Extent of localized tree mortality influences soil biogeochemical response in a beetle-infested coniferous forest

Abstract:Outbreaks of defoliating insects may affect microbial populations in forests and thereby mass balances and ecosystem functioning. Here, we investigated the microbial dynamics in Scots pine (Pinus sylvestris L.) forests during outbreaks of the nun moth (Lymantria monacha L.) and the pine-tree lappet (Dendrolimus pini L.). We used real-time PCR (polymerase chain reaction) to quantify genes that characterize bacterial and fungal abundance and the denitrification processes (nirK, nirS, nosZ clades I and II) in different forest compartments and we analyzed the C and N content of pine needles, insect feces, larvae, vegetation layers, organic layers, and mineral soil horizons. The infestation of the nun moth increased the bacterial abundance on pine needles, in the vegetation layer, and in the upper organic layer, while fungal populations were increased in the vegetation layer and upper organic layer during both outbreaks. In soil, the abundance of nirK increased after insect defoliation, while the C/N ratios decreased. nosZ clades I and II showed variable responses in different soil layers and to different defoliating insects. Our results illustrate changes in the microbial populations in pine forests that were infested by defoliating insects and changes in the chemical soil properties that foster these populations, indicating a genetic potential for increased soil N 2 O emissions during the defoliation peak of insect outbreak events.

Section: Insect Outbreaks Lower the Soil C/n Ratiomentioning

confidence: 74%

“…forest infested with bark beetles (Scolytidae spp.) [34,39]. Therein, the biogeochemical response to the outbreak was most prominent in the mineral soil and dependent on the percentage of dead trees [34,39].…”

Section: Insect Outbreaks Lower the Soil C/n Ratiomentioning

confidence: 99%

The Abundance of Fungi, Bacteria and Denitrification Genes during Insect Outbreaks in Scots Pine Forests

Grüning

Beule

Meyer

et al. 2018

“…Needles with a higher N content, which get into the soil via litterfall, stimulate decomposition later in the season and are introduced into soil in increased rates during pest outbreaks [50]. In addition, the extent of infestation was found to determine the biogeochemical responses as well as the soil bacterial communities [33,35]. Mikkelson et al [34] elegantly highlighted the importance of rare bacterial taxa on the community dynamics and presumably biogeochemical cycling under bark beetle-induced tree mortality.…”

Section: Bacterial Community Of Pine Needles and Soilmentioning

confidence: 99%

“…The effects of outbreaks of single pests either on phyllosphere or soil microbial communities have been studied already (e.g., [21,24,[27][28][29][30][31][32][33][34][35]), but these data did not simultaneously compare the effect of pest outbreaks on phyllosphere and soil microbial communities and did not differentiate between the effects of different pest insects in the same forest ecosystem. Here, we analyzed the effect of outbreaks of two defoliating insects, nun moth or pine tree lappet, in Scots pine stands in eastern Germany on the bacterial and fungal community structure in the soil and the phyllosphere using DGGE.…”

Section: Introductionmentioning

confidence: 99%

Changes of Scots Pine Phyllosphere and Soil Fungal Communities during Outbreaks of Defoliating Insects

Beule

Grüning

Karlovský

et al. 2017

Abstract:Outbreaks of forest pests increase with climate change, and thereby may affect microbial communities and ecosystem functioning. We investigated the structure of phyllosphere and soil microbial communities during defoliation by the nun moth (Lymantria monacha L.) (80% defoliation) and the pine tree lappet (Dendrolimus pini L.) (50% defoliation) in Scots pine forests (Pinus sylvestris L.) in Germany. Ribosomal RNA genes of fungi and bacteria were amplified by polymerase chain reaction (PCR), separated by denaturing gradient gel electrophoresis (DGGE), and subsequently sequenced for taxonomic assignments. Defoliation by both pests changed the structure of the dominant fungal (but not bacterial) taxa of the phyllosphere and the soil. The highly abundant ectomycorrhizal fungal taxon (Russula sp.) in soils declined, which may be attributed to insufficient carbohydrate supply by the host trees and increased root mortality. In contrast, potentially pathogenic fungal taxa in the phyllosphere increased during pest outbreaks. Our results suggest that defoliation of pines by insect pest, change the structure of fungal communities, and thereby indirectly may be contributing to aggravation of tree health.

“…Forests in the Western U.S. are experiencing larger wildfire disturbances attributed to warmer temperatures and earlier spring snowmelts [5], with a 60% increase in large fires from the mid-1980s in the Northern Rocky Mountains and significantly greater extents of severe fires in the Southern Rocky Mountains [6]. Furthermore, unprecedented mountain pine beetle (MPB; Dendroctonous ponderosae) outbreaks in Western North America killed >10 Mha of trees over the last 2-3 decades [7,8], with major impacts on water resources [9,10], nutrient cycling [11], and forest carbon storage [12]. These disturbance-caused changes require consideration when assessing global change risks to the stability of forest carbon [13,14].…”

Section: Introductionmentioning

confidence: 99%

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

Lybrand

Gallery

Trahan

et al. 2018

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 CO 2 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 CO 2 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.