Roeland Samson

Chlorophyll fluorescence performance of sweet almond [Prunus dulcis (Miller) D. Webb] in response to salinity stress induced by NaCl

One-year old sweet almond (Prunus dulcis) seedlings were submitted to four levels of salt stress induced by NaCl, namely 0.3, 0.5, 0.7, and 1.0 S m−1. Effects of salt stress on a range of chlorophyll (Chl) fluorescence parameters (Chl FPs) and Chl contents were investigated in order to establish an eco-physiological characterization of P. dulcis to salinity. Salt stress promoted an increase in F0, Fs, and F0/Fm and a decrease in Fm, F′m, Fv/Fm, qP, ΔF/F′m, Fv/F0, and UQF(rel), in almost all Chl fluorescence yields (FY) and FPs due to its adverse effect on activity of photosystem 2. No significant changes were observed for quenchings qN, NPQ, and qN(rel). The contents of Chl a and b and their ratio were also significantly reduced at increased salt stress. In general, adverse salinity effects became significant when the electric conductivity of the nutrient solution (ECn) exceeded 0.3 S m−1. The most sensitive salt stress indicators were Fv/F0 and Chl a content, and they are thus best used for early salt detection in P. dulcis. Monitoring of a simple Chl FY, such as F0, also gave a good indication of induced salt stress due to the significant correlations observed between the different Chl FYs and FPs. Even essential Chl FYs, like F0, Fm, F′m, and Fs, and mutually independent Chl FPs, like Fv/F0 and qP, were strongly correlated with each other.

Soil‐solution speciation of CD as affected by soil characteristics in unpolluted and polluted soils

Total metal content by itself is insufficient as a measure to indicate actual environmental risk. Understanding the mobility of heavy metals in the soil and their speciation in the soil solution is of great importance for accurately assessing environmental risks posed by these metals. In a first explorative study, the effects of general soil characteristics on Cd mobility were evaluated and expressed in the form of empirical formulations. The most important factors influencing mobility of Cd proved to be pH and total soil content. This may indicate that current legislation expressing the requirement for soil sanitation in Flanders (Belgium) as a function of total soil content, organic matter, and clay does not successfully reflect actual risks. Current legal frameworks focusing on total content, therefore, should be amended with criteria that are indicative of metal mobility and availability and are based on physicochemical soil properties. In addition, soil-solution speciation was performed using two independent software packages (Visual Minteq 2.23 and Windermere Humic Aqueous model VI [WHAM VI]). Both programs largely were in agreement in concern to Cd speciation in all 29 soils under study. Depending on soil type, free ion and the organically complexed forms were the most abundant species. Additional inorganic soluble species were sulfates and chlorides. Minor species in solution were in the form of nitrates, hydroxides, and carbonates, the relative importance of which was deemed insignificant in comparison to the four major species.

Effects of drought stress induced by polyethylene glycol on pigment content and photosynthetic gas exchange of Pistacia khinjuk and P-mutica.

The effects of drought stress induced by polyethylene glycol, PEG (molecular mass 6000) on some ecophysiological characteristics of two wild pistachio species, Mastic and Khinjuk (P. mutica and P. khinjuk) selected as root stocks for production of edible pistachio trees (P. vera) in Iran and Turkey, were studied. Net photosynthetic rate (PN), stomatal conductance (gs), chlorophyll (Chl) fluorescence parameters, leaf water potential (Ψ1), leaf osmotic potential (Ψπ), leaf osmotic adjustment (ΔΨπ), and Chl a and b were measured. All parameters were influenced by increase in concentra-tion of PEG in the nutrient solutions. PN, gs, and Chl a were significantly higher in P. mutica than in P. khinjuk but, compared to the control treatment, P. khinjuk showed a higher resistance to drought stress than P. mutica.

Effects of Osmotic Drought Stress Induced by a Combination of NaCl and Polyethylene Glycol on Leaf Water Status, Photosynthetic Gas Exchange, and Water Use Efficiency of Pistacia khinjuk and P. mutica

Leaf water potential, leaf osmotic potential, chlorophyll a and b contents, stomatal conductance, net photosynthetic rate, and water use efficiency were determined in two pistachio species (Pistacia khinjuk L. and P. mutica L.) grown under osmotic drought stress induced by a combination of NaCl and polyethylene glycol 6000. A decrease in values for all mentioned variables was observed as the osmotic potential of the nutrient solution (Ψs) decreased. The osmotic adjustment (ΔΨπ) of the species increased by decreasing Ψs. Thus P. khinjuk had a higher osmotic drought stress tolerance than P. mutica.

The potential of biomonitoring of air quality using leaf characteristics of white willow (Salix alba L.).

In this study, we assess the potential of white willow (Salix alba L.) as bioindicator for monitoring of air quality. Therefore, shoot biomass, specific leaf area, stomatal density, stomatal pore surface, and stomatal resistance were assessed from leaves of stem cuttings. The stem cuttings were introduced in two regions in Belgium with a relatively high and a relatively low level of air pollution, i.e., Antwerp city and Zoersel, respectively. In each of these regions, nine sampling points were selected. At each sampling point, three stem cuttings of white willow were planted in potting soil. Shoot biomass and specific leaf area were not significantly different between Antwerp city and Zoersel. Microclimatic differences between the sampling points may have been more important to plant growth than differences in air quality. However, stomatal pore surface and stomatal resistance of white willow were significantly different between Zoersel and Antwerp city. Stomatal pore surface was 20% lower in Antwerp city due to a significant reduction in both stomatal length (−11%) and stomatal width (−14%). Stomatal resistance at the adaxial leaf surface was 17% higher in Antwerp city because of the reduction in stomatal pore surface. Based on these results, we conclude that stomatal characteristics of white willow are potentially useful indicators for air quality.

Scaling the spatial distribution of photosynthesis from leaf to canopy in a plant growth chamber

Abstract The aim of this study was to quantify the spatial distribution of the net photosynthesis of a multi-layer crop. A multi-layer model (FORUG) was used to simulate the crop photosynthesis of tomato ( Lycopersicon esculentum Mill.) in the three-dimensional space inside a plant growth chamber. The model inputs were, on the one hand photosynthetic characteristics (maximal photosynthetic rate, quantum efficiency and respiration rate) determined at leaf level, and the microclimatic data on the other hand. Scaling-up to the level of the crop was done, taking into account the spatial distribution of leaf area index (LAI), leaf angle (or extinction coefficient), air temperature and photosynthetically active radiation (PAR). The simulated output was the net carbon exchange at a specific time step or the cumulative net carbon exchange over a specific period of time. Inside the test chamber spatial temperature differences ranged from 22.4 up to 32.9xa0°C at an inlet temperature of 22xa0°C and the lights on. Light intensity decreased gradually within the crop, resulting in very low light intensities at the bottom layers of the climate chamber. This resulted in the observation that the respiration rate was not compensated at low light intensities. The simulated photosynthesis of the 32 ‘cells’ of the test chamber ranged from −1.12 up to 5.94 μmol CO 2 m −2 s −1 . From a sensitivity analysis of the model at low (20% of maximum) and high (80% of maximum) light intensities, it was concluded that the spatial distribution of light, air temperature and LAI should be well known, just as the parameters describing the light response of the photosynthesis process. Moreover, this spatial distribution should be accurately taken into account.

Sap flow dynamics of a beech tree during the solar eclipse of 11 August 1999

Abstract During the solar eclipse of 11 August 1999, measurements of sap flow at branch and stem level were made in a 75-year-old beech tree which was 27xa0m high growing near Ghent, Belgium. The sky was relatively free from clouds during the eclipse which reached its maximum at 10.26xa0h GMT (=10.36xa0h True Solar Time). Measurements also included short-wave radiation, air temperature and vapour pressure deficit. The daily variation of the sap flows and of short-wave radiation and vapour pressure deficit were compared to a reference based on mean diurnal cycles. During the eclipse short-wave radiation, air temperature and vapour pressure deficit showed a maximum reduction between the pre-eclipse maximum and the following minimum of respectively 439xa0W/m 2 , 3.0xa0°C and 0.27xa0kPa. The reduction of the solar energy resulted in the formation of a temporary temperature inversion above the canopy. At the time of maximum eclipse the sap flow rates at branch level and at stem level were reduced by 92 and 76%, respectively, indicating non-stationary flow conditions in the beech tree. Due to the eclipse, the tree reduced its water loss from transpiration by 32.0xa0kg of water, being about 25% of the total amount which is transpired by the beech tree during a sunny day in August. Regression analysis indicated that both short-wave radiation and vapour pressure deficit changed in a nearly linear fashion during the eclipse. Sap flow rates were given by an exponential equation, allowing the description of sap flow dynamics in terms of time lag and rate of change.

MORPHOLOGICAL AND PHYSIOLOGICAL INDICATORS OF TOLERANCE TO ATMOSPHERIC STRESS IN TWO SENSITIVE AND TWO TOLERANT TEA CLONES IN SOUTH AFRICA

Tea ( Camellia sinensis ) clones (PC113 and SFS204) sensitive to very dry air and clones (PC114 and SFS150) that are tolerant, were studied at two tea estates (Tshivhase and Grenshoek) in the Northern Province of the Republic of South Africa. Among the morphological leaf traits studied, stomatal density, pore diameter and pore depth were not linked consistently to stress tolerance. Cuticle thickness was not a good indicator of stress tolerance because genetic differences between clones were confounded by the clonal response of wax production to stress. In contrast, measured leaf conductance to water vapour transport was larger and leaf water potential was lower in sensitive clones, but only with more severe atmospheric stress (Grenshoek). Also the ratio of the calculated maximum stomatal conductance in old and young leaves was higher in sensitive clones, suggesting that the loss of a larger fraction of the total stem flow by old leaves enhanced the stress experienced by the young leaves. However, this indicator was valid only under the more stressful microclimate of Grenshoek. The results indicate that even promising criteria for stress tolerance should be tested by exposure to stress during selection.

Biomagnetic monitoring of atmospheric pollution: a review of magnetic signatures from biological sensors

Biomagnetic monitoring of atmospheric pollution is a growing application in the field of environmental magnetism. Particulate matter (PM) in atmospheric pollution contains readily measurable concentrations of magnetic minerals. Biological surfaces, exposed to atmospheric pollution, accumulate magnetic particles over time, providing a record of location-specific, time-integrated air quality information. This review summarizes current knowledge of biological material (sensors) used for biomagnetic monitoring purposes. Our work addresses the following: the range of magnetic properties reported for lichens, mosses, leaves, bark, trunk wood, insects, crustaceans, mammal and human tissues; their associations with atmospheric pollutant species (PM, NOx, trace elements, PAHs); the pros and cons of biomagnetic monitoring of atmospheric pollution; current challenges for large-scale implementation of biomagnetic monitoring; and future perspectives. A summary table is presented, with the aim of aiding researchers and policy makers in selecting the most suitable biological sensor for their intended biomagnetic monitoring purpose.

POSSIBILITIES FOR ECOHYDROLOGICAL MONITORING IN NATURAL AND MANAGED ECOSYSTEMS IN SOUTHERN CHILE

La ecohidrologia se enfoca sobre las vinculaciones entre las plantas y el ambiente abiotico a partir del ciclo hidrologico. Como estas interacciones mutuas son importantes en muchos ecosistemas, la ecohidrologia tiene una amplia aplicacion. Un aspecto importante de la investigacion en ecohidrologia es la evaluacion y prediccion de la presencia de especies vegetales o tipos vegetacionales en relacion con la hidrologia o condiciones hidrogeoquimicas del habitat. Para ello, diversos modelos han sido publicados (por ejemplo, DEMNAT, ICHORS, ITORS, ITORS-VL). Todos estos modelos necesitan datos. Consecuentemente una red de monitoreo se tiene que instalar en adicion a las bases de datos existentes. Estas redes incluyen el monitoreo de propiedades importantes de los ecosistemas tales como: profundidad de la zona saturada, conductividad electrica del agua subterranea, contenido del agua del suelo, caracteristicas quimicas del agua del suelo (pH, concentraciones ionicas y nutrientes) y composicion de la vegetacion. El modelo ITORS-VL ha sido probado satisfactoriamente para predecir la ocurrencia de comunidades de plantas en los ecosistemas pantanosos de Flanders monitoring and modelling: Peters, J. et al. (Belgica), usando regresiones basadas en variables ambientales que van desde variables hidrologicas como profundidad de la zona saturada a variables quimicas que caracterizan el agua del suelo via concentracion de nitratos y conductividad electrica. Sin embargo, debido a su naturaleza empirica para un ecosistema especifico, este modelo podria no ser adecuado para los ecosistemas en Chile. El presente trabajo investiga la posibilidad de implementar un monitoreo y modelamiento en diferentes ecosistemas del sur de Chile. Los beneficios de esta actividad son variados: (i) una comprension holistica del funcionamiento del ecosistema, (ii) la habilidad para determinar la importancia relativa de las caracteristicas del sitio en varios ecosistemas, y (iii) la posibilidad de predecir estados sucesionales de la vegetacion bajo condiciones ambientales variables. Estos beneficios presentan potenciales roles en la capacidad de gestion, restauracion de ecosistemas y evaluacion del riesgo o impacto ambiental