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1.
Net photosynthetic rate (P N) measured at the same CO2 concentration, the maximum in vivo carboxylation rate, and contents of ribulose-1,5-bisphosphate (RuBP) carboxylase/oxygenase (RuBPCO) and RuBPCO activase were significantly decreased, but the maximum in vivo electron transport rate and RuBP content had no significant change in CO2-enriched [EC, about 200 μmol mol−1 above the ambient CO2 concentration (AC)] wheat leaves compared with those in AC grown wheat leaves. Hence photosynthetic acclimation in wheat leaves to EC is largely due to RuBP carboxylation limitation.  相似文献   

2.
In comparison with its wild type (WT), the transgenic (TG) rice with silenced OsBP-73 gene had significantly lower plant height, grain number per panicle, and leaf net photosynthetic rate (P N). Also, the TG rice showed significantly lower chlorophyll (Chl), ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBPCO), RuBPCO activase, and RuBP contents, photosystem 2 (PS2) photochemical efficiency (Fv/Fm and ΔF/Fm′), apparent quantum yield of carbon assimilation (Φc), carboxylation efficiency (CE), photosynthetic electron transport and photophosphorylation rates as well as sucrose phosphate synthase activity, but higher intercellular CO2 concentration, sucrose, fructose, and glycerate 3-phosphate contents, and non-photochemical quenching of Chl fluorescence (NPQ). Thus the decreased P N in the TG rice leaves is related to both RuBP carboxylation and RuBP regeneration limitations, and the latter is a predominant limitation to photosynthesis.  相似文献   

3.
C3 photosynthesis at high light is often modeled by assuming limitation by the maximum capacity of Rubisco carboxylation (VCmax) at low CO2 concentrations, by electron transport capacity (Jmax) at higher CO2 concentrations, and sometimes by triose-phosphate utilization rate at the highest CO2 concentrations. Net photosynthetic rate (PN) at lower light is often modeled simply by assuming that it becomes limited by electron transport (J). However, it is known that Rubisco can become deactivated at less than saturating light, and it is possible that PN at low light could be limited by the rate of Rubisco carboxylation (VC) rather than J. This could have important consequences for responses of PN to CO2 and temperature at low light. In this work, PN responses to CO2 concentration of common bean, quinoa, and soybean leaves measured over a wide range of temperatures and PPFDs were compared with rates modeled assuming either VC or J limitation at limiting light. In all cases, observed rates of PN were better predicted by assuming limitation by VC rather than J at limiting light both below and above the current ambient CO2. One manifestation of this plant response was that the relative stimulation of PN with increasing the ambient CO2 concentration from 380 to 570 µmol mol–1 did not decrease at less than saturating PPFDs. The ratio of VC to VCmax at each lower PPFD varied linearly with the ratio of PN at low PPFD to PN at high PPFD measured at 380 µmol(CO2) mol–1 in all cases. This modification of the standard C3 biochemical model was much better at reproducing observed responses of light-limited PN to CO2 concentrations from pre-industrial to projected future atmospheric concentrations.  相似文献   

4.
Bunce  J.A.  Sicher  R.C. 《Photosynthetica》2001,39(1):95-101
Midday measurements of single leaf gas exchange rates of upper canopy leaves of soybeans grown in the field at 350 (AC) and 700 (EC) µmol(CO2) mol–1 in open topped chambers sometimes indicated up to 50 % higher net photosynthetic rates (P N) measured at EC in plants grown at AC compared to EC. On other days mean P N were nearly identical in the two growth [CO2] treatments. There was no seasonal pattern to the variable photosynthetic responses of soybean to growth [CO2]. Even on days with significantly lower P N in the plants grown at EC, there was no reduction in ribulose-1,5-bisphosphate carboxylase/oxygenase, chlorophyll, or soluble protein contents per unit of leaf area. Over three years, gas exchange evidence of acclimation occurred on days when either soil was dry or the water vapor pressure deficit was high (n = 12 d) and did not occur on days after rain or on days with low water vapor pressure deficit (n = 9 d). On days when photosynthetic acclimation was evident, midday leaf water potentials were consistently 0.2 to 0.3 MPa lower for the plants grown at EC than at AC. This suggested that greater susceptibility to water stress in plants grown at EC cause the apparent photosynthetic acclimation. In other experiments, plants were grown in well-watered pots in field chambers and removed to the laboratory early in the morning for gas exchange measurements. In these experiments, the amount of photosynthetic acclimation evident in the gas exchange measurements increased with the maximum water vapor pressure deficit on the day prior to the measurements, indicating a lag in the recovery of photosynthesis from water stress. The apparent increase in susceptibility to water stress in soybean plants grown at EC is opposite to that observed in some other species, where photosynthetic acclimation was evident under wet but not dry conditions, and may be related to the observation that hydraulic conductance is reduced in soybeans when grown at EC. The day-to-day variation in photosynthetic acclimation observed here may account for some of the conflicting results in the literature concerning the existence of acclimation to EC in field-grown plants.  相似文献   

5.
Šprtová  M.  Marek  M.V. 《Photosynthetica》1999,37(3):433-445
Functional differentiation of assimilation activity of sun versus shade foliage was analysed in a Norway spruce monoculture stand (age 15 years). The investigated stand density (leaf area index 8.6) and crown structure led to variation in the photosynthetically active photon flux density (PPFD) within the crowns of the sampled trees. At the saturating PPFD, the maximum rate of CO2 uptake (P Nmax) of exposed shoots (E-shoots) was 1.7 times that of the shaded shoots (S-shoots). The apparent quantum yield (α) of E-shoots was 0.9 times that of the S-shoots. A lower ability to use excess energy at high PPFD in photosynthesis was observed in the S-layer. The CO2- and PPFD-saturated rate of CO2 uptake (P Nsat) of the E-shoots was 1.12 times and the carboxylation efficiency (τ) 1.6 times that of the S-shoots. The CO2-saturated rate of ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBPCO) carboxylation (VCmax) and of actual electron transport (Jamax) in the S-needles amounted to 89 and 95 % of VCmax and Jamax in the E-needles. Thus, in addition to the irradiation conditions and thus limitation by low Ja, the important limitation of photosynthesis in shade needles is due to carboxylation. This limitation of photosynthesis is accompanied by lower stomatal conductance. This revised version was published online in June 2006 with corrections to the Cover Date.  相似文献   

6.
Tognetti  R.  Sebastiani  L.  Vitagliano  C.  Raschi  A.  Minnocci  A. 《Photosynthetica》2001,39(3):403-410
Five-year-old plants of two olive cultivars (Frantoio and Moraiolo) grown in large pots were exposed for 7 to 8 months to ambient (AC) or elevated (EC) CO2 concentration in a free-air CO2 enrichment (FACE) facility. Exposure to EC enhanced net photosynthetic rate (P N) and decreased stomatal conductance, leading to greater instantaneous transpiration efficiency. Stomata density also decreased under EC, while the ratio of intercellular (C i) to atmospheric CO2 concentration and chlorophyll content did not differ, except for the cv. Moraiolo after seven months of exposure to EC. Analysis of the relationship between photosynthesis and C i indicated no significant change in carboxylation efficiency of ribulose-1,5-bisphosphate carboxylase/oxygenase after five months of exposure to EC. Based on estimates derived from the P N-C i relationship, there were no apparent treatment differences in daytime respiration, CO2 compensation concentration, CO2-saturated photosynthetic rate, or photosynthetic rate at the mean C i, but there was a reduction in stomata limitation to P N at EC. Thus 5-year-old olive trees did not exhibit down regulation of leaf-level photosynthesis in their response to EC, though some indication of adjustment was evident for the cv. Frantoio with respect to the cv. Moraiolo.  相似文献   

7.
In this study, we tested for the temporal occurrence of photosynthetic acclimation to elevated [CO2] in the flag leaf of two important cereal crops, rice and wheat. In order to characterize the temporal onset of acclimation and the basis for any observed decline in photosynthetic rate, we characterized net photosynthesis, gs, gm, Ci/Ca, Ci/Cc, Vcmax, Jmax, cell wall thickness, content of Rubisco, cytochrome (Cyt) f, N, chlorophyll and carbohydrate, mRNA expression for rbcL and petA, activity for Rubisco, sucrose phosphate synthase (SPS) and sucrose synthase (SS) at full flag expansion, mid‐anthesis and the late grain‐filling stage. No acclimation was observed for either crop at full flag leaf expansion. However, at the mid‐anthesis stage, photosynthetic acclimation in rice was associated with RuBP carboxylation and regeneration limitations, while wheat only had the carboxylation limitation. By grain maturation, the decline of Rubisco content and activity had contributed to RuBP carboxylation limitation of photosynthesis in both crops at elevated [CO2]; however, the sharp decrease of Rubisco enzyme activity played a more important role in wheat. Although an increase in non‐structural carbohydrates did occur during these later stages, it was not consistently associated with changes in SPS and SS or photosynthetic acclimation. Rather, over time elevated [CO2] appeared to enhance the rate of N degradation and senescence so that by late‐grain fill, photosynthetic acclimation to elevated [CO2] in the flag leaf of either species was complete. These data suggest that the basis for photosynthetic acclimation with elevated [CO2] may be more closely associated with enhanced rates of senescence, and, as a consequence, may be temporally dynamic, with significant species variation.  相似文献   

8.
The limiting step of photosynthesis changes depending on CO2 concentration and, in theory, photosynthetic nitrogen use efficiency at a respective CO2 concentration is maximized if nitrogen is redistributed from non‐limiting to limiting processes. It has been shown that some plants increase the capacity of ribulose‐1,5‐bisphoshate (RuBP) regeneration (evaluated as Jmax) relative to the RuBP carboxylation capacity (evaluated as Vcmax) at elevated CO2, which is in accord with the theory. However, there is no study that tests whether this change is accompanied by redistribution of nitrogen in the photosynthetic apparatus. We raised a perennial plant, Polygonum sachalinense, at two nutrient availabilities under two CO2 concentrations. The Jmax to Vcmax ratio significantly changed with CO2 increment but the nitrogen allocation among the photosynthetic apparatus did not respond to growth CO2. Enzymes involved in RuBP regeneration might be more activated at elevated CO2, leading to the higher Jmax to Vcmax ratio. Our result suggests that nitrogen partitioning is not responsive to elevated CO2 even in species that alters the balance between RuBP regeneration and carboxylation. Nitrogen partitioning seems to be conservative against changes in growth CO2 concentration.  相似文献   

9.
Diurnal changes of photosynthesis in the leaves of grapevine (Vitis vinifera × V. labrusca) cultivars Campbell Early and Kyoho grown in the field were compared with respect to gas exchanges and actual quantum yield of photosystem 2 (ΦPS2) in late May. Net photosynthetic rate (PN) of the two cultivars rapidly increased in the morning, saturated at photosynthetic photon flux density (PPFD) from 1200 to 1500 μmol m−2 s−1 between 10:00 and 12:00 and slowly decreased after midday. Maximum PN was 13.7 and 12.5 μmol m−2 s−1 in Campbell Early and Kyoho, respectively. The stomatal conductance (gs) and transpiration rate changed in parallel with PN, indicating that PN was greatly affected by gs. However, the decrease in PN after midday under saturating PPFD was also associated with the observed depression of ΦPS2 at high PPFD. The substantial increase in the leaf to air vapour pressure deficit after midday might also contribute to decline of gs and PN.  相似文献   

10.
J. R. Evans 《Planta》1986,167(3):351-358
Photosynthesis in two cultivars of Triticum aestivum was compared with photosynthesis in two lines having the same nuclear genomes but with cytoplasms derived from T. boeoticum. The in-vitro specific activity of ribulose-1,5-bisphosphate carboxylase (RuBPCase; EC 4.1.1.39) isolated from lines with T. boeoticum cytoplasm was only 71% of that of normal T. aestivum. By contrast, the RuBPCase activities calculated from the CO2-assimilation rate at low partial pressures of CO2, p(CO2), were the same for all lines for a given RuBPCase content. This indicates that both types of RuBPCase have the same turnover numbers in-vivo of 27.5 mol CO2·(mol enzyme)–1·s–1 (23°). The rate of CO2 assimilation measured at normal p(CO2), p a =340 bar, and high irradiance could be quantitatively predicted from the amount of RuBPCase protein. The maximum rate of RuBP regeneration could also predict the rate of CO2 assimilation at normal ambient conditions. Therefore, the maximum capacities for RuBP carboxylation and RuBP regeneration appear to be well-balanced for normal ambient conditions. As photosynthetic capacity declined with increasing leaf age, the capacities for RuBP carboxylation and RuBP regeneration declined in parallel.Abbreviations PAR photosynthetically active radiation - RuBP(Case) ribulose-1,5-bisphosphate (carboxylase)  相似文献   

11.
A biochemical model of C 3photosynthesis has been developed by G.D. Farquhar et al. (1980, Planta 149, 78–90) based on Michaelis-Menten kinetics of ribulose-1,5-bisphosphate (RuBP) carboxylase-oxygenase, with a potential RuBP limitation imposed via the Calvin cycle and rates of electron transport. The model presented here is slightly modified so that parameters may be estimated from whole-leaf gas-exchange measurements. Carbon-dioxide response curves of net photosynthesis obtained using soybean plants (Glycine max (L.) Merr.) at four partial pressures of oxygen and five leaf temperatures are presented, and a method for estimating the kinetic parameters of RuBP carboxylase-oxygenase, as manifested in vivo, is discussed. The kinetic parameters so obtained compare well with kinetic parameters obtained in vitro, and the model fits to the measured data give r 2values ranging from 0.87 to 0.98. In addition, equations developed by J.D. Tenhunen et al. (1976, Oecologia 26, 89–100, 101–109) to describe the light and temperature responses of measured CO2-saturated photosynthetic rates are applied to data collected on soybean. Combining these equations with those describing the kinetics of RuBP carboxylase-oxygenase allows one to model successfully the interactive effects of incident irradiance, leaf temperature, CO2 and O2 on whole-leaf photosynthesis. This analytical model may become a useful tool for plant ecologists interested in comparing photosynthetic responses of different C3 plants or of a single species grown in contrasting environments.Abbreviations PCO photorespiratory carbon oxidation - PCR photosynthetic carbon reduction - PPFD photosynthetic photon-flux density - RuBP ribulose bisphosphate  相似文献   

12.
Tea tree (Melaleuca alternifolia) canopy was sprayed with low concentration of NaHSO3 or mixture of NaHSO3+ KH2PO4. The treatments significantly enhanced net photosynthetic rate (P N), carboxylation efficiency (CE), and the maximum response of P N to intercellular CO2 concentration. The enhancement of P N by foliar application of low concentrations of bisulfite was due to increasing CE relevant to ribulose-1,5-bisphosphate (RuBP) carboxylase/oxygenase activity and regeneration rate of RuBP depending on ATP formation.  相似文献   

13.
Net photosynthetic rate (P N) of leaves grown under free-air CO2 enriched condition (FACE, about 200 μmol mol−1 above ambient air) was significantly lower than P N of leaves grown at ambient CO2 concentration (AC) when measured at CO2 concentration of 580 μmol mol−1. This difference was found in rice plants grown at normal nitrogen supply (25 g m−2; NN-plants) but not in plants grown at low nitrogen supply (15 g m−2; LN-plants). Namely, photosynthetic acclimation to FACE was observed in NN-plants but not in LN-plants. Different from the above results measured in a period of continuous sunny days, such photosynthetic acclimation occurred in NN-plants, however, it was also observed in LN-plants when P N was measured before noon of the first sunny day after rain. Hence strong competition for the assimilatory power between nitrogen (N) and carbon (C) assimilations induced by an excessive N supply may lead to the photosynthetic acclimation to FACE in NN-plants. The hypothesis is supported by the following facts: FACE induced significant decrease in both apparent photosynthetic quantum yield (Φc) and ribulose-1,5-bisphosphate (RuBP) content in NN-plants but not in LN-plants.  相似文献   

14.
The mechanisms responsible for photosynthetic acclimation are not well understood, effectively limiting predictability under future conditions. Least‐cost optimality theory can be used to predict the acclimation of photosynthetic capacity based on the assumption that plants maximize carbon uptake while minimizing the associated costs. Here, we use this theory as a null model in combination with multiple datasets of C3 plant photosynthetic traits to elucidate the mechanisms underlying photosynthetic acclimation to elevated temperature and carbon dioxide (CO2). The model‐data comparison showed that leaves decrease the ratio of the maximum rate of electron transport to the maximum rate of Rubisco carboxylation (Jmax/Vcmax) under higher temperatures. The comparison also indicated that resources used for Rubisco and electron transport are reduced under both elevated temperature and CO2. Finally, our analysis suggested that plants underinvest in electron transport relative to carboxylation under elevated CO2, limiting potential leaf‐level photosynthesis under future CO2 concentrations. Altogether, our results show that acclimation to temperature and CO2 is primarily related to resource conservation at the leaf level. Under future, warmer, high CO2 conditions, plants are therefore likely to use less nutrients for leaf‐level photosynthesis, which may impact whole‐plant to ecosystem functioning.  相似文献   

15.
Our previous study has demonstrated that both RuBP carboxylation limitation and RuBP regeneration limitation exist simultaneously in rice grown under free-air CO2 enrichment (FACE, about 200 μmol mol−1 above the ambient air CO2 concentration) conditions [G.-Y. Chen, Z.-H. Yong, Y. Liao, D.-Y. Zhang, Y. Chen, H.-B. Zhang, J. Chen, J.-G. Zhu, D.-Q. Xu, Photosynthetic acclimation in rice leaves to free-air CO2 enrichment related to both ribulose-1,5-bisphosphate carboxylase limitation and ribulose-1,5-bisphosphate regeneration limitation. Plant Cell Physiol. 46 (2005) 1036–1045]. To explore the mechanism for forming of RuBP regeneration limitation, we conducted the gas exchange measurements and some biochemical analyses in FACE-treated and ambient rice plants. Net CO2 assimilation rate (Anet) in FACE leaves was remarkably lower than that in ambient leaves when measured at the same CO2 concentration, indicating that photosynthetic acclimation to elevated CO2 occurred. In the meantime the maximum electron transport rate (ETR) (Jmax), maximum carboxylation rate (Vcmax) in vivo, and RuBP contents decreased significantly in FACE leaves. The whole chain electron transport rate and photophosphorylation rate reduced significantly while ETR of photosystem II (PSII) did not significantly decrease and ETR of photosystem I (PSI) was significantly increased in the chloroplasts from FACE leaves. Further, the amount of cytochrome (Cyt) f protein, a key component localized between PSII and PSI, was remarkably declined in FACE leaves. It appears that during photosynthetic acclimation the decline in the Cyt f amount is an important cause for the decreased RuBP regeneration capacity by decreasing the whole chain electron transport in FACE leaves.  相似文献   

16.
Nataraja  K.N.  Jacob  J. 《Photosynthetica》1999,36(1-2):89-98
The objective of the present investigation was to examine the extent of variations in single leaf net photosynthetic rate (PN) and its relative dependence on stomatal conductance (gs) and the mesophyll capacity to fix carbon in 12 clones of the natural rubber plant. There were significant variations in PN measured at low and saturating photon flux density (PFD); the extent of variation was larger at low than at saturating PFD. The compensation irradiance (CI) and apparent quantum yield of CO2 assimilation (φc) calculated from the PN/PFD response curves showed significant variations among the clones. PN at low irradiance was positively correlated with φc. Thus a clone with large PN at low irradiance, high φc, and low CI may tolerate shade better and thus produce a high tree stand per hectare. A strong positive correlation existed between PN saturated with radiant energy (Psat) and carboxylation efficiency (CE) estimated from the response curves of PN on intercellular CO2 concentration (Ci), but gs showed a poor correlation with Psat High CO2 compensation concentration (Γ) led to low CE in Hevea clones. A clone with large Psat, high CE, low gs, and low Γ is the one in which photosynthesis is more dependent on the mesophyll factors than stomata. Such a clone may produce relatively high biomass and maintain high water use efficiency. This revised version was published online in September 2006 with corrections to the Cover Date.  相似文献   

17.
We compared the responses of sun and shade acclimated saplings of Picea abies and Pinus cembra to excess photosynthetic photon flux density (PPFD) equivalently exceeding the level for saturating net photosynthetic rate (P N). Exposure for 2 h up to 2000 μmol(photon) m−2 s−1 did not affect radiant energy saturated P N. Photoinhibition of photosynthesis was indicated by a small (10 %) reduction of the potential efficiency of photosystem 2 as derived from measurements of chlorophyll fluorescence (FV/FM). However, the extent of FV/FM reduction and half-time for recovery were similar in sun and shade acclimated saplings of both species. Furthermore, the effect on FV/FM was not stronger when the plants were exposed to excess PPFD at 5 °C instead of 15 °C. Frost-hardening of plants increased slightly their resistance to excess PPFD. Establishment of these conifer saplings usually acclimated to shade in their natural habitat may hardly be endangered by a sudden increase of PPFD, e.g., by gap formation. This revised version was published online in August 2006 with corrections to the Cover Date.  相似文献   

18.
Background and Aims Plants growing under elevated atmospheric CO2 concentrations often have reduced stomatal conductance and subsequently increased leaf temperature. This study therefore tested the hypothesis that under long-term elevated CO2 the temperature optima of photosynthetic processes will shift towards higher temperatures and the thermostability of the photosynthetic apparatus will increase.Methods The hypothesis was tested for saplings of broadleaved Fagus sylvatica and coniferous Picea abies exposed for 4–5 years to either ambient (AC; 385 µmol mol−1) or elevated (EC; 700 µmol mol−1) CO2 concentrations. Temperature response curves of photosynthetic processes were determined by gas-exchange and chlorophyll fluorescence techniques.Key Results Initial assumptions of reduced light-saturated stomatal conductance and increased leaf temperatures for EC plants were confirmed. Temperature response curves revealed stimulation of light-saturated rates of CO2 assimilation (Amax) and a decline in photorespiration (RL) as a result of EC within a wide temperature range. However, these effects were negligible or reduced at low and high temperatures. Higher temperature optima (Topt) of Amax, Rubisco carboxylation rates (VCmax) and RL were found for EC saplings compared with AC saplings. However, the shifts in Topt of Amax were instantaneous, and disappeared when measured at identical CO2 concentrations. Higher values of Topt at elevated CO2 were attributed particularly to reduced photorespiration and prevailing limitation of photosynthesis by ribulose-1,5-bisphosphate (RuBP) regeneration. Temperature response curves of fluorescence parameters suggested a negligible effect of EC on enhancement of thermostability of photosystem II photochemistry.Conclusions Elevated CO2 instantaneously increases temperature optima of Amax due to reduced photorespiration and limitation of photosynthesis by RuBP regeneration. However, this increase disappears when plants are exposed to identical CO2 concentrations. In addition, increased heat-stress tolerance of primary photochemistry in plants grown at elevated CO2 is unlikely. The hypothesis that long-term cultivation at elevated CO2 leads to acclimation of photosynthesis to higher temperatures is therefore rejected. Nevertheless, incorporating acclimation mechanisms into models simulating carbon flux between the atmosphere and vegetation is necessary.  相似文献   

19.
Summary The growth and photosynethetic responses to atmospheric CO2 enrichment of 4 species of C4 grasses grown at two levels of irradiance were studied. We sought to determine whether CO2 enrichment would yield proportionally greater growth enhancement in the C4 grasses when they were grown at low irradiance than when grown at high irradiance. The species studied were Echinochloa crusgalli, Digitaria sanguinalis, Eleusine indica, and Setaria faberi. Plants were grown in controlled environment chambers at 350, 675 and 1,000 l 1-1 CO2 and 1,000 or 150 mol m-2 s-1 photosynthetic photon flux density (PPFD). An increase in CO2 concentration and PPFD significantly affected net photosynthesis and total biomass production of all plants. Plants grown at low PPFD had significantly lower rates of photosynthesis, produced less biomass, and had reduced responses to increases in CO2. Plants grown in CO2-enriched atmosphere had lower photosynthetic capacity relative to the low CO2 grown plants when exposed to lower CO2 concentration at the time of measurement, but had greater rate of photosynthesis when exposed to increasing PPFD. The light level under which the plants were growing did not influence the CO2 compensation point for photosynthesis.  相似文献   

20.
The effect of photosynthetic photon flux density (PPFD) on nitrogen utilization was determined in peas (Pisum sativum L. cv. Alaska) inoculated with Rhizobium leguminosarum and treated with nutrient solutions containing no combined nitrogen, 16 mM NO3?, or 16 mM NH4+. Plants were grown under controlled conditions at three PPFD values ranging from severely limiting to nearly saturating. Carboxylation efficiencies and CO2-exchange rates were highest in the N2-fixing plants and lowest in plants supplied with NH4+, and they generally increased with increasing PPFD. Photoefficiencies increased with PPFD but did not differ appreciably with the form of nitrogen applied. Nitrogen fixation, calculated from C2H2-reduction and H2-evolution data, was inhibited more by NH4+ than by NO3?application. Inhibition was counteracted by increasing PPFD. Percentage nitrogen decreased with increasing PPFD in plants treated with combined nitrogen and increased in the plants dependent on N2 fixation. The data reveal that photosynthetic efficiency and the capacity to fix N2 in peas are functions of PPFD and the availability of combined nitrogen and that these two factors are interrelated.  相似文献   

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