摘要:

ABSTRACTTwo clones of 5‐year‐old Norway spruce [Picea abies(L.) Karst.] were exposed to two atmospheric concentrations of CO2 (350 and 750 μmol mol−1) and O3(20 and 75nmolmol−1) in a phytotron at the GSF‐Forschung‐szentrum (Munich) over the course of a single season (April to October). The phytotron was programmed to recreate an artificial climate similar to that at a high elevation site in the Inner Bavarian Forest, and trees were grown in large containers of forest soil fertilized to achieve contrasting levels of potassium nutrition, designated well‐fertilized or K‐deficient. Measurements of the rate of net CO2assimilation were made on individual needle year age classes over the course of the season, chlorophyll fluorescence kinetics were recorded after approximately 23 weeks, and seasonal changes in non‐structural carbohydrate composition of the current year's foliage were monitored. Ozone was found to have contrasting effects on the rate of net CO2assimilation in different needle age classes. After c. 5 months of fumigation, elevated O3increased (by 33%) the rate of photosynthesis in the current year's needles. However, O3 depressed (by 30%) the photo‐synthetic rate of the previous year's needles throughout the period of exposure. Chlorophyll fluorescence measurements indicated that changes in photosystem II electron transport played no significant role in the effects of O3on photosynthesis. The reasons for the contrasting effects of O3on needles of different ages are discussed in the light of other recent findings. Although O3enhanced the rate at which CO2was fixed in the current year's foliage, this was not reflected in increases in the non‐structural carbohydrate content of the needles. The transfer of ambient CO2‐grown trees to a CO2‐enriched atmosphere resulted in marked stimulation in the photosynthetic rate of current and previous year's foliage. However, following expansion of the current year's growth, the photosynthetic rate of the previous year's foliage declined. The extent of photosynthetic adjustment in response to prolonged exposure to elevated CO2depended upon the clone, providing evidence of intraspecific variation in the long‐term response of photosynthesis to elevated CO2. The increase in photosynthesis induced by CO2enrichment was associated with increased foliar concentrations of glucose, fructose and starch (but no change in sucrose) in the new growth. CO2enrichment significantly enhanced the photosynthetic rate of K‐deficient needles, but there was a strong CO2soil interaction in the current year's needles, indicating that the long‐term response of trees to a high CO2environment may depend on soil fertility. Although the rate of photosynthesis and non‐structural carbohydrate content of the new needles were increased in O3‐treated plants grown at higher levels of CO2, there was no evidence that elevated CO2provided additional protection against O3damage. Simultaneous exposure to elevated O3modified the effects of elevated CO2on needle photosynthesis and non‐structural carbohydrate content, emphasizing the need to take into account not only soil nutrient status but also the impact of concurrent increases in photochemical oxidant pollution in any serious consideration of the effects

ISSN:0140-7791    

DOI:10.1111/j.1365-3040.1995.tb00195.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

ABSTRACTThe responses of photosynthesis to high light and low temperature were studied in vines cultivated in the greenhouse in low light. Exposure to high light (1000 /umol m−2s−1) or low temperature (5 °C) alone had no measurable effect on the photosynthetic processes, but the combination of high light and low temperature caused rapid loss of photosynthetic capacity and a decrease in the efficiency of photosynthetic energy conversion. After a 15 h exposure to 5°C at high light, the Fv/sb/Fmratio had decreased by 80% and the apparent quantum yield by 75%. Nevertheless, when the leaves were returned to low light at 22°C, these parameters recovered rapidly. The foliar pools of ascorbate and glutathione decreased in the first hours of photoinhibitory treatment while the zeaxanthin content increased from negligible levels to about 50% of the total foliar xanthophyll pool. There was a clear correlation between the zeaxanthin content of the leaves and their Fv/Fmratio during both photoinhibition and recovery. However, there was also a good correlation between the decrease in theFvFmratio and the measured decrease in the total foliar levels of the antioxidants ascorbate and glutathione. The amount of D, protein diminished over the same period as the zeaxanthin levels were increasing. This approach, involving simultaneous measurements of several parameters considered to influence photosystemy II activity, clearly demonstrates that measured decreases in Fv/Fmmay not simply be related to zeaxanthin levels or to amounts of D1protein alone but result from multifactoral infl

ISSN:0140-7791    

DOI:10.1111/j.1365-3040.1995.tb00196.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

ABSTRACTWhen14C‐labelled abscisic acid ([14C]ABA) was supplied to isolated protoplasts of the barley leaf at pH 6, initial rates of metabolism were about five times higher in epidermal cell protoplasts than in mesophyll cell protoplasts if equal cytosolic volumes were considered. In spite of the fact that epidermal cells make up only about 35% of the total water space in barley leaves, and despite the small cytosolic volume of these cells, in intact leaves all epidermal cells would thus metabolize half as much ABA per unit time as the mesophyll cells (0–27 and 0–51 mmol h−1m−3leaf water). Therefore, under these conditions epidermal cells seem to be a stronger sink than mesophyll cells for ABA that arrives via the transpiration stream. However, at an apoplastic pH of 7–25, which occurs in stressed leaves, the proportion of total metabolized ABA would be much smaller in epidermal than in mesophyll cells (0–029 and 0–204 mmolh−lm−3leaf water). Our results indicate that under conditions of slightly alkaline apoplastic pH the epidermis may serve as the main source for fast stress‐dependent ABA redistribution into the guard cell apoplast. This is partly the result of ABA transport across the epidermal tonoplast, which is dependent on the apoplastic pH and possibly on the cytosolic calcium concentration. The cuticle seems to be of no particular importance in stress‐induced apoplastic ABA shifts and cannot be regarded as a significant sink for high ABA conc

ISSN:0140-7791    

DOI:10.1111/j.1365-3040.1995.tb00197.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

ABSTRACTTemporal variations in the δ18oxygen (δ18O) content of water transpired by leaves during a simulated diurnal cycle fluctuated around the δ18O content of the source water. Reconstructed variations in the δ18O values of leaf water differed markedly from those predicted by conventional models. Even when transpiring leaves were maintained under constant conditions for at least 3 h, strict isotopic steady‐state conditions of leaf water (equality of the18O/16O ratios in the input and transpired water) were rarely attained in a variety of plant species (Citrus reticu‐lata, Citrus paradisi, Gossypium hirsutum, Helianthus annuns, Musa musaceae and Nicotinia tabacum). Isotopic analysis of water transpired by leaves indicated that leaves approach the isotopic steady state in two stages. The first stage takes 10 to 35 min (with a rate of change of about 3–3%h−1), while in the second stage further approach to the isotopic steady state is asymptotic (with a rate of change of about 0–4% h−1), and under conditions of low transpiration leaves can last for many hours. Substantial spatial isotopic heterogeneity was maintained even when leaves were at or near isotopic steady state. An underlying pattern in this isotopic heterogeneity is often discerned with increasing18O/16O ratios from base to tip, and from the centre to the edges of the leaves. It is also shown that tissue water along these spatial isotopic gradients, as well as the average leaf water, can have18O/16O ratios both lower and higher than those predicted by the conventional Craig and Gordon model. We concluded, first, that at any given time during the diurnal cycle of relative humidity the attainment of an isotopic steady state in leaf water cannot be assumeda prioriand, secondly, that the isotopic enrichment pattern of leaf water reflects gradual enrichment along the water‐flow pathway (e.g. as in a string of pools), rather than a single‐step enrichment from source water, as

ISSN:0140-7791    

DOI:10.1111/j.1365-3040.1995.tb00198.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

ABSTRACTAnalysis of soil solution from forest sites dominated byEucalyptus grandisandEucalyptus maculataindicates that soluble forms of organic nitrogen (amino acids and protein) are present in concentrations similar to those of mineral nitrogen (nitrate and ammonium). Experiments were conducted to determine the extent to which mycorrhizal associations might broaden nitrogen source utilization inEucalyptusseedlings to include organic nitrogen. In isolation, species of ectomycorrhizal fungi from northern Australia show varying abilities to utilize mineral and organic forms of nitrogen as sole sources.Pisolithussp. displayed strongest growth on NH4+, glutamine and asparagine, but grew poorly on protein, whileAmanitasp. grew well both on mineral sources and on a range of organic sources (e.g. arginine, asparagine, glutamine and protein). In sterile culture, non‐mycorrhizal seedlings ofEucalyptus grandisandEucalyptus maculatagrew well on mineral sources of nitrogen, but showed no ability to grow on sources of organic nitrogen other than glutamine. In contrast, mycorrhizal seedlings grew well on a range of organic nitrogen sources. These observations indicate that mycorrhizal associations confer on species ofEucalyptusthe ability to broaden their resource base substantially with respect to nitrogen. This ability to utilize organic nitrogen was not directly related to that of the fungal symbiont in isolation. Seedlings mycorrhizal withPisolithussp. were able to assimilate sources of nitrogen (in particular histidine and protein) on which the fungus in pure culture appeared to grow weakly. Experiments in which plants were fed15N‐labelled ammonium were undertaken in order to investigate the influence of mycorrhizal colonization on the pathway of nitrogen metabolism. In roots and shoots of all seedlings,15N was incorporated into the amide group of glutamine, and label was also found in the amino groups of glutamine, glutamic acid, γ‐aminobutyric acid and alanine. Mycorrhizal colonization appeared to have no effect on the assimilation pathway and metabolism of [15N]H4+; labelling data were consistent with the operation of the glutamate synthase cycle in plants infected with eitherPisolithussp. (which in isolation assimilates via the glutamate synthase cycle) orElaphomycessp. (which assimilates via glutamate dehydrogenase). It is likely that the control of carbon supply to the mycorrhizal fungus from the host may have a profound effect on both the assimilatory pathway and the range of nitrogen sources that can be utilized by the assoc

ISSN:0140-7791    

DOI:10.1111/j.1365-3040.1995.tb00199.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

ABSTRACTFreezing and thawing of the endemic moss speciesGrimmia antarcticiCard, caused photoinhibition. When snow cover was removed from moss in the field, resulting in exposure to fluctuating temperatures and light conditions, photoinhibition, measured as a reduction in the ratio of variable to maximum chlorophyllafluorescence (Fv/Fm), was observed. The extent of photoinhibition was highly variable and appeared to be reversible during periods of warmer temperatures. A series of controlled laboratory studies found that the light conditions that prevail between freezing and thawing events influenced the recovery from photoinhibition observed during freezing and thawing, with low light conditions facilitating the greatest rates of recovery. After four cycles of freezing and thawing, recovery from photoinhibition in hydrated moss was achieved within 12 h of transfer to 5°C and 15 μmol quanta m−2s−1. These results favour the hypothesis that photoinhibition observed during freezing represents a protective process involving the down‐regulation of photo‐system II when photosynthetic carbon assimilation is limited by low tem

ISSN:0140-7791    

DOI:10.1111/j.1365-3040.1995.tb00200.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

ABSTRACTExperiments were carried out to determine whether a semidian (12 h) rhythm in flowering response operates in Pharbitis nil as the basis for photoperiodic time measurement. The effect of 5 min far‐red light followed by 85 min dark (FRD) given 4, 8,14 and 22 h before the end of a 48 h photoperiod on night‐break timing and critical night length was determined. When given 4 h before the end of a 48 h photoperiod, an interruption with FRD advanced the phase of the circadian rhythm in the night‐break inhibition of flowering. In contrast, earlier interruptions of the photoperiod had no effect on the phase of the rhythm. The critical night length was modified by FRD given 4 h (shortened) or 8 h (lengthened) before the end of the photo‐period; when given at other times FRD did not alter the critical night length. The results are discussed in relation to the basis for photoperiodic timekeeping, with particular reference to suggestions for the involvement of a semidian rhythm. A circadian model based on the concept of limit cycles is de

ISSN:0140-7791    

DOI:10.1111/j.1365-3040.1995.tb00201.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

ABSTRACTThe xylem cavitation rate, stem water content, stomatal conductance and leaf water potential of mature Scots pine (Pinus sylvestrisL.) were compared over a period of 18 months at two sites in Britain where trees were planted from the same seed source. The sites were at Thetford in south‐east England, where the climate is relatively warm and dry (average rainfall of 600mm per year), and Aberfoyle in central Scotland, where it is relatively cool and wet (average rainfall of 1500 mm year−1). In the first year of study (1992) the natural difference between the sites was amplified by a severe drought affecting south‐east England. Acoustic emissions (as a result of cavitation) were detected at both sites, but were not an everyday occurrence, and rates depended on short‐term meteorological variation. The relative water content (RWC) of the trunk at breast height at Thetford was significantly lower than at Aberfoyle, and declined in parallel with increasing severity of drought. Following the release from drought a gradual increase in RWC was found, but the pre‐drought RWC was not attained. The same xylem water potential gradient and stomatal conductance was found at the two sites; but on a diurnal basis, as water potential declined, cavitation rates increased. There was no difference in vulnerability to cavitation or in hydraulic conductance between

ISSN:0140-7791    

DOI:10.1111/j.1365-3040.1995.tb00202.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

ABSTRACTSpinach plants were grown in hydroponic culture provided with variable limiting amounts of N. During a complete diurnal cycle, growth of the root and shoot parts, as well as levels of soluble and insoluble sugars and of free amino acids, were monitored. No clear relationship could be detected between the level of N feeding and the levels of free sugars and amino acids. Analysis of variance revealed that the variances in the relative growth rates of plant root and shoot could be correlated with the levels of sugars and amino acids. Root amino acid concentration could be correlated with shoot amino acid concentration and root sugar concentration. No relationship was found between the variances in root and shoot free sugar concentrations.

ISSN:0140-7791    

DOI:10.1111/j.1365-3040.1995.tb00203.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

ABSTRACTThe effects of small changes in natural UV‐B on the photosynthesis, pigmentation, flowering and yield of bean plants (Phaseolus vulgarisL. var. Label) were studied. To obtain a relatively natural growth environment, the plants were grown in small, half‐open greenhouses of UV‐transmitting Plexiglas of different thickness (3 and 5 mm), resulting in an 8% difference in the weighted UV‐B reaching the plants. Although the UV‐B doses used did not significantly influence photosynthesis on a leaf area basis during vegetative growth, important changes in biomass allocation were noted. A UV‐B‐O induced reduction in leaf area during the period of vegetative growth resulted in decreased dry weight after 57 d. During the flowering and pod‐filling stages (57–79.d after planting), however, plants grown at high UV‐B retained their photosynthetic capacity longer: maximal photosynthesis, chlorophyll and N content of the leaves were higher under the higher UV‐B dose at a plant age of 79 d. Combined with an increased allocation under the higher UV‐B dose of both N and biomass to the pods, this resulted in a small increase in yield and an important increase in harvest in

ISSN:0140-7791    

DOI:10.1111/j.1365-3040.1995.tb00204.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY