氮、磷供给比例对实验微藻群落结构的影响

The effect of N ∶ P supply ratios on experimental algal community structure

生态理论预测,生境筛选和物种竞争可能会联合影响生物群落结构.然而,通过实验手段检测两者对群落结构的影响作用,特别是两者的作用效果是否会随时间推移而发生改变的研究还十分有限.本研究构建了实验微藻群落系统,通过改变微藻生长发育所必须的2种限制性因子氮素和磷素的供给比例,对微藻的结构特征及各微藻组分的种群动态变化进行持续跟踪,并通过对各微藻进行单一培养的方式来获取相关的性状指数,用以反映各微藻的耐低氮或耐低磷能力,进而检验生境筛选和物种竞争对微藻群落的影响作用,以及两者作用效果随时间推移而发生的改变.结果表明,生境筛选和物种竞争对微藻群落结构的影响会随着时间的推移而发生变化:实验初期生境筛选和物种竞争的影响作用均较弱;实验中期生境筛选发挥着较为重要的作用,具体表现在水体中氮素和磷素的供给比例直接影响了具有不同耐低氮或耐低磷能力的微藻种群数量分布;而实验末期物种竞争发挥着较为关键的作用,其中纤细角星鼓藻成为绝对优势种,而部分微藻因为竞争排斥作用而从系统中消失.未来的研究应全面考虑不同的时序变化和空间结构下生境筛选和物种竞争对群落结构的综合影响作用.

Theoretically,environmental filtering and species competition should play important roles in affecting community structure.However,empirical studies that test the influence of environmental filtering and species competition over community structure,especially studies that address how the influence of these two factors varies with time are still limited.This study established artificial algal microcosms with five freshwater algal species,and the microcosms were then subjected to resource pulse supplies,with nitrogen and phosphomus as two limiting factors that would directly affect the growth and development of algal species.The dynamics of each component algal species were then tracked through the developmental stage of algal microcosms in order to better understand the influence of environmental filtering and species competition on algal community structure.Meanwhile,the growth traits of algal species were quantified when they were cultivated in monocultures to reflect their nitrogen stress tolerance or phosphorous tolerance.The results indicated that at the early stage,the influence of environmental filtering and species competition over algal community structure was relatively weak because all algal species could develop well with access to sufficient nutrient resources.At the middle stage,however,environmental filtering effect was dominant due to the fact that the abundance of algal species with different stress tolerances was significantly affected by the supply ratios of nitrogen to phosphorous.At the late stage,species competition played an essential role.One of the algal species,Staurastrum gracile,became the dominant species,whereas several inferior competitors went extinct due to competitive exclusion.Therefore,the relative importance of environmental filtering and species competition changed through time in our studied system.Future studies should take into account the effect of both temporal and spatial effect on the relative importance of environmental filtering and species competition during the course of community succession.