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1.
Elevated CO 2 enhances photosynthesis and growth of plants, but the enhancement is strongly influenced by the availability of nitrogen. In this article, we summarise our studies on plant responses to elevated CO 2. The photosynthetic capacity of leaves depends not only on leaf nitrogen content but also on nitrogen partitioning within a leaf. In Polygonum cuspidatum, nitrogen partitioning among the photosynthetic components was not influenced by elevated CO 2 but changed between seasons. Since the alteration in nitrogen partitioning resulted in different CO 2-dependence of photosynthetic rates, enhancement of photosynthesis by elevated CO 2 was greater in autumn than in summer. Leaf mass per unit area (LMA) increases in plants grown at elevated CO 2. This increase was considered to have resulted from the accumulation of carbohydrates not used for plant growth. With a sensitive analysis of a growth model, however, we suggested that the increase in LMA is advantageous for growth at elevated CO 2 by compensating for the reduction in leaf nitrogen concentration per unit mass. Enhancement of reproductive yield by elevated CO 2 is often smaller than that expected from vegetative growth. In Xanthium canadense, elevated CO 2 did not increase seed production, though the vegetative growth increased by 53%. As nitrogen concentration of seeds remained constant at different CO 2 levels, we suggest that the availability of nitrogen limited seed production at elevated CO 2 levels. We found that leaf area development of plant canopy was strongly constrained by the availability of nitrogen rather than by CO 2. In a rice field cultivated at free-air CO 2 enrichment, the leaf area index (LAI) increased with an increase in nitrogen availability but did not change with CO 2 elevation. We determined optimal LAI to maximise canopy photosynthesis and demonstrated that enhancement of canopy photosynthesis by elevated CO 2 was larger at high than at low nitrogen availability. We also studied competitive asymmetry among individuals in an even-aged, monospecific stand at elevated CO 2. Light acquisition (acquired light per unit aboveground mass) and utilisation (photosynthesis per unit acquired light) were calculated for each individual in the stand. Elevated CO 2 enhanced photosynthesis and growth of tall dominants, which reduced the light availability for shorter subordinates and consequently increased size inequality in the stand. 相似文献
2.
There is continuing controversy over whether a degree of C 4 photosynthetic metabolism exists in ears of C 3 cereals. In this context, CO 2 exchange and the initial products of photosynthesis were examined in flag leaf blades and various ear parts of two durum wheat ( Triticum durum Desf.) and two six-rowed barley ( Hordeum vulgare L.) cultivars. Three weeks after anthesis, the CO 2 compensation concentration at 210 mmol mol ?1 O 2 in durum wheat and barley ear parts was similar to or greater than that in flag leaves. The O 2 dependence of the CO 2 compensation concentration in durum wheat ear parts, as well as in the flag leaf blade, was linear, as expected for C 3 photosynthesis. In a complementary experiment, intact and attached ears and flag leaf blades of barley and durum wheat were radio-labelled with 14CO 2 during a 10s pulse, and the initial products of fixation were studied in various parts of the ears (awns, glumes, inner bracts and grains) and in the flag leaf blade. All tissues assimilated CO 2 mainly by the Calvin (C 3) cycle, with little fixation of 14CO 2 into the C 4 acids malate and aspartate (about 10% or less). These collective data support the conclusion that in the ear parts of these C 3 cereals C 4 photosynthetic metabolism is nil. 相似文献
3.
Exposing plants to long-term CO 2 enrichment generally leads to increases in plant biomass, total leaf area and alterations on leaf net photosynthetic rates, stomatal conductance and water use efficiency. However, the magnitude of such effects is dependent on the availability of other potentially limiting resources. The aim of our study was to elucidate the effects of elevated CO 2, applied at different temperature and water availability regimes, on nodulated alfalfa plants. Regardless of water supply, elevated CO 2 enhanced plant growth, especially when combined with increased temperature although no differences were detected until 30 days of treatment. Absence of differences in leaf relative growth rate, and gas exchange measurements, suggested that plants grown in a low water regime adjusted their growth to the amount of available water. Elevated CO 2 enhanced water use efficiency because of reduced water consumption and a greater dry mass production. Increased dry matter production of plants grown under elevated CO 2 and temperature was the result of stimulated photosynthetic rates, greater leaf area and water use efficiency. Lack of CO 2 effect on photosynthesis of plants grown at ambient temperature might be consequence of down-regulation phenomena. Plants grown at 700 μmol mol −1 CO 2 maintained control nitrogen levels, discarding enhanced nitrogen availability as the main factor explaining enhanced dry matter. 相似文献
4.
Summary Cytological comparisons of homologous tissues in blades and stipes by stereological analysis have shown differences exist between blade and stipe organs in Sargassum. Based on measurements of total thylakoid and cristae membrane surface areas in these organs blades were found to contain 61% more thylakoid membrane surface and 65% more cristae membrane than stipes on a per unit volume basis. Assuming photosynthesis and respiration are directly related to the surface area of the internal membranes in the respective organelles it is possible to predict that blades will have a 61% greater photosynthetic and a 65% greater respiratory potential. Photosynthetic and respiratory rates for blades and stipes were determined manometrically and show a 62% greater photosynthetic and 59% greater respiratory rates for the blade tissues agreeing very well with predicted values.Present evidence indicates that photosynthetic and respiratory rate differences observed in the blades and stipes in Sargassum are the result of increased membrane surface areas in the larger cells of the tissues which make up the blade. The basic cell structure, i.e., the percent volume of cell cytoplasm occupied by each organelle, is similar in homologous tissues of both organs regardless of cell size. Therefore physiological differences between the two organs are primarily due to changes in cell size and not in basic cell construction. This provides an interesting mechanism for producing physiological differences without changing basic cell structure in the organs of this plant. 相似文献
5.
Summary Willows ( Salix x dasyclados) were grown for 4 months in growth chambers at four nutrient and CO 2 levels, and photosynthesis measurements were made during the latter half of this period. Photosynthesis became saturated at lower light intensities at low CO 2 concentrations than at higher ones. The effect of CO 2 concentration on photosynthesis was greater at higher temperatures. The willows grown at the highest CO 2 concentration (1000 ppm) had a lower photosynthetic capacity than the others when measured at various concentrations. The effect of nutrient status on photosynthesis clearly increased with rising CO 2 concentrations. Although photosynthetic acclimation took place to a certain extent at higher CO 2 concentrations, photosynthesis still remained higher the higher the growth concentration was. At each CO 2 level photosynthesis increased contemporaneously with leaf nitrogen content, but at each fertilization level a rise in CO 2 concentration slightly increased photosynthesis and reduced the nitrogen content. The relative increase in photosynthesis achieved by a rise in CO 2 was greater than the corresponding increase in biomass growth, whereas the effect of fertilization was greater on biomass growth than on the rate of photosynthesis in the same willows. 相似文献
6.
The effects of global change on the emission rates of isoprene from plants are not clear. A factor that can influence the response of isoprene emission to elevated CO 2 concentrations is the availability of nutrients. Isoprene emission rate under standard conditions (leaf temperature: 30°C, photosynthetically active radiation (PAR): 1000 μmol photons m ?2 s ?1), photosynthesis, photosynthetic capacity, and leaf nitrogen (N) content were measured in Quercus robur grown in well‐ventilated greenhouses at ambient and elevated CO 2 (ambient plus 300 ppm) and two different soil fertilities. The results show that elevated CO 2 enhanced photosynthesis but leaf respiration rates were not affected by either the CO 2 or nutrient treatments. Isoprene emission rates and photosynthetic capacity were found to decrease with elevated CO 2, but an increase in nutrient availability had the converse effect. Leaf N content was significantly greater with increased nutrient availability, but unaffected by CO 2. Isoprene emission rates measured under these conditions were strongly correlated with photosynthetic capacity across the range of different treatments. This suggests that the effects of CO 2 and nutrient levels on allocation of carbon to isoprene production and emission under near‐saturating light largely depend on the effects on photosynthetic electron transport capacity. 相似文献
7.
Spring wheat was grown from emergence to grain maturity in two partial pressures of CO 2 ( pCO 2): ambient air of nominally 37 Pa and air enriched with CO 2 to 55 Pa using a free-air CO 2 enrichment (FACE) apparatus. This experiment was the first of its kind to be conducted within a cereal field without the modifications or disturbance of microclimate and rooting environment that accompanied previous studies. It provided a unique opportunity to examine the hypothesis that continuous exposure of wheat to elevated pCO 2 will lead to acclimatory loss of photosynthetic capacity. The diurnal courses of photosynthesis and conductance for upper canopy leaves were followed throughout the development of the crop and compared to model-predicted rates of photosynthesis. The seasonal average of midday photosynthesis rates was 28% greater in plants exposed to elevated pCO 2 than in contols and the seasonal average of the daily integrals of photosynthesis was 21% greater in elevated pCO 2 than in ambient air. The mean conductance at midday was reduced by 36%. The observed enhancement of photosynthesis in elevated pCO 2 agreed closely with that predicted from a mechanistic biochemical model that assumed no acclimation of photosynthetic capacity. Measured values fell below predicted only in the flag leaves in the mid afternoon before the onset of grain-filling and over the whole diurnal course at the end of grain-filling. The loss of enhancement at this final stage was attributed to the earlier senescence of flag leaves in elevated pCO 2. In contrast to some controlled-environment and field-enclosure studies, this field-scale study of wheat using free-air CO 2 enrichment found little evidence of acclimatory loss of photosynthetic capacity with growth in elevated pCO 2 and a significant and substantial increase in leaf photosynthesis throughout the life of the crop. 相似文献
8.
Winter wheat ( Triticum aestivum L., cv. Mercia) was grown at two different atmospheric CO 2 concentrations (350 and 700 μmol mol −1), two temperatures [ambient temperature (i.e. tracking the open air) and ambient +4°C] and two rates of nitrogen supply (equivalent to 489 kg ha −1 and 87 kg ha −1). Leaves grown at 700 μmol mol −1 CO 2 had slightly greater photosynthetic capacity (10% mean increase over the experiment) than those grown at ambient CO 2 concentration, but there were no differences in carboxylation efficiency or apparent quantum yield. The amounts of chlorophyll, soluble protein and ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) per unit leaf area did not change with long-term exposure to elevated CO 2 concentration. Thus winter wheat, grown under simulated field conditions, for which total biomass was large compared to normal field production, did not experience loss of components of the photosynthetic system or loss of photosynthetic competence with elevated CO 2 concentration. However, nitrogen supply and temperature had large effects on photosynthetic characteristics but did not interact with elevated CO 2 concentration. Nitrogen deficiency resulted in decreases in the contents of protein, including Rubisco, and chlorophyll, and decreased photosynthetic capacity and carboxylation efficiency. An increase in temperature also reduced these components and shortened the effective life of the leaves, reducing the duration of high photosynthetic capacity. 相似文献
9.
We compared the CO 2- and light-dependence of photosynthesis of four tree species ( Acer rubrum, Carya glabra, Cercis canadensis, Liquidambar styraciflua) growing in the understory of a loblolly pine plantation under ambient or ambient plus 200 μl l –1 CO 2. Naturally-established saplings were fumigated with a free-air CO 2 enrichment system. Light-saturated photosynthetic rates were 159–190% greater for Ce. canadensis saplings grown and measured under elevated CO 2. This species had the greatest CO 2 stimulation of photosynthesis. Photosynthetic rates were only 59% greater for A. rubrum saplings under CO 2 enrichment and Ca. glabra and L. styraciflua had intermediate responses. Elevated CO 2 stimulated light-saturated photosynthesis more than the apparent quantum yield. The maximum rate of carboxylation of ribulose-1,5-bisphosphate
carboxylase, estimated from gas-exchange measurements, was not consistently affected by growth in elevated CO 2. However, the maximum electron transport rate estimated from gas- exchange measurements and from chlorophyll fluorescence,
when averaged across species and dates, was approximately 10% higher for saplings in elevated CO 2. The proportionately greater stimulation of light-saturated photosynthesis than the apparent quantum yield and elevated rates
of maximum electron transport suggests that saplings growing under elevated CO 2 make more efficient use of sunflecks. The stimulation of light-saturated photosynthesis by CO 2 did not appear to correlate with shade-tolerance ranking of the individual species. However, the species with the greatest
enhancement of photosynthesis, Ce. canadensis and L. styraciflua, also invested the greatest proportion of soluble protein in Rubisco. Environmental and endogenous factors affecting N partitioning
may partially explain interspecific variation in the photosynthetic response to elevated CO 2.
Received: 16 February 1999 / Accepted: 30 August 1999 相似文献
10.
The effects on photosynthesis of CO 2 and desiccation in Porphyra haitanensis were investigated to establish the effects of increased atmospheric CO 2 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 CO 2 compensation point increased. Emersed net photosynthesis was not saturated by the present atmospheric CO 2 level (about 350?ml?m ?3), and doubling the CO 2 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 CO 2 was greater at higher temperatures and higher levels of desiccation. The photosynthetic production of Porphyra haitanensis may benefit from increasing atmospheric CO 2 concentration during emersion. 相似文献
11.
Trees growing in natural systems undergo seasonal changes in environmental factors that generate seasonal differences in net photosynthetic rates. To examine how seasonal changes in the environment affect the response of net photosynthetic rates to elevated CO 2, we grew Pinus taeda L. seedlings for three growing seasons in open-top chambers continuously maintained at either ambient or ambient + 30 Pa CO 2. Seedlings were grown in the ground, under natural conditions of light, temperature nd nutrient and water availability. Photosynthetic capacity was measured bimonthly using net photosynthetic rate vs. intercellular CO 2 partial pressure ( A-Ci) curves. Maximum Rubisco activity (Vc max) and ribulose 1,5-bisphosphate regeneration capacity mediated by electron transport (J max) and phosphate regeneration (PiRC) were calculated from A-Ci curves using a biochemically based model. Rubisco activity, activation state and content, and leaf carbohydrate, chlorophyll and nitrogen concentrations were measured concurrently with photosynthesis measurements. This paper presents results from the second and third years of treatment. Mean leaf nitrogen concentrations ranged from 13.7 to 23.8 mg g ?1, indicating that seedlings were not nitrogen deficient. Relative to ambient CO 2 seedlings, elevated CO 2 increased light-saturated net photosynthetic rates 60–110% during the summer, but < 30% during the winter. A relatively strong correlation between leaf temperature and the relative response of net photosynthetic rates to elevated CO 2 suggests a strong effect of leaf temperature. During the third growing season, elevated CO 2 reduced Rubisco activity 30% relative to ambient CO 2 seedlings, nearly completely balancing Rubisco and RuBP-regeneration regulation of photosynthesis. However, reductions in Rubisco activity did not eliminate the seasonal pattern in the relative response of net photosynthetic rates to elevated CO 2. These results indicate that seasonal differences in the relative response of net photosynthetic rates to elevated CO 2 are likely to occur in natural systems. 相似文献
12.
Most mistletoe–host ecophysiological studies have paid attention to the influence of parasites on host performance. This paper explored the impact of varying hosts on the photosynthesis of a single mistletoe species. Here, we studied an obligate xylem‐tapping tropical mistletoe ( Dendrophthoe curvata (Blume) Miquel) parasitizing four different hosts ( Acacia auriculiformis A. Cunn. Ex Benth, Andira inermis (W. Wright) DC., Mangifera indica L. and Vitex pinnata L.) in a homo geneous tropical heath forest patch in Brunei Darussalam. We compared photosynthetic capacity and photosynthesis‐related characteristics of the mistletoe on four different hosts to evaluate the overall impact of hosts on the parasite. Results showed that the mistletoe–host patterns of CO 2 assimilation rates, transpiration rates and water use efficiency varied significantly based on the host. In the D. curvata–Vitex pinnata association, the mistletoe exhibited significantly lower CO 2 assimilation rates but showed no significant variations in transpiration rates and water use efficiency when compared to the host. In D. curvata–Andira inermis and D. curvata–Mangifera indica associations, the mistletoe showed significantly higher photosynthetic rates than the hosts, whereas in the D. curvata–Acacia auriculiformis association, there was no significant difference in photosynthetic rates between the counterparts. Host specificity also significantly influenced some mistletoe photosynthetic parameters such as light saturated photosynthesis, specific leaf area, leaf chlorophyll content, CO 2 assimilation rates, stomatal conductance, transpiration rates and water use efficiency. Different tree hosts intrinsically offer different resources to their obligate mistletoe parasites based on their physiology and environmental parameters. We argue that host‐specific responses have driven these intra‐specific variations in mistletoe physiology. This study provides background for future investigation on potential host‐regulated mechanisms that drive functional changes in host‐dependent mistletoes. 相似文献
13.
Summary The effects of CO 2 enrichment on the growth, biomass partitioning, photosynthetic rates, and leaf nitrogen concentration of a grass, Bromus mollis (C 3), were investigated at a favorable and a low level of nitrogen availability. Despite increases in root: shoot ratios, leaf nitrogen concentrations were decreased under CO 2 enrichment at both nitrogen levels. For the low-nitrogen treatment, this resulted in lower photosynthetic rates measured at 650 l/l for the CO 2-enriched plants, compared to photosynthetic rates measured at 350 l/l for the non-enriched plants. At higher nitrogen availability, photosynthetic rates of plants grown and measured at 650 l/l were greater than photosynthetic rates of the non-enriched plants measured at 350 l/l. Water use efficiency, however, was increased in enriched plants at both nitrogen levels. CO 2 enrichment stimulated vegetative growth at both high and low nitrogen during most of the vegetative growth phase but, at the end of the experiment, total biomass of the high and low CO 2 treatments did not differ for plants grown at low nitrogen availability. While not statistically significant, CO 2 tended to stimulate seed production at high nitrogen and to decrease it at low nitrogen. 相似文献
14.
The role of ear photosynthesis in grain filling was studied in a number of durum wheat ( Triticum turgidum var durum L.) landraces and varieties from the Middle East, North Africa, and from the collections of ‘Institut National de la Recherche Agronomique’ (INRA, France) and ‘Centro International de Mejora de Maiz y Trigo’ (CIMMYT, Mexico). Plants were grown in the field in a Mediterranean climate. Flag leaves (blade plus sheath) and ears were kept in the dark from 1 week after anthesis to maturity which reduced grain weight by 22.4% and 59.0%, respectively. In a further experiment, the carbon isotope discrimination ratio (Δ) of ear bracts, awns and flag leaves was measured on samples taken at anthesis and on mature kernels. The mean value of Δ for the water soluble fraction of bracts (17.0‰) and awns (17.7‰) were lower than those of leaves (19.5‰) and fairly similar to those of kernels (17.4‰) averaged across all genotypes. Data indicate that most of the photosynthates in the grain come from ear parts and not from flag leaves. In addition, a higher water use efficiency (WUE) of ear parts than of the flag leaf is suggested by their lower Δ values. Gas exchange in ears and flag leaves was measured during grain filling. Averaged over all genotypes, CO 2 diffusive conductance was about five times higher in the flag leaf than in the spike (with distal portions of awns outside the photosynthetic chamber) 2 weeks after anthesis. In absolute terms, the dark respiration rate (R d) was greater than the net photosynthesis rate (P n) by a factor of 1.74 in the spike, whereas R d was much smaller, only 22.1, 65.7 and 24.8% of P n in blade, sheath and awns, respectively. Data indicate that photosynthesis, and hence the water use efficiency (photosynthesis/transpiration), is greatly underestimated in ears because of the high rates of respiration which diminish the measured rates of net CO 2 exchange. Results of 13C discrimination and gas exchange show that genotypes from North Africa have higher WUE than those from the Middle East. The high R d values of ears as well as their low diffusive conductance suggest that CO 2 from respiration may be used as source of carbon for ear photosynthesis. In the same way, the anatomy of glumes, for example, supports the role of bracts using internal CO 2 as source of photosynthesis. In the first experiment, the Δ in mature grains from culms with darkened ears compared with control culms provided further evidence in support of this hypothesis. Thus, the Δ from kernels of control plants was 0.40 higher than that from ear-darkened plants, probably because of some degree of refixation (recycling) of respired CO 2 in the grains. 相似文献
15.
Acclimation of photosynthesis to growth at elevated CO 2 concentration varies markedly between species. Species functionally classified as stress-tolerators (S) and ruderals (R), are thought to be incapable, or the least capable, of responding positively in terms of growth to elevated [CO 2]. Is this pattern of response also apparent in leaf photosynthesis of wild S- and R-strategists? Acclimatory loss of a photosynthetic and growth response to elevated [CO 2] is assumed to reflect limitation on capacity to utilize additional photosynthate. The doubling of pre-industrial global [CO 2] is expected to coincide with a 3 °C increase in mean temperature which could stimulate growth; will photosynthetic capacity at elevated [CO 2] be greater when the concurrent temperature increase is simulated? Five species from natural grassland of NW Europe and of contrasting ecological strategy were grown in hemispherical greenhouses, environmentally controlled to track the external microclimate. Within a replicated design, plants were grown at (i) current ambient [CO 2] and temperature, (ii) elevated [CO 2] (ambient + 340 μmol mol –1) and ambient temperature, (iii) ambient [CO 2] and elevated temperature (ambient + 3 °C), or (iv) elevated [CO 2] and elevated temperature. After 75–104 days, the CO 2 response of light-saturated rates of photosynthesis (A sat) was analysed in controlled-environment cuvettes in a field laboratory. There was no acclimatory loss of photosynthetic capacity with growth in elevated [CO 2] or elevated temperature over this period in Poa alpina (S), Bellis perennis (R) or Plantago lanceolata (mixed C-S-R strategist), and a significant ( P ? ? bl 0.05) increase in capacity in Helianthemum nummularium (S) and Poa annua (R). Photosynthetic rates of leaves grown and measured in elevated [CO 2] were therefore significantly higher than rates for leaves grown and measured in ambient [CO 2], for all species. With the exception of Poa alpina, stomatal conductance and stomatal limitation on A sat showed no acclimatory response to growth in elevated [CO 2]. Carboxylation efficiency, determined from the initial slope of the response of A sat to intercellular CO 2 concentration was significantly increased by elevated [CO 2] and elevated temperature in H.nummularium, implying a possible increase in in vivo RubisCO activity. Increased carboxylation efficiency of this species was also reflected by an increase in the CO 2- and light-saturated rates of photosynthesis, indicating an increased capacity for regeneration of the primary CO 2 acceptor in photosynthesis. The results show that R-strategists and slow-growing S-strategists, are inherently capable of large increases in leaf photosynthetic capacity with growth in elevated [CO 2] in contrast to expectations from growth studies. With the exception of P.annua, where there was a significant negative interaction between CO 2 and temperature, concurrent increase in growth temperature had little effect on this pattern of response. 相似文献
16.
The relationship between single leaf photosynthesis and conductance was examined in cotton ( Gossypium hirsutum L.) across a range of environmental conditions. The purpose of this research was to separate and define the degree of stomatal and nonstomatal limitations in the photosynthetic process of field-grown cotton. Photosynthetic rates were related to leaf conductance of upper canopy leaves in a curvilinear manner. Increases in leaf conductance of CO2 in excess of 0.3 to 0.4 mole per square meter per second did not result in significant increases in gross or net photosynthetic rates. No tight coupling between environmental influences on photosynthetic rates and those affecting conductance levels was evident, since photosynthesis per unit leaf conductance did not remain constant. Slowly developing water stress caused greater reductions in photosynthesis than in leaf conductance, indicating nonstomatal limitations of photosynthesis. Increases in external CO2 concentration to levels above ambient did not produce proportional increases in photosynthesis even though substomatal or intercellular CO2 concentration increased. The lack of a linear increase in photosynthetic rate in response to increases in leaf conductance and in response to increases in external CO2 concentration demonstrated that nonstomatal factors are major photosynthetic rate determinants of cotton under field conditions. 相似文献
17.
The photosynthetic behavior of leaves and twigs was compared in Hymenoclea salsola T. and G., a subshrub of the Mohave and Sonoran deserts, in which both leaves and green twigs make substantial contributions to whole-plant carbon gain. Light saturated photosynthesis in twigs was 0.62 times that of leaves (36.9 μmol m -2 s -1) when plants were well watered. Similar ratios were consistently observed in contrasting the photosynthetic responses of the two organ types to light, temperature, and intercellular CO 2, regardless of whether rates were compared under saturating or highly limiting conditions of light or intercellular CO 2. These scalar differences in photosynthetic rate between leaves and green twigs under a wide range of conditions were correlated with contrasting anatomical features such as chlorenchyma volume per projected area. Under normal ambient CO 2 concentrations (350 μl 1 -1), twigs on well watered plants operated at lower intercellular CO 2 concentrations than the leaves. Possible causes of this difference are discussed with respect to performance under well-watered conditions, organ lifespans, and contrasting anatomical constraints. Twigs require larger investments than do leaves of both carbon and nitrogen per projected area of the respective organs, yet they realize lower photosynthetic rates per intercepted light. Twigs, however, fulfill additional roles besides photosynthesis such as structural support and vascular transport which does not allow them to be as anatomically specialized as leaves for photosynthesis. Twigs also have a longer expected lifespan than leaves with a larger fraction of them surviving the summer drought period. This was correlated with a greater tolerance of twig than leaf photosynthesis to low plant water potentials. 相似文献
18.
Carbon uptake by forests constitutes half of the planet’s terrestrial net primary production; therefore, photosynthetic responses
of trees to rising atmospheric CO 2 are critical to understanding the future global carbon cycle. At the Swiss Canopy Crane, we investigated gas exchange characteristics
and leaf traits in five deciduous tree species during their eighth growing season under free air carbon dioxide enrichment
in a 35-m tall, ca. 100-year-old mixed forest. Net photosynthesis of upper-canopy foliage was 48% (July) and 42% (September)
higher in CO 2-enriched trees and showed no sign of down-regulation. Elevated CO 2 had no effect on carboxylation efficiency ( V
cmax) or maximal electron transport ( J
max) driving ribulose-1,5-bisphosphate (RuBP) regeneration. CO 2 enrichment improved nitrogen use efficiency, but did not affect leaf nitrogen (N) concentration, leaf thickness or specific
leaf area except for one species. Non-structural carbohydrates accumulated more strongly in leaves grown under elevated CO 2 (largely driven by Quercus). Because leaf area index did not change, the CO 2-driven stimulation of photosynthesis in these trees may persist in the upper canopy under future atmospheric CO 2 concentrations without reductions in photosynthetic capacity. However, given the lack of growth stimulation, the fate of
the additionally assimilated carbon remains uncertain. 相似文献
19.
During the past 25 Myr, partial pressures of atmospheric CO 2 ( Ca) imposed a greater limitation on C 3 than C 4 photosynthesis. This could have important downstream consequences for plant nitrogen economy and biomass allocation. Here, we report the first phylogenetically controlled comparison of the integrated effects of subambient Ca on photosynthesis, growth and nitrogen allocation patterns, comparing the C 3 and C 4 subspecies of Alloteropsis semialata. Plant size decreased more in the C 3 than C 4 subspecies at low Ca, but nitrogen pool sizes were unchanged, and nitrogen concentrations increased across all plant partitions. The C 3, but not C 4 subspecies, preferentially allocated biomass to leaves and increased specific leaf area at low Ca. In the C 3 subspecies, increased leaf nitrogen was linked to photosynthetic acclimation at the interglacial Ca, mediated via higher photosynthetic capacity combined with greater stomatal conductance. Glacial Ca further increased the biochemical acclimation and nitrogen concentrations in the C 3 subspecies, but these were insufficient to maintain photosynthetic rates. In contrast, the C 4 subspecies maintained photosynthetic rates, nitrogen‐ and water‐use efficiencies and plant biomass at interglacial and glacial Ca with minimal physiological adjustment. At low Ca, the C 4 carbon‐concentrating mechanism therefore offered a significant advantage over the C 3 type for carbon acquisition at the whole‐plant scale, apparently mediated via nitrogen economy and water loss. A limiting nutrient supply damped the biomass responses to Ca and increased the C 4 advantage across all Ca treatments. Findings highlight the importance of considering leaf responses in the context of the whole plant, and show that carbon limitation may be offset at the expense of greater plant demand for soil resources such as nitrogen and water. Results show that the combined effects of low CO 2 and resource limitation benefit C 4 plants over C 3 plants in glacial–interglacial environments, but that this advantage is lessened under anthropogenic conditions. 相似文献
20.
The regulation of photosynthesis through changes in light absorption, photochemistry, and carboxylation efficiency has been studied in plants grown in different environments. Iron deficiency was induced in sugar beet ( Beta vulgaris L.) by growing plants hydroponically in controlled growth chambers in the absence of Fe in the nutrient solution. Pear ( Pyrus communis L.) and peach ( Prunus persica L. Batsch) trees were grown in field conditions on calcareous soils, in orchards with Fe deficiency-chlorosis. Gas exchange parameters were measured in situ with actual ambient conditions. Iron deficiency decreased photosynthetic and transpiration rates, instantaneous transpiration efficiencies and stomatal conductances, and increased sub-stomatal CO 2 concentrations in the three species investigated. Photosynthesis versus CO 2 sub-stomatal concentration response curves and chlorophyll fluorescence quenching analysis revealed a non-stomatal limitation of photosynthetic rates under Fe deficiency in the three species investigated. Light absorption, photosystem II, and Rubisco carboxylation efficiencies were down-regulated in response to Fe deficiency in a coordinated manner, optimizing the use of the remaining photosynthetic pigments, electron transport carriers, and Rubisco. 相似文献
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