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1.
The CO2 dynamics were measured in an organic soil in eastern Finland during the growing season and wintertime, and the annual CO2 balance was calculated for plots where barley or grass was grown. During the summer, the CO2 dynamics were measured by transparent and opaque chambers using a portable infrared gas analyser for the CO2 analyses. During the winter, the CO2 release was measured by opaque chambers analysing the samples in the laboratory with a gas chromatograph. Statistical response functions for CO2 dynamics were constructed to evaluate the annual CO2 exchange from the climatic data. The net CO2 exchange was calculated for every hour in the snow‐free season. The carbon balance varied extensively depending on the weather conditions, and type and phenology of vegetation. During the growing season, the grassland was a net source while the barley field was a net sink for CO2. However, both soils were net sources for CO2 when autumn, winter and spring were included also. The annual CO2 emissions from the grassland and barley soil were 750 g CO2‐C m?2 and 400 g CO2‐C m?2, respectively. The carbon accumulated in root and shoot biomass during the growing season was 330 g m?2 for grass and 520 g m?2 for barley. The C in the aboveground plant biomass ranged from 43 to 47% of the carbon fixed in photosynthesis (PG) and the proportion of C in the root biomass was 10% of the carbon fixed in photosynthesis. The bare soils had 10–60% higher net CO2 emission than the vegetated soils. These results indicate that the carbon balance of organic soils is affected by the characteristics of the prevailing plant cover. The dry summer of 1997 may have limited the growth of grass in the late summer thus reducing photosynthesis, which could be one reason for the high CO2 release from this grass field.  相似文献   

2.
We analysed the impact of elevated CO2 on water relations, water use efficiency and photosynthetic gas exchange in barley (Hordeum vulgare L.) under wet and drying soil conditions. Soil moisture was less depleted under elevated compared to ambient [CO2]. Elevated CO2 had no significant effect on the water relations of irrigated plants, except on whole plant hydraulic conductance, which was markedly decreased at elevated compared to ambient CO2 concentrations. The values of relative water content, water potential and osmotic potential were higher under elevated CO2 during the entire drought period. The better water status of water-limited plants grown at elevated CO2 was the result of stomatal control rather than of osmotic adjustment. Despite the low stomatal conductance produced by elevated CO2, net photosynthesis was higher under elevated than ambient CO2 concentrations. With water shortage, photosynthesis was maintained for longer at higher rates under elevated CO2. The reduction of stomatal conductance and therefore transpiration, and the enhancement of carbon assimilation by elevated CO2, increased instantaneous and whole plant water use efficiency in both irrigated and droughted plants. Thus, the metabolism of barley plants grown under elevated CO2 and moderate or mild water deficit conditions is benefited by increased photosynthesis and lower transpiration. The reduction in plant water use results in a marked increase in soil water content which delays the onset and severity of water deficit.  相似文献   

3.
A careful restudy of the photosynthetic process of barley (Hordeum vulgare) infected with powdery mildew (Erysiphe graminis f. sp. hordei) is reported. Unlike previous reports, which indicated a stimulation in infected host tissue photosynthesis during early stages of the disease followed by a rapid decline in activity, this study observed no stimulation but instead a biphasic inhibition in infected host photosynthesis under physiological concentrations of CO2. Under high CO2 (1.0%) a stimulation was observed during early stages of infection. The inhibition in low CO2 and stimulation in high CO2 of infected host photosynthesis was shown to occur in healthy host tissue when in the presence of 10−2m α-hydroxy-2-pyridinemethanesulfonic acid. The possible significance of these similar results is discussed.  相似文献   

4.
We constructed a carbon budget for young birch trees grown in ambient and elevated CO2 concentrations over their fourth year of growth. The annual total of net leaf photosynthesis was 110% more in elevated CO2 than in ambient CO2. However, the trees in elevated CO2 grew only 59% more biomass than the trees in ambient CO2 over the year. Modelling studies showed that larger loss of carbon from fine-root production and growth of the root-associated mycorrhiza by the trees in elevated CO2 probably accounted for all the remaining difference in net photosynthesis between the two treatments. Our modelling also showed that the fraction of net photosynthate consumed by respiration of nonleaf tissue was similar in the two CO2 treatments, and was 26% and 24% for trees in ambient and elevated CO2, respectively. Trees in elevated CO2 had 43% more leaves, and produced 110% more net photosynthate than trees in ambient CO2, even though the maximum rate of carboxylation per unit leaf nitrogen decreased by 21%. Sensitivity studies showed that down-regulation reduced the annual net photosynthetic production of the trees in elevated CO2 by only 6%. Direct effects of higher CO2 on photosynthesis and greater leaf area of the trees in elevated CO2 increased the net photosynthesis of the trees by 68% and 60%, respectively; and together accounted for most of the difference in net photosynthesis between the two treatments.  相似文献   

5.
The changes caused by NaCl salinity and jasmonic acid (JA) treatment (8 days) on growth and photosynthesis of barley plants (Hordeum vulgare L., var. Alfa) have been studied. Gas exchange measurements and analysis of enzyme activities were used to study the reactions of photosynthesis to salinity and JA. Both 100 mm NaCl and 25 μm JA treatment led to a noticeable decrease in both the initial slope of the curves representing net photosynthetic rate vs intercellular CO2 concentration and the maximal rate of photosynthesis. The calculated values of the intercellular CO2 concentration, CO2 compensation point, and maximal carboxylating efficiency of ribulose-1,5-bisphosphate carboxylase support the suggestion that biochemical factors are involved in the response of photosynthesis to JA and salinity stress. The activities of phosphoenolpyruvate carboxylase and carbonic anhydrase increased more than twofold. Pretreatment with JA for 4 days before salinization diminished the inhibitory effect of high salt concentration on the growth and photosynthesis. The results are discussed in terms of a possible role of JA in increasing salinity tolerance of the barley plants. Received September 8, 1997; accepted May 19, 1998  相似文献   

6.
Distribution of assimilates in cultivars of spring barley with different resistance against powdery mildew (Erysiphe graminis f. sp. hordei) Transport and distribution of radioactive labelled assimilates in spring barley cultivars with different degrees of resistance to powdery mildew were studied after 14CO2-treatment of single leaves. Plants of the cultivars ‘Amsel’ (susceptible), ‘Asse’ (adult plant resistant), and ‘Rupee’ (resistant) were analyzed at the vegetative growth stage (5. leaf unfolded) and the generative growth stage (anthesis). At the vegetative growth stage the assimilate export from the mildew inoculated 5. leaf of ‘Amsel’ and ‘Rupee’ is decreased; in ‘Asse’, there is no considerable change of assimilate distribution due to infection. At the generative growth stage the assimilate export from the infected flag leaf of ‘Amsel’ is reduced when the fungus, is sporulating. In the cultivar ‘Asse’ the assimilates are bound at the infection site until the seventh day after inoculation, then the transport of assimilates to the ear is increased. In ‘Rupee’ mildew inoculation causes an enhanced assimilate transport to the ear. The changes in assimilate distribution due to mildew inoculation are discussed with respect to the different types of host-parasite-interactions and the source-sink-activities in the different cultivars.  相似文献   

7.
The effects on photosynthesis of CO2 and desiccation in Porphyra haitanensis were investigated to establish the effects of increased atmospheric CO2 on this alga during emersion at low tides. With enhanced desiccation, net photosynthesis, dark respiration, photosynthetic efficiency, apparent carboxylating efficiency and light saturation point decreased, while the light compensation point and CO2 compensation point increased. Emersed net photosynthesis was not saturated by the present atmospheric CO2 level (about 350?ml?m?3), and doubling the CO2 concentration (700?ml?m?3) increased photosynthesis by between 31% and 89% at moderate levels of desiccation. The relative enhancement of emersed net photosynthesis at 700?ml?m?3 CO2 was greater at higher temperatures and higher levels of desiccation. The photosynthetic production of Porphyra haitanensis may benefit from increasing atmospheric CO2 concentration during emersion.  相似文献   

8.
A comparison was made of stomatal behaviour, and related phenomena,between leaves of garden pea (Pisum sativum cv. Feltham First)inoculated with powdery mildew fungus (Erysiphe pisi) and uninfectedleaves on healthy plants. Twenty four hours after inoculation,stomata opened more widely in the light in infected leaves thanin healthy leaves. Thereafter, stomatal opening was progressivelyreduced by infection and stomata failed to close completelyin the dark until, 7 d after inoculation, all movements ceasedand stomata remained partly open. Transpiration in the lightfollowed closely the pattem of stomatal opening and, after anearly increase compared with healthy controls, was progressivelyreduced by infection. Evidence is presented that transpirationfrom the fungus was less than the reduction in transpiraationfrom the leaf which was caused when development of the myceliumincreased the boundary layer resistance of the leaf. Seven daysafter inoculation, transpiration in the dark was greater frominfected leaves than from healthy leaves because of partly openstomata in the dark. Net photosynthesis in infected leaves was reduced within 24h of inoculation to a level below that found in healthy leavesand thereafter it declined progressively. The initial reductionwas due to a transient increase in photorespiration, for whenthe glycolate pathway was inhibited by a 2% O2 concentrationthere was no difference between the (gross) photosynthetic ratesof healthy and infected leaves. Changes in photorespirationrate were confirmed from the interpretation of the CO2 burston darkening. Reduced stomatal opening was a contributory causeof the reduction in net photosynthesis in the later stages ofinfection. Since the rate of gross photosynthesis, but not therate of photorespiration, of infected plants fell below thatof healthy plants, and infected plants had a higher rate ofrelease of CO2 in the dark than healthy plants from the thirdday after inoculation onwards, infected plants consume an increasinglygreater proportion of their photosynthate in respiratory processesthan do healthy plants. The CO2 compensation point of infectedplants increased at every time of sampling after inoculation.  相似文献   

9.
Two branches of a field-grown Chamaecy-paris obtusa tree were enclosed in chambers of an open gas exchange system for continuous CO2 exchange measurements. One branch was subjected to ambient air (CO2, 370 μmol mol–1) and the other was subjected to CO2-enriched air (800 μmol mol–1). The CO2 exchange rate of the branches, air temperature and photosynthetic photon flux density were recorded every 4 min by a computer during the two experimental periods of July 1994 to June 1995 (experiment 1) and April 1996 to August 1997 (experiment 2). The response of CO2 gas exchange rate to light changed with the seasonal temperature. The highest saturated rate of net photosynthesis on a leaf area basis was observed in May and October in both CO2 treatments when the mean daytime temperature was about 18–19°C. This temperature was almost equal to the yearly mean daytime temperature. Above and below this temperature, the saturated net photosynthesis rate decreased. The net photosynthesis rate was usually higher in the elevated CO2 treatment. The ratio of monthly net photosynthesis rate in elevated CO2 to that in ambient CO2 was linearly related to the monthly mean daytime temperature. This ratio increased by 3.3% for each 1°C increase in the monthly mean daytime temperature; the highest ratio of 1.8 occurred in August. When the ratio was 1.0, the temperature was about 5–6°C, which was close to the mean daytime temperature of the coldest month. Elevated CO2 increased per unit area net photosynthesis by 38.5% and 43.7% in experiments 1 and 2, respectively. Received: 29 March 1999 / Accepted: 22 October 1999  相似文献   

10.
The gas exchange of barley ears and awns was measured in the field using a gas analysis system and a diffusion porometer. Awn stomatal resistance decreased with increasing irradiance but to a smaller extent than leaf stomatal resistance. Measurements on ears immediately before and after successively removing awns showed that awn transpiration and photosynthesis were proportional to awn area and that awns accounted for 73% of transpiration by the ear. Although the maximum rates of photosynthesis of which awns were capable declined with age, awns accounted for 80–115% of the net CO2 uptake of complete ears because the ears-less-awns could respire more CO2 than they absorbed. Ear photosynthesis accounted for 52% of the weekly increment in ear dry weight after ear emergence, but 5 weeks later photosynthesis by the ear balanced respiration. Overall photosynthesis by the ear accounted for 35 % of its final weight. Differences in the light response curves of leaves and ears can be fully accounted for by the different relationships between stomatal resistance and irradiance of the two organs.  相似文献   

11.
Photosynthesis and photorespiration in whole plants of wheat   总被引:12,自引:11,他引:1       下载免费PDF全文
Wheat was cultivated in a small phytotronic chamber. 18O2 was used to measure the O2 uptake by the plant, which was recorded simultaneously with the O2 evolution, net CO2 uptake, and transpiration. At normal atmospheric CO2 concentration, photorespiration, measured as O2 uptake, was as important as the net photosynthesis. The level of true O2 evolution was independent of CO2 concentration and stayed nearly equal to the sum of net CO2 photosynthesis and O2 uptake. We conclude that at a given light intensity, O2 and CO2 compete for the reducing power produced at constant rate by the light reactions of photosynthesis.  相似文献   

12.
In many plant species that remain leafless part of the year, CO2 fixation occurring in green stems represents an important carbon gain. Traditionally, a distinction has been made between stem photosynthesis and corticular photosynthesis. All stem photosynthesis is, sensu stricto, cortical, since it is carried out largely by the stem cortex. We proposed the following nomenclature: stem net photosynthesis (SNP), which includes net CO2 fixation by stems with stomata in the epidermis and net corticular CO2 fixation in suberized stems, and stem recycling photosynthesis (SRP), which defines CO2 ling in suberized stems. The proposed terms should reflect differences in anatomical and physiological traits. SNP takes place in the chlorenchyma below the epidermis with stomata, where the net CO2 uptake occurs, and it resembles leaf photosynthesis in many characteristics. SRP is found in species where the chlorenchyma is beneath a well-developed stomata-free periderm and where reassimilation of internally respired CO2 occurs. SNP is common in plants from desert ecosystems, rates reaching up to 60% of the leaf photosynthetic rate. SRP has been demonstrated in trees from temperate forests and it offsets partially a carbon loss by respiration of stem nonphotosynthetic tissues. Reassimilation can vary between 7 and 123% of respired CO2, the latter figure implying net CO2 uptake from the atmosphere. Both types of stem photosynthesis contribute positively to the carbon economy of the species, in which they occur; they are advantageous to the plant because they allow the maintenance of physiological activity during stress, an increase of integrated water use efficiency, and they provide the carbon source used in the production of new organs.  相似文献   

13.
Leaf photosynthesis of the sensitive plant Mimosa pudica displays a transient knockout in response to electrical signals induced by heat stimulation. This study aims at clarifying the underlying mechanisms, in particular, the involvement of respiration. To this end, leaf gas exchange and light reactions of photosynthesis were assessed under atmospheric conditions largely eliminating photorespiration by either elevated atmospheric CO2 or lowered O2 concentration (i.e. 2000 μmol mol?1 or 1%, respectively). In addition, leaf gas exchange was studied in the absence of light. Under darkness, heat stimulation caused a transient increase of respiratory CO2 release simultaneously with stomatal opening, hence reflecting direct involvement of respiratory stimulation in the drop of the net CO2 uptake rate. However, persistence of the transient decline in net CO2 uptake rate under illumination and elevated CO2 or 1% O2 makes it unlikely that photorespiration is the metabolic origin of the respiratory CO2 release. In conclusion, the transient knockout of net CO2 uptake is at least partially attributed to an increased CO2 release through mitochondrial respiration as stimulated by electrical signals. Putative CO2 limitation of Rubisco due to decreased activity of carbonic anhydrase was ruled out as the photosynthesis effect was not prevented by elevated CO2.  相似文献   

14.
The future environment may be altered by high concentrations of salt in the soil and elevated [CO2] in the atmosphere. These have opposite effects on photosynthesis. Generally, salt stress inhibits photosynthesis by stomatal and non-stomatal mechanisms; in contrast, elevated [CO2] stimulates photosynthesis by increasing CO2 availability in the Rubisco carboxylating site and by reducing photorespiration. However, few studies have focused on the interactive effects of these factors on photosynthesis. To elucidate this knowledge gap, we grew the barley plant, Hordeum vulgare (cv. Iranis), with and without salt stress at either ambient or elevated atmospheric [CO2] (350 or 700 μmol mol−1 CO2, respectively). We measured growth, several photosynthetic and fluorescence parameters, and carbohydrate content. Under saline conditions, the photosynthetic rate decreased, mostly because of stomatal limitations. Increasing salinity progressively increased metabolic (photochemical and biochemical) limitation; this included an increase in non-photochemical quenching and a reduction in the PSII quantum yield. When salinity was combined with elevated CO2, the rate of CO2 diffusion to the carboxylating site increased, despite lower stomatal and internal conductance. The greater CO2 availability increased the electron sink capacity, which alleviated the salt-induced metabolic limitations on the photosynthetic rate. Consequently, elevated CO2 partially mitigated the saline effects on photosynthesis by maintaining favorable biochemistry and photochemistry in barley leaves.  相似文献   

15.
The aim of the presented work was to study whether the efficiency of photosynthesis may influence resistance of hardened plants to disease. Seedlings of spring barley, meadow fescue and winter oilseed rape were chilled at 5 °C for 2, 4 or 6 weeks and at these deadlines the changes in cell membrane permeability (expressed as electrolyte leakage), chlorophyll fluorescence (initial fluorescence - F0, maximal fluorescence - Fm, quantum yield of PSII - Fv/Fm) and net photosynthesis rate (FN) were measured. Also, the influence of cold on the degree of plant resistance to economically important pathogens -Bipolaris sorokiniana or Phoma lingam was estimated. Two, four or six week-hardened plants were artificially infected: barley and fescue by B. sorokiniana, and oilseed rape by P. lingam. Hardening at 5 °C stimulated resistance of barley, fecue and rape to their specific pathogens. Six-week long acclimation was the most effective for plant resistance. Cold significantly changed cell membrane permeability and decreased chlorophyll fluorescence (F0, Fm and Fv/Fm) of all studied plant species, while net photosynthesis rate was found to decrease only in barley. The results indicate that cold-induced resistance of plants to pathogens was correlated with a decrease in cell membrane permeability. In the case of fescue and barley a significant connection between the quantum yield of PSII and their resistance to B. sorokiniana was shown. Additionally, the resistance of barley to fungus was depended on net photosynthesis rate. In general this research shows that the efficiency of photosynthesis may be used as an indicator of plant resistance to disease.  相似文献   

16.
The relationship between photosynthesis and photorespiration was determined in normal and 26 mutants of barley (Hordeum vulgare L. var. Himalaya). The rate of apparent photosynthesis ranged from 1 to 30 milligrams of CO2 per square decimeter per hour. The variation in rate of photosynthesis was due, in some cases, to differences in chlorophyll content, in others to stomatal resistance, and in still others to unknown factors; but no single factor accounted for the variation. Photorespiratory activity, as determined by the 14CO2/12CO2 technique, CO2 evolution into CO2-free air, and the response of photosynthesis to low and high O2 concentrations, was positively and significantly correlated with photosynthesis. This supports the idea that the two processes are integrally and tightly coupled. There appears to be no competition between photosynthesis and photorespiration, and the probability of finding plants with high rates of photosynthesis and low rates of photorespiration measured under natural conditions, appears to be very low.  相似文献   

17.
Kellomäki  Seppo  Wang  Kai-Yun 《Plant Ecology》1998,136(2):229-248
Starting in early spring of 1994, naturally regenerated, 30-year-old Scots pine (Pinus sylvestris L.) trees were grown in open-top chambers and exposed in situ to doubled ambient O3,doubled ambient CO2 and a combination of O3 and CO2 from 15 April to 15 September. To investigate daily and seasonal responses of CO2 exchange to elevated O3 and CO2, the CO2 exchange of shoots was measured continuously by an automatic system for measuring gas exchange during the course of one year (from 1 Januray to 31 December 1996). A process-based model of shoot photosynthesis was constructed to quantify modifications in the intrinsic capacity of photosynthesis and stomatal conductance by simulating the daily CO2 exchange data from the field. Results showed that on most days of the year the model simulated well the daily course of shoot photosynthesis. Elevated O3 significantly decreased photosynthetic capacity and stomatal conductance during the whole photosynthetic period. Elevated O3 also led to a delay in onset of photosynthetic recovery in early spring and an increase in the sensitivity of photosynthesis to environmental stress conditions. The combination of elevated O3 and CO2 had an effect on photosynthesis and stomatal conductance similar to that of elevated O3 alone, but significantly reduced the O3-induced depression of photosynthesis. Elevated CO2 significantly increased the photosynthetic capacity of Scots pine during the main growing season but slightly decreased it in early spring and late autumn. The model calculation showed that, compared to the control treatment, elevated O3 alone and the combination of elevated O3 and CO2 decreased the annual total of net photosynthesis per unit leaf area by 55% and 38%, respectively. Elevated CO2 increased the annual total of net photosynthesis by 13%.  相似文献   

18.
Decrease in net photosynthesis caused by respiration   总被引:11,自引:10,他引:1       下载免费PDF全文
Bravdo BA 《Plant physiology》1968,43(4):479-483
CO2 exchange between air and leaf is conceived as a current along a resistor with a respiratory current, unaffected by CO2 concentration, entering the resistor. The conclusion follows that a plant placed in an atmosphere free of CO2 will increase the CO2 concentration to the compensation concentration along a curve determined by the resistor and the volume of the atmosphere. This was verified. Also a photosynthesis rate calculated from the parameters of the observed curve agreed with an independent observation of photosynthesis in CO2-free air. The decrease in net photosynthesis caused by respiration is, according to the model, the CO2 compensation concentration divided by the concentration in the atmosphere.  相似文献   

19.
Measurements of carbon dioxide exchange and transpiration were made, at various air temperatures, on wheat and barley using a field enclosure system. From these were derived the stomatal and mesophyll resistances to carbon dioxide transfer. Optimum temperatures for net CO2 uptake were about 24°C for wheat and barley. Above these optima, as temperature increased so net CO2 uptake rates decreased, because of increasing stomatal and mesophyll resistances; transpiration rates decreased in wheat but were constant in barley. In laboratory growth cabinets, wheat plants were subjected to different regimes of temperature and humidity. Optimum temperature for net CO2 uptake of individual leaves was 25°C. At constant humidity, a decline in net uptake rates above 25°C was associated with large increases in mesophyll resistance. At a constant 25°C, as the vapour pressure deficit (v.p.d. was increased above 1 k Pa (10 mb) v.p.d. the net uptake declined, with an increase in mesophyll resistance and a small increase in stomatal resistance. When the v.p.d. exceeded 1 k Pa at a temperature of 30°C, conditions that are experienced by field plants, then there were large increases in both mesophyll and stomatal resistances and the net uptake rates declined. Photo-respiration, as measured by CO2 uptake in oxygen-free air, was independent of temperature, but both dark respiration and CO2 compensation concentration increased with temperature.  相似文献   

20.
Summary Thalli of Ramalina maciformis were moistened to their maximal water holding capacity, thus, simulating actual conditions following a heavy rainfall. Time courses of net photosynthesis at 17° C and 750 E m-2 s-1 light intensity (PAR) were obtained during drying of the thalli. At ambient CO2 concentrations from 200 to 1,000 ppm, CO2 uptake of the moist lichens was depressed at high water content. After a certain water loss, net photosynthesis increased to a maximal value and decreased again with further drying of the thalli. The degree of initial depression of photosynthesis decreased with increasing ambient CO2 concentration, and it was fully absent at 1,600 ppm ambient CO2. Under these conditions of CO2 saturation, net photosynthesis remained constant at maximum for many hours and decreased only when substantial amounts of water had been lost. We conclude that the carboxylation capacity of the lichen is not affected by high contents of liquid water. Therefore, the depression of CO2 uptake of the water saturated lichen at lower (e.g. natural) ambient CO2 must be due exclusively to increased resistance to CO2 diffusion from the external air to the sites of carboxylation.  相似文献   

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