Annals of botany最新文献

Backgrounds and aims: Shading, water deficit, and crop load shape plant development in a very plastic way. They directly influence the plant's carbon supply and demand to and from the different organs via metabolic, hydraulic and hormonal mechanisms. However, how the multiple environmental factors combine through these mechanisms and how they interplay with carbon status, vegetative and reproductive development and carbon assimilation of the plant needs to be investigated in the context of current climatic and technological constraints.

Methods: With this aim, two experiments were conducted on potted grapevines, subjected to ten combinations of treatments. Axis organogenesis, berry characteristics at harvest (weight, number and total soluble content) and a series of leaf traits (gas exchanges, non-structural carbohydrate contents, water potential and SPAD values) were measured.

Key results: Grapevine development showed different responses corresponding to different sink priorities: under shade, vegetative development was maintained at the expense of berries, whereas under high crop load and water deficit, berry growth was the priority sink. These responses were accompanied by changes in the specific leaf area in agreement with the shade avoidance syndrome. These different strategies affected the plant carbon status as estimated through the starch content in leaves. Leaf starch content was not affected by shade, while it decreased under water deficit and crop load conditions. Carbon assimilation was decreased under water deficit, low crop load and shading conditions. Hydraulic properties and leaf nitrogen content correlated withthis decrease while plant carbon status has a very low impact. Finally, no major interaction between the different types of constraints were observed both on morphological and functional variables.

Conclusions: Depending on the type of abiotic constraints, grapevine exhibits specific morphogenetic responses at plant and leaf levels. The absence of interaction between the different constraints showed that grapevine is able to exhibit independent responses to shade and water deficit. This result is of major importance to further design new agricultural systems facing multiple abiotic constraints, such as those in agroforestery and agrivolatic system.

Background and aims: Oophytum (Aizoaceae) is a locally endemic genus of the extremely fast evolving subfamily Ruschioideae and consists of only two formally accepted species (O. nanum and O. oviforme). Both species are leaf-succulent dwarf shrubs and habitat specialists on quartz fields in the Knersvlakte, a renowned biodiversity hotspot in the arid winter-rainfall Succulent Karoo Biome of South Africa. Quartz fields present specialised patchy habitats with an island-like distribution in the landscape. Oophytum oviforme grows in the south-western part, whereas O. nanum covers most of the remaining Knersvlakte. These species co-occur in a small area but within different quartz islands. We investigated the effects of the patchy distribution, environmental conditions and potential effects of paleoclimatic changes on the genetics of Oophytum.

Methods: Phylogenetic and population genetic analyses of 35 populations of the genus, covering its entire distribution area, were conducted using four cpDNA markers and an AFLP dataset. These were combined with environmental data via a principal component analysis and comparative heatmap analyses.

Key results: The genetic pattern of the Oophytum metapopulation is a tripartite division with a northern, central and western group. This geographical pattern does not correspond to the two-species concept of Oophytum. Only the western O. oviforme populations form a monophyletic lineage, whereas the central populations of O. oviforme are genetic hybrids of O. nanum populations. The highly restricted gene flow often resulted in private gene pools with very low genetic diversity, in contrast to the hybrid gene pools of the central and edge populations.

Conclusions: Oophytum is an exceptional example of an extremely fast-evolving genus that illustrates the high speciation rate of the Ruschioideae and their success as one of the leading plant groups of the drought-prone succulent Karoo Biome. The survival strategy of these dwarf quartz-field endemics is an interplay of adaptation to diverse island habitats, highly restricted gene flow, occasional long-distance dispersal, migration, founder effects and hybridisation events within a small and restricted area caused by glacial and interglacial changing climate conditions from Pleistocene up to Present. These findings have important implications for future conservation management strategies.

Background and aims: Bamboo is a grass in the Poaceae family with various applications. Bamboo leaves can accumulate high silica. However, silica deposition in bamboo has received limited study. Therefore, this research investigated silica accumulation in Dendrocalamus copelandii leaves. The study includes the localisation of silica through phytolith morphology, examination of the distribution patterns of phytoliths in epidermal tissues, analysis of silica accumulation within specialised silica cells (short cells), and analysis of silicon concentration across various leaf developmental stages.

Methods: We employed imaging techniques, including Differential interference contrast and Scanning electron microscope incorporated with an energy-dispersive X-ray spectrometer, to investigate silica accumulation in bamboo leaves. We also analysed silicon concentration using Inductively coupled plasma-optical emission spectroscopy.

Key results: Leaves of D. copelandii exhibited 11 phytolith morphotypes, such as BILOBATE, POLYLOBATE, SADDLE, ACUTE, ACUTE BULBOSUS, MICROHAIR, STOMATA, BULLIFORM FLABELLATE, ELONGATE SINUATE, ELONGATE ENTIRE and TRACHEARY. Most of these phytoliths were found in short cells (BILOBATE, POLYLOBATE and SADDLE) of epidermal tissues. The short cells were arranged transversely along the leaf length. BILOBATE was found in both the abaxial and adaxial epidermis, while SADDLE was found only in the abaxial epidermis. Silica accumulation in the short cells of unexpanded leaves begins at the leaf apex, spreads to the middle and base positions, and accumulates first in the abaxial before the adaxial epidermis. Moreover, bamboo leaves accumulate more silicon concentration as they age.

Conclusions: Phytolith morphotypes and silica accumulation in epidermal short cells are key factors in understanding silica deposition. Leaf age and climate significantly impact silicon concentration in bamboo leaves. Our findings are informative for archaeological studies and for plant taxonomical classification. The results are also applicable for biotechnological applications.

Background: Research on the parasitic plant genus Cuscuta has flourished since the genomes of several of its species were published. Most of the research revolves around the iconic infection organ that secures the parasite's sustenance: the haustorium. The interest in understanding the structure-function-regulation relationship of the haustorium is based as much on the wish to find ways to keep the parasite under control as on the opportunities it offers to shed light on various open questions in plant biology.

Scope: The review will briefly introduce parasitism among plants, using the genus Cuscuta as main example, before presenting its haustorium alongside the terminology that is used to describe its architecture. Possible evolutionary origins of this parasitic organ are presented. The haustorium is then being followed from its initiation to maturity under contemplation of the molecular landscape that accompanies the morphological changes and in the light of the challenges it must overcome before gaining access to the vascular cells of its hosts. The fact that Cuscuta has an unusually broad host range stresses how efficient its infection strategy is. Therefore, special consideration will be given in the final chapter to a comparison with the process of grafting, being the only other type of tissue connection that involves interspecific vascular continuity.

Conclusions: Studies on Cuscuta haustoriogenesis have revealed many molecular details that explain its success. They have also unearthed some mysteries, that wait to be solved. With a better understanding of the complexity of the infection with its combination of universal as well as host-specific elements that allow Cuscuta to parasitize on a wide range of host plant species, we may be many steps closer to not only containing the parasite better but also exploiting its tricks where they can serve us in the quest of producing more and better food and fodder.

Background and aims: Ecological speciation is frequently invoked as a driver of plant radiation, but the behaviour of environmental niches during radiation is contentious, with patterns ranging from niche conservatism to niche divergence. Here we investigated climatic and edaphic niche shifts during radiation in a western Mediterranean lineage of the genus Linaria (Plantaginaceae).

Methods: Detailed distributional, phylogenomic and environmental data were integrated to analyse changes in climatic and edaphic niches in a spatiotemporal context, including calculation of niche overlap, niche equivalency and similarity tests, maximum entropy modelling, phylogenetic comparative methods and biogeographic analyses.

Key results: Active divergence of climatic and edaphic niches within a limited subset of available conditions was detected among the eight study species, and particularly between sister species. Speciation and niche divergence is estimated to have happened in the southern Iberian Peninsula under Mediterranean conditions, followed by waxing and waning of distribution ranges resulting from the Quaternary climatic cycles.

Conclusions: Results support the idea that the prevalence of niche conservatism or niche divergence patterns is a matter of phylogenetic scale. Habitat isolation pertaining to both climatic and soil conditions appears to have played a role in plant speciation in the western Mediterranean biodiversity hotspot, most likely in combination with pollinator isolation and some degree of geographic isolation. These findings are in agreement with an adaptive radiation scenario incorporating certain non-adaptive features.

Background and aims: Root axes with greater penetration ability are often considered to be beneficial in hard soils. We hypothesized that maize root phenotypes with greater plasticity (meaning reduced elongation in response to mechanical impedance, i.e. a 'stop signal') have fitness advantages over phenotypes with reduced plasticity (i.e. unimpeded root elongation) in native (virgin, uncultivated) soils, by reallocating root foraging to softer, presumably wetter, soil domains, and that the value of the stop signal reduced with soil cultivation and crop domestication.

Methods: We used OpenSimRoot to simulate native and cultivated soils and evaluated maize root phenotypes with varying axial and lateral root penetration ability in water, nitrogen, and impedance regimes associated with Neolithic agriculture.

Key results: The stop signal was advantageous in native soils but was less beneficial in cultivated, irrigated soils. Reduced root foraging in hard, dry topsoil enabled root growth in deeper domains where water is available, resulting in an improved balance of resource expenditure and acquisition. The value of the stop signal declined during crop domestication with the advent of irrigation, which increased water availability in the topsoil. Soil cultivation reduced N availability, while irrigation increased N leaching, resulting in a shift in the fitness landscape, with greater lateral root length (i.e. reduced plasticity) being advantageous by colocalizing root foraging with N availability. The importance of the stop signal is evident in modern high-input systems in which drought is a limiting factor.

Conclusions: Our results support the hypotheses that the reduction of lateral root growth by mechanical impedance is adaptive in native soil, but became less adaptive with soil cultivation and irrigation associated with Neolithic agriculture.

Background and aims: Plant regeneration by seeds is driven by a set of physiological traits, many of which show functional intraspecific variation along biogeographic gradients. In many species, germination phenology depends on a germination delay imposed by the need for post-dispersal embryo growth (a.k.a. morphological dormancy). Such growth occurs as a function of environmental temperatures and shows base, optimum and ceiling temperatures (i.e. cardinal temperatures or thermal thresholds). However, the biogeographical variation in such thresholds has not been tested.

Methods: We used a thermal time approach and field experiments to assess intraspecific variation at the continental scale in the embryo growth thermal thresholds of the geophyte Conopodium majus (Apiaceae) across its distribution from the Iberian Peninsula to Scandinavia.

Key results: Thermal thresholds for embryo growth varied across the latitudinal gradient, with the estimated optimum temperatures between 2.5 and 5.2 ºC, ceiling temperatures between 12 and 20.5 ºC and base temperatures between -6.6 and -2.7 ºC. Germination in the field peaked in the months of January and February. The limiting factor for embryo growth was the ceiling temperature, which was negatively correlated with latitude and the bioclimatic environment of each population. In contrast, the optimal and base temperature were independent of local climate.

Conclusions: These results indicate that thermal thresholds for embryo growth are functional ecophysiological traits that drive seed germination phenology and seed responses to soil climatic environment. Therefore, post-dispersal embryo growth can be a key trait impacting climate change effects on phenology and species distributions.

Background: Orchidaceae are one of the two largest families of angiosperms; they exhibit a host of changes -- morphological, ecological and molecular -- that make them excellent candidates for evolutionary study. Such studies are most effectively performed in a phylogenetic context, which provides direction to character change. Understanding of orchid relationships began in the pre-evolutionary classification systems of the 1800's that were based solely on morphology, and now is largely based on genomic analysis. The resulting patterns have been used to update family classification and to test many evolutionary hypotheses in the family.

Scope: Recent analyses with dense sampling and large numbers of nuclear loci have yielded well-supported trees that have confirmed many longstanding hypotheses and overturned others. They are being used to understand evolutionary change and diversification in the family. These include dating the origination of the family, analysis of change in ecological habit (from terrestrial to epiphytic and back again in some cases), revealing significant plastid genome change in leafless holomycotrophs, studying biogeographic patterns in various parts of the world, and interpreting patterns of fungal associations with orchids.

Conclusion: Understanding of orchid relationships has progressed significantly in recent decades, especially since DNA sequence data have been available. These data have contributed to an increasingly refined classification of orchids and the pattern has facilitated many studies on character evolution and diversification in the family. Whole genome studies of the family are just beginning and promise to reveal fine-level details underlying structure and function in these plants, and, when set in a phylogenetic context, provide a much richer understanding of how the family has been so successful in diversification.