Sarah R. Carrino-Kyker

Mycorrhizal Response to Experimental pH and P Manipulation in Acidic Hardwood Forests

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., <pH 5) are particularly vulnerable to P limitation. Results from previous studies in these systems are mixed with evidence both for and against P limitation. We hypothesized that shifts in mycorrhizal colonization and community structure help temperate forest ecosystems overcome an underlying P limitation by accessing mineral and organic P sources that are otherwise unavailable for direct plant uptake. We examined arbuscular mycorrhizal (AM) and ectomycorrhizal (EcM) communities and soil microbial activity in an ecosystem-level experiment where soil pH and P availability were manipulated in mixed deciduous forests across eastern Ohio, USA. One year after treatment initiation, AM root biomass was positively correlated with the most available P pool, resin P, while AM colonization was negatively correlated. In total, 15,876 EcM root tips were identified and assigned to 26 genera and 219 operational taxonomic units (97% similarity). Ectomycorrhizal richness and root tip abundance were negatively correlated with the moderately available P pools, while the relative percent of tips colonized by Ascomycetes was positively correlated with soil pH. Canonical correspondence analysis revealed regional, but not treatment, differences in AM communities, while EcM communities had both treatment and regional differences. Our findings highlight the complex interactions between mycorrhizae and the soil environment and further underscore the fact that mycorrhizal communities do not merely reflect the host plant community.

Temporal and Spatial Patterns of Eukaryotic and Bacterial Communities Found in Vernal Pools

ABSTRACT 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.

SEASONAL PHYSICOCHEMICAL CHARACTERISTICS OF THIRTY NORTHERN OHIO TEMPORARY POOLS ALONG GRADIENTS OF GIS-DELINEATED HUMAN LAND-USE

Human development pollutes runoff and ground water. Temporary pools are good habitats to study the influence of general non-point source pollution because they are created by runoff and ground water, among other processes, which, in northern Ohio, can contain substances accumulated over the winter. Furthermore, little information on land-use effects on temporary pools exists. To ascertain if general human activities influenced the water quality of northern Ohio temporary pools, monthly measurements of pH, dissolved oxygen, temperature, conductivity, and depth were monitored from March–June 2004 in 30 dispersed pools of the Cuyahoga River basin, Ohio, USA. Nutrient measurements for most pools were taken in May and June 2004. Pools were located in ten sub-watersheds containing differing percentages of geographic information system (GIS)-delineated urban/suburban and agricultural lands. General water quality characteristics of northern Ohio temporary pools were variable, both spatially and temporally. Nutrient levels were generally low (oligotrophic). Spearman rank correlation coefficients between the characteristics and percent land-use showed that conductivity and percent agriculture were positively correlated, while depth and percent urban were negatively correlated. Temporally, dissolved oxygen and depth showed fairly strong seasonal decreases from March–June. Some measurements from pools in mostly natural sub-watersheds suggested poor water quality. Although large-scale (watershed) land-use influences can affect the physicochemical nature of temporary pools, local anthropogenic influences, both past and present, probably also affect the quality of temporary pool wetlands.

The effects of pH change and NO−3 pulse on microbial community structure and function: a vernal pool microcosm study

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.

Mycorrhizal fungal communities respond to experimental elevation of soil pH and P availability in temperate hardwood forests

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.

Seasonal variation in mycorrhizal fungi colonizing roots of Allium tricoccum (wild leek) in a mature mixed hardwood forest

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.

The effects of increased hay-to-grain ratio on behavior, metabolic health measures, and fecal bacterial communities in four Masai giraffe (Giraffa camelopardalis tippelskirchi) at Cleveland Metroparks Zoo

We evaluated whether increasing the hay-to-grain ratio offered to Masai giraffe (Giraffa camelopardalis tippelskirchi) at Cleveland Metroparks Zoo would reduce oral stereotypies and alter feeding behaviors, maintain or increase serum calcium-to-phosphorus ratio, decrease serum insulin-to-glucose ratio and salivary insulin, and alter fecal bacterial community structure. Giraffe transitioned to a ∼90:10 hay-to-grain ratio in even increments over 8 weeks. A ration balancer was added during the seventh week of transition to ensure proper mineral and nutrient balance. We collected (1) behavioral data collected approximately daily using instantaneous focal sampling; (2) serum collections every other week for insulin-to-glucose and calcium-to-phosphorus ratio analysis and saliva weekly for insulin analysis; and (3) weekly fecal sample collections to examine changes in bacterial community structure during the 8 weeks preceding and following the diet change. After the diet change, giraffe spent significantly more time feeding and less time performing tongue and mouth stereotypies, people-directed and alert behaviors. Salivary and serum insulin and serum insulin-to-glucose ratio decreased, and fecal bacterial community structure changed significantly. However, serum calcium-to-phosphorus ratio remained >1:1 throughout the study. While further studies are needed to elucidate the nature and implications of the change in fecal bacterial community structure and metabolic hormones, the results of this study show promise for incremental improvements in health and welfare from feeding a higher proportion of forage in the diet.