Association among starch storage, metabolism, related genes and growth of Moso bamboo (Phyllostachys heterocycla) shoots.

BACKGROUND: Both underground rhizomes/buds and above-ground Moso bamboo (Phyllostachys heterocycla) shoots/culms/branches are connected together into a close inter-connecting system in which nutrients are transported and shared among each organ. However, the starch storage and utilization mechanisms during bamboo shoot growth remain unclear. This study aimed to reveal in which organs starch was stored, how carbohydrates were transformed among each organ, and how the expression of key genes was regulated during bamboo shoot growth and developmental stages which should lay a foundation for developing new theoretical techniques for bamboo cultivation. RESULTS: Based on changes of the NSC content, starch metabolism-related enzyme activity and gene expression from S0 to S3, we observed that starch grains were mainly elliptical in shape and proliferated through budding and constriction. Content of both soluble sugar and starch in bamboo shoot peaked at S0, in which the former decreased gradually, and the latter initially decreased and then increased as shoots grew. Starch synthesis-related enzymes (AGPase, GBSS and SBE) and starch hydrolase (α-amylase and ß-amylase) activities exhibited the same dynamic change patterns as those of the starch content. From S0 to S3, the activity of starch synthesis-related enzyme and starch amylase in bamboo rhizome was significantly higher than that in bamboo shoot, while the NSC content in rhizomes was obviously lower than that in bamboo shoots. It was revealed by the comparative transcriptome analysis that the expression of starch synthesis-related enzyme-encoding genes were increased at S0, but reduced thereafter, with almost the same dynamic change tendency as the starch content and metabolism-related enzymes, especially during S0 and S1. It was revealed by the gene interaction analysis that AGPase and SBE were core genes for the starch and sucrose metabolism pathway. CONCLUSIONS: Bamboo shoots were the main organ in which starch was stored, while bamboo rhizome should be mainly functioned as a carbohydrate transportation channel and the second carbohydrate sink. Starch metabolism-related genes were expressed at the transcriptional level during underground growth, but at the post-transcriptional level during above-ground growth. It may be possible to enhance edible bamboo shoot quality for an alternative starch source through genetic engineering.

Drought stress stimulates endocytosis and modifies membrane lipid order of rhizodermal cells of Medicago truncatula in a genotype-dependent manner.

BACKGROUND: Drought stress negatively affects plant growth and productivity. Plants sense soil drought at the root level but the underlying mechanisms remain unclear. At the cell level, we aim to reveal the short-term root perception of drought stress through membrane dynamics. RESULTS: In our study, 15 Medicago truncatula accessions were exposed to a polyethylene glycol (PEG)-induced drought stress, leading to contrasted ecophysiological responses, in particular related to root architecture plasticity. In the reference accession Jemalong A17, identified as drought susceptible, we analyzed lateral roots by imaging of membrane-localized fluorescent probes using confocal microscopy. We found that PEG stimulated endocytosis especially in cells belonging to the growth differentiation zone (GDZ). The mapping of membrane lipid order in cells along the root apex showed that membranes of root cap cells were more ordered than those of more differentiated cells. Moreover, PEG triggered a significant increase in membrane lipid order of rhizodermal cells from the GDZ. We initiated the membrane analysis in the drought resistant accession HM298, which did not reveal such membrane modifications in response to PEG. CONCLUSIONS: Our data demonstrated that the plasma membranes of root cells from a susceptible genotype perceived drought stress by modulating their physical state both via a stimulation of endocytosis and a modification of the degree of lipid order, which could be proposed as mechanisms required for signal transduction.

Costs of plant defense priming: exposure to volatile cues from a specialist herbivore increases short-term growth but reduces rhizome production in tall goldenrod (Solidago altissima).

BACKGROUND: By sensing environmental cues indicative of pathogens or herbivores, plants can "prime" appropriate defenses and deploy faster, stronger responses to subsequent attack. Such priming presumably entails costs-else the primed state should be constitutively expressed-yet those costs remain poorly documented, in part due to a lack of studies conducted under realistic ecological conditions. We explored how defence priming in goldenrod (Solidago altissima) influenced growth and reproduction under semi-natural field conditions by manipulating exposure to priming cues (volatile emissions of a specialist herbivore, Eurosta solidaginis), competition between neighbouring plants, and herbivory (via insecticide application). RESULTS: We found that primed plants grew faster than unprimed plants, but produced fewer rhizomes, suggesting reduced capacity for clonal reproduction. Unexpectedly, this effect was apparent only in the absence of insecticide, prompting a follow-up experiment that revealed direct effects of the pesticide esfenvalerate on plant growth (contrary to previous reports from goldenrod). Meanwhile, even in the absence of pesticide, priming had little effect on herbivore damage levels, likely because herbivores susceptible to the primed defences were rare or absent due to seasonality. CONCLUSIONS: Reduced clonal reproduction in primed plants suggest that priming can entail significant costs for plants. These costs, however, may only become apparent when priming cues fail to provide accurate information about prevailing threats, as was the case in this study. Additionally, our insecticide data indicate that pesticides or their carrier compounds can subtly, but significantly, affect plant physiology and may interact with plant defences.

Does hybrid Phragmites australis differ from native and introduced lineages in reproductive, genetic, and morphological traits?

PREMISE OF THE STUDY: Hybridization between previously isolated species or lineages can stimulate invasiveness because of increased genetic diversity and inherited traits facilitating competitive and reproductive potential. We evaluated differences in stand characteristics and sexual and vegetative reproduction among native, introduced, and hybrid Phragmites australis lineages in the southwestern United States. We also assessed the degree of hybridization among lineages and backcrossing of hybrids with parental lineages. METHODS: Growth and morphological characteristics were measured in native, introduced, and hybrid Phragmites stands to evaluate relative cover and dominance in associated plant communities. Panicles were collected from stands to evaluate germination, dormancy, and differences in seed traits. Seedlings from germination trials were genotyped to determine frequency of crossing and backcrossing among lineages. KEY RESULTS: Introduced and hybrid Phragmites stands had significantly greater stem and panicle densities than native stands and were more likely to be dominant members of their respective plant communities. Hybrid seed outputs were significantly greater, but hybrid seeds had lower germination rates than those from native and introduced lineages. We detected a novel hybridization event between native and introduced lineages, but found no strong evidence of hybrids backcrossing with parental lineages. CONCLUSIONS: Hybrid Phragmites in the Southwest exhibits reproductive, genetic, and morphological characteristics from both parental lineages that facilitate dispersal, establishment, and aggressive growth, including high reproductive output, rhizome viability, and aboveground biomass, with smaller seeds and greater genetic diversity than its progenitors. Our results show hybrids can inherit traits that confer invasiveness and provide insight for managing this species complex and other cryptic species with native and introduced variants with potential for intraspecific hybridization.

Effect of the population density on belowground bud bank of a rhizomatous clonal plant Leymus secalinus in Mu Us sandy land.

Clonal propagation is the main strategy for clonal plants to adapt to wind-sand habitat, and underground bud bank could reflect the potential ability of clonal propagation. However, the effects of population density on belowground bud bank are unknown, hindering efforts in the process of dune stabilization. We investigated the horizontal density and vertical distribution of belowground bud bank of a typical rhizomatous grass Leymus secalinus, and soil water content in four dune types with different population density (dune type I: 11.2 ± 1.7 no. m-2, type II: 24.2 ± 2.6 no. m-2, type III: 40.0 ± 4.0 no. m-2, and type IV: 53.5 ± 7.2 no. m-2) in Mu Us sandy land. Our results showed that (1) total bud density of population increased markedly with increasing population density, but it did not exhibit significant difference between dune types III and IV, where density was about 130 buds m-2; and tiller bud density of population first increased, then decreased, and reached a maximum in dune type III. (2) Total bud density per individual in dune type III was significantly larger than that in other dune types (P < 0.05), whereas rhizome and tiller bud density per individual did not show significant differences in dune types II, III and IV (P > 0.05). (3) Buds tended to be concentrated at 10-30 cm soil layer in all dune types, and be buried deeper in dune types III and IV than that in dune types I and II. (4) No pronounced relationship was shown between bud density and soil water content in 10-30 cm soil layer with increasing population density. Our results suggest that moderate population density (40.0 ± 4.0 no. m-2) significantly increase the bud bank density of L. secalinus population and individual. Soil water content was not the main factor responsible for the density of L. secalinus bud bank. These results can provide important information for implementation of effective sand fixation measures and species selection for desertification control in semiarid sandy land ecosystems.

Networks of highly branched stigmarian rootlets developed on the first giant trees.

Lycophyte trees, up to 50 m in height, were the tallest in the Carboniferous coal swamp forests. The similarity in their shoot and root morphology led to the hypothesis that their rooting (stigmarian) systems were modified leafy shoot systems, distinct from the roots of all other plants. Each consists of a branching main axis covered on all sides by lateral structures in a phyllotactic arrangement; unbranched microphylls developed from shoot axes, and largely unbranched stigmarian rootlets developed from rhizomorphs axes. Here, we reexamined the morphology of extinct stigmarian systems preserved as compression fossils and in coal balls from the Carboniferous period. Contrary to the long-standing view of stigmarian systems, where shoot-like rhizomorph axes developed largely unbranched, root-hairless rootlets, here we report that stigmarian rootlets were highly branched, developed at a density of ∼25,600 terminal rootlets per meter of rhizomorph, and were covered in root hairs. Furthermore, we show that this architecture is conserved among their only extant relatives, herbaceous plants in the Isoetes genus. Therefore, despite the difference in stature and the time that has elapsed, we conclude that both extant and extinct rhizomorphic lycopsids have the same rootlet system architecture.

Belowground rhizomes in paleosols: The hidden half of an Early Devonian vascular plant.

The colonization of terrestrial environments by rooted vascular plants had far-reaching impacts on the Earth system. However, the belowground structures of early vascular plants are rarely documented, and thus the plant-soil interactions in early terrestrial ecosystems are poorly understood. Here we report the earliest rooted paleosols (fossil soils) in Asia from Early Devonian deposits of Yunnan, China. Plant traces are extensive within the soil and occur as complex network-like structures, which are interpreted as representing long-lived, belowground rhizomes of the basal lycopsid Drepanophycus The rhizomes produced large clones and helped the plant survive frequent sediment burial in well-drained soils within a seasonal wet-dry climate zone. Rhizome networks contributed to the accumulation and pedogenesis of floodplain sediments and increased the soil stabilizing effects of early plants. Predating the appearance of trees with deep roots in the Middle Devonian, plant rhizomes have long functioned in the belowground soil ecosystem. This study presents strong, direct evidence for plant-soil interactions at an early stage of vascular plant radiation. Soil stabilization by complex rhizome systems was apparently widespread, and contributed to landscape modification at an earlier time than had been appreciated.

Transcription Profiles Reveal the Regulatory Synthesis of Phenols during the Development of Lotus Rhizome (Nelumbo nucifera Gaertn).

Lotus (Nelumbo nucifera Gaertn) is a wetland vegetable famous for its nutritional and medicinal value. Phenolic compounds are secondary metabolites that play important roles in the browning of fresh-cut fruits and vegetables, and chemical constituents are extracted from lotus for medicine due to their high antioxidant activity. Studies have explored in depth the changes in phenolic compounds during browning, while little is known about their synthesis during the formation of lotus rhizome. In this study, transcriptomic analyses of six samples were performed during lotus rhizome formation using a high-throughput tag sequencing technique. About 23 million high-quality reads were generated, and 92.14% of the data was mapped to the reference genome. The samples were divided into two stages, and we identified 23,475 genes in total, 689 of which were involved in the biosynthesis of secondary metabolites. A complex genetic crosstalk-regulated network involved in the biosynthesis of phenolic compounds was found during the development of lotus rhizome, and 25 genes in the phenylpropanoid biosynthesis pathway, 18 genes in the pentose phosphate pathway, and 30 genes in the flavonoid biosynthesis pathway were highly expressed. The expression patterns of key enzymes assigned to the synthesis of phenolic compounds were analyzed. Moreover, several differentially expressed genes required for phenolic compound biosynthesis detected by comparative transcriptomic analysis were verified through qRT-PCR. This work lays a foundation for future studies on the molecular mechanisms of phenolic compound biosynthesis during rhizome formation.

Niche partitioning of intertidal seagrasses: evidence of the influence of substrate temperature.

The influence of soil temperature on rhizome depths of four intertidal seagrass species was investigated in central Queensland, Australia. We postulated that certain intertidal seagrass species are soil temperature-sensitive and vertically stratify rhizome depths. Below-ground vertical stratification of intertidal seagrass rhizome depths was analysed based upon microclimate (soil temperature) and microhabitat (soil type). Soil temperature profiles exhibited heat transfer from surface layers to depth that varied by microhabitat, with vertical stratification of rhizome depths between species. Halodule uninervis rhizomes maintain a narrow median soil temperature envelope; compensating for high surface temperatures by occupying deeper, cooler soil substrates. Halophila decipiens, Halophila ovalis and Zostera muelleri rhizomes are shallow-rooted and exposed to fluctuating temperatures, with broader median temperature envelopes. Halodule uninervis appears to be a niche specialist, with the two Halophila species considered as generalist niche usage species. The implications of niche use based upon soil temperature profiles and rhizome rooting depths are discussed in the context of species' thermal tolerances and below-ground biomass O2 demand associated with respiration and maintenance of oxic microshields. This preliminary evidence suggests that soil temperature interaction with rhizome rooting depths may be a factor that influences the distribution of intertidal seagrasses.

Integrated Metabolomics and Proteomics Approach To Identify Metabolic Abnormalities in Rats with Dioscorea bulbifera Rhizome-Induced Hepatotoxicity.

Previous studies have shown that Dioscorea bulbifera rhizome (DBR) can induce hepatotoxicity in clinical practice. However, its underlying mechanisms remain largely unexplored. In the present study, we investigated the global effect of DBR exposure on the proteomic and metabolomic profiles in rats over a 12-week administration using an integrated proteomics and metabolomics approach. The abundance of 1366 proteins and 58 metabolites in the liver of rats after subchronic exposure to DBR was dose-dependently altered. The results indicated that DBR mainly damaged hepatic cells through the aberrant regulation of multiple systems mainly including purine metabolism, pyrimidine metabolism, taurine and hypotaurine metabolism, and bile acid metabolism. Notably, the deregulated proteins including Pnp, Dpyd, Upp1, and Tymp and the differential metabolites including uridine, uracil, cytidine, thymine, adenine, adenosine, adenosine 3'-monophosphate, and deoxycytidine were well correlated to purine and pyrimidine metabolism, which might be novel pathways involved in metabolic abnormalities in rats with DBR-induced liver damage. Collectively, these findings not only contributed to understanding the mechanisms underlying the hepatotoxicity of DBR, but also illustrated the power of integrated proteomics and metabolomics approaches to improve the identification of metabolic pathways and biomarkers indicative of herb-induced liver injury.

A functional-structural model of ephemeral seagrass growth influenced by environment.

Background and Aims: Ephemeral seagrasses that respond rapidly to environmental changes are important marine habitats. However, they are under threat due to human activity and are logistically difficult and expensive to study. This study aimed to develop a new functional-structural environmentally dependent model of ephemeral seagrass, able to integrate our understanding of ephemeral seagrass growth dynamics and assess options for potential management interventions, such as seagrass transplantation. Methods: A functional-structural plant model was developed in which growth and senescence rates are mechanistically linked to environmental variables. The model was parameterized and validated for a population of Halophila stipulacea in the Persian Gulf. Key Results: There was a good match between empirical and simulated results for the number of apices, net rhizome length or net number of internodes using a 330 d simulation. Simulated data were more variable than empirical data. Simulated structural patterns of seagrass rhizome growth qualitatively matched empirical observations. Conclusions: This new model successfully simulates the environmentally dependent growth and senescence rates of our case-study ephemeral seagrass species. It produces numerical and visual outputs that help synthesize our understanding of how the influence of environmental variables on plant functional processes affects overall growth patterns. The model can also be used to assess the potential outcomes of management interventions like seagrass transplantation, thus providing a useful management tool. It is freely available and easily adapted for new species and locations, although validation with more species and environments is required.

Surprisingly complex community discovered in the mid-Devonian fossil forest at Gilboa.

The origin of trees by the mid-Devonian epoch (398-385 million years ago) signals a major change in terrestrial ecosystems with potential long-term consequences including increased weathering, drop in atmospheric CO(2), modified climate, changes in sedimentation patterns and mass extinction. However, little is known about the ecology of early forests or how changes in early terrestrial ecosystems influenced global processes. One of the most famous palaeontological records for this time is the 'oldest fossil forest' at Riverside Quarry, Gilboa, New York, USA, discovered in the 1920s. Hundreds of large Eospermatopteris sandstone casts, now thought to represent the bases of standing cladoxylopsid trees, were recovered from a horizon that was originally interpreted as a muddy swamp. After quarry operations ceased, relatively minor outcrops of similar fossils at nearby localities have provided limited opportunities to evaluate this pervasive view using modern methods. In 2010, removal of the quarry backfill enabled reappraisal of the palaeoecology of this important site. Here we describe a 1,200 m(2) map showing numerous Eospermatopteris root systems in life position within a mixed-age stand of trees. Unexpectedly, large woody rhizomes with adventitious roots and aerial branch systems identified as aneurophytalean progymnosperms run between, and probably climb into, Eospermatopteris trees. We describe the overall habit for these surprisingly large aneurophytaleans, the earliest fossil group having wood produced by a bifacial vascular cambium. The site also provides evidence for arborescence within lycopsids, extending the North American range for trees in this ecologically critical group. The rooting horizon is a dark grey sandy mudstone showing limited root penetration. Although clearly belonging to a wetland coastal plain environment, the forest was probably limited in duration and subject to periodic disturbance. These observations provide fundamental clarification of the palaeoecology of this mixed-group early forest, with important implications for interpreting coeval assemblage data worldwide.

Elymus repens biomass allocation and acquisition as affected by light and nutrient supply and companion crop competition.

BACKGROUND AND AIMS: Competitive crops are a central component of resource-efficient weed control, especially for problematic perennial weeds such as Elymus repens Competition not only reduces total weed biomass, but denial of resources can also change the allocation pattern - potentially away from the underground storage organs that make perennial weeds difficult to control. Thus, the competition mode of crops may be an important component in the design of resource-efficient cropping systems. Our aim was to determine how competition from companion crops with different modes of competition affect E. repens biomass acquisition and allocation and discuss that in relation to how E. repens responds to different levels of light and nutrient supply. METHODS: Greenhouse experiments were conducted with E. repens growing in interspecific competition with increasing density of perennial ryegrass or red clover, or growing at three levels of both light and nutrient supply. KEY RESULTS: Elymus repens total biomass decreased with increasing biomass of the companion crop and the rate of decrease was higher with red clover than with perennial ryegrass, particularly for E. repens rhizome biomass. A reduced nutrient supply shifted E. repens allocation towards below-ground biomass while a reduced light supply shifted it towards shoot biomass. Red clover caused no change in E. repens allocation pattern, while ryegrass mostly shifted the allocation towards below-ground biomass, but the change was not correlated with ryegrass biomass. CONCLUSIONS: The companion crop mode of competition influences both the suppression rate of E. repens biomass acquisition and the likelihood of shifts in E. repens biomass allocation.

Effect of Increasing Salinity on Development of Giant Reed (Arundo donax) from Rhizome and Culms.

Arundo donax (giant reed) has great potential for bioenergy biomass production in constructed wetlands. Large scale use of A. donax in constructed wetlands will require the use of either established plants sourced from nurseries, or the use of cuttings or rhizomes and stems from mother plants derived from nurseries or wild stands. The results of this study suggest that cuttings and rhizomes are not sensitive to salinity up to an EC ~ 4500 µS cm- 1. Plants used to establish a constructed wetland should have stems of at least 300 mm length, with well established roots. Moreover, culms will emerge from small pieces of stems with viable nodes regardless of salinity, albeit the fresher the water the less likely salinity will subsequently affect the emerging shoot. From a practical perspective, this suggests that wetlands can be planted with giant reed using horizontally laid stems. Unless using plants pre-stressed to a salinity matching that of the wastewater to be treated, giant reed should be established using reasonable quality water (EC < 1000 µS cm- 1) until the plants are of a reasonable size, e.g. > 500 mm in height, after which undiluted wastewater can be used.

[Tropisms in underground shoots ­ stolons and rhizomes].

In the review, the problem of plant movements (photo- and gravitropism) is discussed. The contemporary data on physiological and molecular mechanisms of tropisms in underground shoots and roots are presented. Special attention is paid to diagravitropism phenomenon in underground shoots (stolons and rhizomes) that grow in perpendicular direction to the Earth's gravitational axis. The role of phytochrome control in maintaining the horizontal growth of stolons and rhizomes is demonstrated, and physiological mechanisms of photo- and diagravitropism are discussed. It is shown that switching of an underground shoot tip from diatropic to ortotropic (vertical) growth is dependent on the carbohydrate and phytohor-mone balance. The perspectives are outlined for further exploratory studies on mechanisms of growth orientation and morphogenesis of underground diagravitropic shoots.

Hormone regulation of rhizome development in tall fescue (Festuca arundinacea) associated with proteomic changes controlling respiratory and amino acid metabolism.

BACKGROUND AND AIMS: Rhizomes are underground stems with meristematic tissues capable of generating shoots and roots. However, mechanisms controlling rhizome formation and growth are yet to be completely understood. The objectives of this study were to investigate whether rhizome development could be regulated by cytokinins (CKs) and gibberellic acids (GAs), and determine underlying mechanisms of regulation of rhizome formation and growth of tall fescue (Festuca arundinacea) by a CK or GA through proteomic and transcript analysis. METHODS: A rhizomatous genotype of tall fescue ('BR') plants were treated with 6-benzylaminopurine (BAP, a synthetic cytokinin) or GA3 in hydroponic culture in growth chambers. Furthermore, comparative proteomic analysis of two-dimensional electrophoresis and mass spectrometry were performed to investigate proteins and associated metabolic pathways imparting increased rhizome number by BAP and rhizome elongation by GA3 KEY RESULTS: BAP stimulated rhizome formation while GA3 promoted rhizome elongation. Proteomic analysis identified 76 differentially expressed proteins (DEPs) due to BAP treatment and 37 DEPs due to GA3 treatment. Cytokinin-related genes and cell division-related genes were upregulated in the rhizome node by BAP and gibberellin-related and cell growth-related genes in the rhizome by GA3 CONCLUSIONS: Most of the BAP- or GA-responsive DEPs were involved in respiratory metabolism and amino acid metabolism. Transcription analysis demonstrated that genes involved in hormone metabolism, signalling pathways, cell division and cell-wall loosening were upregulated by BAP or GA3 The CK and GA promoted rhizome formation and growth, respectively, by activating metabolic pathways that supply energy and amino acids to support cell division and expansion during rhizome initiation and elongation in tall fescue.

A simple model for the influence of habitat resource availability on lateral clonal spread.

Plant clonal spread is ubiquitous and of great interest, owing both to its key role in plant community assembly and its suitability for plant behaviour research. However, mechanisms that govern spreading distance are not well known. Here we link spacer costs and below-ground competition in a simple model of growth in a homogeneous below-ground environment, in which optimal distance between ramets is based on minimizing the sum of these costs. Using this model, we predict a high prevalence of clonal growth that does not employ spacers in resource-poor environments and a nonlinear increase in spreading distance in response to increasing below-ground resource availability. Analysis of database data on clonal growth in relationship to below-ground resource availability revealed that patterns of the spread based on stolons is compatible with the model's predictions. As expected, model prediction failed for rhizomatous species, where spacer sizes are likely to be selected mainly to play roles other than spread. The model's simplicity makes it useful as a null model in testing hypotheses about the effects of environmental heterogeneity on clonal spread.

Winter cold-tolerance thresholds in field-grown Miscanthus hybrid rhizomes.

The cold tolerance of winter-dormant rhizomes was evaluated in diploid, allotriploid, and allotetraploid hybrids of Miscanthus sinensis and Miscanthus sacchariflorus grown in a field setting. Two artificial freezing protocols were tested: one lowered the temperature continuously by 1°C h(-1) to the treatment temperature and another lowered the temperature in stages of 24h each to the treatment temperature. Electrolyte leakage and rhizome sprouting assays after the cold treatment assessed plant and tissue viability. Results from the continuous-cooling trial showed that Miscanthus rhizomes from all genotypes tolerated temperatures as low as -6.5 °C; however, the slower, staged-cooling procedure enabled rhizomes from two diploid lines to survive temperatures as low as -14 °C. Allopolyploid genotypes showed no change in the lethal temperature threshold between the continuous and staged-cooling procedure, indicating that they have little ability to acclimate to subzero temperatures. The results demonstrated that rhizomes from diploid Miscanthus lines have superior cold tolerance that could be exploited to improve performance in more productive polyploid lines. With expected levels of soil insulation, low winter air temperatures should not harm rhizomes of tolerant diploid genotypes of Miscanthus in temperate to sub-boreal climates (up to 60°N); however, the observed winter cold in sub-boreal climates could harm rhizomes of existing polyploid varieties of Miscanthus and thus reduce stand performance.

Plant traits respond to the competitive neighbourhood at different spatial and temporal scales.

BACKGROUND AND AIMS: Clonal plants can plastically modify their traits in response to competition, but little is known regarding the spatio-temporal scale at which a competitive neighbourhood determines the variability in species traits. This study tests the hypothesis that the local neighbourhood can be expected to influence the processes that are involved in competition tolerance and avoidance, and that this effect depends on organ lifespan. METHODS: Fragments of the rhizomatous Elytrigia repens (Poaceae) were sampled in 2012 in experimental plant communities that varied in species identity and abundance. These communities had been cultivated since 2009 in mesocosms in a common garden. Fragment performance, shoot and clonal traits were measured, and the effects of past and present local neighbourhoods of five different radius sizes (5-25 cm) were examined. Past and present local neighbourhood compositions were assessed in 2011 and 2012, respectively. KEY RESULTS: Most of the measured traits of E. repens responded to the local neighbourhood (5-10 cm radius), with an additional effect of the larger neighbourhood (20-25 cm radius) on ramet height, leaf dry matter content, maximal internode length and specific rhizome mass. Contrary to the expectation of the hypothesis, the temporal influence was not due to the organ lifespan. Indeed, five of the eight traits studied responded to both the past and present neighbourhoods. With the exception of specific rhizome mass, all trait responses were explained by the abundance of specific species. CONCLUSIONS: This study demonstrates that the traits of a single clonal individual can respond to different competitive environments in space and time. The results thus contribute to the understanding of competition mechanisms.

Species delimitation in plants using the Qinghai-Tibet Plateau endemic Orinus (Poaceae: Tridentinae) as an example.

BACKGROUND AND AIMS: Accurate identification of species is essential for the majority of biological studies. However, defining species objectively and consistently remains a challenge, especially for plants distributed in remote regions where there is often a lack of sufficient previous specimens. In this study, multiple approaches and lines of evidence were used to determine species boundaries for plants occurring in the Qinghai-Tibet Plateau, using the genus Orinus (Poaceae) as a model system for an integrative approach to delimiting species. METHODS: A total of 786 individuals from 102 populations of six previously recognized species were collected for niche, morphological and genetic analyses. Three plastid DNA regions (matK, rbcL and trnH-psbA) and one nuclear DNA region [internal transcribed space (ITS)] were sequenced. KEY RESULTS: Whereas six species had been previously recognized, statistical analyses based on character variation, molecular data and niche differentiation identified only two well-delimited clusters, together with a third possibly originating from relatively recent hybridization between, or historical introgression from, the other two. CONCLUSIONS: Based on a principle of integrative species delimitation to reconcile different sources of data, the results provide compelling evidence that the six previously recognized species of the genus Orinus that were examined should be reduced to two, with new circumscriptions, and a third, identified in this study, should be described as a new species. This empirical study highlights the value of applying genetic differentiation, morphometric statistics and ecological niche modelling in an integrative approach to re-circumscribing species boundaries. The results produce relatively objective, operational and unbiased taxonomic classifications of plants occurring in remote regions.