Bioavailable DOC: reactive nutrient ratios control heterotrophic nutrient assimilation—An experimental proof of the macronutrient-access hypothesis

Medientyp: E-Artikel

Titel: Bioavailable DOC: reactive nutrient ratios control heterotrophic nutrient assimilation—An experimental proof of the macronutrient-access hypothesis

Beteiligte: Graeber, Daniel [VerfasserIn]; Tenzin, Youngdoung [VerfasserIn]; Stutter, Marc [VerfasserIn]; Weigelhofer, Gabriele [VerfasserIn]; Shatwell, Tom [VerfasserIn]; von Tümpling, Wolf [VerfasserIn]; Tittel, Jörg [VerfasserIn]; Wachholz, Alexander [VerfasserIn]; Borchardt, Dietrich [VerfasserIn]; Aquatic Ecosystem Analysis and Management, Helmholtz-Centre for Environmental Research – UFZ, Magdeburg, Germany [VerfasserIn]; Environmental and Biochemical Sciences, The James Hutton Institute, Aberdeen, UK [VerfasserIn]; WasserCluster Lunz, Lunz am See, Austria [VerfasserIn]; Lake Research, Helmholtz-Centre for Environmental Research – UFZ, Magdeburg, Germany [VerfasserIn]; River Ecology, Helmholtz-Centre for Environmental Research – UFZ, Magdeburg, Germany [VerfasserIn]

Erschienen: Springer International Publishing, 2021-06-08

Sprache: Englisch

DOI: https://doi.org/10.1007/s10533-021-00809-4

Schlagwörter: Phosphate ; PARAFAC ; Ecological stoichiometry ; Dissolved organic nitrogen ; Dissolved inorganic nitrogen ; Ternary plots

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Beschreibung: We investigate the "macronutrient-access hypothesis", which states that the balance between stoichiometric macronutrient demand and accessible macronutrients controls nutrient assimilation by aquatic heterotrophs. Within this hypothesis, we consider bioavailable dissolved organic carbon (bDOC), reactive nitrogen (N) and reactive phosphorus (P) to be the macronutrients accessible to heterotrophic assimilation. Here, reactive N and P are the sums of dissolved inorganic N (nitrate-N, nitrite-N, ammonium-N), soluble-reactive P (SRP), and bioavailable dissolved organic N (bDON) and P (bDOP). Previous data from various freshwaters suggests this hypothesis, yet clear experimental support is missing. We assessed this hypothesis in a proof-of-concept experiment for waters from four small agricultural streams. We used seven different bDOC:reactive N and bDOC:reactive P ratios, induced by seven levels of alder leaf leachate addition. With these treatments and a stream-water specific bacterial inoculum, we conducted a 3-day experiment with three independent replicates per combination of stream water, treatment, and sampling occasion. Here, we extracted dissolved organic matter (DOM) fluorophores by measuring excitation-emission matrices with subsequent parallel factor decomposition (EEM-PARAFAC). We assessed the true bioavailability of DOC, DON, and the DOM fluorophores as the concentration difference between the beginning and end of each experiment. Subsequently, we calculated the bDOC and bDON concentrations based on the bioavailable EEM-PARAFAC fluorophores, and compared the calculated bDOC and bDON concentrations to their true bioavailability. Due to very low DOP concentrations, the DOP determination uncertainty was high, and we assumed DOP to be a negligible part of the reactive P. For bDOC and bDON, the true bioavailability measurements agreed with the same fractions calculated indirectly from bioavailable EEM-PARAFAC fluorophores (bDOC r 2 = 0.96, p < 0.001; bDON r 2 = 0.77, p < 0.001). Hence we could predict ...

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