Gas exchange and hydraulic properties in the crowns of two tree species in a Panamanian moist forest

Hydraulic properties and gas exchange were measured in branches of two tropical tree species (Simarouba amara Aubl. and Tapirira guianensis Aubl.) in a moist lowland forest in Panama. Branch-level sapflow, leaf-level stomatal conductance, and water potential measurements, along with measurements of specific hydraulic conductivity of stems in crown tops, were used to relate hydraulic parameters to leaf conductance in two individuals of each species. Branches of the taller trees for each species (28 m, 31 m) showed much higher leaf-specific hydraulic conductance and leaf vapor-phase conductance than those of the smaller trees (18m, 23m). This was probably related to the leaf-to-sapwood area ratio in branches of taller trees, which was less than half that in branches of smaller trees. Dye staining showed evidence of massive cavitation in all trees, indicating that stomata do not control leaf water potential to prevent xylem cavitation in these species. Stomatal conductance of intact leaves also appeared to be insensitive to leaf area removal treatment of nearby foliage. Nevertheless, a simple mass-balance model of water flux combining hydraulic and vapor transport was in close agreement with observed maximal vapor-phase conductance in the four trees (r²=0.98, P=0.006). Our results suggest that the major organismal control over water flux in these species is by structural (leaf area) rather than physiological (stomatal) means.     

东北地区森林资源生态风险评价研究

根据区域生态风险评价的理论和方法体系,对东北地区森林资源进行了生态风险评价．东北林区生态风险问题形成的主要胁迫包括物理胁迫、化学胁迫、生物胁迫和社会胁迫,其权重系数分别为0．30、0．22、0．11和0．37．东北93个林业局中,轻风险占64．4％,中风险占21．2％,重风险占13．3％。严重风险占1．1％,符合偏正态分布．东北区森林生态风险的地域分异明显,靠近长白山区的森林处于轻风险和中风险等级,向西生态风险越来越重,处于重风险和严重风险等级的林业局主要集中在小兴安岭地区．必须加强东北区风险管理和森林景观的修复与重建。     

Predicting insect pest status under climate change scenarios: combining experimental data and population dynamics modelling

Climate change could profoundly affect the status of agricultural insect pests. Several approaches have been used to predict how the temperature and precipitation changes could modify the abundances, distributions or status of insect pests. In this article it is demonstrated how the use of simple models, such as Ricker’s classic equation, including a mechanistic representation of the influence of exogenous forces may improve our predictive capacity of the dynamic behaviour of insect populations. Using data from classical experiments in population ecology, we evaluate how temperature and humidity influence the density of two stored grain insect pest, Tribolium confusum and Callosobruchus chinensis, and then, using the A2 and B2 scenarios proposed by the Intergovernmental Panel on Climate Change and the previous modelling, we develop predictions over the future pest status of T. confusum along South America austral region, and specifically for eight cities in the continental Chilean territory. Tribolium confusum and C. chinensis show qualitatively different responses to the exogenous forcing of temperature and humidity, respectively. Our simulations predict a change in the equilibrium density of T. confusum from 10 to 14% under the moderate B2 scenario and 12 to 22% under the extreme A2 scenario to the period, 2071–2100. Both results imply a severe change in the pest status of this species in the southern region. This study illustrates how the use of theoretically based models may improve our predictive capacity. This approach provides an opportunity to examine the link between invasive species and climate change and how new suitable habitat may become available for species whose niche space is limited in some degree by climatic conditions. The use of different scenarios allows us to examine the sensitivity of the predictions, and to improve the communication with the general public and decision‐makers; a key aspect in integrated pest management.     

Ecophysiological responses of Japanese forest tree species to ozone, simulated acid rain and soil acidification

In this review, I summarized the results obtained from experimental studies on the ecophysiological responses of Japanese forest tree species to O₃, simulated acid rain and soil acidification. Based on the studies conducted in Japan, exposure to ambient levels of O₃ below 100 nl·l⁻¹ (ppb) for several months is sufficient to inhibit dry matter production and net photosynthesis of sensitive Japanese forest tree species such as Siebold's beech and Japanese zelkova. On the other hand, exposure to simulated acid rain with a pH of 4.0 or above for several months cannot induce any adverse effects on dry matter production and physiological functions of Japanese forest tree species. However, when the pH of simulated rain or fog is lowered below 4.0, negative effects appear on dry matter production and physiological functions such as transpiration in several sensitive Japanese forest tree species such as Japanese fir and Nikko fir. Based on limited information, it may be concluded that (1) Al dissolved into soil solution is the most important limiting factor for dry matter production, physiological functions and nutrient status of Japanese forest tree species grown in acidic soil, (2) the (Ca+Mg+K)/Al molar ratio in soil solution is a useful indicator to evaluate and predict the effects of soil acidification due to acid deposition on whole-plant dry matter production of Japanese forest tree species at the present time and in the future, and (3) Japanese coniferous tree species such as Japanese cedar and red pine are relatively sensitive to a reduction in (Ca+Mg+K)/Al molar ratio in soil solution compared with European forest tree species such as Norway spruce.     

Biological assessment of ozone therapy on experimental oral candidiasis in immunosuppressed rats

Immunosuppressive drugs can compromise local or general defense mechanisms and can lead to oral candidiasis. Ozone therapy has a wide range of applications in almost every field of dentistry. Its unique properties include immunostimulant, analgesic, antihypnotic, detoxicating, and antimicrobial actions. Sixty male healthy rats were immunosuppressed with dexamethasone in their drinking water one week before candida infection. The animals were divided into four equal groups. Rats of group 1 were kept without any manipulation and those of group II were given oral inoculums of C. albicans on the dorsal surface of the tongue. Group III rats were handled as group II and instead the rats were treated by daily mycostatin drops local applicator as a routine treatment. Meanwhile, group IV rats were handled as group II and instead the rats were received daily intraperitoneal injection of 1 cm³ of ozone oxygen gas mixture with concentration of ozone 70 μg/cm³. After two weeks, all rats were euthanized and tongue specimens were prepared for histological staining with Haematoxylin & Eosin and CD3 immunohistochemical staining. Histological examination revealed that treatment with ozone therapy lead to gradual decrease in lingual papillary atrophy and invasion of candida yeast. Immunohistochemical study showed significant decrease in CD3 counting. We can conclude that ozone acts as an excellent fungicidal agent also, ozone is capable of alerting the immune system.     

The influence of Carboniferous palaeoatmospheres on plant function: an experimental and modelling assessment

Geochemical models of atmospheric evolution predict that during the late Carboniferous, ca. 300 Ma, atmospheric oxygen and carbon dioxide concentrations were 35% and 0.03%, respectively. Both gases compete with each other for ribulose-1,5-bisphosphate carboxylase/oxygenase-the primary C-fixing enzyme in C₃ land plants: and the absolute concentrations and the ratio of the two in the atmosphere have the potential to strongly influence land-plant function. The Carboniferous therefore represents an era of potentially strong feedback between atmospheric composition and plant function. We assessed some implications of this ratio of atmospheric gases on plant function using experimental and modelling approaches. After six weeks growth at 35% O₂ and 0.03% carbon dioxide, no photosynthetic acclimation was observed in the woody species Betula pubescens and Hedera helix relative to those plants grown at 21% O₂. Leaf photosynthetic rates were 29% lower in the high O₂ environment compared to the controls. A global-scale analysis of the impact of the late Carboniferous climate and atmospheric composition on vegetation function was determined by driving a process-based vegetation-biogeochemistry model with a Carboniferous global palaeoclimate simulated by the Universities Global Atmospheric Modelling Programme General Circulation Model. Global patterns of net primary productivity, leaf area index and soil carbon concentration for the equilibrium model solutions showed generally low values everywhere, compared with the present day, except for a central band in the northern land mass extension of Gondwana, where high values were predicted. The areas of high soil carbon accumulation closely match the known distribution of late Carboniferous coals. Sensitivity analysis with the model indicated that the increase in O₂ concentration from 21% to 35% reduced global net primary productivity by 18.7% or by 6.3 GtC yr^-1. Further work is required to collate and map at the global scale the distribution of vegetation types, and evidence for wildfires, for the late Carboniferous to test our predictions.     

Interactive effects of ozone and climate on tree growth and water use in a southern Appalachian forest in the USA

* A lack of data on responses of mature tree growth and water use to ambient ozone (O(3)) concentrations has been a major limitation in efforts to understand and model responses of forests to current and future changes in climate. * Here, hourly to seasonal patterns of stem growth and sap flow velocity were examined in mature trees from a mixed deciduous forest in eastern Tennessee (USA) to evaluate the effects of variations in ambient O(3) exposure and climate on patterns of stem growth and water use. * Ambient O(3) caused a periodic slowdown in seasonal growth patterns that was attributable in part to amplification of diurnal patterns of water loss in tree stems. This response was mediated by statistically significant increases in O(3)-induced daily sap flow and led to seasonal losses in stem growth of 30-50% for most species in a high-O(3) year. * Decreased growth and increased water use of mature forest trees under episodically high ambient O(3) concentrations suggest that O(3) will amplify the adverse effects of increasing temperatures on forest growth and forest hydrology.     

Biokinetic and toxicodynamic modelling and its role in toxicological research and risk assessment

Toxicological risk assessment for chemicals is still mainly based on highly standardised protocols for animal experimentation and exposure assessment. However, developments in our knowledge of general physiology, in chemicobiological interactions and in (computer-supported) modelling, have resulted in a tremendous change in our understanding of the molecular mechanisms underlying the toxicity of chemicals. This permits the development of biologically based models, in which the biokinetics as well as the toxicodynamics of compounds can be described. In this paper, the possibilities are discussed of developing systems in which the systemic (acute and chronic) toxicities of chemicals can be quantified without the heavy reliance on animal experiments. By integrating data derived from different sources, predictions of toxicity can be made. Key elements in this integrated approach are the evaluation of chemical functionalities representing structural alerts for toxic actions, the construction of biokinetic models on the basis of non-animal data (for example, tissue-blood partition coefficients, in vitro biotransformation parameters), tests or batteries of tests for determining basal cytotoxicity, and more-specific tests for evaluating tissue or organ toxicity. It is concluded that this approach is a useful tool for various steps in toxicological hazard and risk assessment, especially for those forms of toxicity for which validated in vitro and other non-animal tests have already been developed.     

Water-use efficiency as a means of modelling net assimilation in boreal forests

Although the processes governing photosynthesis are well understood, scaling from shoot to canopy in coniferous forests is complex. Development of different sap-flow techniques has made it possible to measure transpiration of whole trees and thereby also of whole canopies. There is a strong link between photosynthesis and transpiration, for which reason it would be interesting to test whether measurements of canopy transpiration could also be used to estimate canopy photosynthesis. As a first step towards this, water-use efficiency (WUE) was studied at branch and canopy scales on the basis of branch gas-exchange measurements, with half-hourly and daily temporal resolution. Half-hourly and daily WUE at both branch and canopy scales showed a strong dependency on vapour-pressure deficit ('e). Branch photosynthesis modelled from branch transpiration and 'e mimicked well measured branch photosynthesis. Also, modelled photosynthesis, scaled to canopy and compared to net forest CO₂ exchange measured by the eddy-covariance technique, occasionally showed good agreement. In spite of these seemingly promising results, there was a difference in the response to 'e between branches and between years, which needs to be better understood.     

Conspicuous males suffer higher predation risk: visual modelling and experimental evidence from lizards

Colour pattern variation is a striking and widespread phenomenon. Differential predation risk between individuals is often invoked to explain colour variation, but empirical support for this hypothesis is equivocal. We investigated differential conspicuousness and predation risk in two species of Australian rock dragons, Ctenophorus decresii andC. vadnappa . To humans, the coloration of males of these species varies between ‘bright’ and ‘dull’. Visual modelling based on objective colour measurements and the spectral sensitivities of avian visual pigments showed that dragon colour variants are differentially conspicuous to the visual system of avian predators when viewed against the natural background. We conducted field experiments to test for differential predation risk, using plaster models of ‘bright’ and ‘dull’ males. ‘Bright’ models were attacked significantly more often than ‘dull’ models suggesting that differential conspicuousness translates to differential predation risk in the wild. We also examined the influence of natural geographical range on predation risk. Results from 22 localities suggest that predation rates vary according to whether predators are familiar with the prey species. This study is among the first to demonstrate both differential conspicuousness and differential predation risk in the wild using an experimental protocol. Copyright 2003 Published by Elsevier Ltd on behalf of The Association for the Study of Animal Behaviour.      

Ecological risk assessment of transgenic pasture plants: a community gradient modelling approach

The extension of transgene technology to pasture species presents new challenges for ecological risk assessment because, unlike most crops, pasture plants are well adapted for persistence in mixed plant communities and are an important source of invasive species worldwide. Despite this, the impact of transgenic pasture plants on native ecosystems remains relatively unstudied. Here we use a community gradient modelling approach to investigate the performance of subterranean clover containing a nutrition‐enhancing transgene over a range of ecologically important grassland communities at a study site in south‐eastern Australia. Our data, which were collected over a full annual growing season, show that the transgenic clover line has different seedling survival and seed dormancy breakdown rates than the commercial non‐transgenic line, which suggests that transgenic populations will decline faster than non‐transgenic ones in perennial native grassland communities but could, under optimal climatic conditions, have potentially higher growth rates in grazed annual grasslands. These results demonstrate that changes to ecologically important demographic parameters can occur in plants containing transgenes that are not typically considered fitness enhancing, and that genotype by environment interactions and management regimes that impact on these parameters may influence the invasiveness of transgenic plants. Our study also demonstrates the utility of incorporating plant community gradient modelling into ecological risk assessment protocols designed for transgenic pasture plants.     

Small rodents as significant dispersers of tree seeds in a Neotropical forest

Abstract. Through seed dispersal and predation, terrestrial mammals should be an important component of the mechanisms that determine patterns of tree recruitment in tropical forests. Despite their great abundance and ubiquity in Neotropical forests, small rodents as seed predators and dispersers remain largely forgotten. To investigate the fates of seeds in a hunted primary forest in Belize, we tagged seeds of Astrocaryum mexicanum (Palmae), Ampelocera hottlei (Ulmaceae), and Pouteria sapota (Sapotaceae) and placed them into open plots, exclosures accessible only to small mammals, and exclosures accessible to medium-sized and small mammals. The exclosure experiments and fates of the seeds show that the spiny pocket mouse, Heteromys desmarestianus (Heteromyidae), was the dominant handler of seeds of the first two species and also removed a significant proportion of the very large-seeded Pouteria. Most of the seeds were killed immediately upon removal, but many of the seeds (3–18 %) of the first two species were scatterhoarded (dispersed and buried in the soil) by Heteromys. Some of the scatterhoarded seeds (29%) remain buried and therefore protected from predation by other animals. Agoutis (Dasyprocta punctata), a caviomorph rodent, buried 13 % of the seeds of Pouteria, and Heteromys consumed and dispersed but did not bury Pouteria seeds. Results of this study support predictions by some researchers that small rodents are dominant terrestrial granivores in Neotropical forests. The role of small rodents as seed dispersers, however, has never been fully appreciated.     

Anaesthesiological risk assessment in young/adult and elderly dental patients

Objective: Analysing the differences in number of diseases reported, medicines taken and American Society of Anaesthesiologists (ASA) scores in young/adult and elderly dental patients. Subject: Forty‐seven young/adult and 47 elderly dental patients living in the community. Setting: Private dental practice. Main outcome measures: Age, number of systemic diseases reported during anamnesis, number of medicines taken, seriousness of pre‐existent diseases measured according to the ASA (American Society of Anaesthesiologist) scale. Study design: Analytical study. Results: The differences between young/adult and elderly dental patients as far as self‐reported medical conditions, medicines taken and ASA scores were statistically significant (p < 0.001). Conclusion: The number of elderly patients’ medical conditions are greater than young/adults’. It is therefore necessary to adequately assess the elderly patient before starting any dental treatment.     

Cover crop mixtures including legume produce ecosystem services of nitrate capture and green manuring: assessment combining experimentation and modelling

Background and aims

During the fallow period, non-legume cover crop species can capture mineral nitrogen (N) and thus decrease nitrate leaching, whereas legume cover crop species can provide a green manuring service that increases N availability for the subsequent crop. The aim of our study was to investigate the ability of bispecific mixtures to simultaneously produce these two services of N management in relation to their interspecific interactions.

Methods

Three field experiments were conducted at contrasting sites from summer to autumn to evaluate 25 mixtures and 10 sole crops. We measured biomass, N acquisition, C:N ratio and soil mineral N. Ecosystem services were assessed using both experimental data and simulation model predictions.

Results

Overall, prediction of N mineralized from cover crop residues was significantly higher for mixtures than for non-legume sole crops. Predictions of nitrate leached after mixtures did not differ significantly from those after non-legume sole crops and remained significantly lower than those under bare soil, especially for mixtures with turnip rape which benefitted greatly from being in mixtures.

Conclusions

Some of the mixtures provided a choice of compromises between the two ecosystem services, which helps define solutions for adapting mixture choice according to the site’s soil and climate characteristics and to fallow period management.

     

Modelling ozone effects on adult beech trees through simulation of defence, damage, and repair costs: Implementation of the CASIROZ ozone model in the ANAFORE forest model

Ozone affects adult trees significantly, but effects on stem growth are hard to prove and difficult to correlate with the primary sites of ozone damage at the leaf level. To simulate ozone effects in a mechanistic way, at a level relevant to forest stand growth, we developed a simple ozone damage and repair model (CASIROZ model) that can be implemented into mechanistic photosynthesis and growth models. The model needs to be parameterized with cuvette measurements on net photosynthesis and dark respiration. As the CASIROZ ozone sub-model calculates effects of the ozone flux, a reliable representation of stomatal conductance and therefore ozone uptake is necessary to allow implementation of the ozone sub-model. In this case study the ozone sub-model was used in the ANAFORE forest model to simulate gas exchange, growth, and allocation. A preliminary run for adult beech (FAGUS SYLVATICA) under different ozone regimes at the Kranzberg forest site (Germany) was performed. The results indicate that the model is able to represent the measured effects of ozone adequately, and to distinguish between immediate and cumulative ozone effects. The results further help to understand ozone effects by distinguishing defence from damage and repair. Finally, the model can be used to extrapolate from the short-term results of the field study to long-term effects on tree growth. The preliminary simulations for the Kranzberg beech site show that, although ozone effects on yearly growth are variable and therefore insignificant when measured in the field, they could become significant at longer timescales (above 5 years, 5 % reduction in growth). The model offers a possible explanation for the discrepancy between the significant effects on photosynthesis (10 to 30 % reductions simulated), and the minor effects on growth. This appears to be the result of the strong competition and slow growth of the Kranzberg forest, and the importance of stored carbon for the adult beech (by buffering effects on carbon gain). We finally conclude that inclusion of ozone effects into current forest growth and yield models can be an important improvement into their overall performance, especially when simulating younger and less dense forests.     

Unaided dispersal risk of Magallana gigas into and around the UK: combining particle tracking modelling and environmental suitability scoring

Marine non-indigenous species are a significant threat to marine ecosystems with prevention of introduction and early detection considered to be the only effective management strategy. Knowledge of the unaided pathway has received relatively little attention, despite being integral to the implementation of robust monitoring and surveillance. Here, particle tracking modelling is combined with spatial analysis of environmental suitability, to highlight UK coastal areas at risk of introduction and spread of Magallana gigas by the unaided pathway. ‘Introduction into UK’ scenarios were based on spawning from the continental coast, Republic of Ireland, Channel Islands and Isle of Man and ‘spread within UK’ scenarios were based on spawning from known UK wild populations and aquaculture sites. Artificial structures were included as spawning sites in an introduction scenario. The UK coast was scored, based on parameters influencing larval settlement, to reflect environmental suitability. Risk maps were produced to highlight areas of the UK coast at elevated risk of introduction and spread of M. gigas by the unaided pathway. This study highlights that introduction of M. gigas into UK waters via the unaided pathway is possible, with offshore structures increasing the potential geographical extent of introduction. Further, there is potential for substantial secondary spread from aquaculture sites and wild populations in the UK. The results of the study are considered in the context of national M. gigas management, whilst the approach is contextualised more broadly as a tool to further understanding of a little-known, yet significant pathway.