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1.
During 4 years continuous measurements of N-trace gas exchange were carried out at the forest floor-atmosphere interface at the Höglwald Forest that is highly affected by atmospheric N-deposition. The measurements included spruce control, spruce limed and beech sites. Based on these field measurements and on intensive laboratory measurements of N2-emissions from the soils of the beech and spruce control sites, a total balance of N-gas emissions was calculated. NO2-deposition was in a range of –1.6 –2.9 kg N ha–1 yr–1 and no huge differences between the different sites could be demonstrated. In contrast to NO2-deposition, NO- and N2O-emissions showed a huge variability among the different sites. NO emissions were highest at the spruce control site (6.4–9.1 kg N ha–1 yr–1), lowest at the beech site (2.3–3.5 kg N ha–1 yr–1) and intermediate at the limed spruce site (3.4–5.4 kg N ha–1 yr–1). With regard to N2O-emissions, the following ranking between the sites was found: beech (1.6–6.6 kg N ha–1 yr–1) >> spruce limed (0.7–4.0 kg N ha–1 yr–1) > spruce control (0.4–3.1 kg N ha–1 yr–1). Average N-trace gas emissions (NO, NO2, N2O) for the years 1994–1997 were 6.8 kg N ha–1 yr–1 at the spruce control site, 3.6 kg N ha–1 yr–1 at the limed spruce site and 4.5 kg N ha–1 yr–1 at the beech site. Considering N2-losses, which were significantly higher at the beech (12.4 kg N ha–1 yr–1) than at the spruce control site (7.2 kg N ha–1 yr–1), the magnitude of total gaseous N losses, i.e. N2-N + NO-N + NO2-N + N2O-N, could be calculated for the first time for a forest ecosystem. Total gaseous N-losses were 14.0 kg N ha–1 yr–1 at the spruce control site and 15.5 kg N ha–1 yr–1 at the beech site, respectively. In view of the huge interannual variability of N-trace gas fluxes and the pronounced site differences in N-gas emissions it is concluded that more research is needed in order to fully understand patterns of microbial N-cycling and N-gas production/emission in forest ecosystems and mechanisms of reactions of forest ecosystems to the ecological stress factor of atmospheric N-input. 相似文献
2.
In order to gain information about seasonal and interannual variations of CH4-fluxes at a spruce control site, a limed spruce site and a beech site of the Höglwald Forest, Bavaria, Germany, complete annual cycles of CH4-exchange between the soil and the atmosphere with 2-hourly resolution were followed for 4 consecutive years. The ranges of CH4 fluxes observed for the different sites were: +12.4 to –69.4 g CH4 m–2 h–1 (spruce control site), +11.7 to –51.4 g CH4 m–2 h–1 (limed spruce site), and –4.4 to –167.3 g CH4 m–2 h–1 (beech site). Lowest rates of atmospheric CH4-uptake or even a weak net-emission of CH4 by the soils were observed during winter/spring times, whereas highest rates of CH4-uptake were always found in summer/spring. Over the entire observation period of 4 years, mean CH4-uptake rates were –1.82 kg CH4-C ha–1 yr–1 at the spruce control site, –1.31 kg CH4-C ha–1 yr–1 at the limed spruce site, and –4.84 kg CH4-C ha–1 yr–1 at the beech site. The results obtained in this study demonstrate that in view of the huge interannual variations in CH4-fluxes of approx. 1 kg CH4-C ha–1 yr–1, multiple year measurements of CH4-fluxes are necessary to accurately characterize the sink strength of temperate forest for atmospheric CH4. By comparison of CH4-fluxes measured at the spruce control site and the limed spruce site, a significant negative effect of forest floor liming on CH4-uptake could be demonstrated. Compared to the spruce stand, the beech stand showed on average approx. 3 times higher rates of atmospheric CH4-uptake, most likely due to pronounced differences between both sites with regard to the organic layer structure and bulk density of the mineral soil. Regression analysis between CH4-fluxes and environmental parameters revealed that at all sites the dominating factors regulating temporal variations of CH4 fluxes were soil moisture and soil temperature. Field measurements of CH4 concentrations in the soil profile and laboratory measurements of CH4-oxidation and CH4-production activity on soil samples taken from different soil depths showed that the CH4-flux at the Höglwald Forest sites is the net-result of simultaneous occurring production and consumption of CH4 within the soil. Highest CH4-oxidation activity was found in the uppermost centimeters of the mineral soil, whereas highest potential CH4-production activity was found in the organic layer. 相似文献
3.
L. Adamec 《Biologia Plantarum》2005,49(2):247-255
Various ecophysiological investigations on carnivorous plants in wet soils are presented. Radial oxygen loss from roots of Droseraceae to an anoxic medium was relatively low 0.02 – 0.07 mol(O2) m– 2 s–1 in the apical zone, while values of about one order of magnitude greater were found in both Sarracenia rubra roots and Genlisea violacea traps. Aerobic respiration rates were in the range of 1.6 – 5.6 mol kg–1 (f.m.) s–1 for apical root segments of seven carnivorous plant species and 0.4 – 1.1 mol kg–1 (f.m.) s–1 for Genlisea traps. The rate of anaerobic fermentation in roots of two Drosera species was only 5 – 14 % of the aerobic respiration. Neither 0.2 mM NaN3 nor 0.5 mM KCN influenced respiration rate of roots and traps. In all species, the proportion of cyanide-resistant respiration was high and amounted to 65 – 89 % of the total value. Mean rates of water exudation from excised roots of 12 species ranged between 0.4 – 336 mm 3 kg–1 (f.m.) s–1 with the highest values being found in the Droseraceae. Exudation from roots was insensitive to respiration inhibitors. No significant difference was found between exudation rates from roots growing in situ in anoxic soil and those kept in an aerated aquatic medium. Carnivorous plant roots appear to be physiologically very active and well adapted to endure permanent soil anoxia. 相似文献
4.
Petz M Stabentheiner A Crailsheim K 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》2004,174(7):511-518
The CO2 production of individual larvae of Apis mellifera carnica, which were incubated within their cells at a natural air humidity of 60–80%, was determined by an open-flow gas analyzer in relation to larval age and ambient temperature. In larvae incubated at 34 °C the amount of CO2 produced appeared to fall only moderately from 3.89±1.57 µl mg–1 h–1 in 0.5-day-old larvae to 2.98±0.57 µl mg–1 h–1 in 3.5-day-old larvae. The decline was steeper up to an age of 5.5 days (0.95±1.15 µl mg–1 h–1). Our measurements show that the respiration and energy turnover of larvae younger than about 80 h is considerably lower (up to 35%) than expected from extrapolations of data determined in older larvae. The temperature dependency of CO2 production was determined in 3.5-day-old larvae, which were incubated at temperatures varying from 18 to 38 °C in steps of 4 °C. The larvae generated 0.48±0.03 µl mg–1 h–1 CO2 at 18 °C, and 3.97±0.50 µl mg–1 h–1 CO2 at 38 °C. The temperature-dependent respiration rate was fitted to a logistic curve. We found that the inflection point of this curve (32.5 °C) is below the normal brood nest temperature (33–36 °C). The average Q10 was 3.13, which is higher than in freshly emerged resting honeybees but similar to adult bees. This strong temperature dependency enables the bees to speed up brood development by achieving high temperatures. On the other hand, the results suggest that the strong temperature dependency forces the bees to maintain thermal homeostasis of the brood nest to avoid delayed brood development during periods of low temperature.Abbreviations m body mass - R rate of development or respiration - TI inflexion point of a logistic (sigmoid) curve - TL lethal temperature - TO temperature of optimum (maximum) developmentCommunicated by G. Heldmaier 相似文献
5.
Effect of tree distance on N2O and CH4-fluxes from soils in temperate forest ecosystems 总被引:5,自引:2,他引:3
Complete annual cycles of N2O and CH4 flux in forest soils at a beech and at a spruce site at the Höglwald Forest were followed in 1997 by use of fully automatic measuring systems. In order to test if on a microsite scale differences in the magnitude of trace gas exchange between e.g. areas in direct vicinity of stems and areas in the interstem region at both sites exist, tree chambers and gradient chambers were installed in addition to the already existing interstem chambers at our sites. N2O fluxes were in a range of –4.6–473.3 g N2O-N m–2 h–1 at the beech site and in a range of –3.7–167.2 g N2O-N m–2 h–1 at the spruce site, respectively. Highest N2O emissions were observed during and at the end of a prolonged frost period, thereby further supporting previous findings that frost periods are of crucial importance for controlling annual N2O losses from temperate forests. Fluxes of CH4 were in a range of +10.4––194.0 g CH4 m–2 h–1 at the beech site and in a range of –4.4––83.5 g CH4 m–2 h–1 at the spruce site. In general, both N2O-fluxes as well as CH4-fluxes were higher at the beech site. On a microsite scale, N2O and CH4 fluxes at the beech site were highest within the stem area (annual mean: 49.6±3.3 g N2O-N m–2 h–1; –77.2±3.1 g CH4 m–2 h–1), and significantly lower within interstem areas (18.5±1.4 g N2O-N m–2 h–1; –60.2±1.8 g CH4 m–2 h–1). Significantly higher values of total N, C and pH in the organic layer, as well as increased soil moisture, especially in spring, in the stem areas, are likely to contribute to the higher N2O fluxes within the stem area of the beech. Also for the spruce site, such differences in trace gas fluxes could be demonstrated to exist (mean annual N2O emission within (a) stem areas: 9.7±0.9 g N2O-N m–2 h–1 and (b) interstem areas: 6.2±0.6 g N2O-N m–2 h–1; mean annual CH4 uptake within (a) stem areas: –26.1±0.6 g CH4 m–2 h–1 and (b) interstem areas: –38.4±0.8 g CH4 m–2 h–1), though they were not as pronounced as at the beech site. 相似文献
6.
In order to quantify N2-emissions from a spruce and a beech site at the Höglwald Forest, a new measuring system was developed, that allowed simultaneous, direct determination of N2- and N2O-emission with high accuracy (detection limit approx. 10 g N m–2 h–1 for N2 and <1 g for N2O) using a gas-flow core method. This method requires exchange of the soil atmosphere with an artificial atmosphere, that differs only in that N2 is substituted by He. The measuring system, the methodology of measurements and validation experiments are described in detail. Due to the huge heterogeneity of denitrification activity in different soil cores taken from our forest sites, no general trends of N2 and N2O production in relation to soil moisture and temperature could be demonstrated. Based on reasonable number of measurements, this work gives for the first time an estimate of the magnitude of N2-losses from temperate forest soils. Both the magnitude of N2-emissions (spruce: 7.2±0.7 kg N2-N ha–1 yr–1; beech: 12.4±3.1 kg N2-N ha–1 yr–1), as well as the N2O–N2 ratio (spruce: 0.136±0.04; beech: 0.52±0.19) were significantly higher for soils from the beech sites as compared to soils from the spruce site. The results suggests that N2-emissions from N-saturated forest soils, still receiving high loads of atmospheric N-deposition, are approx. 30% of atmospheric N-input at the spruce site, and approx. 50% at the beech site. Our results demonstrate that losses of nitrogen in the form of N2 cannot be neglected in the context of calculating N-balances for given forest sites. 相似文献
7.
Seedlings of loblolly pine (Pinus taeda L.) were grown under varying conditions of soil nitrogen and atmospheric carbon dioxide availability to investigate the interactive effects of these resources on the energetic requirements for leaf growth. Increasing the ambient CO2 partial pressure from 35 to 65 Pa increased seedling growth only when soil nitrogen was high. Biomass increased by 55% and photosynthesis increased by 13% after 100 days of CO2 enrichment. Leaves from seedlings grown in high soil nitrogen were 7.0% more expensive on a g glucose g–1 dry mass basis to produce than those grown in low nitrogen, while elevated CO2 decreased leaf cost by 3.5%. Nitrogen and CO2 availability had an interactive effect on leaf construction cost expressed on an area basis, reflecting source-sink interactions. When both resources were abundant, leaf construction cost on an area basis was relatively high (81.8±3.0 g glucose m–2) compared to leaves from high nitrogen, low CO2 seedlings (56.3±3.0 g glucose m–2) and low nitrogen, low CO2 seedlings (67.1±2.7 g glucose m–2). Leaf construction cost appears to respond to alterations in the utilization of photoassimilates mediated by resource availability. 相似文献
8.
Strawberry (Fragaria ananassaDuch. cv. Fengxiang) plantlets were cultured under two in vitroenvironments for rooting, and then acclimatized under two ex vitroirradiance conditions. At the end of rooting stage plant height, fresh weight and specific leaf area of T1-plants grown under high sucrose concentration (3 sucrose), low photosynthetic photon flux density (30 mol m–2 s–1) and normal CO2 concentration (350–400 l l–1) were significantly higher than those of T2-plantlets grown under low sucrose concentration (0.5), high photosynthetic photon flux density (90 mol m–2 s–1) and elevated CO2 concentration (700–800 l l–1). But T2-plantlets had higher net photosynthetic rate (Pn), effective photochemical quantum yield of PSII (PSII), effective photosynthetic electron transport rate (ETR), photochemical quenching (qP) and ratio of chlorophyll fluorescence yield decrease (Rfd). After transfer, higher irradiance obviously promoted the growth of plantlets and was beneficial for the development of photosynthetic functions during acclimatization. T2-plantlets had higher fresh weight, leaf area, PSII and ETR under higher ex vitroirradiance condition. 相似文献
9.
In C4 grasses belonging to the NADP-malic enzyme-type subgroup, malate is considered to be the predominant C4 acid metabolized during C4 photosynthesis, and the bundle sheath cell chloroplasts contain very little photosystem-II (PSII) activity. The present studies showed that Flaveria bidentis (L.), an NADP-malic enzyme-type C4 dicotyledon, had substantial PSII activity in bundle sheath cells and that malate and aspartate apparently contributed about equally to the transfer of CO2 to bundle sheath cells. Preparations of bundle sheath cells and chloroplasts isolated from these cells evolved O2 at rates between 1.5 and 2 mol · min–1 · mg–1 chlorophyll (Chl) in the light in response to adding either 3-phosphoglycerate plus HCO
3
–
or aspartate plus 2-oxoglutarate. Rates of more than 2 mol O2 · min–1 · mg–1 Chl were recorded for cells provided with both sets of these substrates. With bundle sheath cell preparations the maximum rates of light-dependent CO2 fixation and malate decarboxylation to pyruvate recorded were about 1.7 mol · min–1 · mg–1 Chl. Compared with NADP-malic enzyme-type grass species, F. bidentis bundle sheath cells contained much higher activities of NADP-malate dehydrogenase and of aspartate and alanine aminotransferases. Time-course and pulse-chase studies following the kinetics of radiolabelling of the C-4 carboxyl of C4 acids from 14CO2 indicated that the photosynthetically active pool of malate was about twice the size of the aspartate pool. However, there was strong evidence for a rapid flux of carbon through both these pools. Possible routes of aspartate metabolism and the relationship between this metabolism and PSII activity in bundle sheath cells are considered.Abbreviations DHAP
dihydroxyacetone phosphate
- NADP-ME(-type)
NADP-malic enzyme (type)
- NADP-MDH
NADP-malate dehydrogenase
- OAA
oxaloacetic acid
- 2-OG
2-oxoglutarate
- PEP
phosphoenolpyruvate
- PGA
3-phosphoglycerate
- Pi
orthophosphate
- Ru5P
ribulose 5-phosphate 相似文献
10.
Summary From acetylene reduction assays over a 10-month period starting in April 1979, nodule activities averaged 18.78 (se 4.67) moles C2H4 g nodule dw–1 h–1 forAlnus rubra and 59.95 (se 12.14) moles C2H4 g nodule dw–1 h–1 forCytisus scorparius. Plant rates were 1.91 (se. 47) moles C2H4 plant–1 h–1 forA. rubra and 0.55 (se. 17) moles C2H4 plant–1 h–1 forC. Scoparius. Plant activity and total leaf N were strongly correlated with the dw of other plant parts, but nodule activity and percent leaf N were not. Plant and nodule activities were not associated with temperature, moisture stress, precipitation events or percent light for either species over the growing season nor for 54A. rubra sampled in mid-season 1979 on one replication. After 5 to 6 growing seasons, 14A. rubra on the same site ranged from 30 to 332 cm in height and showed strong correlation between nodule dw, leaf dw, plant size and total leaf N. Results from this study and others indicate logistic equations may be modified to predict the effect of adding a N2 fixing plant to a population of non N2 fixing trees. 相似文献
11.
Influence of cis-[Re2GABA2Cl4]Cl2 on the antioxidant defense system parameters of normal human blood
The effect of the rhenium complex cis-[Re2GABA2Cl4]Cl2 on the antioxidant parameters of normal human blood in vitro have been studied. The results suggest that the complex influences various enzymes in the cascade of reactions utilizing active oxygen metabolites. However, the manifestation of this activity varies over the studied concentration range of the complex in the preincubation medium (10–12-10–4 M), so the effects appear to be concentration-dependent. The largest differences in antioxidant parameters in comparison with control were observed for the concentrations 10–8, 10–5, and 10–4 M. Thus, correlations between the peroxidation level, superoxide dismutase (SOD) activity, antioxidant factor (F), and indexes of resistance of erythrocytes for hemolysis (TR) were found. 相似文献
12.
Turnover and distribution of root exudates of Zea mays 总被引:1,自引:0,他引:1
Decomposition and distribution of root exudates of Zea mays L. were studied by means of 14CO2 pulse labeling of shoots on a loamy Haplic Luvisol. Plants were grown in two-compartment pots, where the lower part was separated from the roots by monofilament gauze. Root hairs, but not roots, penetrated through the gauze into the lower part of the soil. The root-free soil in the lower compartment was either sterilized with cycloheximide and streptomycin or remained non-sterile. In order to investigate exudate distribution, 3 days after the 14C labeling, the lower soil part was frozen and sliced into 15, one-mm thick layers using a microtome. Cumulative 14CO2 efflux from the soil during the first 3 days after 14C pulse labeling did not change during plant growth and amounted to about 13–20% of the total recovered 14C (41–55% of the carbon translocated below ground). Nighttime rate of total CO2 efflux was 1.5 times lower than during daytime because of tight coupling of exudation with photosynthesis intensity. The average CO2 efflux from the soil with Zea mays was about 74 g C g–1 day–1 (22 g C m–2 day–1), although, the contribution of plant roots to the total CO2 efflux from the soil was about 78%, and only 22% was respired from the soil organic matter. Zea mays transferred about 4 g m–2 of carbon under ground during 26 days of growth. Three zones of exudate concentrations were identified from the distribution of the 14C-activity in rhizosphere profiles after two labeling periods: (1) 1–2 (3) mm (maximal concentration of exudates) 2) 3–5 mm (presence of exudates is caused by their diffusion from the zone 1); (3) 6–10 mm (very insignificant amounts of exudates diffused from the previous zones). At the distance further than 10 mm no exudates were found. The calculated coefficient of exudate diffusion in the soil was 1.9 × 10–7 cm2 s–1. 相似文献
13.
We studied the export of inorganic carbon and nitrous oxide (N2O) from a Danish freshwater wetland. The wetland is situated in an agricultural catchment area and is recharged by groundwater enriched with nitrate (NO3
–) (1000 M). NO3
– in recharging groundwater was reduced (57.5 mol NO3
– m–2 yr–) within a narrow zone of the wetland. Congruently, the annual efflux of carbon dioxide (CO2) from the sediment was 19.1 mol C m–2 when estimated from monthly in situ measurements. In comparison the CO2 efflux was 4.8 mol C m–2 yr–1 further out in the wetland, where no NO3
– reduction occurred. Annual exports of inorganic carbon in groundwater and surface water was 78.4 mol C m–2 and 6.1 mol C m–2 at the two sites, respectively. N2O efflux from the sedimenst was detectable on five out of twelve sampling dates and was significantly (P < 0.0001) higher in the NO3
– reduction zone (0.35–9.40 mol m–2 h–1, range of monthly means) than in the zone without NO3
– reduction (0.21–0.41 mol m–2 h–1). No loss of dissolved N2O could be measured. Total annual export of N2O was not estimated. The reduction of oxygen (O2) in groundwater was minor throughout the wetland and did not exceed 0.2 mol 02 m–2yr–1. Sulfate (SO4
––) was reduced in groundwater (2.1 mol SO4
–– m–2 yr–1) in the zone without NO3
– reduction. Although the NO3
– in our wetland can be reduced along several pathways our results strongly suggest that NO3
– loading of freshwater wetlands disturb the carbon balance of such areas, resulting in an accelerated loss of inorganic carbon in gaseous and dissolved forms. 相似文献
14.
The carrageenan-producing red algaKappaphycus alvarezii (Doty) Doty was brought to Vietnam from Japan in 1993. Branch fragments of this species were cultivated in a pond, lagoon, inlet and offshore in Vietnam for the first time. The best daily growth rate (DGR) of plants grown in the lagoon area attained 9–11 % day–1 in May to June (cold season). The water temperature and salinity in this area ranged from 27.2–32.4 °C and 31.4–33.7 °C, respectively. DGR of plants grown in the inlet ranged from 7 to 9% day–1 in June. Grazing by fish has been observed to occur in this area. The DGR of plants grown in the pond ranged from 5–6% in January–July, but decreased to less than 4% day–1 in August (hot season).
K. alvarezii in Vietnam showed a carrageenan yield of 18.8–24.6% and gel strength of 1566–1712 g cm–2. These values are similar ones obtained fromK. alvarezii cultivated in the Philippines and Indonesia. 相似文献
15.
Antony R. Crofts 《Journal of bioenergetics and biomembranes》1986,18(5):437-445
Turnover of the ubiquinol oxidizing site of the UQH2:cyt c2 oxidoreductase (b/c
1 complex) ofRps. sphaeroides can be assayed by measuring the rate of reduction of cytb
561 in the presence of antimycin (AA). Oxidation of ubiquinol is a second-order process, with a value ofk
2 of about 3 × 105 M–1. The reaction shows saturation at high quinol concentrations, with an apparentK
m of about 6–8 mM (with respect to the concentration of quinol in the membrane). When the quinone pool is oxidized before illumination, reduction of the complex shows a substantial lag (about 1 ms) after a flash, indicating that the quinol produced as a result of the photochemical reactions is not immediately available to the complex. We have suggested that the lag may be due to several factors, including the leaving time of the quinol from the reaction center, the diffusion time to the complex, and the time for the head group to cross the membrane. We have suggested aminimal value for the diffusion coefficient of ubiquinone in the membrane (assuming that the lag is due entirely to diffusion) of about 10–9 cm–2 sec–1. The lag is reduced to about 100 µsec when the pool is significantly reduced, showing that quinol from the pool is more rapidly available to the complex than that from the reaction center. With the pool oxidized, similar kinetics are seen when the reduction of cytb
561 occurs through the AA-sensitive site (with reactions at the quinol oxidizing site blocked by myxothiazol). These results show that there is no preferential reaction pathway for transfer of reducing equivalents from reaction center tob/c
1 complex. Oxidation of cytb
561 through the AA-sensitive site can be assayed from the slow phase of the carotenoid electrochromic change, and by comparison with the kinetics of cytb
561. As long as the quinone pool is significantly oxidized, the reaction is not rate-determining for the electrogenic process. On reduction of the pool below 1 quinone per complex, a slowing of the electrogenic process occurs, which could reflect a dependence on the concentration of quinone. If the process is second-order, the rate constant must be about 2–5 times greater than that for quinol oxidation, since the effect on rate is relatively small compared with the effect seen at the quinol oxidizing site when the quinol concentration is changed over theE
h range where the first few quinols are produced on reductive titration. When the quinone pool is extracted (experiments in collaboration with G. Venturoli and B. A. Melandri), the slowing of the electrochromic change on reduction of the pool is not enhanced; we assume that this is due to the fact that a minimum of one quinone per active complex is produced by turnover of the quinol oxidizing site. Two lines of research lead us to revise our previous estimate for the minimal value of the quinone diffusion coefficient. These relate to the relation between the diffusion coefficient and the rate constants for processes involving the quinones: (a) The estimated rate constant for reaction of quinone at the AA-site approaches the calculated diffusion limited rate constant, implying an improbably efficient reaction. (b) From a preliminary set of experiments, the activation energy determined by measuring the variation of the rate constant for quinol oxidation with temperature, is about 8 kcal mol–1. Although we do not know the contribution of entropic terms to the pre-exponential factor, the result is consistent with a considerably larger value for the diffusion coefficient than that previously suggested. 相似文献
16.
Significance of the Leaf Area Ratio in Hevea brasiliensis Under High Irradiance and Low Temperature Stress 总被引:1,自引:1,他引:0
Adjustment in leaf area : mass ratio called leaf area ratio (LAR) is one of the strategies to optimize photon harvesting. LAR was recorded for 10 genotypes of Hevea brasiliensis under high irradiance and low temperature and the genotypes were categorized into two groups, i.e. high LAR and low LAR types. Simultaneously, the growth during summer as well as winter periods, photosynthetic characteristics, and in-vitro oxidative damage were studied. Low LAR (19.86±0.52 m2 kg–1) types, recorded an average of 18.0 % chlorophyll (Chl) degradation under high irradiance and 7.1 % Chl degradation under low temperature. These genotypes maintained significantly higher net photosynthetic rate (P
N) of 10.4 mol(CO2) m–2 s–1 during winter season. On the contrary, the high LAR (24.33±0.27 m2 kg–1) types recorded significantly lower P
N of 4 mol(CO2) m–2 s–1 and greater Chl degradation of 37.7 and 13.9 % under high irradiance and low temperature stress, respectively. Thus LAR may be one of the physiological traits, which are possibly involved in plant acclimation process under both stresses studied. 相似文献
17.
Methane emission and rhizospheric CH4 oxidation were studied in stands of Equisetum fluviatile, a common cryptogam in boreal lakes. The experiment was performed in mesocosms with organic sediment or sand bottoms under natural variation of temperature and light using the light-oxic – dark-anoxic chamber (LO/DA) technique. Net CH4 emission from the organic sediment during the growing season varied between 3.4 and 19.0 mg m–2 h–1, but from sand the net CH4 emission was only 3–10% of that measured from the organic sediment. In the organic sediment net CH4 emission was very significantly correlated with sediment temperature (r2 = 0.92). In the sand mesocosms the variation of net CH4 emission was better correlated with the shoot biomass than with sediment temperature variation during the growing season, indicating that methanogens were severely limited by substrate availability and were probably dependent on substrates produced by E. fluviatile. The proportion of the methane oxidized of the potential CH4 emission in summer did not differ significantly between the bottom types. The net CH4 emission during the growing season as a proportion of the seasonal maximum of the shoot biomass was significantly higher in the organic sediment mesocosms (6.5%) than in sand (1.7%). The high CH4 emissions observed from dense well-established E. fluviatile stands in the field appear to be more related to temperature-regulated turnover of detritus in the anaerobic sediment and less to CH4 oxidation and seasonal variation in plant growth dynamics 相似文献
18.
Laboratory-cultured Streptocephalus torvicornis were offered 8 concentrations (from 6 to 800 ind. ml–1) of Anuraeopsis fissa for periods of 2 h 30 min. Two size classes, small (male: 14.7 mm± 1.6, female: 15.4 mm± 1.3) and large (male: 20.0 mm±2.0, female: 23.1 mm± 1.5), of S. torvicornis were used. Functional response for large S. torvicornis (both sexes) plateaued at 400 rotifers ml–1, while in small specimens it did so at 200 prey ml–1. Females consumed significantly more (30%) prey than males. Large males consumed maximum 4730 rotifers h–1, females 6560 h–1. 相似文献
19.
H2 production from glucose by Ruminococcus albus was almost completely inhibited by 10–5 M molybdate only when sulfide was present in the growth medium. Inhibition was accompanied by a significant increase in the production of formate. Extracts of molybdate-sulfide-grown cells did not contain hydrogenase activity. Active enzyme in extracts of uninhibited cells was not inhibited by the molybdate-sulfide-containing growth medium. The results indicate that a complex formed from molybdate and sulfide prevents the formation of active hydrogenase and electrons otherwise used to form H2 are used to reduce CO2 to formate. Growth was significantly inhibited when molybdate was increased to 10–4 M. Reversal of growth inhibition but not inhibition of H2 production occurred between 10–4 and 10–3 M molybdate. H2 production by R. bromei but not by R. flavefaciens, Butyrivibrio fibrisolvens, Veillonella alcalescens, Klebsiella pneumoniae and Escherichia coli was inhibited by molybdate and sulfide. 相似文献
20.
Cellulose in wastewater was converted into H2 by a mixed culture in batch experiments at 55°C with various wastewaters pH (5.5–8.5) and cellulose concentrations (10–40 g l–1). At the optimal pH of 6.5, the maximum H2 yield was 102 ml g–1 cellulose and the maximum production rate was 287 ml d–1 for each gram of volatile suspended solids (VSS). Analysis of 16S rDNA sequences showed that the cellulose-degrading mixed culture was composed of microbes closely affiliated to genus Thermoanaerobacterium. 相似文献