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1.
Growth at elevated CO2 often decreases photosynthetic capacity (acclimation) and leaf N concentrations. Lower-shaded canopy leaves may undergo both CO2 and shade acclimation. The relationship of acclimatory responses of flag and lower-shaded canopy leaves of wheat (Triticum aestivum L.) to the N content, and possible factors affecting N gain and distribution within the plant were investigated in a wheat crop growing in field chambers set at ambient (360 μmol mol−1) and elevated (700 μmol mol−1) CO2, and with two amounts of N fertilizer (none and 70 kg ha−1 applied on 30 April). Photosynthesis, stomatal conductance and transpiration at a common measurement CO2, chlorophyll and Rubisco levels of upper-sunlit (flag) and lower-shaded canopy leaves were significantly lower in elevated relative to ambient CO2-grown plants. Both whole shoot N and leaf N per unit area decreased at elevated CO2, and leaf N declined with canopy position. Acclimatory responses to elevated CO2 were enhanced in N-deficient plants. With N supply, the acclimatory responses were less pronounced in lower canopy leaves relative to the flag leaf. Additional N did not increase the fraction of shoot N allocated to the flag and penultimate leaves. The decrease in photosynthetic capacity in both upper-sunlit and lower-shaded leaves in elevated CO2 was associated with a decrease in N contents in above-ground organs and with lower N partitioning to leaves. A single relationship of N per unit leaf area to the transpiration rate accounted for a significant fraction of the variation among sun-lit and shaded leaves, growth CO2 level and N supply. We conclude that reduced stomatal conductance and transpiration can decrease plant N, leading to acclimation to CO2 enrichment.  相似文献   

2.
The main goal of this study was to test the effect of [CO2] on C and N management in different plant organs (shoots, roots and nodules) and its implication in the responsiveness of exclusively N2-fixing and NO3-fed plants. For this purpose, exclusively N2-fixing and NO3-fed (10 mM) pea (Pisum sativum L.) plants were exposed to elevated [CO2] (1000 μmol mol−1 versus 360 μmol mol−1 CO2). Gas exchange analyses, together with carbohydrate, nitrogen, total soluble proteins and amino acids were determined in leaves, roots and nodules. The data obtained revealed that although exposure to elevated [CO2] increased total dry mass (DM) in both N treatments, photosynthetic activity was down-regulated in NO3-fed plants, whereas N2-fixing plants were capable of maintaining enhanced photosynthetic rates under elevated [CO2]. In the case of N2-fixing plants, the enhanced C sink strength of nodules enabled the avoidance of harmful leaf carbohydrate build up. On the other hand, in NO3-fed plants, elevated [CO2] caused a large increase in sucrose and starch. The increase in root DM did not contribute to stimulation of C sinks in these plants. Although N2 fixation matched plant N requirements with the consequent increase in photosynthetic rates, in NO3-fed plants, exposure to elevated [CO2] negatively affected N assimilation with the consequent photosynthetic down-regulation.  相似文献   

3.
Peanut (Arachis hypogaea L. cv. Florunner) was grown from seed sowing to plant maturity under two daytime CO2 concentrations ([CO2]) of 360 μmol mol−1 (ambient) and 720 μmol mol−1 (elevated) and at two temperatures of 1.5 and 6.0 °C above ambient temperature. The objectives were to characterize peanut leaf photosynthesis responses to long-term elevated growth [CO2] and temperature, and to assess whether elevated [CO2] regulated peanut leaf photosynthetic capacity, in terms of activity and protein content of ribulose bisphosphate carboxylase-oxygenase (Rubisco), Rubisco photosynthetic efficiency, and carbohydrate metabolism. At both growth temperatures, leaves of plants grown under elevated [CO2] had higher midday photosynthetic CO2 exchange rate (CER), lower transpiration and stomatal conductance and higher water-use efficiency, compared to those of plants grown at ambient [CO2]. Both activity and protein content of Rubisco, expressed on a leaf area basis, were reduced at elevated growth [CO2]. Declines in Rubisco under elevated growth [CO2] were 27–30% for initial activity, 5–12% for total activity, and 9–20% for protein content. Although Rubisco protein content and activity were down-regulated by elevated [CO2], Rubisco photosynthetic efficiency, the ratio of midday light-saturated CER to Rubisco initial or total activity, of the elevated-[CO2] plants was 1.3- to 1.9-fold greater than that of the ambient-[CO2] plants at both growth temperatures. Leaf soluble sugars and starch of plants grown at elevated [CO2] were 1.3- and 2-fold higher, respectively, than those of plants grown at ambient [CO2]. Under elevated [CO2], leaf soluble sugars and starch, however, were not affected by high growth temperature. In contrast, high temperature reduced leaf soluble sugars and starch of the ambient-[CO2] plants. Activity of sucrose-P synthase, but not adenosine 5′-diphosphoglucose pyrophosphorylase, was up-regulated under elevated growth [CO2]. Thus, in the absence of other environmental stresses, peanut leaf photosynthesis would perform well under rising atmospheric [CO2] and temperature as predicted for this century.  相似文献   

4.
We report the results of a baseline study on the effects of Russian wheat aphid infestation on barley lines grown under ambient and elevated (450 and 550 μmol mol 1) CO2 concentrations [CO2]. Elevated CO2 impacted on plant biomass, C:N ratios and leaf nitrogen concentrations. Visible manifestation of aphid feeding related damage was assessed by examining resultant chlorosis and leaf roll under ambient and two elevated [CO2] levels using a control and three resistant barley host combinations. Elevated [CO2] had a significant positive effect on the growth of the four barley lines that were not infested by the aphids. However under the same conditions aphid feeding under elevated CO2 conditions caused very high biomass loss, which was more noticeable in experiments involving non-resistant PUMA than in the resistant barley lines. The results of this study demonstrate that CO2 enrichment substantially increases aphid populations of RWASA1 and RWASA2 on the four barley lines investigated. Furthermore, aphid populations were higher on non-resistant PUMA than the three resistant lines and the RWASA2 biotype out-performed RWASA1 in each case. Under elevated [CO2], aphid feeding, resulted in a significant increase in the leaf C:N ratios (as a percentage change) in most treatments, compared to levels recorded on uninfested plants. The resistant lines also showed a significant reduction in leaf nitrogen (~ 40% for PUMA and not less than 30% for the resistant STARS lines tested). C:N ratio changes and N loss correlated to [CO2] and aphid biotype. By 28 days of infestation, most of the non-resistant PUMA line in particular showed significant irrecoverable levels of leaf chlorosis. At level 9 rating on the chlorosis scale (i.e. plant death when recovery was not possible), experiments were terminated. As aphid success is unlikely to be the sole product of [CO2], but also of other limiting nutrients such as N, it may be worth further investigating the effect of plant quality and ultimately plant nutrition on the population growth of aphids.  相似文献   

5.
N2-fixing alfalfa plants were grown in controlled conditions at different CO2 levels (350 μmol mol?1 versus 700 μmol mol?1) and water-availability conditions (WW, watered at maximum pot water capacity versus WD, watered at 50% of control treatments) in order to determine the CO2 effect (and applied at two water regimes) on plant growth and nodule activity in alfalfa plants. The CO2 stimulatory effect (26% enhancement) on plant growth was limited to WW plants, whereas no CO2 effect was observed in WD plants. Exposure to elevated CO2 decreased Rubisco carboxylation capacity of plants, caused by a specific reduction in Rubisco (EC 4.1.1.39) concentration (11% in WW and 43% in WD) probably explained by an increase in the leaf carbohydrate levels. Plants grown at 700 μmol mol?1 CO2 maintained control photosynthetic rates (at growth conditions) by diminishing Rubisco content and by increasing nitrogen use efficiency. Interestingly, our data also suggest that reduction in shoot N demand (reflected by the TSP and especially Rubisco depletion) affected negatively nodule activity (malate dehydrogenase, EC 1.1.1.37, and glutamate-oxaloacetate transaminase, EC 2.6.1.1, activities) particularly in water-limited conditions. Furthermore, nodule DM and TSS data revealed that those nodules were not capable to overcome C sink strength limitations.  相似文献   

6.
In a previous study, we found that enhanced CO2 subjected to nodulated alfalfa plants grown at different temperatures (ambient and ambient + 4 °C) and water availability regimes could protect PSII from photodamage. The main objective of this study was to determine the mechanism(s) involved in the photoprotection of PSII at elevated CO2 levels in this plant. Elevated CO2 reduced carboxylation capacity-induced photosynthetic acclimation and reduced enzymatic and/or nonenzymatic antioxidant activities, suggesting that changes in electron flow did not cause any photooxidative damage (which was also confirmed by H2O2 and lipid peroxidation analyses). Enhanced nonphotochemical quenching and xanthophyll cycle pigments revealed that plants grown at 700 μmol mol−1 CO2 compensated for the reduction in energy sink with a larger capacity for nonphotochemical dissipation of excitation energy as heat, i.e., modulating the status of the VAZ components. Elevated CO2 induced the de-epoxidation of violaxanthin to zeaxanthin, facilitating thermal dissipation and protecting the photosynthetic apparatus against the deleterious effect of excess excitation energy.  相似文献   

7.
Haberlea rhodopensis is a homoiochlorophyllous resurrection plant that shows a low rate of leaf net CO2 uptake (4–6 μmol m?2 s?1) under saturating photosynthetic photon flux densities in air (21% O2 and about 390 ppm CO2). However, leaf net CO2 uptake reaches values of 17–18 μmol m?2 s?1 under saturating CO2 and light. H. rhodopensis leaves have a very low mesophyll CO2 conductance that can partly explain the low rate of leaf net CO2 uptake in normal air. Experimental evidences suggest that mesophyll conductance is not sensitive to temperature in the 20–35 °C range. In addition, it is shown that the (1) transpiration rate of H. rhodopensis is nearly linearly related to the vapour pressure difference between the leaf and the ambient air within the interval from 0.5 kPa to 2.5 kPa at a leaf temperature of 25 °C and (2) leaf net CO2 uptake in normal air under saturating light does not change much with leaf temperature (between 20 °C and 30 °C). At a leaf relative water content of between 90% and 30%, the decrease of leaf net CO2 assimilation during drought can be explained by a decrease of leaf CO2 diffusional conductance. Accordingly the non-photochemical chlorophyll fluorescence quenching decreases only at relative water contents lower than 20%, indicating that photosynthetic activity maintains a trans-thylakoidal proton gradient over a wide range of leaf water contents. Moreover, PSII photochemistry (as estimated by the Fv/Fm ratio and the thermoluminescence B band intensity) is only affected at leaf relative water contents lower than about 20%, thus confirming that primary photosynthetic reactions are resistant to drought. Interestingly, the effect of leaf desiccation on photosynthetic capacity, measured at very high ambient CO2 molar ratios under saturating PPFD, is identical to that observed for three non-resurrection C3 mesophytes. This demonstrates that the photosynthetic apparatus of H. rhodopensis is not more resistant to desiccation when compared to other C3 plants. Since the leaf area decreases by more than 50% when the leaf relative water content is reduced to about 40% during drought it is supposed, following Farrant et al. [Farrant, J.M., Vander, W.C., Lofell, D.A., Bartsch, S., Whittaker, A., 2003. An investigation into the role of light during desiccation of three angiosperms resurrection plants. Plant Cell Environ. 26, 1275–1286], that H. rhodopensis leaf cells avoid mechanical stress.  相似文献   

8.
Exposing plants to long-term CO2 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 CO2, applied at different temperature and water availability regimes, on nodulated alfalfa plants. Regardless of water supply, elevated CO2 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 CO2 enhanced water use efficiency because of reduced water consumption and a greater dry mass production. Increased dry matter production of plants grown under elevated CO2 and temperature was the result of stimulated photosynthetic rates, greater leaf area and water use efficiency. Lack of CO2 effect on photosynthesis of plants grown at ambient temperature might be consequence of down-regulation phenomena. Plants grown at 700 μmol mol−1 CO2 maintained control nitrogen levels, discarding enhanced nitrogen availability as the main factor explaining enhanced dry matter.  相似文献   

9.
The kinetics of a stomatal response to sudden increases or decreases of CO2 concentrations ([CO2]) was studied in 13 plant species growing in the field. Plants were well supplied with water. In each plant, gas exchange measurements were made on a fully developed leaf that was first left to achieve steady-state stomatal conductance (gs) at 400 μmol (CO2) mol−1) and then exposed to a step change of [CO2] (to 700 μmol mol−1 in one experiment; and to 700 and back to 400 μmol mol−1 in a second experiment). Porometric data were captured in intervals of 3 s until a new steady state was reached.A comparison of t1/2, the half-time needed to achieve new gs, indicates similar responses of stomata in grasses when compared to herbs. The stomata of C4 plants responded in approximately 5 min, the highest closure rate was detected in Echinochloa crus-galli and Digitaria sanguinalis. Opening rates were similar to closing rates and the response as a whole was rather symmetric. In C3 plants, the full response of stomata was much slower. Analysis revealed differences in absolute rates of gs change between C3 and C4 plants. These differences can be related to the specificities of the type of photosynthetic metabolism. C4 photosynthesis enables plants to reduce gs, which can hasten further changes of diffusivity in response to the environmental signals. A possible coupling of C4 metabolism to the regulation of guard cells also has to be taken into account when explaining the observed results.  相似文献   

10.
《Aquatic Botany》2005,81(2):157-173
The main photosynthesis and respiration parameters (dark respiration rate, light saturated production rate, saturation irradiance, photosynthetic efficiency) were measured on a total of 23 macrophytes of the Thau lagoon (2 Phanerogams, 5 Chlorophyceae, 10 Rhodophyceae and 6 Phaeophyceae). Those measurements were performed in vitro under controlled conditions, close to the natural ones, and at several seasons. Concomitantly, measurements of pigment concentrations, carbon, phosphorous and nitrogen contents in tissues were performed. Seasonal intra-specific variability of photosynthetic parameters was found very high, enlightening an important acclimatation capacity. The highest photosynthetic capacities were found for Chlorophyceae (e.g. Monostroma obscurum thalli at 17 °C, 982 μmol O2 g−1 dw h−1 and 9.1 μmol O2 g−1 dw h−1/μmol photons m−2 s−1, respectively for light saturated net production rate and photosynthetic efficiency) and Phanerogams (e.g. Nanozostera noltii leaves at 25 °C, 583 μmol O2 g−1 dw h−1 and 2.6 μmol O2 g−1 dw h−1/μmol photons m−2 s−1 respectively for light saturated net production rate and photosynthetic efficiency). As expected, species with a high surface/volume ratio were found to be more productive than coarsely branched thalli and thick blades shaped species. Contrary to Rd (ranging 6.7–794 μmol O2 g−1 dw h−1, respectively for Rytiphlaea tinctoria at 7 °C and for Dasya sessilis at 25 °C) for which a positive relationship with water temperature was found whatever the species studied, the evolution of P/I curves with temperature exhibited different responses amongst the species. The results allowed to show summer nitrogen limitation for some species (Gracilaria bursa-pastoris and Ulva spp.) and to propose temperature preferences based on the photosynthetic parameters for some others (N. noltii, Zostera marina, Chaetomorpha linum).  相似文献   

11.
The introduced shrub Tamarix ramosissima invades riparian zones, but loses competitiveness under flooding. Metabolic effects of flooding could be important for T. ramosissima, but have not been previously investigated. Photosynthesis rates, stomatal conductance, internal (intercellular) CO2, transpiration, and root alcohol dehydrogenase (ADH) activity were compared in T. ramosissima across soil types and under drained and flooded conditions in a greenhouse. Photosynthesis at 1500 μmol quanta m−2 s−1 (A1500) in flooded plants ranged from 2.3 to 6.2 μmol CO2 m−2 s−1 during the first week, but A1500 increased to 6.4–12.7 μmol CO2 m−2 s−1 by the third week of flooding. Stomatal conductance (gs) at 1500 μmol quanta m−2 s−1 also decreased initially during flooding, where gs was 0.018 to 0.099 mol H2O m−2 s−1 during the first week, but gs increased to 0.113–0.248 mol H2O m−2 s−1 by the third week of flooding. However, photosynthesis in flooded plants was reduced by non-stomatal limitations, and subsequent increases indicate metabolic acclimation to flooding. Root ADH activities were higher in flooded plants compared to drained plants, indicating oxygen stress. Lower photosynthesis and greater oxygen stress could account for the susceptibility of T. ramosissima at the onset of flooding. Soil type had no effect on photosynthesis or on root ADH activity. In the field, stomatal conductance, leaf water potential, transpiration, and leaf δ13C were compared between T. ramosissima and other flooded species. T. ramosissima had lower stomatal conductance and water potential compared to Populus deltoides and Phragmites australis. Differences in physiological responses for T. ramosissima could become important for ecological concerns.  相似文献   

12.
Anthropogenic impact on CO2 levels was studied in the Bear Chamber of the Výpustek Cave, a show cave in the Moravian Karst (Czech Republic), during a period of active ventilation and enhanced attendance. The study showed that the natural CO2 levels were controlled by (i) the natural CO2 influxes from soils/epikarst (up to ∼5.64 × 10−2 mol s−1); and, (ii) the advective CO2 fluxes out of cave atmosphere (up to 4.66 × 10−2 mol s−1). During visitor presence, the anthropogenic CO2 flux into the chamber reached up to ∼0.13 mol s−1 and exceeded all other CO2 fluxes. The reachable anthropogenic steady states at sufficient duration of stay (up to 2.65 × 10−1 mol m−3) could exceed the natural CO2 levels by factor of more than nine based on the number of visitors. Recession analysis of anthropogenic pulses showed that intervals between individual visitor groups would have to be up to ∼6 h long if the cave environment has to return to natural conditions. As such pauses between individual tours are hardly realizable, a risk analysis was conducted to find the consequences of breaking natural conditions. It showed that the condition under which dripwater becomes aggressive to calcite (i.e., the point when PCO2 in cave atmosphere exceeds the hypothetical CO2 concentrations in epikarst that has participated on the water formation, PCO2(H) = 10−1.56) is potentially reachable under extreme conditions only (enormous visitor stay period and visitor number). In case of condensed water, however, any increase in CO2 concentration will cause an increase of water aggressiveness to calcite. Therefore, in the periods and sites of enhanced condensation, it is important to strive for preservation of natural conditions.  相似文献   

13.
We assessed the effect of growth at either 400 μmol mol?1 (ambient) or 1000 μmol mol?1 (elevated) CO2 and 0 g L?1 (deprivation) or 30 g L?1 (supplementation) sugar on morphological traits, photosynthetic attributes and intrinsic elements of the CAM pathway using the CAM orchid Phalaenopsis ‘Amaglade’. The growth of shoot (retarded) and root (induced) was differently affected by CO2 enrichment and mixotrophic regime (+sugar). The Fv/Fm ratio was 14% more in CO2-enriched treatment than at ambient level during in vitro growth. At elevated level of CO2 and sugar treatment, the content of Chl(a + b), Chl a/b and Chl/Car was enhanced while carotenoid content remained unaltered. During in vitro growth, gas-exchange analysis indicated that increased uptake of CO2 accorded with the increased rate of transpiration and unchanged stomatal conductance at elevated level of CO2 under both photo- and mixotrophic growth condition. At elevated level of CO2 and sugar deprivation, activities of Rubisco (26.4%) and PEPC (74.5%) was up-regulated. Among metabolites, the content of sucrose and starch was always higher under CO2 enrichment during both in vitro and ex vitro growth. Our results indicate that plantlets grown under CO2 enrichment developed completely viable photosynthetic apparatus ready to be efficiently transferred to ex vitro condition that has far-reaching implications in micropropagation of Phalaenopsis.  相似文献   

14.
15.
In a previous study, we found that enhanced CO2 subjected to nodulated alfalfa plants grown at different temperatures (ambient and ambient + 4 °C) and water availability regimes could protect PSII from photodamage. The main objective of this study was to determine the mechanism(s) involved in the photoprotection of PSII at elevated CO2 levels in this plant. Elevated CO2 reduced carboxylation capacity-induced photosynthetic acclimation and reduced enzymatic and/or nonenzymatic antioxidant activities, suggesting that changes in electron flow did not cause any photooxidative damage (which was also confirmed by H2O2 and lipid peroxidation analyses). Enhanced nonphotochemical quenching and xanthophyll cycle pigments revealed that plants grown at 700 μmol mol?1 CO2 compensated for the reduction in energy sink with a larger capacity for nonphotochemical dissipation of excitation energy as heat, i.e., modulating the status of the VAZ components. Elevated CO2 induced the de-epoxidation of violaxanthin to zeaxanthin, facilitating thermal dissipation and protecting the photosynthetic apparatus against the deleterious effect of excess excitation energy.  相似文献   

16.
In response to an osmotic stress, Dunaliella tertiolecta osmoregulates by metabolizing intracellular glycerol as compatible solute. Upon the application of a salt stress to 0.17 M or 0.7 M NaCl grown D. tertiolecta cells, rates of total glycerol synthesis were substantially higher than that arising from photosynthetic 14CO2 fixation into glycerol. The source of this extra carbon is the reserve starch pool. The contribution of carbon from the starch breakdown to glycerol synthesis was estimated from the difference between the total glycerol synthesized and that arising from 14CO2 fixation. The maximum observed flux of carbon from 14CO2 to glycerol from photosynthesis was of the order of 15–20 μmol 14C-glycerol mg−1 Chl h−1, whereas the total glycerol synthesis reached about 70 μmol glycerol mg−1 Chl h−1. The contribution of products of starch breakdown to glycerol synthesis increased progressively with increasing salt stress. In light, contrary to prevailing assumptions, both the photosynthesis and the starch breakdown contribute carbon to glycerol biosynthesis. The relative contributions of these two processes in the light, while cells were actively photosynthesizing, depended on the magnitude of the salt stress. On application of dilution stress, the flux of carbon from newly photosynthetically fixed 14CO2 into glycerol was reduced progressively with increasing dilution stress that was also accompanied by a decline in total glycerol contents of the cell. The maximum observed rate of glycerol dissimilation was about 135 μmol glycerol mg−1 Chl h−1.  相似文献   

17.
《Aquatic Botany》2005,83(1):71-81
The aquatic plant Elodea nuttallii (Planch.) St. John has been shown to express plasticity in the source of inorganic carbon it uses for photosynthesis. An investigation was undertaken to determine what effect the switch from CO2 to HCO3 use had on the growth of E. nuttallii. Plants were grown under reduced CO2 availability that favoured the switch, together with control plants (CO2 at equilibrium with air) that continued to use CO2 only. The extent to which both sets of plants could utilise HCO3 was determined (as the ratio of oxygen evolution at pH 9 and 6.5), and several measures of growth were made. Although reduced CO2 availability produced an increase in HCO3 utilisation, no differences were found in the measured growth of the plants. Therefore, it was possible to estimate, from the difference between the estimated rate of photosynthesis of the plants utilising HCO3 and those using CO2 only, the approximate cost of constructing, maintaining and running the bicarbonate utilisation mechanism in this species as 69 μmol photons m−2 s−1. This value can be used to estimate an irradiance of circa 80 μmol m−2 s−1 below which HCO3 use would not be expected in this species, an irradiance commonly experienced by submerged macrophytes in the field.  相似文献   

18.
Global atmospheric carbon dioxide concentrations (Ca) are rising. As a consequence, recent climate models have projected that global surface air temperature may increase 1.4–5.8 °C with the doubling of Ca by the end of the century. Because, changes in Ca and temperature are likely to occur concomitantly, it is important to evaluate how the temperature dependence of key physiological processes are affected by rising Ca in major crop plants including maize (Zea mays L.), a globally important grain crop with C4 photosynthetic pathway. We investigated the temperature responses of photosynthesis, growth, and development of maize plants grown at five temperature regimes ranging from 19/13 to 38.5/32.5 °C under current (370 μmol mol−1) and doubled (750 μmol mol−1) Ca throughout the vegetative stages using sunlit controlled environmental chambers in order to test if the temperature dependence of these processes was altered by elevated Ca. Leaf and canopy photosynthetic rates, C4 enzyme activities, leaf appearance rates, above ground biomass accumulation and leaf area were measured. We then applied temperature response functions (e.g., Arrhenius and Beta distribution models) to fit the measured data in order to provide parameter estimates of the temperature dependence for modeling photosynthesis and development at current and elevated Ca in maize. Biomass, leaf area, leaf appearance rate, and photosynthesis measured at growth Ca was not changed in response to CO2 enrichment. Carboxylation efficiency and the activities of C4 enzymes were reduced with CO2 enrichment indicating possible photosynthetic acclimation of the C4 cycle. All measured parameters responded to growth temperatures. Leaf appearance rate and leaf photosynthesis showed curvilinear response with optimal temperatures near 32 and 34 °C, respectively. Total above ground biomass and leaf area were negatively correlated with growth temperature. The dependence of leaf appearance rate, biomass, leaf area, leaf and canopy photosynthesis, and C4 enzyme activities on growth temperatures was comparable between current and elevated Ca. The results of this study suggest that the temperature effects on growth, development, and photosynthesis may remain unchanged in elevated Ca compared with current Ca in maize.  相似文献   

19.
The responses of soil-atmosphere carbon (C) exchange fluxes to growing atmospheric nitrogen (N) deposition are controversial, leading to large uncertainty in the estimated C sink of global forest ecosystems experiencing substantial N inputs. However, it is challenging to quantify critical load of N input for the alteration of the soil C fluxes, and what factors controlled the changes in soil CO2 and CH4 fluxes under N enrichment. Nine levels of urea addition experiment (0, 10, 20, 40, 60, 80, 100, 120, 140 kg N ha−1 yr−1) were conducted in the needle-broadleaved mixed forest in Changbai Mountain, Northeast China. Soil CO2 and CH4 fluxes were monitored weekly using the static chamber and gas chromatograph technique. Environmental variables (soil temperature and moisture in the 0–10 cm depth) and dissolved N (NH4+-N, NO3-N, total dissolved N (TDN), and dissolved organic N (DON)) in the organic layer and the 0–10 cm mineral soil layer were simultaneously measured. High rates of N addition (≥60 kg N ha−1 yr−1) significantly increased soil NO3-N contents in the organic layer and the mineral layer by 120%-180% and 56.4%-84.6%, respectively. However, N application did not lead to a significant accumulation of soil NH4+-N contents in the two soil layers except for a few treatments. N addition at a low rate of 10 kg N ha−1 yr−1 significantly stimulated, whereas high rate of N addition (140 kg N ha−1 yr−1) significantly inhibited soil CO2 emission and CH4 uptake. Significant negative relationships were observed between changes in soil CO2 emission and CH4 uptake and changes in soil NO3-N and moisture contents under N enrichment. These results suggest that soil nitrification and NO3-N accumulation could be important regulators of soil CO2 emission and CH4 uptake in the temperate needle-broadleaved mixed forest. The nonlinear responses to exogenous N inputs and the critical level of N in terms of soil C fluxes should be considered in the ecological process models and ecosystem management.  相似文献   

20.
The effects of two anion/Cl? channel inhibitors, Zn2+ and niflumic acid (NA), on seedling photosynthetic and fluorescent parameters of two Glycine soja populations (salt-tolerant BB52; salt-sensitive N23227) and Glycine max cultivar (salt-tolerant Lee68) were studied and compared under salt stress. Treatments with Zn2+ and NA only (10, 20 μmol L?1) were also imposed for comparisons. Results showed that, there were non-toxic and non-nutritional effects of Zn2+ and NA treatments alone on seed germination and seedling growth of soybeans. Under 150 mmol L?1 NaCl for 6 d, leaf chlorophyll and carotenoid contents, net photosynthetic rate (Pn), stomatal conductance (Gs), intercellular CO2 concentration (Ci), transpiration rate (Tr), and the maximum photochemical efficiency of photosystem II (PS II) (Fv/Fm) except the stomatal limitation (Ls) significantly decreased in three kinds of soybean seedlings when compared with their control plants. The NaCl stress plus additional 20 μmol L?1 Zn showed an obvious enhancement of leaf chlorophyll and carotenoid contents, Pn, Gs, Ci and Tr, especially for the G. max cultivar Lee68, but the supplementation of 20 μmol L?1 NA showed the reverse effects.  相似文献   

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