Berggren Martin, Bergström Ann-Kristin, Karlsson Jan
Department of Physical Geography and Ecosystem Science, Lund University, Lund, Sweden.
Department of Ecology and Environmental Science, Umeå University, Umeå, Sweden.
PLoS One. 2015 Mar 12;10(3):e0120575. doi: 10.1371/journal.pone.0120575. eCollection 2015.
Seasonal patterns in assimilation of externally produced, allochthonous, organic matter into aquatic food webs are poorly understood, especially in brown-water lakes. We studied the allochthony (share biomass of terrestrial origin) in cladoceran, calanoid and cyclopoid micro-crustacean zooplankton from late winter to fall during two years in a small humic lake (Sweden). The use of allochthonous resources was important for sustaining a small population of calanoids in the water column during late winter. However, in summer the calanoids shifted to 100% herbivory, increasing their biomass several-fold by making efficient use of the pelagic primary production. In contrast, the cyclopoids and cladocerans remained at high levels of allochthony throughout the seasons, both groups showing the mean allochthony of 0.56 (range in mean 0.17-0.79 and 0.34-0.75, for the respective group, depending on model parameters). Our study shows that terrestrial organic matter can be an important resource for cyclopoids and cladocerans on an annual basis, forming a significant link between terrestrial organic matter and the higher trophic levels of the food web, but it can also be important for sustaining otherwise herbivorous calanoids during periods of low primary production in late winter.
外界产生的、异源的有机物质被同化进入水生食物网的季节性模式仍知之甚少，尤其是在褐水湖中。我们在瑞典一个小型腐殖质湖中，对两年间从冬末到秋季的枝角类、哲水蚤类和剑水蚤类微型甲壳动物浮游动物中的异源物质（陆地来源生物量的占比）进行了研究。在冬末，利用异源资源对于维持水柱中少量的哲水蚤类种群很重要。然而，在夏季，哲水蚤类转变为完全食草，通过有效利用浮游初级生产使其生物量增加了几倍。相比之下，剑水蚤类和枝角类在整个季节中保持着较高水平的异源物质占比，两组的平均异源物质占比均为0.56（根据模型参数，各自组的平均范围为0.17 - 0.79和0.34 - 0.75）。我们的研究表明，陆地有机物质在全年都可能是剑水蚤类和枝角类的重要资源，在陆地有机物质与食物网较高营养级之间形成了重要联系，但在冬末初级生产较低的时期，它对于维持原本食草的哲水蚤类也可能很重要。
