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Forests 2018, 9(2), 97; https://doi.org/10.3390/f9020097

Disturbance Alters the Relative Importance of Topographic and Biogeochemical Controls on Microbial Activity in Temperate Montane Forests

1
Department of Crop and Soil Science, Oregon State University, Corvallis, OR 97331, USA
2
School of Natural Resources and the Environment, University of Arizona, Tucson, AZ 85721, USA
3
Department of Ecology and Evolutionary Biology, University of Arizona, Tucson, AZ 85721, USA
*
Author to whom correspondence should be addressed.
Received: 7 December 2017 / Revised: 3 February 2018 / Accepted: 12 February 2018 / Published: 24 February 2018
(This article belongs to the Special Issue How Topography Impacts Forests under Global Change?)
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Abstract

Fire and pathogen-induced tree mortality are the two dominant forms of disturbance in Western U.S. montane forests. We investigated the consequences of both disturbance types on the controls of microbial activity in soils from 56 plots across a topographic gradient one year after the 2012 High Park wildfire in Colorado. Topsoil biogeochemistry, soil CO2 efflux, potential exoenzyme activities, and microbial biomass were quantified in plots that experienced fire disturbance, beetle disturbance, or both fire and beetle disturbance, and in plots where there was no recent evidence of disturbance. Soil CO2 efflux, N-, and P-degrading exoenzyme activities in undisturbed plots were positively correlated with soil moisture, estimated from a topographic wetness index; coefficient of determinations ranged from 0.5 to 0.65. Conversely, the same estimates of microbial activities from fire-disturbed and beetle-disturbed soils showed little correspondence to topographically inferred wetness, but demonstrated mostly negative relationships with soil pH (fire only) and mostly positive relationships with DOC/TDN (dissolved organic carbon/total dissolved nitrogen) ratios for both disturbance types. The coefficient of determination for regressions of microbial activity with soil pH and DOC/TDN reached 0.8 and 0.63 in fire- and beetle-disturbed forests, respectively. Drivers of soil microbial activity change as a function of disturbance type, suggesting simple mathematical models are insufficient in capturing the impact of disturbance in forests. View Full-Text
Keywords: carbon; biogeochemistry; disturbance ecology; exoenzyme activity (EEA); extracellular enzymes; fire; Mountain Pine Bark Beetle; Ponderosa pine (Pinus ponderosae); soil microbial community; SAGA wetness index; topographic wetness index; topography carbon; biogeochemistry; disturbance ecology; exoenzyme activity (EEA); extracellular enzymes; fire; Mountain Pine Bark Beetle; Ponderosa pine (Pinus ponderosae); soil microbial community; SAGA wetness index; topographic wetness index; topography
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Lybrand, R.A.; Gallery, R.E.; Trahan, N.A.; Moore, D.J.P. Disturbance Alters the Relative Importance of Topographic and Biogeochemical Controls on Microbial Activity in Temperate Montane Forests. Forests 2018, 9, 97.

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