析了造成负值生长率出现的因素,以及这些因素对实验结果的影响,并提出了防止不利影响产生的措施。负值生长率的出现不能简单地视为实验失败的标志,培养光照和温度条件、取样误差、无颗粒水污染、营养盐污染和限制等都可能造成负生长率的出现,且对实验结果的影响不同。同时,根据实验结果,演示浮游植物光适应、取样误差、无颗粒水污染和加富营养盐对稀释实验的影响。结果显示,光照条件可以改变细胞色素含量,且不同浮游植物类群对光照条件的响应不同,从而导致基于色素分析的稀释实验结果出现误差;取样混合不均,可造成取值偏低,导致浮游植物生长率估值偏低,甚至为负值,但可能不影响对摄食率的估算。另外,实验污染(无颗粒水和加富营养盐污染)往往会抑制浮游植物生长,甚至造成浮游植物死亡。因此,培养条件模拟和人为干扰控制是稀释实验成功的关键。

Dilution technique is one the most commonly-used methods for studies of microzooplankton grazing and phytoplankton growth. Negative phytoplankton growth rates were usually observed in dilution experiments. We reviewed the factors may accounting for these negative values, and analyzed their impact on the results of dilution experiments. Measures can avoid the adverse effects of these factors were reviewed and analyzed. We conclude that it is not reasonable to simply take the negative phytoplankton growth rate as the failure symbol of dilution experiments. A lot of factors including the light and temperature regimes during incubation, sampling error, contamination of particle-free water and the added nutrients, and nutrient limitation can lead to the negative rates of phytoplankton growth, and impact the results of dilution experiments differently. Simultaneously, we demonstrate the effects of phytoplankton photo-acclimation, sampling error, contamination of particle-free water, and nutrient enrichment on dilution experiments based on our experiments. The results indicate that change of light conditions can lead to the changing of cellular pigment content of phytoplankton, and specific groups of phytoplankton responded differently, thus lead to the underestimation or overestimation of dilution experiment results based on pigment analysis; insufficient mixing before pigment sampling may cause the underestimation of the phytoplankton biomass afterincubation, which lead to the underestimation of phytoplankton growth rate （even negative values）, but may play no effect on the estimation of microzooplankton grazing rate; in addition, contamination from the added nutrients or particle-free water may inhibit phytoplankton growth, and even lead to phytoplankton death. In a word, the simulation of incubation conditions, and the control of man-made disturbance are critical factors for the success of the dilution experiment.