Increases in temperature increase enzymatic activity, so one expects growth to also increase. However, this is not always the case. We show that when organisms are resource-limited, an increase in temperature can actually reduce growth, but these physiological effects do not directly translate into a community response.
Plankton communities respond to climate change either through direct effects of temperature or through changes in the physical environment. The former is commonly assumed to simply increase growth rate of organisms. However, it turns out that when resources are limiting, an increase in temperature can reduce growth.
Growth is governed by the intake of resources, synthesis of new biomass and maintenance costs. Unicellular plankton tend to acquire nutrients by diffusion, carbon through photosynthesis and both by prey ingestion. Yet, all these resource-acquiring processes increase less with temperature than synthesis of biomass and respiration. Therefore, if resource-limited, respiration responds faster to temperature than uptake of resources does, and therefore growth decreases as costs outweigh gains.
Nevertheless, these physiological effects of temperature do not necessarily translate into community response. The planktonic community is diverse, and turnover of species that are better adapted to environmental conditions is quick. This can dampen the predictions made through effects in physiology. In our paper, we show that climate change will enhance production of the community, but will also promote the dissolved pathway relative to the detrital pathway, strengthening the role of the microbial loop.
Read the paper here.
Camila Serra-Pompei, George I. Hagstrom, André W. Visser, Ken H. Andersen. Resource limitation determines temperature response of unicellular plankton communities. Limnol. Oceanogr. 2019
Image Credit: NASA