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Abstract Background and aimsPlant interactions with soil microbial communities are critical for understanding plant health, improving horticultural and agricultural outcomes, and maintaining diverse natural communities. In some cases, disease suppressive soils enhance plant survival in the presence of pathogens. However, species-specific differences and seasonal variation complicate our understanding of the drivers of soil fungal communities and their consequences for plants. Here, we aim to describe soil fungal communities acrossRhododendronspecies and seasons as well as the test for fungal indicators ofRhododendronspecies in the soil. Further, we test possible mechanisms governing disease suppressive soils to the oomycete pathogenPhytophthora cinnamomi. Variation in disease susceptibility to this pathogen across species and clades allows us to test for possible fungal drivers of disease suppressive soils. MethodsWe conducted high throughput sequencing of the fungal communities found in soil collected under 14Rhododendronspecies and across 2 seasons (April, October) at two sites in Ohio, USA. Phylogenetic analyses were used to ask whether fungal community composition correlated with increased plant survival with the addition of whole soil communities from a prior greenhouse experiment. ResultsEffects ofRhododendronspecies (R² = 0.13), season (R² = 0.01) and their interaction on fungal communities (R² = 0.11) were statistically significant. Fungal community composition negatively correlated with survival following exposure to whole soil microbial communities, though this result depended on the presence ofR. minus. Forty-fiveTrichodermataxa were identified across our soil samples, and someTrichodermawere significantly associated with particularRhododendronspecies (e.g.Trichoderma atroviridewas associated withR. molle) in indicator species analyses. ConclusionThe correlation between plant responses to soil biotic communities and fungal community composition, as well as the presence of potential beneficial taxa such asTrichodermaand mycorrhizal fungi, are consistent with fungal-mediated survival benefits from the pathogenPhytophthora cinnamomi. 

Abstract Phytophthora cinnamomi, which causes the disease root rot, is an oomycete pathogen that is damaging to woody plants, including many horticulturally important groups, such as Rhododendron. Infecting the root of plants, Phytophthora cinnamomi inhibits water uptake, leading to root damage, wilting, and increased rates of plant mortality. Some observations suggest that P. cinnamomi infection corresponds to changes in leaf coloration, though whether this indicates a plant stress response or plant damage is generally unknown. We used leaf color analysis to test for differences in leaf discoloration between plants inoculated with the pathogen and control plants. We demonstrate a significant link between leaf discoloration in Rhododendron species and Phytophthora cinnamomi inoculation. This method was most useful when mortality was not exceptionally high, and analyzers must consider mortality as well as leaf damage in quantifying effects of the pathogen. Plants with leaf discoloration were 3.3 times more likely to die 2 weeks from our leaf census than plants with no leaf discoloration (P =0.005). This method is particularly inexpensive to implement, making it a valuable alternative to multi-spectral or hyperspectral imaging, especially in contexts such as horticulture and citizen science, where the high speed and low-cost nature of this technique might prove valuable. Species used in this study: root rot disease pathogen (Phytophthora cinnamomi Rands); Rhododendron atlanticum (Ashe) Rehder; Rhododendron brachycarpum D.Don ex G.Don; Rhododendron kiusianum Makino; Rhododendron maximum L.; Rhododendron minus Michx.; Rhododendron calendulaceum (Michx.) Torr.; Rhododendron kaempferi Planch.; Rhododendron keiskei Miq. Chemicals used in this study: Fosal Select Aliette/aluminum phosphite. 

Ecotones, the transitional zones between distinct habitats, are vital for ecosystem functioning and habitat diversity. Traditional management practices frequently create abrupt boundaries, leading to stressful conditions for organisms. To address this challenge, an underutilized land management technique called “edge feathering”, which involves gradual thinning of the canopy along the forest edge, has been introduced. This study, conducted at Holden Arboretum in Kirtland, Ohio, investigated the effects of edge feathering on light availability and understory plant diversity in edge feathered and control treatments. We calculated the coefficient of variation in light availability as light heterogeneity and plant diversity indices at the plot level. Edge feathering increased light heterogeneity by more than 2.5-fold. It also significantly increased biodiversity, yielding twice the species richness and approximately 1.5 times higher Shannon and Simpson’s Diversity (1/D) indices compared to unmanaged control plots. Furthermore, greater light heterogeneity exhibited a strong positive correlation with increased understory plant diversity. These effects were observed within just 3.5 years of implementation, underscoring the rapid and measurable benefits of edge feathering for plant community diversity. Our results further suggest the hypothesis that light heterogeneity might be an important driver of small-scale plant community diversity in this system, which could be tested directly in the future. 

Combining ecological questions with evolutionary con- text generates novel insight into both ecology and evo- lution. However, our ability to draw broad inferences can be limited by the taxonomic diversity present within and across species at a site. Public gardens (including botan- ical gardens and arboreta) may focus solely on aesthetics in developing their gardens, but some public gardens include scientific inquiry and conservation at the core of their missions (Hohn, 2022). These scientifically oriented public gardens follow community standards of excellence (Hohn, 2022) to provide unique access to curated plant collections specifically designed to gather high levels of biodiversity, both among and within species, at a single geographic location. These research‐grade collections include long‐lived species cared for over many decades. Such public gardens have long histories of conducting and supporting research harnessing the power inherent in these diverse collections, including explorations of sys- tematics, ecophysiology, and ecology. By bringing together species, as well as individuals within species, from across broad spatial ranges into a single site, these collections offer living repositories of diversity ripe for scientific exploration as de facto common gardens (Dosmann, 2006; Dosmann and Groover, 2012; Primack et al., 2021). 

Ecotones, the transitional zones between distinct habitats, are vital for ecosystem functioning. Traditional management practices frequently create abrupt boundaries, leading to stressful conditions for organisms. To address this challenge, a novel land management technique called ‘edge feathering’, which involves gradual thinning of the canopy, has been introduced. This study, conducted at Holden Arboretum in Kirtland, Ohio, investigated the effects of edge feathering on light availability and understory plant diversity in edge feathered and control treatments. Three transects per treatment with 6 plots each were established in a gradient from the forest interior toward the meadow. We calculated the coefficient of variation in light availability as light heterogeneity, and plant diversity indices at the plot level. Edge feathering increased light heterogeneity by more than 2.5 fold (p=0.0001957), species richness by twofold (p less than 0.0001), and both Shannon’s and Simpson’s diversity indices by approximately 1.5-fold (p less than 0.05) compared to the control. These findings demonstrate that higher light heterogeneity is strongly associated with greater understory plant diversity. These effects were observed within just 3.5 years of implementation, underscoring the rapid and measurable benefits of edge feathering. 

Background and aims Plant interactions with soil microbial communities are critical for understanding plant health, improving horticultural and agricultural outcomes, and maintaining diverse natural communities. In some cases, disease suppressive soils enhance plant survival in the presence of pathogens. However, species-specific differences and seasonal variation complicate our understanding of the drivers of soil fungal communities and their consequences for plants. Here, we aim to describe soil fungal communities across Rhododendron species and seasons and as well as the test for fungal indicators of species and seasons in the soil. Further, we tested for correlations between fungal community composition and prior experimental quantification of disease suppressive soils. Methods We conducted high throughput sequencing of the fungal communities found in soil collected under 14 Rhododendron species and across 2 seasons (April, October) at two sites in Ohio, USA. We described these soils and used phylogenetic analyses to ask whether fungal community composition correlated with increased plant survival with the addition of whole soil communities from a prior greenhouse experiment. Results We found effects of Rhododendron species and season on fungal communities. Fungal community composition correlated with survival following exposure to whole soil microbial communities, though this result depended on the presence of R. minus. We identified 45 Trichoderma taxa across our soil samples, and some Trichoderma were significantly associated with particular Rhododendron species in indicator species analyses. Conclusion The correlation between plant responses to soil biotic communities and fungal community composition, as well as the presence of potential beneficial taxa such as Trichoderma and mycorrhizal fungi, are consistent with fungal-mediated survival benefits from the pathogen Phytophthora cinnamomi. 

Background and Aims The soil-borne pathogen Phytophthora cinnamomi causes a deadly plant disease. Phosphite is widely used as an effective treatment to protect plants from Phytophthora cinnamomi. Phosphite as a common fungicide might influence the composition of soil fungal communities. However, whether the belowground effects of phosphitemediated protections are direct or indirectly mediated through soil biota are unknown. Therefore, exploring belowground effects could contribute to the evaluation of the sustainability of phosphite use and tests hypotheses about direct versus indirect effects in pathogen response. Methods Our greenhouse pot experiment on Rhododendron species had either an after-pathogen or a before-pathogen use of phosphite to compare and evaluate plant and soil fungal responses to phosphite and the presence of an oomycete pathogen Phytophthora cinnamomi. The factorial experiment also included with and without pathogen and soil biota treatments, for a test of interactive effects. High throughput sequencing analyzed the soil fungal communities, and we measured the diversity, evenness and richness of soil fungi. Results Phosphite effectively increased survival of Rhododendron species. It altered the composition of soil fungal communities, and the timing of using phosphite determined the way in which the fungal communities changed. Trichoderma taxa also responded to soil phosphite and Phytophthora cinnamomi. Conclusions The benefits of antagonistic fungi such as Trichoderma are context-dependent, suggesting protection against pathogens depends on the timing of phosphite application. This study provides evidence that phosphite-mediated pathogen protection includes both direct benefits to plants and indirect effects mediated through the soil fungal community. 

Understanding the mechanisms governing biological invasions has implications for population dynamics, biodiversity, and community assembly. The enemy escape hypothesis posits that escape from enemies such as herbivores and predators that were limiting in the native range helps explain rapid spread in the introduced range. While the enemy escape hypothesis has been widely tested aboveground, data limitations have prevented comparisons of belowground mechanisms for invasive and noninvasive introduced species, which limits our understanding of why only some introduced species become invasive. We assessed the role of soil biota in driving plant invasions in a phylogenetic meta−analysis, incorporating phylogeny in the error structure of the models, and comparing live and sterilized conditioned soils. We found 29 studies and 396 effect size estimates across 103 species that compared live and sterilized soils. We found general positive effects of soil biota for plants (0.099, 95% CI = 0.0266, 0.1714), consistent with a role of soil mutualists. The effect size of soil biota among invaders was 3.2× higher than for natives, the strength of effects was weaker for older conditioning species with a longer introduced history, and enemy escape was stronger for distant relatives. In addition, invasive species had a weaker allocation tradeoff than natives. By demonstrating that the net effect of soil biota is more positive for invasive than native and noninvasive introduced species, weakens over time since introduction, and strengthens as phylogenetic distance increasing, we provide mechanistic insights into the considerable role of soil biota in biological invasions, consistent with the predictions of the enemy escape hypothesis. 

The soil-borne pathogen Phytophthora cinnamomi causes a deadly plant disease. Phosphite is widely used as an effective treatment to protect plants from Phytophthora cinnamomi. Phosphite as a common fungicide might influence the composition of soil fungal communities. However, whether the belowground mechanisms of phosphite-mediated protections are direct or indirectly mediated through soil biota are unknown. Therefore, exploring belowground mechanisms could contribute to the evaluation of the sustainability of phosphite use and tests hypotheses about direct versus indirect mechanisms in pathogen response. Our greenhouse pot experiment on Rhododendron species had either an after-pathogen or a before-pathogen use of phosphite to compare and evaluate plant and soil fungal responses to phosphite and the presence of an oomycete pathogen phytophthora cinnamomi. The factorial experiment also included with and without pathogen and soil biota treatments, for a test of interactive effects. High throughput sequencing analyzed the soil fungal communities, and we measured the diversity, evenness and richness of soil fungi. Phosphite effectively increased survival of Rhododendron species. It altered the composition of soil fungal communities, and the timing of using phosphite determined the way in which the fungal communities changed. Trichoderma taxa also responded to soil phosphite and Phytophthora cinnamomi. The benefits of antagonistic fungi such as Trichoderma are context-dependent, suggesting protection against pathogens depends on the timing of phosphite application. This study provides the first evidence that phosphite-mediated pathogen protection includes both direct benefits to plants and indirect effects mediated through the soil microbial community. 

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.