Department of Biological Sciences and the Center for Freshwater Studies, University of Alabama, 2109 Bevill Building, Tuscaloosa, AL, 35487, USA.
School of Biological, Environmental, and Earth Sciences, University of Southern Mississippi, 118 College Dr. #5018, Hattiesburg, MS, 39402, USA.
Oecologia. 2021 Jan;195(1):187-198. doi: 10.1007/s00442-020-04821-7. Epub 2021 Jan 2.
Nutrient recycling by consumers can strongly impact nutrient availability for autotrophic and heterotrophic microbes, thus impacting functions such as primary production and decomposition. Filter-feeding freshwater mussels form dense, multispecies assemblages in aquatic ecosystems and have been shown to play a critical role in nutrient cycling. Mussel excretion can enhance benthic primary production and influence algal species composition. However, the role of mussels in brown or detritus-based food webs and species-specific differences has received considerably less attention. Here, using mesocosm experiments, we assessed how three species of freshwater mussels that occupy three different phylogenetic tribes influenced benthic algal accrual, ecosystem metabolism, cotton strip decomposition, leaf litter (Acer saccharum) decomposition, and litter-associated fungal biomass measured as ergosterol. Additionally, we measured mussel excretion and biodeposition rates and assessed the stoichiometry (C:N, C:P, and N:P) of the benthic algae, cotton strips, and leaf litter. In comparison to controls without mussels, generally, mussel treatments had higher benthic algal biomass composed of more diatoms, higher gross primary productivity and net ecosystem production rates, and higher cotton strip tensile strength loss, but there was not a difference in ecosystem respiration rates, leaf litter decomposition rates, or fungal biomass. Benthic algae had lower C:N and higher N:P in mussel treatment tanks and cotton strip C:N was lower in mesocosms with mussels. Our results suggest that nutrient regeneration by mussels most strongly regulates green food webs, with some impacts to brown food webs, suggesting that consumers have interactive effects on microbial functioning in freshwaters.
消费者的营养回收可以强烈影响自养和异养微生物的营养可用性，从而影响初级生产和分解等功能。滤食性淡水贻贝在水生生态系统中形成密集的多物种组合，并已被证明在营养循环中发挥关键作用。贻贝排泄可以增强底栖初级生产，并影响藻类物种组成。然而，贻贝在棕色或碎屑为基础的食物网以及特定物种差异中的作用受到的关注要少得多。在这里，我们使用中观实验评估了占据三个不同系统发育部落的三种淡水贻贝如何影响底栖藻类的积累、生态系统代谢、棉条分解、落叶（糖枫）分解以及用麦角固醇测量的与落叶相关的真菌生物量。此外，我们测量了贻贝排泄和生物沉积率，并评估了底栖藻类、棉条和落叶的化学计量（C:N、C:P 和 N:P）。与没有贻贝的对照相比，一般来说，贻贝处理具有更高的底栖藻类生物量，其中包含更多的硅藻，更高的总初级生产力和净生态系统生产力以及更高的棉条拉伸强度损失，但生态系统呼吸率、落叶分解率或真菌生物量没有差异。底栖藻类在贻贝处理罐中的 C:N 较低，N:P 较高，而在有贻贝的中观实验中，棉条的 C:N 较低。我们的结果表明，贻贝的营养再生最强烈地调节了绿色食物网，对棕色食物网有一些影响，这表明消费者对淡水微生物功能具有相互作用的影响。
