氮添加对沙质草地微生物呼吸与根系呼吸的影响

土壤呼吸可以细化为根系呼吸和微生物呼吸,二者对氮添加的响应有所不同.本文以科尔沁沙质草地为研究对象,探讨氮添加对土壤CO₂排放的影响,并细化为微生物呼吸和根系呼吸的响应特征.结果表明: 在观测期(5—10月),土壤呼吸、微生物呼吸月动态均呈先升高后降低的趋势;微生物呼吸是土壤呼吸的主要贡献者,占82.6%;观测期内根系呼吸贡献率随月份而变化,根系呼吸贡献率两个峰值分别出现在5月(占49.4%)和8月(占41.9%),6个月的平均贡献率为17.4%;在10 ℃条件下,根系呼吸较微生物呼吸对氮添加的响应更为敏感,微生物呼吸速率在氮添加后降低了3.9%,而根系呼吸降低了17.7%;氮添加提高了土壤呼吸、微生物呼吸温度敏感性Q₁₀值,也提高了二者对土壤水分变化的敏感程度.     

The amino acid nutrition of respiration deficient and respiration competentSaccharomyces

Respiration deficient variants and normal, respiration competent strains ofSaccharomyces require an exogenous supply of arginine, glutamic acid, leucine, lysine and valine to attain optimal growth. The growth of variant cells, however, is stimulated by these compounds to a far greater proportionate extent than that of normal cells. The petite condition, therefore, exaggerates the limitations in amino acid biosyntheses existent in normal yeasts but does not create new ones. The relative respiratory limitations characteristic of petite and normal cells during growth will account for the qualitative and quantitative aspects of their amino acid requirements.     

土壤-玉米系统中土壤呼吸强度及各组分贡献

用特殊设计的气体采集箱法对玉米生长期间潮土呼吸强度进行了测定。结果表明,施用150kgNhm^-2的裸地土壤CO2累积排放量是294g C m^-2,约为种植玉米土壤的一半。用根去除法测得的玉米对土壤呼吸的贡献率,苗期小于20％,拔节到收获期波动在30％-70％之间,全生长期平均为46％。玉米生长期间因土壤有机碳分解而释放出的CO2总量为2．94MgChm^-2,大约是0—40cm土层中土壤有机碳总储存量的8％,因此需要输入7．35Mghm^-2的碳含量40％的作物残留物才能平衡土壤中有机碳的损失,约为玉米收获时残留于土壤中根量的一倍,但与残留根量及玉米生长期间根系分泌到土壤的有机物量的总和相当,因此土壤中有机碳总体处于平衡状态。在玉米生长期间,施用氮肥可使土壤CO2排放量降低10％。土壤排放CO2主要受土壤温度的影响,温度效应Q10为1．90-2．88。     

Effects of respiration on cardiac performance

The conventional explanation for the fall in left ventricular stroke volume (LVSV) with inspiration is that blood pools in the lungs, thereby decreasing pulmonary venous return. In anesthetized dogs, we have found an increase in left ventricular filling pressure (LVFP) with both constant and increasing lung volume during an inspiratory effort. Transmural aortic diastolic pressure rises as LVSV falls and LVFP rises consistent with the hypothesis that a fall in pleural pressure afterloads the left ventricle. Additionally the increase found in right ventricular filling pressure with inspiration may adversely affect LV performance by decreasing LV compliance and/or contractility. Our findings are incompatible with pooling of blood in the lungs being the primary determinant of the fall in LVSV with inspiration.     

Effect of respiratory apparatus on respiration

A mouthpiece plus noseclip (MP + NC) is frequently used in performing measurements of breathing patterns. Although the effects the apparatus exerts on breathing patterns have been studied, the mechanism of the changes it causes remains unclear. The current study examines the effects on respiratory patterns of a standard (17-mm-diam) MP + NC during room air (RA) breathing and the administration of 2 and 4% CO2 in normal volunteers and in patients 2-4 days after abdominal operation. When compared with values obtained with a noninvasive canopy system, the MP + NC induced increases in minute ventilation (VE), tidal volume (VT), and mean inspiratory flow (VT/TI), but not frequency (f) or inspiratory duty cycle, during both RA and CO2 administration. The percentage increase in VE, VT, and VT/TI caused by the MP + NC decreased as the concentration of CO2 increased. During RA breathing, the application of noseclip alone resulted in a decrease in f and an increase in VT, but VE and VT/TI were unchanged. The changes were attenuated during the administration of 2 and 4% CO2. Reducing the diameter of the mouthpiece to 9 mm abolished the alterations in breathing pattern observed with the larger (17-mm) diameter MP.     

Enzymes of aerobic respiration on iron

Abstract: Bacteria capable of aerobic respiration on ferrous ions are spread throughout eubacterial and archaebacterial phyla. Comparative spectroscopic analyses revealed that phylogenetically distinct organisms expressed copious quantities of spectrally distinct redox-active biomolecules during autotrophic growth on soluble iron. Thiobaeillus ferrooxidans, Leptospirillum ferrooxidans, Sulfobacillus thermosulfidooxidans , and Metallosphaera sedula possessed iron respiratory chains dominated by a blue copper protein, a novel red cytochrome, a novel yellow protein, and a novel yellow cytochrome, respectively. Further investigation of each type of respiratory chain will be necessary to deduce the advantages and disadvantages of each.     

Investigations on microbial sulfur respiration

The reduction of elemental or sulfane sulfur to hydrogen sulfide by eubacteria was investigated. Spirillum 5175 had the most active sulfur oxidoreductase. It could be cultivated with fumarate (F), elemental sulfur (S) or nitrate (N) as electron acceptor. Maximum activity was found for Spirillum 5175_S but activity was also present in Spirillum 5175_F and Spirillum 5175_N, i.e. the sulfur oxidoreductase is a constitutive enzyme. It was localized in the membrane, and no activity was found in the cytoplasm in contrast to Desulfovibrio baculatus. Different procedures were applied for the measurement of the sulfur oxidoreductase activity. In the manometric assay hydrogenase was coupled to the sulfur oxidoreductase, and the uptake of dihydrogen was measured in the presence of elemental sulfur. Alternatively, H₂S was assayed directly or was trapped in 12% NaOH and determined by the methylene blue procedure. Using ³⁵S sulfur and ³⁵S-labelled compounds both the substrate and H₂S could be measured. A further increase in sensitivity was achieved using phenosafranin. It was reduced photochemically, and served as the electron donor to the sulfur oxidoreductase, i.e. no hydrogenase was required. This was an important result in view of the fact that not all sulfur-reducing bacteria contain hydrogenase. However, in those cases the hydrogenase isolated from Clostridium pasteurianum could be coupled to the sulfur oxidoreductase. Among the different forms of elemental sulfur Janek sulfur gave the best results in terms of activity and reproducibility. The reduction of elemental sulfur to hydrogen sulfide had a pH optimum at pH 8.7–8.9. There was always a lag-phase which was pH-dependent. During this period the turbidity of the solution changed. Addition of thiols, such as GSH, shortened the lag-phase and caused an increase in activity of the sulfur oxidoreductase. In the presence of p-chloromercuribenzenesulfonic acid the reaction rate decreased significantly. Comparable reaction rates and activity values of the sulfur oxidoreductase in Spirillum 5175_F were obtained with organic trisulfides, RS-S-SR. In contrast to elemental sulfur RS-S-SR are well-defined chemical compounds suitable for quantitative and mechanistic investigations. Labelling the central sulfur of RS-S-SR with ³⁵S gave a satisfactory recovery of the total radioactivity in form of (³⁵S) H₂S in our assay. Trisulfides were shown to be formed as reactive intermediates in bacteria. This process required the sulfur transferase rhodanese which was present in Spirillum 5175, or other sulfur-reducing eubacteria.Abbreviations EPR Electron Paramagnetic Resonance - A Absorbance - PCMS p-chloromercuribenzenesulfonic acid - Sp. 5175_F Splrillum 5175 grown with fumarate - Sp. 5175_S with sulfur - Sp. 5175_N with nitrate - SCE Standard Calomel Electrode