Hybridization and ecology of Geum rivale L. and Geum urbanum L. (Rosaceae) at Malham Tarn, Yorkshire

Geum urbanum L. (Rosaceae) at Malham Tarn, Yorkshire. A large population of Geum rivale, G. urbanum and their hybrids at Malham Tarn, Yorkshire were examined morphometrically. Principal components analysis and cluster analysis of various floral and vegetative characters scored from 203 individuals completely separated the parent species. A few hybrids were grouped with G. urbanum , and some were grouped separately from either parent species, but many others were grouped with G. rivale. This confirmed subjective visual examination of the population, which suggested that while hybrids remained distinct from G. urbanum , the delimitation of hybrids from G. rivale was difficult and not practical. Measurements of soil water content and of transmitted photosynthetically active radiation (PAR) indicated that the habitat range of G. urbanum at Malham Tarn was limited to well-drained shady sites, while G. rivale occurred in sites with a very varied degree of shading and soil water content. Hybrids were most frequent and most variable in the well-drained and heavily shaded 'urbanum-type' habitats. Hybrids very similar to G. rivale were found in waterlogged sites, but in unshaded sites only G. rivale occurred, with little evidence of hybridization. The availability of intermediate 'hybrid' habitats was not a major factor in determining the pattern of morphological variation in the hybrid population, and a number of alternative hypotheses are suggested.     

Spectral Transmission and the Aerial Profile in Mature Stands of Mercurialis perennis L.

The passage of light through mature stands of the woodland perennialherb Mercurialis perennis L. is investigated. Less than 3 percent of each of seven discrete wavelengths in the visible wavebandreach the herb layer in the sites considered. Percentage transmissionof the 750 nm wavelength was far greater, and the proportionof this light passing deep into the herb profile increased astotal light transmission decreased. Mean specific leaf area of M. perennis is negatively correlatedwith shoot height and weight. Leaf area/shoot increases exponentiallywith shoot height, but linearly with shoot weight. Shoot leafweight ratio remains virtually constant over a range of shootsizes, but shoot leaf area ratio is negatively correlated withshoot height and shoot weight. Most leaf pairs are borne between10–30 cm above ground level and 71 per cent of the totalleaf area occurs between 15–30 cm above ground. Averageleaf area/leaf pair increases from the lowest layers in theprofile upwards except for the highest strata where many leavesare not fully expanded. Chlorophyll content of leaves, expressedon either a weight or an area basis, increases from the bottomto the top of the herb profile; the ratio of chlorophyll a:bdoes not alter through the stand.     

Lipophilic constituents from aerial and root parts of Mercurialis perennis L.

Introduction – Dog's mercury (Mercurialis perennis L.) is a perennial herb used in remedies for medicinal purposes. The plant is supposed to contain potentially active substances but its constituents have only been rarely studied. Objective – Detailed studies on the phytochemical composition are of great interest to broaden the knowledge on the chemotaxonomy and pharmacognosy of M. perennis. Methodology – Chloroform and hexane extracts from roots and aerial parts were investigated using GC/MS and LC/MS. Results – The whole plant exhihited a broad spectrum of structurally diverse constituents, mainly alkaloids, terpenes, sterols and simple aromatic compounds. Closer inspection of the piperidine alkaloid hermidin revealed its inherent instability towards air oxygen. To obtain quantitative data on these alkaloids the synthesis of the more stable reference compound 4‐methoxy‐1‐methylpyridine‐2,6(1H,3H)‐dione (MMPD) was required. In this study, MMPD was detected for the first time as a genuine compound in Mercurialis. Hermidine quinone and hermidin dimers originating from hermidin via a free anionic radical reaction were also confirmed by GC/MS. Moreover, volatile compounds such as benzylalcohol, 2‐phenylethanol, 4‐methoxy‐ and 3,4‐dimethoxyphenol, (?)‐cis‐ and (+)‐trans‐myrtanol, (?)‐cis‐myrtanal as well as squalene were predominantely present in Mercurialis roots. In contrast, aerial parts mainly contained phytol derivatives, sterols and tocopherols. By changing solvent polarity, lipid and wax‐containing fractions were obtained. LC/MS‐studies on hexane extracts showed the presence of several mixed triglycerides constituted by linolenic, linoleic, oleic, stearic and palmitic acids, as well as lutein, carotenes and pheophytins. Conclusions – The phytochemical data presented complement our knowledge on the rarely studied plant M. perennis and may broaden its use in future phytotherapy. Copyright © 2009 John Wiley & Sons, Ltd.     

An approach to the chemotaxonomic differentiation of two European dog's mercury species: Mercurialis annua L. and M. perennis L

Mercurialis annua and M. perennis are medicinal plants used in complementary medicine. In the present work, analytical methods to allow a chemotaxonomic differentiation of M. annua and M. perennis by means of chemical marker compounds were established. In addition to previously published compounds, the exclusive presence of pyridine-3-carbonitrile and nicotinamide in CH(2) Cl(2) extracts obtained from the herbal parts of M. annua was demonstrated by GC/MS. Notably, pyridine-3-carbonitrile was identified for the first time as a natural product. Further chromatographic separation of the CH(2) Cl(2) extracts via polyamide yielded a MeOH fraction exhibiting a broad spectrum of side-chain saturated n-alkylresorcinols. While the n-alkylresorcinol pattern was similar for both plant species, some specific differences were observed for particular n-alkylresorcinol homologs. Finally, the investigation of H(2) O extracts by LC/MS/MS revealed the presence of depside constituents. Whereas, in M. perennis, a mixture of mercurialis acid (=(2R)-[(E)-caffeoyl]-2-oxoglutarate) and phaselic acid (=(E)-caffeoyl-2-malate) could be detected, in M. annua solely phaselic acid was found. By comparison with synthesized enantiomerically pure (2R)- and (2S)-phaselic acids, the configuration of the depside could be determined as (2S) in M. annua and as (2R) in M. perennis.     

Overview of the physiological ecology of carbon metabolism in seagrasses

The small but diverse group of angiosperms known as seagrasses form submersed meadow communities that are among the most productive on earth. Seagrasses are frequently light-limited and, despite access to carbon-rich seawaters, they may also sustain periodic internal carbon limitation. They have been regarded as C3 plants, but many species appear to be C3–C4 intermediates and/or have various carbon-concentrating mechanisms to aid the Rubisco enzyme in carbon acquisition. Photorespiration can occur as a C loss process that may protect photosynthetic electron transport during periods of low CO₂ availability and high light intensity. Seagrasses can also become photoinhibited in high light (generally>1000 μE m⁻² s⁻¹) as a protective mechanism that allows excessive light energy to be dissipated as heat. Many photosynthesis–irradiance curves have been developed to assess light levels needed for seagrass growth. However, most available data (e.g. compensation irradiance I_c) do not account for belowground tissue respiration and, thus, are of limited use in assessing the whole-plant carbon balance across light gradients. Caution is recommended in use of I_k (saturating irradiance for photosynthesis), since seagrass photosynthesis commonly increases under higher light intensities than I_k; and in estimating seagrass productivity from H_sat (duration of daily light period when light equals or exceeds I_k) which varies considerably among species and sites, and which fails to account for light-limited photosynthesis at light levels less than I_k. The dominant storage carbohydrate in seagrasses is sucrose (primarily stored in rhizomes), which generally forms more than 90% of the total soluble carbohydrate pool. Seagrasses with high I_c levels (suggesting lower efficiency in C acquisition) have relatively low levels of leaf carbohydrates. Sucrose-P synthase (SPS, involved in sucrose synthesis) activity increases with leaf age, consistent with leaf maturation from carbon sink to source. Unlike terrestrial plants, SPS apparently is not light-activated, and is positively influenced by increasing temperature and salinity. This response may indicate an osmotic adjustment in marine angiosperms, analogous to increased SPS activity as a cryoprotectant response in terrestrial non-halophytic plants. Sucrose synthase (SS, involved in sucrose metabolism and degradation in sink tissues) of both above- and belowground tissues decreases with tissue age. In belowground tissues, SS activity increases under low oxygen availability and with increasing temperatures, likely indicating increased metabolic carbohydrate demand. Respiration in seagrasses is primarily influenced by temperature and, in belowground tissues, by oxygen availability. Aboveground tissues (involved in C assimilation and other energy-costly processes) generally have higher respiration rates than belowground (mostly storage) tissues. Respiration rates increase with increasing temperature (in excess of 40°C) and increasing water-column nitrate enrichment (Z. marina), which may help to supply the energy and carbon needed to assimilate and reduce nitrate. Seagrasses translocate oxygen from photosynthesizing leaves to belowground tissues for aerobic respiration. During darkness or extended periods of low light, belowground tissues can sustain extended anerobiosis. Documented alternate fermentation pathways have yielded high alanine, a metabolic ‘strategy’ that would depress production of the more toxic product ethanol, while conserving carbon skeletons and assimilated nitrogen. In comparison to the wealth of information available for terrestrial plants, little is known about the physiological ecology of seagrasses in carbon acquisition and metabolism. Many aspects of their carbon metabolism — controls by interactive environmental factors; and the role of carbon metabolism in salt tolerance, growth under resource-limited conditions, and survival through periods of dormancy — remain to be resolved as directions in future research. Such research will strengthen the understanding needed to improve management and protection of these environmentally important marine angiosperms.     

Metabolic Fate of Depsides and Alkaloid Constituents in Aqueous Extracts from Mercurialis perennis L. during Fermentation

Dog's mercury (Mercurialis perennis L.) is an old medicinal plant, nowadays used in complementary medicine. Aqueous fermented extracts of the plant are being mainly applied in remedies to treat external inflammations, but a thorough phytochemical characterization is still lacking. Therefore, the conversion of characteristic compound classes from M. perennis extracts during fermentation and storage was investigated. The microbial transformation of the two main depsides phaselic acid (=(2R)‐O‐[(E)‐caffeoyl]malic acid; 1 ) and mercurialis acid (=(2R)‐[(E)‐caffeoyloxy]glutaric acid; 2 ) was monitored by HPLC‐DAD. The degradation followed a second‐order kinetic, and the calculated half‐life periods of both constituents were 67 and 30 months, respectively. Several depside metabolites were detected by GC/MS in AcOEt extracts as ^tBuMe₂Si (TBDMS) derivatives after derivatization, mainly dihydrocinnamic acids. Moreover, numerous α‐hydroxy acids were found, allegedly as degradation products from amino acids or peptides. The microbial alteration of the main alkaloid hermidin was also examined. After three days of fermentation, three novel N‐metabolites were formed and thoroughly assigned in CH₂Cl₂ extracts as a mixture of 3‐ethylhermidin, 3‐ethylhermidin quinone, and (E/Z)‐3‐ethylidenehermidin by GC/MS and NMR methods, as well as by means of total synthesis. A mechanism for the formation of these N‐metabolites starting from dimeric hermidin oxidation products is proposed. The obtained results reveal the complex pathways plant constituents may undergo during the fermentation of the extracts.     

Isolation and characterization of microsatellite loci in Geum urbanum (Rosaceae) and their transferability within the genus Geum

Thirteen novel polymorphic microsatellite loci are presented for Geum urbanum (Rosaceae). The microsatellites will be useful tools to analyse the influence of landscape structure and land‐use intensity in agricultural landscapes on genetic diversity within and among populations of Geum urbanum. Transferability was tested in 19 other Geum species and two Waldsteinia species. In most species polymerase chain reaction (PCR) products of the expected range were obtained, therefore the markers reported here appear to be applicable across the whole genus.     

An Approach to the Chemotaxonomic Differentiation of Two European Dog's Mercury Species: Mercurialis annua L. and M. perennis L.

Mercurialis annua and M. perennis are medicinal plants used in complementary medicine. In the present work, analytical methods to allow a chemotaxonomic differentiation of M. annua and M. perennis by means of chemical marker compounds were established. In addition to previously published compounds, the exclusive presence of pyridine‐3‐carbonitrile and nicotinamide in CH₂Cl₂ extracts obtained from the herbal parts of M. annua was demonstrated by GC/MS. Notably, pyridine‐3‐carbonitrile was identified for the first time as a natural product. Further chromatographic separation of the CH₂Cl₂ extracts via polyamide yielded a MeOH fraction exhibiting a broad spectrum of side‐chain saturated n‐alkylresorcinols. While the n‐alkylresorcinol pattern was similar for both plant species, some specific differences were observed for particular n‐alkylresorcinol homologs. Finally, the investigation of H₂O extracts by LC/MS/MS revealed the presence of depside constituents. Whereas, in M. perennis, a mixture of mercurialis acid (=(2R)‐[(E)‐caffeoyl]‐2‐oxoglutarate) and phaselic acid (=(E)‐caffeoyl‐2‐malate) could be detected, in M. annua solely phaselic acid was found. By comparison with synthesized enantiomerically pure (2R)‐ and (2S)‐phaselic acids, the configuration of the depside could be determined as (2S) in M. annua and as (2R) in M. perennis.     

Canopy structure,nitrogen distribution and whole canopy photosynthetic carbon gain in growing and flowering stands of tall herbs

Using a combination of mathematical modeling and field studies we showed that in dense stands of growing herbaceous plants the vertical pattern of leaf nitrogen distribution resembles the pattern of mean light attenuation in the stand and hence tends to maximize total daily photosynthetic carbon gain of the whole stand. Flowering represents a strong sink of nitrogen away from the photosynthetic apparatus and in herbs like Solidago altissima it induces leaf shedding. We studied both the effect of nitrogen reallocation and leaf shedding on the whole canopy photosynthesis and changes in leaf nitrogen distributions in stands moving from the growing to the flowering stage. Despite a decrease in leaf area index and total nitrogen available for photosynthesis in the flowering stand, the leaf nitrogen distribution here also leads to an almost maximum canopy photosynthesis. In both the growing and the flowering stands the leaf area index was higher than calculated optimum values. It is pointed out that this should not necessarily be interpreted as non-adaptive.     

A cell-based model for the photoacclimation and CO2-acclimation of the photosynthetic apparatus

We have developed a mathematical model based on the underlying mechanisms concerning the responses of the photosynthetic apparatus of a microalga cell which grows under constant incident light intensity and ambient CO₂ concentration. Photosynthesis involves light and carbon-fixation reactions which are mutually dependent and affect each other, but existing models for photosynthesis don't account for both reactions at once. Our modeling approach allows us to derive distinct equations for the rates of oxygen production, NADPH production, carbon dioxide fixation, carbohydrate production, and rejected energy, which are generally different. The production rates of the photosynthesis products are hyperbolic functions of light and CO₂ concentration. The model predicts that in the absence of photoinhibition, CO₂-inhibition, photorespiration, and chlororespiration, a cell acclimated to high light and/or CO₂ concentration has higher photosynthetic capacity and lower photosynthetic efficiency than does a cell acclimated to low conditions. This results in crossing between the two curves which represent the oxygen production rates and carbon fixation rates in low and high conditions. Finally, in the absence of photoinhibition and CO₂-inhibition, the model predicts the carbohydrate production rate in terms of both light intensity and CO₂ concentration.     

A preliminary study of the responsiveness to seasonal atmospheric and rainfall patterns of wash woodland species in the arid Richtersveld

Seasonal carbon and water relations were compared among seven tree or shrub wash woodland species in the winter rainfall desert of the Richtersveld National Park, South Africa. Plants were generally aseasonal with respect to gas exchange, but responsive to rainfall events with respect to water relations and phenology. Relatively narrow annual ranges in potential evapotranspiration due to the maritime influence could explain why these plants respond more to fluctuations in water acquisition potential than to evaporative demand. Two species were summer-deciduous, but one of them (Ozoroa concolor) responded to aseasonal summer rainfall by leafing out and flowering. These two species had high shoot xylem water potentials when in leaf. All other species were sclerophyllous evergreens with low water potentials, particularly the shallow-rooted shrub Zygophyllum prismatocarpum, and Boscia albitrunca which may have a different rooting pattern to the other phreatophytes. The latter species was also unique due to its high leaf nitrogen contents, photosynthetic rates and stomatal conductances, despite very low leaf water potentials. Leaf stable carbon isotope composition C¹³C) varied between species (–22 to –27), but was lower than the mean for arid regions worldwide. The values indicated moderately high levels of water use efficiency, but a less conservative strategy in two species, including Boscia albitrunca. The affinities of these species to summer rainfall biomes, their apparent decline in the western arid regions in recent geological history following aridification, and their absence southwards in the winter rainfall regions, suggest that these wash species rely on sporadic summer rainfall events to some extent. They may be at risk if predicted increases in temperature and changes in rainfall patterns alter their effective moisture availability.     

两种五倍子蚜虫冬寄主藓类植物的光合特性及其与光照、温度和植物体水分含量变化的关系

使用CI-301PS(CID Inc.USA)对生长于冬季和春季的大羽藓(Thuidium cymbifolium)与垂藓(Chrysocladium retrorsum)的净光合速率(Pn)及其与光照、温度和植物体水分含量的关系进行了研究.结果表明,大羽藓和垂藓的光合能力分别达到141和117μmolCO₂kg^-1·dw·s^-1,光合能力从冬季到春季呈上升趋势.这两种藓类植物的光响应曲线比较相似,光饱和点高达800～900μmol·m^-2s^-1,光补偿点为40～50μmol·m^-2s^-1,光合作用最适温度在春季为25～36℃,而冬季为20～30℃.同时对于低温又具有很强的抗性,在冰点以下的温度条件下(-15～0℃)能够保持一定的净光合.净光合速率的水分响应曲线表明,这两种藓类的最适水分含量为200～300(400)%dw,水分含量降低到150%dw时光合作用开始受到抑制,在40%～50%dw时净光合降低到零或略变为负数.结果表明,大羽藓和垂藓都属于耐干旱、强阳性的藓类,但垂藓在这几个方面略逊于大羽藓.     

Diurnal and seasonal variations in photosynthetic and morphological traits of the tree ferns Dicksonia antarctica (Dicksoniaceae) and Cyathea australis (Cyatheaceae) in wet sclerophyll forests of Australia

Steady state and dynamic responses of two tree fern species of contrasting origins, Dicksonia antarctica (of Gondwanan origin) and Cyathea australis (Pan-tropical), were studied over two consecutive years under field conditions in a wet sclerophyll forest of south-east Australia. Irrespective of their different origins, there were no significant differences in photosynthetic performance between the two species. Growth irradiance and leaf temperature, but not plant water status, was significantly related to photosynthetic and morphological traits. At a common leaf temperature, maximum light-use efficiency of photosystem II (F_v/F_m) was significantly lower in winter than in summer, suggesting some limitation to PSII efficiency potentially associated with cold winter mornings. Both species displayed seasonal acclimation in a number of measured photosynthetic parameters and frond traits (i.e. F_v/F_m, A_sat, g_s, N_A, total chlorophyll, SLA). Acclimation of stomatal density to spatial variation in growth irradiance seemed limited in both species, although stomatal pattern differed between species. Because there were no significant differences between the two species in photosynthetic parameters, both species can be described by common carbon gain and water use models at the leaf scale.     

两种匍灯藓属植物夏季和冬季光合特性的比较研究

分别对生长于冬季和夏季的五倍子蚜虫冬寄主藓类植物湿地匍灯藓(Plagiomnium acutum(Lindb.)T.Kop.)和侧枝葡灯藓(Plagiomnium maximoviczii(Lindb.)T.Kop.)的净光合速率及其与光照、温度的关系进了比较研究.结果表明,2种藓类的最大光合能力在夏季分别为125.67和94.63μmolCO2     

Landscape genetics of the self-compatible forest herb Geum urbanum: effects of habitat age, fragmentation and local environment

To investigate the role of habitat fragmentation, fragment age and local environment in shaping the genetics of plant populations, we examined the genetic structure of the self-compatible forest herb Geum urbanum using microsatellite markers. A historical land-use reconstruction assigned the studied populations to two age classes: populations in primary forest fragments, and populations in secondary fragments. Local environmental conditions were quantified on the basis of the herb-layer community composition. A stepwise general linear model revealed that levels of within-population genetic diversity were best explained by population size, landscape connectivity and the interaction between both. Connectivity was positively correlated with the genetic diversity of small populations, but did not significantly affect the diversity of large populations. Contrary to what we expected, secondary-forest populations showed lower divergence relative to populations located in primary patches. Small populations were genetically more diverged compared to large populations. Mantel tests showed no significant isolation by distance and no significant correlation between habitat similarity and genetic differentiation. We conclude that gene flow has probably prevented founder events from being reflected in the present genetic structure of G. urbanum. Gene flow towards low-connectivity populations, however, seemed to be insufficient to counteract the effects of drift in small populations.     

环境因子对小球藻(Chlorella sp.XQ-20044)光合作用的影响

小球藻(Chlorella sp.XQ-20044)是一株具有应用潜力的产油微藻,本文利用测定净光合放氧速率的方法研究了光照强度、温度、pH值和盐度对其光合作用的影响。研究结果表明:小球藻适宜的光照强度为500~1200μmol·m-2·s-1,光补偿点约30μmol·m-2·s-1,光饱和点在600μmol·m-2·s-1附近;光合作用适宜的温度范围为30~42.5℃,最适温度为40℃;适宜的pH值范围7.0~10.0,最适pH值为8.0;适宜盐度范围0.1~0.3 mol/L,最适盐度为0.2 mol/L。从光合作用特性来看,小球藻能适应较强的光照强度、较高的温度、偏碱性和较高的盐度环境,其中可耐受较高盐度的特性,有助于预防敌害生物的污染,对于实现规模培养,特别是利用开放系统进行规模培养较为有利。