Conversion and conservation of light energy in a photosynthetic microbial mat ecosystem

Here we present, to the best of our knowledge, the first balanced light energy budget for a benthic microbial mat ecosystem, and show how the budget and the spatial distribution of the local photosynthetic efficiencies within the euphotic zone depend on the absorbed irradiance (Jabs). Our approach uses microscale measurements of the rates of heat dissipation, gross photosynthesis and light absorption in the system, and a model describing light propagation and conversion in a scattering-absorbing medium. The energy budget was dominated by heat dissipation on the expense of photosynthesis: in light-limiting conditions, 95.5% of the absorbed light energy dissipated as heat and 4.5% was channeled into photosynthesis. This energy disproportionation changed in favor of heat dissipation at increasing irradiance, with >99% of the absorbed light energy being dissipated as heat and 700 μmol photon m-2 s -1 (>150 J m-2 s-1). Maximum photosynthetic efficiencies varied with depth in the euphotic zone between 0.014-0.047 O 2 per photon. Owing to steep light gradients, photosynthetic efficiencies varied differently with increasing irradiances at different depths in the euphotic zone; for example, at Jabs >700 μmol photon m-2 s-1, they reached around 10% of the maximum values at depths 0-0.3 mm and progressively increased toward 100% below 0.3 mm. This study provides the base for addressing, in much more detail, the photobiology of densely populated photosynthetic systems with intense absorption and scattering. Furthermore, our analysis has promising applications in other areas of photosynthesis research, such as plant biology and biotechnology. © 2010 International Society for Microbial Ecology All rights reserved

Seasonal, diurnal and vertical variation of chlorophyll fluorescence on **Phyllostachys humilis** in Ireland

In recent years, temperate bamboo species have been introduced in Europe not only as an ornamental plant, but also as a new biomass crop. To measure adaptation stress of bamboo to the climate of Western Europe, chlorophyll fluorescence was measured on a diurnal and seasonal basis in Ballyboughal, Co. Dublin, Ireland. Measurements were attained on the leaves of each node of Phyllostachys humilis. The most frequently used parameter in chlorophyll fluorescence is the photosynthetic efficiency (Fv/Fm). A seasonal dip - as well as a larger variation - of Fv/Fm in spring compared to the rest of the year was observed. Over the year, the upper leaves of the plant perform better than the bottom leaves. These findings were linked to environmental factors such as light intensity, air temperature and precipitation, as increased light intensities, decreasing air temperatures and their interactions, also with precipitation levels have an effect on the photosynthetic efficiency (Fv/Fm) in these plants

Arctic Micromonas uses protein pools and non-photochemical quenching to cope with temperature restrictions on Photosystem II protein turnover

Micromonas strains of small prasinophyte green algae are found throughout the world’s oceans, exploiting widely different niches. We grew arctic and temperate strains of Micromonas and compared their susceptibilities to photoinactivation of Photosystem II, their counteracting Photosystem II repair capacities, their Photosystem II content, and their induction and relaxation of non-photochemical quenching. In the arctic strain Micromonas NCMA 2099, the cellular content of active Photosystem II represents only about 50 % of total Photosystem II protein, as a slow rate constant for clearance of PsbA protein limits instantaneous repair. In contrast, the temperate strain NCMA 1646 shows a faster clearance of PsbA protein which allows it to maintain active Photosystem II content equivalent to total Photosystem II protein. Under growth at 2 °C, the arctic Micromonas maintains a constitutive induction of xanthophyll deepoxidation, shown by second-derivative whole-cell spectra, which supports strong induction of non-photochemical quenching under low to moderate light, even if xanthophyll cycling is blocked. This non-photochemical quenching, however, relaxes during subsequent darkness with kinetics nearly comparable to the temperate Micromonas NCMA 1646, thereby limiting the opportunity cost of sustained downregulation of PSII function after a decrease in light

Role of Mineral Nutrients in Plant Growth Under Extreme Temperatures

Food productivity is decreasing with the drastic increase in population, while it is expected that the global population will be nine to ten billion in 2050. Growth, production, and development on whole plant, cell, and subcellular levels are extremely affected by environmental factors particularly with the extreme temperature events (high- or low-temperature stress). Increase in the fluidity of lipid membrane, protein accumulation, and denaturation are the direct effects of high temperature on a plant. Membrane integrity loss, protein deprivation, protein synthesis inhabitation, and inactivation of mitochondrial and chloroplast enzymes are the indirect effects of high temperature. Similarly, the oval abortion, alteration of the pollen tube, reduction in fruit set, pollen sterility, and flower abscission are the consequences of low temperature at the time of product development, which in turn lowers the yield. The judicious nutrient management is essential for improving the plant nutrition status to mitigate the drastic effects of temperature stress as well as for sustainable plant yield under extreme temperature events, because nutrient deficiency results in growth and development problems in 60% cultivars worldwide. Additionally, effective nutrient management increases the temperature stress tolerance in plants. Therefore, the appropriate nutrient application rates and timings are imperative for alleviating the heat stress in plants and can serve as an effective and decent strategy. To minimize the contrasting effects of the environmental stresses, particularly heat stress, several examples of the supplemental applications of N, P, K, Ca, Mg, Se, and Zn are given in detail in this study, to observe how these nutrients reduce the effects of temperature stress in plants. This study concluded that judicious nutrient management minimizes the heat stress and increases the growth and yield of plants