Plant Nitrogen Dynamics in Shortgrass Steppe under Elevated Atmospheric Carbon Dioxide

The direct and indirect effects of increasing levels of atmospheric carbon dioxide (CO₂) on plant nitrogen (N) content were studied in a shortgrass steppe ecosystem in northeastern Colorado, USA. Beginning in 1997 nine experimental plots were established: three open-top chambers with ambient CO₂ levels (approximately 365 mol mol^–1), three open-top chambers with twice-ambient CO₂ levels (approximately 720 mol mol^–1), and three unchambered control plots. After 3 years of growing-season CO₂ treatment, the aboveground N concentration of plants grown under elevated atmospheric CO₂ decreased, and the carbon–nitrogen (C:N) ratio increased. At the same time, increased aboveground biomass production under elevated atmospheric CO₂ conditions increased the net transfer of N out of the soil of elevated-CO₂ plots. Aboveground biomass production after simulated herbivory was also greater under elevated CO₂ compared to ambient CO₂. Surprisingly, no significant changes in belowground plant tissue N content were detected in response to elevated CO₂. Measurements of individual species at peak standing phytomass showed significant effects of CO₂ treatment on aboveground plant tissue N concentration and significant differences between species in N concentration, suggesting that changes in species composition under elevated CO₂ will contribute to overall changes in nutrient cycling. Changes in plant N content, driven by changes in aboveground plant N concentration, could have important consequences for biogeochemical cycling rates and the long-term productivity of the shortgrass steppe as atmospheric CO₂ concentrations increase.     

Increases in Desert Shrub Productivity under Elevated Carbon Dioxide Vary with Water Availability

Productivity of aridland plants is predicted to increase substantially with rising atmospheric carbon dioxide (CO₂) concentrations due to enhancement in plant water-use efficiency (WUE). However, to date, there are few detailed analyses of how intact desert vegetation responds to elevated CO₂. From 1998 to 2001, we examined aboveground production, photosynthesis, and water relations within three species exposed to ambient (around 38 Pa) or elevated (55 Pa) CO₂ concentrations at the Nevada Desert Free-Air CO₂ Enrichment (FACE) Facility in southern Nevada, USA. The functional types sampled—evergreen (Larrea tridentata), drought-deciduous (Ambrosia dumosa), and winter-deciduous shrubs (Krameria erecta)—represent potentially different responses to elevated CO₂ in this ecosystem. We found elevated CO₂ significantly increased aboveground production in all three species during an anomalously wet year (1998), with relative production ratios (elevated:ambient CO₂) ranging from 1.59 (Krameria) to 2.31 (Larrea). In three below-average rainfall years (1999–2001), growth was much reduced in all species, with only Ambrosia in 2001 having significantly higher production under elevated CO₂. Integrated photosynthesis (mol CO₂ m⁻² y⁻¹) in the three species was 1.26–2.03-fold higher under elevated CO₂ in the wet year (1998) and 1.32–1.43-fold higher after the third year of reduced rainfall (2001). Instantaneous WUE was also higher in shrubs grown under elevated CO₂. The timing of peak canopy development did not change under elevated CO₂; for example, there was no observed extension of leaf longevity into the dry season in the deciduous species. Similarly, seasonal patterns in CO₂ assimilation did not change, except for Larrea. Therefore, phenological and physiological patterns that characterize Mojave Desert perennials—early-season lags in canopy development behind peak photosynthetic capacity, coupled with reductions in late-season photosynthetic capacity prior to reductions in leaf area—were not significantly affected by elevated CO₂. Together, these findings suggest that elevated CO₂ can enhance the productivity of Mojave Desert shrubs, but this effect is most pronounced during years with abundant rainfall when soil resources are most available.     

Carbon Dioxide Concentrations and Temperatures within Tour Buses under Real-Time Traffic Conditions

This study monitored the carbon dioxide (CO₂) concentrations and temperatures of three 43-seat tour buses with high-passenger capacities in a course of a three-day, two-night school excursion. Results showed that both driver zones and passenger zones of the tour buses achieved maximum CO₂ concentrations of more than 3000 ppm, and maximum daily average concentrations of 2510.6 and 2646.9 ppm, respectively. The findings confirmed that the CO₂ concentrations detected in the tour buses exceeded the indoor air quality standard of Taiwan Environmental Protection Administration (8 hr-CO₂: 1000 ppm) and the air quality guideline of Hong Kong Environmental Protection Department (1 hr-CO₂: 2500 ppm for Level 1 for buses). Observations also showed that high-capacity tour bus cabins with air conditioning system operating in recirculation mode are severely lacking in air exchange rate, which may negatively impact transportation safety. Moreover, the passenger zones were able to maintain a temperature of between 20 and 25°C during travel, which effectively suppresses the dispersion of volatile organic compounds. Finally, the authors suggest that in the journey, increasing the ventilation frequency of tour bus cabin, which is very beneficial to maintain the travel safety and enhance the quality of travel.     

Effects of Elevated Carbon Dioxide on Plant Biomass Production and Competition in a Simulated Neutral Grassland Community

Using open-top chambers, four prominent species (Lolium perenne,Cynosurus cristatus, Holcus lanatusandAgrostis capillaris) ofIrish neutral grasslands were grown at ambient and elevated(700 µmol mol^-1) atmospheric CO₂for a period of 8 months.The effects of interspecific competition on plant responsesto CO₂enrichment were investigated by growing the species ina four-species mixture. The results indicate that the speciesdiffer in their ability to respond to elevated CO₂. CO₂-enrichmenthad the largest effect on the biomass production ofH. lanatus,but substantial stimulations in biomass production were alsofound for the other three species. The CO₂-stimulation of biomassproduction forH. lanatuswas accompanied by increased tillering.In addition, reductions in specific leaf area were found forall species. Exposure to elevated CO₂increased the communitybiomass of the four-species mixture. This increase can be mainlyattributed to a significant increase in the biomass ofH. lanatusatelevated CO₂. No statistically-significant changes in speciescomposition of community biomass were found. However,H. lanatusdidincrease its share of community biomass at each of the harvests,with the other three species, mainlyL. perenne, suffering lossesin their shares at elevated CO₂. The results show that: (1)the species varied in their response to elevated CO₂; and (2)species composition in natural plant communities is likely tochange at elevated CO₂, but these changes may occur rather slowly.Much longer periods of exposure to elevated atmospheric CO₂maybe required to permit detection of significant changes in speciescomposition.Copyright 1998 Annals of Botany Company Carbon dioxide (CO₂) enrichment, competition, Lolium perenne,Cynosurus cristatus, Holcus lanatus, Agrostis capillaris, biomass, specific leaf area, tillering.     

Functional Body Capacities under the Conditions of Various Concentrations of Carbon Dioxide and Oxygen

We determined a permissible ratio between carbon dioxide and oxygen concentrations during accidental situations. The experiments (n = 138, 10 h each) on the effect of various concentrations of carbon dioxide and oxygen in the inhaled air were conducted on male volunteers aged 20–40 years subjected to a special medical examination. All experiments were divided into five series: hypercapnia + normoxia, hypercapnia + hyperoxia, hypercapnia + hypoxia, normocapnia + hypoxia, and ambient air (control). The results showed that functional capacities of the body are less impaired under the conditions of hypercapnia combined with hyperoxia. Thus, in accidental situations associated with rapid accumulation of carbon dioxide in the atmosphere of airtight chambers, a synchronous increase in pO₂ to 220–230 torr can provide for the highest work capacity.     

Overexpression of Tomato SIZ2 in Arabidopsis Improves Plant Salinity Tolerance

Small ubiquitin-like modifier (SUMO) conjugation to target proteins is an important post-translational modification, which regulates plant tolerance to biotic and abiotic stresses. SIZ1, a well-characterized SUMO E3 ligase, facilitates the conjugation of SUMO to target proteins. Here, a SIZ/PAIS-type protein SlSIZ2 was identified in tomato (Solanum lycopersicum) that is a homolog of AtSIZ1 and SlSIZ1. SlSIZ2 was expressed in tomato vegetative and reproductive tissues, and induced by ABA and NaCl. Nucleus-localized SlSIZ2 partially rescued atsiz1-2 dwarfism and also alleviated the sensitivity of atsiz1-2 to ABA and NaCl, suggesting the functional replacement of SlSIZ2 to AtSIZ1. Moreover, SlSIZ2-overexpressing Arabidopsis has higher cotyledon expansion rate, lateral root density and survival rate under salinity stress. These results suggested the contribution of SlSIZ2 to the tolerance of salinity stress.

     

The Influence of Partial Pressure of Carbon Dioxide upon Carbon Metabolism in the Tomato Leaf

The incorporation of radioactive carbon into various photosyntheticproducts was investigated with tomato plants in atmospherescontaining between 40 and 1400 parts/10⁶ carbon dioxide. A significantlygreater proportion of ¹⁴C entered sucrose and alcohol-insolublematerial at high concentrations of carbon dioxide. Incorporationinto glycine and serine was significantly greater at lower carbon-dioxideconcentrations. The pool size of these intermediates was alsodetermined and it was concluded that in the presence of highpartial pressures of carbon dioxide the flow of carbon fromthe photosynthetic cycle through the C² pathway is decreased.     

An Analysis of Some Effects of Humidity on Photosynthesis by a Tomato Canopy under Winter Light Conditions and a Range of Carbon Dioxide Concentrations

The rates of net photosynthesis by closed canopies of tomatoplants were measured at three CO₂ concentrations and three humiditiesover a range of natural light flux densities. The data havebeen analysed using a model of canopy photosynthesis which allowsfor variation in leaf area index and other leaf and canopy characteristics.The model also deals explicitly with the effects of CO₂ concentration,leaf conductance, and photorespiration on the leaf photochemicalefficiency, . The leaves were found to have a photochemicalefficiency in the absence of photorespiration, _m, of 12?6 ?10^–9 kg (CO₂) J^–1. At a CO₂ concentration of 0?73 ? 10^–3 kg m^–3 (400vpm) the leaf photochemical efficiency, , and canopy light utilizationefficiency, _c, were 18 per cent greater at a vapour pressuredeficit of 0?5 kPa than at 1?0 kPa. At a CO₂ concentration of2?2 ? 10^–3 kg m^–3 (1200 vpm) they were only 5 percent greater.     

Effect of Potassium Nutrition on Some Enzymes of the Tomato Plant

Abstract line 12: for ‘below 2.03, 0.53 and 0.28 mequiv.K⁺l^–1 respectively’ read ‘below 0.28, 0.53and 2.03 mequiv. K⁺l^–1 respectively.’     

CO2与养分交互作用对番茄幼苗根生长的影响

在营养液栽培条件下,以番茄（合作906）为研究材料,设计不同的CO2及养分浓度处理,采用定期取样的方法研究番茄定植后根重齄的动态变化及CO2与不同养分供应强度的交互作用对根中碳氮含量与碳氮比的影响。结果表明：番茄苗期根干物质在生长前期积累速率较慢,中后期积累速率较快,在育苗后期CO2对根干物质积累的影响大于前期,根干重对CO2的响应随营养液离子浓度的改变而变化,表明对天番茄幼苗根的生长发育,CO2施肥结合高养分浓度的营养液,才能达到最佳效果。定量分析番茄根干鲜重与生长时间的关系,结果表明：生长条件的改变,会改变番茄根系的生长,对于根鲜重．在较高的CO2条件下,1／2山崎番茄营养液与1／4山崎番茄营养液里生长的根系鲜重在拟合方程中以幂函数拟合得到的相关系数最大,其余处理以二次曲线方程拟合得到的相关系数最大;对于根干重,在较高的CO2条件下,1／2山崎番茄营养液里生长的根系干重在所拟合的方程中以幂函数拟合的相关系数最大,其余的处理以二次曲线方程拟合的相关系数最大。CO2降低了在1／2山崎番茄营养液中生长的根系中的N含量,升高其它营养液处理中的根的N含量,降低了在1／2、1／4山崎番茄营养液中生长的番茄根系中Ｃ的百分含量,增加在1／8、1／16山崎番茄营养液中生长的番茄根系中Ｃ的百分含量,增加所有营养液浓度条件下的Ｃ、N总量,降低根系中的Ｃ／N比,在同一CO2条件下C／N比随营养液浓度的降低而升高。     

光合作用对光和二氧化碳响应的观测方法探讨

用便携式光合仪LI-6400观测自然条件下生长的盆栽蚕豆叶片光合作用对光和二氧化碳的响应发现：（1）用未经过光合诱导的叶片观测光合作用对光的响应会得到即使在全太阳光强下光合作用仍然不饱和的假象;（2）利用某些经验方程计算的饱和光强远低于实际观测值;（3）在观测光合作用对CO2的响应过程中,每一次CO2浓度变化都应当伴随一次光合仪的匹配步骤,否则所得结果偏差很大;（4）在不饱和光下观测光合作用对CO2的响应,会导致对叶片光合能力的低估。     

Effect of Elevated Carbon Dioxide Concentration on the Stomatal Parameters of Rice Cultivars

The response of stomatal parameters of four rice cultivars to atmospheric elevated CO₂ concentration (EC) was studied using open top chambers. EC brought about reduction in stomatal conductance and increase in stomatal index, size of stomatal guard cells, stroma, and epidermal cells. Such acclimation helped the regulation of photosynthesis to EC. These changes in stomatal characters made rice cultivars adjustable to EC environment.     

Effects of Elevated Carbon Dioxide Concentration in the Dark on the Growth of Soybean Seedlings

Previous work has shown that elevated carbon dioxide (CO₂) concentrationsin the dark reversibly reduce the rate of CO₂ efflux from soybeans.Experiments were performed exposing soybean plants continuallyto concentrations of 350 or 700 cm³ m^-3 for 24 h d^-1, or to350 during the day and 700 cm³ m^-3 at night, in order to determinethe importance of the reduced rate of dark CO₂ efflux for plantgrowth. High CO₂ applied only at night conserved carbon andincreased dry mass during initial growth compared with the constant350 cm³ m^-3 treatment. Long-term net assimilation rate was increasedby high CO₂ in the dark, without any increase in daytime leafphotosynthesis. However, leaf area ratio was reduced by thedark CO₂ treatment to values equal to those of plants continuallyexposed to the higher concentration. From days 14-21, leaf areawas less for the elevated night-time CO₂ treatment than foreither the constant 350 or 700 cm³ m^-3 treatments. For the days7-21-period, relative growth rate was significantly reducedby the high night CO₂ treatment compared with the 350 cm³ m^-3continuous treatment. The results indicate that some functionallysignificant component of respiration was reduced by the elevatedCO₂ concentration in the dark.Copyright 1995, 1999 AcademicPress Glycine max L. (Merr.), carbon dioxide, plant growth, respiration     

Microbial Community Responses to Atmospheric Carbon Dioxide Enrichment in a Warm-Temperate Forest

Forest productivity depends on nutrient supply, and sustained increases in forest productivity under elevated carbon dioxide (CO₂) may ultimately depend on the response of microbial communities to changes in the quantity and chemistry of plant-derived substrates, We investigated microbial responses to elevated CO₂ in a warm-temperate forest under free-air CO₂ enrichment for 5 years (1997–2001). The experiment was conducted on three 30 m diameter plots under ambient CO₂ and three plots under elevated CO₂ (200 ppm above ambient). To understand how microbial processes changed under elevated CO₂, we assayed the activity of nine extracellular enzymes responsible for the decomposition of labile and recalcitrant carbon (C) substrates and the release of nitrogen (N) and phosphorus (P) from soil organic matter. Enzyme activities were measured three times per year in a surface organic horizon and in the top 15 cm of mineral soil. Initially, we found significant increases in the decomposition of labile C substrates in the mineral soil horizon under elevated CO₂; this overall pattern was present but much weaker in the O horizon. Beginning in the 4th year of this study, enzyme activities in the O horizon declined under elevated CO₂, whereas they continued to be stimulated in the mineral soil horizon. By year 5, the degradation of recalcitrant C substrates in mineral soils was significantly higher under elevated CO₂. Although there was little direct effect of elevated CO₂ on the activity of N- and P-releasing enzymes, the activity of nutrient-releasing enzymes relative to those responsible for C metabolism suggest that nutrient limitation is increasingly regulating microbial activity in the O horizon. Our results show that the metabolism of microbial communities is significantly altered by the response of primary producers to elevated CO₂. We hypothesize that ecosystem responses to elevated CO₂ are shifting from primary production to decomposition as a result of increasing nutrient limitation.