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1. Differentiating spatial from environmental effects on foliar fungal communities of Populus trichocarpa

   https://doi.org/10.1111/jbi.13641  

   Barge, Edward G. ; Leopold, Devin R. ; Peay, Kabir G. ; Newcombe, George ; Busby, Posy E. ( June 2019 , Journal of Biogeography)

   Foliar fungi – pathogens, endophytes, epiphytes – form taxonomically diverse communities that affect plant health and productivity. The composition of foliar fungal communities is variable at spatial scales both small (e.g. individual plants) and large (e.g. continents), yet few studies have attempted to tease apart spatial from climatic factors influencing these communities. Moreover, few studies have sampled in more than 1 year to gauge interannual variation in community structure.

   The Pacific Northwest of western North America.

   Foliar fungi associated with the deciduous treePopulus trichocarpa.

   In two consecutive years, we used DNA metabarcoding to characterize foliar fungal communities ofPopulus trichocarpaacross its geographic range, which encompasses a sharp climatic transition as it crosses the Cascade Mountain Range. We used multivariate analyses to (a) test for and differentiate spatial and environmental factors affecting community composition and (b) test for temporal variation in community composition across spatial and environmental gradients.

   In both study years, we found that foliar fungal community composition varied among sites and between regions (east vs. west of the Cascades). We found that climate explained more variation in community composition than geographic distance, although the majority of variation explained by each was shared. We also found that interannual variation in community composition depended on environmental context: communities located in the dry, eastern portion of the tree's geographic range varied more between study years than those located in the wet, western portion of the tree's range.

   Our results suggest that the environment plays a greater role in structuring foliar fungal communities than dispersal limitation.

    

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2. Variable influences of soil and seed-associated bacterial communities on the assembly of seedling microbiomes

   https://doi.org/10.1038/s41396-021-00967-1  

   Walsh, Corinne M. ; Becker-Uncapher, Isadore ; Carlson, Madeline ; Fierer, Noah ( March 2021 , The ISME Journal)

   Plants grown in distinct soils typically harbor distinct microbial communities, but the degree of the soil microbiome influence on plant microbiome assembly remains largely undetermined. We also know that the microbes associated with seeds can contribute to the plant microbiome, but the magnitude of this contribution is likely variable. We quantified the influence of soil and seed microbiomes on the bacterial community composition of seedlings by independently inoculating seeds from a single cultivar of wheat (Triticum aestivum) with 219 unique soil slurries while holding other environmental factors constant, determining the composition of the seed, soil, and seedling bacterial communities via cultivation-independent methods. Soil bacterial communities exert a strong, but variable, influence on seedling bacterial community structure, with the extent of the soil bacterial contribution dependent on the soil in question. By testing a wide range of soils, we were able to show that the specific composition of the seedling microbiome is predictable from knowing which bacterial taxa are found in soil. Although the most ubiquitous taxa associated with the seedlings were seed derived, the contributions of the seed microbiome to the seedling microbiome were variable and dependent on soil bacterial community composition. Together this work improves our predictive understanding of how the plant microbiome assembles and how the seedling microbiome could be directly or indirectly manipulated to improve plant health.

    

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3. Similarity between seed rain and neighbouring mature tree communities in an old-growth temperate forest

   https://doi.org/10.1007/s11676-019-01027-3  

   Wang, Yunyun ; LaMontagne, Jalene M. ; Lin, Fei ; Yuan, Zuoqiang ; Ye, Ji ; Wang, Xugao ; Hao, Zhanqing ( September 2019 , Journal of Forestry Research)

   Seed distribution and deposition patterns around parent trees are strongly affected by functional traits and therefore influence the development of plant communities. To assess the limitations of seed dispersal and the extent to which diaspore and neighbouring parental traits explain seed rain, we used a 9-year seed data set based on 150 seed traps in a 25-ha area of a temperate forest in the Changbai Mountain. Among 480,598 seeds belonging to 12 families, 17 genera, and 26 species were identified, only 54% of the species with mature trees in the community were represented in seeds collected over the 9 years, indicating a limitation in seed dispersal. Understory species were most limited; overstory species were least limited. Species with wind-dispersed seed had the least limitation, while the lowest similarity in species richness was for animal-dispersed species followed by gravity-dispersed species; fleshy-fruited species had stronger dispersal limitations than dry-fruited species. Generalized linear mixed models showed that relative basal area had a significant positive effect on seed abundance in traps, while the contribution of diaspore traits was low for nearly all groups. These results suggest that tree traits had the strongest contribution to seed dispersal and deposition for all functional groups examined here. These findings strengthen the knowledge that tree traits are key in explaining seed deposition patterns, at least at the primary dispersal stage. This improved knowledge of sources of seeds that are dispersed could facilitate greater understanding of seedling and community dynamics in temperate forests. 

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4. Nativity and seed dispersal mode influence species’ responses to habitat connectivity and urban environments

   https://doi.org/10.1111/geb.12760  

   Lopez, Bianca E. ; Urban, Dean ; White, Peter S. ( July 2018 , Global Ecology and Biogeography)

   Urbanization alters local environmental conditions and the ability of species to disperse between remnant habitat patches within the urban matrix. Nonetheless, despite the ongoing growth of urban areas worldwide, few studies have investigated the relative importance of dispersal and local environmental conditions for influencing species composition within urban and suburban landscapes. Here, we explore this question using spatial patterns of plant species composition.

   The Research Triangle area, which includes the cities of Raleigh, Durham, Chapel Hill and Cary, in central North Carolina, USA.

   2012–2014.

   Vascular plants.

   We sampled riparian forest plant communities along an urban‐to‐rural gradient and used redundancy analysis to identify predictors of species composition patterns for groups of species categorized by nativity and seed dispersal mode. We first compared the ability of different models of habitat connectivity (least‐cost paths that avoided urban land cover versus Euclidean and along‐stream distance) to explain spatial patterns of species composition. We then partitioned the variation in species composition explained by habitat connectivity models, local environmental conditions and measures of urbanization in the surrounding landscape.

   We found that several groups of native species were best explained by least‐cost path models that avoided urban development, suggesting that urbanization impedes dispersal within this landscape, particularly for short‐dispersed species. Environmental variables related to urbanization (e.g., temperature, stream incision) were important predictors of species composition for many species groups, but measures of urbanization in the surrounding landscape were more important for exotic than for native species.

   Our results demonstrate that urbanization influences plant species composition via its effects on both habitat connectivity and environmental conditions. However, the strength of these effects varies somewhat predictably across seed dispersal modes and between native and exotic species. These results highlight the importance of landscape‐scale planning for urban conservation.

    

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5. Fruit traits of pioneer trees structure seed dispersal across distances on tropical deforested landscapes: Implications for restoration

   https://doi.org/10.1111/1365-2664.13697  

   Camargo, Paulo H. S. A. ; Pizo, Marco A. ; Brancalion, Pedro H. S. ; Carlo, Tomás A. ; Hampe, ed., Arndt ( July 2020 , Journal of Applied Ecology)

   Pioneer trees with fleshy fruits are typically planted in restoration projects to attract frugivores as a mean to increase dispersal and accelerate forest regeneration. However, differences in fruit traits of pioneer trees can potentially influence dispersal and their restoration outcomes.

   Here we investigated the effects of bird and plant traits, and distance to forest fragments, on the seed rain using a tree‐planting experiment replicated in 12 deforested sites in Brazil. Factors were fruit traits of pioneer trees (wind‐dispersed, bird‐dispersed with lipids or with carbohydrates and controls) and distance (10, 50, 300 m) from forest fragments.

   We found that density and richness of birds and seeds decreased exponentially with distance from fragments, yet these effects were minor compared to the effects of fruit traits on the structure of the seed rain.

   Overall, plots with fleshy fruited pioneers attracted much greater bird activity and seed dispersal than plots with wind‐dispersal pioneers and the controls. For instance, plots with carbohydrate‐rich fruits received more than twice the average species richness and density of birds and seeds of plots with lipid‐rich pioneer trees, surpassing wind‐dispersed pioneers by more than 80%, and controls by over 90%. Furthermore, the fruit trait treatments resulted in morphological shifts in the average traits of visiting birds. Significant differences in bill gape and flight capacities (wing‐loading) were associated with the differences in the seed rain associated with each treatment.

   Synthesis and applications. Understanding how trait‐matching processes mediating mutualistic seed dispersal by frugivores interact with distance‐dependent dispersal limitation on deforested tropical landscapes is critical for improving forest restoration efforts. This is especially relevant in the context of applied nucleation. As shown here, avian seed dispersal can thus be manipulated in restoration projects in order to increase connectivity and speed up forest recovery and the provision of the multiple ecosystem services that follow forest succession.

    

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