N-limited consumer growth and low nutrient regeneration N:P ratios in lakes with low N deposition

Sammanfattning

Nutrient limitation of primary producers and their consumers can have a large influence on ecosystem productivity. The nature and strength of nutrient limitation is driven both by external factors (e.g., nutrient loading) and internal processes (e.g., consumer-driven nutrient regeneration). Here we present results from a field study in 10 low productive headwater lakes in northern subarctic Sweden, where nitrogen (N) deposition is low and phytoplankton is primarily N-limited. We assessed the carbon:nitrogen:phosphorus (C:N:P) stoichiometry of seston and zooplankton and estimated the N:P ratio of consumer-driven nutrient regeneration. Based on stoichiometric models, the estimated elemental imbalances between seston and zooplankton suggest that zooplankton were mainly N-limited and regenerated nutrients with low N:P ratios (median 11.9, atomic ratio). The predicted N:P regeneration ratios were consistent with results from phytoplankton nutrient limitation bioassays in mid-summer, i.e., the N:P regeneration was predicted to be low when phytoplankton were N-limited, and high when phytoplankton were P-limited. During other seasons, when water discharge was high, nutrient loading from the surrounding catchments apparently had the strongest effect on phytoplankton nutrient limitation. We propose that lakes with higher N:P ratios than the open ocean is an effect of N deposition, that N-limitation of consumers and phytoplankton is further enhanced by low nutrient regeneration N:P ratios, and that in the absence of N deposition, lake and ocean N:P stoichiometry are similar.

Nyckelord

consumer driven nutrient cycling; ecological stoichiometry; nitrogen; nutrient limitation; phosphorus; phytoplankton; zooplankton

Publicerad i

Ecosphere
2015, volym: 6, nummer: 1, artikelnummer: 9
Utgivare: ECOLOGICAL SOC AMER

SLU författare

• Vrede, Tobias

  • Institutionen för vatten och miljö, Sveriges lantbruksuniversitet
    

UKÄ forskningsämne

Ekologi

Publikationens identifierare

• DOI: https://doi.org/10.1890/ES14-00333.1

Permanent länk till denna sida (URI)

https://res.slu.se/id/publ/76160