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Low CO2 (low + co2)
Selected AbstractsC3,C4 composition and prior carbon dioxide treatment regulate the response of grassland carbon and water fluxes to carbon dioxideFUNCTIONAL ECOLOGY, Issue 1 2007H. W. POLLEY Summary 1Plants usually respond to carbon dioxide (CO2) enrichment by increasing photosynthesis and reducing transpiration, but these initial responses to CO2 may not be sustained. 2During May, July and October 2000, we measured the effects of temporarily increasing or decreasing CO2 concentration by 150,200 µmol mol,1 on daytime net ecosystem CO2 exchange (NEE) and water flux (evapotranspiration, ET) of C3,C4 grassland in central Texas, USA that had been exposed for three growing seasons to a CO2 gradient from 200 to 560 µmol mol,1. Grassland grown at subambient CO2 (< 365 µmol mol,1) was exposed for 2 days to an elevated CO2 gradient (> 365 µmol mol,1). Grassland grown at elevated CO2 was exposed for 2 days to a subambient gradient. Our objective was to determine whether growth CO2 affected the amount by which grassland NEE and ET responded to CO2 switching (sensitivity to CO2). 3The NEE per unit of leaf area was greater (16,20%) and ET was smaller (9,20%), on average, at the higher CO2 concentration during CO2 switching in May and July. The amount by which NEE increased at the higher CO2 level was smaller at elevated than subambient growth concentrations on both dates, but relationships between NEE response and growth CO2 were weak. Conversely, the effect of temporary CO2 change on ET did not depend on growth CO2. 4The ratio of NEE at high CO2 to NEE at low CO2 during CO2 change in July increased from 1·0 to 1·26 as the contribution of C3 cover to total cover increased from 26% to 96%. Conversely, in May, temporary CO2 enrichment reduced ET more in C4 - than C3 -dominated grassland. 5For this mesic grassland, sensitivity of NEE and ET to brief change in CO2 depended as much on the C3,C4 composition of vegetation as on physiological adjustments related to prior CO2 exposure. [source] Mechanism of low CO2 -induced activation of the cmp bicarbonate transporter operon by a LysR family protein in the cyanobacterium Synechococcus elongatus strain PCC 7942MOLECULAR MICROBIOLOGY, Issue 1 2008Takashi Nishimura Summary The cmp operon of the cyanobacterium Synechococcus elongatus strain PCC 7942, encoding the subunits of the ABC-type bicarbonate transporter, is activated under CO2 -limited growth conditions in a manner dependent on CmpR, a LysR family transcription factor of CbbR subfamily. The 0.7 kb long regulatory region of the operon carried a single promoter, which responded to CO2 limitation. Using the luxAB reporter system, three cis -acting elements involved in the low-CO2 activation of transcription, each consisting of a pair of LysR recognition signatures overlapping at their ends, were identified in the regulatory region. CmpR was shown to bind to the regulatory region, yielding several DNA,protein complexes in gel shift assays. Addition of ribulose-1,5-bisphosphate (> 1 mM) or 2-phosphoglycolate (> 10 ,M) enhanced the binding of CmpR in a concentration-dependent manner, promoting formation of large DNA,protein complexes. Given the involvement of O2 in adaptive responses of cyanobacteria to low-CO2 conditions, our results suggest that 2-phosphoglycolate, which is produced by oxygenation by ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) of ribulose-1,5-bisphosphate under CO2 -limited conditions, acts as the co-inducer in the activation of the cmp operon by CmpR. [source] Klimapolitik: Kyoto-Protokoll und Emissionshandel für CO2 -Zertifikate in der EU1PERSPEKTIVEN DER WIRTSCHAFTSPOLITIK, Issue 3 2005Wolfgang Ströbele Also every economist knows that the institutional conditions and the rules of the game are important. This basic idea stood behind the introduction of a CO2 -emissions trading system within the European Community starting in 2005. Since the starting point is the Kyoto-protocol with its subset of relevant states involved and the rules agreed upon there, one must ask whether the EU CO2-trading system is really an instrument that helps to reach the Kyoto goals more efficiently. A positive answer to this question is very doubtful. The new European subsystem is only valid for CO2 while Kyoto knows six greenhouse gases, the EU trading periods are 2005,2007 and 2008,2012 while Kyoto is only relevant for the second period, the integration with all flexible instruments of Kyoto is not guaranteed from the beginning. The plants involved are power plants and plants with high energy intensity. Since the technological levels of these plants are rather similar in Europe, the difference in marginal abatement cost will not be large enough to offset the rather high transaction cost of the special EU system. Furthermore, the heating systems and small scale plants of industry are not included in the trading system. The same holds true for traffic, households and the service sector. Drawing a borderline between CO2 -policy there and the trading activities will cause inefficiencies. If CO2 -prices are high, the main incentive of the trading system will be a large shift from domestic production to production abroad without any CO2 -restrictions. Leakage-effects will then be dominant. With low CO2 -prices the special European bureaucratic system will not create enough efficiency gains to cover the trading system's cost. [source] Stomatal responses to CO2 during a diel Crassulacean acid metabolism cycle in Kalanchoe daigremontiana and Kalanchoe pinnataPLANT CELL & ENVIRONMENT, Issue 5 2009SUSANNE VON CAEMMERER ABSTRACT To investigate the diurnal variation of stomatal sensitivity to CO2, stomatal response to a 30 min pulse of low CO2 was measured four times during a 24 h time-course in two Crassulacean acid metabolism (CAM) species Kalanchoe daigremontiana and Kalanchoe pinnata, which vary in the degree of succulence, and hence, expression and commitment to CAM. In both species, stomata opened in response to a reduction in pCO2 in the dark and in the latter half of the light period, and thus in CAM species, chloroplast photosynthesis is not required for the stomatal response to low pCO2. Stomata did not respond to a decreased pCO2 in K. daigremontiana in the light when stomata were closed, even when the supply of internal CO2 was experimentally reduced. We conclude that stomatal closure during phase III is not solely mediated by high internal pCO2, and suggest that in CAM species the diurnal variability in the responsiveness of stomata to pCO2 could be explained by hypothesizing the existence of a single CO2 sensor which interacts with other signalling pathways. When not perturbed by low pCO2, CO2 assimilation rate and stomatal conductance were correlated both in the light and in the dark in both species. [source] | ||||||||||