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Kirtland, OH, United States

Westerband A.,University of Miami | Dovciak M.,New York University | La Quay-Velazquez G.,University of Puerto Rico at San Juan | Medeiros J.S.,Holden Arboretum
Southwestern Naturalist

Global climate change is expected to increase the aridity of semiarid landscapes by increasing heat stress and decreasing soil moisture, negatively impacting plant survival, growth, and reproduction and forcing major shifts in plant community composition. To better understand potential vegetation shifts, we investigated how aspect-mediated differences in soil moisture and nitrogen influence tree-grass and tree species coexistence in pinyon-juniper woodlands in the southwestern United States (at the Sevilleta Long Term Ecological Research Station in New Mexico). We measured soil moisture, total mineralized soil nitrogen, grass cover, and woody cover and demography of the two dominant trees-two-needle pinyon pine (Pinus edulis) and one-seeded juniper (Juniperus monosperma)-along 32 transects on north-facing and south-facing slopes. Tree cover was greater on north-facing than on south-facing slopes, reflecting significantly higher soil moisture on northern aspects. Aspect did not affect soil nitrogen or grass cover. Population structure for juniper was influenced by aspect while reproductive output was influenced by aspect in both species, suggesting that differences in drought tolerance between these codominant tree species may be responsible for differences in the utilization of resources in our study area. Our results suggest that soil moisture can affect tree cover and tree-grass coexistence more than does nitrogen. Increasing aridity due to global climate change is likely to decrease woody cover in semiarid landscapes, resulting in systems codominated by grasses and woody species. Source

Gupta V.,University of Toronto | Smemo K.A.,Holden Arboretum | Smemo K.A.,Kent State University | Yavitt J.B.,Cornell University | And 3 more authors.
Environmental Science and Technology

Peatlands are an important source of the atmospheric greenhouse gas methane (CH4). Although CH4 cycling and fluxes have been quantified for many northern peatlands, imprecision in process-based approaches to predicting CH4 emissions suggests that our understanding of underlying processes is incomplete. Microbial anaerobic oxidation of CH 4 (AOM) is an important CH4 sink in marine sediments, but AOM has only recently been identified in a few nonmarine systems. We used 13C isotope tracers and followed the fate of 13C into CO2 and peat in order to study the geographic extent, relative importance, and biogeochemistry of AOM in 15 North American peatlands spanning a ∼1500 km latitudinal transect that varied in hydrology, vegetation, and soil chemistry. For the first time, we demonstrate that AOM is a widespread and quantitatively important process across many peatland types and that anabolic microbial assimilation of CH4-C occurs. However, AOM rate is not predicted by CH4 production rates and the primary mechanism of C assimilation remains uncertain. AOM rates are higher in fen than bog sites, suggesting electron acceptor constraints on AOM. Nevertheless, AOM rates were not correlated with porewater ion concentrations or stimulated following additions of nitrate, sulfate, or ferric iron, suggesting that an unidentified electron acceptor(s) must drive AOM in peatlands. Globally, we estimate that AOM could consume a large proportion of CH4 produced annually (1.6-49 Tg) and thereby constrain emissions and greenhouse gas forcing. © 2013 American Chemical Society. Source

Krynak K.L.,Case Western Reserve University | Burke D.J.,Holden Arboretum | Benard M.F.,Case Western Reserve University

Recent global declines, extirpations and extinctions of wildlife caused by newly emergent diseases highlight the need to improve our knowledge of common environmental factors that affect the strength of immune defense traits. To achieve this goal, we examined the influence of acidification and shading of the larval environment on amphibian skin-associated innate immune defense traits, pre and post-metamorphosis, across two populations of American Bullfrogs (Rana catesbeiana), a species known for its wide-ranging environmental tolerance and introduced global distribution. We assessed treatment effects on 1) skinassociated microbial communities and 2) post-metamorphic antimicrobial peptide (AMP) production and 3) AMP bioactivity against the fungal pathogen Batrachochytrium dendrobatidis (Bd). While habitat acidification did not affect survival, time to metamorphosis or juvenile mass, we found that a change in average pH from 7 to 6 caused a significant shift in the larval skin microbial community, an effect which disappeared after metamorphosis. Additionally, we found shifts in skin-associated microbial communities across life stages suggesting they are affected by the physiological or ecological changes associated with amphibian metamorphosis. Moreover, we found that post-metamorphic AMP production and bioactivity were significantly affected by the interactions between pH and shade treatments and interactive effects differed across populations. In contrast, there were no significant interactions between treatments on post-metamorphic microbial community structure suggesting that variation in AMPs did not affect microbial community structure within our study. Our findings indicate that commonly encountered variation in the larval environment (i.e. pond pH and degree of shading) can have both immediate and long-term effects on the amphibian innate immune defense traits. Our work suggests that the susceptibility of amphibians to emerging diseases could be related to variability in the larval environment and calls for research into the relative influence of potentially less benign anthropogenic environmental changes on innate immune defense traits. © 2015 Krynak et al. Source

A replicated field trial containing Rhododendron cultivars, species, and experimental hybrids was repeatedly flooded during one growing season to test for resistance to Phytophthora cinnamomi under stress conditions. At the end of the season root rot disease scores were assigned based on visual assessment of root, crown, and shoot necrosis using a numerical rating scale of 1 (healthy fine roots) to 5 (dead plant). Under flooding conditions, the average disease score of three resistant cultivars (controls used as benchmarks) was 4.1, which was a 90 percent increase above their previously determined average of 2.2 under non-flooded conditions. In contrast, disease scores of the resistant species R. hyperythrum were 35 percent higher under flooded (2.7) than non-flooded (2.0) treatments. Eight F1 hybrids derived from R. hyperythrum had an average disease score of 3.3 and were significantly less diseased than the resistant benchmark cultivars under flooded field conditions. Loss of root rot resistance in flooded soils could result from conditions that favor pathogen development and infection and from physiological changes in host plants that predispose them to disease. Under flooding conditions, R. hyperythrum appears to be less predisposed to root rot than resistant genotypes with different genetic backgrounds. While the basis for this difference in stress response is not currently known, it appears to be heritable in the F1 generation and represents a valuable trait for root rot resistance breeding. © ISHS 2013. Source

Changes in atmospheric carbon dioxide concentration ([CO2]) affect plant carbon/water tradeoffs, with implications for drought tolerance. Leaf-level studies often indicate that drought tolerance may increase with rising [CO2], but integrated leaf and xylem responses are not well understood in this respect. In addition, the influence of the low [CO2] of the last glacial period on drought tolerance and xylem properties is not well understood. We investigated the interactive effects of a broad range of [CO2] and plant water potentials on leaf function, xylem structure and function and the integration of leaf and xylem function in Phaseolus vulgaris. Elevated [CO2] decreased vessel implosion strength, reduced conduit-specific hydraulic conductance, and compromised leaf-specific xylem hydraulic conductance under moderate drought. By contrast, at glacial [CO2], transpiration was maintained under moderate drought via greater conduit-specific and leaf-specific hydraulic conductance in association with increased vessel implosion strength. Our study involving the integration of leaf and xylem responses suggests that increasing [CO2] does not improve drought tolerance. We show that, under glacial conditions, changes in leaf and xylem properties could increase drought tolerance, while under future conditions, greater productivity may only occur when higher water use can be accommodated. © 2013 New Phytologist Trust. Source

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