Department of River Ecology, Helmholtz Centre for Environmental Research-UFZ, Brückstrasse 3a, 39114, Magdeburg, Germany.
Workgroup Aquatic Chemical Ecology, University of Cologne, Zülpicherstrasse 47b, 50674, Cologne, Germany.
Sci Rep. 2021 Nov 3;11(1):21621. doi: 10.1038/s41598-021-00856-9.
Algal biofilms in streams are simultaneously controlled by light and nutrient availability (bottom-up control) and by grazing activity (top-down control). In addition to promoting algal growth, light and nutrients also determine the nutritional quality of algae for grazers. While short-term experiments have shown that grazers increase consumption rates of nutrient-poor algae due to compensatory feeding, nutrient limitation in the long run can constrain grazer growth and hence limit the strength of grazing activity. In this study, we tested the effects of light and phosphorus availability on grazer growth and thus on the long-term control of algal biomass. At the end of the experiment, algal biomass was significantly affected by light, phosphorus and grazing, but the interactive effects of the three factors significantly changed over time. At both high light and phosphorus supply, grazing did not initially reduce algal biomass, but the effect of grazing became stronger in the final three weeks of the experiment. Snail growth was enhanced by light, rather than phosphorus, suggesting that algal quantity rather than quality was the main limiting factor for grazer growth. Our results highlight the role of feedback effects and the importance of long-term experiments in the study of foodweb interactions.
溪流中的藻类生物膜同时受到光和养分供应（自上而下的控制）以及摄食活动（自下而上的控制）的控制。除了促进藻类生长外，光和养分还决定了藻类对摄食者的营养质量。虽然短期实验表明，由于补偿性摄食，摄食者会增加对营养贫乏藻类的消耗率，但从长远来看，养分限制会限制摄食者的生长，从而限制摄食活动的强度。在这项研究中，我们测试了光和磷供应对摄食者生长的影响，从而测试了藻类生物量的长期控制。在实验结束时，藻类生物量受到光、磷和摄食的显著影响，但三个因素的相互作用随时间显著变化。在高光和高磷供应的情况下，摄食最初并没有降低藻类生物量，但在实验的最后三周，摄食的影响变得更强。光而不是磷促进了蜗牛的生长，这表明藻类的数量而不是质量是限制摄食者生长的主要因素。我们的研究结果强调了反馈效应的作用以及长期实验在食物网相互作用研究中的重要性。
