Annals of botany最新文献

Background and aims: Ornamental hortensias are bred from a reservoir of over 200 species in the genus Hydrangea s.l. (Hydrangeaceae), and are valued in gardens, households and landscapes across the globe. The phenotypic diversity of hortensia cultivars, hybrids and wild relatives is mirrored by their genomic variation, with differences in genome size, base chromosome numbers and ploidy level. We aim to understand the genomic and chromosomal basis of hortensia genome variation. Therefore, we analysed six hortensias with different origins and chromosomal setups for repeatome divergence, the genome fraction with the highest sequence turnover. This holds information from the hortensias' evolutionary paths and can guide breeding initiatives.

Methods: We compiled a hortensia genotype panel representing members of the sections Macrophyllae, Hydrangea, Asperae and Heteromallae and reconstructed a plastome-based phylogenetic hypothesis as the evolutionary basis for all our analyses. We comprehensively characterized the repeatomes by whole-genome sequencing and comparative repeat clustering. Major tandem repeats were localized by multicolour FISH.

Key results: The Hydrangea species show differing repeat profiles reflecting their separation into the two major Hydrangea clades: diploid Hydrangea species from Japan show a conserved repeat profile, distinguishing them from Japanese polyploids as well as Chinese and American hortensias. These results are in line with plastome-based phylogenies. The presence of specific repeats indicates that H. paniculata was not polyploidized directly from the common ancestor of Japanese Hydrangea species, but evolved from a distinct progenitor. Major satellite DNAs were detected over all H. macrophylla chromosomes.

Conclusions: Repeat composition among the Hydrangea species varies in congruence with their origins and phylogeny. Identified species-specific satDNAs may be used as cytogenetic markers to identify Hydrangea species and cultivars, and to infer parental species of old Hydrangea varieties. This repeatome and cytogenetics information helps to expand the genetic toolbox for tracing hortensia evolution and guiding future hortensia breeding.

Background and aims: Phytoliths are microscopic siliceous structures produced in specific tissues by many plant families. The morphological features of phytoliths are diagnostic for many plant taxa, and given their inorganic composition often become part of the fossil record. We use phytolith remains from lacustrine sediments to document the conclusive presence of Arecaceae (palms) in subarctic Canada during the late early Eocene (48 Ma).

Methods: Palm phytoliths and aquatic microfossils were extracted from lacustrine mudstones in a drill core taken from the Giraffe kimberlite pipe locality using a combination of acid and oxidation treatments under low heat. Light microscopy and scanning electron microscopy were used to identify, examine, and image the microfossils.

Key results: Spherical echinate-shaped palm phytoliths with cone-shaped surface tubercles, likely belonging to the tribe Trachycarpeae (subfamily Coryphoideae), were uncovered in 45 strata over a 37-meter section of core. We further document in-situ linear arrays of phytoliths, or stegmata, from partially-decomposed palm foliage. Additionally, four aquatic organisms, largely restricted to warm subtropical and tropical localities today, were also uncovered in the same strata harboring the palm phytoliths.

Conclusions: The presence of palm phytoliths allows inference of a warm regional climate during the late early Eocene, with mean cold-month temperatures above freezing despite prolonged winter darkness. This conclusion is supported by the presence of multiple warm water aquatic organisms that grew extensively in the maar lake. Our findings will help to document the extent and timing of perennial ice formation in the northern hemisphere during the Cenozoic. Finally, the discovery of stegmata documents that this morphological trait had evolved by early Eocene.

Background and aims: As winter and spring temperatures continue to increase, the timing of flowering and leaf-out is advancing in many seasonally cold regions. This advancement could put plants that flower early in the spring at risk of decreased reproduction in years when there are late freeze events. Unfortunately, relatively little is known about floral freezing tolerance in forest communities. In this study, we examined the impact of freezing temperatures on the flowers of woody plants in a region where there is rapid winter warming in North America.

Methods: We subjected the flowers of 25 woody species to a hard (-5 °C) and a light freeze (0 °C). We assessed tissue damage using electrolyte leakage. In a subset of species, we also examined the impact of a hard freeze on pollen tube growth. To determine if the vulnerability of flowers to freezing damage relates to flowering time and to examine the responsiveness of flowering time to spring temperature, we recorded the date of first flower for our study species for 3 years.

Key results and conclusions: Across species, we found that floral freezing tolerance was strongly tied to flowering time, with the highest freezing tolerance occurring in plants that bloomed earlier in the year. We hypothesize that these early blooming species are unlikely to be impacted by a false spring. Instead, the most vulnerable species to a false spring should be those that bloom later in the season. The flowering time in these species is also more sensitive to temperature, putting them at a great risk of experiencing a false spring. Ultimately, floral damage in one year will not have a large impact on species fitness, but if false springs become more frequent, there could be long-term impacts on reproduction of vulnerable species.

Background and aims: Pollen germination and tube growth are essential processes for successful fertilization. They are among the most temperature-vulnerable stages and subsequently affect seed production and determine population persistence and species distribution under climate change. Our study aims to investigate intra- and interspecific variations in the temperature dependence of pollen germination and tube length growth and to explore how these variations differ for pollen from elevational gradients.

Methods: We focused on three conifer species, Pinus contorta, Picea engelmannii and Pinus ponderosa, with pollen collected from 350 to 2200 m elevation in Washington State, USA. We conducted pollen viability tests at temperatures from 5 to 40 °C in 5 °C intervals. After testing for 4 d, we took images of these samples under a microscope to monitor pollen germination percentage (GP) and tube length (TL). We applied the gamma function to describe the temperature dependence of GP and TL and estimated key parameters, including the optimal temperature for GP (Topt_GP) and TL (Topt_TL).

Key results: Results showed that pollen from three species and different elevations within a species have different GP, TL, Topt_GP, and Topt_TL. The population with a higher Topt_GP would also have a higher Topt_TL, while Topt_TL was generally higher than Topt_GP, i.e. a positive but not one-to-one relationship. However, only Pinus contorta showed that populations from higher elevations have lower Topt_GP and Topt_TL and vice versa. The variability in GP increased at extreme temperatures, whereas the variability in TL was greatest near Topt_TL.

Conclusions: Our study demonstrates the temperature dependences of three conifers across a wide range of temperatures. Pollen germination and tube growth are highly sensitive to temperature conditions and vary among species and elevations, affecting their reproduction success during warming. Our findings can provide valuable insights to advance our understanding of how conifer pollen responds to rising temperatures.

Background and aims: Over the last few decades, many plant species have shown changes in phenology, such as the date on which they germinate, bud or flower. However, some species are changing more slowly than others, potentially owing to daylength (photoperiod) requirements.

Methods: We combined data on flowering-time advancement with published records of photoperiod sensitivity to try to predict which species are advancing their flowering time. Data availability limited us to the Northern Hemisphere.

Key results: Cross-species analyses showed that short-day plants advanced their flowering time by 1.4 days per decade and day-neutral plants by 0.9 days per decade, but long-day plants delayed their flowering by 0.2 days per decade. However, photoperiod-sensitivity status exhibited moderate phylogenetic conservation, and the differences in flowering-time advancement were not significant after phylogeny was accounted for. Both annual and perennial herbs were more likely to have long-day photoperiod cues than woody species, which were more likely to have short-day photoperiod cues.

Conclusions: Short-day plants are keeping up with plants that do not have photoperiod requirements, suggesting that daylength requirements do not hinder changes in phenology. However, long-day plants are not changing their phenology and might risk falling behind as competitors and pollinators adapt to climate change.

Background and aims: Anthropogenic disturbances are causing a co-occurring increase in biotic (ungulate herbivory) and abiotic (drought) stressors, threatening plant reproduction in oak-dominated ecosystems. However, could herbivory compensate for the adverse impact of drought by reducing evapotranspiration? Thus, we investigated the isolated and joint effects of herbivory and drought on oak seedlings of two contrasting Mediterranean species that differ in leaf habit and drought resistance.

Methods: California oak seedlings from the evergreen, and more drought-resistant, Quercus agrifolia and the deciduous Q. lobata (n = 387) were assigned to a fully crossed factorial design with herbivory and drought as stress factors. Seedlings were assigned in a glasshouse to three to four clipping levels simulating herbivory and three to four watering levels, depending on the species. We measured survival, growth and leaf attributes (chlorophyll, secondary metabolites, leaf area and weight) once a month (May-September) and harvested above- and below-ground biomass at the end of the growing season.

Key results: For both oak species, simulated herbivory enhanced seedling survival during severe drought or delayed its adverse effects, probably due to reduced transpiration resulting from herbivory-induced leaf area reduction and compensatory root growth. Seedlings from the deciduous, and less drought-resistant species benefited from herbivory at lower levels of water stress, suggesting different response across species. We also found complex interactions between herbivory and drought on their impact on leaf attributes. In contrast to chlorophyll content which was not affected by herbivory, anthocyanins increased with herbivory - although water stress reduced differences in anthocyanins due to herbivory.

Conclusions: Herbivory seems to allow Mediterranean oak seedlings to withstand summer drought, potentially alleviating a key bottleneck in the oak recruitment process. Our study highlights the need to consider ontogenetic stages and species-specific traits in understanding complex relationships between herbivory and drought stressors for the persistence and restoration of multi-species oak savannas.

Background and aims: The majority of the Earth's land area is currently occupied by humans. Measuring how terrestrial plants reproduce in these pervasive environments is essential for understanding their long-term viability and their ability to adapt to changing environments.

Methods: We conducted hierarchical and phylogenetically independent meta-analyses to assess the overall effects of anthropogenic land-use changes on pollination, and male and female fitness in terrestrial plants.

Key results: We found negative global effects of land-use change (i.e. mainly habitat loss and fragmentation) on pollination and on female and male fitness of terrestrial flowering plants. Negative effects were stronger in plants with self-incompatibility systems and in plants pollinated by invertebrates, regardless of life form and sexual expression. Pollination and female fitness of pollination-generalist and pollination-specialist plants were similarly negatively affected by land-use change, whereas male fitness of specialist plants showed no effects.

Conclusions: Our findings indicate that angiosperm populations remaining in fragmented habitats negatively affect pollination, and female and male fitness, which will probably decrease the recruitment, survival and long-term viability of plant populations remaining in fragmented landscapes. We underline the main current gaps of knowledge for future research agendas and call not only for a decrease in the current rates of land-use changes across the world but also to embark on active restoration efforts to increase the area and connectivity of remaining natural habitats.

Background: The frequency and intensity of droughts are expected to increase under global change, driven by anthropogenic climate change and water diversion. Precipitation is expected to become more episodic under climate change, with longer and warmer dry spells, although some areas might become wetter. Diversion of freshwater from lakes and rivers and groundwater pumping for irrigation of agricultural fields are lowering water availability to wild plant populations, increasing the frequency and intensity of drought. Given the importance of seasonal changes and extremes in soil moisture to influence plant reproduction, and because the majority of plants are flowering plants and most of them depend on pollinators for seed production, this review focuses on the consequences of drought on different aspects of reproduction in animal-pollinated angiosperms, emphasizing interactions among drought, flowering and pollination.

Scope: Visual and olfactory traits play crucial roles in attracting pollinators. Drought-induced floral changes can influence pollinator attraction and visitation, together with pollinator networks and flowering phenology, with subsequent effects on plant reproduction. Here, we review how drought influences these different aspects of plant reproduction. We identify knowledge gaps and highlight areas that would benefit from additional research.

Conclusions: Visual and olfactory traits are affected by drought, but their phenotypic responses can vary with floral sex, plant sex, population and species. Ample phenotypic plasticity to drought exists for these traits, providing an ability for a rapid response to a change in drought frequency and intensity engendered by global change. The impact of these drought-induced changes in floral traits on pollinator attraction, pollen deposition and plant reproductive success does not show a clear pattern. Drought affects the structure of plant-pollinator networks and can modify plant phenology. The impact of drought on plant reproduction is not always negative, and we need to identify plant characteristics associated with these more positive responses.

Background and aims: Fire may favour plant flowering by opening up the vegetation and increasing abiotic resource availability. Increased floral display size can attract more pollinators and increase absolute fruit and seed production immediately after a fire. However, anthropogenic increases in fire frequency may alter these responses. We aim to assess the effects of fire on the pollination and reproductive success of plants at the global scale.

Methods: We performed a systematic literature review and meta-analyses to examine overall fire effects as well as different fire parameters on pollination and on plant reproduction. We also explored to what extent the responses vary among pollinators, pollination vectors, plant regeneration strategies, compatibility systems, vegetation types and biomes.

Key results: Most studies were conducted in fire-prone ecosystems. Overall, single fires increased pollination and plant reproduction but this effect was overridden by recurrent fires. Floral visitation rates of pollinators were enhanced immediately following a wildfire, and especially in bee-pollinated plants. Fire increased the absolute production of fruits or seeds but not fruit or seed set. The reproductive benefits were mostly observed in wind-pollinated (graminoids), herbaceous and resprouter species. Finally, fire effects on pollination were positively correlated with fire effects on plant reproductive success.

Conclusions: Fire has a central role in pollination and plant sexual reproduction in fire-prone ecosystems. The increase in the absolute production of fruits and seeds suggests that fire benefits to plant reproduction are probably driven by increased abiotic resources and the consequent floral display size. However, reproduction efficiency, as measured by fruit or seed set, does not increase with fire. In contrast, when assessed on the same plant simultaneously, fire effects on pollination are translated into reproduction. Increased fire frequency due to anthropogenic changes can alter the nature of the response to fire.