Kilroy Cathy, Bothwell Max
National Institute of Water & Atmospheric Research Ltd., Christchurch 8440, New ZealandEnvironment Canada, Pacific Biological Station, Nanaimo, British Columbia, Canada.
J Phycol. 2011 Oct;47(5):981-9. doi: 10.1111/j.1529-8817.2011.01029.x. Epub 2011 Aug 9.
Blooms of the freshwater stalked diatom Didymosphenia geminata (Lyngb.) M. Schmidt in A. Schmidt typically occur in oligotrophic, unshaded streams and rivers. Observations that proliferations comprise primarily stalk material composed of extracellular polymeric substances (EPS) led us to ask whether or not the production of excessive EPS is favored under nutrient-limited, high-light conditions. We conducted experiments in outdoor flumes colonized by D. geminata using water from the oligotrophic, D. geminata-affected Waitaki River, South Island, New Zealand, to determine the relationship between D. geminata stalk length, cell division rates, and light intensity under ambient and nutrient-enriched conditions. Stalk lengths were measured in situ, and cell division rates were estimated as the frequency of dividing cells (FDC). FDC responded positively to increasing light intensity and to nutrient additions (N+P and P). Under ambient conditions, stalk length increased as light level increased except at low ambient light levels and temperature. Nutrient enrichment resulted in decreased stalk length and negative correlations with FDC, with this effect most evident under high light. Our results are consistent with the hypothesis that extensive stalk production in D. geminata occurs when cell division rates are nutrient limited and light levels are high. Thus, photosynthetically driven EPS production in the form of stalks, under nutrient-limited conditions, may explain the development of very high biomass in this species in oligotrophic rivers. The responses of FDC and stalk length under nutrient-replete conditions are also consistent with occurrences of D. geminata as a nondominant component of mixed periphyton communities in high-nutrient streams.
淡水具柄硅藻双眉藻（Didymosphenia geminata (Lyngb.) M. Schmidt in A. Schmidt）水华通常出现在贫营养、无遮蔽的溪流和河流中。观察发现水华主要由细胞外聚合物（EPS）组成的柄状物质构成，这促使我们思考在营养有限、高光条件下，过量EPS的产生是否受到青睐。我们利用来自新西兰南岛受双眉藻影响的贫营养怀塔基河的水，在室外水槽中进行了双眉藻定殖实验，以确定在环境条件和营养丰富条件下，双眉藻柄长、细胞分裂率与光照强度之间的关系。原位测量柄长，并将细胞分裂率估计为分裂细胞频率（FDC）。FDC对光照强度增加和添加营养物质（N + P和P）呈正响应。在环境条件下，除了低环境光照水平和温度外，柄长随光照水平增加而增加。营养物质富集导致柄长缩短，并与FDC呈负相关，这种效应在高光条件下最为明显。我们的结果与以下假设一致：当细胞分裂率受到营养限制且光照水平较高时，双眉藻会大量产生柄。因此，在营养有限的条件下，以柄的形式通过光合作用驱动的EPS产生，可能解释了该物种在贫营养河流中形成非常高生物量的原因。FDC和柄长在营养充足条件下的响应也与双眉藻作为高营养溪流中混合周丛生物群落的非优势成分的出现情况一致。
