Soil seed banks serve as reservoirs for future plant communities, and when diverse and abundant can buffer vegetation communities against environmental fluctuations. Sparse seed banks, however, may lead to future declines of already rare species. Seed banks in wetland communities are often robust and can persist over long time periods, making wetlands model systems for studying the spatial and temporal links between above- and belowground communities. In a recent study in AoB PLANTS, Faist et al. found that the belowground community in the soil seed bank of restored ephemeral wetlands (vernal pools) in California’s Central Valley, USA, has been less invaded by exotic plants and is a reservoir for rare and native plant species. They also found that seed bank community structure most closely resembled the aboveground community structure from five to eight years prior to seed bank sampling rather than more recent years. The maintenance of rare and native plant species in soil seed banks, even while aboveground vegetation communities are being invaded by exotic plants, is an exciting finding with important implications for management and restoration efforts in annual plant communities.
The transition of a breeding system from outcrossing to selfing has been considered to be a widespread evolutionary trend in flowering plants, allowing species to colonize new habitats after long-distance dispersal. Moreover, Darwin realized that autonomous self-pollination could be an adaptation to reproduction if pollinator services were lost or extremely unpredictable. In a recent study published in AoB PLANTS, Xiong et al. tested a hypothesis that the persistence of Himalayan mayapple (Podophyllum hexandrum), an early spring flowering herb in the Himalayan region, is attributable to the transition from self-incompatibility to self-compatibility i.e. the capacity for selfing in an unpredictable pollination environment. To clarify whether automatic self-pollination is achieved by movement of the pistil as suggested in a previous study, they measured incline angles of the pistil and observed flower movement during anthesis. They found that automatic self-pollination was facilitated by petals closing and stamens moving simultaneously to contact the stigma. A scarcity of pollinators may have driven the shift to delayed selfing in Podophyllum hexandrum.
In a novel analysis by Gornish published in AoB PLANTS, a regression-design life-table response experiment was used to determine how the interaction of fire and density affected vital rates of the perennial composite Pityopsis aspera, and ultimately how these changes in vital rates contributed to differences in estimated population growth rates. The shape of the relationship between population growth rate (λ) and density was modified by fire, primarily as a result of contributions from adult flowering stasis and survival, and first-year survival probabilities. Fire modified and even reversed the effect of extreme densities on adult flowering stasis and survival and of first-year survival, resulting in more positive contributions from these transitions to λ at the lowest and highest density values. These results demonstrate the first application of a regression-design life-table response experiment to elucidating the interactive effects of density and fire. They highlight the utility of this approach for both capturing the complex dynamics of populations and establishing a means of determining how vital rates might contribute to differences in demography across densities.
Taxonomic resources are essential for the effective management of invasive plants because biosecurity strategies, legislation dealing with invasive species, quarantine, weed surveillance and monitoring all depend on accurate and rapid identification of non-native taxa, and incorrect identifications can impede ecological studies. On the other hand, biological invasions have provided important tests of basic theories about species concepts. Modern taxonomy therefore needs to integrate both classical and new concepts and approaches to improve the accuracy of species identification and further refine taxonomic classification at the level of populations and genotypes in the field and laboratory. In a recent review in AoB PLANTS, Pysek et al. explore how a lack of taxonomic expertise, and by implication a dearth of taxonomic products such as identification tools, has hindered progress in understanding and managing biological invasions. They also explore how the taxonomic endeavour could benefit from studies of invasive species.
Crop domestication is a remarkable example of the evolution of wild plants into cultivable forms through human selection. Following the domestication of rice almost 10,000 years ago, ancient farmers selected many rice lineages for diverse agronomic and cultural traits, such as grain size, shape and colour; awn length; pest resistance; and aroma. A recent study in AoB PLANTS by Ray et al. examined the phenotypic traits of a large collection of Indian rice landraces (all accessed from Vrihi, rice seed bank, www.cintdis.org/vrihi) and found that a few grain, panicle and leaf traits are major drivers of the huge phenotypic diversity observed. They also demonstrated the existence of short grain aromatic landraces perhaps with independently evolved aroma traits. The independent origin of aroma in indica rice is fascinating as it explores lesser known aspects of indica rice domestication and diversification.
We have a fundamental and applied understanding of how differences in the wood chemistry of trees affects the durability of wood products. By comparison, relatively little is known about the ecological causes and consequences of species differences in wood chemistry; even less is known about how or why wood chemistry differs within species, across trees of different sizes. In a study published in AoB PLANTS, Martin et al. find strong and consistent differences in the wood chemistry of saplings and canopy trees, in several tropical hardwood species. These differences point to the importance of pathogens and tree biomechanics as evolutionary causes of size-dependent changes in wood chemistry.
The genetic characteristics of species impact their capacity to maintain populations and colonize new areas, and the presence of genetic diversity is especially important for plant populations in highly stochastic environments like the Arctic. Purple saxifrage, Saxifraga oppositifolia, is a circumpolar, ecologically and morphologically variable species with a wide range of habitats. Although not endangered at the moment, climate change, the potential warming or drying of northern areas, and increased UV radiation could become a threat in the future. In a recent study published in AoB PLANTS, Pietiläinen and Korpelainen used DNA markers and sequencing to investigate patterns of genetic variability in this species in the isolated Arctic Svalbard archipelago. They found that both genetic variation and differentiation levels are modest, outcrossing is the main mating system, and that dispersal and gene flow are important phenomena within Svalbard, probably attributable to strong winds and human and animal vectors.
Pietilainen M. & Korpelainen H. (2013). Population genetics of purple saxifrage (Saxifraga oppositifolia) in the high Arctic archipelago of Svalbard, AoB Plants, 5 plt024-plt024 DOI: 10.1093/aobpla/plt024
AoB PLANTS has been accepted for indexing in Thomson–Reuters products including Science Citation Index, Current Contents, BIOSIS Previews, and Biological Abstracts. AoB PLANTS content will begin to appear in Web of Science next month, and our initial Impact Factor will be announced in June 2014. Stay tuned for updates!
There are, I’m told, some people who prefer decaffeinated coffee to my normal beverage (triple espresso), and while I don’t personally understand that, there’s no doubt that the market for decaf is big. But removing the caffeine from coffee beans can be expensive, not to mention altering the taste of the delicious java, so maybe it’s better not to put it in there in the first place?
A recent paper in AoB PLANTS examines a new variety of naturally decaffinated coffee and describes how the flowers differ from the parent strain by lacking sticky colleters. Colleters are little hair-like organs which are thought to protect dormant coffee flower buds from dehydration during the dry season, and could also play a part in resistance to insect damage. In normal flowers, the viscosity of the colleter exudate seems to hold the petals together, acting as an adhesive, and does not allow them to open until they absorb water, swell and can then overcome the barrier imposed by the exudate. Furthermore, the exudate seems to protect against dehydration through the formation of a thick layer on the young flower buds, which have numerous stomata on the external petal surface. This is the first direct evidence for a functional role of colleters and their exudate.
The low caffeine Decaffito® plants have very low caffeine content in all tissues, and this characteristic is associated with precocious flower opening. Similar to natural mutants of Coffea arabica, Decaffito plants accumulate theobromine, indicating a metabolic blockade of the last step of caffeine biosynthesis. Although it is still not clear what controls caffeine biosynthesis in Decaffito coffee mutants, the associated and undesirable precocious flower opening characteristic provides the first functional proof of the role of colleters and their exudate in protecting flowers against exposure to dry atmospheres and acting as an adhesive to keep the petals united until anthesis.
A functional role for the colleters of coffee flowers. AoB PLANTS (2013) 5: plt029 doi: 10.1093/aobpla/plt029
Colleters are protuberances or trichomes that produce and release an exudate that overlays vegetative or reproductive buds. Colleters have a functional definition, as they are thought to protect young tissues against dehydration and pest attack. Decaffeinated coffee plants, named Decaffito®, have recently been obtained through chemical mutagenesis, and in addition to the absence of the alkaloid, the flowers of these plants open precociously. Decaffito mutants exhibit minimal production and secretion of the exudate by the colleters. We compared these mutants with normal coffee plants to infer the functional role of colleters and the secreted exudate covering flower buds. Decaffito mutants were obtained by sodium azide mutagenesis of Coffea arabica cv. Catuaí seeds. Wild-type plants were used as controls and are referred to as Catuaí. The flower colleters were analysed by scanning and transmission electron microscopy in addition to histochemical analysis. Histochemical analysis indicated the presence of heterogeneous exudate in the secretory cells of the colleters of both variants of coffee trees. Alkaloids were detected in Catuaí but not in Decaffito. Transmission electron microscopy revealed that the secretory cells in the Catuaí colleters possessed the normal and common characteristics found in secretory structures. In the secretory cells of the Decaffito colleters, it was not possible to identify any organelles or even the nucleus, but the cells had a darkened central cytoplasm, indicating that the secretion is produced in low amounts but not released. Our results offer a proof of concept of colleters in coffee, strongly indicating that the exudate covering the flower parts works as an adhesive to keep the petals together and the flower closed, which in part helps to avoid dehydration. Additionally, the exudate itself helps to prevent water loss from the epidermal cells of the petals.