共查询到20条相似文献,搜索用时 31 毫秒
1.
Summary The uptake of C 14O 2 by the roots of intact tomato plants from solution containing Na 2C 14O 3 was studied at different light intensities as well as in darkness.Where plants had previously been starved for CO 2 for 12 hours, a higher rate of C 14 uptake was observed than with plants which had been transferred directly from the soil to the radioactive solution.In general, the C 14 content of the roots was slightly higher than that of the shoots. At light intensities under the compensation point and in darkness the C 14 content of the shoots relative to the roots decreased. This was accompanied by release of C 14O 2 during respiration, indicating that the absorbed C 14 was readily translocated upwards and released as C 14O 2 under these conditions. At light intensities above the compensation point no C 14O 2 was released. 相似文献
2.
A white Thermus sp. strain, NCIMB 11245, showed high levels of anteiso C 17:0, anteiso C 17:1, normal C 16:1, and iso C 16:0 with low levels of iso C 15:0 + iso C 17:0 in comparison to yellow-pigmented strains. The fatty acid composition may be associated with precursor metabolism or the absence of carotene pigmentation. 相似文献
3.
Summary The concentration, uptake and element use efficiency of N, P and K in one C 3 annual ( Polypogon monspeliensis) and two C 4 ( Echinochloa colonum, an annual, and Dichathium annulatum, a perennial) grasses were determined during winter and summer seasons in monocultures raised in field plots at three moisture
levels, viz. full, half and one-fourth of field capacity. At each moisture regime the plants were clipped thrice at moderate and severe
levels corresponding to 40 and 80% of live green. The concentration of these elements was characteristic of the growth habit
of these plants; e.g. the build up of concentration was maximum in leaf of the annuals while it was comparable in crown and leaf of Dichanthium.
The N level was maximum in Polypogon. The nutrient use effiency was comparable in the two annuals and maximum K and N use
were obtained in Polypogon and Dichanthium, respectively. 相似文献
4.
Summary Four coexisting annual plant species were grown in competition at three levels of CO 2 (300, 600, and 1,200 ppm) and two levels of soil moisture (moist and dry). Plant height was higher at high CO 2 concentrations for the three C 3 species but not for the C 4 species ( Amaranthus retroflexus). Total community biomass increased with increasing CO 2 at both soil moisture levels. The contribution of each species to total community biomass was influenced by CO 2 concentration. The effects were especially pronounced for Polygonum pensylvanicum which contributed more to community production as CO 2 and soil moisture increased. Amaranthus behaved in exactly the reverse way; it did best under ambient CO 2 and dry soil moisture conditions. The results suggest that changes in competitive interactions and community structure will occur with the anticipated rise in global CO 2 concentration. 相似文献
5.
Summary This study examined the mode of photosynthesis (C 3 or C 4), daily and seasonal patterns of xylem water potential, seasonal patterns of field photosynthesis, and the laboratory gas exchange characterisitcs of plants which grow on or in the vicinity of Eureka Dunes, Inyo County, California. The perennial duneendemic Swallenia alexandrae was found to possess the C 4 pathway while all other taxa surveyed were C 3. Plants which grew on the dunes exhibited: 1) significantly less negative xylem water potentials, 2) dampened seasonal changes in predawn water potentials, and 3) smaller seasonal amplitudes of water potential than plants of the adjoining flats. The minimum water potentials experienced by Swallenia during the hot summer months were a third of those endured by adjacent non-dune Larrea. Non-endemics growing on the dune had more negative xylem water potentals than dune endemics, but still never approached the low values of non-dune plants. The poor moisture retention properties of sand may have selected for moisture-conserving traits (stomatal closure at relatively high water potentials, high water use efficiency) rather than moisture-expending ones (osmoregulation, high leaf conductances) in the endemic perennials. Field measurements of photosynthesis showed that dune-restricted (but not necessarily endemic) plants had high photosynthetic capacities and sustained summer carbon assimilation, the latter being protracted months beyond the last pulse of precipitation. The C 3 annual Dicoria canescens ssp. clarkae maintained photosynthetic rates well exceeding those of the C 4
Swallenia throughout the summer and may represent a previously undescribed physiological life form in desert plants. Laboratory measurements supplemented the field data and compared the water use efficiencies of two dune endemics. It is suggested that high photosynthetic productivity, high water use efficiency, and carbon allocation to the longitudinal growth of roots and shoots are important physiological adaptations to shifting sand and substrate moisture depletion at Eureka Dunes. 相似文献
6.
In order to reveal the drought resistance and adaptation of the C 4 desert plant Haloxylon ammodendron under artificially controlled soil moisture regimes, representative plants were selected to measure canopy photosynthesis
using canopy photosynthetic measurement system. The results showed that appropriate soil moisture significantly enhances the
canopy and leaf photosynthetic capacity, and extremely high soil moisture is not conducive to the photosynthesis of H. ammodendron. 相似文献
7.
Summary The leaf anatomy was investigated with respect to the arrangement of cells involved in photosynthesis. The full-grown leaf has one vascular bundle consisting mainly of phioem cells. In similarity to terrestrial C 4 plants the vascular bundle is surrounded by mesophyll bundle sheath cells. However, in contrast to C 4 plants, these cells do not contain chlorophyll or starch in Ceratophyllum. The early products in photosynthesis (10 seconds 14C labelling) were analyzed. Although no complete separation of all radioactivity in the plant extracts was reached, it was clear that malate was the major labelled component, indicating C 4 activity in the plants. No light saturation could be proven in Ceratophyllum in several stages of post-dormancy in a statistically significant way, although a tendency to light saturation was observed at intensities higher than 36 Wm –2. The photosynthetic activity was only slightly depressed by enhancement of the O 2 concentration in the medium. 相似文献
8.
Four C 3 plants and a C 4 plant were grown from seeds at four levels (30, 45, 60, and 75 %) of relative humidity. All plants were subjected to a 16 h day, at 500 μE/m 2.s ?1 photon flux density. Mature leaves were analyzed for their carbon isotopic composition. Isotope fractionation decreased by up to 3 ‰ with decreasing relative humidity in all C 3 plants, while the opposite trend was observed in the C 4 plant. The observed shifts in both C 3 and C 4 plants are attributed to decreased stomatal conductance at low relative humidity, resulting in a smaller P i. 相似文献
9.
Palaeoecological reconstructions based on a single proxy are limited, but by combining pollen, biogeochemistry and grass cuticle analysis, ecosystem structure and function can be better understood. Lake Rutundu is a small, subalpine lake on the northeast flank of Mt Kenya. During the last glacial, pollen evidence suggests a shrub grassland dominated by Afroalpine taxa and Poaceae, representing a dry, cold, open environment. The δ 13C values of terrestrial biomarkers imply a high proportion of C 4 plants. Grass cuticle analysis allows resolution of the different C 4 subtypes and shows that the vegetation was dominated by tall C 4 panicoid grasses, prone to frequent fires. During the Holocene, Poaceae pollen declined while subalpine shrubs increased. The δ 13C values of terrestrial biomarkers imply a C 3-dominated vegetation. Together with an expansion of rainforest at lower altitudes, this suggests wetter conditions more favourable to C 3 plants. Increased percentages of C 3 pooid grass cuticles confirm a reduction in moisture stress. 相似文献
10.
The objectives of this synthesis are (1) to review the factors that influence the ecological, geographical, and palaeoecological
distributions of plants possessing C 4 photosynthesis and (2) to propose a hypothesis/model to explain both the distribution of C 4 plants with respect to temperature and CO 2 and why C 4 photosynthesis is relatively uncommon in dicotyledonous plants (hereafter dicots), especially in comparison with its widespread
distribution in monocotyledonous species (hereafter monocots). Our goal is to stimulate discussion of the factors controlling
distributions of C 4 plants today, historically, and under future elevated CO 2 environments. Understanding the distributions of C 3/C 4 plants impacts not only primary productivity, but also the distribution, evolution, and migration of both invertebrates and
vertebrates that graze on these plants. Sixteen separate studies all indicate that the current distributions of C 4 monocots are tightly correlated with temperature: elevated temperatures during the growing season favor C 4 monocots. In contrast, the seven studies on C 4 dicot distributions suggest that a different environmental parameter, such as aridity (combination of temperature and evaporative
potential), more closely describes their distributions. Differences in the temperature dependence of the quantum yield for
CO 2 uptake (light-use efficiency) of C 3 and C 4 species relate well to observed plant distributions and light-use efficiency is the only mechanism that has been proposed
to explain distributional differences in C 3/C 4 monocots. Modeling of C 3 and C 4 light-use efficiencies under different combinations of atmospheric CO 2 and temperature predicts that C 4-dominated ecosystems should not have expanded until atmospheric CO 2 concentrations reached the lower levels that are thought to have existed beginning near the end of the Miocene. At that time,
palaeocarbonate and fossil data indicate a simultaneous, global expansion of C 4-dominated grasslands. The C 4 monocots generally have a higher quantum yield than C 4 dicots and it is proposed that leaf venation patterns play a role in increasing the light-use efficiency of most C 4 monocots. The reduced quantum yield of most C 4 dicots is consistent with their rarity, and it is suggested that C 4 dicots may not have been selected until CO 2 concentrations reached their lowest levels during glacial maxima in the Quaternary. Given the intrinsic light-use efficiency
advantage of C 4 monocots, C 4 dicots may have been limited in their distributions to the warmest ecosystems, saline ecosystems, and/or to highly disturbed
ecosystems. All C 4 plants have a significant advantage over C 3 plants under low atmospheric CO 2 conditions and are predicted to have expanded significantly on a global scale during full-glacial periods, especially in
tropical regions. Bog and lake sediment cores as well as pedogenic carbonates support the hypothesis that C 4 ecosystems were more extensive during the last glacial maximum and then decreased in abundance following deglaciation as
atmospheric CO 2 levels increased.
Received: 12 February 1997 / Accepted: 20 June 1997 相似文献
11.
Abstract CO 2 FIXATION IN CUSCUTA EPITHYMUM. — Seedlings of Cuscuta epithymum fixe approximately the same amount of C14O2 irrespectively of age, pigmentation, presence or absence of light. Examination by paper chromatography of the extracts of plants exposed to C11O2 revealed that most, or all, of the radioactivity is concentrated in the area of the organic acids and of the acidic amino acids. It is tentatively concluded that C. epithymum fixes carbon dioxide through a mechanism different from that involving ribulose-1,5-diphosphate carboxylase and carboxydismutase. 相似文献
12.
It is plausible that the nutritional quality of C 3 plants will decline more under elevated atmospheric CO 2 than will the nutritional quality of C 4 plants, causing herbivorous insects to increase their feeding on C 3 plants relative to C 4 plants. We tested this hypothesis with a C 3 and C 4 grass and two caterpillar species with different diet breadths. Lolium multiflorum (C 3) and Bouteloua curtipendula (C 4) were grown in outdoor open top chambers at ambient (370 ppm) or elevated (740 ppm) CO 2. Bioassays compared the performance and digestive efficiencies of Pseudaletia unipuncta (a grass-specialist noctuid) and Spodoptera frugiperda (a generalist noctuid). As expected, the nutritional quality of L. multiflorum changed to a greater extent than did that of B. curtipendula when grown in elevated CO 2; levels of protein (considered growth limiting) declined in the C 3 grass, while levels of carbohydrates (sugar, starch and fructan) increased. However, neither insect species increased its feeding rate on the C 3 grass to compensate for its lower nutritional quality when grown in an elevated CO 2 atmosphere. Consumption rates of P. unipuncta and S. frugiperda were higher on the C 3 grass than the C 4 grass, the opposite of the result expected for a compensatory response to the lower nutritional quality of the C 4 grass. Although our results do not support the hypothesis that grass-specialist insects compensate for lower nutritional quality by increasing their consumption rates more than do generalist insects, the performance of the specialist was greater than that of the generalist on each grass species and at both CO 2 levels. Mechanisms other than compensatory feeding, such as increased nutrient assimilation efficiency, appear to determine the relative performance of these herbivores. Our results also provide further evidence against the hypothesis that C 4 grasses would be avoided by insect herbivores because a large fraction of their nutrients is unavailable to herbivores. Instead, our results are consistent with the hypothesis that C 4 grasses are poorer host plants primarily because of their lower nutrient levels, higher fiber levels, and greater toughness. 相似文献
13.
Previous studies on microwave exposure on plants have revealed variations in sensitivity of plants to different microwave frequencies, exposure durations, and power intensities. However, the effects of different polarizations of microwaves on plants have not been studied. Therefore, we investigated the effect of horizontally and vertically polarized 2 GHz continuous microwaves on Myriophyllum aquaticum plants at 1.8 W m -2 power density. The electric potential variation along the vascular tissues were investigated for 1.5 h and growth parameters, pigmentation, and H 2O 2 formation were studied during 48 h microwave exposure. Exposure to horizontally polarized microwaves, decreased standard deviation of electric potential variation and increased H 2O 2 content significantly. Vertically polarized microwaves increased the standard deviation of electric potential variation and photosynthetic pigments significantly. However, none of the polarizations altered growth parameters (shoot length, stem diameter, and internodal length). Thermographic images taken for 1 h continuous microwave exposure did not indicate alteration in the temperature of the plants for both vertical and horizontal polarities. 相似文献
14.
Summary Diurnal patterns of CO 2 exchange and titratable acidity were monitored in six species of evergreen rosette plants growing in controlled environment chambers and under outdoor environmental conditions. These patterns indicated that two of the species, Yucca baccata and Y. torreyi, were constituitive CAM plants while the other species, Y. elata, Y. campestris, Nolina microcarpa and Dasylirion wheeleri, were C 3 plants. The C 3 species did not exhibit CAM when grown in any of several different temperature, photoperiod, and moisture regimes. Both photosynthetic pathway types appear adapted to desert environments and all species show environmentally induced changes in their photosynthetic responses consistent with desert adaptation. The results of this study do not indicate that changes in the photosynthetic pathway type are an adaptation in any of these species. 相似文献
15.
The photosynthetic linear electron transport rate in excess of that used for CO 2 reduction was evaluated in Sorghum bicolor Moench. [NADP-malic enzyme (ME)-type C 4 plant], Amaranthus cruentus L. (NAD-ME-type C 4 plant) and Helianthus annuus L. (C 3 plant) leaves at different CO 2 and O 2 concentrations. The electron transport rate ( J
F) was calculated from fluorescence using the light partitioning factor (relative PSII cross-section) determined under conditions
where excess electron transport was assumed to be negligible: low light intensities, 500 μmol CO 2 · mol −1 and 2% O 2. Under high light intensities there was a large excess of J
F/4 at 10–100% O 2 in the C 3 plant due to photorespiration, but very little in sorghum and somewhat more in amaranth, showing that photorespiration is
suppressed, more in the NADP-ME- and less in the NAD-ME-type species. It is concluded that when C 4 photosynthesis is limited by supply of atmospheric CO 2 to the C 4 cycle, the C 3 cycle becomes limited by regeneration of ribulose 1,5-bisphosphate (RuBP) which in turn limits RuBP oxygenase activity and
photorespiration. The rate of excess electron transport over that consumed for CO 2 fixation in C 4 plants was very sensitive to the presence of O 2 in the gas phase, rapidly increasing between 0.01 and 0.1% O 2, and at 2% O 2 it was about two-thirds of that at 21% O 2. This shows the importance of the Mehler O 2 reduction as an electron sink, compared with photorespiration in C 4 plants. However, the rate of the Mehler reaction is still too low to fully account for the extra ATP which is needed in C 4 photosynthesis.
Received: 8 November 1997 / Accepted: 26 December 1997 相似文献
16.
Summary To examine the effect of barley roots on denitrification, a pot experiment was designed to compare N 2O production and denitrification in soils with and without barley plants. Denitrification, N 2O resulting from denitrification and nitrification, and respiration were estimated by incubating pots with soil with and without
intact plants in plastic bags at high moisture levels. C 2H 2-inhibition of nitrous oxide reductase (partial pressure of 10 kPa C 2H 2) was used to determine total denitrification rates while incubations with ambient air and with C 2H 2 at partial pressures of 2.5–5 Pa were used to estimate the amounts of N 2O released from autotrophic nitrification and from denitrification processes. Other sources of N 2O were presumed to be negligible. Potential denitrification, nitrification and root biomass were measured in subsamples collected
from four soil depths.
A positive correlation was found between denitrification rates and root biomass. N 2 was the predominant denitrification product found close to roots; N 2O formed by non autotrophic nitrifiers, assumed to be denitrifiers originated in soil not affected by growing roots. Apparently,
roots promote denitrification because they consumed oxygen, thereby increasing the anaerobic volume of the soil. The ratio
of actual to potential denitrification rates increased over time, especially in the presence of roots. 相似文献
17.
Summary A non destructive intact-plant assay for estimating nitrogenase activity (C 2H 2 reduction) of pot-grown sorghum and millet plants is described. Plants with intact shoots sustained more activity than plants whose tops were removed prior to the assay. With this technique individual plants can be assayed several times during their life cycle. The C 2H 2 reduction was linear up to 16h incubation in this assay procedure. More rapid diffusion of C 2H 2 was achieved by injection through a Suba seal in the bottom of the pot. The equlibration of injected C 2H 2 in the gas phase of the pots filled with sand and sand:FYM media was completed within 1 h. Significantly higher nitrogenase activity and better growth of sorghum and millet plants occurred when plants were grown in a mixture of sand and farmyard manure (FYM) than when plants were grown in vermiculite, soil, or sand + soil medium. Nitrogenase activity and plant growth were greater in a mixture of sand with 2 and 3% FYM than with 0.5 and 1% FYM. Activity was higher when the plants were incubated at 33°C and 40°C than at 27°C. Activity also increased with increasing soil moisture. There were significant differences amongst 15 sorghum cultivars screened for associated nitrogenase activity. This new technique has good prospects for screening cultivars of millet, sorghum and other grain crops for their nitrogen-fixing ability.Submitted as Journal article No. 358 by the International Crops Research Institute for the Semi-Arid Tropics (ICRISAT). 相似文献
18.
Ecotypic differences in the photosynthetic carbon metabolism of Mollugo verticillata were studied. Variations in C 3 and C 4 cycle activity are apparently due to differences in the activities of enzymes associated with each pathway. Compared to C 4 plants, the activities of C 4 pathway enzymes were generally lower in M. verticillata, with the exception of the decarboxylase enzyme, NAD malic enzyme. The combined total carboxylase enzyme activity of M. verticillata was greater than that of C 3 plants, possibly accounting for the high photosynthetic rates of this species. Unlike either C 3 or C 4 plants, ribulose bisphosphate carboxylase was present in both mesophyll and bundle sheath cell chloroplasts in M. verticillata. The localization of this enzyme in both cells in this plant, in conjunction with an efficient C 4 acid decarboxylation mechanism most likely localized in bundle sheath cell mitochondria, may account for intermediate photorespiration levels previously observed in this species. 相似文献
19.
The increasing CO 2 concentration in Earths atmosphere is expected to cause a greater decline in the nutritional quality of C 3 than C 4 plants. As a compensatory response, herbivorous insects may increase their feeding disproportionately on C 3 plants. These hypotheses were tested by growing the grasses Lolium multiflorum C 3) and Bouteloua curtipendula C 4) at ambient (370 ppm) and elevated (740 ppm) CO 2 levels in open top chambers in the field, and comparing the growth and digestive efficiencies of the generalist grasshopper Melanoplus sanguinipes on each of the four plant × CO 2 treatment combinations. As expected, the nutritional quality of the C 3 grass declined to a greater extent than did that of the C 4 grass at elevated CO 2; protein levels declined in the C 3 grass, while levels of carbohydrates (sugar, fructan and starch) increased. However, M. sanguinipes did not significantly increase its consumption rate to compensate for the lower nutritional quality of the C 3 grass grown under elevated CO 2. Instead, these grasshoppers appear to use post-ingestive mechanisms to maintain their growth rates on the C 3 grass under elevated CO 2. Consumption rates of the C 3 and C 4 grasses were also similar, demonstrating a lack of compensatory feeding on the C 4 grass. We also examined the relative efficiencies of nutrient utilization from a C 3 and C 4 grass by M. sanguinipes to test the basis for the C 4 plant avoidance hypothesis. Contrary to this hypothesis, neither protein nor sugar was digested with a lower efficiency from the C 4 grass than from the C 3 grass. A novel finding of this study is that fructan, a potentially large carbohydrate source in C 3 grasses, is utilized by grasshoppers. Based on the higher nutrient levels in the C 3 grass and the better growth performance of M. sanguinipes on this grass at both CO 2 levels, we conclude that C 3 grasses are likely to remain better host plants than C 4 grasses in future CO 2 conditions. 相似文献
20.
Proto-Kranz plants represent an initial phase in the evolution from C3 to C3–C4 intermediate to C4 plants. The ecological and adaptive aspects of C3–C4 plants would provide an important clue to understand the evolution of C3–C4 plants. We investigated whether growth temperature and nitrogen (N) nutrition influence the expression of C3–C4 traits in Chenopodium album (proto-Kranz) in comparison with Chenopodium quinoa (C3). Plants were grown during 5 weeks at 20 or 30 °C under standard or low N supply levels (referred to as 20SN, 20LN, 30SN, and 30LN). Net photosynthetic rate and leaf N content were higher in 20SN and 30SN plants than in 20LN and 30LN plants of C. album but did not differ among growth conditions in C. quinoa. The CO2 compensation point (Γ) of C. album was lowest in 30LN plants (36 µmol mol–1), highest in 20SN plants (51 µmol mol–1), and intermediate in 20LN and 30SN plants, whereas Γ of C. quinoa did not differ among the growth conditions (51–52 µmol mol–1). The anatomical structure of leaves was not considerably affected by growth conditions in either species. However, ultrastructural observations in C. album showed that the number of mitochondria per mesophyll or bundle sheath (BS) cell was lower in 20LN and 30LN plants than in 20SN and 30SN plants. Immunohistochemical observations revealed that lower accumulation level of P-protein of glycine decarboxylase (GDC-P) in mesophyll mitochondria than in BS mitochondria is the major factor causing the decrease in Γ values in C. album plants grown under low N supply and high temperature. These results suggest that high growth temperature and low N supply lead to the expression of C3–C4 traits (the reduction of Γ) in the proto-Kranz plants of C. album through the regulation of GDC-P expression. 相似文献
|