title: Potassium enrichment stimulates the growth and reproduction of a clone of Daphnia dentifera.
abstract: Nutrient limitation commonly constrains organisms in natural ecosystems. Typically, ecologists focus on limitation by N and P. However, other nutrients can limit growth or reproduction. Here we focus on K limitation of invertebrate consumers (Daphnia dentifera) and phytoplankton in freshwater lakes. All organisms require K for several metabolic processes. In freshwater, K could limit growth because low external concentrations can increase the energetic costs of accumulating K. Furthermore, in a study linking K to disease, we previously found that K enrichment of water from one low-K lake stimulated the growth and reproduction of Daphnia. Here we test whether K could limit the production of Daphnia and phytoplankton across lakes and years. We repeated a life table experiment using water collected from a low-K lake during a different year. K again stimulated Daphnia reproduction. We also enriched water from 12 lakes with K or P and measured short-term growth of Daphnia and the resident algal community. Both nutrients increased Daphnia growth in five lakes. However, only P enhanced algal production. P stimulation of Daphnia positively correlated with algal quantity and the ratio of C to P in seston. However, K stimulation of Daphnia was not correlated with these factors or the background concentration of K. Thus, this study shows repeatable K-limited animal physiology in nature. Further, we can exclude the hypothesis that K stimulates Daphnia indirectly by enhancing algal production. These patterns call for future physiological studies to uncover the mechanistic basis of K limitation in natural systems.
authors.affiliation: Department of Biology, Indiana University, Bloomington, IN, USA, civitello@usf.edu.
authors.forename: David J
authors.initials: DJ
authors.lastname: Civitello
authors.forename: Jessica L
authors.initials: JL
authors.lastname: Hite
authors.forename: Spencer R
authors.initials: SR
authors.lastname: Hall
mesh_terms: D000818:Animals; D003621:Daphnia / Q000254:growth & development* / Q000502:physiology; D017753:Ecosystem; D060106:Lakes / Q000737:chemistry*; D010839:Phytoplankton / Q000254:growth & development; D011188:Potassium / Q000032:analysis / Q000378:metabolism*; D012098:Reproduction
chemical_list: D011188:Potassium
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