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Title: Invariant soil water potential at zero microbial respiration explained by hydrological discontinuity in dry soils

We report that soil microbial respiration rates decrease with soil drying, ceasing below water potentials around -15 MPa. A proposed mechanism for this pattern is that under dry conditions, microbes are substrate limited because solute diffusivity is halted due to breaking of water film continuity. However, pore connectivity estimated from hydraulic conductivity and solute diffusivity (at Darcy's scale) is typically interrupted at much less negative water potentials than microbial respiration (-0.1 to -1 MPa). It is hypothesized here that the more negative respiration thresholds than at the Darcy's scale emerge because microbial activity is restricted to microscale soil patches that retain some hydrological connectivity even when it is lost at the macroscale. This hypothesis is explored using results from percolation theory and meta-analyses of respiration-water potential curves and hydrological percolation points. Lastly, when reducing the spatial scale from macroscale to microscale, hydrological and respiration thresholds become consistent, supporting the proposed hypothesis.
Authors:
 [1] ;  [2]
  1. Stockholm Univ. (Sweden). Department of Physical Geography and Quaternary Geology
  2. Duke Univ., Durham, NC (United States). Nicholas School of the Environment and Department of Civil and Environmental Engineering
Publication Date:
Grant/Contract Number:
SC0006967; SC0011461
Type:
Accepted Manuscript
Journal Name:
Geophysical Research Letters
Additional Journal Information:
Journal Volume: 41; Journal Issue: 20; Journal ID: ISSN 0094-8276
Publisher:
American Geophysical Union
Research Org:
Duke Univ., Durham, NC (United States)
Sponsoring Org:
USDOE Office of Science (SC)
Country of Publication:
United States
Language:
English
Subject:
58 GEOSCIENCES; percolation theory; microbial water stress; soil respiration; upscaling; drought; soil moisture
OSTI Identifier:
1454925

Manzoni, S., and Katul, G.. Invariant soil water potential at zero microbial respiration explained by hydrological discontinuity in dry soils. United States: N. p., Web. doi:10.1002/2014GL061467.
Manzoni, S., & Katul, G.. Invariant soil water potential at zero microbial respiration explained by hydrological discontinuity in dry soils. United States. doi:10.1002/2014GL061467.
Manzoni, S., and Katul, G.. 2014. "Invariant soil water potential at zero microbial respiration explained by hydrological discontinuity in dry soils". United States. doi:10.1002/2014GL061467. https://www.osti.gov/servlets/purl/1454925.
@article{osti_1454925,
title = {Invariant soil water potential at zero microbial respiration explained by hydrological discontinuity in dry soils},
author = {Manzoni, S. and Katul, G.},
abstractNote = {We report that soil microbial respiration rates decrease with soil drying, ceasing below water potentials around -15 MPa. A proposed mechanism for this pattern is that under dry conditions, microbes are substrate limited because solute diffusivity is halted due to breaking of water film continuity. However, pore connectivity estimated from hydraulic conductivity and solute diffusivity (at Darcy's scale) is typically interrupted at much less negative water potentials than microbial respiration (-0.1 to -1 MPa). It is hypothesized here that the more negative respiration thresholds than at the Darcy's scale emerge because microbial activity is restricted to microscale soil patches that retain some hydrological connectivity even when it is lost at the macroscale. This hypothesis is explored using results from percolation theory and meta-analyses of respiration-water potential curves and hydrological percolation points. Lastly, when reducing the spatial scale from macroscale to microscale, hydrological and respiration thresholds become consistent, supporting the proposed hypothesis.},
doi = {10.1002/2014GL061467},
journal = {Geophysical Research Letters},
number = 20,
volume = 41,
place = {United States},
year = {2014},
month = {9}
}