TY  - JOUR
A1  - Mehner, T.
A1  - Attermeyer, Katrin
A1  - Brauns, Mario
A1  - Brothers, Soren M.
A1  - Diekmann, J.
A1  - Gaedke, Ursula
A1  - Grossart, Hans-Peter
A1  - Koehler, J.
A1  - Lischke, Betty
A1  - Meyer, N.
A1  - Scharnweber, Inga Kristin
A1  - Syvaranta, J.
A1  - Vanni, M. J.
A1  - Hilt, S.
T1  - Weak Response of Animal Allochthony and Production to Enhanced Supply of
Terrestrial Leaf Litter in Nutrient-Rich Lakes
JF  - Ecosystems
N2  - Ecosystems are generally linked via fluxes of nutrients and energy across their boundaries. For example, freshwater ecosystems in temperate regions may receive significant inputs of terrestrially derived carbon via autumnal leaf litter. This terrestrial particulate organic carbon (POC) is hypothesized to subsidize animal production in lakes, but direct evidence is still lacking. We divided two small eutrophic lakes each into two sections and added isotopically distinct maize litter to the treatment sections to simulate increased terrestrial POC inputs via leaf litter in autumn. We quantified the reliance of aquatic consumers on terrestrial resources (allochthony) in the year subsequent to POC additions by applying mixing models of stable isotopes. We also estimated lake-wide carbon (C) balances to calculate the C flow to the production of the major aquatic consumer groups: benthic macroinvertebrates, crustacean zooplankton, and fish. The sum of secondary production of crustaceans and benthic macroinvertebrates supported by terrestrial POC was higher in the treatment sections of both lakes. In contrast, total secondary and tertiary production (supported by both autochthonous and allochthonous C) was higher in the reference than in the treatment sections of both lakes. Average aquatic consumer allochthony per lake section was 27-40%, although terrestrial POC contributed less than about 10% to total organic C supply to the lakes. The production of aquatic consumers incorporated less than 5% of the total organic C supply in both lakes, indicating a low ecological efficiency. We suggest that the consumption of terrestrial POC by aquatic consumers facilitates a strong coupling with the terrestrial environment. However, the high autochthonous production and the large pool of autochthonous detritus in these nutrient-rich lakes make terrestrial POC quantitatively unimportant for the C flows within food webs.
KW  - stable isotopes
KW  - terrestrial subsidy
KW  - carbon budget
KW  - ecological efficiency
KW  - benthic food web
KW  - pelagic food web
Y1  - 2016
U6  - https://doi.org/10.1007/s10021-015-9933-2
SN  - 1432-9840
SN  - 1435-0629
VL  - 19
SP  - 311
EP  - 325
PB  - Springer
CY  - New York
ER  - 
TY  - JOUR
A1  - Lukas, Marcus
A1  - Wacker, Alexander
T1  - Constraints by oxygen and food quality on carbon pathway regulation: a co-limitation study with an aquatic key herbivore
JF  - Ecology : a publication of the Ecological Society of America
N2  - In food webs, herbivores are often constrained by low food quality in terms of mineral and biochemical limitations, which in aquatic ecosystems can co-occur with limited oxygen conditions. As low food quality implies that carbon (C) is available in excess, and therefore a regulation to get rid of excess C is crucial for the performance of consumers, we examined the C pathways (ingestion, feces release, excretion, and respiration) of a planktonic key herbivore (Daphnia magna). We tested whether consumer C pathways increase due to mineral (phosphorus, P) or biochemical (cholesterol and fatty acid) limitations and how these regulations vary when in addition oxygen is low. Under such conditions, at least the capability of the upregulation of respiration may be restricted. Furthermore, we discussed the potential role of the oxygen-transporting protein hemoglobin (Hb) in the regulation of C budgets. Different food quality constraints led to certain C regulation patterns to increase the removal of excess dietary C: P-limited D. magna increased excretion and respiration, while cholesterol-limited Daphnia in addition upregulated the release of feces. In contrast, the regulative effort was low and only feces release increased when D. magna was limited by a long-chain polyunsaturated fatty acid (eicosapentaenoic acid, EPA). Co-limiting oxygen did not always impact the discharge of excess C. We found the food-quality-induced upregulation of respiration was still present at low oxygen. In contrast, higher excretion of excess C was diminished at low oxygen supply. Besides the effect that the Hb concentration increased under low oxygen, our results indicate a low food-quality-induced increase in the Hb content of the animals. Overall, C budgeting is phenotypically plastic towards different (co-) limiting scenarios. These trigger specific regulation responses that could be the result of evolutionary adaptations.
KW  - carbon budget
KW  - carbon stoichiometry
KW  - cholesterol
KW  - co-limitation
KW  - Daphnia
KW  - EPA
KW  - hemoglobin
KW  - oxygen
KW  - phosphorus
KW  - polyunsaturated fatty acid
KW  - zooplankton
Y1  - 2014
SN  - 0012-9658
SN  - 1939-9170
VL  - 95
IS  - 11
SP  - 3068
EP  - 3079
PB  - Wiley
CY  - Washington
ER  -