Category Archives: AoB PLANTS

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.

DNA analysis of soil extracts can be used to investigate fine root depth distribution of trees

Mango tree in rootstock field trial with six soil coring positions 0.5 m from trunk marked by red tape on wire pegs (image source: S.L. Bithell).

Mango tree in rootstock field trial with six soil coring positions 0.5 m from trunk marked by red tape on wire pegs (image source: S.L. Bithell).

Knowledge of a tree species’ or cultivar’s fine root distribution is important. However, the time and resource requirements of established soil core based methods where live from dead root determination is required, act as a constraint to large studies. In a new study published in AoB PLANTS, Bithell et al. developed a method to determine live fine root DNA density for mango (Mangifera indica). Large roots were separated from soil samples by sieving (min. 2 mm aperture) and DNA extraction was performed on the sieved soil containing fine root fragments that had passed through the sieve. The authors showed that the DNA yields of these samples could determine fine root distribution.

Genetic diversity and floral width variation in introduced and native populations of a long-lived woody perennial

Rhododendron ponticum in Ireland is genetically distinct and has flowers with significantly wider nectar tubes than ancestral populations in Spain (photo by Jane C. Stout)

Rhododendron ponticum in Ireland is genetically distinct and has flowers with significantly wider nectar tubes than ancestral populations in Spain (photo by Jane C. Stout)

Populations of introduced species in their new environments are expected to differ from native populations, due to processes such as genetic drift, founder effects, and local adaptation, which can often result in rapid phenotypic change. Such processes can also lead to changes in the genetic structure of these populations. In a new study published in AoB PLANTS, Stout et al. demonstrate that invasive populations of Rhododendron ponticum in Ireland are genetically distinct from ancestral populations in Spain and produce flowers that have wider floral tubes. Although Irish populations are spreading and Spanish ones are declining, they found low genetic diversity among individual plants within populations in both regions, and limited between-population gene flow. Wider floral tubes may have evolved in response to novel pollinators in Ireland, and although few studies examine invasive species in both their introduced and native habitats, this approach is needed to understand invasive species’ evolution and ecology.

Introduced and invasive cactus species–a global review

Flattened-padded: the most represented growth form among the invasive cactus taxa

Flattened-padded: the most represented growth form among the invasive cactus taxa

Understanding which species are introduced and become invasive are central questions in invasion science. In this sense, the cactus family is an interesting case study. Only 57 of the 1922 cactus species are currently recorded as invasive. There are three invasion hotspots: South Africa, Australia, and Spain. However, in a new study published in AoB PLANTS, Novoa et al. identified large areas of the world with suitable climates for cactus invasions that are at risk of future invasion – in particular parts of China, eastern Asia and central Africa. The invasive taxa represent an interesting subset of the total pool: they occur in two of the three major phylogenetic clades and in 13 of the 130 cactus genera, and possess four of the 12 cactus growth forms. Moreover, invasive species tend to have significantly larger native ranges than non-invasive species, and none of the invasive species are of conservation concern in their native range. These results suggest fairly robust correlates of invasiveness that can be used for proactive management and risk assessments.

Pollinator limitation on reproductive success in Iris tuberosa

Photo of Iris tuberosa by G. Pellegrino

Photo of Iris tuberosa by G. Pellegrino

Variation in plant and floral size can have conflicting effects on pollination and fruit production in flowering plants. In a new study published in AoB PLANTS, Pellegrino measured the effect of varying pollinator visits on fruit production in order to understand pollination strategy in Iris tuberosa, and assessed the effects of plant and floral display size on pollination to understand how these factors influence reproductive success. He found that I. tuberosa was pollinated exclusively by hymenopteran species, mainly during sunny days, and that plant and floral size did not affect fruit set and pollinator attraction. Thus, the sexual reproduction of I. tuberosa is fairly limited by pollinators and not by resource limitation.