---
res:
  bibo_abstract:
  - 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 r2 = 0.96, p < 0.001;
    bDON r2 = 0.77, p < 0.001). Hence we could predict bDOC and bDON concentrations
    based on the EEM-PARAFAC fluorophores. The ratios of bDOC:reactive N (sum of bDON
    and DIN) and bDOC:reactive P (equal to SRP) exerted a strong, predictable stoichiometric
    control on reactive N and P uptake (R2 = 0.80 and 0.83). To define zones of C:N:P
    (co-)limitation of heterotrophic assimilation, we used a novel ternary-plot approach
    combining our data with literature data on C:N:P ranges of bacterial biomass.
    Here, we found a zone of maximum reactive N uptake (C:N:P approx. > 114: < 9:1),
    reactive P uptake (C:N:P approx. > 170:21: < 1) and reactive N and P co-limitation
    of nutrient uptake (C:N:P approx. > 204:14:1). The “macronutrient-access hypothesis”
    links ecological stoichiometry and biogeochemistry, and may be of importance for
    nutrient uptake in many freshwater ecosystems. However, this experiment is only
    a starting point and this hypothesis needs to be corroborated by further experiments
    for more sites, by in-situ studies, and with different DOC sources.@eng
  bibo_authorlist:
  - foaf_Person:
      foaf_givenName: Daniel
      foaf_name: Graeber, Daniel
      foaf_surname: Graeber
  - foaf_Person:
      foaf_givenName: Youngdoung
      foaf_name: Tenzin, Youngdoung
      foaf_surname: Tenzin
  - foaf_Person:
      foaf_givenName: Marc
      foaf_name: Stutter, Marc
      foaf_surname: Stutter
  - foaf_Person:
      foaf_givenName: Gabriele
      foaf_name: Weigelhofer, Gabriele
      foaf_surname: Weigelhofer
  - foaf_Person:
      foaf_givenName: Tom
      foaf_name: Shatwell, Tom
      foaf_surname: Shatwell
      foaf_workInfoHomepage: http://www.librecat.org/personId=86424
    orcid: 0000-0002-4520-7916
  - foaf_Person:
      foaf_givenName: Wolf
      foaf_name: von Tümpling, Wolf
      foaf_surname: von Tümpling
  - foaf_Person:
      foaf_givenName: Jörg
      foaf_name: Tittel, Jörg
      foaf_surname: Tittel
  - foaf_Person:
      foaf_givenName: Alexander
      foaf_name: Wachholz, Alexander
      foaf_surname: Wachholz
  - foaf_Person:
      foaf_givenName: Dietrich
      foaf_name: Borchardt, Dietrich
      foaf_surname: Borchardt
  bibo_doi: 10.1007/s10533-021-00809-4
  bibo_issue: '1'
  bibo_volume: 155
  dct_date: 2021^xs_gYear
  dct_isPartOf:
  - http://id.crossref.org/issn/0168-2563
  - http://id.crossref.org/issn/1573-515X
  dct_language: eng
  dct_publisher: Springer @
  dct_title: 'Bioavailable DOC: reactive nutrient ratios control heterotrophic nutrient
    assimilation—An experimental proof of the macronutrient-access hypothesis@'
...