			Home About us Contact

CO2 Responses (co2 + response)

Distribution by Scientific Domains

Life Sciences	75%

Selected Abstracts

Photosynthetic responses of Mojave Desert shrubs to free air CO2 enrichment are greatest during wet years

GLOBAL CHANGE BIOLOGY, Issue 2 2003
Elke Naumburg
Abstract It has been suggested that desert vegetation will show the strongest response to rising atmospheric carbon dioxide due to strong water limitations in these systems that may be ameliorated by both photosynthetic enhancements and reductions in stomatal conductance. Here, we report the long-term effect of 55 Pa atmospheric CO2 on photosynthesis and stomatal conductance for three Mojave Desert shrubs of differing leaf phenology (Ambrosia dumosa,drought-deciduous, Krameria erecta,winter-deciduous, Larrea tridentata,evergreen). The shrubs were growing in an undisturbed ecosystem fumigated using FACE technology and were measured over a four-year period that included both above and below-average precipitation. Daily integrated photosynthesis (Aday) was significantly enhanced by elevated CO2 for all three species, although Krameria erecta showed the greatest enhancements (63% vs. 32% for the other species) enhancements were constant throughout the entire measurement period. Only one species, Larrea tridentata, decreased stomatal conductance by 25,50% in response to elevated CO2, and then only at the onset of the summer dry season and following late summer convective precipitation. Similarly, reductions in the maximum carboxylation rate of Rubisco were limited to Larrea during spring. These results suggest that the elevated CO2 response of desert vegetation is a function of complex interactions between species functional types and prevailing environmental conditions. Elevated CO2 did not extend the active growing season into the summer dry season because of overall negligible stomatal conductance responses that did not result in significant water conservation. Overall, we expect the greatest response of desert vegetation during years with above-average precipitation when the active growing season is not limited to ,2 months and, consequently, the effects of increased photosynthesis can accumulate over a biologically significant time period. [source]

Initial cultivation of a temperate-region soil immediately accelerates aggregate turnover and CO2 and N2O fluxes

GLOBAL CHANGE BIOLOGY, Issue 8 2006
A. STUART GRANDY
Abstract The immediate effects of tillage on protected soil C and N pools and on trace gas emissions from soils at precultivation levels of native C remain largely unknown. We measured the response to cultivation of CO2 and N2O emissions and associated environmental factors in a previously uncultivated U.S. Midwest Alfisol with C concentrations that were indistinguishable from those in adjacent late successional forests on the same soil type (3.2%). Within 2 days of initial cultivation in 2002, tillage significantly (P=0.001, n=4) increased CO2 fluxes from 91 to 196 mg CO2 -C m,2 h,1 and within the first 30 days higher fluxes because of cultivation were responsible for losses of 85 g CO2 -C m,2. Additional daily C losses were sustained during a second and third year of cultivation of the same plots at rates of 1.9 and 1.0 g C m,2 day,1, respectively. Associated with the CO2 responses were increased soil temperature, substantially reduced soil aggregate size (mean weight diameter decreased 35% within 60 days), and a reduction in the proportion of intraaggregate, physically protected light fraction organic matter. Nitrous oxide fluxes in cultivated plots increased 7.7-fold in 2002, 3.1-fold in 2003, and 6.7-fold in 2004 and were associated with increased soil NO3, concentrations, which approached 15 ,g N g,1. Decreased plant N uptake immediately after tillage, plus increased mineralization rates and fivefold greater nitrifier enzyme activity, likely contributed to increased NO3, concentrations. Our results demonstrate that initial cultivation of a soil at precultivation levels of native soil C immediately destabilizes physical and microbial processes related to C and N retention in soils and accelerates trace gas fluxes. Policies designed to promote long-term C sequestration may thus need to protect soils from even occasional cultivation in order to preserve sequestered C. [source]

Roles of CmpR, a LysR family transcriptional regulator, in acclimation of the cyanobacterium Synechococcus sp. strain PCC 7942 to low-CO2 and high-light conditions

MOLECULAR MICROBIOLOGY, Issue 3 2004
Yukari Takahashi
Summary The cmp operon of Synechococcus sp. strain PCC 7942, encoding a high-affinity bicarbonate transporter, is induced under low CO2 conditions by a LysR family protein CmpR. CmpR was found to be required also for induction of the operon by transfer of the cells from low-light to high-light conditions, indicating involvement of a common mechanism in the high-light- and low-CO2 -responsive regulation. Expression of the high-light inducible genes psbAII and psbAIII, on the other hand, was found to be induced also by low-CO2 conditions. A single promoter was responsible for the high-light and low-CO2 induction of each of psbAII and psbAIII, suggesting involvement of a common regulatory mechanism in the light and CO2 responses of the psbA genes. CmpR was, however, not required for the induction of psbAII and psbAIII, indicating the presence of multiple mechanisms for induction of genes under high-light and low-CO2 conditions. The CmpR-deficient mutant nevertheless showed lower levels of the psbAII and psbAIII transcripts than the wild-type strain under all the light and CO2 conditions examined. Gel shift assays showed that CmpR binds to the enhancer elements of psbAII and psbAIII, through specific interaction with a sequence signature conforming to the binding motif of similar LysR family proteins. These findings showed that CmpR acts as a trans -acting factor that enhances transcription of the photosystem II genes involved in acclimation to high light, revealing a complex network of gene regulation in the cyanobacterium. [source]

Evaluation of transcutaneous CO2 responses following acute changes in PaCO2 in healthy subjects

RESPIROLOGY, Issue 3 2009
Satoshi FUKE
ABSTRACT Background and objective: Transcutaneous blood gas-monitoring systems with miniaturized SpO2 (peripheral blood oxygen saturation)/PCO2 combined sensors (TOSCATM) have been widely used. There are no reports of the inter- and intra-individual variability in transcutaneous measurements of PaCO2 (PtcCO2) in response to acute progressive changes in PaCO2. This study examined inter- and intra-individual variability of PtcCO2 measurements under semi-steady-state conditions, and characterized the behaviour of PtcCO2 in response to acute progressive changes in PaCO2. Methods: Subjects breathed mixed gases through a mouthpiece connected to an automatic arterial blood gas controller. Using end-tidal PCO2 and PO2 as guides, PaCO2 was controlled to increase and/or decrease between baseline and , 60 mm Hg, in a stepwise (n = 9) or progressive fashion (n = 6). Arterial blood was sampled when needed. Results: Intra-individual correlation coefficients between PtcCO2 and PaCO2 were excellent in all subjects (0.971,0.989); however, the slope of the regression line varied among subjects (1.040,1.335). Bias and limits of agreement (± 2 SD from bias) between PtcCO2 and PaCO2 were ,1.8 mm Hg and ,7.7 to 4.1 mm Hg. Changes in PtcCO2 in response to acute progressive changes in PaCO2 also varied among subjects. Conclusion: The PtcCO2 measurement system allows reliable estimation of PaCO2 in a given subject. However, caution is needed when comparing absolute values between subjects or when acute changes in PaCO2 occur. [source]