Floral synorganization and its influence on mechanical isolation and autogamy in Marantaceae

The flowers of Marantaceae (～ 550 species) exhibit a highly derived pollination mechanism within Zingiberales, with a rapid and irreversible style movement based on a close synorganization of different floral parts. Given the complexity of the structure, we assume that little variation is possible if functionality is to be maintained. To test this, we investigated how much floral diversity exists in the clade and whether this diversity potentially influences the breeding system and placement of pollen on the pollinator. Flowers of 66 species covering the five major phylogenetic clades of the family were analysed. All species are similar in their basic flower construction: the fleshy staminode forms the tunnel‐shaped roof of the flower and narrows the tube with stiff swellings, and the hooded staminode holds the style under tension and narrows the flower entrance with its trigger appendage. Despite morphological diversity of the pollination apparatus, functionality is maintained by coordinated variation of the fleshy and hooded staminodes. Autogamy is usually avoided by herkogamy. However, in a few exceptions, subtle morphological changes alter the breeding system from allogamy to autogamy. Variable floral proportions allow for differential pollen deposition potentially causing mechanical isolation between sister taxa. This study clearly illustrates that structural variation is not only present in the highly synorganized flowers of Marantaceae, but that it also creates potentially new options for evolutionary diversification. © 2012 The Linnean Society of London, Botanical Journal of the Linnean Society, 2012, 168 , 300–322.     

A global analysis of fine root production as affected by soil nitrogen and phosphorus

Fine root production is the largest component of belowground production and plays substantial roles in the biogeochemical cycles of terrestrial ecosystems. The increasing availability of nitrogen (N) and phosphorus (P) due to human activities is expected to increase aboveground net primary production (ANNP), but the response of fine root production to N and P remains unclear. If roots respond to nutrients as ANNP, fine root production is anticipated to increase with increasing soil N and P. Here, by synthesizing data along the nutrient gradient from 410 natural habitats and from 469 N and/or P addition experiments, we showed that fine root production increased in terrestrial ecosystems with an average increase along the natural N gradient of up to 0.5 per cent with increasing soil N. Fine root production also increased with soil P in natural conditions, particularly at P < 300 mg kg(-1). With N, P and combined N + P addition, fine root production increased by a global average of 27, 21 and 40 per cent, respectively. However, its responses differed among ecosystems and soil types. The global average increases in fine root production are lower than those of ANNP, indicating that above- and belowground counterparts are coupled, but production allocation shifts more to aboveground with higher soil nutrients. Our results suggest that the increasing fertilizer use and combined N deposition at present and in the future will stimulate fine root production, together with ANPP, probably providing a significant influence on atmospheric CO(2) emissions.     

Mycorrhizal‐mediated nitrogen acquisition in switchgrass under elevated temperatures and N enrichment

Arbuscular mycorrhizal fungi (AMF) can perform key roles in ecosystem functioning through improving host nutrient acquisition. Nitrogen (N) is an essential nutrient for plant growth, however, anthropogenic N loading (e.g. crop fertilization and deposition from combustion sources) is increasing so that N now threatens ecosystem sustainability around the world by causing terrestrial and aquatic eutrophication and acidification. It is important to better understand the capacity of AMF to directly uptake N from soils and transfer it to host plants because this process may increase N recycling and retention within ecosystems. In addition to understanding the role of AMF in the N cycle in the present day it is important to understand how AMF function may change as global change proceeds. Currently the net effects of N enrichment and elevated temperature predicted with global change on AMF are unknown. In this study, we examined the effects of N enrichment by simulated N‐deposition loading, elevated temperatures expected by future global changes and their interactions on growth and AMF‐mediated N acquisition of switchgrass (Panicum virgatum var. Alamo), an important species for biofuel production. Switchgrass plants were grown in microcosm units that divided mycorrhizal roots from AMF hyphae and organic residues enriched with ¹⁵N by compartments separated by an air gap to reduce N diffusion. While AMF did not enhance switchgrass biomass, mycorrhizas significantly increased ¹⁵N in shoots and total shoot N. Neither N enrichment nor elevated temperatures influenced this mycorrhizal‐mediated N uptake and transfer. Results from this study can aid in developing sustainable bioethanol and switchgrass production practices that are less reliant on synthetic fertilizers and more dependent on internal N recycling from AMF.     

The human‐induced imbalance between C,N and P in Earth's life system

Human‐induced carbon and nitrogen fertilization are generating a strong imbalance with P. This imbalance confers an increasingly important role to P availability and N : P ratio in the Earth's life system, affecting carbon sequestration potential and the structure, function and evolution of the Earth's ecosystems.     

Contrasting effects of low and high nitrogen additions on soil CO2 flux components and ectomycorrhizal fungal sporocarp production in a boreal forest

Nitrogen (N) added through atmospheric deposition or as fertilizer to boreal and temperate forests reduces both soil decomposer activity (heterotrophic respiration) and the activity of roots and mycorrhizal fungi (autotrophic respiration). However, these negative effects have been found in studies that applied relatively high levels of N, whereas the responses to ambient atmospheric N deposition rates are still not clear. Here, we compared an unfertilized control boreal forest with a fertilized forest (100 kg N ha^?1 yr^?1) and a forest subject to N‐deposition rates comparable to those in Central Europe (20 kg N ha^?1 yr^?1) to investigate the effects of N addition rate on different components of forest floor respiration and the production of ectomycorrhizal fungal sporocarps. Soil collars were used to partition heterotrophic (R_h) and autotrophic (R_a) respiration, which was further separated into respiration by tree roots (R_tr) and mycorrhizal hyphae (R_m). Total forest floor respiration was twice as high in the low N plot compared to the control, whereas there were no differences between the control and high N plot. There were no differences in R_h respiration among plots. The enhanced forest floor respiration in the low N plot was, therefore, the result of increased R_a respiration, with an increase in R_tr respiration, and a doubling of R_m respiration. The latter was corroborated by a slightly greater ectomycorrhizal (EM) fungal sporocarp production in the low N plot as compared to the control plot. In contrast, EM fungal sporocarp production was nearly eliminated, and R_m respiration severely reduced, in the high N plot, which resulted in significantly lower R_a respiration. We thus found a nonlinear response of the R_a components to N addition rate, which calls for further studies of the quantitative relations among N addition rate, plant photosynthesis and carbon allocation, and the function of EM fungi.     

Quality control compartments coming of age

Maintenance of proteome integrity (proteostasis) is essential for cellular and organismal survival. Various cellular mechanisms work to preserve proteostasis by ensuring correct protein maturation and efficient degradation of misfolded and damaged proteins. Despite this cellular effort, under certain circumstances subsets of aggregation-prone proteins escape the quality control surveillance, accumulate within the cell and form insoluble aggregates that can lead to the development of disorders including late-onset neurodegenerative diseases. Cells respond to the appearance of insoluble aggregates by actively transporting them to designated deposition sites where they often undergo degradation. Although several protein aggregate deposition sites have been described and extensively studied, key questions regarding their biological roles and how they are affected by aging remained unanswered. Here we review the recent advances in the field, describe the different subtypes of these cellular compartments and outline the evidence that these structures change their properties over time. Finally, we propose models to explain the possible mechanistic links between aggregate deposition sites, neurodegenerative disorders and the aging process.     

Looking for a similar partner: host plants shape mating preferences of herbivorous insects by altering their contact pheromones

The role of phenotypical plasticity in ecological speciation and the evolution of sexual isolation remains largely unknown. We investigated whether or not divergent host plant use in an herbivorous insect causes assortative mating by phenotypically altering traits involved in mate recognition. We found that males of the mustard leaf beetle Phaedon cochleariae preferred to mate with females that were reared on the same plant species to females provided with a different plant species, based on divergent cuticular hydrocarbon profiles that serve as contact pheromones. The cuticular hydrocarbon phenotypes of the beetles were host plant specific and changed within 2 weeks after a shift to a novel host plant species. We suggest that plant-induced phenotypic divergence in mate recognition cues may act as an early barrier to gene flow between herbivorous insect populations on alternative host species, preceding genetic divergence and thus, promoting ecological speciation.     

Chemodiversity of Nonacosan‐10‐ol and n‐Alkanes in the Needle Wax of Pinus heldreichii

This is the first report of individual variability and population diversity of the contents of nonacosan‐10‐ol and n‐alkanes in the needle cuticular waxes of Bosnian pines originated from Montenegro, regarded as Pinus heldreichii var. leucodermis, and from Serbia, regarded as P. heldreichii var. pan?i?i. The amount of nonacosan‐10‐ol varied individually from 27.4 to 73.2% (55.5% in average), but differences between the four investigated populations were not statistically confirmed. The size of the n‐alkanes ranged from C₁₈ to C₃₃. The most abundant n‐alkanes were C₂₃, C₂₇, and C₂₅ (12.2, 11.2, and 10.8% in average, resp.). The carbon preference index (CPI) of the n‐alkanes ranged from 0.8 to 3.1 (1.6 in average), while the average chain length (ACL) ranged from 20.9 to 26.5 (24.4 in average). Long‐chain and mid‐chain n‐alkanes prevailed (49.6 and 37.9% in average, resp.). It was also found that the populations of P. heldreichii var. leucodermis had predominantly a narrower range of n‐alkanes (C₁₈? C₃₁) than the trees of the variety pan?i?i (C₁₈? C₃₃). Differences between the varieties were also significant for most of the other characteristics of the n‐alkane pattern (e.g., most abundant n‐alkanes, CPI, ACL, and relative proportion of short‐, mid‐, and long‐chain n‐alkanes). The principle component and cluster analyses of eleven n‐alkanes confirmed the significant diversity of these two varieties.     

APPLICATION OF THE PDMPO TECHNIQUE IN STUDYING SILICA DEPOSITION IN NATURAL POPULATIONS OF FRAGILARIA CROTONENSIS (BACILLARIOPHYCEAE) AT DIFFERENT DEPTHS IN A EUTROPHIC RESERVOIR1

At weekly intervals from July to October 2006, we measured silica deposition in the summer diatom assemblage at various depths in the eutrophic ?ímov Reservoir (Czech Republic) using PDMPO, the 2‐(4‐pyridyl)‐5{[4‐(2‐dimethylaminoethyl‐aminocarbamoyl)‐methoxy]phenyl}oxazole labeling technique. Fluorescence microscopy coupled with image analysis allows quantifying silicon (Si) deposition over time and a simple distinction between cells that are actively depositing Si and those that are not. Diatom assemblage was exclusively dominated by Fragilaria crotonensis Kitton, which formed pronounced subsurface maxima (2–6.5 m). Concentrations of the main nutrients (Si and phosphorus, P) were low over the whole season; however, at depth, the nutrient availability was higher than at the surface. Fragilaria silica deposition rates were eight times higher at the surface than at depth. Half the population was involved in silica deposition at the surface, while only 20% active cells were doing so at depth. At the surface, silica deposition was limited by P deficiency; the effect of dissolved Si (DSi) was not statistically significant. Silica deposition at depth was significantly constrained by low light availability despite the 1% average light attenuation at depth, which is supposed sufficient for photosynthesis. This study represents the first attempt to employ the PDMPO technique coupled with quantitative image analysis of PDMPO fluorescence in freshwater ecology. On the basis of our results, PDMPO probe appears to be an appropriate proxy for the study of resource limitation in natural diatom populations.     

Haemocyte response associated with induction of shell regeneration in the deep-sea vent mussel Bathymodiolus azoricus (Bivalvia: Mytilidae)

This study reports on the haemocyte responses after induction of shell regeneration in the hydrothermal mussel Bathymodiolus azoricus. Haemolymph was drawn from live mussels collected at Menez Gwen hydrothermal vent site (850 m depth) at the Mid Atlantic Ridge (MAR) and was compared with those collected following laboratory acclimatisation (1 atm and Ca-rich algal diet) and also with induced specimen for up to 30 days. Simultaneously, histological changes in mantle micro-morphology with the histochemical detection of Ca mobilisation in tissues were conducted.On the basis of light- and transmission electron microscopy, it is concluded that the physiological equipment involved in shell regeneration in the deep sea bivalve closely resembles that in littoral mytilids, a group that B. azoricus is closely related. This in spite of previously alleged molecular and cellular adaptations to extreme conditions typical at deep sea hydrothermal vents. Three types of blood cells were identified sharing various morphological similarities with those in many non-vent bivalves. Significant increase in the number of circulating haemocytes was detected from day 5 after induction shell regeneration. It is suggested that the increase may be a result of migration of haemocytes from the connective tissue, probably to the shell growth frontline. It is alleged that a first peak in haemocyte number is a non-specific immune response related wound healing, which renders changes in the pallial fluid that are favourable for CaCO₃ deposition. The conspicuous presence of an unidentified, acid soluble, highly refractive structure in the haemolymph of induced mussels was detected, which may play a role in Ca nucleation.This study has set the stage for investigations underway on the influence of hydrostatic pressure on shell biomineralisation in B. azoricus subjected to post-capture hyperbaric simulations.