No silver bullet: different soil handling techniques are useful for different research questions, exhibit differential type I and II error rates, and are sensitive to sampling intensity A response to Reinhart & Rinella (2016). 'A common soil handling technique can generate incorrect estimates of soil biota effects on plants.'

Recent mountain pine beetle outbreaks in western North America killed millions of lodgepole pine trees, leaving few survivors. However, the mechanism underlying the ability of trees to survive bark beetle outbreaks is unknown, but likely involve phytochemicals such as monoterpenes and fatty acids that can drive beetle aggregation and colonization on their hosts. Thus, we conducted a field survey of beetle-resistant lodgepole pine (Pinus contorta) trees to retrospectively deduce whether these phytochemicals underlie their survival by comparing their chemistry to that of non-attacked trees in the same stands. We also compared beetle attack characteristics between resistant and beetle-killed trees. Beetle-killed trees had more beetle attacks and longer ovipositional galleries than resistant trees, which also lacked the larval establishment found in beetle-killed trees. Resistant trees contained high amounts of toxic and attraction-inhibitive compounds and low amounts of pheromone-precursor and synergist compounds. During beetle host aggregation and colonization, these compounds likely served three critical roles in tree survival. First, low amounts of pheromone-precursor (α-pinene) and synergist (mycrene, terpinolene) compounds reduced or prevented beetles from attracting conspecifics to residual trees. Second, high amounts of 4-allyanisole further inhibited beetle attraction to its pheromone. Finally, high amounts of toxic limonene, 3-carene, 4-allyanisole, α-linolenic acid, and linoleic acid inhibited beetle gallery establishment and oviposition. We conclude that the variation of chemotypic expression of local plant populations can have profound ecological consequences including survival during insect outbreaks.

American beech (Fagus grandifolia) in the eastern United States and Canada has experienced more than a century of mortality under a steady expansion of disease agents collectively causing beech bark disease (BBD). In North America, BBD consists of insect (e.g., Cryptococcus fagisuga [beech scale] and Xylococculus betulae) and phytopathogenic fungal (Neonectria faginata and N. ditissima) components that can variously interact with host and environment to cause extensive aboveground mortality of beech (i.e., killing front stage). This heavy mortality causes cascading impacts on forest ecosystems, resulting in altered biotic and abiotic conditions in which BBD-inducted mortality persists at reduced levels (i.e., aftermath stage). New evidence

Disturbances have altered community dynamics in boreal forests with unknown consequences for belowground ecological processes. Soil fungi are particularly sensitive to such disturbances; however, the individual response of fungal guilds to different disturbance types is poorly understood. Here, we profiled soil fungal communities in lodgepole pine forests following a bark beetle outbreak, wildfire, clear-cut logging, and salvage-logging. Using Illumina MiSeq to sequence ITS1 and SSU rDNA, we characterized communities of ectomycorrhizal, arbuscular mycorrhizal, saprotrophic, and pathogenic fungi in sites representing each disturbance type paired with intact forests. We also quantified soil fungal biomass by measuring ergosterol. Abiotic disturbances changed the community composition of ectomycorrhizal fungi and shifted the dominance from ectomycorrhizal to saprotrophic fungi compared to intact forests. The disruption of the soil organic layer with disturbances correlated with the decline of ectomycorrhizal and the increase of arbuscular mycorrhizal fungi. Wildfire changed the community composition of pathogenic fungi but did not affect their proportion and diversity. Fungal biomass declined with disturbances that disrupted the forest floor. Our results suggest that the disruption of the forest floor with disturbances, and the changes in C and nutrient dynamics it may promote, structure the fungal community with implications for fungal biomass-C.

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Mountain pine beetle (Dendroctonus ponderosae) has killed millions of hectares of pine forests in western North America. Beetle success is dependent upon a community of symbiotic fungi comprised of Grosmannia clavigera, Ophiostoma montium, and Leptographium longiclavatum. Factors regulating the dynamics of this community during pine infection are largely unknown. However, fungal volatile organic compounds (FVOCs) help shape fungal interactions in model and agricultural systems and thus may be important drivers of interactions among bark beetle-associated fungi. We investigated whether FVOCs can mediate interspecific interactions among mountain pine beetle’s fungal symbionts by affecting fungal growth and reproduction. Headspace volatiles were collected and identified to determine species-specific volatile profiles. Interspecific effects of volatiles on fungal growth and conidia production were assessed by pairing physically-separated fungal cultures grown either on a carbon-poor or -rich substrate, inside a shared-headspace environment. Fungal VOC profiles differed by species and influenced the growth and/or conidia production of the other species. Further, our results showed that FVOCs can be used as carbon sources for fungi developing on carbon-poor substrates. This is the first report demonstrating that FVOCs can drive interactions among bark beetle fungal symbionts, and thus are important factors in beetle attack success.

Beech bark disease (BBD) has affected the composition, structure, and function of forests containing a significant proportion of American beech (Fagus grandifolia Ehrh.) across North America. BBD spread has been investigated at landscape and regional scales, but few studies have examined spatial patterns of disease severity and spread within stands where forest management mitigation measures can be implemented. We analyzed changes in forest composition between 1985 and 2009 and fine-scale spatial patterns of BBD between 2000 and 2009 in a ϳ2 ha northern hardwood stand in the Adirondack Mountains of New York using location and disease severity of beech trees. A bivariate point pattern analysis was implemented to examine spatial patterns of beech thicket formation and BBD spread to beech saplings. Abundance of beech saplings increased near highly diseased canopy beech trees and around dead beech and sugar maple (Acer saccharum Marsh.). Disease severity of beech saplings was highest in close proximity to highly cankered canopy beech trees. Thus, BBD leads to the formation of beech thickets, and thickets are often located where saplings are most likely to become infected, increasing the likelihood that secondary killing fronts will develop and lead to heavy BBD-induced mortality in aftermath northern hardwood forests of North America.Résumé : La maladie corticale du hêtre (MCH) a eu un impact sur la composition, la structure et la fonction des forêts composées d'une proportion importante de hêtre d'Amérique (Fagus grandifolia Ehrh.) partout en Amérique du Nord. La propagation de la MCH a été étudiée à l'échelle régionale et à l'échelle du paysage, mais peu d'études ont examiné le profil spatial de la propagation et de la sévérité de la maladie dans des peuplements où des pratiques d'aménagement visant à atténuer l'impact de la maladie peuvent être mis en oeuvre. Nous avons analysé les changements dans la composition de la forêt entre 1985 et 2009 ainsi que la répartition spatiale à une échelle fine de la MCH entre 2000 et 2009 dans un peuplement de feuillus nordiques d'environ deux hectares situé dans les monts Adirondack, dans l'État de New York, en utilisant la position des hêtres et la sévérité de la maladie. Une analyse bidimensionnelle de semis de points a été utilisée pour étudier la structure spatiale de la formation des fourrés de hêtre et la propagation de la MCH sur les gaules de hêtre. L'abondance des gaules de hêtre a augmenté près des hêtres dans le couvert forestier qui étaient très affectés par la maladie et autour des hêtres et des érables à sucre (Acer saccharum Marshall) morts. La sévérité de la maladie sur les gaules de hêtre était la plus élevée à proximité des hêtres dans le couvert forestier qui étaient sévèrement chancrés. La MCH entraîne par conséquent la formation de fourrés de hêtre qui sont souvent situés là où les gaules sont les plus sujettes à devenir infectées, ce qui augmente la probabilité que des fronts de mortalité secondaires se développent et entraînent une mortalité élevée induit...