Examination of the method for measuring soil respiration in cultivated land: Effect of carbon dioxide concentration on soil respiration

An acceleration of soil respiration with decreasing CO₂ concentration was suggested in the field measurements. The result supporrs that obtained in laboratory experiments in our previous study. The CO₂ concentrations in a chamber of the alkali absorption method (the AA-method) were about 150–250 parts/10⁶ lower than that in the atmosphere (about 350 parts/10⁶), while those observed in the open-flow IRGA method (the OF-method) were nearly equal to the soil surface CO₂ levels. The AA-method at such low CO₂ levels in the chamber appears to overestimate the soil respiration. Our results showed that the rates obtained by the AA-method were about twice as large as those by the OF-method in field and laboratory measurements. This finding has important consequences with respect to the validity of the existing data obtained by the AA-method and the estimation of changes in the terrestrial carbon flow with elevated CO₂     

The development of oral vaccines based on live attenuated Salmonella strains

Abstract Safe, live attenuated Salmonella strains can be produced by introducing defined non-reverting mutations into the chromosome. Such rationally attenuated strains have proved to be excellent oral vaccines in several animal species and can therefore be considered as candidate vaccines against invasive salmonellosis in both animals and man. A panel of attenuating lesions is now available from which it is possible to tailor the level of attenuation and hence produce strains with different immunogenic properties. Because of the spectrum of immune responses produced by such Salmonella vaccine strains they have been utilised extensively as vectors for delivering heterologous antigens to the mammalian immune system. We have focussed on the development of a single dose oral tetanus vaccine based on attenuated Salmonella strains expressing a non-toxic, immunogenic protein derived from tetanus toxin (fragment C). Several different expression systems have been used for fragment C and candidate vaccine strains have been constructed that are capable of protecting orally immunised mice against a lethal challenge with tetanus toxin. An oral tetanus vaccine may help to reduce the mortality rate from tetanus in the developing world by overcoming the problems associated with the implementation of vaccine programmes using the current parenteral vaccine.     

Novel Miscanthus hybrids: Modelling productivity on marginal land in Europe using dynamics of canopy development determined by light interception

New biomass crop hybrids for bioeconomic expansion require yield projections to determine their potential for strategic land use planning in the face of global challenges. Our biomass growth simulation incorporates radiation interception and conversion efficiency. Models often use leaf area to predict interception which is demanding to determine accurately, so instead we use low-cost rapid light interception measurements using a simple laboratory-made line ceptometer and relate the dynamics of canopy closure to thermal time, and to measurements of biomass. We apply the model to project the European biomass potentials of new market-ready hybrids for 2020–2030. Field measurements are easier to collect, the calibration is seasonally dynamic and reduces influence of weather variation between field sites. The model obtained is conservative, being calibrated by crops of varying establishment and varying maturity on less productive (marginal) land. This results in conservative projections of miscanthus hybrids for 2020–2030 based on 10% land use conversion of the least (productive) grassland and arable for farm diversification, which show a European potential of 80.7–89.7 Mt year⁻¹ biomass, with potential for 1.2–1.3 EJ year⁻¹ energy and 36.3–40.3 Mt year⁻¹ carbon capture, with seeded Miscanthus sacchariflorus × sinensis displaying highest yield potential. Simulated biomass projections must be viewed in light of the field measurements on less productive land with high soil water deficits. We are attempting to model the results from an ambitious and novel project combining new hybrids across Europe with agronomy which has not been perfected on less productive sites. Nevertheless, at the time of energy sourcing issues, seed-propagated miscanthus hybrids for the upscaled provision of bioenergy offer an alternative source of renewable energy. If European countries provide incentives for growers to invest, seeded hybrids can improve product availability and biomass yields over the current commercial miscanthus variety.     

PHOTOADAPTATION AND THE “PACKAGE” EFFECT IN DUNALIELLA TERTIOLECTA (CHLOROPHYCEAE)1

In the marine unicellular chlorophyte, Dunaliella tertiolecta Butcher, the spectrally averaged m vivo absorption cross section, normalized to chlorophyll a (so-called a* values), vary two-fold in response to changes in growth irradiance. We used a kinetic approach to examine the specific factors which account for these changes in optical properties as cells photoadapt. Using Triton X-100 to solubilize membranes, we were able to differentiate between “package” effects and pigmentation effects. Our analyses suggest that 43–49% of the variability in a* is due to changes in pigmentation, whereas 51–57% is due to the “package” effect. Further analyses revealed that changes in cell sue did not significantly affect packaging, while thylakoid stacking and the transparency of thylakoid membranes were important factors. Our results suggest that thylakoid membrane protein/lipid ratios change during photoadaptation, and these changes influence the effective rate of light harvesting per unit chlorophyll a.     

NITROGEN LIMITATION IN ISOCHRYSIS GALBANA (HAPTOPHYCEAE). I. PHOTOSYNTHETIC ENERGY CONVERSION AND GROWTH EFFICIENCIES1

The effect of steady-state nitrogen limitation on photo-synthetic characteristics and growth efficiency was examined in the marine haptophyte Isochrysis galbana Green. Nitrate limited chemostats were maintained at nine dilution rates, ranging from 0.18-0.96 d^?1, under continuous irradiance levels of 175 μmole quanta·m^?2·s^?1, an irradiance level which saturated photosynthesis at all growth rates. Nitrogen limitation led to an overall reduction in pigmentation and a decrease in the cellular concentration of reaction centers; however, the optical absorption cross section, normalized to Chl a, increased. Moreover, Chl c/a ratios were higher in nitrogen-limited cells: the change in Chl c/a ratios were correlated with an increase in the functional size of Photosystem II. Both light saturated photosynthetic rates normalized per cell and specific respiratory losses were positively linearly correlated with growth rate. Light saturated photosynthetic rates normalized to Chl a remained relatively insensitive to the rate of nitrogen supply. The minimum quantum requirement for gross photosynthetic oxygen evolution increased from 12.4 to 17.0 quanta/O₂. At the growth irradiance, the quantum requirement increased 88%, from 19.9 to 37.5 quauta/O₂ Photosynthesis/respiration ratios remained relatively constant at dilution rates greater than 35% of the maximum relative growth rate. Consequently, net growth efficiency, defined as the ratio of the specific growth rate, μ, to specific gross photosynthesis, P, also remained relatively constant over this range of growth rates averaging 85 ± 3%.     

小麦籽粒充实期氮素的吸收和再分配及6－苄氨基嘌呤的调节作用

小麦从开花至成熟,其根、茎和叶中的Ｎ素不断地进行着分配和再分配,主要是向穗子输出。成熟时穗Ｎ含量占植株总Ｎ的８２％。在总Ｎ净输出的同时各营养器官也有相当程度的对当前土壤Ｎ的净吸收。在籽粒充实阶段用ＢＡ处理叶式穗均影响营养器官及穗子的Ｎ素吸收、分配和再分配。     

Absorption and imagery locate immune responses in the body

Imagery instructions specifying mucosal immunity should alter mucosal immunoglobulin A (m-IgA) levels in high absorbers, whose intent concentration evokes intense physiological responses. After screening for health status, 121 high or low absorbers were randomly assigned to either Relaxation Alone (R), Relaxation with Mucosal Immune Imagery (RI), or Vigilance Task control (VT). Before and after one 60-min intervention, subjects reported theory-relevant psychological variables and provided 5ml whole saliva, which was immediately frozen and assayed lateren masse with enzyme-linked immunoabsorbence (ELISA). MANOVA analysis of psychological variables replicated past research. ANOVA on residualized m-IgA found Time × Absorption interaction and Condition main effects. High more than low absorbers responded to relaxation with mucosal immune imagery by producing higher m-IgA. High absorbers appear able to locate where their immune systems will respond. Individual differences like absorption level need to be emphasized in diagnosis and treatment responsiveness.National Institutes of HealthM. Banks (Jasnoski) Gregerson, Department of Psychology, The George Washington University, changed to The Family Therapy Institute; Ingram M. Roberts, The George Washington University Medical Center, changed to Department of Medicine, Bridgeport Hospital; and Michael M. Amiri, The George Washington University Medical Center, changed to the Department of Neuroscience, NINDS Branch, National Institutes of Health. This research supported by an intra-mural BioMedical Research Grant from The George Washington University, was presented at the 1992 Annual Meeting of the Eastern Psychological Association, Boston, Massachusetts. Special thanks are extended to the following students who assisted instrumentally at various stages: undergraduates Lina Alathari, S. Theodor King, Beth Lieberman, Parisa Lotfi, Anita McClenon, and Karen Siscoe, and graduate student Mariken Hasert.     

Nutrient uptake relationship to root characteristics of rice

Data on root parameters and distribution are important for an improved understanding of the factors influencing nutrient uptake by a crop. Therefore, a study was conducted on a Crowley silt loam at the Rice Research and Extension Center near Stuttgart, Arkansas to measure root growth and N, P and K uptake by three rice (Oryza sativa L.) cultivars at active tillering (36 days after emergence (DAE)), maximum tillering (41 DAE), 1.25 cm internode elongation (55 DAE), booting (77 DAE) and heading (88 DAE). Soil-root core samples were taken to a depth of 40 cm after plant samples were removed, sectioned into 5 cm intervals, roots were washed from soil and root lengths, dry weights and radii were measured. Root parameters were significantly affected by the soil depth × growth stage interaction. In addition, only root radius was affected by cultivar. At the 0- to 5-cm soil depth, root length density ranged from 38 to 93 cm cm^-3 throughout the growing season and decreased with depth to about 2 cm cm^-3 in the 35- to 40-cm depth increment. The increase in root length measured with each succeeding growth stage in each soil horizon also resulted in increased root surface area, hence providing more exposed area for nutrient uptake. About 90% of the total root length was found in the 0- to 20-cm soil depth throughout the season. Average root radius measured in the 0- to 5-cm and 35- to 40-cm depth increments ranged from 0.012 to 0.013 cm and 0.004 to 0.005 cm, respectively throughout the season. Total nutrient uptake by rice differed among cultivars only during vegetative growth. Differences in total nutrient uptake among the cultivars in the field appear to be related to absorption kinetics of the cultivars measured in a growth chamber study. Published with permission of the Arkansas Agricultural Experiment Station.     

Functional analysis of the iron-stress induced CP 43′ polypeptide of PS II in the cyanobacterium Synechococcus sp. PCC 7942

Under conditions of iron-stress, the Photosystem II associated chlorophyll a protein complex designated CP 43, which is encoded by the isiA gene, becomes the major pigment-protein complex in Synechococcus sp. PCC 7942. The isiB gene, which is located immediately downstream of isiA, encodes the protein flavodoxin, which can functionally replace ferredoxin under conditions of iron stress. We have constructed two cyanobacterial insertion mutants which are lacking (i) the CP 43 apoprotein (designated isiA ^–) and (ii) flavodoxin (designated isiB ^–). The function of CP 43 was studied by comparing the cell characteristics, PS II functional absorption cross-sections and Chl a fluorescence parameters from the wild-type, isiA ^– and isiB ^– strains grown under iron-stressed conditions. In all strains grown under iron deprivation, the cell number doubling time was maintained despite marked changes in pigment composition and other cell characteristics. This indicates that iron-starved cells remained viable and that their altered phenotype suggests an adequate acclimation to low iron even in absence of CP 43 and/or flavodoxin. Under both iron conditions, no differences were detected between the three strains in the functional absorption crossection of PS II determined from single turnover flash saturation curves of Chl a fluorescence. This demonstrates that CP 43 is not part of the functional light-harvesting antenna for PS II. In the wild-type and the isiB ^– strain grown under iron-deficient conditions, CP 43 was present in the thylakoid membrane as an uncoupled Chl-protein complex. This was indicated by (1) an increase of the yield of prompt Chl a fluorescence (F_o) and (2) the persistence after PS II trap closure of a fast fluorescence decay component showing a maximum at 685 nm.Abbreviations Chl chlorophyll - CP 43, CP 47 and CP 43 Chl a binding protein complexes of indicated molecular mass - DCMU 3-(3,4-dichlorophenyl)-1,1-dimethylurea - F_m and F_m fluorescence when all PS II reaction centers are dosed in dark- and light-acclimated cells, respectively - F_o fluorescence when all PS II reaction centers are open in dark acclimated cells - F_v variable fluorescence after dark acclimation (F_m–F_o)