title: Joint effect of phosphorus limitation and temperature on alkaline phosphatase activity and somatic growth in Daphnia magna.
abstract: Alkaline phosphatase (AP) is a potential biomarker for phosphorus (P) limitation in zooplankton. However, knowledge about regulation of AP in this group is limited. In a laboratory acclimation experiment, we investigated changes in body AP concentration for Daphnia magna kept for 6 days at 10, 15, 20 and 25 °C and fed algae with 10 different molar C:P ratios (95-660). In the same experiment, we also assessed somatic growth of the animals since phosphorus acquisition is linked to growth processes. Overall, non-linear but significant relationships of AP activity with C:P ratio were observed, but there was a stronger impact of temperature on AP activity than of P limitation. Animals from the lowest temperature treatment had higher normalized AP activity, which suggests the operation of biochemical temperature compensation mechanisms. Body AP activity increased by a factor of 1.67 for every 10 °C decrease in temperature. These results demonstrate that temperature strongly influences AP expression. Therefore, using AP as a P limitation marker in zooplankton needs to consider possible confounding effects of temperature. Both temperature and diet affected somatic growth. The temperature effect on somatic growth, expressed as the Q (10) value, responded non-linearly with C:P, with Q(10) ranging between 1.9 for lowest food C:P ratio and 1.4 for the most P-deficient food. The significant interaction between those two variables highlights the importance of studying temperature-dependent changes of growth responses to food quality.
authors.affiliation: Department of Biology, University of Oslo, Post Office Box 1027, Blindern, 0316 Oslo, Norway. marcin.wojewodzic@bio.uio.no
authors.forename: Marcin W
authors.initials: MW
authors.lastname: Wojewodzic
authors.forename: Marcia
authors.initials: M
authors.lastname: Kyle
authors.forename: James J
authors.initials: JJ
authors.lastname: Elser
authors.forename: Dag O
authors.initials: DO
authors.lastname: Hessen
authors.forename: Tom
authors.initials: T
authors.lastname: Andersen
mesh_terms: D000469:Alkaline Phosphatase / Q000378:metabolism*; D000818:Animals; D002244:Carbon / Q000378:metabolism; D003621:Daphnia / Q000254:growth & development / Q000378:metabolism*; D009584:Nitrogen / Q000378:metabolism; D016226:Phosphorus, Dietary / Q000378:metabolism*; D013696:Temperature; D013997:Time Factors; D015048:Zooplankton / Q000254:growth & development / Q000378:metabolism
chemical_list: D016226:Phosphorus, Dietary; D002244:Carbon; D000469:Alkaline Phosphatase; D009584:Nitrogen