CO2 Dm Research Articles

Measurements of14C Incorporation by Illuminated Intact Leaves of Coffee Plants from Gas Mixtures Containing14CO2

A study was made of the incorporation of 14C by intact leaves oi'Coffea arabica (cultivars Mundo Novo, Catuai, 1130-13, and H 6586-2) and Coffea canephora (cultivar Guarini) supplied with gas mixtures containing 14CC>2 under controlled conditions. Samples of the leaves were com busted and the 14C in the CO2 produced measured using a liquid scintillation counter. The results were used to estimate photosynthetic rates. The effects of changing the partial pressures of O2 and CO2 on the photosynthetic rate were studied and estimates made of the CO2 com pensation point and photorespiration. The data obtained show differences between the mean net photosynthetic rates of the C. arabica cultivare (6-14 mg CO2 dm-2 h_1) and the mean rate for the C. canephora cultivar (3-96 mg CO2 dm-2 h-1). The cultivar of the latter species photorespired more rapidly than the cultivar Catuai of G. arabica. Rates of photosynthesis in coffee measured using the 14CC>2 method were similar to rates obtained by others using an infrared gas analyser. The 14CC>2 method proved to be reliable for photosynthetic measurements and the apparatus is suitable for use in field conditions.

Relationship of Net Photosynthesis to Carbon Dioxide Concentration and Leaf Characteristics in Selected Peanut (Arachis) Genotypes1

Abstract Five genotypes, including two cultivars of Arachis hypogaea L. and three wild species of Arachis, were tested for their photosynthetic capacity at atmospheric CO2 concentrations and for photorespiration in CO2-free air. Photosynthetic response to CO2 concentrations in the range of 50 to 600 ppm was also tested. Diffusive resistance (DRH2O) of the adaxial surface of the five genotypes was measured with a diffusive resistance porometer. Several other leaf characteristics related to CO2 exchange were measured. There was a linear increase in net photosynthesis (Pn) for four of the five genotypes as CO2 concentration was increased from 50 to 600 ppm. The increase in Pn of an A. hypogaea genotype from Tanganyika appeared to be progressively less at CO2 concentrations near 600 ppm. The florunner cultivar of A. hppogaea had the highest Pn at CO2 concentrations of 300 ppm and above; A. pintoi had the lowest. Photorespiration as measured by CO2 evolution into CO2-free air averaged about 4 mg CO2 dm -2 hr -1 and did not differ among genotypes. Dark respiration was higher in leaves of wild species than in the two genotypes of A. hypogaea. Diffusive resistance of A. hypogaea, A. pintoi and A. sp. (glabrata?) leaves remained constant from 9 a.m. to 3 p.m. EST and then increased up to the last measurement at 10 p.m. The DRH2O of A. hypogaea and A. pintoi were similar during the daytime and ranged from 1.5 to 5.0 sec cm -1 between 9 a.m. and 3 p.m. A. villosulicarpa and A. sp. (glabrata?) had higher DRH2O values during the same time period, ranging from 5 to 12 sec cm-1. At 10 p.m. DRH2O of A. hypogaea was 84 sec cm-1 compared to only about 20 sec cm-1 for A. pintoi. Net photosynthesis of leaves of the five Arachis genotypes was not closely related to DRH2O nor leaf characteristics including chlorophyll content, stomatal frequency, leaf nitrogen content or specific leaf weight.

Photosynthesis in Peanut (Arachis) Genotypes1

Abstract Research was undertaken to assess the variation in photosynthetic capacity within the genus Arachis and to determine associations between photosynthesis and other leaf characteristics. Photosynthetic rates of attached leaves of thirty-one peanut genotypes, including six wild (Arachis L.) species and twenty-four genotypes of the cultivated species, Arachis hypogaea L., were measured by gas exchange. Genotypes of A. hypogaea showed a range in photosynthetic rates from 24 to 37 mg CO2 dm-2 hr-1. Florunner, a recently developed US cultivar, consistently had higher photosynthetic rates than most other peanut genotypes. The rates were approximately 41 and 30 mg CO2 dm-2 hr-1 in two pot experiments and a field test, respectively. Wild species had generally lower photosynthetic rates than did A. hypogaea. A. pintoi Krap. et Greg. had the lowest rate of photosynthesis and the lowest specific leaf weight in the three experiments. Photosynthetic rate was positively correlated, though weakly, with percent nitrogen and chlorophyll content of leaves in two out of three experiments. Specific leaf weight was positively correlated with photosynthesis in only one out of three experiments. Stomatal frequency and photosynthetic rates were negatively correlated. The relationship between photosynthesis and leaf characteristics is discussed.

Photosynthesis in the Rose; Effect of Light Intensity, Water Potential and Leaf Age1

Abstract The net rate of 14CO2 uptake was determined on individual leaves of Rosa hybrida, cv. ‘Forever Yours’, budded on Rosa manetti and grown in gravel. Rose leaves were found to reach an average peak of 11 mg CO2 dm−2 hr−1 about 6 days after the red color disappeared on the leaf underside, or 32 days after harvesting the previous flower on the parent cane. Thereafter, CO2 uptake declined during 14 days to 5 to 6 mg CO2 dm−2 hr−1. At ambient CO2 concentrations of 500 ppm, the maximum net uptake was near 3400 ft-c. However, internal plant water potential influenced the CO2 uptake by reducing it at each increase of radiant energy. This resulted in light saturation at lower energies the lower the plant water potential. Radiant energy affected both net CO2 uptake and water potential. Wilting was generally observed to occur at about –13 bars, and maximum rates of CO2 uptake were found at potentials of –8 bars or higher, over a range of 350 to 450 microeinsteins, or 3000 to 3500 ft-c.

Photosynthetic Characteristics of Panicum milioides, a Species with Reduced Photorespiration1

A species (Panicum milioides Nees ex. Trin.), has been found which apparently has a reduced rate of photorespiration compared to other C3 plants. It was found in preliminary studies that the response of net photosynthesis (Pn) to O2 concentration was less for this species than for other C3 plants. Therefore, this work was conducted to characterize for five accessions of P. milioides the CO2 exchange related to photorespiration. Panicum maximum Jacq. (C4), P. laevifolium Htack. (C4), and tall fescue (Festuca arundinacea Schreb. (C3) were included for comparison. Leaf cross‐sections of P. milioides were examined for characteristics known to be related to photosynthetic carbon pathways. 13C/12C ratios were determined on P. milioides tissue.P. milioides photorespired less than tall fescue and more than P. maximum as determined by the three criteria: Pn response to O2, CO2 evolution in the light, and CO2 compensation concentration. The change in Pn for each 1% increase in O2 was from −0.36 to −0.48 mg CO2 dm−2 h−1 for five accessions of P. milioides compared to −0.10, −0.13, and −0.61 mg dm−2 h−1 for P. maximum, P. laevifolium, and tall fescue, respectively. P. milioides evolved an average of 0.85 mg CO2 dm−2 h−1 in the light at 20% O2 compared to 0.02 mg dm−2 h−1 for P. maximum and 2.96 mg dm−2 h−1 for tall fescue. CO2 compensation concentrations determined by a Mylar bag technique were 0.4, 15.8, and 54 ppm for P. maximum, P. milioides, and tall fescue, respectively. Determination of CO2 compensation from Pn response to CO2 gave a similar trend, although actual concentrations were different. P. milioides tissue had δ 13C values of about −25 ‰, characteristic of C3 species. A leaf anatomical study showed that P. milioides had enlarged parenchyma sheath cells with centripetally located chloroplasts and mesophyll cells arranged in a radial manner around the parenchyma sheath. The parenchyma sheath cell walls appeared to be thicker than those of most C3 species. It is concluded that while P. milioides exhibits mostly C3 characteristics, its reduced photorespiration rate and some C4‐like anatomical characteristics indicate a degree of intermediacy between C3 and C4.

Environmental influences on light and dark CO2 fixation by Kalanchoe daigremontiana

The influence of day length, light quality, temperature, drought, and oxygen concentration on gas exchange of Kalanchoe daigremontiana was investigated. The ratio of photosynthesis to dark CO2 fixation with plants under a long-day and short-warm-night regime was 2.0 and under a short-day and long-cool-night regime, 0.2. With drought conditions this value may be less than 0.02. Under low oxygen concentrations high photosynthetic rates of about 20 mg CO2 dm−2 h−1 were observed with a compensation point of about 20 ppm. Restricting CO2 supply to dark periods produced plants with a δ13C value of −10.6‰. Restricting CO2 supply to light periods gave a δ13C value of −25.9‰, whereas no control of CO2 gave δ13C values of −15‰. The data obtained suggest that variations in δ13C values in Kalanchoe result from changes in the proportion of light and dark CO2 fixation.Far-red light and oxygen promoted the release of CO2 from Kalanchoe after the plants had undergone a period of dark CO2 fixation. Maximum release occurred within about 1 h. The effect could be reversed by removal of either far-red light or oxygen. Decreases in the acidity of the plants accompanied CO2 release, which indicated that decarboxylation of a C4 acid was the source of the CO2.

Productivity of Vegetable Crops in a Region of High Solar Input. IV. Field Chamber Measurements on French Beans (Phaseolus vulgaris L.) And Cabbages (Brassica oleracea L.)

Net CO2 uptakes have been measured for crop canopies of French beans and cabbages, sown at two plant densities, using a large field assimilation chamber and a semi-closed gas-analysis system. For both species, the maximum rates of uptake were a little less than 40 mg CO2 dm-2 (ground area) h-1, and light saturation of the canopy occurred at 600-650 W m-2 (French beans) or about 800 W m-2 (cabbages). Net CO2 uptake decreased with leaf area index at values below about 5, but was relatively insensitive to temperature over the range used. Once this leaf area index was reached, the relationship between net uptake and solar radiation remained fairly constant throughout the growth period. For both species, dark respiration rates were markedly dependent on temperature, and also were lower at night than during the day when measured at the same temperature. For both French beans and cabbages, growth analyses showed the maximum growth rates to be 18-19 g dry weight m-2 (ground area) day-1. The mean growth rate from emergence to harvest for an overwintered cabbage crop was 5.5 g m-2 day-1. It is suggested that the main advantage of the region in terms of plant productivity lies in the long frost-free growing season and the ability of frost-tolerant crops to maintain fairly high growth rates throughout a mild and comparatively sunny winter.

Characteristics of photosynthesis in peach leaves

Seasonal photosynthetic patterns of Loring peach (Prunus persica (L). Batsch) leaves were monitored throughout the 1974 growing season. Using leaves on detached branches, CO2 exchange was measured under controlled light and temperature conditions. Net photosynthesis rate varied from 9 to 12.4 mg CO2 dm(-2) leaf area h(-1) and was correlated with fruit development, with the highest values occurring during the final stage of fruit maturation. The proximity of fruits to leaves also regulated photosynthesis, with the highest rates occurring in leaves closest to fruit. Soluble-sugar content in fruits and fruit yield were highest in tree areas with greatest exposure to direct sunlight although leaf area was evenly distributed throughout the tree. Light and temperature optimum for photosynthesis in peach leaves was 9.5×10(-3) erg cm(-2) s(-1) and 30°, respectively.

Frond development and CO2-fixation in Laminaria hyperborea

Discs punched out of different zones of the found of Laminaria hyperborea (Gunn.) Fossl. were exposed to H(14)CO3 (-) in the light and in the dark for various lengths of time. Photosynthetic rates in young and old parts were in the same range, 12-39 μmol CO2 dm(-2) h(-1) at 4°C, whereas dark fixation was remarkably higher in the growing zone than in the old frond: 13-28% of the corresponding light fixation in the young phylloid and only 2-6% in the old one. In all parts of the frond the reductive pentose phosphate cycle is the main system of carboxylation, and is accompanied by a notable primary synthesis of amino acids. In the growing zone heavy and primary labelling of malate and aspartate parallel to 3-PGA is due to the undiminshed activity of the dark fixation system (PEP-carboxykinase) in the light. Mannitol synthesis seems to be enhanced with increasing age of the phylloid, but rapid and primary (14)C-incorporation into amino acids was found in all parts of the frond.The data presented here suggest a possible significance of the high dark fixation rates for the growth of the sublittoral Laminaria hyperborea. Translocation of mobilized storage material from the old phylloid might supply the young tissue with reduced material during the growth season when the light intensity is low in the habitat of this alga.

Genetic Variability for Net Photosynthesis in Tall Fescue1

Significant differences in net carbon exchange (NCE) were detected among tall fescue (Festuca arundinacea Schreb.) clonal lines and among their polycross progenies under sward conditions in the field. On dates when differences among parental lines were significant, heritability values ranged from 0.57 to 0.83 in the broad sense, and from 0.22 to 0.44 in the narrow sense. In those instances, expected genetic advance with selection of the upper 5% of the population ranged from 0.77 to 3.13 mg CO2 dm∗2 hr∗1. Genetic variation was from four to six times greater among the parental lines than their polycross progenies. Rates of NCE were significantly increased by irrigation during periods of drought stress. The magnitude of the genetic variability was also greater under more favorable moisture conditions; however, relative differences among genotypes were not consistent under the two moisture regimes. It appears that genetic progress can be made through selection for NCE rate in tall fescue, but the environment must be considered during selection

Product Inhibition of Photosynthesis in Alfalfa Leaves as Related to Specific Leaf Weight

Diurnal changes in SLW (specific leaf weight‐mg dry wt cm−2 leaf area) of recently fully expanded leaves reflect the photosynthate production‐translocation balance within the leaf. Therefore, SLW should increase when synthesis exceeds transport and should decrease when transport exceeds synthesis. SLW had a close negative correlation with NCE (net carbon dioxide exchange rate‐mg CO2 dm−2 hr−1) as measured on attached alfalfa (Medicago sativa L.) leaves. Since maximum NCE coincided with minimum SLW (after about 1 hr illumination) and furthermore, a secondary maximum NCE occurred concomitantly with a secondary minimum SLW (after about 4‐hr illumination) a causal relationship between the changes in NCE and SLW is suggested. The close negative relationship between NCE and SLW is interpreted as additional evidence for a feed‐back inhibition of photosynthesis.

COMPARATIVE DATA ON THE RATE OF PHOTOSYNTHESIS, RESPIRATION, AND TRANSPIRATION OF DIFFERENT ORGANS IN AWNED AND AWNLESS ISOGENIC LINES OF WHEAT

Net photosynthesis, respiration, and transpiration were determined on heads and flag leaves of two isogenic lines of wheat (Triticum aestivum L. em Thell) by measuring the difference in CO2 and water-vapor concentrations between the incoming and outgoing air streams of an open cuvette system. Net photosynthetic rates (mg CO2 dm−2 hr−1) of the awnless, awned, and awned-clipped heads were not significantly different, but the amount of photosynthesis (mg CO2 hr−1) per head was greater for the awned than for the awnless isogenic line. Net photosynthetic rates of the heads were 20–26% of the net photosynthetic rates of the flag leaves. Respiration rates were nearly two times greater for the awnless and awn-clipped heads than for the awned head. Respiration rates of the heads were 1.7 and 3.0 times greater than the respiration rates of the flag leaves of the awned and awnless isogenics, respectively. Transpiration per head was 34 and 43% of the transpiration per flag leaf for awnless and awned isogenics, respectively. Comparing P/T ratios showed that the awnless isogenic head had a 20% greater water-use efficiency than the awned. This study not only confirmed the work of others, by associating awnedness with increased wheat yield, but also showed how the chlorophyll-containing area of the head is related to photosynthesis, respiration, and transpiration.

Carbon dioxide exchange by native Great Plains grasses

Carbon dioxide exchange in relation to light and moisture stress was determined for dominants of three grassland plant communities of western North Dakota. These range from Bouteloua gracilis on very dry sites to Stipa viridula on less dry positions to Sporobolus heterolepis in moist ravines. Maximum net photosynthesis of sod transplants ranged from 10 to 12 mg CO2 g−1 h−1 (6 × 104 lx), corrected for soil respiration of about 3 mg CO2 dm−1 h−1. In B. gracilis and S. viridula, net photosynthesis declined steadily to 25% of maximum when moisture stress was increased to −30 bars soil matric water potential. Net photosynthesis declined less rapidly in S. heterolepis when moisture stress increased to −10 bars, but decreased to zero when stress reached −30 bars. The implications regarding distribution of the species are discussed.

Screening for Photosynthetic Efficiency1

Maize (Zea mays L.), sorghum (Sorghum vulgare L.) and several other plants have maximum rates of photosynthesis of 50 to 60 mg CO2 dm−2 hr−1 and have CO2 compensation concentrations (Γ) near 0 ppm. In contrast, small grains and many other plants have maximum rates of photosynthesis of 20 to 30 mg CO2 dm−2 hr−1 and Γ values near 60 ppm. By growing a mixture of these high and low Γ plants together in a closed chamber, a CO2 concentration below that necessary for survival of the high Γ plants was obtained. Only low Γ plants remained alive after 5 to 8 days in the chamber. This is a rapid and simple method for screening populations of plants for high photosynthetic rates.

Specific Leaf Weight and Photosynthesis in Alfalfa1

Specific leaf weight (SLW = leaf dry weight per unit leaf area) and net photosynthesis (Pn) of 13 alfalfa (Medicago sativa L.) clones were positively correlated (r = 0.790). Pn increased from 20 ± 7 to 50 ± 8 mg CO2, dm−2 hr−1 when SLW increased from 1.9 to 5.3 mg cm−2. The SLW‐Pn relationship was the same whether SLW was influenced by genetics or environment.Selections from four alfalfa populations (MSA‐C4, MSB‐11, ‘Vernal,’ and ‘DuPuits’) were grown in high (37.7 klux) and low (12.9 klux) light growth chambers. Except for DuPuits, they showed a SLW‐Pn relationship similar to the 13 clones mentioned above. At high light, the Pn of DuPuits did not exceed 33 ± 6 mg CO2 dm−2 hr−1 even when SLW was greater than 4 mg cm−2.SLW‐Pn relationships were similar for attached and detached leaves. Leaves selected for high SLW had the highest Pn at several light intensities between 6.3 and 64.0 klux. The possibility of increasing Pn by selecting for SLW is discussed.

Varietal Effects in Soybean Photosynthesis and Photorespiration1

The rate of photosynthesis for seedlings of 36 varieties of soybean [Glycine max (L.) Merrill] ranged from 12 mg CO2 assimilated dm−2 hr−1 in ‘Patterson’ to 24 mg CO2 dm−2 hr−1 in ‘Richland’ at saturating light intensity, determined to be 43 kilolux. Comparing the photosynthetic rate and average seed yield of several varieties indicates that varietal yield differences are not caused by differences in photosynthetic rate, although in some instances yield can be related to total photosynthate production. The photosynthetic rate of ‘Wayne’ seedlings was identical when grown in vermiculite, in sterilized soil, or in soils of medium and high productivity.The photosynthetic rates in air are 5 to 6 mg CO2 dm−2 hr−1 less than the rates obtained in a low oxygen atmosphere. Calculations based on photosynthetic rates and compensation points indicate that slightly more than onehalf of the decrease in photosynthesis in air is due to photorespiration, and that the remainder is due to an oxygen inhibition of photosynthesis. The compensation point at 43 kilolux was approximately 40 ppm CO2 for all varieties tested. Analysis of leaf extracts for glycolate oxidase activity indicated no correlation with photorespiratory activities, suggesting that although this enzyme may be required for photorespiration, it is not the limiting factor.

Photosynthesis of Alfalfa Leaves as Influenced by Age and Environment1

Net photosynthesis (Pn) was measured on alfalfa, Medicago saliva L., leaves of different ages from a growth chamber and from normal and thinned field plots. Pn declined with leaf age after full expansion. The mean Pn for young leaves was 52 mg CO2 dm$#x2212;2 hr−1 when grown in the field and 35 mg CO2 dm−2 hr−1 when grown in the growth chamber. However, when photosynthesis was expressed on a dry weight basis this difference no longer existed. Leaves remained alive more than 60 days in the growth chamber but lived only half as long in the field. Thinning field plots delayed senescence.Specific leaf weight (SLW = leaf dry weight/leaf area) was influenced by the light intensity and its change within the environment. SLW for young leaves was 5 mg cm2 when grown in the field and 3 mg cm−2 when grown in the growth chamber. SLW increased with leaf age in the growth chamber but decreased with leaf age in unthinned field plots.

Effect of assimilate utilization on photosynthetic rate in wheat

Two weeks after anthesis, when the grain is filling rapidly, the rate of photosynthesis by flag leaves of wheat cv. Gabo was between 20 and 30 mg CO2 dm(-2) leaf surface hour(-1) under the conditions used. About 45% of flag-leaf assimilates were translocated to the ear, and only about 12% to the roots and young shoots.On removing the ear, net photosynthesis by the flag leaves was reduced by about 50% within 3-15 hours, and there was a marked reduction in the outflow of (14)C-labelled assimilates from the flag leaves.Subsequent darkening of all other leaves on plants without ears led to recovery of flag-leaf photosynthesis, as measured by gas analysis and (14)CO2 fixation, and to increased translocation of assimilates to the roots and young shoots. Minor changes in the rates of dark respiration accompanied these major, reversible changes in photosynthetic rate.After more than a week in continuous, high-intensity light, the rate of photosynthesis by flag leaves of intact plants had fallen considerably, but could be restored again by a period in darkness, or by inhibiting photosynthesis in the ears by spraying them with DCMU. The inhibition of ear photosynthesis increased translocation of labelled assimilates from the flag leaf to the ears, without affecting leaf sugar levels.The application of TIBA to the culm below the ear inhibited auxin movement throught the culm, but had no influence on flag-leaf photosynthesis.These results suggest that, at least in this system, photosynthesis by the flag leaf is regulated directly by the demand for assimilates from the flag leaf and not indirectly through action in the leaf of auxins produced by the "sink" organs.