Search for: All records

Abstract Seedling recruitment is an important mode of establishment utilized by many invasive plants. In widespread invasive plants, regional variation in the rates of seedling recruitment can contribute to differences in invasion intensity across regions. In this study, we examined regional variation in reproductive traits and seedling performance in a cosmopolitan invasive wetland grass,Phragmites australis. We tested whether nitrogen levels and regions with different histories and intensities of invasion would affect reproductive traits and seedling performance. We sampled invasivePhragmitesinflorescences from 34 populations across three regions in North America: The Northeast (old, most intense invasion), the Midwest (recent, intense invasion), and Southeast (recent, sparse invasion). We hypothesized that NortheastPhragmitespopulations would have the highest reproductive output and seedling performance, and that populations experiencing high nitrogen pollution would have higher reproductive output and seedling performance under high nitrogen conditions. We found that populations in the Northeast had the highest inflorescence mass, as expected. We also found that despite sparse distribution ofPhragmitesin the Southeast, populations from the Southeast displayed a high potential for sexual reproduction. However, increasing watershed-level nitrogen (kg/km²) decreased percent seed germination in Southeastern populations, suggesting that Southeastern populations are sensitive to rising nitrogen levels. While elevated nitrogen improved seedling performance through increased belowground growth in SoutheasternPhragmitesseedlings, elevated nitrogen decreased belowground growth in Midwestern seedlings. These results suggest that the southeastern region of North America may be primed to become an emergent invasion front ofPhragmites, warranting more research into the possible management ofPhragmitesspread in the region. 

The tree diversity-productivity relationship is key to effective forest restoration and management; however, it remains unclear what role foliar chemical diversity and interactions between trees and their enemies play in driving this relationship. Trees produce chemical metabolites in their leaves that impact herbivory and pathogen infection. If trees alter the diversity of metabolites they produce when grown in more diverse communities, this could impact interactions with herbivores and pathogens. Ultimately, these tropic interactions with plant enemies, mediated by chemical diversity, could be important drivers of diversity-productivity relationships. Using a large-scale tree diversity experiment, we used a focal tree sampling design from 14 species across a gradient of tree species richness to assess the role of foliar chemicals and trophic interactions in the diversity-productivity relationship. We used untargeted metabolomics to measure foliar phytochemical diversity, monitored tree-enemy interactions, including foliar fungal pathogens, caterpillar communities, and deer browsing, and modelled their relationship to tree growth using path analysis. We unraveled significant evidence for top-down mediation of the diversity-productivity relationship driven primarily by herbivores rather than foliar pathogens, and contrasting effects of foliar chemical diversity on different enemy types. Individual trees growing in more diverse communities had higher phytochemical diversity and higher caterpillar richness, but lower leaf fungal pathogen richness. Leaf phytochemical diversity was positively associated with caterpillar richness and fungal pathogen richness, but negatively associated with browsing by white-tailed deer (Odocoileus virginianus). Path analysis revealed that phytochemical diversity, caterpillar richness, insect damage, and deer damage – but not foliar pathogens – all mediated positive indirect effects of tree richness on tree growth rate. Synthesis: We highlight the significant mediation of diversity-productivity relationships via contrasting effects of phytochemical diversity on plant-enemy interactions. Ultimately, our study underscores the importance of incorporating trophic interactions into biodiversity-ecosystem function studies. 

Abstract Forest canopy complexity (i.e., the three‐dimensional structure of the canopy) is often associated with increased species diversity as well as high primary productivity across natural forests. However, canopy complexity, tree diversity, and productivity are often confounded in natural forests, and the mechanisms of these relationships remain unclear. Here, we used two large tree diversity experiments in North America to assess three hypotheses: (1) increasing tree diversity leads to increased canopy complexity, (2) canopy complexity is positively related to tree productivity, and (3) the relationship between tree diversity and tree productivity is indirect and driven by the positive effects of canopy complexity. We found that increasing tree diversity from monocultures to mixtures of 12 species increases canopy complexity and productivity by up to 71% and 73%, respectively. Moreover, structural equation modeling indicates that the effects of tree diversity on productivity are indirect and mediated primarily by changes in internal canopy complexity. Ultimately, we suggest that increasing canopy complexity can be a major mechanism by which tree diversity enhances productivity in young forests. 

The tree diversity–productivity relationship is key to effective forest restoration and management; however, it remains unclear what role foliar chemical diversity and interactions between trees and their enemies play in driving this relationship. Trees produce chemical metabolites in their leaves that impact herbivory and pathogen infection. If trees alter the diversity of metabolites they produce when grown in more diverse communities, this could impact interactions with herbivores and pathogens. Ultimately, these tropic interactions with plant enemies, mediated by chemical diversity, could be important drivers of diversity–productivity relationships. Using a large‐scale tree diversity experiment, we used a focal tree sampling design from 14 species across a gradient of tree species richness to assess the role of foliar chemicals and trophic interactions in the diversity–productivity relationship. We used untargeted metabolomics to measure foliar phytochemical diversity, monitored tree–enemy interactions, including foliar fungal pathogens, caterpillar communities and deer browsing, and modelled their relationship to tree growth using path analysis. We unravelled significant evidence for top‐down mediation of the diversity–productivity relationship driven primarily by herbivores rather than foliar pathogens and contrasting effects of foliar chemical diversity on different enemy types. Individual trees growing in more diverse communities had higher phytochemical diversity and higher caterpillar richness, but lower leaf fungal pathogen richness. Leaf phytochemical diversity was positively associated with caterpillar richness and fungal pathogen richness, but negatively associated with browsing by white‐tailed deer (Odocoileus virginianus). Path analysis revealed that phytochemical diversity, caterpillar richness, insect damage and deer damage—but not foliar pathogens—all mediated positive indirect effects of tree richness on tree growth rate. Synthesis: We highlight the significant mediation of diversity–productivity relationships via contrasting effects of phytochemical diversity on plant–enemy interactions. Ultimately, our study underscores the importance of incorporating trophic interactions into biodiversity–ecosystem function studies. 

Abstract Efforts to catalog global biodiversity have often focused on aboveground taxonomic diversity, with limited consideration of belowground communities. However, diversity aboveground may influence the diversity of belowground communities and vice versa. In addition to taxonomic diversity, the structural diversity of plant communities may be related to the diversity of soil bacterial and fungal communities, which drive important ecosystem processes but are difficult to characterize across broad spatial scales. In forests, canopy structural diversity may influence soil microorganisms through its effects on ecosystem productivity and root architecture, and via associations between canopy structure, stand age, and species richness. Given that structural diversity is one of the few types of diversity that can be readily measured remotely (e.g., using light detection and ranging—LiDAR), establishing links between structural and microbial diversity could facilitate the detection of belowground biodiversity hotspots. We investigated the potential for using remotely sensed information about forest structural diversity as a predictor of soil microbial community richness and composition. We calculated LiDAR‐derived metrics of structural diversity as well as a suite of stand and soil properties from 38 forested plots across the central hardwoods region of Indiana, USA, to test whether forest canopy structure is linked with the community richness and diversity of four key soil microbial groups: bacteria, fungi, arbuscular mycorrhizal (AM) fungi, and ectomycorrhizal (EM) fungi. We found that the density of canopy vegetation is positively associated with the taxonomic richness (alpha diversity) of EM fungi, independent of changes in plant taxonomic richness. Further, structural diversity metrics were significantly correlated with the overall community composition of bacteria, EM, and total fungal communities. However, soil properties were the strongest predictors of variation in the taxonomic richness and community composition of microbial communities in comparison with structural diversity and tree species diversity. As remote sensing tools and algorithms are rapidly advancing, these results may have important implications for the use of remote sensing of vegetation structural diversity for management and restoration practices aimed at preserving belowground biodiversity. 

Symbioses are ubiquitous in nature and influence individual plants and populations. Orchids have life history stages that depend fully or partially on fungi for carbon and other essential resources. As a result, orchid populations depend on the distribution of orchid mycorrhizal fungi (OMFs). We focused on evidence that local-scale distribution and population dynamics of orchids can be limited by the patchy distribution and abundance of OMFs, after an update of an earlier review confirmed that orchids are rarely limited by OMF distribution at geographic scales. Recent evidence points to a relationship between OMF abundance and orchid density and dormancy, which results in apparent density differences. Orchids were more abundant, less likely to enter dormancy, and more likely to re-emerge when OMF were abundant. We highlight the need for additional studies on OMF quantity, more emphasis on tropical species, and development and application of next-generation sequencing techniques to quantify OMF abundance in substrates and determine their function in association with orchids. Research is also needed to distinguish between OMFs and endophytic fungi and to determine the function of nonmycorrhizal endophytes in orchid roots. These studies will be especially important if we are to link orchids and OMFs in efforts to inform conservation. 

Marine multicellular organisms host a diverse collection of bacteria, archaea, microbial eukaryotes, and viruses that form their microbiome. Such host-associated microbes can significantly influence the host’s physiological capacities; however, the identity and functional role(s) of key members of the microbiome (“core microbiome”) in most marine hosts coexisting in natural settings remain obscure. Also unclear is how dynamic interactions between hosts and the immense standing pool of microbial genetic variation will affect marine ecosystems’ capacity to adjust to environmental changes. Here, we argue that significantly advancing our understanding of how host-associated microbes shape marine hosts’ plastic and adaptive responses to environmental change requires (i) recognizing that individual host–microbe systems do not exist in an ecological or evolutionary vacuum and (ii) expanding the field toward long-term, multidisciplinary research on entire communities of hosts and microbes. Natural experiments, such as time-calibrated geological events associated with well-characterized environmental gradients, provide unique ecological and evolutionary contexts to address this challenge. We focus here particularly on mutualistic interactions between hosts and microbes, but note that many of the same lessons and approaches would apply to other types of interactions. 

Green plants (Viridiplantae) include around 450,000–500,000 species of great diversity and have important roles in terrestrial and aquatic ecosystems. Here, as part of the One Thousand Plant Transcriptomes Initiative, we sequenced the vegetative transcriptomes of 1,124 species that span the diversity of plants in a broad sense (Archaeplastida), including green plants (Viridiplantae), glaucophytes (Glaucophyta) and red algae (Rhodophyta). Our analysis provides a robust phylogenomic framework for examining the evolution of green plants. Most inferred species relationships are well supported across multiple species tree and supermatrix analyses, but discordance among plastid and nuclear gene trees at a few important nodes highlights the complexity of plant genome evolution, including polyploidy, periods of rapid speciation, and extinction. Incomplete sorting of ancestral variation, polyploidization and massive expansions of gene families punctuate the evolutionary history of green plants. Notably, we find that large expansions of gene families preceded the origins of green plants, land plants and vascular plants, whereas whole-genome duplications are inferred to have occurred repeatedly throughout the evolution of flowering plants and ferns. The increasing availability of high-quality plant genome sequences and advances in functional genomics are enabling research on genome evolution across the green tree of life.