Direct effects of atmospheric carbon dioxide concentration on whole canopy dark respiration of rice

The purpose of this study was to test for direct inhibition of rice canopy apparent respiration by elevated atmospheric carbon dioxide concentration ([CO₂]) across a range of short‐term air temperature treatments. Rice (cv. IR‐72) was grown in eight naturally sunlit, semiclosed, plant growth chambers at daytime [CO₂] treatments of 350 and 700 μmol mol^?1. Short‐term night‐time air temperature treatments ranged from 21 to 40 °C. Whole canopy respiration, expressed on a ground area basis (R_d), was measured at night by periodically venting the chambers with ambient air. This night‐time chamber venting and resealing procedure produced a range of increasing chamber [CO₂] which we used to test for potential inhibitory effects of rising [CO₂] on R_d. A nitrous oxide leak detection system was used to correct R_d measurements for chamber leakage rate (L) and also to determine if apparent reductions in night‐time R_d with rising [CO₂] could be completely accounted for by L. The L was affected by both CO₂ concentration gradient between the chamber and ambient air and the inherent leakiness of each individual chamber. Nevertheless, after correcting R_d for L, we detected a rapid and reversible, direct inhibition of R_d with rising chamber [CO₂] for air temperatures above 21 °C. This effect was larger for the 350 compared with the 700 μmol mol^?1 daytime [CO₂] treatment and was also increased with increasing short‐term air temperature treatments. However, little difference in R_d was found between the two daytime [CO₂] treatments when night‐time [CO₂] was at the respective daytime [CO₂]. These results suggest that naturally occurring diurnal changes in both ambient [CO₂] and air temperature can affect R_d. Because naturally occurring diurnal changes in both [CO₂] and air temperature can be expected in a future higher CO₂ world, short‐term direct effects of these environmental variables on rice R_d can also be expected.     

The effect of high levels of carbon dioxide on dark respiration and growth of plants

Abstract Raising ambient levels of CO₂ during the night, between 350 and 950cm³m^?3, reduced the dark respiration rate of Medicago sativum seedlings. The percentage effect was greater for maintenance respiration than for dark respiration as a whole, and when the plants were in a low photosynthate status. Twenty-four h carbon balance studies confirmed a reduction in night time respiration and an increase of net carbon gain when night time [CO₂] was high. Growth experiments showed a small but significant increase of dry weight in Medicago sativum seedlings exposed to high [CO₂] (～ 1200 cm³m^?3) at night. This effect was greater for plants grown with Rhizobium nodules than for plants grown with nitrate in the absence of Rhizobium. A similar, but smaller and statistically non-significant effect of high night time [CO₂] on growth was found for Xanthium strumarium seedlings. The significance of these findings is discussed in relation to the rising CO₂ content of the atmosphere.     

The effect of carbon dioxide concentration on respiration of growing and mature soybean leaves

Soybean plants were grown continuously at 350 and 700cm³m^?3 CO₂ at constant temperature. Respiration rates of third trifoliolate leaves were measured at the growth CO₂ concentration for the whole dark period from 5d before through to 5d after full area expansion. The short-term response of respiration rate to the measurement CO₂ concentration was also determined at each age. Respiration rates per unit of dry mass declined with age and were significantly less at a given age or RGR in leaves grown and measured at the elevated CO₂. The difference in respiration rate was largest in mature leaves and resulted from the different measurement CO₂ concentrations. The respiratory costs of the tissue synthesis, estimated from the elemental composition of the tissue, did not differ substantially between CO₂ treatments. The response of respiration rate to carbon dioxide concentration was not strongly affected by the form of nitrogen supplied. Maintenance respiration calculated by subtracting growth respiration from total respiration was negative in rapidly growing leaves for both CO₂ treatments. This indicates that CO₂ efflux in the dark does not accurately reflect the average 24 h rate of energy expenditure on growth and maintenance for soybean leaves.     

Responses of respiration to increasing atmospheric carbon dioxide concentrations

It has been recently recognized that increases in carbon dioxide concentration such as are anticipated for the earth's atmosphere in the next century often reduce plant respiration. There can be both a short-term reversible effect of unknown cause, and long-term acclimation, which may reflect the synthesis and maintenance of less metabolically expensive materials in plants grown at elevated carbon dioxide concentrations. Because respiration provides energy and carbon intermediates for growth and maintenance, reductions in respiration by increasing carbon dioxide concentrations may have effects on physiology beyond an improvement in plant carbon balance. As atmospheric carbon dioxide concentration increases, reduced respiration could be as important as increased photosynthesis in improving the ability of terrestrial vegetation to act as a sink for carbon, but it could also have other consequences.     

Increased night temperature reduces the stimulatory effect of elevated carbon dioxide concentration on methane emission from rice paddy soil

To determine how elevated night temperature interacts with carbon dioxide concentration ([CO₂]) to affect methane (CH₄) emission from rice paddy soil, we conducted a pot experiment using four controlled‐environment chambers and imposed a combination of two [CO₂] levels (ambient: 380 ppm; elevated: 680 ppm) and two night temperatures (22 and 32 °C). The day temperature was maintained at 32 °C. Rice (cv. IR72) plants were grown outside until the early‐reproductive growth stage and then transferred to the chambers. After onset of the treatment, day and night CH₄ fluxes were measured every week. The CH₄ fluxes changed significantly with the growth stage, with the largest fluxes occurring around the heading stage in all treatments. The total CH₄ emission during the treatment period was significantly increased by both elevated [CO₂] (P=0.03) and elevated night temperature (P<0.01). Elevated [CO₂] increased CH₄ emission by 3.5% and 32.2% under high and low night temperature conditions, respectively. Elevated [CO₂] increased the net dry weight of rice plants by 12.7% and 38.4% under high and low night temperature conditions, respectively. These results imply that increasing night temperature reduces the stimulatory effect of elevated [CO₂] on both CH₄ emission and rice growth. The CH₄ emission during the day was larger than at night even under the high‐night‐temperature treatment (i.e. a constant temperature all day). This difference became larger after the heading stage. We observed significant correlations between the night respiration and daily CH₄ flux (P<0.01). These results suggest that net plant photosynthesis contributes greatly to CH₄ emission and that increasing night temperature reduces the stimulatory effect of elevated [CO₂] on CH₄ emission from rice paddy soil.     

A comparison of the effects of carbon dioxide concentration and temperature on respiration, translocation and nitrate reduction in darkened soybean leaves

BACKGROUND AND AIMS: Respiration of autotrophs is an important component of their carbon balance as well as the global carbon dioxide budget. How autotrophic respiration may respond to increasing carbon dioxide concentrations, [CO(2)], in the atmosphere remains uncertain. The existence of short-term responses of respiration rates of plant leaves to [CO(2)] is controversial. Short-term responses of respiration to temperature are not disputed. This work compared responses of dark respiration and two processes dependent on the energy and reductant supplied by dark respiration, translocation and nitrate reduction, to changes in [CO(2)] and temperature. METHODS: Mature soybean leaves were exposed for a single 8-h dark period to one of five combinations of air temperature and [CO(2)], and rates of respiration, translocation and nitrate reduction were determined for each treatment. KEY RESULTS: Low temperature and elevated [CO(2)] reduced rates of respiration, translocation and nitrate reduction, while increased temperature and low [CO(2)] increased rates of all three processes. A given change in the rate of respiration was accompanied by the same change in the rate of translocation or nitrate reduction, regardless of whether the altered respiration was caused by a change in temperature or by a change in [CO(2)]. CONCLUSIONS: These results make it highly unlikely that the observed responses of respiration rate to [CO(2)] were artefacts due to errors in the measurement of carbon dioxide exchange rates in this case, and indicate that elevated [CO(2)] at night can affect translocation and nitrate reduction through its effect on respiration.     

Effect of carbon dioxide concentration on microbial respiration in soil

In order to assess the validity of conventional methods for measuring CO₂ flux from soil, the relationship between soil microbial respiration and ambient CO₂ concentration was studied using an open-flow infra-red gas analyser (IRGA) method. Andosol from an upland field in central Japan was used as a soil sample. Soil microbial respiration activity was depressed with the increase of CO₂ concentration in ventilated air from 0 to 1000 ppmv. At 1000 ppmv, the respiration rate was less than half of that at 0 ppmv. Thus, it is likely that soil respiration rate is overestimated by the alkali absorption method, because CO₂ concentration in the absorption chamber is much lower than the normal level. Metabolic responses to CO₂ concentration were different among groups of soil microorganisms. The bacteria actinomycetes group cultivated on agar medium showed a more sensitive response to the CO₂ concentration than the filamentous fungi group.     

Growth and maintenance components of leaf respiration of cotton grown in elevated carbon dioxide partial pressure

Elevated atmospheric carbon dioxide partial pressures have been shown to have variable direct and indirect effects on plant respiration rates. In this study, growth, leaf respiration, and leaf nitrogen and carbohydrate partitioning were measured in Gossypium hirsutum L. grown in 35 and 65 Pa CO₂ for 30d. Growth and maintenance coefficients of leaf respiration were estimated using gas exchange techniques both at night and during the day. Elevated CO₂ stimulated biomass production (107%) and net photo-synthetic rates (35–50%). Total day-time respiration (R_d) was not significantly affected by growth CO₂ partial pressure. However, night respiration (R_n) of leaves grown in 65 Pa CO₂ was significantly greater than that of plants grown in 35 Pa CO₂. Correlation of R_d and R_n with leaf expansion rates indicated that plants in both CO₂ treatments had equivalent growth respiration coefficients but maintenance respiration was significantly greater in elevated CO₂. Increased maintenance coefficients in elevated CO₂ appeared to be related to increased starch accumulation rather than to changes in leaf nitrogen.     

Long-term growth at elevated carbon dioxide stimulates methane emission in tropical paddy rice

Recent anthropogenic emissions of key atmospheric trace gases (e.g. CO₂ and CH₄) which absorb infra-red radiation may lead to an increase in mean surface temperatures and potential changes in climate. Although sources of each gas have been evaluated independently, little attention has focused on potential interactions between gases which could influence emission rates. In the current experiment, the effect of enhanced CO₂ (300 μL L^–1 above ambient) and/or air temperature (4 °C above ambient) on methane generation and emission were determined for the irrigated tropical paddy rice system over 3 consecutive field seasons (1995 wet and dry seasons 1996 dry season). For all three seasons, elevated CO₂ concentration resulted in a significant increase in dissolved soil methane relative to the ambient control. Consistent with the observed increases in soil methane, measurements of methane flux per unit surface area during the 1995 wet and 1996 dry seasons also showed a significant increase at elevated carbon dioxide concentration relative to the ambient CO₂ condition (+49 and 60% for each season, respectively). Growth of rice at both increasing CO₂ concentration and air temperature did not result in additional stimulation of either dissolved or emitted methane compared to growth at elevated CO₂ alone. The observed increase in methane emissions were associated with a large, consistent, CO₂-induced stimulation of root growth. Results from this experiment suggest that as atmospheric CO₂ concentration increases, methane emissions from tropical paddy rice could increase above current projections.     

Effect of carbon dioxide concentration on the bioleaching of a pyrite-arsenopyrite ore concentrate

The effect of carbon dioxide concentration on the bacterial leaching of a pyrite-arsenopyrite ore concentrate was studied in continuous-flow reactors. Steady-state operation with two feed slurry densities, 6 wt% and 16 wt% solids, were tested for the effect of carbon dioxide concentration. Bacterial growth rates were estimated via the measurement of carbon dioxide consumption rates. Aqueous-phase carbon dioxide concentrations in excess of 10 mg/L were found to be inhibitory to bacterial growth. (c) 1993 John Wiley & Sons, Inc.     

Modeling the effects of snowpack on heterotrophic respiration across northern temperate and high latitude regions: Comparison with measurements of atmospheric carbon dioxide in high latitudes

Simulations by global terrestrial biogeochemical models (TBMs) consistently underestimate the concentration of atmospheric carbon dioxide (CO₂ at high latitude monitoring stations during the non-growing season. We hypothesized that heterotrophic respiration is underestimated during the nongrowing season primarily because TBMs do not generally consider the insulative effects of snowpack on soil temperature. To evaluate this hypothesis, we compared the performance of baseline and modified versions of three TBMs in simulating the seasonal cycle of atmospheric CO₂ at high latitude CO₂ monitoring stations; the modified version maintained soil temperature at 0 °C when modeled snowpack was present. The three TBMs include the Carnegie-Ames-Stanford Approach (CASA), Century, and the Terrestrial Ecosystem Model (TEM). In comparison with the baseline simulation of each model, the snowpack simulations caused higher releases of CO₂ between November and March and greater uptake of CO₂ between June and August for latitudes north of 30° N. We coupled the monthly estimates of CO₂ exchange, the seasonal carbon dioxide flux fields generated by the HAMOCC3 seasonal ocean carbon cycle model, and fossil fuel source fields derived from standard sources to the three-dimensional atmospheric transport model TM2 forced by observed winds to simulate the seasonal cycle of atmospheric CO₂ at each of seven high latitude monitoring stations. In comparison to the CO₂ concentrations simulated with the baseline fluxes of each TBM, concentrations simulated using the snowpack fluxes are generally in better agreement with observed concentrations between August and March at each of the monitoring stations. Thus, representation of the insulative effects of snowpack in TBMs generally improves simulation of atmospheric CO₂ concentrations in high latitudes during both the late growing season and nongrowing season. These simulations highlight the global importance of biogeochemical processes during the nongrowing season in estimating carbon balance of ecosystems in northern high and temperate latitudes.     

Response of respiration of soybean leaves grown at ambient and elevated carbon dioxide concentrations to day-to-day variation in light and temperature under field conditions

BACKGROUND AND AIMS: Respiration is an important component of plant carbon balance, but it remains uncertain how respiration will respond to increases in atmospheric carbon dioxide concentration, and there are few measurements of respiration for crop plants grown at elevated [CO(2)] under field conditions. The hypothesis that respiration of leaves of soybeans grown at elevated [CO(2)] is increased is tested; and the effects of photosynthesis and acclimation to temperature examined. METHODS: Net rates of carbon dioxide exchange were recorded every 10 min, 24 h per day for mature upper canopy leaves of soybeans grown in field plots at the current ambient [CO(2)] and at ambient plus 350 micromol mol(-1) [CO(2)] in open top chambers. Measurements were made on pairs of leaves from both [CO(2)] treatments on a total of 16 d during the middle of the growing seasons of two years. KEY RESULTS: Elevated [CO(2)] increased daytime net carbon dioxide fixation rates per unit of leaf area by an average of 48 %, but had no effect on night-time respiration expressed per unit of area, which averaged 53 mmol m(-2) d(-1) (1.4 micromol m(-2) s(-1)) for both the ambient and elevated [CO(2)] treatments. Leaf dry mass per unit of area was increased on average by 23 % by elevated [CO(2)], and respiration per unit of mass was significantly lower at elevated [CO(2)]. Respiration increased by a factor of 2.5 between 18 and 26 degrees C average night temperature, for both [CO(2)] treatments. CONCLUSIONS: These results do not support predictions that elevated [CO(2)] would increase respiration per unit of area by increasing photosynthesis or by increasing leaf mass per unit of area, nor the idea that acclimation of respiration to temperature would be rapid enough to make dark respiration insensitive to variation in temperature between nights.     

Stomatal conductance, photosynthesis and respiration of temperate deciduous tree seedlings grown outdoors at an elevated concentration of carbon dioxide

Seedlings of temperate deciduous tree species were grown outdoors at ambient and at an elevated concentration of carbon dioxide to examine how aspects of their gas exchange would be altered by growth at elevated carbon dioxide concentration. Leaf conductances to water vapour and net carbon dioxide exchange rates were determined periodically near midday. Whole-plant carbon dioxide efflux rates in darkness were also determined. The stomatal conductance of leaves of plants grown and measured at 700 cm³ m^?3 carbon dioxide did not differ from that of plants grown and measured at 350 cm³ m^?3 in Malus domestica, Quercus prinus and Quercus robur at any measurement time. In Acer saccharinum, lower conductances occurred for plants grown and measured at elevated carbon dioxide concentration only at measurement temperatures above 33°C. Photo-synthetic adjustment to elevated carbon dioxide concentration was evident only in Q. robur. All species examined had lower rates of dark respiration per unit of mass when grown and measured at elevated carbon dioxide concentration.     

舍饲绵羊甲烷和二氧化碳的日排放动态

运用密闭呼吸代谢箱系统,对3只舍饲绵羊24h(有间断)甲烷(CH4)和二氧化碳(CO2)日排放特征进行了研究.供试3只甘肃细毛羊体况相近(平均体重为(25±5)kg),其基础日粮为燕麦干草和玉米精料,粗精比为 6∶4.结果表明:供试绵羊CH4和CO2的平均排放量分别为11g/d和147 g/d,CH4排放的峰值分别出现在17:00和22:00左右,达0.4217g/h和0.8082 g/h,直到0:00降至最小为0.2993g/h;之后趋于平稳,次日8:00左右再次达到排放高峰,排放量为0.6587 g/h.而CO2在各个测定时间段内差异不显著(p＞0.05).因此,舍饲条件下绵羊CH4和CO2排放量动态(g/min)变化不同步.由此,推算出舍饲绵羊(25±5)kg年排放CH4和CO2总量分别约为4.38 kg和53.66 kg.     

Effects of humidity on short-term responses of stomatal conductance to an increase in carbon dioxide concentration

The magnitude of the response of stomatal conductance to a change in the concentration of carbon dioxide external to the leaf from 350 to 700 cm³ m^–3 was found to be extremely variable from day to day in the field in Glycine max , Hordeum vulgare and Triticum aestivum . It was found that the leaf-to-air water vapour pressure difference (LAVPD) during the midday measurements of the stomatal response to carbon dioxide affected the magnitude of the response. On days when LAVPD was low, no significant change in conductance occurred with the increase in carbon dioxide concentration. When LAVPD was higher, conductance decreased by 24–52% with the increase in carbon dioxide within a few minutes. The sensitivity of conductance was approximately linearly related to LAVPD in wheat and barley. Experiments with G. max in the field indicated that, on days with low LAVPD, increasing the LAVPD just around the measured portion of a leaflet made stomatal conductance responsive to increased carbon dioxide. This result was also obtained under laboratory conditions with G. max , Helianthus annuus and Amaranthus retroflexus . In G. max , it was determined that leaves in which conductance was not responsive to the increase in carbon dioxide could be made responsive even at low LAVPD by the injection of abscisic acid into their petioles. Because it is known that abscisic acid sensitizes stomata to carbon dioxide, these results are consistent with the idea that abscisic acid may be involved in the response of stomatal conductance to changes in LAVPD.     

Effects of NAD kinase 2 overexpression on primary metabolite profiles in rice leaves under elevated carbon dioxide

The concentration of carbon dioxide (CO₂) in the atmosphere is projected to double by the end of the 21st century. In C₃ plants, elevated CO₂ concentrations promote photosynthesis but inhibit the assimilation of nitrate into organic nitrogen compounds. Several steps of nitrate assimilation depend on the availability of ATP and sources of reducing power, such as nicotinamide adenine dinucleotide phosphate (NADPH). Plastid‐localised NAD kinase 2 (NADK2) plays key roles in increasing the ATP/ADP and NADP(H)/NAD(H) ratios. Here we examined the effects of NADK2 overexpression on primary metabolism in rice (Oryza sativa) leaves in response to elevated CO₂. By using capillary electrophoresis mass spectrometry, we showed that the primary metabolite profile of NADK2‐overexpressing plants clearly differed from that of wild‐type plants under ambient and elevated CO₂. In NADK2‐overexpressing leaves, expression of the genes encoding glutamine synthetase and glutamate synthase was up‐regulated, and the levels of Asn, Gln, Arg, and Lys increased in response to elevated CO₂. The present study suggests that overexpression of NADK2 promotes the biosynthesis of nitrogen‐rich amino acids under elevated CO₂.     

Stem respiration and carbon dioxide efflux of young <Emphasis Type="Italic">Populus deltoides</Emphasis> trees in relation to temperature and xylem carbon dioxide concentration

Oxidative respiration is strongly temperature driven. However, in woody stems, efflux of CO₂ to the atmosphere (E _A), commonly used to estimate the rate of respiration (R _S), and stem temperature (T _st) have often been poorly correlated, which we hypothesized was due to transport of respired CO₂ in xylem sap, especially under high rates of sap flow (f _s). To test this, we measured E _A, T _st, f _s and xylem sap CO₂ concentrations ([CO₂*]) in 3-year-old Populus deltoides trees under different weather conditions (sunny and rainy days) in autumn. We also calculated R _S by mass balance as the sum of both outward and internal CO₂ fluxes and hypothesized that R _S would correlate better with T _st than E _A. We found that E _A sometimes correlated well with T _st, but not on sunny mornings and afternoons or on rainy days. When the temperature effect on E _A was accounted for, a clear positive relationship between E _A and xylem [CO₂*] was found. [CO₂*] varied diurnally and increased substantially at night and during periods of rain. Changes in [CO₂*] were related to changes in f _s but not T _st. We conclude that changes in both respiration and internal CO₂ transport altered E _A. The dominant component flux of R _S was E _A. However, on a 24-h basis, the internal transport flux represented 9–18% and 3–7% of R _S on sunny and rainy days, respectively, indicating that the contribution of stem respiration to forest C balance may be larger than previously estimated based on E _A measurements. Unexpectedly, the relationship between R _S and T _st was sometimes weak in two of the three trees. We conclude that in addition to temperature, other factors such as water deficits or substrate availability exert control on the rate of stem respiration so that simple temperature functions are not sufficient to predict stem respiration.     

Partitioning net carbon dioxide fluxes into photosynthesis and respiration using neural networks

The eddy covariance (EC) technique is used to measure the net ecosystem exchange (NEE) of CO₂ between ecosystems and the atmosphere, offering a unique opportunity to study ecosystem responses to climate change. NEE is the difference between the total CO₂ release due to all respiration processes (RECO), and the gross carbon uptake by photosynthesis (GPP). These two gross CO₂ fluxes are derived from EC measurements by applying partitioning methods that rely on physiologically based functional relationships with a limited number of environmental drivers. However, the partitioning methods applied in the global FLUXNET network of EC observations do not account for the multiple co‐acting factors that modulate GPP and RECO flux dynamics. To overcome this limitation, we developed a hybrid data‐driven approach based on combined neural networks (NN_C‐part). NN_C‐part incorporates process knowledge by introducing a photosynthetic response based on the light‐use efficiency (LUE) concept, and uses a comprehensive dataset of soil and micrometeorological variables as fluxes drivers. We applied the method to 36 sites from the FLUXNET2015 dataset and found a high consistency in the results with those derived from other standard partitioning methods for both GPP (R² > .94) and RECO (R² > .8). High consistency was also found for (a) the diurnal and seasonal patterns of fluxes and (b) the ecosystem functional responses. NN_C‐part performed more realistic than the traditional methods for predicting additional patterns of gross CO₂ fluxes, such as: (a) the GPP response to VPD, (b) direct effects of air temperature on GPP dynamics, (c) hysteresis in the diel cycle of gross CO₂ fluxes, (d) the sensitivity of LUE to the diffuse to direct radiation ratio, and (e) the post rain respiration pulse after a long dry period. In conclusion, NN_C‐part is a valid data‐driven approach to provide GPP and RECO estimates and complementary to the existing partitioning methods.