American Journal of Botany最新文献

Premise: Populations can locally adapt to the biotic and abiotic factors of environments. However, detecting adaptation to biotic factors can depend on the abiotic conditions in which the adaptation is tested, and vice versa. The microbiome is one important aspect of the biotic environment: Interactions between microbiomes and their hosts are critical for host fitness and trait expression. If hosts adapt to local microbiomes, they may therefore depend on interactions with local microbes to express trait values adapted to the local abiotic environment.

Methods: Using Lemna minor (duckweed) as a model host, we examined differences in host fitness when grown in local and nonlocal microbiomes and in local and nonlocal water. We experimentally recombined duckweeds, microbes, and water from four ponds around Durham, New Hampshire (United States) in well-plate microcosms in a growth chamber.

Results: The source of duckweeds, microbes, and water all affected microbial growth, duckweed growth, and duckweed traits. However, weak, marginally significant local adaptation resulted in higher frond area only when duckweeds were paired with their local water and local microbes. Microbial growth was also marginally reduced when duckweeds were paired with microbes and water from their local site.

Conclusions: While microbiome impacts on duckweed growth and traits varied across abiotic contexts, local microbiomes provided only limited growth benefits. Harnessing the effects of plant microbiomes is an exciting area of applied research. Despite our findings, bioprospecting in local microbiomes could still be fruitful: It may be ecologically safer, and other plants may locally adapt to microbiomes.

Interpretations of evolutionary outcomes are limited without incorporation of physiological ecology, and ecophysiological interpretations would benefit from incorporating evolutionary perspectives. Although there has been a rise of studies in the last 20 years between these fields, evolutionary studies that incorporate plant physiology have largely focused on the same traits (e.g., flowering time, specific leaf area), neglecting cellular and developmental traits. This neglect is largely due to the high throughput demands in evolutionary studies and the lack of technological advancements in ecophysiology. However, this bias in measured traits has resulted in limiting our understanding of the evolution of plant form and function. On the other hand, most detailed studies on plant physiological and anatomical responses to the environment are either in applied sciences, focused on economically important plants, or examine model organisms rather than wild populations. These detailed ecophysiological studies generally do not incorporate evolutionary discourse, even though they often study adaptation. The aim of this synthesis is to offer a comprehensive resource, building upon previous works, for researchers to bridge the gap between ecophysiology and evolutionary ecology.

Premise: Declines in pollinator populations can reduce pollination services to plants, resulting in lower seed production. In response to these reductions, plants could increase the probability of pollinator visitation by plastically extending floral longevity. However, whether extended floral longevity increases seed production as pollinators decline depends on the limits to and costs of plasticity in longevity, both of which could be affected by drought stress.

Methods: To test whether drought stress affects the limits to and costs of plasticity in floral longevity in response to pollinator decline, we exposed Lobelia siphilitica to droughted and well-watered treatments and measured floral longevity and the number of seeds produced by flowers pollinated on day 1 vs. day 5 of the female phase. If floral longevity is shorter in the droughted treatment, then drought stress could limit the expression of extended longevity. If delaying pollination until day 5 reduces seed production more in the droughted treatment, then drought stress could increase the cost of extended longevity.

Results: The droughted treatment reduced floral longevity by ~18% but did not affect the number of seeds produced by flowers pollinated on day 1 vs. day 5. Instead, delaying pollination until day 5 reduced the number of seeds by ~24% in both the droughted and well-watered treatments.

Conclusions: Drought stress does not affect the cost of plasticity in floral longevity but could limit the expression of extended longevity. Consequently, whether extended floral longevity could increase seed production as pollinators decline may depend on human-induced changes in precipitation.

Premise: The maintenance of gynodioecy, female and hermaphroditic coexistence in plants, requires females to have a reproductive advantage over hermaphrodites in offspring quality, quantity, or both. Pollinators can influence this by mediating the reproductive success of females and hermaphrodites. We measured differences in pollinator-mediated fitness components between female and hermaphroditic plants in Sidalcea campestris to evaluate the role of pollinator-mediated selection in maintaining gynodioecy.

Methods: We studied sex-biased pollinator dynamics across 28 gynodioecious populations of S. campestris and conducted pollen supplementation experiments in 20 of these populations. Using pollinator surveys and pollen supplementation experiments, we tested for differences in pollinator visitation rates, pollinator community composition, seed production, and pollen limitation between sexes.

Results: Hermaphrodites received an average of 2.24 times more visits than females, although pollinator community composition was similar for both sexes. The estimated average probability of female seed set was 1.7 times higher than hermaphrodites for open-pollinated flowers and 2.0 times higher for hand-pollinated flowers, providing evidence of a female reproductive advantage. Seed set in both sexes was pollen limited, and females were not more limited than hermaphrodites. Female pollen limitation was unaffected by population-level female frequency.

Conclusions: These results revealed complex pollinator-mediated fitness differences between females and hermaphrodites. While our study demonstrated that females achieve the expected reproductive advantage for cytonuclear gynodioecy, the lack of differential pollen limitation and frequency-dependent female fitness are inconsistent with expectations of stable gynodioecy. Additional environmental, ecological, and genetic factors may regulate population dynamics in this gynodioecious system.

Premise: There is an ongoing shift about how best to infer ancestral chromosome numbers in plants. From 1938 to 2020, this was done by focusing on meiotic counts in extant species and using them to infer a hypothetical base chromosome number for larger clades, even when not found empirically. Since 2017, comparative-genomic studies provide a different approach that focuses on syntenic blocks in chromosome-level genome assemblies. For flowering plants, the two approaches have yielded drastically different results, namely either a base number around n = 7 or instead around 16.

Methods: Here I review how hypothetical base numbers and an assumed general evolutionary progression from lower to higher numbers-ideas that go back to benchmark papers by G. L. Stebbins-have hampered botanists' inference of plausible ancestral chromosome numbers.

Results: Model-based studies of chromosome number evolution into the 2020 s have perpetuated some of the traditional biases by constraining numbers near or at the root of angiosperm phylogenies to be low, which may explain the discrepancies between their low inferred ancestral number (e.g., n = 7) and the higher number inferred from in silico comparison of syntenic blocks in chromosome-level genome assemblies (n = 16).

Conclusions: Data available at this point, including from chromosome counts in early-diverging lineages (which were not known in Stebbins's time), argue against the long-assumed general low-to-high trend for changes in chromosome number across flowering plants.

Premise: Long-lived clonal plants that rarely or never reproduce sexually raise important questions about persistence, genetic diversity, and extinction risk. Arundinaria appalachiana, an upland bamboo endemic to the southern Appalachian Mountains, has never been observed to flower. We investigated the spatial genetic structure and demography of this species to assess how it persists and to inform its conservation status.

Methods: We used genotype-by-sequencing of microsatellite loci to characterize clonal structure in two populations separated by 19 km on the southern Cumberland Plateau in Tennessee, USA. Rhizome networks were mapped over 8 yr to estimate rates of clonal expansion and infer genet age. Ramet density was monitored annually to detect demographic changes.

Results: Both populations were dominated by a few large, ancient genets; the largest covered >30 ha and was estimated to be >1700 yr old. Clonal diversity was low, and no flowering was observed during the 9 yr study. Rhizome mapping showed slow expansion (0.12-0.30 m yr^-1) and local fragmentation. Ramet density declined significantly in one population, while remaining stable in the other.

Conclusions: Arundinaria appalachiana persists through clonal growth alone, forming extensive, ancient genets in the absence of sexual reproduction. This clonal longevity enables persistence, but the lack of genetic renewal raises concerns about long-term viability in changing environments. Our findings highlight the importance of understanding spatial genetic structure in clonal plant populations and its consequences for conservation planning.

Premise: The carnivorous plant genus Pinguicula (Lentibulariaceae) exhibits remarkable floral diversity associated with pollination, particularly in the largest subgenus Temnoceras, which spans Mexico and Central America. Despite this diversity, the relationships between species and the evolution of key floral traits remain unresolved. Here, we employed whole-genome sequencing to reconstruct a robust phylogeny and examine the evolution of pollination syndromes and potential pollinator-prey conflicts.

Methods: We generated nuclear and plastid genomic data for 32 Pinguicula species. Phylogenetic relationships were inferred using 2189 BUSCO loci analyzed through ASTRAL. Morphological traits associated with pollination and carnivory were assessed with ancestral state reconstruction, principal component analysis, and phylogenetic linear models. Loss and pseudogenization of ndh genes implicated in potential shifts in trophic strategies were evaluated in both nuclear and plastid genomes.

Results: Our genome-scale phylogeny resolved six monophyletic clades within Temnoceras, refining infrageneric classification. Most ndh genes are either lost or pseudogenized across both genomic compartments. Floral morphology strongly clusters by pollinator type, with fly-pollinated species forming a distinct clade characterized by cylindrical spurs and tubes. Ancestral reconstructions indicate multiple independent transitions in spur and tube morphology. Phylogenetic linear modeling revealed a significant evolutionary correlation between scape length and carnivorous leaf area, suggesting that spatial separation may represent an adaptive response to mitigate pollinator-prey conflict.

Conclusions: This study provides a refined phylogenetic framework for Pinguicula subgenus Temnoceras and highlights how pollinator specialization and carnivory-related traits contribute to floral evolution.The repeated loss of ndh genes implies relaxed selective pressure on photosynthesis-related pathways in these carnivorous species.

Premise: Species of Deuterocohnia (17 spp.) show extraordinary variation in elevation (0-3900 m a.s.l.) and growth forms, and many have narrow geographic distributions in the west-central Andes and the Peru-Chile coast. Previous research using few plastid and nuclear loci failed to produce well-resolved or supported phylogenies. Here we sequenced 1815 single-copy nuclear genes and whole plastomes to infer relationships, screen for reticulation, reconstruct evolution of vegetative and floral characters, and evaluate species groups and their historical biogeography.

Methods: We developed the Bromeliad1815 bait set to capture low-copy nuclear genes across Bromeliaceae, producing nuclear and plastome phylogenies for Deuterocohnia and outgroups in six bromeliad subfamilies using maximum likelihood, ASTRAL, and network analyses; test for cytonuclear conflict and its potential causes; and evaluate evolution of morphological characters in relation to each other and elevation using phylogenetic PCA and phylogenetic regression.

Results: We produced fully resolved, strongly supported nuclear and plastome phylogenies for Deuterocohnia, with crown ages of 5.5 and 8.0 Mya, respectively. Cytonuclear conflict appears driven mainly by hybridization/introgression, consistent with several species co-occurring in small areas. Vegetative organs and growth form become increasingly compact with elevation, reflecting adaptation to desiccation, wind exposure, and cold soils. Deuterocohnia arose in southeastern Bolivia and repeatedly evolved up- and downslope into other habitats from Andean Yungas at mid-elevation.

Conclusions: Our results imply rapid adaptive divergence (e.g., in strobilifera-chrysantha), convergent evolution (two origins of the cushion growth-form), phylogeny consistent with form in some cases (e.g., seramisiana-brevispicata-meziana) and recurrent effects of the Rio Pilcomayo barrier on speciation and chloroplast capture.

Premise: A number of ecologically important tropical trees form symbiotic ectomycorrhizal (EcM) fungal associations including the Dipterocarpaceae, that dominate lowland forests of South-east Asia. Whilst numerous pot-based studies have focused on the importance of EcMs for dipterocarp seedling growth and performance, few field studies have been undertaken.

Methods: In a 20-month field experiment in Malaysian Borneo, two species with contrasting light requirements-shade-tolerant Hopea nervosa and the more light-demanding Parashorea tomentella-were subjected to the factorial addition of fungicide (to reduce EcM colonization) and nutrients.

Results: Fungicide addition reduced EcM colonization by a small but significant percentage. Reductions in foliar nitrogen, phosphorus, and chlorophyll concentrations in both species and in calcium and magnesium concentrations in H. nervosa did not translate into reduced biomass in either species. When given additional nutrients, H. nervosa had no increase in foliar nutrient concentrations or biomass, but P. tomentella had an increase in foliar nitrogen, phosphorus, and magnesium concentrations and more than doubled its biomass. When nutrients were added but EcM reduced, P. tomentella did not increase in biomass.

Conclusions: EcM fungi can play an important role in influencing dipterocarp seedling mineral nutrition, and P. tomentella may require EcMs to effectively utilize additional mineral nutrient sources. The importance of nutrient uptake for biomass production is less clear and may be confounded by the use of fungicide to control EcM colonization.

Premise: Seed dispersal can mediate species interactions between plants across life stages. Plants can physically stop seed movement (seed trapping) and prevent further dispersal following entrapment (seed retention). We therefore hypothesized seed trapping and retention rates depend on the physical attributes of interacting seeds and plants, including seed traits and plant length.

Methods: For combinations of co-occurring plant species in an alpine community, we experimentally measured seed trapping and retention potential. To measure seed trapping, we determined the rate at which seeds were unable to physically pass through vegetation without stopping after being launched at plants. To assess seed retention, we compared the rate that seeds left vegetation following entrapment across plant and seed species and by seed traits.

Results: Seed trapping rates were higher for larger-sized plants and differed among plant species but not seed species. Seed trapping and retention rates were higher for plant species with denser vegetation. Seeds with a pappus were retained less than seeds without, and we observed interactive effects between plant and seed species identity on retention rates.

Conclusions: Seed trapping and retention rates are influenced by species identities and the physical attributes of plants and seeds. Because both processes can contribute to where a seed is ultimately dispersed, seed trapping and retention may mediate species co-occurrence and further species interactions.