Annals of botany最新文献

Background and aims: Success during colonization likely depends on growing quickly and tolerating novel and stressful environmental conditions. However, rapid growth, stress avoidance, and stress tolerance are generally considered divergent physiological strategies.

Methods: We evaluate how white clover (Trifolium repens) has evolved to a divergent water regime following introduction to North America. We conduct RNAseq within a dry-down experiment utilizing accessions from low and high latitude populations from native and introduced ranges, and assess variation in dehydration avoidance (ability to avoid wilting) and dehydration tolerance (ability to survive wilting).

Key results: Introduced populations are better at avoiding dehydration, but poorer at tolerating dehydration than native populations. There is a strong negative correlation between avoidance and tolerance traits and expression of most drought-associated genes exhibits similar tradeoffs. Candidate genes with expression strongly associated with dehydration avoidance are linked to stress signaling, closing stomata, and producing osmoprotectants. However, genes with expression linked to dehydration tolerance are associated with avoiding excessive ROS production and toxic bioproducts of stress responses. Several candidate genes show differential expression patterns between native and introduced ranges, and could underlie differences in drought resistance syndromes between ranges.

Conclusions: These results suggest there has been strong selection following introduction for dehydration avoidance at the cost of surviving dehydration. More broadly, tradeoffs between dehydration avoidance and tolerance responses likely exist both at the genetic and phenotypic scales that will influence evolutionary responses and potentially limit the global spectrum of plant form and function.

Background and aims: We have abundant knowledge on drought responses of plants or soil microorganisms individually. However, there is a severe lack of knowledge regarding interactions in the plant-soil-microbiome continuum, and specifically root-soil interface traits including the role of root hairs. Here, we investigated how water limitation propagates in a plant-soil-microbiome system upon stopping irrigation. We used two Zea mays genotypes (rth3 and its isogenic wildtype B73), differing in root hair formation, to elucidate the effect of rhizosphere extension under water limitation.

Methods: For 22 days, WT and rth3 were grown in a climate chamber, with irrigation stopped for drought treatment during the last 7 days. Daily measurements included soil water status, plant evapotranspiration and gas exchange. At harvest, root exudates, shoot relative water content, osmolality and nutrients, root morphological traits and transcriptomics, and soil microbial β-diversity and enzyme activity were determined.

Key results: In line with a larger plant size, drought stress developed more rapidly and the number of differentially expressed genes was higher in the WT compared to rth3. Under water limitation, root exudation rates increased and soil enzyme activities decreased more strongly in the WT rhizosphere. In both genotypes, water level significantly altered microbial β-diversity in the bulk soil, particularly affecting fungi more than bacteria/archaea. The genotype affected only bacteria/archaea and was more pronounced in rhizosphere than in bulk soil.

Conclusions: This interdisciplinary study assessed how a short drought stress manifested in a plant-soil-microbiome system. Water limitation altered microbial (fungal) diversity more distant from the root surface. Genotype-specific stress-induced increases in exudation rates modified microbial activity in root proximity, possibly pointing to root hair functions under water limitation. Less intense drought responses of rth3 were confirmed at all levels of investigation and may be due at least in part to its smaller plant size.

Background and aims: While we know a lot about variation of root traits across large set of species, knowledge on differences in root traits among species with different ecological optima, simultaneously considering species life span and phylogeny, is limited. We also do not know if inter-specific differences in root traits measured in one environment apply in another environment. Such knowledge is crucial to predict species responses to future environments.

Methods: Using 65 species cultivated under uniform conditions, we studied effects of species habitat preference, describing under which conditions the species naturally occur, on root morphological and chemical traits and allocation to roots while also considering species life span, phenology at harvest and phylogeny. In a subset of species, we explored if species rankings in values of different traits depend on specific substrate of growth.

Key results: Inter-specific trait differences were strongly linked to species habitat preferences. The best predictor was indicator value for soil disturbance with roots of species preferring disturbed habitats having higher specific root length and lower diameter, suggesting low collaboration with mutualists. While life span and phylogeny also determined trait values, their inclusion into models did not change effects of habitat preferences. The patterns are thus not a result of species niche conservatism, but contemporary species adaptations. Species ranking in different substrates was more consistent for root morphology than for root chemistry and root/shoot ratio.

Conclusions: Root trait variation is driven by species habitat preferences indicating that inter-specific root trait variation is a result of species adaptations to different environments. Interestingly, disturbance indicator value was a better predictor of root trait variation than other, more commonly, considered habitat characteristics. Inter-specific differentiation in root morphology is consistent among substrates and can thus be compared across studies, but root chemistry and allocation data have to be used with caution.

Background and aims: Seed covering structure hardness could play a role in defence/predation, physical dormancy and in situ longevity/persistence. However, research to date has been limited regarding quantification methods, plant diversity and geographic distribution. In this study, we determined global variation in seed covering structure hardness of woody species with desiccation tolerant seeds and analysed its relationships with relevant climatic variables, seed traits and ecological processes.

Methods: We measured seed covering structure hardness of 476 species from 459 genera and 113 families using puncture force. We used phylogenetic-informed regressions to test covering structure hardness against potential quantitative predictors (19 climate variables [n=405], 10 seed morphological traits [n=413], elevation [n=405], genus age [n=375]) and response variables (ex situ seed longevity [n=67], germination rate [n=82], species distribution/range size [n=403]). Categorical predictors (geographical region [n=444], plant lifeform [n=428], seed dormancy type [n=146], seed physical dormancy in the Fabaceae family [n=76], dispersal unit or mechanism [n=484], fruit type [n=427]) were tested using pairwise comparisons.

Key results: Seed covering structure hardness ranged from 0.13 to 366.38 N and seed and fruit (seed/fruit) size, seed/fruit roundness, seed/fruit colour (lightness) and precipitation of the driest quarter were significantly associated with hardness. In addition, dormancy types (vs non-dormancy), dispersal as fruit (vs seed), or certain fruit types (fleshy vs dry, drupes vs other types), as well as animal dispersal (vs other mechanisms) showed higher levels of hardness. Furthermore, covering structure roundness was higher in animal dispersed seeds/fruits (vs other dispersal strategies). Finally, covering structure hardness was shown to predict germination rate but not ex situ seed longevity or species range size.

Conclusions: Our results suggest roles for morphology, dormancy, dispersal and precipitation in explaining part of the global variation in seed covering structure hardness of woody species with orthodox seeds. However, we showed that the presence of physical dormancy does not always imply having a harder covering structure than non-dormant seeds and therefore terms like "hardseeded" or "hard coat" should no longer be used as synonyms for this trait.

Background and aims: Widespread dieback and mortality have occurred in mature artificial forests in recent decades. It is unclear how anatomical structures and physiological activities determine the dieback and even mortality of the canopy.

Methods: We analyzed the variation in anatomical structure, hydraulic function, and non-structural carbohydrates among canopy levels along the drought gradient.

Results: We found that (1) Robinia pseudoacacia coordinated hydraulic efficiency and safety by increasing the vessel diameter, vestured overlap, and decreasing the total pit membrane area in xylem with increasing drought stress. (2) The hydraulic conductivity within the canopy gradually decreased from the bottom to the upper canopy, while embolism increased. As precipitation decreases, the upper twigs may first dieback owing to hydraulic failure, accompanied by a substantial reduction (approximately 2.20% total dry mass) in soluble sugar and starch within these branches. (3) Although the upper canopy branches did not reach the hydraulic safety margin, the soluble sugar and starch contents reduced significantly (around 1.59% total dry mass). Meanwhile, the content of nonstructural carbohydrates in other canopy tissues increased to cope with drought stress.

Conclusions: In conclusion, dieback of upper canopy twigs may be a result of hydraulic failure, while the nonstructural carbohydrates of the upper canopy's branches decreased, which can be viewed as an adjustment of carbon allocation and avoidance of water loss at the whole tree level, contributing to plant survival under drought stress.

Background and aims: Climate change is causing increasing temperatures and drought, creating new environmental conditions, which species must cope with. Plant species can respond to these shifting environments by escaping to more favorable environments, undergoing adaptive evolution, or exhibiting phenotypic plasticity. In this study, we investigate genotype responses to variation in environmental conditions (genotype-by-environment interactions; G × E) over multiple years to gain insights into the plasticity and potential adaptive responses of plants to environmental changes in the face of climate change.

Methods: We reciprocally transplanted 16 European genotypes of Fragaria vesca (Rosaceae), the woodland strawberry, between four sites along a latitudinal gradient from 40°N (Spain) to 70°N (northern Finland). We examined G × E interactions in plant performance traits (fruit and stolon production and rosette size) under ambient weather conditions and a reduced precipitation treatment (as a proxy for drought), at these sites over two years.

Key results: Our findings reveal signals of local adaptation for fruit production at the latitudinal extremes of F. vesca distribution. No clear signals of local adaptation for stolon production were detected. Genotypes from higher European latitudes were generally smaller than genotypes from lower latitudes across almost all sites, years and both treatments, indicating a strong genetic control of plant size in these genotypes. We found mixed responses to reduced precipitation: while several genotypes exhibited poorer performance under the reduced precipitation treatment across most sites and years, with the effect being most pronounced at the driest site, other genotypes responded to reduced precipitation by increasing fruit and/or stolon production and/or growing larger across most sites and years, particularly at the wettest site.

Conclusions: This study provides insights into the influence of different environments on plant performance at a continental scale. While woodland strawberry seems locally adapted in more extreme environments, reduced precipitation results in winners and losers among its genotypes. This may ultimately reduce genetic variation in the face of increasing drought frequency and severity, with implications for the species' capacity to adapt.

Background and aims: Ambophily, an intriguing pollination system in which plant species present adaptations to both biotic and abiotic pollination, has been scarcely reported. Most studies have been conducted with a single or few related species from wind-pollinated genera. We here assess for the first time the frequency of ambophily at the community level.

Methods: We evaluated pollen carried by wind in 63 animal-pollinated species from a Brazilian campos de altitude. For those with pollen carried by wind, we evaluated the contribution of wind and animals to seed production with controlled pollination experiments, as well as floral traits and floral visitor assemblages.

Key results: Pollen of 23 species was carried by wind (~37 %). Animals and wind contributed to the reproduction of seven species (~11 %), including one pollinated by hummingbirds, large bees and wind. These seven ambophilous species presented unrestrictive floral morphologies and generalist pollination.

Conclusions: We found a high frequency of ambophily in a single community (11 %), which represented an increment of ~5 % of species relative to all ambophilous species reported in the literature so far. Investigating pollen transport by wind in zoophilous species combined with controlled experiments helped detect ambophily in species that are usually ignored in wind pollination studies. Our results showed that putative zoophilous species may actually be ambophilous, suggesting that the selective pressures towards ambophily also occur in zoophilous lineages.

Background and aims: Rock outcrop vegetation is distributed worldwide and hosts a diverse and unique flora that evolved under harsh environmental conditions. Unfortunately, seed ecology in such ecosystems has received little attention, especially regarding seed traits, germination responses to abiotic factors and the potential role of phylogenetic relatedness in shaping such features. Here, we provide the first quantitative and phylogenetically informed synthesis of the seed functional ecology of Brazilian rock outcrop vegetation, with a particular focus on quartzitic and ironstone campo rupestre.

Methods: Using a database of functional trait data, we calculated the phylogenetic signal for seven seed traits for 371 taxa and tested whether they varied among growth forms, geographic distribution and microhabitats. We also conducted meta-analyses that included 4252 germination records for 102 taxa to assess the effects of light, temperature and fire-related cues on the germination of campo rupestre species and explored how the aforementioned ecological groups and seed traits modulate germination responses.

Key results: All traits and germination responses showed a moderate to strong phylogenetic signal. Campo rupestre species responded positively to light and had maximum germination between 20 and 25 °C. The effect of temperatures beyond this range was moderated by growth form, species geographic distribution and microhabitat. Seeds exposed to heat shocks above 80 °C lost viability, but smoke accelerated germination. We found a moderating effect of seed mass for responses to light and heat shocks, with larger, dormant seeds tolerating heat better but being less sensitive to light. Species from xeric habitats evolved phenological strategies to synchronize germination during periods of increased soil water availability.

Conclusions: Phylogenetic relatedness plays a major role in shaping the seed ecology of Brazilian rock outcrop vegetation. Nevertheless, seed traits and germination responses varied significantly between growth forms, species geographic distribution and microhabitats, providing support to the regeneration niche hypothesis and the role of functional traits in shaping germination in these ecosystems.

Background and aims: Byblis liniflora (Byblidaceae) is a carnivorous plant that has developed sticky flypaper traps with two types of glandular trichomes producing digestive enzymes and sticky mucilage. This study aimed to analyse the ultrastructure of these glandular leaf trichomes based on rapid freeze-fixation and conventional chemical fixation in the attempt to understand their functional contribution to the carnivorous performance of the plants.

Methods: The Byblis cells were studied in transmission electron microscopy, scanning electron microscopy and scanning transmission electron microscopy using cryo-techniques for fixation and substitution in addition to conventional chemical fixation.

Key results: We show in detail the architecture of both the digestive glands and the mucilage glands with their relevant sets of organelles. Both mitochondria and plastids have a conspicuous plasticity, with branches and constrictions, and they associate to form clusters. The glandular cells appear to be transfer cells with cell wall ingrowths. Digestive glands occur in different states of development. Their cuticle forms discontinuities that are unique among glands of carnivorous plants. They look like cuticular holes - the cuticle separates from the cell wall in only one spot and then ruptures. Cuticular discontinuities thus differ from the cuticular gaps and cuticular pores so far described in carnivorous plants. We therefore propose for them the term 'cuticular holes'.

Conclusions: Application of cryo-techniques made it possible to show the true structure of the cell wall and the relationship between cell wall ingrowths and organelles, as well as the morphology and structure of organelles and their associations.