The control of respiration in wheat (Triticum aestivum L.) leaves

The aim of this work was to discover whether the respiration of wheat (Triticum aestivum L. cv. Huntsman) leaves, transferred to darkness after 7 h photosynthesis, showed an initial period of wasteful respiration. For young and old leaves, CO₂ production and O₂ uptake after 7 h photosynthesis were up to 56% higher than at the end of an 8-h night. The maximum catalytic activities of citrate synthase (EC 4.1.3.7), aconitase (EC 4.2.1.3), fumarase (EC 4.2.1.2) and cytochrome-c oxidase (EC 1.9.3.1) at the end of the day did not differ from those at the end of the night. Changes in the contents of glucose 6-phosphate, fructose-1,6-bisphosphate, dihydroxyacetone phosphate, and -ketoglutarate did not as a group parallel the changes in the rate of respiration. The detailed distribution of label from [U-¹⁴C] sucrose supplied to leaves in the dark was similar at the end of the day and the end of the night. No correlation was observed between the rates of leaf respiration and extension growth. It is argued that the higher rate of respiration at the beginning of the night cannot be attributed to wasteful respiration.Abbreviation RQ respiratory quotient We thank Dr H. Thomas and Professor C.J. Pollock, Institute for Grassland and Environmental Research, Plas Gogerddan, Aberystwyth, UK for their generous help in measuring leaf extension. R.H.A. thanks the Science and Engineering Research Council for a studentship.     

长白山地区红松树干呼吸的研究

采用土壤呼吸气室于2003年5～10月测定了长白山阔叶红松林主要树种红松不同径阶不同方位的树干呼吸,同时监测了树干温度和林内温度.结果表明,树干呼吸速率具有明显的季节变化趋势,呈单峰曲线,8月出现最大值,2月呼吸速率最低.树干呼吸速率与树干温度具有显著幂指数关系,同时表现出大径阶树干呼吸速率与温度因子间曲线拟合效果好于小径阶红松.不同径阶树干呼吸速率均呈南面高于北面,并随树干径阶的减小南北面呼吸速率差异降低.不同径阶红松树干平均维持呼吸占总树干呼吸63.63%,红松树干径阶越大维持呼吸所占比例越大.依树干径阶大小顺序分别为66.76%、73.29%和50.84%.不同径阶红松树干呼吸Q₁₀值在2.56～3.32之间,利用呼吸Q₁₀值分别获得不同径阶树干R_t和R_m的季节变化趋势.因此,当估算生态系统呼吸时应考虑树干不同部位和不同径阶之间的差异.     

Linkage of formate hydrogenlyase with anaerobic respiration in Proteus mirabilis

The linkage between the enzyme system catalysing formate hydrogenlyase and reductases involved in anaerobic respiration in intact cells of anaerobically grown Proteus mirabilis was studied. Reduction of nitrate and fumarate by molecular hydrogen or formate was possible under all growth conditions; reduction of tetrathionate and thiosulphate occurred only in cells harvested at late growth phase from a pH-regulated batch culture and not in cells harvested at early growth phase or in cells grown in pH-auxostat culture. Under all conditions, cells possessed the enzyme tetrathionate reductase. We conclude that linkage between tetrathionate reductase (catalysing also reduction of thiosulphate) and the formate hydrogenlyase chain is dependent on growth conditions. During reduction of high-potential oxidants such as fumarate, tetrathionate (when possible) or the artificial electron acceptor methylene blue by formate, there was no simultaneous H₂ evolution due to the formate hydrogenlyase reaction. H₂ production started only after complete reduction of methylene blue or fumarate, in the case of methylene blue after a lag phase without gas production. In preparations with a low fumarate reduction activity this was accompanied by an acceleration in CO₂ production. During reduction of thiosulphate (a low-potential oxidant) or of tetrathionate in the presence of benzyl viologen (a low-potential mediator) by formate, H₂ was evolved simultaneously. From this we conclude that formate hydrogenlyase is regulated by a factor that responds to the redox state of any electron acceptor couple present such that lyase activity is blocked when the acceptor couple is oxidised to too great an extent.     

The electrochemical proton potential and the proton/electron ratio of the electron transport with fumarate in Wolinella succinogenes

The electrochemical proton potential across the cytoplasmic membrane ( ) as well as the H⁺ / e ratio, which were brought about by the electron transport of Wolinella succinogenes, was measured with the aim of understanding the mechanism of electron-transport-coupled phosphorylation in this anaerobic bacterium. (1) Inverted vesicles derived from the bacterial membrane were found to take up protons from the external medium on initiation of fumarate reduction by H₂. Proton uptake was dependent on the presence of K⁺ within the vesicles, was enhanced by the presence of valinomycin and DCCD and high internal buffer concentration, and was abolished by protonophores. The maximum H⁺ / e ratio slightly exceeded 1. (2) The vesicles accumulated thiocyanate in the steady state of fumarate reduction by H₂. The concentration ratio (internal / external) was close to 1000 at an external thiocyanate concentration below 10 μM. Under the same conditions the uptake of methylamine was negligible. Thiocyanate uptake was abolished by the presence of a protonophore. (3) Cells of W. succinogenes accumulated tetraphenylphosphonium cation (TPP) in the steady state of fumarate reduction with H₂ or formate. Under the same conditions the uptake of benzoic acid was negligible. From the amount of TPP taken up by the bacteria, the free internal concentration of TPP was evaluated according to the procedure of Zaritsky et al. (Zaritsky, A., Kihara, M. and MacNab, R.M. (1981) J. Membrane Biol. 63, 215–231). The concentration ratio (internal / external) was 700 in the absence and close to 1 in the presence of a protonophore or in the absence of external Na⁺. (4) The experimental results are consistent with the view that the energy transduction from electron transport to phosphorylation is done by means of the across the bacterial membrane.     

Respiratory responses of higher plants to atmospheric CO2 enrichment

Although the respiratory response of native and agricultural plants to atmospheric CO₂ enrichment has been reported over the past 75 years, only recently have these effects emerged as prominent measures of plant and ecosystem response to the earth's changing climate. In this review we discuss this rapidly expanding field of study and propose that both increasing and decreasing rates of leaf and whole-plant respiration are likely to occur in response to rising CO₂ concentrations. While the stimulatory effects of CO₂ on respiration are consistent with our knowledge of leaf carbohydrate status and plant metabolism, we wish to emphasize the rather surprising short-term inhibition of leaf respiration by elevated CO₂ and the reported effects of long-term CO₂ exposure on growth and maintenance respiration. As is being found in many studies, it is easier to document the respiratory response of higher plants to elevated CO₂ than it is to assign a mechanistic basis for the observed effects. Despite this gap in our understanding of how respiration is affected by CO₂ enrichment, data are sufficient to suggest that changes in leaf and whole-plant respiration may be important considerations in the carbon dynamics of terrestrial ecosystems as global CO₂ continues to rise. Suggestions for future research that would enable these and other effects of CO₂ on respiration to be unravelled are presented.     

Terrestrial higher-plant response to increasing atmospheric [CO2] in relation to the global carbon cycle

Terrestrial higher plants exchange large amounts of CO₂ with the atmosphere each year; c. 15% of the atmospheric pool of C is assimilated in terrestrial-plant photosynthesis each year, with an about equal amount returned to the atmosphere as CO₂ in plant respiration and the decomposition of soil organic matter and plant litter. Any global change in plant C metabolism can potentially affect atmospheric CO₂ content during the course of years to decades. In particular, plant responses to the presently increasing atmospheric CO₂ concentration might influence the rate of atmospheric CO₂ increase through various biotic feedbacks. Climatic changes caused by increasing atmospheric CO₂ concentration may modulate plant and ecosystem responses to CO₂ concentration. Climatic changes and increases in pollution associated with increasing atmospheric CO₂ concentration may be as significant to plant and ecosystem C balance as CO₂ concentration itself. Moreover, human activities such as deforestation and livestock grazing can have impacts on the C balance and structure of individual terrestrial ecosystems that far outweigh effects of increasing CO₂ concentration and climatic change. In short-term experiments, which in this case means on the order of 10 years or less, elevated atmospheric CO₂ concentration affects terrestrial higher plants in several ways. Elevated CO₂ can stimulate photosynthesis, but plants may acclimate and (or) adapt to a change in atmospheric CO₂ concentration. Acclimation and adaptation of photosynthesis to increasing CO₂ concentration is unlikely to be complete, however. Plant water use efficiency is positively related to CO₂ concentration, implying the potential for more plant growth per unit of precipitation or soil moisture with increasing atmospheric CO₂ concentration. Plant respiration may be inhibited by elevated CO₂ concentration, and although a naive C balance perspective would count this as a benefit to a plant, because respiration is essential for plant growth and health, an inhibition of respiration can be detrimental. The net effect on terrestrial plants of elevated atmospheric CO₂ concentration is generally an increase in growth and C accumulation in phytomass. Published estimations, and speculations about, the magnitude of global terrestrial-plant growth responses to increasing atmospheric CO₂ concentration range from negligible to fantastic. Well-reasoned analyses point to moderate global plant responses to CO₂ concentration. Transfer of C from plants to soils is likely to increase with elevated CO₂ concentrations because of greater plant growth, but quantitative effects of those increased inputs to soils on soil C pool sizes are unknown. Whether increases in leaf-level photosynthesis and short-term plant growth stimulations caused by elevated atmospheric CO₂ concentration will have, by themselves, significant long-term (tens to hundreds of years) effects on ecosystem C storage and atmospheric CO₂ concentration is a matter for speculation, not firm conclusion. Long-term field studies of plant responses to elevated atmospheric CO₂ are needed. These will be expensive, difficult, and by definition, results will not be forthcoming for at least decades. Analyses of plants and ecosystems surrounding natural geological CO₂ degassing vents may provide the best surrogates for long-term controlled experiments, and therefore the most relevant information pertaining to long-term terrestrial-plant responses to elevated CO₂ concentration, but pollutants associated with the vents are a concern in some cases, and quantitative knowledge of the history of atmospheric CO₂ concentrations near vents is limited. On the whole, terrestrial higher-plant responses to increasing atmospheric CO₂ concentration probably act as negative feedbacks on atmospheric CO₂ concentration increases, but they cannot by themselves stop the fossil-fuel-oxidation-driven increase in atmospheric CO₂ concentration. And, in the very long-term, atmospheric CO₂ concentration is controlled by atmosphere-ocean C equilibrium rather than by terrestrial plant and ecosystem responses to atmospheric CO₂ concentration.     

Oxygen-exchange studies in Chlamydomonas mutants deficient in photosynthetic electron transport: Evidence for a Photosystem II-dependent oxygen uptake in vivo

Photosynthetic oxygen exchange has been measured using ¹⁸O₂ and the mass-spectrometric technique in two mutant strains of Chlamydomonas reinhardtii deficient in electron transport. In the F15 mutant, deficient in PS I, O₂ was evolved in the light at a constant rate of about 145 nmol O₂/min per mg chlorophyll. At the same time, O₂ uptake was increased in the light by about 28%. O₂ evolution and the light-stimulation of O₂ uptake were inhibited by 3-(3,4-dichlorophenyl)-1,1-dimethylurea. Antimycin A and salicylhydroxamic acid, both inhibitors of mitochondrial respiration, when added together, inhibited dark respiration and also the light-dependent O₂ evolution by about 80%. Similar properties were observed in a mutant strain of Chlamydomonas (F18) lacking the cytochrome b₆-f complex. We conclude from these results that in the absence of active Photosystem I, a permanent electron flow can occur in the light from Photosystem II to molecular O₂. This electron transfer pathway would involve the plastoquinone pool and the mitochondrial electron transport chain. Because O₂ evolution measured in the F15 mutant was severely inhibited by the uncoupler cyanide m-chlorophenylhydrazone, we propose that an energy-dependent reverse electron transfer similar to that of Rhodospirillaceae might occur in the chloroplast of Chlamydomonas.     

九段沙不同演替阶段湿地土壤微生物呼吸的差异性及其影响因素

通过分析九段沙不同演替阶段湿地土壤微生物呼吸及其土壤微环境因子,研究了不同类型湿地土壤微生物呼吸的差异性及其影响因素。结果表明,处于不同植被演替阶段的湿地土壤微生物呼吸具有显著差异(P0.05),海三棱藨草区高于芦苇区,互花米草区最高(0.367 mg.g-1.(24h)-1),互花米草的引种及蔓延增强了入侵区域土壤微生物呼吸。综合考虑不同植被类型湿地土壤微生物呼吸及植被生物量,芦苇区呼吸微弱、植被生物量最高,在理论上具有更高的有机碳碳汇聚能力。通径分析结果显示,影响土壤微生物呼吸强度的主要生物因素有:原核微生物多样性(Shannon指数)和土壤微生物生物量;土壤有机质、硝态氮及土壤含水量对上述微生物活性指标有显著影响,因此也属于土壤微生物呼吸的主要影响因素。     

Arbuscular mycorrhizal colonization on carbon economy in perennial ryegrass: quantification by 13CO2/12CO2 steady-state labelling and gas exchange

Effects of the arbuscular mycorrhizal fungus (AMF) Glomus hoi on the carbon economy of perennial ryegrass (Lolium perenne) were investigated by comparing nonmycorrhizal and mycorrhizal plants of the same size, morphology and phosphorus status. Plants were grown in the presence of CO2 sources with different C isotope composition (delta13C -1 or -44). Relative respiration and gross photosynthesis rates, and belowground allocation of C assimilated during one light period ('new C'), as well as its contribution to respiration, were quantified by the concerted use of 13CO2/12CO2 steady-state labelling and 13CO2/12CO2 gas-exchange techniques. AMF (G. hoi) enhanced the relative respiration rate of the root + soil system by 16%, inducing an extra C flow amounting to 3% of daily gross photosynthesis. Total C flow into AMF growth and respiration was estimated at < 8% of daily gross photosynthesis. This was associated with a greater amount of new C allocated belowground and respired in mycorrhizal plants. AMF colonization affected the sources supplying belowground respiration, indicating a greater importance of plant C stores in supplying respiration and/or the participation of storage pools within fungal tissues. When ontogenetic and nutritional effects were accounted for, AMF increased belowground C costs, which were not compensated by increased photosynthesis rates. Therefore the instantaneous relative growth rate was lower in mycorrhizal plants.     

Effects of elevated O3 and CO2 concentrations on photosynthesis and stomatal conductance in Scots pine

Naturally regenerated Scots pines (Pinus sylvestris L.), aged 28–30 years old, were grown in open-top chambers and subjected in situ to three ozone (O₃) regimes, two concentrations of CO₂, and a combination of O₃ and CO₂ treatments From 15 April to 15 September for two growing seasons (1994 and 1995). The gas exchanges of current-year and 1-year-old shoots were measured, along with the nitrogen content of needles. In order to investigate the factors underlying modifications in photosynthesis, five parameters linked to photosynthetic performance and three to stomatal conductance were determined. Elevated O₃ concentrations led to a significant decline in the CO₂ compensation point (Г^*), maximum RuP₂-saturated rate of carboxylation (V_cmax), maximum rate of electron transport (J_max), maximum stomatal conductance (g_smax), and sensitivity of stomatal conductance to changes in leaf-to-air vapour pressure difference (?g_s/?D_v) in both shoot-age classes. However, the effect of elevated O₃ concentrations on the respiration rate in light (R_d) was dependent on shoot age. Elevated CO₂(700 μmol mol^?1) significantly decreased J_max and g_smax but increased R_d in 1-year-old shoots and the ?g_s/?D_v in both shoot-age classes. The interactive effects of O₃ and CO₂ on some key parameters (e.g. V_cmax and J_max) were significant. This may be closely related to regulation of the maximum stomatal conductance and stomatal sensitivity induced by elevated CO₂. As a consequence, the injury induced by O₃ was reduced through decreased ozone uptake in 1-year-old shoots, but not in the current-year shoots. Compared to ambient O₃ concentration, reduced O₃ concentrations (charcoal-filtered air) did not lead to significant changes in any of the measured parameters. Compared to the control treatment, calculations showed that elevated O₃ concentrations decreased the apparent quantum yield by 15% and by 18%, and the maximum rate of photosynthesis by 21% and by 29% in the current-year and 1-year-old shoots, respectively. Changes in the nitrogen content of needles resulting from the various treatments were associated with modifications in photosynthetic components.     

Large annual net ecosystem CO2 uptake of a Mojave Desert ecosystem

The net ecosystem CO₂ exchange (NEE) between a Mojave Desert ecosystem and the atmosphere was measured over the course of 2 years at the Mojave Global Change Facility (MGCF, Nevada, USA) using the eddy covariance method. The investigated desert ecosystem was a sink for CO₂, taking up 102±67 and 110±70 g C m⁻² during 2005 and 2006, respectively. A comprehensive uncertainty analysis showed that most of the uncertainty of the inferred sink strength was due to the need to account for the effects of air density fluctuations on CO₂ densities measured with an open-path infrared gas analyser. In order to keep this uncertainty within acceptable bounds, highest standards with regard to maintenance of instrumentation and flux measurement postprocessing have to be met. Most of the variability in half-hourly NEE was explained by the amount of incident photosynthetically active radiation (PAR). On a seasonal scale, PAR and soil water content were the most important determinants of NEE. Precipitation events resulted in an initial pulse of CO₂ to the atmosphere, temporarily reducing NEE or even causing it to switch sign. During summer, when soil moisture was low, a lag of 3–4 days was observed before the correlation between NEE and precipitation switched from positive to negative, as opposed to conditions of high soil water availability in spring, when this transition occurred within the same day the rain took place. Our results indicate that desert ecosystem CO₂ exchange may be playing a much larger role in global carbon cycling and in modulating atmospheric CO₂ levels than previously assumed – especially since arid and semiarid biomes make up >30% of Earth's land surface.     

夏谷群体呼吸特性及其与群体光合的关系

中秆大穗型和矮秆紧凑型2种不同类型的夏谷群体呼吸速率在整个生育时期的变化呈单峰曲线,且随密度的增大而提高,抽穗开花期达最大值,紧凑型品种后期呼吸速率高于中秆大穗型品种,后期呼吸消耗大是低产的重要原因,群体呼吸日变化为一随温度而变化的单峰曲线,群体呼吸速率在冠层中的分布,依此是上3叶＞茎鞘＞中3叶＞穗＞下部叶,群体呼吸／光合的比值,两品种相近,在47％左右。