American Journal of Botany最新文献

Premise: In the face of novel fire regimes driven by anthropogenic changes to climate, ignitions, and fuels, understanding the evolution and present distribution of fire-adapted traits is critical. Four common fire adaptations in conifers are thick bark, serotinous cones, seedling grass stage, and resprouting.

Methods: We focused on these fire-adapted traits and their abundance in North American conifers within a community phylogenetic context. Using ranges derived from numerous sources, we divided the continent into 20 conifer regions. We assessed regions for species richness, number of fire adaptations, number of taxa with each fire adaptation, and the percent composition of species with fire adaptations. We calculated regional phylogenetic dispersion metrics for each fire adaptation as well.

Results: For almost every analysis, a north-south trend was evident and had strong spatial correspondence with fire intensity and frequency metrics of contemporary fire regimes. Species richness and nearly every measure of fire adaptation abundance, increases with decreasing latitude. Northern latitudes also lack resprouting and the grass stage. We identified three fire-prone regions: California, Mexico and Central America, and the Gulf Coast. In terms of community composition, northern and mid-latitude regions trend toward neutral assembly, while southern regions are phylogenetically clustered. In most regions, fire adaptations are phylogenetically clustered, indicating that even in neutrally assembled ecosystems, fire adaptations are restricted to a few clades.

Conclusions: Given this information, we advocate tailoring management strategies toward present fire adaptations (or lack thereof), emphasizing strengthening fire resilience in fire-adapted ecosystems and maintaining the integrity of fire refugia.

Premise: Apical meristems of land plants have played a fundamental role in the evolution of complex shoot architectures. The most common structure of shoot apical meristems in bryophytes, lycophytes, and ferns is characterized by a single apical cell surrounded by a spiral of apical derivatives. Despite the importance of this type of meristem organization, it remains unclear how it is maintained at the apex.

Methods: We analyzed the distribution of different meristem organizations within a data set of 205 images of shoot apical meristems representing 91 species of bryophytes, lycophytes, and ferns. In parallel, we developed a mathematical and computational model to determine whether the meristem structural types observed empirically are predicted from Sachs's division rules; namely, cells divide symmetrically while positioning their new wall at a right angle to the parental walls.

Results: According to our data set, only four meristem structural types are observed in nature, corresponding to apical cells dividing along one, two, three, or four faces. In addition, the prevalence of the structural types in diverse plant lineages correlates with the shape of the meristems on which they are found. Our model based on Sachs's division rules indicates that as much as six meristem structural types are geometrically possible, but only the four types observed empirically are dynamically stable for realistic meristem geometries.

Conclusions: Simple division rules, which we interpret as biophysical constraints on the assembly of the preprophase band, may therefore explain the cellular organization of the shoot apical meristem in three major groups of land plants.

Premise: A universally understood, precise, and stable system of naming organisms is essential for effective scientific communication. The International Code of Nomenclature for algae, fungi, and plants, of which the most recently published edition is the Shenzhen Code of 2018, provides this system for algae, fungi, and plants. This Code is regularly revised at an International Botanical Congress (IBC), usually held every 6 years, most recently in Madrid, Spain, in July 2024. The Madrid IBC amended the Shenzhen Code, and the changes took effect on 27 July 2024, when the closing plenary session of the IBC approved the decisions of the Nomenclature Section. It is important to promptly publicize this information because the new edition of the Code resulting from these amendments, the Madrid Code, will not be published until mid-2025.

Methods: I selected some of the more important of the 433 published proposals to amend the Code at the Madrid IBC. I sourced details from the proposals themselves, the "Synopsis of Proposals" and the "Report of Congress Action" (all published in the journal Taxon) and from the records made during the Nomenclature Section in Madrid.

Results: For a general botanical audience, I discuss the background, outcomes (acceptance or rejection), and consequences of acceptance of the proposals.

Conclusions: This commentary supplements the technical reports already published and provides an overview of some of the new or amended rules and recommendations in the upcoming Madrid Code.

Premise: Phoradendron (Santalaceae) mistletoes consist of approximately 230 hemiparasitic species across the Americas. As obligate hemiparasites, their distribution depends partly on the distribution of their hosts, reflecting a shared evolutionary history.

Methods: Using network analysis and statistical modeling, we explored the bipartite host-parasite network, focusing on species organization and the likelihood of hosts sharing a Phoradendron species based on phylogenetic, geographic, and environmental factors.

Results: Our analysis suggests a modular and highly specialized interaction network influenced by evolutionary and biogeographical factors. Phoradendron parasitized hosts in genera from various families and orders, primarily Fabales, Malpighiales, and Sapindales. The network exhibited modularity and connectivity, with hosts sharing a higher likelihood of being parasitized by the same Phoradendron species when they were closer in phylogeny, geography, and environment, while phylogenetic distance emerged as the most relevant determinant. Moreover, we established a link between Phoradendron within-module connectivity and host phylogenetic distance, providing an evolutionary framework for understanding ecological patterns and network connectance.

Conclusions: The network of Phoradendron-host interactions is highly specialized, and the structure of this network depends mainly on the phylogenetic distance of the hosts.

Premise: Uncarina contains 14 species of woody plants endemic to Madagascar. Its occurrence across dryland biomes on the island make it an interesting system to study the diversification of the flora.

Methods: Using samples of all species and 512 nuclear loci, we reconstructed phylogenetic trees to examine species relationships and assess their monophyly. We also studied the historical biogeography of the genus and combined leaf trait data derived from SEM photography of trichomes and geometric morphometric analysis of leaf shape to better understand its diversification across dryland biomes.

Results: Uncarina is monophyletic, and major clades showed a clear biogeographical signal. Leaf traits also corroborated relationships among major clades. Although most species are monophyletic, at least one cryptic species exists. Uncarina, like many arid-adapted plant lineages in Madagascar originated in the Miocene or Pleistocene. Geographic movement has been primarily along a south-north axis, with river basins apparently acting as barriers to gene flow. The evolution of leaf traits corroborated movement from the spiny thicket to the dry forest biome.

Conclusions: As with Malagasy lemurs and other animals, riverine barriers may have been involved in the diversification of Uncarina and may apply more broadly to epizoochorous angiosperms of Madagascar. Leaf traits suggest either a loss of adaptations to extremely arid, high irradiance environments or a release from herbivores. As is likely needed in other Malagasy lineages, more thorough population-level sampling and specimen collecting is needed to fully understand the taxonomic and morphological diversity in the genus.

Premise: Extreme-cold events are increasingly recognized as one of the most damaging aspects of climate change in northern temperate ecosystems. However, little data exists describing how native and non-native species may respond to these extreme events, especially as seeds. We used a greenhouse experiment to test how extreme cold reduces seedling establishment in seven woody species common to eastern North America. We hypothesized that the effects of extreme cold depend on provenance (native vs. non-native) and chilling period.

Methods: Following chilling periods of 80, 100, or 120 days, seeds experienced a false-spring with temperatures at 15°C for one week; half of the seeds in each dormancy treatment group experienced a two-day extreme-cold event (-13.9°C) while the rest returned to mild winter temperatures (4°C).

Results: Extreme-cold events universally decreased seedling establishment, but non-native species had four times greater survival in the extreme-cold treatment (mean ± s.e.: 0.108 ± 0.024) compared to native species (0.024 ± 0.018). Furthermore, native seeds were increasingly susceptible to extreme-cold damage following a 120-day chilling period, whereas non-native seeds were able to resist extreme cold equally following all chilling periods.

Conclusions: These results suggest that in eastern North America, cold resistance could be a trait facilitating the success of non-native species. The introduction of non-native species may synergize with climate change to alter community composition, which could have important consequences for forest biodiversity in the Anthropocene.

Premise: The genus Guadua includes some of the largest bamboo species in the neotropics, with certain species of significant economic importance and used since pre-Hispanic times to build houses using the traditional bajareque technique. Guadua species are distributed from Mexico to South America. The potential monophyly of this genus has been suggested based on plastid markers and limited sampling. Here we included more species and nuclear data to study the morphological classification of Guadua and to reconstruct its ancestral area distribution.

Methods: Samples were collected for 16 Guadua taxa (13 species) to use nuclear single nucleotide polymorphisms (SNPs) derived from restriction-site associated DNA sequencing (RADSeq) data to construct a phylogenetic hypothesis using maximum likelihood and coalescent methods. We estimated divergence times using the RelTime method and reconstructed ancestral geographic areas using S-DEC analysis.

Results: The SNP data supported the monophyly of the genus Guadua and the existence of two distinct clades, Amplexifolia and Angustifolia. The origin of Guadua was estimated as approximately 10.47 million years ago in Mesoamerica. The biogeographic distribution of Guadua can likely be explained by a combination of dispersal and vicariant events.

Conclusions: Our study sheds new light on the phylogenetic relationships within Guadua and on its evolutionary history and biogeography, enhancing our understanding of its diversification and distribution across various biogeographic regions.

Premise: Leaf mass per area (LMA) links leaf economic strategies, community assembly, and climate and can be reconstructed from woody non-monocot angiosperm (WNMA) fossils using the petiole metric (PM; petiole width²/leaf area). Reliable interpretation of LMA reconstructed from the fossil record is limited by an incomplete understanding of how PM and LMA are correlated at the community scale and what climatic parameters drive variation of both measured and reconstructed LMA of WNMAs globally.

Methods: A modern, global, community-scale data set of in situ WNMA LMA and PM was compiled to test leading hypotheses for environmental drivers of LMA and quantify LMA-PM relationships. Correlations among PM, LMA, climate (Köppen types and continuous data), and leaf habit were assessed and quantified using several uni- and multivariate methods.

Results: Community mean LMA increased under warmer and less seasonal temperatures. Drought-prone communities had the highest LMA variance, likely due to disparity between riparian and non-riparian microhabitats. PM and LMA were correlated for community mean and variance, and their correlations with climate were similar. These patterns indicate that climatic correlatives of modern LMA can inform relative trends in reconstructed fossil LMA. In contrast, matching "absolute" LMA distributions between fossil and modern sites does not allow reliable inference of analogous climate types.

Conclusions: This study furthers our understanding of processes influencing the assembly of WNMA leaf economic strategies in plant communities, highlighting the importance of temperature seasonality and habitat heterogeneity. We also provide a method to reconstruct, and refine the framework to interpret, community-scale LMA in the fossil record.

Premise: Environmental DNA (eDNA) can be used to determine the composition of the soil biome community, revealing beneficial and antagonistic microbes and invertebrates associated with plants. eDNA analyses can complement traditional soil community studies, offering more comprehensive information for conservation practitioners. Studies are also needed to examine differences between field and greenhouse soil biomes because greenhouse-grown plants are often transplanted in the field during restoration efforts.

Methods: We used eDNA multilocus metabarcoding to test how the soil biome of the federally and state-endangered species, Lupinus nipomensis, differed between wet-cool and dry-warm microhabitats. At Arroyo Grande, California, 20 experimental plots were sampled, representing a factorial combination of wet-cool vs. dry-warm soil and plots that did or did not contain L. nipomensis. In a simultaneous greenhouse study, L. nipomensis was grown in drought and well-watered conditions to compare soil communities between field and greenhouse.

Results: A diversity of carbon-cycling microorganisms but not nitrogen-fixers were overrepresented in the field, and nitrogen-fixing bacteria were overrepresented in some greenhouse treatments. The microbial communities in the field soils were more species-rich and evenly distributed than in greenhouse communities. In field plots, microhabitats significantly influenced community beta diversity, while field plots with or without L. nipomensis had no significant differences in alpha or beta diversity.

Conclusions: Our study shows the utility of eDNA soil analysis in elucidating soil biome community differences for conservation and highlights the influence of plant microhabitats on soil microbe associations.