Category Archives: AoB PLANTS

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.

Genetic diversity and population structure of an extremely endangered species – the world’s largest Rhododendron

The flower of big tree rhododendron. Photo credit: Dr. Shen Shikang

The flower of big tree rhododendron. Photo credit: Dr. Shen Shikang

Comprehensive studies on the genetic diversity and structure of endangered species are urgently needed to promote effective conservation and management activities. A new study by Qin et al. published in AoB PLANTS is the first study of the genetic diversity and structure of the big tree rhododendron, Rhododendron protistum var. giganteum, which is a highly endangered species with only two known endemic populations in a small area in the southern part of Yunnan Province in China. Qin et al. detected moderate to high genetic diversity at the species level, but low genetic differentiation between the two extant populations. These results suggest that some rare and endangered species are able to maintain high levels of genetic diversity even at small population sizes.

Trichomes related to an unusual method of water retention and protection of the stem apex in an arid zone perennial species

Reproductive stem apex of Lychnophora diamantinana (photo credit: Lusa et al.).

Reproductive stem apex of Lychnophora diamantinana (photo credit: Lusa et al.).

The adaptation strategies of plants to harsh environments are among the most interesting subjects in plant biology. Several studies have investigated the role played by trichomes in protecting plant organs in these conditions. In a new study published in AoB PLANTS, Lusa et al. report an unusual way of protecting the stem apex of Lychnophora diamantinana. This species is endemic to the Brazilian campos rupestres (rocky fields), a region characterised by intense solar radiation and water deficits. The authors found that the terminal cell of its non-glandular trichomes undergoes partial degradation of the cell wall, producing a highly hydrated, hyaline material that protects the stem apex against desiccation. The secretion of glandular trichomes may also repel herbivore and pathogen attack.