Biogeochemical impacts of phytoplankton community structure and their alteration by global change stressors

Background/Question/Methods

Phytoplankton are key players in the global carbon cycle, contributing about half of global primary productivity.  Phytoplankton functional groups have distinct impacts on other major biogeochemical cycles, such as nitrogen, silica and phosphorus.  Consequently, changes in phytoplankton community structure may significantly alter elemental cycling at local and global scales. We present several examples of a tight link between phytoplankton community structure and biogeochemistry and show how global change stressors modify phytoplankton biogeochemical impacts

Results/Conclusions

Using a more realistic model of competition between nitrogen-fixers and non-fixers that includes phosphorus costs of N-fixation, we show that different N:P supply ratios produce a diverse range of competitive outcomes that, in turn, impact environmental N and P concentrations.  Using physiological experiments and mechanistic modeling, we show that phytoplankton nutrient utilization strongly depends on temperature and, conversely, temperature preferences depend on the phytoplankton nutrient status. Our data compilation shows that temperature scaling of phytoplankton growth may differ across functional groups, thus potentially changing community dominance patterns.  Taken together, our results illustrate the links between phytoplankton physiology, community structure and biogeochemical processes under diverse conditions and suggest that global change may have profound impacts on biogeochemistry by altering phytoplankton community dynamics and functioning.