Search

Rising CO2 concentrations associated with drought stress is likely to influence not only aboveground growth, but also belowground plant processes. Little is known about root exudation being influenced by elements of climate change. Therefore, this study wanted to clarify whether barley root exudation responds to drought and CO2 enrichment and whether this reaction differs between an old and a recently released malting barley cultivar. Barley plants were grown in pots filled with sand in controlled climate chambers at ambient (380 ppm) or elevated (550 ppm) atmospheric [ CO2] and a normal or reduced water supply. Root exudation patterns were examined at the stem elongation growth stage and when the inflorescences emerged. At both dates, root exudates were analyzed for different compounds such as total free amino acids, proline, potassium, and some phytohormones. Elevated [ CO2] decreased the concentrations in root exudates of some compounds such as total free amino acids, proline, and abscisic acid. Moreover, reduced water supply increased proline, potassium, electric conductivity, and hormone concentrations. In general, the modern cultivar showed higher concentrations of proline and abscisic acid than the old one, but the cultivars responded differentially under elevated CO2. Plant developmental stage had also an impact on the root exudation patterns of barley. Generally, we observed significant effects of CO2 enrichment, watering levels, and, to a lesser extent, cultivar on root exudation. However, we did not find any mitigation of the adverse effects of drought by elevated CO2. Understanding the multitude of relationships within the rhizosphere is an important aspect that has to be taken into consideration in the context of crop performance and carbon balance under conditions of climate change. [ABSTRACT FROM AUTHOR]

In general, yield and fruit quality strongly rely on efficient nutrient remobilization during plant development and senescence. Transcriptome changes associated with senescence in spring oilseed rape grown under optimal nitrogen supply or mild nitrogen deficiency revealed differences in senescence and nutrient mobilization in old lower canopy leaves and younger higher canopy leaves. Having a closer look at this transcriptome analyses, we identified the major classes of seed storage proteins (SSP) to be expressed in vegetative tissue, namely leaf and stem tissue. Expression of SSPs was not only dependent on the nitrogen supply but transcripts appeared to correlate with intracellular H2O2 contents, which functions as well-known signaling molecule in developmental senescence. The abundance of SSPs in leaf material transiently progressed from the oldest leaves to the youngest. Moreover, stems also exhibited short-term production of SSPs, which hints at an interim storage function. In order to decipher whether hydrogen peroxide also functions as a signaling molecule in nitrogen deficiency-induced senescence, we analyzed hydrogen peroxide contents after complete nitrogen depletion in oilseed rape and Arabidopsis plants. In both cases, hydrogen peroxide contents were lower in nitrogen deficient plants, indicating that at least parts of the developmental senescence program appear to be suppressed under nitrogen deficiency. [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]