Abstract
Predicting the effects of multiple global change stressors on microbial communities remains a challenge because of the complex interactions among those factors. Here, we explore the combined effects of major global change stressors on nutrient acquisition traits in marine phytoplankton. Nutrient limitation constrains phytoplankton production in large parts of the present-day oceans, and is expected to increase owing to climate change, potentially favouring small phytoplankton that are better adapted to oligotrophic conditions. However, other stressors, such as elevated pCO2, rising temperatures and higher light levels, may reduce general metabolic and photosynthetic costs, allowing the reallocation of energy to the acquisition of increasingly limiting nutrients. We propose that this energy reallocation in response to major global change stressors may be more effective in large-celled phytoplankton species and, thus, could indirectly benefit large-more than small-celled phytoplankton, offsetting, at least partially, competitive disadvantages of large cells in a future ocean. Thus, considering the size-dependent responses to multiple stressors may provide a more nuanced understanding of how different microbial groups would fare in the future climate and what effects that would have on ecosystem functioning.This article is part of the theme issue ‘Conceptual challenges in microbial community ecology’.
Highlights
Predicting the effects of multiple global change stressors on microbial communities remains a challenge because of the complex interactions among those factors
Looking at traits that are involved in potential phytoplankton responses to different global change stressors and determining how these traits are affected by those stressors, together with assessing potential trade-offs that may be involved, could help us improve the conceptual understanding of multiple stressor effects on different phytoplankton groups
We focus on how phytoplankton nutrient acquisition may be modified by elevated pCO2, warming and higher light availabilities, and what consequences this may have on oceanic ecosystems
Summary
Marine phytoplankton play a pivotal role in the oceanic carbon cycle and fuel the marine food web. To illustrate this complexity, we focus on how phytoplankton nutrient acquisition may be modified by elevated pCO2, warming and higher light availabilities, and what consequences this may have on oceanic ecosystems. Cells may reallocate energy and/or elements to enhance the uptake of a limiting resource, leading to higher nutrient uptake or growth affinities (figure 1b). Being small seems a good strategy to deal with nutrient depletion, as (absolute) nutrient requirements are proportional to size [25,57] Because of their high surface-to-volume ratio, small cells have higher growth and nutrient uptake affinities, and are less likely to become diffusion-limited [25,58,59,60]. The higher flexibility of larger phytoplankton species in response to direct and indirect effects of warming and elevated pCO2 may, at least partially, offset their competitive disadvantage in nutrient acquisition
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