Relations between carbon dioxide fluxes and environmental factors of Kobresia humilis meadows and Potentilla fruticosa meadows

Carbon dioxide fluxes of Kobresia humilis and Potentilla fruticosa shrub meadows, two typical ecosystems in the Qinghai-Tibet Plateau, were measured by eddy covariance technology and the data collected in August 2003 were employed to analyze the relations between carbon dioxide fluxes and environmental factors of the ecosystems. August is the time when the two ecosystems reach their peak leaf area indexes and stay stable, and also the period when the net carbon absorptions of Kobresia humilis and Potentilla fruticosa shrub meadows reach 56.2 g C·m⁻² and 32.6 g C·m⁻², with their highest daily carbon dioxide absorptions standing at 12.7 μmol·m⁻²·s⁻¹ and 9.3 μmol·m⁻²·s⁻¹, and their highest carbon discharges at 5.1 μmol·m⁻²·s⁻¹ and 5.7 μmol·m⁻²·s⁻¹, respectively. At the same photosynthetic photo flux densities (PPFD), the carbon dioxide-uptake rate of the Kobresia humilis meadow is higher than that of the Potentilla fruticosa shrub meadow; where the PPFD are higher than 1,200 μmol·m⁻²·s⁻¹. The carbon dioxide uptake rates of the two ecosystems declined as air temperature increased, but the carbon dioxide uptake rate of the Kobresia humilis meadow decreased more quickly (−0.086) than that of the Potentilla fruticosa shrub meadow (−0.016). Soil moistures exert influence on the soil respirations and this varies with the vegetation type. The daily carbon dioxide absorptions of the ecosystems increase with increased diurnal temperature differences and higher diurnal temperature differences result in higher carbon dioxide exchanges. There exists a negative correlation between the vegetation albedos and the carbon dioxide fluxes. Translated from Acta Bot Boreal—Occident Sin, 2006, 26(1): 133–142 [译自: 西北植物学报]     

Bacterial assemblages in rivers and billabongs of Southeastern Australia

Billabongs, lentic waterbodies common to the floodplain of Australian rivers, differ considerably from the lotic riverine environment in terms of hydrology, physiochemical characteristics, and biological assemblages present. As little is known regarding the bacterial ecology of billabong habitats, a comparison was made of the bacterial assemblages in the water column of seven paired river/billabong sites in the Murray-Darling Basin of southeastern Australia. Billabongs supported larger populations of bacteria (1–157×10⁹ cells liter⁻¹; 11–10,270 μg C liter⁻¹) than did rivers (1–10×10⁹ cells liter⁻¹; 6–143 μg C liter⁻¹). Phospholipid analyses confirmed that billabongs (14–111 μg phospholipid fatty acid liter⁻¹) had larger bacterial populations than rivers (<12 μg liter⁻¹). Bacterial production, measured with³H-leucine, was also greater in billabongs (0.28–3.05 μg C liter⁻¹ hour⁻¹) than rivers (0.05–0.62 μg C liter⁻¹ hour⁻¹). Production calculated from the frequency of dividing cells confirmed this conclusion, and suggested bacterial production in some billabongs could exceed 100 μg C liter⁻¹ hour⁻¹. An INT-formazan method indicated that usually <25% of bacterial cells were active in either habitat, but this was probably an underestimate of the bona fide value. Turnover times of glucose were usually shorter in billabongs, and the cell-specific activity greater for billabong than river assemblages. The factors most likely to be responsible for the differences between the bacterial assemblages in rivers and billabongs relate to hydrological regime and the availability of organic carbon substrates.     

Photosynthetic acclimation to photon irradiance and its relation to chlorophyll fluorescence and carbon assimilation in the halotolerant green alga Dunaliella viridis

This work describes the long-term acclimation of the halotolerant microalga Dunaliella viridis to different photon irradiance, ranging from darkness to 1500 μmol m⁻² s⁻¹. In order to assess the effects of long-term photoinhibition, changes in oxygen production rate, pigment composition, xanthophyll cycle and in vivo chlorophyll fluorescence using the saturating pulse method were measured. Growth rate was maximal at intermediate irradiance (250 and 700 μmol m⁻² s⁻¹). The increase in growth irradiance from 700 to 1500 μmol m⁻² s⁻¹ did not lead to further significant changes in pigment composition or EPS, indicating saturation in the pigment response to high light. Changes in Photosystem II optimum quantum yield (F_v/F_m) evidenced photoinhibition at 700 and especially at 1500 μmol m⁻² s⁻¹. The relation between photosynthetic electron flow rate and photosyntetic O₂ evolution was linear for cultures in darkness shifting to curvilinear as growth irradiance increased, suggesting the interference of the energy dissipation processes in oxygen evolution. Carbon assimilation efficiencies were studied in relation to changes in growth rate, internal carbon and nitrogen composition, and organic carbon released to the external medium. All illuminated cultures showed a high capability to maintain a C:N ratio between 6 and 7. The percentage of organic carbon released to the external medium increased to its maximum under high irradiance (1500 μmol m⁻² s⁻¹). These results suggest that the release of organic carbon could act as a secondary dissipation process when the xanthophyll cycle is saturated. This revised version was published online in June 2006 with corrections to the Cover Date.     

Detection and Quantification with 16S rRNA Probes of Planktonic Methylotrophic Bacteria in a Floodplain Lake

Abstract Two approaches employing 16S rRNA oligonucleotide probes, in situ hybridization combined with ³³P-autoradiography and ³²P-labeled slot-blot hybridizations on nitrocellulose filters, were used to enumerate methylotrophic bacteria in the water column of Ryans 1 Billabong, a small floodplain lake in northeastern Victoria, Australia. Methylotrophic bacterioplankton numbered 0.6–1.2 × 10⁹ cells liter⁻¹ in the winter of 1994, and 0.8–5.5 × 10⁹ cells liter⁻¹ in the summer of 1994–95. This was equivalent to 10–46% of total bacterioplankton cell counts, determined via epifluorescence microscopy. Methylotrophic bacteria were not detected in the water column of the nearby Kiewa River, and a set of laboratory controls indicated that the high abundance of methylotrophs in the billabong samples was not a methodological artifact. There was no change, with water depth, in total bacterioplankton or methylotroph abundance in winter, a result consistent with the water column being well mixed at this time of year (dissolved O₂ concentrations 5–7 mg liter⁻¹; dissolved methane concentrations <60 μg liter⁻¹, or <5% methane saturation, at all depths). In summer the billabong became diurnally stratified (dissolved O₂ concentrations <2 mg liter⁻¹ at water depths of >45 cm; dissolved methane concentrations <100 μg liter⁻¹ at the surface, but >500 μg liter⁻¹ near the sediments) and there was a correspondingly marked increase in the abundance of total bacterioplankton and methylotrophs with depth. In situ hybridizations and slot-blot hybridizations both indicated that type II methylotrophs (detected with a probe specific for the 9-α subgroup of Proteobacteria) were markedly less abundant than were type I and X methylotrophs (detected with a probe specific for the 10-γ subgroup of Proteobacteria). Received: 12 March 1996; Accepted: 2 October 1996     

Somatic embryogenesis and plant regeneration inAzadirachta indica A. Juss

Summary Media for induction of somatic embryogenesis from immature cotyledonary tissues ofAzadirachta indica (Neem) were determined. Callus was initiated on Murashige and Skoog medium supplemented with 0.5 mg·liter⁻¹ of indol-3 acetic acid, 1.0 mg·liter⁻¹ of 6-benzyl amino purine, and 1000 mg·liter⁻¹ of casein hydrolysate. Effect of kinetin was also studied for embryo induction. Carbohydrate source in the form of sucrose and glucose alone and in combination was tested for embryogenic efficiency. Seventy percent embryos showed germination. Healthy plants were potted in sand and soil. Histologic studies confirmed indirect somatic embryogenesis.     

The effect of bacterial contamination on the growth and gas evolution ofIn vitro cultured apricot shoots

Summary Shoots of “San Castrese” and “Portici” apricots (Prunus armeniaca L.) free of cultivable bacteria, shoots of the same origin exhibiting bacterial contamination after repeated subcultures, and contaminated shoots treated with cefotaxime were compared for gas exchange, proliferation rate, and fresh and dry weight. Cultures of San Castrese contaminated byBacillus circulans andSphingomonas paucimobilis, and of Portici contaminated withStaphylococcus hominis andMicrococcus kristinae, including those treated with cefotaxime, showed comparable shoot weights and lower proliferation rates than healthy cultures. Bacteria, even if not visible until the end of subculture, markedly influenced the gaseous composition of the jar headspace. Healthy cultures clearly showed photosynthetic activity at 60 μM·m⁻²·s⁻¹ photosynthetically active radiation; in contrast, oxygen quickly decreased and carbon dioxide increased in contaminated cultures, including those treated with cefotaxime, in which bacteria became visible in the culture medium only after repeated subcultures.     

Factors affecting recurrent shoot multiplication in in vitro cultures of 17- to 20-year-old douglas fir trees

Summary The effects of sucrose concentration, addition of ammonium nitrate, and exposure to N⁶-benzyl-adenine (BA) on multiplication potential with shoots derived from shoot cultures of 17- to 20-yr-old Douglas fir trees [Pseudotsuga menziesii (Mirb.) Franco] were compared. Each of these conditions, when compared independently, affected recurrent shoot multiplication and influenced shoot development, as measured by the abundance of shoot apices. Sucrose concentration was influential, the use of 25 g · liter⁻¹ providing twice the multiplication obtained with 20 g · liter⁻¹, and 14 × that obtained with the 30 g · liter⁻¹ concentration routinely used (tree 11). Ammonium nitrate usage also improved multiplication, a 2.5 times improvement being obtained after incorporation of 100 mg · liter⁻¹ NH₄NO₃ into the medium (tree 33). Shoot cultures were responsive but relatively sensitive to addition of BA, the best improvement in multiplication (5 times) being obtained with brief exposures to 3 mg · liter⁻¹ BA (tree 11). Although shoot cultures were responsive to the conditions investigated, differences in shoot multiplication and development were not displayed for several weeks. It was not possible therefore to repeat all the treatments with more than one genotype; however, when this was possible a genotype-dependent variation in response was evident.     

Direct somatic embryogenesis from axes of mature peanut embryos

Summary Plant regeneration via somatic embryogenesis was obtained in peanut (Arachis hypogaea L.) from axes of mature zygotic embryos. The area of greatest embryogenic activity was a 2-mm region adjacent to and encircling the epicotyl. Somatic embryogenesis was evaluated on Murashige and Skoog media supplemented with a variety of auxin treatments. Maximum production occurred on medium supplemented with 3 mg · liter⁻¹ 4-amino-3,5,6-trichloropicolinic acid. Explant cultures were transferred to half-strength medium supplemented with 1 mg · liter⁻¹ gibberellic acid for somatic embryo germination and early plantlet growth. Plantlets, transferred to soil, were placed in a greenhouse and grown to maturity.     

Photosynthetic Response of Carrots to Varying Irradiances

Response to irradiance of leaf net photosynthetic rates (P _N) of four carrot cultivars: Cascade, Caro Choice (CC), Oranza, and Red Core Chantenay (RCC) were examined in a controlled environment. Gas exchange measurements were conducted at photosynthetic active radiation (PAR) from 100 to 1 000 μmol m⁻² s⁻¹ at 20 °C and 350 μmol (CO₂) mol⁻¹(air). The values of P _N were fitted to a rectangular hyperbolic nonlinear regression model. P _N for all cultivars increased similarly with increasing PAR but Cascade and Oranza generally had higher P _N than CC. None of the cultivars reached saturation at 1 000 μmol m⁻² s⁻¹. The predicted P _N at saturation (P _Nmax) for Cascade, CC, Oranza, and RCC were 19.78, 16.40, 19.79, and 18.11 μmol (CO₂) m⁻² s⁻¹, respectively. The compensation irradiance (I _c) occurred at 54 μmol m⁻² s⁻¹ for Cascade, 36 μmol m⁻² s⁻¹ for CC, 45 μmol m⁻² s⁻¹ for Oranza, and 25 μmol m⁻² s⁻¹ for RCC. The quantum yield among the cultivars ranged between 0.057–0.033 mol(CO₂) mol⁻¹(PAR) and did not differ. Dark respiration varied from 2.66 μmol m⁻² s⁻¹ for Cascade to 0.85 μmol m⁻² s⁻¹ for RCC. As P _N increased with PAR, intercellular CO₂ decreased in a non-linear manner. Increasing PAR increased stomatal conductance and transpiration rate to a peak between 600 and 800 μmol m⁻² s⁻¹ followed by a steep decline resulting in sharp increases in water use efficiency. This revised version was published online in August 2006 with corrections to the Cover Date.     

Dithiothreitol,an inhibitor of violaxanthin de-epoxidation,increases the susceptibility of leaves ofNerium oleander L. to photoinhibition of photosynthesis

Leaves ofNerium oleander L. plants, which had been previously kept in a shaded glasshouse for at least two months, were fed 1 mM dithiothreitol (DTT) through their petioles, either for 12h in darkness (overnight) or for 2h in low light (28 μmol photons·m⁻²·s⁻¹), in each case followed by a 3-h exposure to high light (1260 μmol photons·m⁻²·s⁻¹). During exposure to high light, violaxanthin became converted to zeaxanthin in control leaves, to which water had been fed, whereas zeaxanthin did not accumulate in leaves treated with DTT. Total carbon gain was not reduced by DTT during the photoinhibitory treatment. Exposure to high light led to a decrease in the photochemical efficiency of photosystem II, measured as the ratio of variable over maximum fluorescence emission,F _v/F _M, at both 298 K and 77K. The decrease was much more pronounced in the presence of DTT, mainly owing to a sustained increase in the instantaneous fluorescence,F _o. By contrast, in the control leaves,F _o determined immediately after the high-light treatment showed a transient decrease below theF _o value obtained before the onset of the photoinhibitory treatment (i.e. after 12 h dark adaptation), followed by a rapid return (within seconds) to this original level ofF _o during the following recovery period in darkness. Incubation of leaves with DTT led to large, sustained decreases in the photon-use efficiency of photosynthetic O₂ evolution by bright light, whilst the capacity of photosynthetic O₂ evolution at light and CO₂ saturation was less affected. In the control leaves, only small reductions in the photon yield and in the photosynthetic capacity were observed. These findings are consistent with previous suggestions that zeaxanthin, formed in the xanthophyll cycle by de-epoxidation of violaxanthin, is involved in protecting the photosynthetic apparatus against the adverse effects of excessive light.     

Callus induction and plant regeneration of U.S. rice genotypes as affected by medium constituents

Summary This study was conducted to establish and optimize a regeneration system for adapted U.S. rice genotypes including three commercial rice cultivars (LaGrue, Katy, and Alan) and two Arkansas breeding lines. Factors evaluated in the study were genotype, sugar type, and phytohormone concentration. The system consisted of two phases, callus induction and plant regeneration. In the callus induction phase, mature caryopses were cultured on MS medium containing either 1% sucrose combined with 3% sorbitol or 4% sucrose alone, and 0.5 to 4 mg·L⁻¹ (2.26 to 18.10 μM) 2,4-D with or without 0.5mg·L⁻¹) (2.32 μM) kinetin. In the plant regeneration phase, callus was transferred to 2,4-D-free MS medium containing 0 or 2 mg·L⁻¹ (9.29 μM) kinetin combined with 0 or 0.1 mg·L⁻¹ (0.54 μM) NAA. Callus induction commenced within a week, independent of the treatments. Callus growth and plant regeneration, however, were significantly influenced by interactions among experimental factors. Generally, the greatest callus growth and plant regeneration were obtained with 0.5 mg·L⁻¹ (2.26 μM) 2,4-D and decreased with increasing 2,4-D concentrations. Kinetin enhanced callus growth only when combined with 0.5 mg·L⁻¹ (2.26 μM) 2,4-D, and 4% sucrose. Inducing callus on kinetin-containing medium generally enhanced regeneration capacity in the presence of sucrose but not with a sucrose/sorbitol combination. Media containing sucrose alone generally supported more callus proliferation, but the sucrose/sorbitol combination improved regeneration of some cultivars. NAA and kinetin had little effect on regeneration.     

Antimicrobial activity of an endophytic <Emphasis Type="Italic">Xylaria</Emphasis> sp.YX-28 and identification of its antimicrobial compound 7-amino-4-methylcoumarin

An endophytic Xylaria sp., having broad antimicrobial activity, was isolated and characterized from Ginkgo biloba L. From the culture extracts of this fungus, a bioactive compound P3 was isolated by bioactivity-guided fractionation and identified as 7-amino-4-methylcoumarin by nuclear magnetic resonance, infrared, and mass spectrometry spectral data. The compound showed strong antibacterial and antifungal activities in vitro against Staphylococcus aureus [minimal inhibitory concentrations (MIC) 16 μg·ml⁻¹], Escherichia coli (MIC, 10 μg·ml⁻¹), Salmonella typhia (MIC, 20 μg·ml⁻¹), Salmonella typhimurium (MIC, 15 μg·ml⁻¹), Salmonella enteritidis (MIC, 8.5 μg·ml⁻¹), Aeromonas hydrophila (MIC, 4 μg·ml⁻¹), Yersinia sp. (MIC, 12.5 μg·ml⁻¹), Vibrio anguillarum (MIC, 25 μg·ml⁻¹), Shigella sp. (MIC, 6.3 μg·ml⁻¹), Vibrio parahaemolyticus (MIC, 12.5 μg·ml⁻¹), Candida albicans (MIC, 15 μg·ml⁻¹), Penicillium expansum (MIC, 40 μg·ml⁻¹), and Aspergillus niger (MIC, 25 μg·ml⁻¹). This is the first report of 7-amino-4-methylcoumarin in fungus and of the antimicrobial activity of this metabolite. The obtained results provide promising baseline information for the potential use of this unusual endophytic fungus and its components in the control of food spoilage and food-borne diseases.     

Changes of fluorescence and xanthophyll pigments during dehydration in the resurrection plantSelaginella lepidophylla in low and medium light intensities

The changes in photosynthetic efficiency and photosynthetic pigments during dehydration of the resurrection plantSelaginella lepidophylla (from the Chiuhahuan desert, S.W. Texas, USA) were examined under different light conditions. Changes in the photosynthetic efficiency were deduced from chlorophyll a fluorescence measurements (F_o, F_m, and F_v) and pigment changes were measured by HPLC analysis. A small decrease in F_v/F_m was seen in hydrated stems in high light (650 μmol photons·m⁻²·s⁻¹) but not in low light (50 μmol photons·m⁻²·s⁻¹). However, a pronounced decline in F_v/F_m was observed during dehydration in both light treatments, after one to two hours of dehydration. A rise in F_o was observed only after six to ten hours of dehydration. Concomitant with the decrease in photosynthetic efficiency during dehydration a rise in the xanthophyll zeaxanthin was observed, even in low-light treatments. The increase in zeaxanthin can be related to previously observed photoprotective non-photochemical quenching of fluorescence in dehydrating stems ofS. lepidophylla. We hypothesize that under dehydrating conditions even low light levels become excessive and zeaxanthin-related photoprotection is engaged. We speculate that these processes, as well as stem curling and self shading (Eickmeier et al. 1992), serve to minimize photoinhibitory damage toS. lepidophylla during the process of dehydration.     

Leaf Photosynthesis in Eight Almond Tree Cultivars

Response of gas exchange traits to irradiance were studied in eight almond tree (Prunus amygdalus) cultivars: Desmayo Largueta, Falsa Barese, Garrigues, Lauranne, Marcona, Masbovera, Nonpareil and Ramillete, grafted on a hybrid rootstock almond × peach GF-677. From these responses cultivars can be classified from the best to the worst photosynthetic performance as follows: Falsa Barese, Masbovera, Marcona, Nonpareil, Ramillete, Desmayo Largueta, Lauranne and Garrigues. The highest net photosynthetic rate was 20.3 μmol m⁻² s⁻¹ in Falsa Barese. In the absence of water stress, photosynthetic rate was not limited by stomatal conductance. Consequently, non-stomatal limitations prevailed under such conditions. This revised version was published online in July 2006 with corrections to the Cover Date.     

Function of mitochondria during the transition of barley protoplasts from low light to high light

Mitochondrial contribution to photosynthetic metabolism during the transition from low light (25–100 μmol quanta m⁻² s⁻¹, limiting photosynthesis) to high light (500 μmol quanta m⁻² s⁻¹, saturating photosynthesis) was investigated in protoplasts from barley (Hordeum vulgare) leaves. After the light shift, photosynthetic oxygen evolution rate increased rapidly during the first 30–40 s and then declined up to 60–70 s after which the rate increased to a new steady-state after 80–110 s. Rapid fractionation of protoplasts was used to follow changes in sub-cellular distribution of key metabolites during the light shift and the activation state of chloroplastic NADP-dependent malate dehydrogenase (EC 1.1.1.82) was measured. Although oligomycin (an inhibitor of the mitochondrial ATP synthase) affected the metabolite content of protoplasts following the light shift, the first oxygen burst was not affected. However, the transition to the new steady-state was delayed. Rotenone (an inhibitor of mitochondrial complex I) had similar, but less pronounced effect as oligomycin. From the analysis of metabolite content and sub-cellular distribution we suggest that the decrease in oxygen evolution following the first oxygen burst is due to phosphate limitation in the chloroplast stroma. For the recovery the control protoplasts can utilize ATP supplied by mitochondrial oxidative phosphorylation to quickly overcome the limitation in stromal phosphate and to increase the content of Calvin cycle metabolites. The oligomycin-treated protoplasts were deficient in cytosolic ATP and thereby unable to support Calvin cycle operation. This resulted in a delayed capacity to adjust to a sudden increase in light intensity.     

Effect of NaCl on kinetics ofd-glucosamine uptake in yeasts differing in halotolerance

The initial rate ofd-glucosamine uptake by the non-halotolerant yeastSaccharomyces cerevisiae was approximately halved as the apparent half saturation constant (K_m) and the apparent maximum velocity (V_max) changed from 6.6mm to 16.4mm and from 22 μmol · g⁻¹ · min⁻¹ to 16 μmol · g⁻¹ · min⁻¹, respectively, when the salinity in the medium was increased from zerom to 0.68m NaCl. Corresponding changes in a high affinity transport system in the halotolerant yeastDebaryomyces hansenii were from 1.1mm to 4.6mm and from 3.1 μmol · g⁻¹ · min⁻¹ to 4.5 μmol · g⁻¹ · min⁻¹, implying a practically unchanged transport capacity. In 2.7m NaCl, K_m and V_max in this system were 24.5mm and 1.1 μmol · g⁻¹ · min⁻¹, respectively, representing a marked decrease in transport capability. Nevertheless, the degree of affinity in this extreme salinity must still be regarded as noteworthy. In addition to the high affinity transport system inD. hansenii, a low affinity system, presumably without relevance ind-glucosamine transport, was observed.     

Photoinhibition of photosynthesis in intact kiwifruit (Actinidia deliciosa) leaves: effect of growth temperature on photoinhibition and recovery

Intact leaves of kiwifruit (Actinidia deliciosa (A. Chev.) C.F. Liang et A.R. Ferguson) from plants grown in a range of controlled temperatures from 15/10 to 30/25°C were exposed to a photon flux density (PFD) of 1500 μmol·m⁻²·s⁻¹ at leaf temperatures between 10 and 25°C. Photoinhibition and recovery were followed at the same temperatures and at a PFD of 20 μmol·m⁻²·s⁻¹, by measuring chlorophyll fluorescence at 77 K and 692 nm, by measuring the photon yield of photosynthetic O₂ evolution and light-saturated net photosynthetic CO₂ uptake. The growth of plants at low temperatures resulted in chronic photoinhibition as evident from reduced fluorescence and photon yields. However, low-temperature-grown plants apparently had a higher capacity to dissipate excess excitation energy than leaves from plants grown at high temperatures. Induced photoinhibition, from exposure to a PFD above that during growth, was less severe in low-temperature-grown plants, particularly at high exposure temperatures. Net changes in the instantaneous fluorescence,F ₀, indicated that little or no photoinhibition occurred when low-temperature-grown plants were exposed to high-light at high temperatures. In contrast, high-temperature-grown plants were highly susceptible to photoinhibitory damage at all exposure temperatures. These data indicate acclimation in photosynthesis and changes in the capacity to dissipate excess excitation energy occurred in kiwifruit leaves with changes in growth temperature. Both processes contributed to changes in susceptibility to photoinhibition at the different growth temperatures. However, growth temperature also affected the capacity for recovery, with leaves from plants grown at low temperatures having moderate rates of recovery at low temperatures compared with leaves from plants grown at high temperatures which had negligible recovery. This also contributed to the reduced susceptibility to photoinhibition in low-temperature-grown plants. However, extreme photoinhibition resulted in severe reductions in the efficiency and capacity for photosynthesis.     

Culture phenotype affects on regeneration capacity in the monocotHaworthia comptoniana

Summary Haworthia comptoniana specimens were cultured to determine how benzyladenine (BA) level and in vitro selection for shoot and callus production affected regeneration capacity and plant phenotype. Leaf explants were cultured on Murashige and Skoog medium containing 0 to 10 mg·liter⁻¹ of BA. The highest number of shoots was obtained with 0.5 mg·liter⁻¹ of BA.H. comptoniana stock cultures (hc) maintained with 0.5 mg·liter⁻¹ of BA produced clumps of small shoots interspersed with friable, white, tan, and green callus. A clump of very large shoots was isolated and designated cell line Rhc; it differed from the original hc culture in shoot size, the lack of callus growth, and higher water content. A line of green callus (designated Gc), a line of white callus (Wc), and a line of soft tan callus (Tc) were also isolated from hc. Optimal BA levels for shoot regeneration from lines Gc and Wc were 2 and 5 mg·liter⁻¹, respectively. No normal shoots could be regenerated from Tc. The phenotypes of these cell lines remained stable for 24 subculture generations. The hc line that initially required BA for growth became hormone autotrophic whereas the other lines did not. Culturing using Gelrite and sealing vessels with parafilm promoted vitrification of the hc line. Culturing using GIBCO agar and unsealed vessels reduced vitrification. The ex-vitro greenhouse survival rates for hc and Rhc plantlets were 10 and 80%, respectively. The large size of the Rhc shoots apparently resulted in significantly higher survival rates under greenhouse conditions, but did not result in any phenotypic whole plant changes.     

Characteristics of net ecosystem carbon dioxide exchange (NEE) from August to October of Alpine meadow on the Tibetan Plateau, China

The Alpine meadow is one of the vegetation types widely distributed on the Tibetan Plateau in China with an area of about 1.2 million square kilometers. The Damxung rangeland station, located in the hinterland of the Tibetan Plateau, is covered with an typical vegetation. The continuous carbon flux data (from August to middle October, 2003) measured with the open-path eddy covariance system was used to analyze the diurnal variation pattern of net ecosystem carbon dioxide exchange (NEE) and its relationship with the environmental factors, such as photosynthetically active radiation (PAR), precipitation, and temperature. Results showed that NEE presented obvious diurnal variation pattern with single-peak of diurnal maximum carbon assimilation at 11: 00–12: 00 (local time) with an average of −0.268 mg CO₂·m⁻²·s⁻¹, i.e., −6.08 μmol CO₂·m⁻²·s⁻¹. During the daytime, NEE fitted fairly well with PAR in a rectangular hyperbola function with the apparent quantum yield (0.020 3 μmol CO₂ μmol⁻¹ PAR) and maximum ecosystem assimilation (9.741 1 μmol CO₂·m⁻²·s⁻¹). During the night-time, NEE showed a good exponential relation with the soil temperature at 5 cm depth. __________ Translated from Acta Ecologica Sinica 2005, 25(8): 1948–1952 [译自: 生态学报, 2005, 25(8): 1948–1952]     

Comparative ecophysiology of two representativeQuercus species appearing in different stages of succession

Ecophysiological comparisons were made of the growth and photosynthetic characteristics between seedlings of deciduousQuercus serrata and evergreenQuercus myrsinaefolia. Q. myrsinaefolia seedlings naturally occurring in secondary coppice forests showed exponential-like growth in height with age, while sympatricQ. serrata seedlings were considerably smaller in height, their growth being limited by shortage of light. The photosynthetic characteristics measured under laboratory conditions showed no bases for the differences in growth between the two species on the forest floor: Light compensation points of the seedlings raised under 5% daylight were almost identical for the two species, being about 6.0 μE·m⁻²·s⁻¹. Growth analysis of seedlings planted in a coppice forest showed that bothQ. serrata andQ. myrsinaefolia could hardly grow during the summer under the shrub layer, when relative photon flux density (RPFD) was 0.9±0.5%. In the winter, when RPFD under the leafless canopy increased to 29.3±2.7%, the dry matter production of the evergreen seedlings ofQ. myrsinaefolia was much improved. Current-year seedlings of the species showed NAR of 0.102±0.021 g·dm⁻²·mo⁻¹ during the winter. Temperature dependency of photosynthesis and increment of leaf temperature by direct solar beam also indicated active photosynthesis ofQ. myrsinaefolia on the forest floor during the winter.