Category Archives: AoB PLANTS

SPECIAL ISSUE: Physiology and Ecology of Halophytes – Plants Living in Salt-Rich Environments

Psilocephalus acaciae growing on Acacia tortlis in the southern Arava-Valley near Yotavata. Photo copyright: Maik Veste

Psilocephalus acaciae growing on Acacia tortlis in the southern Arava-Valley near Yotavata. Photo credit: Maik Veste

AoB PLANTS is pleased to announce the publication of a Special Issue examining the roles that can be played by halophytes, extremophiles that tolerate salinities toxic to most plants. It is expected that climate change will bring about rising sea levels and increasing drought, both of which will contribute to increasing salinisation in many regions of the world. There will be consequent effects on our crops, which cannot withstand significant salinisation. Papers in this special issue deal with topics ranging from the effects of rising concentrations of CO2 and flooding on coastal vegetation to the different effects of chlorides and sulphates on the growth of halophytes, the ability of some parasitic plants to develop succulence when growing on halophytic hosts and the interesting finding that halophytes growing in their natural habitat do not show signs of oxidative stress. The importance of identifying genotypes and selecting those best suited for the product required, and optimising the conditions necessary for germination and maximising yield, is also discussed. The consequence of selection for agronomic traits on salt tolerance is evaluated, as is the use of halophytes as green manures. Halophytes are remarkable plants: they are rare in relation to the total number of flowering plants and they tolerate salinities that most species cannot. The papers published in this Special Issue demonstrate that research into halophytes has a distinct place in aiding our understanding of salt tolerance in plants, an understanding that is likely to be of importance as climate change and population growth combine to challenge our ability to feed the human population of the world.

Changes in plant species composition of coastal dune habitats over a 20-year period

14207Coastal sandy ecosystems are increasingly being threatened by human pressure, causing loss of biodiversity, habitat degradation and landscape modifications. However, there are still very few detailed studies focusing on compositional changes in coastal dune plant communities over time. In a new study published in AoB PLANTS, Del Vecchio et al. used phytosociological relevés to conduct a re-visitation study in order to analyse changes in floristic composition during the last twenty years along the central Adriatic coast. They observed a significant increase in cover of fore-dune and thermophilic species, and concluded that even though human activities are major driving forces of change in coastal dune vegetation, the increase in species’ cover that was observed may also be due to a moderate increment in average yearly temperature over the last two decades.

Rainwater in cupulate bracts repels seed herbivores in a bumblebee-pollinated alpine flower

A flowering individual of Pedicularis rex at Shangri-La Alpine Botanical Garden, northwestern China, noting its corolla tubes (part) and ovaries submerged in rainwater-filling bracts.  Photo credit: Shuang-Quan Huang.

A flowering individual of Pedicularis rex at Shangri-La Alpine Botanical Garden, northwestern China, noting its corolla tubes (part) and ovaries submerged in rainwater-filling bracts. Photo credit: Shuang-Quan Huang.

The discovery of new adaptations of organisms to various environments always reminds us how little we know about nature. For example, rainwater surrounding sexual organs has been noted in several flowering plant groups. In a new study published in AoB PLANTS, Sun and Huang used a bumblebee-pollinated alpine flower, Pedicularis rex (Orobanchaceae), which has cup-like bracts holding rainwater and is endemic to southwest China, as an experimental model to examine whether the water-filled cupulate bracts function to deter nectar robbers and/or seed herbivores. They found that neither nectar robbers nor legitimate pollinators discriminated water-drained flowers, but seed predation significantly increased in drained flowers, suggesting that water-filled bracts help protect the flowers from seed herbivores.

Germination and ultrastructural studies of seeds produced by a fast-growing, drought-resistant tree: implications for its domestication and seed storage

Photograph of Moringa oleifera tree growing at the experimental farm of University of Pretoria, Pretoria, South Africa (H. Fotouo).

Photograph of Moringa oleifera tree growing at the experimental farm of University of Pretoria, Pretoria, South Africa (H. Fotouo).

Moringa oleifera, or miracle tree, is known in many parts of the world for its multiple uses as an agroforestry crop. However, seeds of this species lose their viability within 6 to 12 months of harvest, and thus finding appropriate storage conditions to ameliorate deterioration due to ageing is essential. In a new study published in AoB PLANTS, Fotouo et al. investigated the longevity of seed stored in the fruit (capsules). They found that the inner layers of the seed coat that remain attached to the cotyledons probably play a role in seed dormancy of Moringa oleifera. Cotyledons of seeds stored for one year showed no sign of deterioration. In some cells of the three-year-old cotyledons, the membranes of the protein bodies had deteriorated. Cell deterioration was also marked by the collapse of the cell wall adjacent to the intercellular cavity. The decrease in seed viability during storage was associated with the loss of membrane integrity as confirmed by an increase in electrolyte leakage.  The authors concluded that the longevity of Moringa oleifera seeds can be extended if they are stored within their fruits under favourable conditions.

Rangewide ploidy variation and evolution in Acacia senegal: a north-south divide?

Leafless Acacia senegal tree at Dahra experimental field trial, Senegal during the dry season. Middle branch shows characteristic gum arabic ‘nodules’ formed after tapping (debarking) at the beginning of dry season. Bar represents 10 cm (photo credit: Julia Wilson)

Leafless Acacia senegal tree at Dahra experimental field trial, Senegal during the dry season. Middle branch shows characteristic gum arabic ‘nodules’ formed after tapping (debarking) at the beginning of dry season. Bar represents 10 cm (photo credit: Julia Wilson)

Knowledge of rangewide variation in DNA content and ploidy level may be valuable in understanding the evolutionary history of a species. A recent study of Acacia senegal showed a geographic pattern of genetic variation, which differentiated East and Southern African populations from those in the Sudano-Sahelian region. In a new study published in AoB PLANTS, Odee et al. build on this previous research to explore variation in DNA content using the flow cytometry method and chromosome number. A geographic north-south DNA content pattern was detected, reflecting the previous results. These results suggest that DNA content may also be important in elucidating the evolutionary history and distribution of the species. Furthermore, Odee et al.’s use of external tissues of dried twigs in flow cytometry is new, and provides the opportunity to study numerous other dryland woody species.

A mutualistic endophyte alters the niche dimensions of its host plant

Study site in Virginia Basin, Gunnison County, Colorado, USA.  (Image source: Melanie R. Kazenel)

Study site in Virginia Basin, Gunnison County, Colorado, USA. (Image source: Melanie R. Kazenel)

Mutualisms can play important roles in influencing species coexistence and determining community composition. However, few studies have tested whether mutualisms may affect species distributions by altering the niches of partner species. In a new study published in AoB PLANTS, Kazenel et al. show that a fungal endophyte is associated with a shift in the soil moisture niche of its host plant relative to a co-occurring, endophyte-free congener. The endophyte appeared to initially restrict its host’s distribution to wetter microsites before positively affecting its growth, suggesting the value of considering symbiont effects at different partner life stages. Their study identifies a symbiotic relationship as a potential mechanism facilitating the coexistence of two species, suggesting that symbiont effects on host niche may have community-level consequences.

Revisiting spatial scale in the productivity-species richness relationship: fundamental issues and global change implications

14078S1R1The relationship between climate and biodiversity has been long debated. In a changing environment, there is new emphasis to resolve this debate for practical reasons: to manage conservation efforts we need to understand how diversity will change from both our own actions and natural global cycles. In a new study published in AoB PLANTS, McBride et al. show that the roles played by different ecological and evolutionary factors in shaping plant diversity change across the world’s ecoregions, and—critically—that these differences scale with ecoregion size. Ecoregions that are both large and productive are globally important biodiversity sources that shape the biota of the smaller regions around them.

Collaboration between grass seedlings and rhizobacteria to scavenge organic nitrogen in soils

Photo of annual bluegrass seedlings on agarose with 0.01% protein, showing dark brown H2O2 zones around roots of seedlings.

Photo of annual bluegrass seedlings on agarose with 0.01% protein, showing dark brown H2O2 zones around roots of seedlings.

Plants require nitrogen to make proteins, nucleic acids and other biological molecules. It is widely accepted that plants absorb inorganic forms of nitrogen to fill their needs. However, recently it has become clear that plants also have the capacity to absorb organic nitrogen from soils. In a new study published in AoB PLANTS, White et al. describe a new kind of symbiosis involving seed-vectored rhizobacteria and grasses that is targeted at enhancing acquisition of organic nitrogen from soils. The authors propose a diurnal process where during the day roots produce and release hydrogen peroxide that oxidizes microbial exoenzymes around roots; at night hydrogen peroxide production ceases, then roots and symbiotic rhizobacteria secrete proteases that degrade the oxidized proteins to form peptides that are absorbed by roots. The existence of a mechanism for organic nitrogen scavenging in grasses emphasizes the nutritional importance of non-pathogenic microbes that associate with roots. Future applications of this process could result in new methods for the cultivation of crop plants.

Genetic diversity of high-elevation populations of an endangered medicinal plant

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A map representing 24 populations of Podophyllum hexandrum of Indian Himalayan range along with its pictorial representation from nature and bar plots represent STRUCTURE inferences of individual assignments two types of genetic populations.

Intraspecific genetic variation in natural populations governs their potential to overcome challenging ecological and environmental conditions. In addition, knowledge of this variation is critical for the conservation and management of endangered plant taxa. Despite its wide distribution across the entire Himalayan range, the current status of Podophyllum hexandrum, a highly important anti-cancerous herb, remains endangered. In a new study published in AoB PLANTS, Nag et al. characterized the genetic diversity of 24 populations comprising 209 individuals representing the whole of the Indian Himalayas, and found that regardless of geographic location, all of the populations were intermixed and composed broadly of two types of genetic populations. Their findings suggest that these populations have evolved well in response to the environment. This study will help in the formulation of conservation programs for P. hexandrum populations in this region.

Host specificity in vascular epiphytes: a review of methodology, empirical evidence and potential mechanisms

A considerable number of plants depend on structural support by other plants. To understand their diversity and ecology, it is essential to know how strongly potential host species differ in their suitability as hosts. A new review in AoB PLANTS by Wagner et al. focuses on vascular epiphytes, i.e. structurally dependent plants that do not parasitize their hosts. Despite a longstanding interest in the topic, knowledge on the strength of their host specificity is still scanty. This is arguably due to conceptual confusion, but also because of the large complexity of the study system, which makes quantifying host specificity in the field rather challenging. The authors conclude that future research should use a more comprehensive approach by (i) determining the relative importance of various potential mechanisms acting locally and (ii) testing several proposed hypotheses regarding the relative strength of host specificity in different habitats and among different groups of structurally dependent flora.