Oxygen Distribution in Wetland Plant Roots and Permeability Barriers to Gas-exchange with the Rhizosphere: a Microelectrode and Modelling Study with Phragmites australis

Adventitious roots of intact Phragmites plantlets were securedhorizontally 2–3 mm below the surface of an oxygen-depletedfluid agar across which oxygen-free nitrogen was gently streamedto create a constant oxygen sink; the leafy shoot was fullyexposed to air. Radial oxygen profiles through rhizosphere androot at different distances from the apex were obtained polarographicallyusing Clark-type bevelled microelectrodes servo-driven in stepsof 10 µm (root) or 10–50 µm (rhizosphere).The pattern of radial oxygen loss (ROL) typical of wetland plants,viz. high at the apex and declining sharply sub-apically, wasrelated to synergism between ROL, and oxygen consumption andincreasing impedance to diffusion within the epidermal/hypodermalcylinder rather than to a surface resistance. The smallest oxygendeficit (2 kPa) to develop across the 80 µm thick epidermal/hypodermalcylinder was within the apical 10 mm and was consistent withtissue oxygen diffusivities similar to water. At 100 mm fromthe apex, consumption and impedance had increased the deficitto about 15 kPa and reduced ROL almost to zero. The developingimpedance within the epidermal/hypodermal cylinder was leastin cell layers immediately adjoining the cortex and increasedmost in the hypodermal cell layer abutting the epidermis. Thesub-apical decline in ROL appeared to coincide with the appearanceof aerenchyma in the cortex but thin walled ‘passage areas’(windows) in the hypodermal/epidermal cylinder persisted locallyand remained leaky to oxygen to some degree. It is through thesewindows that lateral roots emerge and the cortex in line withthe windows remains non-aerenchymatous. The radial and longitudinaloxygen profiles were consistent with modelling predictions.The shapes of the stelar oxygen profiles were consistent witha higher oxygen demand in the outer region (viz. pericycle,phloem, protoxylem and early metaxylem cylinder) than in theinner core (late metaxylem cylinder and medulla), but the deficitswere relatively small (     

A Method to Estimate Practical Radial Oxygen Loss of Wetland Plant Roots

The estimation of practical radial oxygen loss (ROL) of wetland plant roots was attempted in this study. We have devised a new method to measure ROL of wetland plant roots. The whole root system was bathed in an anoxic nutrient solution. Oxygen released from the root was removed immediately by introducing oxygen-free nitrogen gas (O₂ < 4 nmol L⁻¹) to mimic natural habitats where released oxygen is consumed rapidly due to chemical and biological oxidation processes. Oxygen removed from the root-bathing chamber was simultaneously detected colorimetrically by use of the highly oxygen-sensitive anthraquinone radical anion (AQ·⁻) in a cell outside the root-bathing chamber, which decolorized by a rapid reaction with oxygen. An emergent macrophyte Typha latifolia L. was incubated, and its ROL was measured by both the new method and one of the conventional methods, the closed chamber/electrode method, by which the ROL of Typha latifolia L. had not yet been measured. The new method succeeded in detecting the ROL, whereas the conventional method was not able to detect oxygen, due to the level being below the detection limit of the oxygen electrode. The oxygen supply via the seedlings of Typha latifolia L. was ca. 10 times higher compared with control measurements without plant. Light illumination significantly enhanced the ROL of Typha latifolia L. (0.33 nmol O₂ g⁻¹ root dry weight s⁻¹ under light and 0.18 nmol O₂ g⁻¹ root dry weight s⁻¹ in the dark). Theses values fall between those previously reported by the closed chamber/titanium citrate method and the open chamber/electrode method.     

Species Distribution Models for Crop Pollination: A Modelling Framework Applied to Great Britain

Insect pollination benefits over three quarters of the world''s major crops. There is growing concern that observed declines in pollinators may impact on production and revenues from animal pollinated crops. Knowing the distribution of pollinators is therefore crucial for estimating their availability to pollinate crops; however, in general, we have an incomplete knowledge of where these pollinators occur. We propose a method to predict geographical patterns of pollination service to crops, novel in two elements: the use of pollinator records rather than expert knowledge to predict pollinator occurrence, and the inclusion of the managed pollinator supply. We integrated a maximum entropy species distribution model (SDM) with an existing pollination service model (PSM) to derive the availability of pollinators for crop pollination. We used nation-wide records of wild and managed pollinators (honey bees) as well as agricultural data from Great Britain. We first calibrated the SDM on a representative sample of bee and hoverfly crop pollinator species, evaluating the effects of different settings on model performance and on its capacity to identify the most important predictors. The importance of the different predictors was better resolved by SDM derived from simpler functions, with consistent results for bees and hoverflies. We then used the species distributions from the calibrated model to predict pollination service of wild and managed pollinators, using field beans as a test case. The PSM allowed us to spatially characterize the contribution of wild and managed pollinators and also identify areas potentially vulnerable to low pollination service provision, which can help direct local scale interventions. This approach can be extended to investigate geographical mismatches between crop pollination demand and the availability of pollinators, resulting from environmental change or policy scenarios.     

Restoring Wetland Plant Diversity: A Comparison of Existing and Adaptive Approaches

Most restoration projects are not designed or assessed in ways that identify cause–effect relationships.When plants die, even detailed postmortem examinations cannot pinpoint causes; e.g., mortalities of 7% vs. 90% in two salt marsh transplantation projects were attributable to differences in hypersalinity and sedimentation, but other effects could not be ruled out. Adaptive restoration (the experimental testing of alternative approaches in restoration sites), however, can clarify cause–effect relationships, while simultaneously restoring plant diversity and informing future restoration efforts. Projects in Tijuana Estuary (California) and Greene Prairie (Wisconsin) demonstrate the approach: (1) A large field experiment at Tijuana Estuary showed that species-rich plantings of halophytes accelerated the development of ecosystem structure and function (over single-species plantings) while simultaneously vegetating an intertidal plain. The six-species assemblages produced more complex canopies and accumulated more biomass and nitrogen than singlespecies and unplanted plots. (2) Also at Tijuana Estuary, an experiment is testing the ability of tidal creek networks to accelerate revegetation and increase food-web support (via increased growth of plants, invertebrates, and fish) in an 8-ha project that simultaneously restored tidal flushing. (3) In Greene Prairie, the ability to establish 33 native species is being tested as replacements for an invasive grass (Phalaris arundinacea). In each case, the adaptive approach informs both the science and practice of restoration. Without experimentation, restorationists are hard-pressed to explain past mortality and to suggest better methods for restoring structure and function. Adaptive restoration can provide the knowledge required, especially when large projects are implemented as sequential modules with experiments that sequentially provide essential information.     

Distribution and Ecophysiology of Calanoid Copepods in Relation to the Oxygen Minimum Zone in the Eastern Tropical Atlantic

Oxygen minimum zones (OMZs) affect distribution patterns, community structure and metabolic processes of marine organisms. Due to the prominent role of zooplankton, especially copepods, in the marine carbon cycle and the predicted intensification and expansion of OMZs, it is essential to understand the effects of hypoxia on zooplankton distribution and ecophysiology. For this study, calanoid copepods were sampled from different depths (0–1800 m) at eight stations in the eastern tropical Atlantic (3°47′N to 18°S) during three expeditions in 2010 and 2011. Their horizontal and vertical distribution was determined and related to the extent and intensity of the OMZ, which increased from north to south with minimum O₂ concentrations (12.7 µmol kg⁻¹) in the southern Angola Gyre. Calanoid copepod abundance was highest in the northeastern Angola Basin and decreased towards equatorial regions as well as with increasing depth. Maximum copepod biodiversity was observed in the deep waters of the central Angola Basin. Respiration rates and enzyme activities were measured to reveal species-specific physiological adaptations. Enzyme activities of the electron transport system (ETS) and lactate dehydrogenase (LDH) served as proxies for aerobic and anaerobic metabolic activity, respectively. Mass-specific respiration rates and ETS activities decreased with depth of occurrence, consistent with vertical changes in copepod body mass and ambient temperature. Copepods of the families Eucalanidae and Metridinidae dominated within the OMZ. Several of these species showed adaptive characteristics such as lower metabolic rates, additional anaerobic activity and diel vertical migration that enable them to successfully inhabit hypoxic zones.     

Germination of Species of Caryophyllaceae in Relation to their Geographical Distribution in Europe

Comparisons were made between the germination responses to temperatureof species of Caryophyllaceae collected in the wild from differentparts of Europe. Species occurring predominantly in the Mediterraneanzone were compared with those distributed in the deciduous woodlandzone of central and southern Europe; steppeland and grasslandareas of eastern Europe, and in the Taiga and Tundra of northernEurope. The geo-botanical distributions of different specieswere reflected in their germination responses. Species fromthe Mediterranean germinated over a range with a mean of 4.5to 24.2 °C; those from deciduous woodland over the range11.8 to 30.0 °C; those from steppelands over the range 6.0to 30.0 °C. There was little uniformity in the northernEuropean species. The significance of the results is discussedin relation to the distribution of different species, the variationwithin a species, and the climatic components of the variousgeo-botanical zones.     

Temporal-Spatial Dynamics in Orthoptera in Relation to Nutrient Availability and Plant Species Richness

Nutrient availability in ecosystems has increased dramatically over the last century. Excess reactive nitrogen deposition is known to negatively impact plant communities, e.g. by changing species composition, biomass and vegetation structure. In contrast, little is known on how such impacts propagate to higher trophic levels. To evaluate how nitrogen deposition affects plants and herbivore communities through time, we used extensive databases of spatially explicit historical records of Dutch plant species and Orthoptera (grasshoppers and crickets), a group of animals that are particularly susceptible to changes in the C:N ratio of their resources. We use robust methods that deal with the unstandardized nature of historical databases to test whether nitrogen deposition levels and plant richness changes influence the patterns of richness change of Orthoptera, taking into account Orthoptera species functional traits. Our findings show that effects indeed also propagate to higher trophic levels. Differences in functional traits affected the temporal-spatial dynamics of assemblages of Orthoptera. While nitrogen deposition affected plant diversity, contrary to our expectations, we could not find a strong significant effect of food related traits. However we found that species with low habitat specificity, limited dispersal capacity and egg deposition in the soil were more negativly affected by nitrogen deposition levels. Despite the lack of significant effect of plant richness or food related traits on Orthoptera, the negative effects of nitrogen detected within certain trait groups (e.g. groups with limited disperse ability) could be related to subtle changes in plant abundance and plant quality. Our results, however, suggest that the changes in soil conditions (where many Orthoptera species lay their eggs) or other habitat changes driven by nitrogen have a stronger influence than food related traits. To fully evaluate the negative effects of nitrogen deposition on higher trophic levels it is essential to take into account species life-history traits.     

Species Invasiveness in Biological Invasions: A Modelling Approach

The study of invasiveness, the traits that enable a species to invade a habitat, and invasibility, the habitat characteristics that determine its susceptibility to the establishment and spread of an invasive species, provide a useful conceptual framework to formulate the biological invasion problem in a modelling context. Another important aspect is the complex interaction emerging among the invader species, the noninvader species already present in the habitat, and the habitat itself. Following a modelling approach to the biological invasion problem, we present a spatially explicit cellular automaton model (Interacting Multiple Cellular Automata (IMCA)). We use field parameters from the invader Gleditsia triacanthos and the native Lithraea ternifolia in montane forests of central Argentina as a case study to compare outputs and performance of different models. We use field parameters from another invader, Ligustrum lucidum, and the native Fagara coco from the same system to run the cellular automaton model. We compare model predictions with invasion values from aerial photographs. We discuss in detail the importance of factors affecting species invasiveness, and give some insights into habitat invasibility and the role of interactions between them. Finally, we discuss the relevance of mathematical modelling for studying and predicting biological invasions. The IMCA model provided a suitable context for integrating invasiveness, invasibility, and the interactions. In the invasion system studied, the presence of an invader's juvenile bank not only accelerated the rate of invasion but was essential to ensure invasion. Using the IMCA model, we were able to determine that not only adult survival but particularly longevity of the native species influenced the spread velocity of the invader, at least when a juvenile bank is present. Other factors determining velocity of invasion detected by the IMCA model were seed dispersal distance and age of reproductive maturity. We derived relationships between species' adult survival, fecundity and longevity of both theoretical and applied relevance for biological invasions. Invasion velocities calculated from the aerial photographs agreed well with predictions of the IMCA model.     

Dealing with Noisy Absences to Optimize Species Distribution Models: An Iterative Ensemble Modelling Approach

Species distribution models (SDMs) are widespread in ecology and conservation biology, but their accuracy can be lowered by non-environmental (noisy) absences that are common in species occurrence data. Here we propose an iterative ensemble modelling (IEM) method to deal with noisy absences and hence improve the predictive reliability of ensemble modelling of species distributions. In the IEM approach, outputs of a classical ensemble model (EM) were used to update the raw occurrence data. The revised data was then used as input for a new EM run. This process was iterated until the predictions stabilized. The outputs of the iterative method were compared to those of the classical EM using virtual species. The IEM process tended to converge rapidly. It increased the consensus between predictions provided by the different methods as well as between those provided by different learning data sets. Comparing IEM and EM showed that for high levels of non-environmental absences, iterations significantly increased prediction reliability measured by the Kappa and TSS indices, as well as the percentage of well-predicted sites. Compared to EM, IEM also reduced biases in estimates of species prevalence. Compared to the classical EM method, IEM improves the reliability of species predictions. It particularly deals with noisy absences that are replaced in the data matrices by simulated presences during the iterative modelling process. IEM thus constitutes a promising way to increase the accuracy of EM predictions of difficult-to-detect species, as well as of species that are not in equilibrium with their environment.     

Ion Distribution in Salt-stressed Mature Zea mays Roots in Relation to Ultrastructure and Retention of Sodium

Ultrastructural features and the distribution of soluble ionshave been examined in mature roots of Zea mays plants grownin both NaCl and Na₂SO₄ salinities. When the plants were grown in either salt, the Na concentrationincreased proximally along the root with a concomitant declinein the K concentration. Both trends were reversed in the shoot. X-ray microanalysis of deep-frozen, fully hydrated specimensshowed that in salt-treated roots Na, and Cl, or S were distributedabout stoichiometrically in the cortex and endodermis. Na wasusually less concentrated than the anion in the lumens of thevessels, but was concentrated markedly relative to either Clor S in the adjoining xylem parenchyma cells. In the older, proximal parts of seminal roots of plants grownboth without salt (controls) and in the presence of either NaClor Na₂SO₄, wall developments occurred in xylem parenchyma cellsat the half-bordered pits in which the cell wall became markedlythicker and possessed a loosely packed fibrillar structure.These structures were not comparable with the transfer-celltype of protuberances reported in the roots of other species. In the xylem parenchyma of plants grown in the presence of Na₂SO₄there were dramatic increases in the quantities of rough endoplasmicreticulum, ribosomes, and mitochondria relative both to controlsand NaCl treatments. The results are discussed in relation to the possible functionof the xylem parenchyma of the mature root in the reabsorptionof Na from the xylem sap, which may mitigate adverse effectsof salinity in salt-sensitive glycophytes.     

A Soil-free Plant Growth System to Facilitate Analysis of Plant Pathogen Interactions in Roots

Analysis of the interaction of pathogens with plant roots is often complicated by the growth of plants in a soil substrate. A soil-free plant growth system (SPS) was developed that removes the need for a substrate while supporting the growth of seedlings in a nutrient rich, oxygenated environment. The model legume Lupinus angustifolius was used to compare the growth of seedlings within soil and the SPS. Seedlings grown under both conditions were similar in morphology, anatomy and health (measured by leaf chlorophyll abundance) and importantly there was little difference in root growth and development although straighter and fuller root systems were achieved in the SPS. The ease of access to the root system proved efficient for the analysis of root and pathogen interactions with no interference from soil or adhering particulate matter. Following inoculation of L. angustifolius roots with Phytophthora cinnamomi the host/pathogen interaction was easily observed and tissues sampled undamaged.     

Plant Carbonic Anhydrases: I. Distribution of Types among Species

On the basis of polyacrylamide gradient gel electrophoresis of leaf extracts from 24 species of higher plants, two main forms of carbonic anhydrase (EC 4.2.1.1) were recognized; the “dicotyledon” type and the “monocotyledon” type. More than one band of enzyme was found on gels from most species, suggesting the possibility of carbonic anhydrase isoenzymes in higher plants.     

Vertical Distribution of Three Namatode Species in Relation to Certain Soil Properties

Population densities of Belonolaimus longicaudatus, Pratylenchus brachyurus, and Trichodorus christiei were determined from soil samples taken weekly in Tifton, Georgia during a 14-month period (except for April and May) at 15-cm increments to a depth of 105 cm. Belonolaimus longicaudatus predominately inhabited the top 30 cm of soil that was 87-88% sand, 6-7% silt, and 5-7% clay. No specimens were found below 60 cm where the soil was 76-79% sand, 5-6% silt, and 15-19% clay. Highest population densities occurred during June through September when temperature in the top 30 cm of soil was 22-25 C and soil moisture was from 9 to 20% by volume. Pratylenchus brachyurus was found at all depths, but population densities were greatest 45-75 cm deep where the soil was 78-79% sand, 6% silt, and 15-16% clay. In the months monitored, highest population densities occurred during March, June, and December when the soil temperature 45-75 cm deep was 14-17 C and soil moisture was 22-42%. Trichodorus christiei was found at all depths, but population densities were highest 30 cm deep where the soil was 83% sand, 5% silt, and 12% clay. Highest population densities occurred during December through March when the soil temperature 30 cm deep was 11-17 C and soil moisture was 18-23%.     

Effects of Different Wetland Plant Species on Fresh Unweathered Sulphidic Mine Tailings

Vegetation cover with two Eriophorum species on old unweathered sulphidic mine tailings has earlier been found to reduce the element levels and to prevent production of acidity in drainage water. The present study aims to find out if Carex rostrata Stokes, Eriophorum angustifolium Honck. and Phragmites australis (Cav.) Steud. had other effects on metal and As release in fresh unweathered sulphidic mine tailings, if the species showed different effects and if this depended on plant mechanisms such as O₂, carbonate or organic acid release. Plants were grown in pots with fresh sulphidic mine tailings for 13 months. Arsenic, Cd, Cu, Fe, Pb, Zn, pH, SO ₄ ²⁻ , alkalinity and organic acids in the drainage water as well as metals and As in roots and shoot and O₂ and redox potential in pore water were analysed. The tailings weathered slowly due to high buffering capacity thus no pH decrease was found and therefore similar buffering effects by plants as shown in the previous investigation could not be found. The plants increased the total release of metals and As from the tailings. The release did not depend on carbonate or organic acid release from plants. However, the Fe and As release was due to changed redox potential, caused by O₂ release, and high concentration of Fe and As was found in plant roots. Phragmites australis released more As and Fe but less Cd than E. angustifolium and C. rostrata which make P. australis not suitable for plant establishment on sulphidic mine tailings containing high levels of As. Plants did take up the elements and the lowest translocation of elements to the shoot was found in P. australis while the highest in E. angustifolium.     

毛果苔草湿地植物营养元素分布及其相关性

研究生物与环境中化学因子之间的相互作用过程 ,主要是指化学物质在生态系统中的运移、转化及归趋与效应。化学物质包括营养物质、污染物质和在生物与环境之间、生物与生物之间起媒介作用的次生代谢物质[1] 。对植物不同组织营养成分的季节性变化研究多集中于叶子 ,但对其他部分的研究则较少[10 ] ,分解过程并不是完全始于凋落物到达地面 ,在凋落前就受到渗滤、裂解和真菌的作用[12 ] ;对枯落物中的有机物质和营养物质浓度的了解可以预测枯落物的分解速率[11] 。目前 ,湿地的研究偏重于资源的开发与利用 ,而对湿地生态系统的生态过程的定位…     

The Relation Between Unpalatable Species, Nutrients and Plant Species Richness in Swiss Montane Pastures

In agriculturally marginal areas, the control of unpalatable weeds on species rich pastures may become problematic due to agricultural and socio-economic developments. It is unclear how increased dominance of unpalatable species would affect the botanical diversity of these grasslands. We investigated whether there was any relationship between plant species diversity and the abundance of unpalatable species and whether soil conditions affected this relationship. In three species-rich montane pastures in western Switzerland, we related plant species richness to soil attributes, the relative cover of all unpalatable species and the relative cover of the locally dominant, toxic Veratrum album in 25 plots of 4 m². We furthermore determined species richness in small transects through patches of V. album. Species richness was significantly lower in and near (≤ 0.3 m) patches of V. album. At the field scale, plant species richness was best described by total soil N:P ratio (positive relation) in one site and the relative abundance of unpalatable species (negative relation) and soil N:P ratio (positive relation) in a second site. In the third site, species richness was not significantly related to any measured variable. Vegetation diversity (Simpson's D) was negatively related to the relative abundance of unpalatable species in one site and positively related to pH in another site. The results suggest that no single factor can explain plant species richness and diversity in montane pastures. At very high densities unpalatable species can have adverse effects but soil nutrient status appears to be a more general determinant of plant species richness. Conservation efforts should give priority to the prevention of intensification of these pastures.     

Microbial Ecophysiology of Whey Biomethanation: Comparison of Carbon Transformation Parameters, Species Composition, and Starter Culture Performance in Continuous Culture

Changes in lactose concentration and feed rate altered bacterial growth and population levels in a whey-processing chemostat. The bacterial population and methane production levels increased in relation to increased lactose concentrations comparable to those in raw whey (6%) and converted over 96% of the substrate to methane, carbon dioxide, and cells. Sequential increases in the chemostat dilution rate demonstrated excellent biomethanation performance at retention times as low as 25 h. Retention times shorter than 25 h caused prevalent bacterial populations and methane production to decrease, and intermediary carbon metabolites accumulated in the following order: acetate, butyrate, propionate, lactate, ethanol, and lactose. Bacterial species dominated in the chemostat as a function of their enhanced substrate uptake and growth kinetic properties. The substrate uptake kinetic properties displayed by the mixed chemostat population were equivalent to those of individual species measured in pure culture, whereas the growth kinetic properties of species in mixed culture were better than those measured in pure culture. A designed starter culture consisting of Leuconostoc mesenteroides, Desulfovibrio vulgaris, Methanosarcina barkeri, and Methanobacterium formicicum displayed biomethanation performance, which was similar to that of a diverse adapted mixed-culture inoculum, in a continuous contact digestor system to which 10 g of dry whey per liter was added. Preserved starter cultures were developed and used as inocula for the start-up of a continuous anaerobic digestion process that was effective for biomethanation of raw whey at a retention time of 100 h.