Effects of Elevated CO2 and N Addition on Growth and N2 Fixation of a Legume Subshrub (Caragana microphylla Lam.) in Temperate Grassland in China

It is well demonstrated that the responses of plants to elevated atmospheric CO2 concentration are species-specific and dependent on environmental conditions. We investigated the responses of a subshrub legume species, Caragana microphylla Lam., to elevated CO2 and nitrogen (N) addition using open-top chambers in a semiarid temperate grassland in northern China for three years. Measured variables include leaf photosynthetic rate, shoot biomass, root biomass, symbiotic nitrogenase activity, and leaf N content. Symbiotic nitrogenase activity was determined by the C2H2 reduction method. Elevated CO2 enhanced photosynthesis and shoot biomass by 83% and 25%, respectively, and the enhancement of shoot biomass was significant only at a high N concentration. In addition, the photosynthetic capacity of C. microphylla did not show down-regulation under elevated CO2. Elevated CO2 had no significant effect on root biomass, symbiotic nitrogenase activity and leaf N content. Under elevated CO2, N addition stimulated photosynthesis and shoot biomass. By contrast, N addition strongly inhibited symbiotic nitrogenase activity and slightly increased leaf N content of C. microphylla under both CO2 levels, and had no significant effect on root biomass. The effect of elevated CO2 and N addition on C. microphylla did not show interannual variation, except for the effect of N addition on leaf N content. These results indicate that shoot growth of C. microphylla is more sensitive to elevated CO2 than is root growth. The stimulation of shoot growth of C. microphylla under elevated CO2 or N addition is not associated with changes in N2-fixation. Additionally, elevated CO2 and N addition interacted to affect shoot growth of C. microphylla with a stimulatory effect occurring only under combination of these two factors

Combining EEG, MIDI, and motion capture techniques for investigating musical performance

This article describes a setup for the simultaneous recording of electrophysiological data (EEG), musical data (MIDI), and three-dimensional movement data. Previously, each of these three different kinds of measurements, conducted sequentially, has been proven to provide important information about different aspects of music performance as an example of a demanding multisensory motor skill. With the method described here, it is possible to record brain-related activity and movement data simultaneously, with accurate timing resolution and at relatively low costs. EEG and MIDI data were synchronized with a modified version of the FTAP software, sending synchronization signals to the EEG recording device simultaneously with keypress events. Similarly, a motion capture system sent synchronization signals simultaneously with each recorded frame. The setup can be used for studies investigating cognitive and motor processes during music performance and music-like tasks—for example, in the domains of motor control, learning, music therapy, or musical emotions. Thus, this setup offers a promising possibility of a more behaviorally driven analysis of brain activity

Does GABA increase the efficiency of symbiotic N2 fixation in legumes?

The ability to regulate the rates of metabolic processes in response to changes in the internal and/or external environment is a fundamental feature which is inherent in all organisms. This adaptability is necessary for conserving the stability of the intercellular environment (homeostasis) which is essential for maintaining an efficient functional state in the organism. Symbiotic nitrogen fixation in legumes is an important process which establishes from the complex interaction between the host plant and microorganism. This process is widely believed to be regulated by the host plant nitrogen demand through a whole plant N feedback mechanism in particular under unfavorable conditions. This mechanism is probably triggered by the impact of shoot-borne, phloem-delivered substances. The precise mechanism of the potential signal is under debate, however, the whole phenomenon is probably related to a constant amino acid cycling within the plant, thereby signaling the shoot nitrogen status. Recent work indicating that there may be a flow of nitrogen to bacteroids is discussed in light of hypothesis that such a flow may be important to nodule function. Large amount of γ-aminobutyric acid (GABA) are cycled through the root nodules of the symbiotic plants. In this paper some recent evidence concerning the possible role of GABA in whole-plant-based upregulation of symbiotic nitrogen fixation will be reviewed

Photosynthetic down-regulation in N2-fixing alfalfa under elevated CO2 alters rubisco content and decreases nodule metabolism via nitrogenase and tricarboxylic acid cycle

International audienceAlthough responsiveness of N-2-fixing plants to elevated CO2 conditions have been analyzed in previous studies, important uncertainties remain in relation to the effect enhanced CO2 in nodule proteomic profile and its implication in leaf responsiveness. The aim of our study was to deepen our understanding of the relationship between leaf and nodule metabolism of N-2-fixing alfalfa plants after long-term exposure to elevated CO2. After 30-day exposure to elevated CO2, plants showed photosynthetic down-regulation with reductions in the light-saturated rate of CO2 assimilation (A (sat)) and the maximum rate of rubisco carboxylation (Vc(max)). Under elevated CO2 conditions, the rubisco availability limited potential photosynthesis by around 12 %, which represented the majority of the observed fall in Vc(max). Photosynthetic down-regulation has been associated with decreased N availability even if those plants are capable to assimilate N-2. Diminishment in shoot N demand (as reflected by the lower rubisco and leaf N content) suggests that the lower aboveground N requirements affected negatively nodule performance. In this condition, specific nodule activity was reduced due to an effect on nodule metabolism that manifested as a lower amount of nitrogenase reductase. Moreover, the nodule proteomic approach also revealed that nodule functioning was altered simultaneously in various enzyme quantity apart from nitrogenase. At elevated CO2, the tricarboxylic acid cycle was also altered with a reduced amount of isocitrate synthase protein. The nodule proteome analysis also revealed the relaxation of the antioxidant system as shown by a decline in the amount of catalase and isoflavone reductase protein