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1. Leaf discoloration in Rhododendron species exposed to Phytophthora cinnamomi corresponds with future mortality

   https://doi.org/10.17605/OSF.IO/589PN  

   Cryan, Anna ; Liu, Yu ; S, Juliana Medeiros ; H., Jean Burns ( January 2022 , OSF)

   Phytophthora cinnamomi, also known as root rot, is an oomycete that is particularly damaging to the plant world. Infecting the root of plants, Phytophthora cinnamomi inhibits water uptake in plants, leading to increased rates of plant mortality. Rhododendron species are not impervious to the infestation of root rot, so, as a popular plant among gardeners, decreasing susceptibility to and identification of Phytophthora cinnamomi is beneficial to plant longevity. In this study, phosphite treatment and soil microbial communities are used to potentially prevent root rot from infecting the eight tested Rhododendron species. It is hypothesized that the phosphite treatment will directly attack the oomycete, as well as improve the defense system of the plants themselves. Rhododendrons treated with the live soil microbiota are predicted to be less susceptible to root rot due to increased resilience to disease from the presence of soil biota, potentially including mutualists such as mycorrhizal fungi. Since Phytophthora cinnamomi primarily affects the roots of plants, it is difficult to detect without uprooting those suspected of being diseased, which causes unnecessary and potentially fatal stress on the plant. This is why we used color analysis software to find a link between root rot infection and leaf color. Since Phytophthora cinnamomi decreases water uptake, plants that are infected will begin to wilt, and their leaves will begin to change color. Discovering a significant link between leaf color in Rhododendron species and Phytophthora cinnamomi infection has given a new diagnostic measure that will cause significantly less stress to the plant and will lead to better plant longevity outcomes. Our data also suggests both preventative measures and treatment options for certain Rhododendron species infected with P. cinnamomi, through the use of a combination of phosphite treatments and live soil biota presence. Our results differ by species, which we further analyzed through the utilization of specific leaf area measurements. Using this data, we were able to link our results to current theory, such as growth-defense tradeoffs and implications of tolerance versus resistance. 

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2. Impacts of invasive Amur honeysuckle, Lonicera maackii , leaf litter on multiple trophic levels of detritus‐based experimental wetlands

   https://doi.org/10.1111/fwb.13731  

   Robison, Alexis L. ; Berta, Josey L. ; Mott, Cy L. ; Regester, Kurt J. ( May 2021 , Freshwater Biology)

   Wetlands are especially vulnerable to invasive plants because seasonal movements of sediments, water, nutrients, and debris from adjacent terrestrial habitats create ecological conditions suitable for invasion.Lonicera maackiiis a relatively abundant and broadly distributed invasive shrub in the eastern U.S.A., yet few studies have simultaneously tested for effects of its leaf litter on multiple trophic levels within wetland food webs.

   Hatching success, hatchling survival, and hatchling size of tadpoles (Acris crepitans) were assessed using a laboratory mesocosm experiment with no‐leaf, native‐leaf, andL. maackii‐leaf treatments. In the field, short‐term (c. 3 week) and long‐term (c. 2 years) mesocosm experiments assessed the initial and persistent impacts, respectively, ofL. maackiion measures of primary productivity, invertebrate abundance and community structure, and oviposition preference and larval survival of Cope's gray treefrog (Hyla chrysoscelis).

   Exposure of eggs toL. maackiileaves reduced body size at hatching and larval survival of newly hatchedA. crepitans. In short‐term experiments,L. maackiileaves reduced dissolved oxygen levels, filamentous algal biomass, and macroinvertebrate abundance, and altered macroinvertebrate community structure. In long‐term experiments, duckweed cover was 15× times greater in mesocosms withL. maackiileaf additions. Oviposition by a local population ofH. chrysosceliswas 10× lower in both short‐ and long‐term mesocosms withL. maackiipresent.

   Although ecological impacts ofL. maackiihave been reported for terrestrial systems, our study is the first to demonstrate the simultaneous effects of its leaves on multiple trophic levels within replicated experimental wetlands. The relatively rapid decomposition ofL. maackiileaves, and associated pulse of phenolic compounds, is the most likely proximate mechanism of the bottom‐up effects we observed. The mechanisms, timing, and significance of effects is predicted to vary among natural wetlands.

   Our study demonstrates multiple ecological impacts of a terrestrial invasive shrub within experimental wetlands. Detailed studies on the specific mechanisms, and their spatial and temporal variability in natural systems, will elucidate management strategies and improve the efficiency of wetland conservation efforts.

    

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3. Experimental assessment of tree canopy and leaf litter controls on the microbiome and nitrogen fixation rates of two boreal mosses

   https://doi.org/10.1111/nph.16611  

   Jean, Mélanie ; Holland‐Moritz, Hannah ; Melvin, April M. ; Johnstone, Jill F. ; Mack, Michelle C. ( May 2020 , New Phytologist)

   Nitrogen (N₂)‐fixing moss microbial communities play key roles in nitrogen cycling of boreal forests. Forest type and leaf litter inputs regulate moss abundance, but how they control moss microbiomes and N₂‐fixation remains understudied. We examined the impacts of forest type and broadleaf litter on microbial community composition and N₂‐fixation rates ofHylocomium splendensandPleurozium schreberi.

   We conducted a moss transplant and leaf litter manipulation experiment at three sites with paired paper birch (Betula neoalaskana) and black spruce (Picea mariana) stands in Alaska. We characterized bacterial communities using marker gene sequencing, determined N₂‐fixation rates using stable isotopes (¹⁵N₂) and measured environmental covariates.

   Mosses native to and transplanted into spruce stands supported generally higher N₂‐fixation and distinct microbial communities compared to similar treatments in birch stands. High leaf litter inputs shifted microbial community composition for both moss species and reduced N₂‐fixation rates forH. splendens, which had the highest rates. N₂‐fixation was positively associated with several bacterial taxa, including cyanobacteria.

   The moss microbiome and environmental conditions controlled N₂‐fixation at the stand and transplant scales. Predicted shifts from spruce‐ to deciduous‐dominated stands will interact with the relative abundances of mosses supporting different microbiomes and N₂‐fixation rates, which could affect stand‐level N inputs.

    

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4. Experimental confirmation of effects of leaf litter type and light on tadpole performance for two priority amphibians

   https://doi.org/10.1002/ecs2.3729  

   Burrow, Angela K. ; Maerz, John C. ( September 2021 , Ecosphere)

   Isolated wetlands embedded within longleaf pine savannas support a high proportion of regional biodiversity including many amphibian species. Today, remnant isolated wetlands are often overgrown and hydrologically altered due to fire exclusion or incompatible, cool season fire regimes. In the absence of warm season fires when wetlands are dry, shrubs and trees succeed herbaceous plants, which alters wetland productivity via effects on light and detritus quality. We used a factorial aquatic mesocosm study to test the effects of altered detritus and shade on the growth, development, and survival of tadpoles of two priority amphibian species: gopher frogs (Rana capito) and ornate chorus frogs (Pseudacris ornata). Gopher frog survival was higher among maidencane, sedge, and pine treatments compared to oak and sweetgum treatments. While gopher frog larval periods were lowest in the sedge treatment, there was a nominal general effect of litter type on gopher frog larval periods, growth rates, and mass at metamorphosis. Shading had a nominal and inconsistent effect on gopher frog growth rates, but did extend larval periods in all litter treatments, decreased survival in all litter treatments except oak, and decreased mass at metamorphosis in all litter treatments except pine and sweetgum. Ornate chorus frog survival was minimally affected by shading and litter treatments, but growth rates and mass at metamorphosis were highest in maidencane and sedge treatments, and larval periods were extended with shading in all litter treatments. Shading also decreased growth rates in maidencane and sedge litters and decreased mass at metamorphosis in pine and sweetgum litters. Our results demonstrate that succession of isolated wetlands can reduce tadpole performance for two priority species both through changes in leaf litter and shading, though the effect on survival, larval growth, larval period, and size at metamorphosis can differ between species. These results support management recommendations to restore and maintain open canopy, grassy conditions in isolated wetlands for conservation of priority amphibian species.

    

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5. Activation of the autophagy pathway decreases dengue virus infection in Aedes aegypti cells

   https://doi.org/10.1186/s13071-021-05066-w  

   Chen, Tse-Yu ; Smartt, Chelsea T. ( October 2021 , Parasites & Vectors)

   Mosquito-borne dengue virus (DENV) causes major disease worldwide, impacting 50–100 million people every year, and is spread by the major mosquito vectorAedes aegypti. Understanding mosquito physiology, including antiviral mechanisms, and developing new control strategies have become an important step towards the elimination of DENV disease. In the study reported here, we focused on autophagy, a pathway suggested as having a positive influence on virus replication in humans, as a potential antiviral target in the mosquito.

   To understand the role played by autophagy inAe. aegypti, we examined the activation of this pathway in Aag-2 cells, anAe. aegypti-derived cell line, infected with DENV. Rapamycin and 3-methyladenine, two small molecules that have been shown to affect the function of the autophagy pathway, were used to activate or suppress, respectively, the autophagy pathway.

   At 1-day post-DENV infection in Aag-2 cells, transcript levels of both the microtubule-associated protein light chain 3-phosphatidylethanolamine conjugate (LC3-II) and autophagy-related protein 1 (ATG1) increased. Rapamycin treatment activated the autophagy pathway as early as 1-h post-treatment, and the virus titer had decreased in the Aag-2 cells at 2 days post-infection; in contrast, the 3-methyladenine treatment did not significantly affect the DENV titer. Treatment with these small molecules also impacted the ATG12 transcript levels in DENV-infected cells.

   Our studies revealed that activation of the autophagy pathway through rapamycin treatment altered DENV infection in the mosquito cells, suggesting that this pathway could be a possible antiviral mechanism in the mosquito system. Here we provide fundamental information needed to proceed with future experiments and to improve our understanding of the mosquito’s immune response against DENV.

    

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