Erik A Hobbie

Erik A Hobbie
University of New Hampshire | UNH · Research Center of Earth Systems

PhD

About

114
Publications
24,475
Reads
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7,890
Citations
Citations since 2016
33 Research Items
4228 Citations
20162017201820192020202120220200400600800
20162017201820192020202120220200400600800
20162017201820192020202120220200400600800
20162017201820192020202120220200400600800
Additional affiliations
January 2012 - present
Friedrich-Alexander Universität Erlangen-Nürnberg
January 2006 - present
January 2002 - December 2012

Publications

Publications (114)
Article
Full-text available
Assessment of nitrogen (N) saturation of forests is critical to the evaluation of the manner in which ecosystems will respond to current and future global changes such as N deposition. However, quantifying N saturation remains a challenge. We developed a conceptual model of N saturation stages in forest ecosystems based on (1) a hypothetical relati...
Article
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The impacts of enhanced nitrogen (N) deposition on the global forest carbon (C) sink and other ecosystem services may depend on whether N is deposited in reduced (mainly as ammonium) or oxidized forms (mainly as nitrate) and the subsequent fate of each. However, the fates of the two key reactive N forms and their contributions to forest C sinks are...
Article
Full-text available
A major functional division in ectomycorrhizal fungi is between taxa with hydrophobic ectomycorrhizae (strong proteolytic capabilities, deep nitrogen (N) acquisition, and extensive hyphal development) versus hydrophilic ectomycorrhizae (limited hyphal development, shallow N acquisition, and weak proteolytic capabilities). These two groups may diffe...
Article
The impacts of enhanced nitrogen (N) deposition on the global forest carbon (C) sink and other ecosystem services may depend on whether N is deposited in reduced (mainly as ammonium) or oxidized forms (mainly as nitrate) and the subsequent fate of each. However, the fates of the two key reactive N forms and their contributions to forest C sinks are...
Article
Full-text available
Nitrogen (N) is one of the major nutrients limiting plant growth in terrestrial ecosystems. To avoid plant-microbe competition, previous studies on plant N uptake preference often used hydroponic experiments on fine roots of seedlings and demonstrated ammonium preference for conifer species; however, we lack information about N uptake and transloca...
Preprint
Full-text available
Recently, several saprotrophic genera have been found to invade/interact with plant roots in laboratory growth experiments, and this coincides with reports of abundant saprotrophic fungal sequences in plant roots. However, it is uncertain if this reflects field phenomena, and if reports on coincidentally amplified saprotrophs are simply coincidenta...
Article
The effects of nitrogen (N) deposition on forests largely depend on its fate after entering the ecosystem. While several studies have addressed the forest fate of N deposition using ¹⁵N tracers, the long‐term fate and redistribution of deposited N in tropical forests remains unknown. Here, we applied ¹⁵N tracers to examine the fates of deposited am...
Article
Conifers are considered to prefer to take up ammonium over nitrate. However, this conclusion is mainly based on hydroponic experiments that separate roots from soils. It remains unclear to what extent mature conifers can use nitrate compared to ammonium under field conditions where both roots and soil microbes compete for N. We conducted an in situ...
Article
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Significance Peatlands store up to two-thirds of the world’s soil carbon, but this carbon may be released under warmer conditions, creating an important climate feedback. The belowground warming response of peatlands is particularly uncertain even though factors such as plant root growth regulate ecosystem water, carbon, and nutrient cycles. We stu...
Article
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Carbon (C) fluxes among different components of plant growth are important to forest ecosystem C cycling and are strongly influenced by species composition and resource availability. Although mycorrhizal fungi are crucial for nutrient acquisition and can receive a large fraction of annual net primary production, most studies do not explicitly inclu...
Article
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Sporocarps of wood decay fungi contain functional information about how different taxa partition carbon and nitrogen resources from wood. We combined carbon and nitrogen concentrations, isotopic ratios (¹³C:¹²C, ¹⁵N:¹⁴N, and ¹⁴C:¹²C, expressed as δ¹³C, δ¹⁵N, and Δ¹⁴C values), and compositional patterns in wood, cellulose, and sporocarps to investig...
Article
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Nitrification is a crucial step in ecosystem nitrogen (N) cycling, but scaling up from plot-based measurements of gross nitrification to catchments is difficult. Here, we employed a newly developed method in which the oxygen isotope anomaly (Δ¹⁷O) of nitrate (NO3⁻) is used as a natural tracer to quantify in situ catchment-scale gross nitrification...
Article
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Many plant and fungal species use volatile organic compounds (VOCs) as chemical signals to convey information about the location or quality of their fruits or fruiting bodies to animal dispersers. Identifying the environmental factors and biotic interactions that shape fruit selection by animals is key to understanding the evolutionary processes th...
Article
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Abstract Identifying the mechanisms that structure niche breadth and overlap between species is important for determining how species interact and assessing their functional role in an ecosystem. Without manipulative experiments, assessing the role of foraging ecology and interspecific competition in structuring diet is challenging. Systems with re...
Article
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Fundamental questions of how plant species within secondary forests and plantations in northeast China partition limited nitrogen (N) resource remain unclear. Here we conducted a 15N tracer greenhouse study to determine glycine, ammonium, and nitrate uptake by the seedlings of two coniferous species, Pinus koraiensis (Pinus) and Larix keampferi (La...
Article
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Desertification and land use pressures reduced forest cover in Inner Mongolia by 3% between 1992 and 2001. These forests primarily form symbioses with ectomycorrhizal fungi, and inventory and conservation of this resource is desirable as one tool to promote forest recovery in the future. We reviewed work on 311 ectomycorrhizal fungal species from p...
Article
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Soil carbon models typically scale decomposition linearly with soil carbon (C) concentration, but this linear relationship has not been experimentally verified. Here we investigated the underlying biogeochemical mechanisms controlling the relationships between soil C concentration and decomposition rates. We incubated a soil/sand mixture with incre...
Article
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The Arctic is experiencing rapid climatic and environmental changes, which could alter diets of nonmigratory herbivores both within and between populations. Here, we used carbon and nitrogen stable isotope analysis (δ¹³C and δ¹⁵N) in hair to infer summer dietary differences of Rangifer tarandus platyrhynchus (nonmigratory reindeer) in Nordenskiöldl...
Article
We compared the δ13C and δ15N of forest material with an extensive sporocarp collection to try to elucidate the role of forest litter, wood and soil as fungal carbon and nitrogen sources in Finnish boreal Picea abies-dominated forests. Ectomycorrhizal Hydnum and Cortinarius had higher δ15N than other ectomycorrhizal fungi, suggesting use of 15N-enr...
Article
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To assess how nitrogen (N) availability affected ectomycorrhizal functioning and to test a theoretical model of ectomycorrhizal ¹⁵ N partitioning, we measured C/N and δ ¹⁵ N in soils and nine fungal taxa in two Swedish N addition experiments. Sporocarp C/N and soil C/N decreased with fertilization, implying that N uptake per unit fungal growth incr...
Article
Humans have dramatically increased atmospheric nitrogen (N) deposition globally. At the coarsest resolution, N deposition is correlated with shifts from ectomycorrhizal (EcM) to arbuscular mycorrhizal (AM) tree dominance. At finer resolution, ectomycorrhizal fungal (EcMF) and arbuscular mycorrhizal fungal (AMF) communities respond strongly to long-...
Article
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Several lines of evidence suggest that the agaricoid, non‐ectomycorrhizal members of the family Hygrophoraceae (waxcaps) are biotrophic with unusual nitrogen nutrition. However, methods for the axenic culture and lab‐based study of these organisms remain to be developed, so our current knowledge is limited to field‐based investigations. Addition of...
Article
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Longleaf pine savannas house a diverse community of herbaceous N2-fixing legume species that have the potential to replenish nitrogen (N) losses from fire. Whether legumes fill this role depends on the factors that regulate symbiotic fixation, including soil nutrients such as phosphorus (P) and molybdenum (Mo) and the growth and fixation strategies...
Article
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Widespread decline of whitebark and limber pines in the northern Rocky Mountains (USA) has created an imperative to understand functional diversity in their ectomycorrhizal associates. Because suilloid fungi are likely important in successful reestablishment of pines the nitrogen-related functional traits of 28 high-elevation suilloid isolates were...
Article
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Arctic ground squirrels (Urocitellus parryii) rely primarily on dietary protein derived from plants to fuel gluconeogenesis during hibernation, yet fungal sporocarps may be an important, yet overlooked, protein source. Fungivory levels depend on sporocarp productivity, which varies with the dominant plant species and is higher on acidic than on non...
Article
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Peatlands encode information about past vegetation dynamics, climate, and microbial processes. Here, we used δ¹⁵N and δ¹³C patterns from 16 peat profiles to deduce how the biogeochemistry of the Marcell S1 forested bog in northern Minnesota responded to environmental and vegetation change over the past ∼ 10000 years. In multiple regression analyses...
Article
How climate and rising carbon dioxide concentrations (pCO2) have influenced competition between C3 and C4 plants over the last 50 years is a critical uncertainty in climate change research. Here we used carbon isotope (δ13C) values of the saprotrophic lawn fungus Amanita thiersii to integrate the signal of C3 and C4 carbon in samples collected betw...
Article
Rationale: Carbon isotope measurements on collagen and other tissues are used in modern and paleodiet studies, and relating these patterns to the dietary protein fraction (fdp ) and δ(13) C values of dietary protein and energy (lipids and carbohydrates) remains important for determining diets. Methods: Carbon fluxes from dietary protein to tissu...
Article
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Fungal acquisition of resources is difficult to assess in the field. To determine whether fungi received carbon from recent plant photosynthate, litter or soil-derived organic (C:N bonded) nitrogen, we examined differences in δ¹³C among bulk tissue, structural carbon, and protein extracts of sporocarps of three fungal types: saprotrophic fungi, fun...
Article
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We used δ¹⁵N and δ¹³C patterns from 16 peat depth profiles to interpret changes in C and N cycling in the Marcell S1 forested bog in northern Minnesota over the past ~ 10 000 years. In multiple regression analyses, δ¹⁵N and δ¹³C correlated strongly with depth, plot location, C / N, %N, and each other. Continuous variables in the regression model ma...
Article
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We assessed the nutritional strategy of true morels (genus Morchella) collected in 2003 and 2004 in Oregon and Alaska, 1 or 2 y after forest fires. We hypothesized that the patterns of stable isotopes (δ13C and δ15N) in the sporocarps would match those of saprotrophic fungi and that radiocarbon (∆14C) analyses would indicate that Morchella was assi...
Article
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Phlebopus portentosus is one of the most popular wild edible mushrooms in Thailand and can produce sporocarps in the culture without a host plant. However, it is still unclear whether Phlebopus portentosus is a saprotrophic, parasitic, or ectomycorrhizal (ECM) fungus. In this study, Phlebopus portentosus sporocarps were collected from northern Thai...
Article
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Background and aims The importance of the uptake of nitrogen in organic form by plants and mycorrhizal fungi has been demonstrated in various ecosystems including temperate forests. However, in previous experiments, isotopically labeled amino acids were often added to soils in concentrations that may be higher than those normally available to roots...
Article
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High marsh pools are natural features in New En-gland salt marshes that provide important subtidal refuge for the dominant resident fish, Fundulus heteroclitus (mummi-chog). F. heteroclitus is considered an important component in the trophic transfer pathway for its omnivorous diet and role as a prey species providing connectivity to adjacent near-...
Article
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Abstract High marsh pools are natural features in New England salt marshes that provide important subtidal refuge for the dominant resident fish, Fundulus heteroclitus (mummichog). F. heteroclitus is considered an important component in the trophic transfer pathway for its omnivorous diet and role as a prey species providing connectivity to adjacen...
Article
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Sedecula is a monotypic genus of hypogeous fungi that is rare and endemic to dry conifer forests of the western United States. The only known species, Sedecula pulvinata, was described in 1941 and its taxonomic placement and trophic status have remained uncertain ever since. Here we employ isotopic and molecular phylogenetic analyses to determine i...
Article
Fine roots acquire essential soil resources and mediate biogeochemical cycling in terrestrial ecosystems. Estimates of carbon and nutrient allocation to build and maintain these structures remain uncertain due to challenges in consistent measurement and interpretation of fine-root systems. Traditionally, fine roots have been defined as all roots le...
Article
Quantifying global patterns of terrestrial nitrogen (N) cycling is central to predicting future patterns of primary productivity, carbon sequestration, nutrient fluxes to aquatic systems, and climate forcing. With limited direct measures of soil N cycling at the global scale, syntheses of the 15 N5 14 N ratio of soil organic matter across climate g...
Article
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Understanding microbial transformations in soils is important for predicting future carbon sequestration and nutrient cycling. This review questions some methods of assessing one key microbial process, the uptake of labile organic compounds. First, soil microbes have a starving-survival life style of dormancy, arrested activity, and low activity. Y...
Article
We used natural and tracer nitrogen (N) isotopes in a Pinus taeda free air CO2 enrichment (FACE) experiment to investigate functioning of ectomycorrhizal and saprotrophic fungi in N cycling. Fungal sporocarps were sampled in 2004 (natural abundance and (15) N tracer) and 2010 (tracer) and δ(15) N patterns were compared against litter and soil pools...
Conference Paper
Full-text available
Background / Purpose: Like most carnivorous plant species, Pinguicula vulgaris (common butterwort) obtains nitrogen from both soil pools and insect prey. Prior studies have estimated percent prey-derived nitrogen (%PDN) for the entire plant, but it may be expected that %PDN varies between plant parts. By measuring stable isotopic ratios in the so...
Conference Paper
Background/Question/Methods Like most carnivorous plant species, Pinguicula vulgaris (common butterwort) obtains nitrogen from both soil pools and insect prey. Prior studies have estimated percent prey-derived nitrogen (%PDN) for the entire plant, but it may be expected that %PDN varies between plant parts. By measuring stable isotopic ratios in...
Conference Paper
Background/Question/Methods We used natural and tracer carbon and nitrogen isotopes in a Pinus taeda Free Air CO2 Enrichment experiment at the Duke Forest to investigate the functioning of ectomycorrhizal and saprotrophic fungi in carbon and nitrogen cycling over a six-year period. CO2 enrichment (+200 ppm; resulting CO2 decreased in δ13C by 12‰)...
Article
We used natural abundance 13C:12C (δ13C) and 8 yr of labeling with 13C-depleted CO2 in a Pinus taeda Free Air CO2 Enrichment (FACE) experiment to investigate carbon sources of saprotrophic fungi, ectomycorrhizal fungi, and fungi of uncertain life history. Sporocarp δ13C identified Sistotrema confluens as ectomycorrhizal, as suspected previously fro...
Article
Contents: Summary 367 I. Introduction 367 II. Background on isotopes 368 III. Patterns of soil δ15N 370 IV. Patterns of fungal δ15N 372 V. Biochemical basis for the influence of fungi on δ15N patterns in plant-soil systems 373 VI. Patterns of δ15N in plant and fungal culture studies 374 VII. Mycoheterotrophic and parasitic plants 375 VIII. Patterns...
Article
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Organic nitrogen use by mycorrhizal fungi and associated plants could fuel productivity in nitrogen-limited systems. To test whether fungi assimilated soil-derived organic nitrogen, we compared the 14C signal (expressed as Δ14C) from 1950s to 1960s thermonuclear testing in protein and structural carbon of ectomycorrhizal fungi. As expected, structu...
Conference Paper
Background/Question/Methods The uptake of nitrogen in organic form (for example, as amino acids rather than as ammonium or nitrate) by plants is important in tundra and boreal forest ecosystems, but the process is not as well quantified in temperate forests. One criticism of previous experiments demonstrating organic N uptake is that concentratio...
Article
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Background and aims Detailed analyses of root chemistry by branching order may provide insights into root function, root lifespan and the abundance of root-associated mycorrhizal fungi in forest ecosystems. Methods We examined the nitrogen and carbon stable isotopes (δ15N and δ13C) and concentration (%N and %C) in the fine roots of an arbuscular m...
Article
Isotopes of nitrogen (δ15N) and carbon (δ13C) in ectomycorrhizal and saprotrophic fungi contain important information about ecological functioning, but the complexity of physiological and ecosystem processes contributing to fungal carbon and nitrogen dynamics has limited our ability to explain differences across taxa. Here, we measured δ15N and δ13...
Article
Soil CO2 efflux (Esoil), the main pathway of C movement from the biosphere to the atmosphere, is critical to the terrestrial C cycle but how precipitation and soil moisture influence Esoil remains poorly understood. Here, we irrigated a longleaf pine wiregrass savanna for six years; this increased soil moisture by 41.2%. We tested how an altered pr...
Article
Anthropogenic nitrogen (N) deposition alters ectomycorrhizal fungal communities, but the effect on functional diversity is not clear. In this review we explore whether fungi that respond differently to N deposition also differ in functional traits, including organic N use, hydrophobicity and exploration type (extent and pattern of extraradical hyph...
Article
Full-text available
In radioisotope studies in plankton, bacteria turn over the nanomolar ambient concentrations of dissolved amino acids within a few hours. Uptake follows Michaelis–Menten kinetics. In contrast, within minutes the very abundant bacteria and fungi in soil take up all labeled amino acids added at nanomolar to millimolar final concentrations; uptake kin...
Article
Full-text available
The nutritional modes of genera in Hygrophoraceae (Basidiomycota: Agaricales), apart from the ectomycorrhizal Hygrophorus and lichen-forming taxa, are uncertain. New δ(15)N and δ(13)C values were obtained from 15 taxa under Hygrophoraceae collected in central Massachusetts and combined with isotopic datasets from five prior studies including a furt...
Conference Paper
Background/Question/Methods Understanding nutritional ecology and evolution of fungi gives greater insight into global nutrient cycling and forest ecology, as fungi are critical components of carbon and nutrient cycles. We used isotopic and molecular methods to examine fungal evolution with respect to carbon acquisition strategies in the Hygrophora...
Conference Paper
Background/Question/Methods Ectomycorrhizal fungi are ubiquitous symbionts in many terrestrial systems. Functional aspects of the fungal symbiont have been relatively neglected compared to the tremendous explosion of information on fungal community composition brought on by genetic techniques of the last 20 years. Fungal functionality is necessar...
Conference Paper
Background/Question/Methods Recent work has shown that the relatively crude classification of “fine roots” using a 2mm diameter threshold is not appropriate when trying to understand root function, lifespan, and carbon and nutrient fluxes. Branching order may be a more functionally relevant classification system for roots. Guo et al. (2008) found...
Conference Paper
Background/Question/Methods Recent climate models suggest a possible increase of precipitation in the southeastern United States. To understand the response of ecosystems to increased rainfall, it is necessary to identify both above and belowground mechanisms that regulate carbon (C) and nutrient cycles. Specifically, shifts in the relative C all...