Annals of botany最新文献

Background and aims: Five species of cotton (Gossypium) were exposed to 38 °C days during early vegetative development. Commercial cotton (Gossypium hirsutum) was contrasted with four wild cotton species (Gossypium australe, G. bickii, G. robinsonii and G. sturtianum) that are endemic to central and northern Australia.

Methods: Plants were grown at daytime maxima of 30 or 38 °C for 25 days, commencing at the four-leaf stage. Leaf areas and shoot biomass were used to calculate relative rates of growth and specific leaf areas. Leaf gas exchange measurements revealed assimilation and transpiration rates, in addition to electron transport rates and carboxylation efficiency in steady-state conditions. Finally, leaf morphological traits (mean leaf area and leaf shape) were quantified, along with leaf surface decorations, imaged using scanning electron microscopy.

Key results: Shoot morphology was differentially affected by heat, with three of the four wild species growing faster at 38 than at 30 °C, whereas early growth in G. hirsutum was severely inhibited by heat. Areas of individual leaves and the number of leaves both contributed to these contrasting growth responses, with fewer, smaller leaves at 38 °C in G. hirsutum. CO2 assimilation and transpiration rates of G. hirsutum were also dramatically reduced by heat. Cultivated cotton failed to achieve evaporative cooling, contrasting with the transpiration-driven cooling in the wild species. Heat substantially reduced electron transport rates and carboxylation efficiency in G. hirsutum, with much smaller effects in the wild species. We speculate that leaf shape, as assessed by invaginations of leaf margins, and leaf size contributed to heat dispersal differentially among the five species. Likewise, reflectance of light radiation was also highly distinctive for each species.

Conclusions: These four wild Australian relatives of cotton have adapted to hot days that are inhibitory to commercial cotton, deploying a range of physiological and structural adaptations to achieve accelerated growth at 38 °C.

Background and aims: Long-term exposure over several days to far-red light (FR) increases leaf expansion, whereas short-term exposure (minutes) might enhance the photosystem II operating efficiency (ϕPSII). The interaction between these responses at different time scales and their impact on photosynthesis at the whole-plant level are not well understood. We aimed to assess the effects of FR in an irradiance mimicking the spectrum of sunlight (referred to as artificial solar irradiance), in both the long and short term, on whole-plant CO2 assimilation rates and in leaves at different positions in the plant.

Methods: Tomato (Solanum lycopersicum) plants were grown under artificial solar irradiance conditions with either a severely reduced or normal fraction of FR [SUN(FR-) vs. SUN]. To elucidate the interplay between the growth light treatment and the short-term reduction of FR, we investigated this interaction at both the whole-plant and leaf levels. At the whole-plant level, CO2 assimilation rates were assessed under artificial solar irradiance with a normal fraction and a reduced fraction of FR. At the leaf level, the effects of removal and presence of FR (0FR and 60FR) during transition from high to low light on CO2 assimilation rates and chlorophyll fluorescence were evaluated in upper and lower leaves.

Key results: SUN(FR-) plants had lower leaf area, shorter stems and darker leaves than SUN plants. Although reducing FR during growth did not affect whole-plant photosynthesis under high light intensity, it had a negative impact at low light intensity. Short-term FR removal reduced both plant and leaf CO2 assimilation rates, but only at low light intensity and irrespective of the light treatment during growth and the leaf position. Interestingly, the kinetics of ϕPSII from high to low light were accelerated by 60FR, with a larger effect in lower leaves of SUN than in SUN(FR-) plants.

Conclusions: Growing plants with a reduced amount of FR light lowers whole-plant CO2 assimilation rates at low light intensity through reduced leaf area, despite maintaining similar leaf-level CO2 assimilation to leaves grown with a normal amount of FR. The short-term removal of FR brings about significant but marginal reductions in photosynthetic efficiency at the leaf level, regardless of the long-term growth light treatment.

Background and aims: Polyploidy is an important evolutionary driver for plants and has been linked with higher species richness and increases in diversification rate. These correlations between ploidy and plant radiations could be the result of polyploid lineages exploiting broader niche space and novel niches due to their enhanced adaptability. The evolution of ploidy and its link to plant diversification across the Australian continent is not well understood. Here, we focus on the ploidy evolution of the Australasian Rhamnaceae tribe Pomaderreae.

Methods: We generated a densely sampled phylogeny (90 %, 215/240 species) of the tribe and used it to test for the evolution of ploidy. We obtained 30 orthologous nuclear loci per sample and dated the phylogeny using treePL. Ploidy estimates for each sequenced species were obtained using nQuire, based on phased sequence data. We used MiSSE to obtain tip diversification rates and tested for significant relationships between diversification rates and ploidy. We also assessed for relationships between ploidy level and niche breadth, using distributional records, species distributional modelling and WorldClim data.

Key results: Polyploidy is extensive across the tribe, with almost half (45 %) of species and the majority of genera exhibiting this trait. We found a significant positive relationship between polyploidy and genus size (i.e. species richness), but a non-significant positive relationship between polyploidy and diversification rates. Polyploidy did not result in significantly wider niche space occupancy for Pomaderreae; however, polyploidy did allow transitions into novel wetter niches. Spatially, eastern Australia is the diversification hotspot for Pomaderreae in contrast to the species hotspot of south-west Western Australia.

Conclusions: The relationship between polyploidy and diversification is complex. Ancient polyploidization events likely played an important role in the diversification of species-rich genera. A lag time effect may explain the uncoupling of tip diversification rates and polyploidy of extant lineages. Further studies on other groups are required to validate these hypotheses.

Background and aims: There is ongoing debate about whether offspring perform best next to phylogenetically distantly related adult neighbours (due to the scarcity of enemies and competitors) or next to closely related adults (due to the abundance of mutualists). Here we hypothesize that relatedness of adult neighbours affects which traits confer performance rather than performance itself.

Methods: We studied seed removal, seed germination and sapling growth in sessile oaks (Quercus petraea and hybrids) and how they depend on size, shape and other traits, under both closely and distantly related canopies, manipulating offspring density, presence of insects and fungi, and spatial proximity to oaks.

Key results: We found that phylogenetic distance of adult neighbours affects only little the performance of offspring but strongly affects which traits confer performance on offspring, in particular the size and shape of seeds and saplings. Differences in trait-performance relationships mostly disappear once insects or conspecific competitors are excluded (albeit exclusion of fungi reinforced these differences). Effects of phylogenetic distance of neighbours were not replaceable by the percentage of gymnosperms among neighbours or by the environmental conditions considered.

Conclusions: We suggest that, by responding to a biotic micro-mosaic of selection pressures, sessile oak flexibly succeeds in diverse neighbourhoods. Sessile oak might maintain the potential for both convergence with and divergence from phylogenetically distantly related species, thereby reinforcing or eroding phylogenetic signal of niches.

Background and aims: Understanding how plant species respond to extreme conditions is crucial for predicting their ecological resilience under climate change. Here, we aimed to forecast the ecological resilience of the Mediterranean cliff species Brassica incana (Brassicaceae) by estimating population variation in germination response under novel extreme environmental conditions.

Methods: We investigated the thermal germination responses in 14 populations of B. incana by exposing seeds to temperatures within and outside conditions experienced in their local environment. Then, we quantified among- and within-population variation in germination response to extreme temperatures, estimated genotype-by-environment interactions (G × E) and tested if population performance at extreme temperatures is explained by local climate.

Key results: We found significant among-population differences in germination response, a different level of within-population variability and different mechanisms underlying G × E patterns. Also, populations experiencing higher temperatures in their local environment showed a better performance at both cold and hot extremes while populations experiencing lower temperatures showed a limited ability to germinate under extreme conditions.

Conclusions: Our results suggest that populations experiencing higher temperatures in their local environment have a greater potential to face future thermal extreme conditions and their role is thus crucial to promote species ecological resilience.

Background and aims: The complexity of fossil forest ecosystems is difficult to reconstruct due to the fragmentary nature of the fossil record. However, detailed morpho-anatomical studies of well-preserved individual fossils can provide key information on tree growth and ecology, including in biomes with no modern analogue, such as the lush forests that developed in the polar regions during past greenhouse climatic episodes.

Methods: We describe an unusual-looking stem from Middle Triassic (~240 Ma) deposits of Antarctica with over 100 very narrow growth rings and conspicuous persistent vascular traces through the wood. Sections of the specimen were prepared using the cellulose acetate peel technique to determine its systematic affinities and analyse its growth.

Key results: The new fossil shows similarities to the form genus Woodworthia and with conifer stems from the Triassic of Antarctica, and is assigned to the conifers. Vascular traces are interpreted as those of small branches retained on the trunk. Growth-ring analyses reveal one of the slowest growth rates reported in the fossil record, with an average of 0.2 mm per season. While the tree was growing within the Triassic polar circle, sedimentological data and growth-ring information from other fossil trees, including from the same locality, support the presence of favourable conditions in the region.

Conclusions: The specimen is interpreted as a dwarf conifer tree that grew under a generally favourable regional climate but whose growth was suppressed due to stressful local site conditions. This is the first time that a tree with suppressed growth is identified as such in the fossil record, providing new insights on the structure of polar forests under greenhouse climates and, more generally, on the complexity of tree communities in deep time.

Background and aims: Biological aspects of haustorial parasitism have significant effects on the configuration of the plastid genome. Approximately half the diversity of haustorial parasites belongs to the order Santalales, where a clearer picture of plastome evolution in relation to parasitism is starting to emerge. However, in previous studies of plastome evolution there is still a notable under-representation of members from non-parasitic and deep-branching hemiparasitic lineages, limiting evolutionary inference around the time of transition to a parasitic lifestyle. To expand taxon sampling relevant to this transition we therefore targeted three families of non-parasites (Erythropalaceae, Strombosiaceae and Coulaceae), two families of root-feeding hemiparasites (Ximeniaceae and Olacaceae) and two families of uncertain parasitic status (Aptandraceae and Octoknemaceae). With data from these lineages we aimed to explore plastome evolution in relation to the evolution of parasitism.

Methods: From 29 new samples we sequenced and annotated plastomes and the nuclear ribosomal cistron. We examined phylogenetic patterns, plastome evolution, and patterns of relaxed or intensified selection in plastid genes. Available transcriptome data were analysed to investigate potential transfer of infA to the nuclear genome.

Results: Phylogenetic relationships indicate a single functional loss of all plastid ndh genes (ndhA-K) in a clade formed by confirmed parasites and Aptandraceae, and the loss coincides with major size and boundary shifts of the inverted repeat (IR) region. Depending on an autotrophic or heterotrophic lifestyle in Aptandraceae, plastome changes are either correlated with or pre-date the evolution of parasitism. Phylogenetic patterns also indicate repeated loss of infA from the plastome, and based on the presence of transcribed sequences with presequences corresponding to thylakoid luminal transit peptides, we infer that the genes were transferred to the nuclear genome.

Conclusions: Except for the loss of the ndh complex, relatively few genes have been lost from the plastome in deep-branching root parasites in Santalales. Prior to loss of the ndh genes, they show signs of relaxed selection indicative of their dispensability. To firmly establish a potential correlation between ndh gene loss, plastome instability and evolution of parasitism, it is pertinent to refute or confirm a parasitic lifestyle in all Santalales clades.

Background and aims: Invasive species usually demonstrate remarkable adaptability across diverse environments, successfully inhabiting a wide variety of regions. This adaptability often links to genetic differentiation and phenotypic plasticity, leading to latitudinal trends in phenotypic traits. In this study, we collected seeds of the invasive plant Phytolacca americana from different latitudes and planted them in homogeneous gardens to investigate the latitudinal variation of P. americana phenotypic traits and to evaluate the effects of herbivory and heavy metals on plant growth, defence and reproductive characteristics.

Methods: Phytolacca americana seeds from different latitudes were planted in a homogeneous garden. For the experimental treatment, the seeds were divided into four groups: a heavy metal treatment group and its corresponding control group, and a cover treatment group with its corresponding control group. After the fruits matured, their growth, reproduction and defence indicators were measured.

Key results: Significant latitudinal trends were observed in P. americana's growth and defence characteristics, including changes in branch number, underground biomass, total biomass and leaf tannin content. Compared with previous field surveys on P. americana, our study found that the latitude trends in growth structure and defence traits were consistent, but the latitudinal trend of reproductive structure was different. Moreover, heavy metals and herbivory substantially influenced the plant's growth, reproduction and defence mechanisms, further shaping its latitudinal patterns.

Conclusions: The observed phenotypic variations in P. americana across latitudes can be largely attributed to the synergistic effects of phenotypic plasticity and genetic variation. At a broader geographical scale, adaptations to heavy metal stress and herbivory pressure among different P. americana populations involve distinct trade-offs related to growth, reproduction and defence strategies.

Background and aims: Non-structural carbohydrates (NSC), primarily sugars and starch, play a crucial role in plant metabolic processes and the ability of a plant to tolerate and recover from drought stress. Despite their importance, our understanding of NSC characteristics in the leaves of plants that thrive in hyper-arid and saline environments remains limited.

Methods: To investigate the variations in leaf NSC across different species and spatial scales and to explore their possible causes, we collected 488 leaf samples from 49 native plant species at 115 sites in the desert area of northwestern China. The contents of soluble sugars (SS), starch and total NSC were then determined.

Key results: The average contents of SS, starch and total NSC were 26.99, 60.28 and 87.27 mg g-1, respectively, which are much lower than those reported for Chinese forest plants and global terrestrial plants. Herbaceous and woody plants had similar NSC levels. In contrast, succulent halophytes, a key component of desert flora, showed significantly lower leaf SS and total NSC contents than non-succulent plants. We observed a strong negative correlation between leaf succulence and SS content, suggesting a role of halophytic succulence in driving multispecies NSC pools. Environmental factors explained a minor portion of the spatial variation in leaf NSC, possibly owing to the narrow climatic variation in the study area, and soil properties, particularly soil salinity, emerged as more significant contributors.

Conclusions: Our findings increase the understanding of plant adaptation to drought and salt stress, emphasizing the crucial role of halophytic succulence in shaping the intricate dynamics of leaf NSC across diverse plant species in arid and hyper-arid environments.