Increases in Terrestrial Nitrogen Availability and Microbial Biogeochemical Indicators in Association with Extent of Surrounding Tree Mortality in Bark Beetle Impacted Forests
Abstract
Recent increases in the magnitude and occurrence of bark beetle-induced tree mortality are disrupting evergreen forests globally. To better understand how these perturbed ecosystems respond, we investigated whether the extent of local tree mortality is an important parameter to predict terrestrial biogeochemical and microbial responses in lodgepole pines (Pinus contorta) infested by mountain pine beetles in the Colorado Rocky Mountains. Soil biogeochemical parameters within three near-surface soil horizons were compared between healthy and deceased trees surrounded by varying extents of tree mortality in order to isolate the effects of surrounding tree mortality on carbon and nitrogen cycling. Results revealed that C:N ratios decreased as surrounding tree mortality increased in the upper soil litter and organic horizons. A threshold response was found for ammonium in these layers, which accumulated only under trees surrounded by at least 40% tree mortality. Concurrently, the extent of tree mortality and the C:N ratio also affected the soil microbial community structure and function. Bacterial clades specific to nitrogen cycling and exoenzyme activity were more strongly related to changes in C:N ratio than surrounding tree mortality. Alpha diversity within the bacterial soil community increased and beta diversity clustered in accordance with more extensive surrounding tree mortality. These biogeochemical and microbial indicators suggest that high degrees of beetle-induced mortality may be shifting the terrestrial environment of Rocky Mountain lodgepole pine forests from an N-limited ecosystem to one where N is in excess with implications for forest recovery and nitrogen export.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2016
- Bibcode:
- 2016AGUFM.B13D0644S
- Keywords:
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- 0414 Biogeochemical cycles;
- processes;
- and modeling;
- BIOGEOSCIENCESDE: 0439 Ecosystems;
- structure and dynamics;
- BIOGEOSCIENCESDE: 0465 Microbiology: ecology;
- physiology and genomics;
- BIOGEOSCIENCESDE: 0470 Nutrients and nutrient cycling;
- BIOGEOSCIENCES