Ecosystem Resilience and Limitations Revealed by Soil Bacterial Community Dynamics in a Bark Beetle-Impacted Forest

ABSTRACT Forested ecosystems throughout the world are experiencing increases in the incidence and magnitude of insect-induced tree mortality with large ecologic ramifications. Interestingly, correlations between water quality and the extent of tree mortality in Colorado montane ecosystems suggest co...

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Autores principales:	Kristin M. Mikkelson, Brent M. Brouillard, Chelsea M. Bokman, Jonathan O. Sharp
Formato:	article
Lenguaje:	EN
Publicado:	American Society for Microbiology 2017
Materias:	16S DNA 16S RNA biogeochemistry forest mortality microbial ecology threshold Microbiology QR1-502
Acceso en línea:	https://doaj.org/article/9c6178a7a4304fa6baf42fe98291a111
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spelling	oai:doaj.org-article:9c6178a7a4304fa6baf42fe98291a1112021-11-15T15:51:55ZEcosystem Resilience and Limitations Revealed by Soil Bacterial Community Dynamics in a Bark Beetle-Impacted Forest10.1128/mBio.01305-172150-7511https://doaj.org/article/9c6178a7a4304fa6baf42fe98291a1112017-12-01T00:00:00Zhttps://journals.asm.org/doi/10.1128/mBio.01305-17https://doaj.org/toc/2150-7511ABSTRACT Forested ecosystems throughout the world are experiencing increases in the incidence and magnitude of insect-induced tree mortality with large ecologic ramifications. Interestingly, correlations between water quality and the extent of tree mortality in Colorado montane ecosystems suggest compensatory effects from adjacent live vegetation that mute responses in less severely impacted forests. To this end, we investigated whether the composition of the soil bacterial community and associated functionality beneath beetle-killed lodgepole pine was influenced by the extent of surrounding tree mortality. The most pronounced changes were observed in the potentially active bacterial community, where alpha diversity increased in concert with surrounding tree mortality until mortality exceeded a tipping point of ~30 to 40%, after which diversity stabilized and decreased. Community structure also clustered in association with the extent of surrounding tree mortality with compositional trends best explained by differences in NH4+ concentrations and C/N ratios. C/N ratios, which were lower in soils under beetle-killed trees, further correlated with the relative abundance of putative nitrifiers and exoenzyme activity. Collectively, the response of soil microorganisms that drive heterotrophic respiration and decay supports observations of broader macroscale threshold effects on water quality in heavily infested forests and could be utilized as a predictive mechanism during analogous ecosystem disruptions. IMPORTANCE Forests around the world are succumbing to insect infestation with repercussions for local soil biogeochemistry and downstream water quality and quantity. This study utilized microbial community dynamics to address why we are observing watershed scale biogeochemical impacts from forest mortality in some impacted areas but not others. Through a unique “tree-centric” approach, we were able to delineate plots with various tree mortality levels within the same watershed to see if surviving surrounding vegetation altered microbial and biogeochemical responses. Our results suggest that forests with lower overall tree mortality levels are able to maintain “normal” ecosystem function, as the bacterial community appears resistant to tree death. However, surrounding tree mortality influences this mitigating effect with various linear and threshold responses whereupon the bacterial community and its function are altered. Our study lends insight into how microscale responses propagate upward into larger-scale observations, which may be useful for future predictions during analogous disruptions.Kristin M. MikkelsonBrent M. BrouillardChelsea M. BokmanJonathan O. SharpAmerican Society for Microbiologyarticle16S DNA16S RNAbiogeochemistryforest mortalitymicrobial ecologythresholdMicrobiologyQR1-502ENmBio, Vol 8, Iss 6 (2017)
institution	DOAJ
collection	DOAJ
language	EN
topic	16S DNA 16S RNA biogeochemistry forest mortality microbial ecology threshold Microbiology QR1-502
spellingShingle	16S DNA 16S RNA biogeochemistry forest mortality microbial ecology threshold Microbiology QR1-502 Kristin M. Mikkelson Brent M. Brouillard Chelsea M. Bokman Jonathan O. Sharp Ecosystem Resilience and Limitations Revealed by Soil Bacterial Community Dynamics in a Bark Beetle-Impacted Forest
description	ABSTRACT Forested ecosystems throughout the world are experiencing increases in the incidence and magnitude of insect-induced tree mortality with large ecologic ramifications. Interestingly, correlations between water quality and the extent of tree mortality in Colorado montane ecosystems suggest compensatory effects from adjacent live vegetation that mute responses in less severely impacted forests. To this end, we investigated whether the composition of the soil bacterial community and associated functionality beneath beetle-killed lodgepole pine was influenced by the extent of surrounding tree mortality. The most pronounced changes were observed in the potentially active bacterial community, where alpha diversity increased in concert with surrounding tree mortality until mortality exceeded a tipping point of ~30 to 40%, after which diversity stabilized and decreased. Community structure also clustered in association with the extent of surrounding tree mortality with compositional trends best explained by differences in NH4+ concentrations and C/N ratios. C/N ratios, which were lower in soils under beetle-killed trees, further correlated with the relative abundance of putative nitrifiers and exoenzyme activity. Collectively, the response of soil microorganisms that drive heterotrophic respiration and decay supports observations of broader macroscale threshold effects on water quality in heavily infested forests and could be utilized as a predictive mechanism during analogous ecosystem disruptions. IMPORTANCE Forests around the world are succumbing to insect infestation with repercussions for local soil biogeochemistry and downstream water quality and quantity. This study utilized microbial community dynamics to address why we are observing watershed scale biogeochemical impacts from forest mortality in some impacted areas but not others. Through a unique “tree-centric” approach, we were able to delineate plots with various tree mortality levels within the same watershed to see if surviving surrounding vegetation altered microbial and biogeochemical responses. Our results suggest that forests with lower overall tree mortality levels are able to maintain “normal” ecosystem function, as the bacterial community appears resistant to tree death. However, surrounding tree mortality influences this mitigating effect with various linear and threshold responses whereupon the bacterial community and its function are altered. Our study lends insight into how microscale responses propagate upward into larger-scale observations, which may be useful for future predictions during analogous disruptions.
format	article
author	Kristin M. Mikkelson Brent M. Brouillard Chelsea M. Bokman Jonathan O. Sharp
author_facet	Kristin M. Mikkelson Brent M. Brouillard Chelsea M. Bokman Jonathan O. Sharp
author_sort	Kristin M. Mikkelson
title	Ecosystem Resilience and Limitations Revealed by Soil Bacterial Community Dynamics in a Bark Beetle-Impacted Forest
title_short	Ecosystem Resilience and Limitations Revealed by Soil Bacterial Community Dynamics in a Bark Beetle-Impacted Forest
title_full	Ecosystem Resilience and Limitations Revealed by Soil Bacterial Community Dynamics in a Bark Beetle-Impacted Forest
title_fullStr	Ecosystem Resilience and Limitations Revealed by Soil Bacterial Community Dynamics in a Bark Beetle-Impacted Forest
title_full_unstemmed	Ecosystem Resilience and Limitations Revealed by Soil Bacterial Community Dynamics in a Bark Beetle-Impacted Forest
title_sort	ecosystem resilience and limitations revealed by soil bacterial community dynamics in a bark beetle-impacted forest
publisher	American Society for Microbiology
publishDate	2017
url	https://doaj.org/article/9c6178a7a4304fa6baf42fe98291a111
work_keys_str_mv	AT kristinmmikkelson ecosystemresilienceandlimitationsrevealedbysoilbacterialcommunitydynamicsinabarkbeetleimpactedforest AT brentmbrouillard ecosystemresilienceandlimitationsrevealedbysoilbacterialcommunitydynamicsinabarkbeetleimpactedforest AT chelseambokman ecosystemresilienceandlimitationsrevealedbysoilbacterialcommunitydynamicsinabarkbeetleimpactedforest AT jonathanosharp ecosystemresilienceandlimitationsrevealedbysoilbacterialcommunitydynamicsinabarkbeetleimpactedforest
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Ecosystem Resilience and Limitations Revealed by Soil Bacterial Community Dynamics in a Bark Beetle-Impacted Forest

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