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Background and aims: Given that environmental factors like atmospheric CO2, temperature, and water availability will likely change simultaneously, it is difficult to make accurate predictions about future crop production. Effects of elevated CO2 or drought on aboveground plant growth are relatively well studied, while effects on the rhizosphere are rarely dealt with. The present work investigates the root exudation pattern of different osmotic protectants such as ions and sugars of two cultivars of barley grown under different water and CO2 levels. Methods: Barley (Hordeum vulgare L.) plants were grown in plant containers in climate chambers with an optimal and reduced water supply and two CO2 concentrations (380 and 550 ppm) and harvested at the stem elongation growth stage and when the inflorescences emerged. Results: The responses of root exudation to CO2 enrichment, watering level, and cultivar and their interactions varied with the developmental stage. While K+/Na+ ratio in root exudates remained stable at the stem elongation stage (DC30), it was higher at the booting stage (DC49) in the cv. "Bambina" than in cv. "Golden Promise". At DC30, in general the exudation of sugars, dissolved organic carbon (DOC) and their ratio (SUG/DOC) were lower at e[CO2] compared to ambient CO2 at normal watering conditions. Under reduced watering conditions, plants exuded on average 55% more sucrose than under well-watered conditions. The modern cv. BA exuded on average 53% more fructose than the older cv.GP. In contrast, at DC49, sucrose, DOC and SUG/DOC exudation were not affected by any factor. At e[CO2] plants exuded on average 39% less fructose than under ambient CO2. A water and CO2 interaction on glucose exudation was found at this stage. Under reduced water conditions, plants growing at ambient CO2 exuded less glucose but at e[CO2] exuded similar (GP) or even higher (BA) glucose levels than under normal water supply. Although drought and cultivar factors affected the root exudation of barley, the strongest effects in the exudation pattern were caused by CO2. Conclusions: This study presents a non-destructive percolation method for the collection of root exudates which can be used to give an insight into the complex interaction between global warming-associated environmental factors that cause yield losses and changes in crop quality and components of the belowground plant metabolism. [ABSTRACT FROM AUTHOR]

Background and aims: Given that environmental factors like atmospheric CO2, temperature, and water availability will likely change simultaneously, it is difficult to make accurate predictions about future crop production. Effects of elevated CO2 or drought on aboveground plant growth are relatively well studied, while effects on the rhizosphere are rarely dealt with. The present work investigates the root exudation pattern of different osmotic protectants such as ions and sugars of two cultivars of barley grown under different water and CO2 levels. Methods: Barley (Hordeum vulgare L.) plants were grown in plant containers in climate chambers with an optimal and reduced water supply and two CO2 concentrations (380 and 550 ppm) and harvested at the stem elongation growth stage and when the inflorescences emerged. Results: The responses of root exudation to CO2 enrichment, watering level, and cultivar and their interactions varied with the developmental stage. While K+/Na+ ratio in root exudates remained stable at the stem elongation stage (DC30), it was higher at the booting stage (DC49) in the cv. "Bambina" than in cv. "Golden Promise". At DC30, in general the exudation of sugars, dissolved organic carbon (DOC) and their ratio (SUG/DOC) were lower at e[CO2] compared to ambient CO2 at normal watering conditions. Under reduced watering conditions, plants exuded on average 55% more sucrose than under well-watered conditions. The modern cv. BA exuded on average 53% more fructose than the older cv.GP. In contrast, at DC49, sucrose, DOC and SUG/DOC exudation were not affected by any factor. At e[CO2] plants exuded on average 39% less fructose than under ambient CO2. A water and CO2 interaction on glucose exudation was found at this stage. Under reduced water conditions, plants growing at ambient CO2 exuded less glucose but at e[CO2] exuded similar (GP) or even higher (BA) glucose levels than under normal water supply. Although drought and cultivar factors affected the root exudation of barley, the strongest effects in the exudation pattern were caused by CO2. Conclusions: This study presents a non-destructive percolation method for the collection of root exudates which can be used to give an insight into the complex interaction between global warming-associated environmental factors that cause yield losses and changes in crop quality and components of the belowground plant metabolism. [ABSTRACT FROM AUTHOR]

Two North American tall perennials, Sida hermaphrodita L. Rusby and Silphium perfoliatum L. have been recognized in Europe as high-yielding novel bioenergy species. While the latter is recommended for biogas production in Germany, the ligno-cellulosic stems of S. hermaphrodita are widely used as a solid fuel in Poland. Since information on the adaptation of the species to drought and heat and interactions with the CO 2 fertilization effect were lacking, growth chamber experiments were performed with seed-grown and established plants. A full factorial combination of two temperatures, two water levels and two CO 2 levels was applied using the long-term seasonal climate of southwestern Germany as a reference. Non-destructive parameters (length, phenology and senescence) and five harvests served to identify treatment effects on growth and allocation patterns. Shoot material was subjected to chemical and bioenergetic analyses (methane production and energy contents) and NIR-spectroscopy. While seedlings showed stronger growth responses to the treatments than established plants, interspecific differences of the responses were mostly related to allocation patterns and senescence. S. perfoliatum , which has a greater proportion of leaf mass was able to profit from CO 2 fertilization even under dry conditions, while in S. hermaphrodita such effects were absent. Chemical quality (crude protein, ash, fat and fibre) was mainly affected by the reduced water supply and energetic values in S. hermaphrodita and specific methane yields of S. perfoliatum tended to be lower. NIR spectra showed a good representation of percentage leaf mass, which in both species determines the quality of the shoot. [ABSTRACT FROM AUTHOR]

Elevated atmospheric carbon dioxide concentrations ([CO]) might change the abundance and the function of soil microorganisms in the depth profile of agricultural soils by plant-mediated reactions. The seasonal pattern of abundance and activity of nitrate-reducing bacteria was studied in a Mini-FACE experiment planted with oilseed rape ( Brassica napus). Three depths (0-10, 10-20 and 20-30 cm) were sampled. Analyses of the abundances of total (16S rRNA gene) and nitrate-reducing bacteria ( narG, napA) revealed strong influences of sampling date and depth, but no [CO] effects. Abundance and activity of nitrate reducers were higher in the top soil layer and decreased with depth but were not related to extractable amounts of nitrogen and carbon in soil. Dry periods reduced abundances of total and nitrate-reducing bacteria, whereas the potential activity of the nitrate reductase enzyme was not affected. Enzyme activity was only weakly correlated to the abundance of nitrate-reducing bacteria but was related to NH and NO concentrations. Our results suggest that in contrast to the observed pronounced seasonal changes, the elevation of atmospheric [CO] has only a marginal impact on nitrate reducers in the investigated arable ecosystem. [ABSTRACT FROM AUTHOR]

Future atmospheric CO [sub 2] concentrations are predicted to increase, and directly affect host plant phenology, which, in turn, is assumed to mediate the performance of herbivorous insects indirectly as well as the abundance and epidemiology of plant diseases. In a 4-year field experiment, spring wheat (Triticum aestivum L. cv. Triso) and spring oilseed rape (Brassica napus L. cv. Campino) were grown using a mini- free-air CO [sub 2] enrichment (FACE) system, which consisted of a control (CON), an ambient treatment (AMB) and FACE treatments. The CON and AMB treatments did not receive additional CO [sub 2], whereas the FACE plots were moderately elevated by 150 μL L-1 CO [sub 2]. The impact of elevated CO [sub 2] was examined with regard to plant phenology, biomass, leaf nitrogen and carbon, abundance of insect pest species and their relative population growth by either direct counts or yellow sticky traps. Occurrence and damage of plants by pathogens on spring wheat and oilseed rape were directly assessed. Disease infestations on plants were not significantly different between ambient and elevated CO [sub 2] in any of the years. Plant phenology, aboveground biomass, foliar nitrogen and carbon concentrations were also not significantly affected by CO [sub 2] enrichment. In contrast, the abundance of some species of insects was significantly influenced by elevated CO [sub 2], showing either an increase or a decrease in infestation intensity. Future atmospheric carbon dioxide levels are likely to double in concentration, affecting agricultural crops, herbivorous insects and the possible progression of various plant diseases. The abundance of insects significantly changed under elevated CO [sub 2] in our study, whereas plant characteristics (phenology, aboveground biomass, foliar nitrogen and carbon contents) and development of fungal plant pathogens did not. [ABSTRACT FROM AUTHOR]