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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]

Current atmospheric CO 2 levels are unprecedented for the last 800,000 years and require assessments of their potential effects. Free Air Carbon dioxide Enrichment (FACE) is regarded as the most appropriate exposure system for experimental field investigations. While the early FACE technology involved fans for pre-dilution of CO 2 , now systems both with fans and without fans operating with pure CO 2 are employed. The most often used construction in FACE technology involves peripheral injection from a circular or octagonal plenum with CO 2 release pipes and jet holes surrounding the experimental plot which can create [CO 2 ] gradients across the plot. Here, we present a new FACE design for short vegetation (crops and grassland) that does not involve peripheral injection but distributes CO 2 directly within the plot canopy. The system involves numerous CO 2 release holes in porous tubes that hang down from the upper canopy surface and stretch into the canopy. They can be adjusted in height according to crop growth. Plot size was 2 m × 2 m which allows for a high number of replicates at low CO 2 consumption costs (6.5 tons CO 2 in one season at five replicate plots = 3.5 kg CO 2 per m 2 usable plot area and day during 24hr operation). System performance in terms of CO 2 control was very good both in time and space, with 93% of all instantaneous readings during daylight hours matching ±20% deviation from the set point, and low variation of [CO 2 ] at a given moment within the exposed canopy. Some shading (c. 4% at full canopy development) resulted from the FACE structure at the plots but hardly any other microclimatic artifacts were observed. The FACE system is of modular construction and highly flexible and adaptable to various types of short vegetation. [ABSTRACT FROM AUTHOR]