C02 Assimilation Rate Research Articles

El efecto de sequía en el crecimiento, la fotosíntesis y la intercepción de luz en frijol cumún.

The effect of water deficit on leaf area index, light interception, stomatal conductance, and dry matter production in dry beans was studied in this investigation carried out at Michigan State University, where drought treatments were imposed at different phenological stages such as vegetative (VS), initial flowering (IF) and seed fiJling (SF). Water stress rapidly reduced the Jeaf area index, mostly in IF, causing a significant decrease in light interception. Stomatal conductance and photosynthesis were also reduced by water deficit. However, the C02 assimilation rate had a significant decrease only when stomatal conductance was lower than 0.8 cm/sec. Dry matter production was cJosely related to light interception. Nevertheless, at the same amount of intercepted radiation, production of dry matter in IF lagged behind the control by 6.5%.

Variations in leaf pigment content and photosynthetic activity of Phragmites australis in healthy and die-back reed stands of Lake Fertõ/Neusiedlersee

The photosynthetic capacity of the common reed (Phragmites australis /Cav./ Trin. ex Steudel) was studied in various reed stands in the littoral zone of Lake Fert6. Measurements were performed in three healthy and two die­ back reed stands in the summer of 1997. In the leaves of declining reeds, the chlorophyll content was lower than in the vigorous sites. In the former sites, there was a significant rise in the total carotenoid pool (320- 480 mmol mol-1chl (a + b)) as compared to that of the vigorous sites (250- 350 mmol mol- 1 chi (a + b). The size of the xanthophyll cycle pool and the ,B-carotene content of leaves significantly increased in the die-back sites. In early summer, the potential photochemical quantum efficiency of Photosystem II (Fv/Fm) did not differ considerably (0. 79-0.81) from site to site, yet by August it significantly decreased (0.74-0.77) in the die-back sites as compared to the vigorous sites. The maximum C02 assimilation rate measured on the 3rd and 4th leaves ranged from 11 to 17 C02f..i.mol m-2 s-1 and from 9 to 12 C02f..i.mol m-2 s-1 in the vigorous sites and the die-back sites, respectively. The stomatal conductance was also lower in the die-back sites (200-350 mmol H20 m-2 s-1) than in the vigorous reed stands (380-510 mmol H20 m-2s- 1) which might result in the functional impairment of the gas ventilation system of the declining reeds, and consequently in oxygen deficiency and damage to the rhizome.

Effects of Paclobutrazol on Podding and Photosynthetic Characteristics in Peanut

The effects of paclobutrazol (PB) on podding habits and photosynthetic characteristics (COz assimilation rate, quantum yield of photosystem II (ΦSII) and chlorophyll content) were examined in peanut. Application of PB at the start of the pod formation stage increased the percentage of podding, particularly in early-blooming flowers and seed yield. The major factor for this effect may be an acceleration of dry matter distribution to the early-bearing pods, which resulted from the inhibition of stem growth by PB. Application of PB at the early pod-formation stage increased chlorophyll content and ΦSII, resulting in enhanced C02 assimilation rates. In the long term, PB tended to increase crop growth rate and net assimilation rate though not significantly. The effects of PB on the photosynthetic character¬istics, however, were observed only during a short period at a restricted growing stage, suggesting that an increase in the photosynthetic rate would not be the main factor for the PB-induced increase in seed yield.

Ультраструктурные изменения клеток мезофилла и скорость фиксации С02 клиностатированных растений арабидопсиса

Ультраструктурные изменения клеток мезофилла и скорость фиксации С02 клиностатированных растений арабидопсиса

Effect of differing irrigation regimes on fruit quality, yield, fruit size and net CO2 assimilation of ‘Mihowase’ satsuma

SummaryInternal fruit quality of ‘Mihowase’ satsuma (Citrus unshiu Marc.) is marginal when irrigation is not carefully controlled. Three deficit irrigation trials were conducted over two seasons to investigate the effect of different irrigation regimes on fruit quality, productivity variables and tree physiology in the Western Cape region of South Africa (34°S 19°E, ca. 100 m altitude). During the 1994/95 growing seasons, four irrigation regimes were imposed, viz. –30, –50, –70, and –100 kPa (soil water tension at 30 cm depth, determined by tensiometer) from ca. three weeks after the "physiological fruit drop" period (i.e. December drop, APFD) to the first selective fruit picking date (late March). Based on the results of the 1994/95 season, two new irrigation trials were laid out during the 1995/96 season on two soil types to determine the interaction of deficit irrigation level and duration. The deficit irrigation, to a soil water tension of –60 kPa at 60 cm depth, initiated at (i) 0–2 weeks APFD in a sandy–loam soil or (ii) 0–4 weeks APFD in a clay–loam soil, significantly (P<0.05) increased total soluble solids (TSS) compared with the normal irrigation level, when soil water tension reached –30 kPa at 60 cm depth. Only a slight influence on peel colour, titratable acidity (TA) and TSS/TA ratio and no effect on juice content were recorded. The percentage of fruit selectively picked at different dates was not affected by any of the irrigation regimes. Soil type affected irrigation cycles and the intervals between irrigation, thereby affecting yield and fruit size distribution. Decreased irrigation tended to decrease leaf C02 assimilation rate (A), with high deficit irrigation levels (above –70 kPa at 30 cm and –60 kPa at 60 cm soil depth) greatly reducing A. Leaf chlorophyll and N contents were significantly (P<0.05) decreased in the –100 kPa regime with no real differences between the other three regimes (Trial A). Our data suggest that deficit irrigation, to a soil water tension of –60 kPa at 60 cm soil depth, and initiated at 0–4 weeks APFD (clay-loam) or 0–2 weeks APFD (sandy-loam), seems to be a viable option for commercial practice to attain the desired goal, viz. an increase in TSS content.

Low temperatures decrease CO2 assimilation and growth in the tropical rambutan

SummaryIn glasshouse experiments, high temperatures increased vegetative growth in the tropical rambutan (Nephelium lappaceum L. seedlings of cv. Rapiah). In absolute terms, there was generally a greater response to night temperature (day/night temperatures of 32714°C vs. 32728°C) than to day temperature (22714°C vs. 32714°C), and better growth at 32728°C than at 32722°C. The effects of temperature on nutrient concentrations were small, whereas average leaf water potential (ΨL) during the day was -1.5 MPa at 32728°C, 0.1 to 0.4 MPa higher with nights of 14° or 22°C, and 0.7 MPa higher at 22714°C. Average net C02 assimilation rate (A) was 5.3 μ-mol m−2 s−1 at 32722° and 32728°C, 50% lower at 32714°C and 80% lower at 22714°C. When seedlings of cv. Rapiah were grown in water baths, the two critical root temperatures at which 90% of maximum plant weight occurred were similar for leaves and stems (about 24° to 30°C), but lower for roots (19° to 25°C). There was only a small effect of temperature on the concentration of most nutrients, and on average day time ΨL, whereas average A was 4.5 (μmol m s−1 at 28°C, 30% lower at 20°C, and 80% lower at 15° and 38°C. These experiments show that rambutan growth was strongly reduced when night or root temperatures fell to 14° or 15°C. The main effect was through lower Co−2 assimilation, whereas the changes in water and nutrient status were relatively small. Areas where night or root temperatures remain at or below 14°C for prolonged periods should be avoided for rambutan production.

Light Dependency of Carboxylation Efficiency and Ribulose-1, 5-Bisphosphate Carboxylase Activation inTrifolium subterraneumL. Leaves

The effect of photosynthetic photon flux density (PPFD) on carboxylation efficiency, estimated as the initial slope (IS) of net C02 assimilation rate versus intercellular C02 partial pressure response curve, as well as on ribulose-l,5-6wphosphate carboxylase (Rubisco) activation was measured in Trifolium subterraneum L. leaves under field conditions. The relationship between IS and PPFD fits a logarithmic curve. Rubisco activation accounts for the IS increase only up to a PPFD of 550 jumol photons m-2 s1. Further IS increase, between 550 and 1000 /xmol photons m~ 2 s_1, could be related to a higher ribulose ?«phosphate (RuBP) availability. The slow, but sustained IS increase above 1000 ??mol photons m~2 s-1 could be explained by the mesophyll C02 diffusion barriers associated with the high chlorophyll and protein content in field developed leaves.

GROWTH, WATER RELATIONS, AND PHOTOSYMTHESIS ARE REDUCED BY DECREASING SOIL MOISTURE IN 'MARY WASHINGTON ' AND 'SYN 4-56' ASPARAGUS SEEDLINGS

Seedlings of the asparagus cvs Mary Washington (MW) and Syn 4-56 (4-56) were grown at minimum soil matric potentials (SMP) of -0.05, -0.10, and -0.30, -0.50 or -1.5 MPa. Decreases in shoot dry weight leaf area, storage and fibrous root dry weights, and total root and plant dry weight were an exponential function of soil moisture in both cvs. Most of the growth inhibition occurred between the -0.05 and the -0.30 MPa levels of soil moisture, with little further response to SMP drier than -0.30 MPa. Consistent differences between the two cvs, regardless of SMP were apparent in leaf area, shoot dry weight, storage and fibrous root dry weights and root/shoot ratios. MW produced greater leaf area and shoot dry weights than did 4-56 at high SMP and exhibited greater inhibition of shoot dry weight by low SMP than did 4-56. Conversely, 4-56 produced greater storage root dry weight than MW at all SMP., although in mature field-grown plants, 4-56 produced greater fern weight, crown weight and number and stem numbers than MW. Root/shoot ratios generally increased with decreasing SMP. However, the root/shoot ratio of 4-56 was greater than that of MW over the entire range of soil moisture and increased more with decreasing SMP than did MW. Stomatal conductance (gs), fern xylem potential (), and net C02 assimilation rates decreased with decreasing SMP in a similar manner in both cvs. were

Stomatal and Mesophyll Limitations of Photosynthesis in Phosphate Deficient Sunflower, Maize and Wheat Plants

The effects of phosphate deficiency on the composition and photosynthetic C02 assimilation rates of fully expanded leaves of sunflower, maize and wheat plants are described. The regulation of photosynthesis by stomatal and mesophyll characteristics of leaves of different phosphate status is analysed and related to structure. Phosphate deficient leaves had small concentrations of inorganic phosphate, Pi, in the tissue water. Rate of photosynthesis in leaves and stomatal conductance were smaller in plants grown with inadequate phosphate when measured under any given light intensity or C02 partial pressure. Despite the decrease in stomatal conductance (and without evidence of patchy stomatal closure), the relative stomatal limitation of photosynthesis was similar in the plants grown with deficient or abundant phosphate. However, the mesophyll capacity for photosynthesis was greatly limited by phosphate deficiency. Leaves deficient in phosphate had larger numbers of small size cells per unit leaf area than leaves with adequate phosphate. The total soluble protein content of leaves decreased with phosphate deficiency in all three species; however, the leaf chlorophyll content was decreased only in sunflower and maize and not in wheat. These results suggest that stomatal conductance did not restrict the C02 diffusion rate, rather the metabolism of the mesophyll was the limiting factor. This is shown by poor carboxylation efficiency and decreased apparent quantum yield for C02 assimilation, both of which contributed to the increase in relative mesophyll limitation of photosynthesis in phosphate deficient plants.

Limitations of Gas Exchanges in Intact Leaves during Ontogeny of Field-grown Chickpeas

The ontogenic changes in several component processes of photosynthesis were measured in chickpeas. Gas exchange characteristics of intact leaves were studied to analyse the effects of ambient conditions under which chickpeas are usually grown. The C02 assimilation rate per unit leaf area remained fairly high during the vegetative stage, reaching a peak at early pod-fill and declining subsequently throughout pod development. The intercellular C02 partial pressure (Ci) remained more or less constant (~ 195 /?bar) during vegetative growth and the early stages of seed-filling. With falling RWC and PAR interception, the stomatal conductance declined more rapidly than the C02 assimilation rate resulting in a value of C, less than that normally existing under ambient conditions. From the ^/?i-analysis, C02 assimilation during pod-filling appears to be limited by the RuBP-regeneration capacity because the carboxylation efficiency and in vitro RuBPCase activity were initially unaffected. However, as leaves aged, the carboxylation efficiency and in vitro RuBPCase activity decreased abruptly with increasing leaf temperatures above 30 °C, and the Ci was greater than normally existing values (~ 195 /?bar), suggesting an increased mesophyll limitation of photosynthesis. It is suggested that a decline in the C02 assimilation rate of leaves during pod development and an accelerated senescence are induced by adverse ambient conditions, particularly plant water stress and high leaf temperature.