Co-limitation by N and P Characterizes Phytoplankton Communities Across Nutrient Availability and Land Use

• Published in: Ecosystems (New York) Vol. 23; no. 6; pp. 1121 - 1137
• Main Authors: Bratt, A. R., Finlay, J. C., Welter, J. R., Vculek, B. A., Van Allen, R. E.
• Format: Journal Article
• Language: English
• Published: New York Springer Science + Business Media 01.09.2020; Springer US; Springer; Springer Nature B.V
• Subjects: Agricultural management; Algae; Aquatic ecosystems; Availability; Biomedical and Life Sciences; Ecology; Environmental Management; Fixation; Fresh water; freshwater; Freshwater lakes; Geoecology/Natural Processes; Human influences; humans; Hydrology/Water Resources; Lakes; Land use; Life Sciences; metabolism; Minnesota; Nitrogen; Nitrogen fixation; Nitrogenation; Nutrient availability; Nutrient concentrations; Nutrient status; Original Papers; Perturbation; Phosphorus; Physiological aspects; Phytoplankton; Plankton; Plant Sciences; Primary production; primary productivity; Resource availability; Strategic management; Suburban areas; summer; total nitrogen; Urban agriculture; Water circulation; Water column; watersheds; Zoology; Minnesota; nutrient limitation; phytoplankton; land use; co-limitation; biogeochemical cycles; phosphorus paradigm
• DOI: 10.1007/s10021-019-00459-6
• ISSN: 1432-9840

Historically, freshwater lakes have been widely assumed to be singly limited by phosphorus (P) because the dominant paradigm assumes that nitrogen fixation (N₂ fixation) will compensate for any nitrogen (N) deficits. However, a growing body of evidence demonstrates that primary producer response to nutrient manipulation most frequently indicates co-limitation by N and P. Differences in N and P supply ratio have been shown to influence the identity and severity of nutrient limitation, but whether N and P concentration and the ratio of N to P concentrations can explain the frequency of co-limitation in aquatic primary producer assemblages remains unclear, especially in ecosystems subject to human perturbation that strongly increase nutrient availability. We determined how resource availability influences nutrient limitation by N and P of phytoplankton primary production across 12 lakes in Minnesota that vary in watershed land use and lake nutrient levels. We measured epilimnetic lake metabolism and indicators of N₂ fixation to evaluate their influence on nutrient limitation status of planktonic algal assemblages. Despite large differences in land use (agricultural, urban, and suburban) and water column N and P availability, planktonic algal response to nutrient manipulation was consistently characterized by co-limitation by N and P across years and months. Neither P availability (as concentrations of total and inorganic forms) nor N₂-flux rate predicted responses to nutrient additions. N availability significantly influenced responses of phytoplankton to nutrient additions across years, but this effect was small. The ratio of total N to total P significantly influenced the response to single additions of N and P (these effects were negative and positive, respectively) in summer 2013. Importantly, higher lake primary production and heterocyte count (number of nitrogen fixing cells) were also associated with a stronger, positive response to N + P addition. Overall, these data suggest that planktonic algal assemblages are predominantly characterized by co-limitation by N and P despite large and diverse human impacts on nutrient inputs. Additionally, higher rates of primary production increase the likelihood of co-limitation. Together, these results further support the paradigm shift toward dual management of N and P in aquatic ecosystems.