Jan Gloser

Visualized photosynthetic characteristics of the lichen Xanthoria elegans related to daily courses of light, temperature and hydration: a field study from Galindez Island, maritime Antarctica.

Diurnal courses of photosystem II (PS II) activity of Xanthoria elegans were continuously monitored using a novel technique of chlorophyll fluorescence imaging in the field (maritime Antarctica) over a period of 7 days. The lichen specimens grew on stone surfaces in a North-facing coastal area of Galindez Island (Argentine Islands). A portable fluorometer FluorCam equipped with a CCD camera and image analysis software was placed over a thallus so that false color images of FV/FM and quantum yield of photochemical processes in PS II (śII) distribution over the thallus could be taken in the course of a day. Simultaneously, microclimatic parameters of the habitat were recorded: air and thallus temperature, relative air humidity, PAR (photosynthetically active radiation) and global radiation. Photosynthetic processes in X. elegans were activated by rainfall or water from melting snow. After thallus hydration, FV/FM and śII gradually decreased from their maximal values due to evaporation and progressive loss of water from the thallus. Chlorophyll fluorescence imaging showed that the thallus dehydration started from margins and moved towards central thicker thallus parts that exhibited higher activity of PS II than margins throughout a day. The rate of inhibition of photosynthetic processes in PS II was faster in marginal than in central thallus parts. Dependence of śII on thallus water potential (WP) was investigated during gradual dehydration under laboratory conditions. After decrease of WP form zero to ĄV7 MPa, X. elegans exhibited only 13.8 % decrease in śII from its maximal value. Within the range of WP of from ĄV8 to ĄV20 MPa, śII decrease was more rapid reaching critical point (śII = 0) at WP about ĄV25 MPa. Chlorophyll fluorescence imaging and WP measurements documented that X. elegans is capable to maintain detectable photosynthetic activity even at extremely low WP. Based on our microclimatological data, X. elegans may be photosynthetically active under field conditions for several hours after being wetted from rain or snowfall. It is suggested that chlorophyll fluorescence imaging is a powerfull technique, transferable to field conditions and capable to visualize heterogeneity of photosyntetic processes over a lichen thallus subjected to periodic dehydration.

Nitrogen and base cation uptake in seedlings of Acer pseudoplatanus and Calamagrostis villosa exposed to an acidified environment

The effects of solution acidity and form of nitrogen on net nutrient uptake rates in Acer pseudoplatanus and Calamagrostis villosa seedlings were examined as part of a complex ecological study. Uptake rates were measured by the depletion method under controlled conditions (temperature 20 °C, irradiance 400 μmol m−2 s−1 PAR) from a nutrient solution containing 1.5 mM nitrogen in the form of nitrate or ammonium or an equimolar mixture of both. The solution acidity was kept constant at pH 5.5 (control treatment), 4.5 or 3.5 (low pH treatments). Strongly acid pH decreased or stopped the uptake rates of NO3−, Mg2+ and Ca2+, but the uptake of NH4+ was not changed in both species. Ammonium ions reduced the uptake rate of NO3− in Acer but increased the uptake rate in Calamagrostis. Ammonium as the sole source of nitrogen had a strong negative impact on the uptake rates of calcium and magnesium and this effect was independent of the media acidification usually connected with NH4+ uptake and assimilation. However, the negative effect of ammonium ions on the base cation uptake was more pronounced at low pH values.

Heterogeneity of chlorophyll fluorescence over thalli of several foliose macrolichens exposed to adverse environmental factors: Interspecific differences as related to thallus hydration and high irradiance

Spatial heterogeneity of chlorophyll (Chl) fluorescence over thalli of three foliose lichen species was studied using Chl fluorescence imaging (CFI) and slow Chl fluorescence kinetics supplemented with quenching analysis. CFI values indicated species-specific differences in location of the most physiologically active zones within fully hydrated thalli: marginal thallus parts (Hypogymnia physodes), central part and close-to-umbilicus spots (Lasallia pustulata), and irregulary-distributed zones within thallus (Umbilicaria hirsuta). During gradual desiccation of lichen thalli, decrease in Chl fluorescence parameters (FO - minimum Chl fluorescence at point O, FP - maximum Chl fluorescence at P point, Φ2 - effective quantum yield of photochemical energy conversion in photosystem 2) was observed. Under severe desiccation (>85 % of water saturation deficit), substantial thalli parts lost their apparent physiological activity and the resting parts exhibited only a small Chl fluorescence. Distribution of these active patches was identical with the most active areas found under full hydration. Thus spatial heterogeneity of Chl fluorescence in foliose lichens may reflect location of growth zones (pseudomeristems) within thalli and adjacent newly produced biomass. When exposed to high irradiance, fully-hydrated thalli of L. pustulata and U. hirsuta showed either an increase or no change in FO, and a decrease in FP. Distribution of Chl fluorescence after the high irradiance treatment, however, remained the same as before the treatment. After 60 min of recovery in the dark, FO and FP did not recover to initial values, which may indicate that the lichen used underwent a photoinhibition. The CFI method is an effective tool in assessing spatial heterogeneity of physiological activity over lichen thalli exposed to a variety of environmental factors. It may be also used to select a representative area at a lichen thallus before application of single-spot fluorometric techniques in lichens.

Effects of Thallus Temperature and Hydration on Photosynthetic Parameters of Cetraria Islandica from Contrasting Habitats

Two methods of induced in vivo chlorophyll (Chl) fluorescence were used to investigate the effects of varying thallus temperature and hydration on the performance of photosynthetic apparatus of a foliar lichen Cetraria islandica: slow Chl fluorescence induction kinetic with the analysis of quenching mechanisms, and rapid irradiance response curves of photosynthesis derived from quantum yield of photochemical reactions of photosystem 2 (Φ2) recorded at increasing irradiances. We compared responses of photosynthetic apparatus in populations of C. islandica growing in lower altitude (LAP: 1 350 m a.s.l.) and in higher altitude (HAP: 2 000 m a.s.l.). At each altitude, the samples were collected both in fully irradiated sites (HI) and in shade (LI). Temperature optimum of photosynthetic processes was the same for LAP and HAP thalli of LI populations (18 °C), while it was significantly lower for HI HAP (14 °C). Gradual dehydration of fully hydrated thalli led to initial increase (up to 20 % of water saturation deficit, WSD) in FV/FM and Φ2, no change at 20–50 % WSD, and a dramatic decrease of the parameters within 50–80 % of WSD. LI HAP of C. islandica was the best adapted population to low temperature having higher rates of photochemical processes of photosynthesis than HI HAP within temperature range of −5 to +5 °C. The differences between populations were apparent also in Chl content and thallus morphology.

Changes in spectral reflectance of a foliar lichen Umbilicaria hirsuta during desiccation

Water potential (ψw) and water saturation deficit (WSD), and several reflectance (R) indexes were assessed in an aerophytic lichen Umbilicaria hirsuta (Sw. ex Westr.) Hoffm. The water index (WI, R900/R970) and normalized difference vegetation index, NDVI [(R900-R680)/(R900+R680)] were strongly correlated both with the ψw and the WSD of lichen thalli. No significant changes during desiccation were found in structural independent pigment index, SIPI [(R800-R445)/(R800-R680)]. Sensitivity of the spectral detection of water status was rather small at high hydration level (WSD < 25 %, or ψw > −1 MPa), but this is not much limiting its value and potential use, because physiological processes in lichens are usually inhibited at much lower values of ψw than in leaves of vascular plants.

Project Tocoen. The fate of selected organic compounds in the environment. The growth response of maize to increasing concentrations of fluoranthene

Abstract The influence of increasing concentration of fluoranthene (FLT) in the nutrient solution (10, 100 and 1000 μg l‐1) on the growth, the content of assimilation pigments and the rate of photosynthesis of maize plants was studied. Accumulation of FLT in individual leaves and other organs was also measured. As early as after 10 days of cultivation a significant inhibition of the root and shoot growth was found in plants at FLT concentrations of 100 and 1000 μg l ‐1. At 1000 μg l ‐1 significant drop of chlorophyll content a was registered. After 24 days of cultivation, in plants from all treatments a significant inhibition of root and shoot growth was observed and the concentration of photosynthetic pigments was also much lowered. Net photosynthetic rate was significantly inhibited in plants from FLT 100 and FLT 1000 treatments. The highest concentration of FLT was found in roots of the experimental plants from all treatments during the whole period of cultivation. Translocation of some amount of FLT i...

Regrowth dynamics of Calamagrostis epigejos after defoliation as affected by nitrogen availability.

Young plants of a rhizomatous grass Calamagrostis epigejos (L.) Roth were grown from seed in nutrient solutions containing nitrogen in concentrations 0.1, 1.0, and 10 mM. After six weeks of cultivation the plants were defoliated and changes in growth parameters and in content of storage compounds were measured in the course of regrowth under highly reduced nitrogen availability. Plants grown at higher nitrogen supply before defoliation had higher amount of all types of nitrogen storage compounds (nitrates, free amino acids, soluble proteins), which was beneficial for their regrowth rate, in spite of lower content of storage saccharides. Amino acids and soluble proteins from roots and stubble bases were the most important sources of storage compounds for regrowth of the shoot. Faster growth of plants with higher N content was mediated by greater leaf area expansion and greater number of leaves. In plants with lower contents of N compounds number of green leaves decreased after defoliation significantly and senescing leaves presumably served as N source for other growing organs. Results suggest that internal N reserves can support regrowth of plants after defoliation even under fluctuating external N availability. Faster regrowth of C. epigejos with more reserves was mediated mainly by changes in plant morphogenesis.

Growth rate and total nonstructural saccharides content in Alopecurus pratensis L.

Total nonstructural saccharides (TNS) content in young plant ofAlopecurus pratensis was always above 4% of dry matter even at several types of stress treatment (nitrogen deficiency, low irradiance). TNS content was in negative correlation with concentration of total nitrogen in all cases. Positive correlation was found between the TNS content in plants and relative increase in their root growth rate.

Changes in photosynthetic parameters of evolutionary different species of Triticum and Aegilops grown at high and low nitrogen availability.

Modern highly productive cultivars of hexaploid crop wheat (Triticum aestivum) developed from wild diploid and tetraploid wheat species and from two species of the genus Aegilops. Several attempts have been undertaken recently to explain the physiological background of differences in growth rate and yield among species representing certain stages of the evolution of crop wheat. It was soon recognized, that no simple relation could be defined between productivity and specific rate of net photosynthetic CO2 uptake (P) by leaves. Evans and Dunstone (1) reported surprising finding that maximum P in flag leaves of modern wheat cultivars is lower than in the wild progenitors. As found in some other studies, the decrease is usually connected with lower nitrogen content in leaves (2), lower rate of Hill reaction (3), and lower content of chlorophyll per leaf mass unit (4). However, the amount of Rubisco was not different among genotypes with different ploidity and its specific activity was found to be higher in hexaploid species (5). It was shown in several other experiments that the potential rate of electron transport reached highest value in tetraploid species (4), and that P may be in some cases considerably higher in hexaploid cultivars than in primitive diploid species. The contrasting results found in the literature could be caused, to some extent, by different cultivation conditions, including variation in nutrient supply. To test this hypothesis we have done our experiments at two levels of mineral nitrogen in substrate.

Photosynthetic Performance of Acer pseudoplatanus L. Seedlings as Affected by Light Availability and Source of Nitrogen

Effects of nitrogen (N) supply on photosynthetic parameters and plant sensitivity to photoinhibition has been studied mostly in plants grown at different N availability, e.g. Marques da Silva et Arrabaca (1). Among those studies, only limited number took into account plant response to different form of N: nitrate - NO3, ammonium - NH4. This is, however, of great importance because in field conditions the amount and form of available N varies dynamically. Different form of N combined with low pH of growth substrate leads to differences in uptake rates of N and other minerals, basic cations in particular; Gloser and Gloser (2). Those differences may lead to altered rate of protein synthesis in all plant parts, particularly the proteins located in thylakoid membranes of chloroplasts. Also the amount of Rubisco might be affected in this way. We hypothesized that those alternations may lead to changes in photosynthetic apparatus. In this study, we addressed two questions: (i) Is the effect of exclusive NO3/NH4 nutrition on photosynthetic parameters different in high light- compared to low light-cultivated plants?, (ii) Does form of N supplied to plants alter sensitivity to photoinhibition?