Many temperate forests of the Northeastern United States and Europe have received significant anthropogenic acid and nitrogen (N) deposition over the last century. Although temperate hardwood forests are generally thought to be N-limited, anthropogenic deposition increases the possibility of phosphorus (P) limiting productivity in these forest ecosystems. Moreover, inorganic P availability is largely controlled by soil pH and biogeochemical theory suggests that forests with acidic soils (i.e.,

Many forests are affected by chronic acid deposition, which can lower soil pH and limit the availability of nutrients such as phosphorus (P), but the response of mycorrhizal fungi to changes in soil pH and P availability and how this affects tree acquisition of nutrients is not well understood. Here, we describe an ecosystem-level manipulation in 72 plots, which increased pH and/or P availability across six forests in Ohio, USA. Two years after treatment initiation, mycorrhizal fungi on roots were examined with molecular techniques, including 454-pyrosequencing. Elevating pH significantly increased arbuscular mycorrhizal (AM) fungal colonization and total fungal biomass, and affected community structure of AM and ectomycorrhizal (EcM) fungi, suggesting that raising soil pH altered both mycorrhizal fungal communities and fungal growth. AM fungal taxa were generally negatively correlated with recalcitrant P pools and soil enzyme activity, whereas EcM fungal taxa displayed variable responses, suggesting that these groups respond differently to P availability. Additionally, the production of extracellular phosphatase enzymes in soil decreased under elevated pH, suggesting a shift in functional activity of soil microbes with pH alteration. Thus, our findings suggest that elevating pH increased soil P availability, which may partly underlie the mycorrhizal fungal responses we observed.

The community of arbuscular mycorrhizal (AM) fungi colonizing roots of the forest herb Allium tricoccum Ait. (wild leek) was examined to assess whether colonization varied seasonally and spatially within the forest. Whole plants were collected to coincide with observed phenological stages, and the perennial tissue (i.e., the bulb) was used to analyze total C, N, and P over the growing season. AM fungal community composition, structure, and abundance were assessed in roots by terminal restriction fragment length polymorphism analysis and quantitative PCR. It was found that A. tricoccum rDNA co-amplified using the general AM primers NS31/AM1, and a new primer for qPCR was designed that discriminated against plant DNA to quantify AM colonization. Community structure of AM fungi did not vary seasonally, but did change spatially within the forest, and AM fungal communities were correlated with the presence of overstory tree species. Fungal colonization of roots, however, did change seasonally with a maximum observed in late winter and early spring following leaf emergence. Maximum AM fungal colonization was associated with declines in bulb N and P, suggesting that leaf emergence and growth were responsible for both declines in stored nutrients and increases in AM fungal colonization. Plant N and P contents increased between late summer and early spring while C contents remained unchanged. The observed increase in nutrient content during a time when A. tricoccum lacks leaves indicates that the roots or AM fungi are metabolically active and acquire nutrients during this time, despite an absence of photosynthesis and thus a direct supply of C from A. tricoccum.

No abstract

Forest vernal pools experience strong environmental fluctuations, such as changes in water chemistry, which are often correlated with changes in microbial community structure. However, very little is known about the extent to which these community changes influence ecosystem processes in vernal pools. This study utilized experimental vernal pool microcosms to simulate persistent pH alteration and a pulse input of nitrate (NO3 -), which are common perturbations to temperate vernal pool ecosystems. pH was manipulated at the onset and microbial respiration was monitored throughout the study (122 days). On day 29, NO3 - was added and denitrification rate was measured and bacterial, fungal, and denitrifier communities were profiled on day 30 and day 31. Microbial respiration and both bacterial and fungal community structure were altered by the pH treatment, demonstrating both structural and functional microbial responses. The NO3 - pulse increased denitrification rate without associated changes in community structure, suggesting that microbial communities responded functionally without structural shifts. The functioning of natural vernal pools, which experience both persistent and short-term environmental change, may thus depend on the type and duration of the change or disturbance.

No abstract

Predicting potential responses of soil fungal communities and fungal diversity to environmental change is limited by relatively few long‐term data sets, despite the important role fungi play in ecosystem processes. In this study, we examined the relative importance of environmental factors (weather or climate factors and chemical factors) on fungal communities over a period of five years. We examined fungal communities in an old‐growth beech‐maple forest in northeastern Ohio, located within the snow belt of Lake Erie, which receives an average of 287 cm of snowfall. Soil was collected every month from long‐term plots and divided into different soil depths; a total of 1080 samples were collected and used for fungal community and chemical analysis. We used DNA fragment analysis methods to examine fungal community response to environmental factors, and used next‐generation sequencing to examine specific responses of fungal species and quantify diversity in forest soil. Tests for phylogenetic signal were used to explore whether fungal responses are similar among close relatives or divergent within clades. Fungal communities responded significantly to chemical factors such as soil phosphorus but responded weakly to climate factors such as soil temperature, suggesting that fungal community composition reflects temporal variation in microsite environmental conditions. Sequencing revealed high degrees of fungal species richness, with an average of 384 operational taxonomic units (OTUs) within each soil core and more than 1000 OTUs within our study site. Fungal taxa associated with phosphorus availability and soil moisture were also distributed broadly across fungal clades (e.g., Basidiomycota, Ascomycota). Our study suggests that microsite chemical factors (e.g., soil moisture, P availability) correlate more strongly with fungal community variation than climate factors (e.g., soil temperature). In addition, environmental responses were not conserved among close relatives, suggesting that relatedness may not be sufficient to predict potential responses to these factors.

In this study, we examined the effects of physicochemical variability on the microbial communities of vernal pools. Denaturing gradient gel electrophoresis revealed temporal changes to be more pronounced than spatial changes in eukaryotic and bacterial communities. Sequencing revealed high degrees of richness in decomposers, which supports the notion that vernal pools are heterotrophic habitats.Vernal pools are seasonally flooded ecosystems that are subject to variability in abiotic conditions (8). Although previous studies have documented the importance of abiotic conditions for vernal-pool macroorganisms (3,9,10,12,18,20), little is known about abiotic influences on microorganisms. Given the abundance of vernal pools in the landscape (e.g., reference 5) and their highly variable physicochemical natures (2,4,6,17,19), vernal pools can serve as a model system to explore abiotic influences on microbial communities. Further, while the diversity of vernal-pool macroorganisms has been welldocumented, comparable studies of microbial biodiversity are rare (see reference 8 for a review). In one survey of a single snowmelt pool, 76% of the identified biota were protists or bacteria (15), which suggests that these organisms dominate temporary water bodies in terms of both species richness and abundance (8). The main objective of this study was to characterize the microbial (eukaryotic and bacterial) communities of vernal pools in northeastern Ohio and to illustrate any spatial and temporal variations in these communities in relation to abiotic factors.This study was conducted at Case Western Reserve University's Squire Valleevue and Valley Ridge Farms (41°29Ј53ЉN, 81°25Ј27ЉW; elevation, 320 m), where five vernal pools (one man-made pool, called the salamander pond, and four natural pools), which ranged in size from 16 to 20 m 2 , were studied. The pools were located within an 80-year-old secondarygrowth forest, which is characterized by well-drained, silt loam soils and a canopy dominated by Acer saccharum and Fagus grandifolia. From each pool, overlying water, organic detritus (i.e., leaf matter), and soil were collected on 1 April, 4 May, and 2 June 2004. These three collection times were shortly after snow melting and prior to the drying of the pools. Three replicate samples (of each sample type) were collected from the shore of each pool and combined. Specifically, soil samples were cores collected with sterile 1-ml pipette tips, and water samples were collected with 0.2-m-pore-size polycarbonate filters through which 50 ml of water was filtered. At the time of sampling, dissolved oxygen concentrations, pHs, average depths, and terrestrial light levels were measured in situ. Relative conductivities of water samples were determined in the lab.Community profile analysis was carried out by PCR-denaturing gradient gel electrophoresis (DGGE). DGGE was performed first to compare a subset of pool samples (three pool samples from three different sampling dates) of each individual sample type (water, soil, and organic detritu...