03381nas a2200409 4500008004100000245007100041210006900112300000900181490000700190520222500197100001902422700001902441700002002460700002002480700002102500700002002521700002602541700001902567700001702586700002102603700001402624700001802638700001702656700001902673700002202692700001402714700002102728700002102749700002002770700001302790700001802803700001702821700001902838700002102857700002002878856007302898 2017 eng d00aDrivers of nitrogen transfer in stream food webs across continents0 aDrivers of nitrogen transfer in stream food webs across continen a30550 v983 a
Studies of trophic-level material and energy transfers are central to ecology. The use of isotopic tracers has now made it possible to measure trophic transfer efficiencies of important nutrients and to better understand how these materials move through food webs. We analyzed data from thirteen 15N-ammonium tracer addition experiments to quantify N transfer from basal resources to animals in headwater streams with varying physical, chemical, and biological features. N transfer efficiencies from primary uptake compartments (PUCs; heterotrophic microorganisms and primary producers) to primary consumers was lower (mean 11.5%, range <1% to 43%) than N transfer efficiencies from primary consumers to predators (mean 80%, range 5% to >100%). Total N transferred (as a rate) was greater in streams with open compared to closed canopies and overall N transfer efficiency generally followed a similar pattern, although was not statistically significant. We used principal component analysis to condense a suite of site characteristics into two environmental components. Total N uptake rates among trophic levels were best predicted by the component that was correlated with latitude, DIN:SRP, GPP:ER, and percent canopy cover. N transfer efficiency did not respond consistently to environmental variables. Our results suggest that canopy cover influences N movement through stream food webs because light availability and primary production facilitate N transfer to higher trophic levels.
1 aNorman, B., C.1 aWhiles, M., R.1 aCollins, S., M.1 aFlecker, A., S.1 aHamilton, S., K.1 aJohnson, S., L.1 aRosi-Marshall, E., J.1 aAshkenas, L.R.1 aBowden, W.B.1 aCrenshaw, C., L.1 aCrowl, T.1 aDodds, W., K.1 aHall, R., O.1 aEl-Sabaawi, R.1 aGriffiths, N., A.1 aMarti, E.1 aMcDowell, W., H.1 aPeterson, S., D.1 aRantala, H., M.1 aRiis, T.1 aSimon, K., S.1 aTank, J., L.1 aThomas, S., A.1 avon Schiller, D.1 aWebster, J., R. uhttps://esajournals.onlinelibrary.wiley.com/doi/abs/10.1002/ecy.2009