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1.
Summary Seedlings of the Caesalpinoids Hymenaea courbaril, H. parvifolia and Copaifera venezuelana, emergent trees of Amazonian rainforest canopies, and of the Araucarian conifers Agathis microstachya and A. robusta, important elements in tropical Australian rainforests, were grown at 6% (shade) and 100% full sunlight (sun) in glasshouses. All species produced more leaves in full sunlight than in shade and leaves of sun plants contained more nitrogen and less chlorophyll per unit leaf area, and had a higher specific leaf weight than leaves of shade plants. The photosynthetic response curves as a function of photon flux density for leaves of shade-grown seedlings showed lower compensation points, higher quantum yields and lower respiration rates per unit leaf area than those of sun-grown seedlings. However, except for A. robusta, photosynthetic acclimation between sun and shade was not observed; the light saturated rates of assimilation were not significantly different. Intercellular CO 2 partial pressure was similar in leaves of sun and shade-grown plants, and assimilation was limited more by intrinsic mesophyll factors than by stomata. Comparison of assimilation as a function of intercellular CO 2 partial pressure in sun- and shade-grown Agathis spp. showed a higher initial slope in leaves of sun plants, which was correlated with higher leaf nitrogen content. Assimilation was reduced at high transpiration rates and substantial photoinhibition was observed when seedlings were transferred from shade to sun. However, after transfer, newly formed leaves in A. robusta showed the same light responses as leaves of sun-grown seedlings. These observations on the limited potential for acclimation to high light in leaves of seedlings of rainforest trees are discussed in relation to regeneration following formation of gaps in the canopy. 相似文献
2.
Effects of salinity and nutrients on carbon gain in relation to water use were studied in the grey mangrove, Avicennia marina, growing along a natural salinity gradient in south‐eastern Australia. Tall trees characterized areas of seawater salinities (fringe zone) and stunted trees dominated landward hypersaline areas (scrub zone). Trees were fertilized with nitrogen (+N) or phosphorus (+P) or unfertilized. There was no significant effect of +P on shoot growth, whereas +N enhanced canopy development, particularly in scrub trees. Scrub trees maintained greater CO 2 assimilation per unit water transpired (water‐use efficiency, WUE) and had lower nitrogen‐use efficiency (NUE; CO 2 assimilation rate per unit leaf nitrogen) than fringe trees. The CO 2 assimilation rates of +N trees were similar to those in other treatments, but were achieved at lower transpiration rates, stomatal conductance and intercellular CO 2 concentrations. Maintaining comparable assimilation rates at lower stomatal conductance requires greater ribulose 1·5‐bisphosphate carboxylase/oxygenase activity, consistent with greater N content per unit leaf area in +N trees. Hence, +N enhanced WUE at the expense of NUE. Instantaneous WUE estimates were supported by less negative foliar δ13C values for +N trees and scrub control trees. Thus, nutrient enrichment may alter the structure and function of mangrove forests along salinity gradients. 相似文献
3.
The rate of photosynthesis and its relation to tissue nitrogen content was studied in leaves and siliques of winter oilseed
rape ( Brassica napus L.) growing under field conditions including three rates of nitrogen application (0, 100 or 200 kg N ha -1) and two levels of irrigation (rainfed or irrigated at a deficit of 20 mm).
The predominant effect of increasing N application under conditions without water deficiency was enhanced expansion of photosynthetically
active leaf and silique surfaces, while the rate of photosynthesis per unit leaf or silique surface area was similar in the
different N treatments. Thus, oilseed rape did not increase N investment in leaf area expansion before a decline in photosynthetic
rate per unit leaf area due to N deficiency could be avoided. Much less photosynthetically active radiation penetrated into
high-N canopies than into low-N canopies. The specific leaf area increased markedly in low light conditions, causing leaves
in shade to be less dense than leaves exposed to ample light.
In both leaves and siliques the photosynthetic rate per unit surface area responded linearly to increasing N content up to
about 2 g m -2, thus showing a constant rate of net CO 2 assimilation per unit increment in N (constant photosynthetic N use efficiency). At higher tissue N contents, photosynthetic
rate responded less to changes in N status. Expressed per unit N, light saturated photosynthetic rate was three times higher
in leaves than in silique valves, indicating a more efficient photosynthetic N utilization in leaves than in siliques. Nevertheless,
from about two weeks after completion of flowering and onwards total net CO 2 fixation in silique valves exceeded that in leaves because siliques received much higher radiation intensities than leaves
and because the leaf area declined rapidly during the reproductive phase of growth.
Water deficiency in late vegetative and early reproductive growth stages reduced the photosynthetic rate in leaves and, in
particular, siliques of medium- and high-N plants, but not of low-N plants. 相似文献
4.
Abstract Field gas exchange measurements on intact peach (Prunus persica (L.) Batsch) leaves indicate that leaf nitrogen content (N L) and leaf weight per unit leaf area (Wa) are highly correlated with CO 2 assimilation rate (A) and mesophyll conductance (g m). Therefore, N L and W a were used to study seasonal relationships between leaf carboxylation capacity and natural light exposure in tree canopies. From mid-season onwards, N L and Wa were linearly correlated with light exposure expressed as the amount of time during a clear day that a leaf was exposed to a photosynthetic photon flux density (Q) of ≥ 100 μmol m ?2 s ?1. The data support the hypothesis that whole-tree photosynthesis is optimized by partitioning of photosynthetic capacity among leaves in deciduous tree canopies with respect to natural light exposure. 相似文献
5.
Few studies have investigated the effects of elevated CO 2 on the physiology of symbiotic N 2-fixing trees. Tree species grown in low N soils at elevated CO 2 generally show a decline in photosynthetic capacity over time relative to ambient CO 2 controls. This negative adjustment may be due to a reallocation of leaf N away from the photosynthetic apparatus, allowing for more efficient use of limiting N. We investigated the effect of twice ambient CO 2 on net CO 2 assimilation (A), photosynthetic capacity, leaf dark respiration, and leaf N content of N2-fixing Alnus glutinosa (black alder) grown in field open top chambers in a low N soil for 160 d. At growth CO 2, A was always greater in elevated compared to ambient CO 2 plants. Late season A vs. internal leaf p(CO 2) response curves indicated no negative adjustment of photosynthesis in elevated CO 2 plants. Rather, elevated CO 2 plants had 16% greater maximum rate of CO 2 fixation by Rubisco. Leaf dark respiration was greater at elevated CO 2 on an area basis, but unaffected by CO 2 on a mass or N basis. In elevated CO 2 plants, leaf N content (μg N cm ?2) increased 50% between Julian Date 208 and 264. Leaf N content showed little seasonal change in ambient CO 2 plants. A single point acetylene reduction assay of detached, nodulated root segments indicated a 46% increase in specific nitrogenase activity in elevated compared to ambient CO 2 plants. Our results suggest that N 2-fixing trees will be able to maintain high A with minimal negative adjustment of photosynthetic capacity following prolonged exposure to elevated CO 2 on N-poor soils. 相似文献
6.
Summary The scale insect, Toumeyella sp., feeds exclusively on the subtropical hammock tree lignum vitae ( Guaiacum sanctum L.). The combined effects of scale herbivory and shading on leaf gas exchange characteristics and growth of lignum vitae trees were studied using a factorial design. Trees grown in full sun or in 75% shade were manually infested with scale or left noninfested. Beginning 4 weeks after infestation, net CO 2 assimilation, stomatal conductance, transpiration, internal partial pressure of CO 2, and water-use efficiency were determined on single-leaves at 4-week intervals for trees in each treatment. At the end of the experiment, net CO 2 assimilation was determined for whole plants. Total leaf area, leaf, stem, and root dry weights, and leaf chlorophyll and nitrogen concentrations were also determined. Scale infested trees generally had lower net CO 2 assimilation, stomatal conductance, and transpiration rates as well as less leaf area, and root, stem, and leaf dry weights than noninfested trees. Twenty four weeks after the shade treatment was imposed, sun-grown trees had approximately twice the leaf area of shade-grown trees. Shade-grown trees compensated for the reduced leaf area by increasing their photosynthetic efficiency. This resulted in no difference in light saturated net CO 2 assimilation on a whole plant basis between sun-grown and shade-grown trees. Chlorophyll and nitrogen concentrations per unit leaf area were greater in leaves of shade-grown trees than in leaves of sun-grown trees. Shading and herbivory by Toumeyella sp. each resulted in decreased growth of Guaiacum sanctum. Scale insect herbivory did not result in greater detrimental effects on leaf gas exchange characteristics for shade-grown than for sun-grown trees. Herbivory by Toumeyella resulted in a greater decrease in tree growth for sun-grown than for shade-grown trees. 相似文献
7.
Summary Photosynthetic rates and nutrient contents of spruce needles were measured in a region with high levels of air pollution in NE Bavaria, Germany (FRG), and compared to spruce grown under clean air conditions at Craigieburn, in the South Island of New Zealand (NZ). The absolute rates of CO 2 uptake, the slope of the CO 2 response curve at 240 l l –1 internal CO 2 concentration, and the change of photosynthetic rates with needle age at ambient and saturated CO 2 concentrations were virtually identical at both measuring sites. These results confirm an earlier conclusion, that there is no long-term effect of atmospheric pollutants directly on photosynthetic CO 2 uptake rates with persistent exposure at the FRG site to high levels of anthropogenic air pollution. Photosynthetic capacity at saturating CO 2 concentration was three times higher in the NZ spruce. Needles with high photosynthetic capacity in NZ had lower nitrogen and higher calcium concentrations per unit dry weight but higher concentrations of nitrogen, phosphorus, potassium, magnesium and calcium per unit leaf area, and twice the specific leaf weight. 相似文献
8.
Seedlings of Eucalyptus grandis were grown at five different rates of nitrogen supply. Once steady‐state growth rates were established, a detailed set of CO 2 and water vapour exchange measurements were made to investigate the effects of leaf nitrogen content ( N), as determined by nitrogen supply rate, on leaf structural, photosynthetic, respiratory and stomatal properties. Gas exchange data were used to parametrize the Farquhar–von Caemmerer photosynthesis model. Leaf mass per area (LMA) was negatively correlated to N. A positive correlation was observed between both day ( Rd) and night respiration ( Rn) and N when they were expressed on a leaf mass basis, but no correlation was found on a leaf area basis. An Rd/ Rn ratio of 0·59 indicated a significant inhibition of dark respiration by light. The maximum net CO 2 assimilation rate at ambient CO 2 concentration ( Amax), the maximum rate of potential electron transport ( Jmax) and the maximum rate of carboxylation ( Vcmax) significantly increased with N, particularly when expressed on a mass basis. Although the maximum stomatal conductance to CO 2 ( gscmax) was positively correlated with Amax, there was no relationship between gscmax and N. Leaf N content influenced the allocation of nitrogen to photosynthetic processes, resulting in a decrease of the Jmax/ Vcmax ratio with increasing N. It was concluded that leaf nitrogen concentration is a major determinant of photosynthetic capacity in Eucalyptus grandis seedlings and, to a lesser extent, of leaf respiration and nitrogen partitioning among photosynthetic processes, but not of stomatal conductance. 相似文献
9.
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
10.
We evaluated the hypothesis that photosynthetic traits differ between leaves produced at the beginning (May) and the end
(November–December) of the rainy season in the canopy of a seasonally dry forest in Panama. Leaves produced at the end of
the wet season were predicted to have higher photosynthetic capacities and higher water-use efficiencies than leaves produced
during the early rainy season. Such seasonal phenotypic differentiation may be adaptive, since leaves produced immediately
preceding the dry season are likely to experience greater light availability during their lifetime due to reduced cloud cover
during the dry season. We used a construction crane for access to the upper canopy and sampled 1- to 2-month-old leaves marked
in monthly censuses for six common tree species with various ecological habits and leaf phenologies. Photosynthetic capacity
was quantified as light- and CO 2-saturated oxygen evolution rates with a leaf-disk oxygen electrode in the laboratory (O 2max) and as light-saturated CO 2 assimilation rates of intact leaves under ambient CO 2 (A max). In four species, pre-dry season leaves had significantly higher leaf mass per unit area. In these four species, O 2max and A max per unit area and maximum stomatal conductances were significantly greater in pre-dry season leaves than in early wet season
leaves. In two species, A max for a given stomatal conductance was greater in pre-dry season leaves than in early wet season leaves, suggesting a higher
photosynthetic water-use efficiency in the former. Photosynthetic capacity per unit mass was not significantly different between
seasons of leaf production in any species. In both early wet season and pre-dry season leaves, mean photosynthetic capacity
per unit mass was positively correlated with nitrogen content per unit mass both within and among species. Seasonal phenotypic
differentiation observed in canopy tree species is achieved through changes in leaf mass per unit area and increased maximum
stomatal conductance rather than by changes in nitrogen allocation patterns.
Received: 7 March 1996 / Accepted: 1 August 1996 相似文献
11.
Summary CO 2 assimilation in relation to light intensity and the relationship between leaf nitrogen and phosphorus concentrations and CO 2 assimilation in 14 species of ecologically important Zimbabwean trees were examined. Eight of the species are members of the Fabaceae (Leguminosae). In the majority of Zimbabwean climax woodlands, the dominant trees are non-nodulating members of the sub-family Caesalpinioideae. The species examined have higher light saturation points (>700 mol m –2 s –1) than woody species from temperate areas; one species, Acacia nigrescens, did not reach saturation at photon fluxes greater than 1500 mol m –2 sec –1. Higher leaf nitrogen content was found to correlate positively with higher CO 2 assimilation rates ( r=0.85; P0.0003); there was no correlation between leaf phosphorus content and CO 2 uptake rates. There were no significant differences between sites in terms of leaf nitrogen or phosphorus content, but the mean photosynthetic rate at one of the sites (Chizedzi) was lower. Taxa from the nodulating legumes were found to have higher leaf nitrogen contents (309.1±SD 22 mmol m –2) than those of the non-nodulating species (239±33); the lowest nitrogen contents were found in nonleguminous trees (179±42), with the exception of Ziziphus mucronata. This species may form an association with an N 2-fixing actinomycete. 相似文献
12.
The growth responses of a grass, Poa pratensis, to elevated CO 2 and nitrogen were investigated. Light-saturated photosynthetic rate per unit leaf area increased with exposure to elevated
CO 2, while dry weight did not respond to increased CO 2. Patterns of biomass allocation within plants, including leaf area, leaf area ratio, specific leaf area, and root to shoot
ratios, were not altered by elevated CO 2, but changed considerably with N treatment Shoot and whole-plant tissue N concentrations were significantly diluted by elevated
CO 2 (Tukey test, P < 0.05). Total N content did not differ significantly among CO 2 treatments. The absence of a concomitant increase in N uptake under elevated CO 2 may have caused a dilution in plant tissue [N], probably negating the positive effects of increased photosynthesis on biomass
accumulation. 相似文献
13.
ABSTRACT After a 3-year exposure to elevated CO 2, young trees of Sitka spruce ( Picea sitchensis (Bong.) Carr.) were planted in native, nutrient-deficient forest soil and grown for two more years with three CO 2 treatments in open-top chambers, and with two nutrient treatments (with and without supplied N). Elevated CO 2 resulted in larger fresh mass, dry mass, leaf area and leaf thickness in two-year old needles, but had no effect on one-year old and current needles. Tree height, basal diameter and biomass production also increased, regardless of N supply. In trees without added N, elevated CO 2 resulted in higher root-to-shoot and absorbing roots-to-stump ratios. Regardless of N supply, trees grown in elevated CO 2 had lower photosynthetic rates on a leaf area basis. Photosynthesis reduction was accompanied by a decline in Rubisco activity and leaf N concentration. Under elevated CO 2, added N elevated photosynthesis and Rubisco activity, suggesting a dependence on N availability of the photosynthetic response to elevated CO 2. Stomatal conductance of trees grown with added N decreased in response to elevated CO 2. This may account for the larger reduction in intercellular CO 2 concentration, and hence photosynthesis, in the trees supplied with N than in those without N supply. 相似文献
14.
Declining net primary production (NPP) with forest age is often attributed to a corresponding decline in gross primary production (GPP). We tested two hypotheses explaining the decline of GPP in ageing stands (14–115 years old) of Pinus taeda L.: (1) increasing N limitation limits photosynthetic capacity and thus decreases GPP with increasing age; and (2) hydraulic limitations increasingly induce stomatal closure, reducing GPP with increasing age. We tested these hypotheses using measurements of foliar nitrogen, photosynthesis, sap‐flow and dendroclimatological techniques. Hypothesis (1) was not supported; foliar N retranslocation did not increase and declines were not observed in foliar N, leaf area per tree or photosynthetic capacity. Hypothesis (2) was supported; declines were observed in light‐saturated photosynthesis, leaf‐ and canopy‐level stomatal conductance, concentration of CO 2 inside leaf air‐spaces (corroborated by an increase in wood δ13C) and specific leaf area (SLA), while stomatal limitation and the ratio of sapwood area (SA) to leaf area increased. The sensitivity of radial growth to inter‐annual variation in temperature and drought decreased with age, suggesting that tree water use becomes increasingly conservative with age. We conclude that hydraulic limitation increasingly limits the photosynthetic rates of ageing loblolly pine trees, possibly explaining the observed reduction of NPP. 相似文献
15.
This work investigated the agronomic, physiological and biochemical response of Stevia rebaudiana Bertoni grown under different nitrogen (N) rates. A pot trial in open air conditions was set up in 2012 with the aim to evaluate the effect of four N rates on the biometric and productive characteristics, steviol glycoside (SG) content as well as on leaf gas exchanges, chlorophyll fluorescence, photosynthetic pigments, Rubisco activity and N use efficiency. N deficiency caused a decrease in leaf N content, chlorophylls and photosynthetic CO 2 assimilation, resulting in a lower dry matter accumulation as well as in reduced SG production. The application of 150 kg N ha ? 1 seems to be the most effective treatment to improve rebaudioside A (Reb A) content, Reb A/stevioside ratio, photosynthetic CO 2 assimilation, stomatal conductance, N use efficiency, ribulose-1,5-bis-phosphate carboxylase/oxygenase (Rubisco) and PSII efficiency. The results demonstrate that by using an appropriate N rate it is possible to modulate the SG biosynthesis, with a significant increase in the Reb A content and in the ratio between Reb A and stevioside. This finding is of great relevance in order to obtain a raw material designed to meet consumer needs and bio-industry requirements for high-quality, Reb A content, and safe and environmentally friendly products. 相似文献
16.
Summary A simulation model for radiation absorption and photosynthesis was used to test the hypothesis that observed nonuniform distributions of nitrogen concentrations in young Eucalyptus grandis trees result in greater amounts of daily assimilation than in hypothetical trees with uniform N distributions. Simulations were performed for trees aged 6, 9, 12 and 16 months which had been grown in plantations under a factorial combination of two levels of fertilization and irrigation. Observed leaf N distribution patterns yielded daily assimilation rates which were only marginally greater (<5%) than for hypothetical trees with uniform distributions. Patterns of assimilation distribution in individual tree crowns closely resembled those for absorbed radiation, rather than for N. These conclusions were unaffected by three choices of alternative leaf area density distributions. The simulation model was also used to calculate hourly and daily rates of canopy assimilation to investigate the relative importance of radiation absorption and total canopy nitrogen on assimilation. Simulated hourly rates of carbon assimilation were often lightsaturated, whereas daily carbon gain was directly proportional to radiation absorbed by the tree crown and to total mass of N in the leaves. Leaf nitrogen concentrations determined photosynthetic capacity, whereas total leaf area determined the amount of radiation absorbed and thus the degree to which capacity was realized. Observed total leaf area and total crown N were closely correlated. The model predicted that nitrogen use efficiences (NUE, mol CO 2 mol –1 N) were 60% higher for unfertilized than for fertilized trees at low levels of absorbed photosynthetically active radiation (PAR). Nitrogen use efficiency was dependent on fertilizer treatment and on the amount of absorbed PAR; NUE declined with increasing absorbed PAR, but decreased more rapidly for unfertilized than for fertilized trees. Annual primary productivity was linearly related to both radiation absorbed and to mass of N in the canopy. 相似文献
17.
Estimation of leaf photosynthetic rate ( A) from leaf nitrogen content ( N) is both conceptually and numerically important in models of plant, ecosystem, and biosphere responses to global change. The relationship between A and N has been studied extensively at ambient CO 2 but much less at elevated CO 2. This study was designed to (i) assess whether the A–N relationship was more similar for species within than between community and vegetation types, and (ii) examine how growth at elevated CO 2 affects the A–N relationship. Data were obtained for 39 C3 species grown at ambient CO 2 and 10 C3 species grown at ambient and elevated CO 2. A regression model was applied to each species as well as to species pooled within different community and vegetation types. Cluster analysis of the regression coefficients indicated that species measured at ambient CO 2 did not separate into distinct groups matching community or vegetation type. Instead, most community and vegetation types shared the same general parameter space for regression coefficients. Growth at elevated CO 2 increased photosynthetic nitrogen use efficiency for pines and deciduous trees. When species were pooled by vegetation type, the A–N relationship for deciduous trees expressed on a leaf-mass basis was not altered by elevated CO 2, while the intercept increased for pines. When regression coefficients were averaged to give mean responses for different vegetation types, elevated CO 2 increased the intercept and the slope for deciduous trees but increased only the intercept for pines. There were no statistical differences between the pines and deciduous trees for the effect of CO 2. Generalizations about the effect of elevated CO 2 on the A–N relationship, and differences between pines and deciduous trees will be enhanced as more data become available. 相似文献
18.
The gas exchange of spinach plants, salt-stressed by adding NaCl to the nutrient solution in increments of 25 millimolar per day to a final concentration of 200 millimolar, was studied 3 weeks after starting NaCl treatment. Photosynthesis became light saturated at 1100 to 1400 micromoles per square meter per second in salt-treated plants and at approximately 2000 micromoles per square meter per second in control plants. Photosynthetic capacity of the mesophyll measured as a function of intercellular partial pressure of CO 2 at the light intensity prevailing during growth and at light saturation were both decreased in the salttreated plants. The CO 2 compensation points and relative enhancements of photosynthesis at low O 2 were not affected by salinity. The lower photosynthetic rates in salt-treated leaves at 450 micromoles per square meter per second were associated with a 70% reduction in stomatal conductance and low intercellular CO 2 (219 microbars; cf. 285 microbars for controls). Increasing photon flux density to light saturation extended the linear portions of the CO 2 response curves, increased stomatal conductances, increased intercellular CO 2 in the salt-treated plants, but lowered it in controls, and accentuated differences in photosynthetic rate (area basis) between the treatments. Leaves from salt-treated plants were thicker but contained about 73% of the chlorophyll per unit area of control plants. When photosynthetic rates were expressed on a chlorophyll basis there was no difference in initial slope of assimilation versus intercellular CO2 between treatments. Photosynthetic rates (chlorophyll basis) at light saturation differed only by 20% which was also observed earlier with isolated, intact chloroplasts (Robinson et al. 1983 Plant Physiol 73: 238-242). Measurement of carbon isotope ratio revealed less discrimination against 13C with salt treatment and confirmed the persistence of low intercellular partial pressures of CO2 during plant growth. The development of a thicker leaf with less chlorophyll per unit area during salt treatment permitted stomatal conductance and intercellular partial pressure of CO2 to decline without restricting photosynthesis and had the benefit of greatly increasing water use efficiency. 相似文献
19.
Seasonal drought can severely impact leaf photosynthetic capacity. This is particularly important for Mediterranean forests, where precipitation is expected to decrease as a consequence of climate change. Impacts of increased drought on the photosynthetic capacity of the evergreen Quercus ilex were studied for two years in a mature forest submitted to long‐term throughfall exclusion. Gas exchange and chlorophyll fluorescence were measured on two successive leaf cohorts in a control and a dry plot. Exclusion significantly reduced leaf water potential in the dry treatment. In both treatments, light‐saturated net assimilation rate ( Amax), stomatal conductance ( gs), maximum carboxylation rate ( Vcmax), maximum rate of electron transport ( Jmax), mesophyll conductance to CO 2 ( gm) and nitrogen investment in photosynthesis decreased markedly with soil water limitation during summer. The relationships between leaf photosynthetic parameters and leaf water potential remained identical in the two treatments. Leaf and canopy acclimation to progressive, long‐term drought occurred through changes in leaf area index, leaf mass per area and leaf chemical composition, but not through modifications of physiological parameters. 相似文献
20.
Recent evidence indicates that winter-red leaf phenotypes in the mastic tree ( Pistacia lentiscus) are more vulnerable to chronic photoinhibition during the cold season relative to winter-green phenotypes occurring in the same high light environment. This was judged by limitations in the maximum quantum yield of photosystem II (PSII), found in previous studies. In this investigation, we asked whether corresponding limitations in leaf gas exchange and carboxylation reactions could also be manifested. During the cold (“red”) season, net CO 2 assimilation rates (A) and stomatal conductances (g s) in the red phenotype were considerably lower than in the green phenotype, while leaf internal CO 2 concentration (Ci) was higher. The differences were abolished in the “green” period of the year, the dry summer included. Analysis of A versus Ci curves indicated that CO 2 assimilation during winter in the red phenotype was limited by Rubisco content and/or activity rather than stomatal conductance. Leaf nitrogen levels in the red phenotype were considerably lower during the red-leaf period. Consequently, we suggest that the inherently low leaf nitrogen levels are linked to the low net photosynthetic rates of the red plants through a decrease in Rubisco content. Accordingly, the reduced capacity of the carboxylation reactions to act as photosynthetic electron sinks may explain the corresponding loss of PSII photon trapping efficiency, which cannot be fully alleviated by the screening effect of the accumulated anthocyanins. 相似文献
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