SciCombinator

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Concept: Plant morphology

283

Here we present evidence of phytoliths preserved in carbonised food deposits on prehistoric pottery from the western Baltic dating from 6,100 cal BP to 5750 cal BP. Based on comparisons to over 120 European and Asian species, our observations are consistent with phytolith morphologies observed in modern garlic mustard seed (Alliaria petiolata (M. Bieb) Cavara & Grande). As this seed has a strong flavour, little nutritional value, and the phytoliths are found in pots along with terrestrial and marine animal residues, these findings are the first direct evidence for the spicing of food in European prehistoric cuisine. Our evidence suggests a much greater antiquity to the spicing of foods than is evident from the macrofossil record, and challenges the view that plants were exploited by hunter-gatherers and early agriculturalists solely for energy requirements, rather than taste.

Concepts: Plant morphology, Taste, Circumstantial evidence, Flavor, Cooking, Spices, Food, Plant

209

BACKGROUND: Both competitive and facilitative interactions between species play a fundamental role in shaping natural communities. A recent study showed that competitive interactions between plants can be mediated by some alternative signalling channel, extending beyond those channels studied so far (i.e. chemicals, contact and light). Here, we tested whether such alternative pathway also enables facilitative interactions between neighbouring plant species. Specifically, we examined whether the presence of a ‘good’ neighbouring plant like basil positively influenced the germination of chilli seeds when all known signals were blocked. For this purpose, we used a custom-designed experimental set-up that prevented above- and below-ground contact and blocked chemical and light-mediated signals normally exchange by plants. RESULTS: We found that seed germination was positively enhanced by the presence of a ‘good’ neighbour, even when the known signalling modalities were blocked, indicating that light, touch or chemical signals may not be indispensible for different plant species to sense each other’s presence. CONCLUSIONS: We propose that this alternative signalling modality operates as a general indicator of the presence of heterospecifics, enabling seeds to detect and identify a neighbour prior to engaging in a more finely-tuned, but potentially more costly, response.

Concepts: Seedling, Love Thy Neighbour, Embryo, Germination, Plant morphology, Fruit, Plant, Seed

191

Cliff sides are extreme habitats, often sheltering a rich and unique flora. One example is the dioecious herb Borderea chouardii (Dioscoreaceae), which is a Tertiary, tropical relict, occurring only on two adjacent vertical cliffs in the world. We studied its reproductive biology, which in some aspects is extreme, especially the unusual double mutualistic role of ants as both pollinators and dispersers. We made a 2-year pollination census and four years of seed-dispersal experiments, recording flower visitors and dispersal rates. Fruit and seed set, self-sowing of seeds, seedling recruitment, and fate of seedlings from seeds sowed by different agents were scored over a period of 17 years. The ants Lasius grandis and L. cinereus were the main pollinators, whereas another ant Pheidole pallidula dispersed seeds. Thus ants functioned as double mutualists. Two thirds of all new seedlings came from self-sown seeds, and 1/3 was dispersed by ants, which gathered the seeds with their oil-rich elaiosome. Gravity played a minor role to dispersal. Both ant dispersal and self-sowing resulted in the same survival rate of seedlings. A double mutualism is a risky reproductive strategy, but B. chouardii buffers that by an unusual long-term demographic stability (some individuals exceed 300 years in lifespan) and its presence in a climatically very stable habitat, inaccessible to large herbivores. Such a combination of traits and habitat properties may explain the persistence of this relict species.

Concepts: Plant morphology, Plant reproduction, Sexual reproduction, Mutualism, Reproduction, Plant, Symbiosis, Seed

176

This study presents a novel way of enhancing plant growth through the use of a non-petroleum based product. We report here that exposing either roots or seeds of multicellular plants to extremely low concentrations of dissolved hydrogen sulfide at any stage of life causes statistically significant increases in biomass including higher fruit yield. Individual cells in treated plants were smaller (∼13%) than those of controls. Germination success and seedling size increased in, bean, corn, wheat, and pea seeds while time to germination decreases. These findings indicated an important role of H2S as a signaling molecule that can increase the growth rate of all species yet tested. The increased crop yields reported here has the potential to effect the world’s agricultural output.

Concepts: Yield, Germination, Legume, Pea, Plant, Plant morphology, Fruit, Seed

173

Plants continuously extend their root and shoot systems through the action of meristems at their growing tips. By regulating which meristems are active, plants adjust their body plans to suit local environmental conditions. The transport network of the phytohormone auxin has been proposed to mediate this systemic growth coordination, due to its self-organising, environmentally sensitive properties. In particular, a positive feedback mechanism termed auxin transport canalization, which establishes auxin flow from active shoot meristems (auxin sources) to the roots (auxin sinks), has been proposed to mediate competition between shoot meristems and to balance shoot and root growth. Here we provide strong support for this hypothesis by demonstrating that a second hormone, strigolactone, regulates growth redistribution in the shoot by rapidly modulating auxin transport. A computational model in which strigolactone action is represented as an increase in the rate of removal of the auxin export protein, PIN1, from the plasma membrane can reproduce both the auxin transport and shoot branching phenotypes observed in various mutant combinations and strigolactone treatments, including the counterintuitive ability of strigolactones either to promote or inhibit shoot branching, depending on the auxin transport status of the plant. Consistent with this predicted mode of action, strigolactone signalling was found to trigger PIN1 depletion from the plasma membrane of xylem parenchyma cells in the stem. This effect could be detected within 10 minutes of strigolactone treatment and was independent of protein synthesis but dependent on clathrin-mediated membrane trafficking. Together these results support the hypothesis that growth across the plant shoot system is balanced by competition between shoot apices for a common auxin transport path to the root and that strigolactones regulate shoot branching by modulating this competition.

Concepts: Plant morphology, Shoot, Protein, Feedback, Meristem, Plant, Root, Plant stem

171

Floral displays are under selection to both attract pollinators and deter antagonists. Here we show that a common floral trait, a nectar guide pattern, alters the behavior of bees that can act opportunistically as both pollinators and as antagonists. Generally, bees access nectar via the floral limb, transporting pollen through contact with the plant’s reproductive structures; however bees sometimes extract nectar from a hole in the side of the flower that they or other floral visitors create. This behavior is called “nectar robbing” because bees may acquire the nectar without transporting pollen. We asked whether the presence of a symmetric floral nectar guide pattern on artificial flowers affected bumble bees' (Bombus impatiens) propensity to rob or access nectar “legitimately.” We discovered that nectar guides made legitimate visits more efficient for bees than robbing, and increased the relative frequency of legitimate visits, compared to flowers lacking nectar guides. This study is the first to show that beyond speeding nectar discovery, a nectar guide pattern can influence bees' flower handling in a way that could benefit the plant.

Concepts: Pollination syndrome, Bumblebee, Plant morphology, Pollen, Pollinator decline, Bee, Flower, Pollination

171

Community compensatory trend (CCT) is thought to facilitate persistence of rare species and thus stabilize species composition in tropical forests. However, whether CCT acts over broad geographical ranges is still in question. In this study, we tested for the presence of negative density dependence (NDD) and CCT in three forests along a tropical-temperate gradient. Inventory data were collected from forest communities located in three different latitudinal zones in China. Two widely used methods were used to test for NDD at the community level. The first method considered relationships between the relative abundance ratio and adult abundance. The second method emphasized the effect of adult abundance on abundance of established younger trees. Evidence for NDD acting on different growth forms was tested by using the first method, and the presence of CCT was tested by checking whether adult abundance of rare species affected that of established younger trees less than did abundance of common species. Both analyses indicated that NDD existed in seedling, sapling and pole stages in all three plant communities and that this effect increased with latitude. However, the extent of NDD varied among understory, midstory and canopy trees in the three communities along the gradient. Additionally, despite evidence of NDD for almost all common species, only a portion of rare species showed NDD, supporting the action of CCT in all three communities. So, we conclude that NDD and CCT prevail in the three recruitment stages of the tree communities studied; rare species achieve relative advantage through CCT and thus persist in these communities; CCT clearly facilitates newly established species and maintains tree diversity within communities across our latitudinal gradient.

Concepts: Common species, Trees, Plant morphology, Rainforest, Plant, Forest, Rare species, Tree

166

Floral longevity reflects a balance between gains in pollinator visitation and the costs of flower maintenance. Because rewards to pollinators change over time, older flowers may be less attractive, reducing the value of extended longevity. Un-pollinated figs, the inflorescences of Ficus species, can remain receptive for long periods, but figs that are older when entered by their host-specific fig wasp pollinators produce fewer seeds and fig wasp offspring. Our field experiments with Ficushispida, a dioecious fig tree, examined how the length of time that receptive figs have remained un-pollinated influences the behaviour and reproductive success of its short-lived fig wasp pollinator, Ceratosolensolmsi marchali. The results were consistent in three different seasons, and on male and female trees, although receptivity was greatly extended during colder months. Pollinators took longer to find the ostioles of older figs, and longer to penetrate them. They also became increasingly unwilling to enter figs as they aged, and increasing numbers of the wasps became trapped in the ostiolar bracts. Larger individuals were particularly unwilling to enter older figs, resulting in older figs being pollinated by smaller wasps. On female trees, where figs produce only seeds, seed production declined rapidly with fig age. On male trees, the numbers and size of fig wasp offspring declined, and a higher proportion were male. Older male figs are harder to enter, especially for larger individuals, and offer poorer quality oviposition opportunities. This study opens an interesting new perspective on the coevolution of figs and their pollinators, especially factors influencing pollinator body size and emphasises the subtleties of interactions between mutualists.

Concepts: Reproduction, Inflorescence, Plant morphology, Fruit, Pollination, Flower, Fig wasp, Ficus

165

BackgroundAs proposed by Darwin, climbers have been assumed to allocate a smaller fraction of biomass to support organs in comparison with self-supporting plants. They have also been hypothesized to possess a set of traits associated with fast growth, resource uptake and high productivity.ScopeIn this review, these hypotheses are evaluated by assembling and synthesizing published and unpublished data sets from across the globe concerning resource allocation, growth rates and traits of leaves, stems and roots of climbers and self-supporting species.ConclusionsThe majority of studies offer little support for the smaller allocation of biomass to stems or greater relative growth rates in climbers; however, these results are based on small sized (<1 kg) plants. Simulations based on allometric biomass equations demonstrate, however, that larger lianas allocate a greater fraction of above-ground biomass to leaves (and therefore less biomass to stems) compared with similar sized trees. A survey of leaf traits of lianas revealed their lower average leaf mass per area (LMA), higher N and P concentration and a slightly higher mass-based photosynthetic rate, as well as a lower concentration of phenolic-based compounds than in woody self-supporting species, consistent with the specialization of lianas towards the fast metabolism/rapid turnover end of the global trait spectra. Liana stems have an efficient hydraulic design and unique mechanical features, while roots appear to penetrate deeper soil levels than in trees and are often able to generate hydraulic pressure. Much remains to be learned, however, about these and other functional specializations of their axial organs and the associated trade-offs. Developmental switches between self-supporting, searcher and climbing shoots within the same individual are a promising field of comparative studies on trait association in lianas. Finally, some of the vast trait variability within lianas may be reduced when species with different climbing mechanisms are considered separately, and when phylogenetic conservatism is accounted for.

Concepts: Leaf, Climbing, Resource allocation, Plant morphology, Photosynthesis

149

The development of outgrowths from plant shoots depends on formation of epidermal sites of cell polarity convergence with high intracellular auxin at their centre. A parsimonious model for generation of convergence sites is that cell polarity for the auxin transporter PIN1 orients up auxin gradients, as this spontaneously generates convergent alignments. Here we test predictions of this and other models for the patterns of auxin biosynthesis and import. Live imaging of outgrowths from kanadi1 kanadi2 Arabidopsis mutant leaves shows that they arise by formation of PIN1 convergence sites within a proximodistal polarity field. PIN1 polarities are oriented away from regions of high auxin biosynthesis enzyme expression, and towards regions of high auxin importer expression. Both expression patterns are required for normal outgrowth emergence, and may form part of a common module underlying shoot outgrowths. These findings are more consistent with models that spontaneously generate tandem rather than convergent alignments.

Concepts: Cell, Gene, Adenosine triphosphate, Bud, Plant stem, Convergence, Shoot, Plant morphology