Journal of Experimental Botany, Vol. 51, No. 348, pp. 1289-1297,
July 2000
© 2000 Oxford University Press
Original papers |
Evidence that P deficiency induces N feedback regulation of symbiotic N2 fixation in white clover (Trifolium repens L.)
1 Escola Superior Agrária, I.P., 6000 Castelo Branco, Portugal
2 Institute of Plant Sciences, Swiss Federal Institute of Technology, Universitätstrasse 2, 8092 Zurich, Switzerland
Received 30 November 1999; Accepted 24 March 2000
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Abstract |
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Trifolium repens L. was grown to test the following hypotheses: when P is deficient (i) N2 fixation decreases as a result of the plant's adaptation to the low N demand, regulated by an N feedback mechanism, and (ii) the decrease in the photosynthetic capacity of the leaves does not limit N2 fixation. Severe P deficiency prevented nodulation or stopped nodule growth when the P deficiency occurred after the plants had formed nodules. At low P, the proportion of whole-plant-N derived from symbiotic N2 fixation decreased, whereas specific N2 fixation increased and compensated partially for poor nodulation. Leaf photosynthesis was reduced under P deficiency due to low Vc,max and Jmax. Poor growth or poor performance of the nodules was not due to C limitation, because (i) the improved photosynthetic performance at elevated pCO2 had no effect on the growth and functioning of the nodules, (ii) starch accumulated in the leaves, particularly under elevated pCO2, and (iii) the concentration of WSC in the nodules was highest under P deficiency. Under severe P deficiency, the concentrations of whole-plant-N and leaf-N were the highest, indicating that the assimilation of N exceeded the amount of N required by the plant for growth. This was clearly demonstrated by a strong increase in asparagine concentrations in the roots and nodules under low P supply. This indicates that nodulation and the proportion of N derived from symbiotic N2 fixation are down-regulated by an N feedback mechanism.
Key words: Elevated CO2, nodule, photosynthesis, carbohydrate, asparagine.
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Introduction |
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TopAbstractIntroductionMaterials and methodsResultsDiscussionReferences |
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In field experiments on fertile soil, grassland legumes respond much more strongly to elevated atmospheric partial pressure of carbon dioxide (pCO2) than grasses (Hebeisen et al., 1997
; Lüscher et al., 1998). The specific advantage of the response of legumes to pCO2 is the result of symbiotic fixation of di-nitrogen (N2) (Zanetti et al., 1996, 1997; Lüscher et al., 2000), while the response of grasses to elevated pCO2 was limited by N (Fischer et al., 1997; Zanetti et al., 1997; Rogers et al., 1998; Daepp et al., 2000). However, under unfavourable environmental conditions (e.g. low P or K), legumes may lose the distinct advantage of an unlimited source of symbiotic N (Hartwig et al., 1996; Lüscher et al., 1996, 1998). Indeed, when P is very deficient, legumes no longer respond to elevated pCO2 by increasing biomass (Stöcklin et al., 1998; Almeida et al., 1999), and fixation of symbiotic N2 is greatly reduced (Cadisch et al., 1989, 1993). As a result, two crucial questions arise: (1) When P is deficient, do legumes such as white clover (Trifolium repens L.) no longer respond to elevated pCO2 because symbiotic N2 fixation is severely hindered? (2) How is the effect of low P availability on N2 fixation regulated?
It is well known that the rate of N2 fixation in plants deficient in P is reduced. This is usually explained by an effect of low P supply on the growth of the host plant, on the growth and functioning of the nodule, or on the growth of both the plant and the nodule (Robson et al., 1981; Jakobsen, 1985; Israel, 1987, 1993; Sa and Israel, 1991). However, some of these experiments were conducted under field conditions, or the plants were grown in soil in pots. Therefore, the effect ascribed to the addition of mineral P on N2 fixation may actually be due to the interactive effects of P and N in the soil; i.e. P fertilization would stimulate the growth of soil organisms or non-leguminous plants which, in turn, would compete for soil mineral N and thus, indirectly, lead to increased symbiotic N2 fixation in legumes (Hartwig, 1998). Moreover, in all these experiments, N2 fixation was assessed indirectly by estimating the short-term nitrogenase activity (acetylene reducing assays), which is a non-integral method.
Early studies suggested that low P reduces shoot growth and, as a consequence, that the lower rate of photosynthesis limits the supply of C to the nodules (Jakobsen, 1985), thereby decreasing N2 reduction (Israel, 1987, 1993; Sa and Israel, 1991, 1998). The N2 reduction process requires about 2.9 mg C mg-1 fixed N; this demand can account for up to 32% of the current photosynthetic rate (Minchin and Pate, 1973; Warembourg and Roumet, 1989). Studies on the effect of P deficiency report that the supply of photosynthates from the shoots to the nodules does play a key role in N2 fixation. However, the effects of P supply on important parameters such as photosynthesis, non-structural carbohydrate, N2 fixation, and the N status of the plant were not considered together in any of those studies. Reports on the effect of other stress factors, however, suggest that the supply of non-structural carbohydrate to the nodules does not primarily control N2 fixation (Hartwig et al., 1990, 1994; Weisbach et al., 1996; Gordon et al., 1997; Curioni et al., 1999), whereas N demand does control N2 fixation (Heim et al., 1993; Parsons et al., 1993; Hartwig et al., 1994; Neo and Layzell, 1997; Hartwig, 1998).
P deficiency decreases the rate of plant growth and, thus, the plant's N requirement. Therefore, several reports concluded that P-deficient plants, even when fully dependent on N2 fixation, are not limited by N (Robson et al., 1981; Jakobsen, 1985; Israel, 1987). This indicates a balancing mechanism between N source and N sink in the legume. If this were to apply to P deficiency, then (1) the decrease in N2 fixation would be the result of the adaptation to a lower N requirement, as mediated by an N feedback mechanism, and (2) photosynthesis would be decreased by a separate mechanism that balances the reduced C demand due to P-limited plant growth, but would not directly control nodule growth and functioning. Thus, (3) the biomass of P-deficient white clover plants would no longer respond to elevated pCO2, not because N supply limits growth as a result of C-limited N2 fixation, but primarily because P directly limits growth. This chain of hypotheses was tested by growing white clover in a controlled environment. A wide range of P supply levels were combined with two atmospheric CO2 partial pressures (pCO2) to achieve a large variation in the C source and in the requirement of N for growth in order to assess their involvement in controlling N2 fixation. The asparagine concentration in the roots was measured as an indicator of the concentration of free asparagine in the vascular tissue in order to evaluate a possible N feedback regulation of symbiotic N2 fixation (Hartwig, 1998). To avoid interactions between P supply and soil nutrients, quartz sand was used as the substrate together with a nutrient solution with a low concentration of 15N-enriched N.
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Materials and methods |
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In the main experiment with nodulated plants the following key factors were measured: photosynthesis, C and N partitioning, N derived from symbiosis, and plant and nodule growth. In the nodulation experiment, the interactive effect of sub-optimal P concentrations and pCO2 on the establishment of nodules was investigated.
Plant material and growth conditions
The main experiment with nodulated plants has been described in full previously (Almeida et al., 1999). Briefly, uniform plants from cuttings of white clover (Trifolium repens L. cv. Milkanova) were grown in growth rooms (PGV-36, Conviron, Winnipeg, Canada) for 25 d (25 DAP, days after planting) in boxes (40x17.5x12.5 cm depth), filled with quartz sand (0.7–1.2 mm), irrigated with 0.075 mM KH2PO4 and 1.5 mM N in a nutrient solution, at an atmospheric pCO2 of 35 Pa, day/night temperatures of 18/13 °C, relative humidity of 75%, light/dark periods of 16/8 h, and an irradiance of 550µmol m-2 s-1 PAR. At 25 DAP, the nutrient solution was replaced by four solutions with different concentrations of P (0.0027, 0.075, 0.67, and 2 mM KH2PO4) and combined with two atmospheric pCO2 (35 Pa=ambient, 70 Pa=elevated), and the other conditions were maintained for an additional 30 d (55 DAP). In our experience, the P concentration in a standard nutrient solution of about 0.5 mM is optimal under similar growth conditions at ambient pCO2. The plants were inoculated with Rhizobium leguminosarum biovar trifolii (strain RBL 5020, Leiden, NL) at 0, 7 and 14 DAP. From 25 to 55 DAP, the 1.5 mM N in the nutrient solution was labelled with 0.9% U-15N NH4NO3 (Isotec, Mimisburg, OH and Matheson, Secaucus, NJ, USA). The experiment was conducted in a randomized complete block design with four replicates.
Nodulation experiment: white clover cuttings were grown and inoculated under the same conditions as in the main experiment. However, from the beginning (0 DAP), two levels of suboptimal P (0.0027 and 0.075 mM KH2PO4) were combined with two levels of atmospheric pCO2 (35 and 70 Pa) for 44 d. The experiment was conducted in a randomized complete block design with four replicates.
Plant sampling
Plants were harvested at 25 and 55 DAP in the main experiment with nodulated plants and at 0, 22 and 44 DAP in the nodulation experiment; they were separated into root and shoot fractions at each harvest (Almeida et al., 1999). The samples of the first plant harvested from each pot were frozen immediately on dry ice and stored at -20 °C until lyophilization. After lyophilization, nodules were separated from roots and cleaned under a dissection microscope. The samples were then used for analysing non-structural carbohydrates and for determining total P and N content. The samples of the second plant harvested from the same pots were oven-dried at 65 °C for 48 h, weighed, and pooled for analysis of whole plant contents of N, 15N, and P.
Chemical analyses
Water-soluble carbohydrate (WSC), starch, and total P contents were determined as described previously (Almeida et al., 1999). Total N and 15N were determined from 1 mg ground plant material using a continuous-flow mass spectrometer (Europa Scientific, Cambridge, UK). The concentrations of N in leaves, roots, and nodules were calculated on the basis of the dry mass corrected for starch content. Asparagine concentrations in freeze-dried, ground material were determined using a standard enzymatic assay (Boehringer, Mannheim, Germany). The relative contribution of symbiotically fixed N to total plant N (%Nsym) was determined using the 15N-isotope-dilution method (Sangakkara et al., 1996a) from 25 to 55 DAP.
Leaf gas exchange
Rates of photosynthetic CO2 assimilation (A) on the youngest fully unfolded leaf were determined on each plant in the morning at 25 and 55 DAP with an infrared gas analyser (Ciras-1, PP-Systems) equipped with a Parkinson leaf cuvette (type Broad Leaf, PP-Systems) and an incandescent light unit operating at near saturating PAR (870µmol m-2 s-1 PAR). The pCO2 concentration in the leaf cuvette was set to different values (5, 10, 15, 25, 35, 70, 90, 110, and 150 Pa) in order to obtain different internal concentrations (Ci) in the leaf.
The apparent maximum rate of carboxylation with non limiting ribulose-1,5-biphosphate (Vc,max) and the apparent potential rate of electron transport at light saturation (Jmax) were calculated for each leaf from the fit of the A/Ci values to the biochemical model of Farquhar and von Caemmerer (Farquhar and von Caemmerer, 1982) as described by Kirschbaum and Farquhar (Kirschbaum and Farquhar, 1984). Stomatal limitation of photosynthesis (l) was calculated using A recorded at the growing pCO2 regime (Ca) and the photosynthetic rate (A0) estimated from the A/Ci response at Ci=Ca according to l=100x(A0-A)/A0(Long and Drake, 1992).
Statistical data analysis
Statistical analyses were carried out using the ANOVA procedure of the SAS statistical analysis package (SAS Institute, Cary, NC, USA). If needed, data were transformed to correct for non-normal distribution and non-homogeneity of variance. The 95% confidence level was used in all tests.
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Results |
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Nodule mass and plant growth
In the main experiment, low P concentration in the nutrient solution strongly reduced the growth of white clover plants (Fig. 1A
). The effect of elevated pCO2 on total plant mass depended on the P concentration of the nutrient solution; at low P no increase in plant mass occurred, whereas at the highest P concentration plant mass increased by 30%. When plants had developed nodules, by 25 DAP at 0.075 mM P (Fig. 1B), lowering the P concentration to 0.0027 mM stopped further nodule growth for the remaining 30 d of the experiment (no increase in nodule mass between 25 and 55 DAP). At 0.075 mM P, nodule growth continued from 25 to 55 DAP and increased further with increasing P concentration. Atmospheric pCO2 had no effect on nodule mass (Fig. 1B). As a result of the stronger effect of the P concentration of the nutrient solution on nodule mass (Fig. 1B) than on total plant mass (Fig. 1A), the mass ratio (nodule/total plant) strongly increased with increasing P concentration, independent of pCO2 (data not shown).
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In the nodulation experiment, a very low concentration of P in the nutrient solution (0.0027 mM P) from the beginning of growth prevented nodulation at both elevated and ambient pCO2, while nodulation occurred at 0.075 mM P (Table 1
). With 0.075 mM P in the nutrient solution, plant mass increased considerably compared to 0.0027 mM P in the nutrient solution.
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%Nsymand N partitioning
The %Nsym integrated from 25 to 55 DAP increased with increasing P in the nutrient solution, but was not affected by pCO2 (Fig. 1C
). Specific N2 fixation (N from symbiosis/nodule mass) decreased with increasing P concentration but was not affected by pCO2 (Fig. 1D).
Total N per plant at 55 DAP increased with increasing P in the nutrient solution (Fig. 2A). Reducing the P concentration to 0.0027 mM for 30 d impaired N assimilation to a much lesser extent (N content at 25 DAP versus 55 DAP) than it did plant growth (Fig. 1A). As a result, the concentration of N in the whole plant (not shown) and in starch-free leaf dry mass at 55 DAP was highest at 0.0027 mM P and decreased with increasing P concentration (Fig. 2B). At 0.67 mM P, the concentration of leaf N was lower under elevated pCO2 than under ambient pCO2. The concentration of N in the roots was affected neither by P concentration nor by pCO2 (Fig. 2C). The concentration of N in the nodules was lower at a concentration of 0.0027 mM P in the nutrient solution than at the other P concentrations, especially at ambient pCO2 (Fig. 2D).
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Photosynthesis and carbohydrate partitioning
Increasing the concentration of P in the nutrient solution enhanced leaf photosynthesis by increasing Vc,max and Jmax (Table 2). As compared to ambient pCO2, white clover leaves at elevated pCO2 had a lower Vc,max only at 0.67 mM P. At elevated pCO2, the rate of photosynthesis increased (Almeida et al., 1999) due to reduced stomatal limitation of photosynthesis (Table 2). Under ambient pCO2, stomatal limitation of photosynthesis (l) was not significantly affected by the P concentration, but limitation tended to increase at 2 mM P. Under elevated pCO2, however, stomatal limitation of photosynthesis decreased with increasing P concentration.
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Doubling the pCO2 increased the concentration of starch in the leaves at all P concentrations in the nutrient solution (Table 3
). By contrast, the concentrations of starch and WSC in the roots were not affected by pCO2 or by P concentration (Fig. 3A, C). The concentration of starch in the nodules was lower and the concentration of WSC higher at the lowest P concentration than at higher P concentrations (Fig. 3B, D).
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Asparagine concentration in roots and nodules
Compared to an ample P concentration in the nutrient solution, plants grown under severe P deficiency showed a 7-fold increase in the concentration of asparagine in the roots; this response was not affected by atmospheric pCO2 (Table 4). There was a higher asparagine concentration in the nodules than in the roots. Plants at severe P deficiency showed a 2.5-fold increase in the concentration of asparagine in the nodules (determined only at elevated pCO2 due to insufficient sample material, Table 4).
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Discussion |
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Growth of white clover and its response to elevated pco2 was not limited by N assimilation under P deficiency
The total N concentration in the plant (not shown) and in the leaves (Fig. 2B
) and the N/P mass ratio (Fig. 4) were highest under severe P deficiency. This clearly suggests that plant growth and growth response to elevated pCO2 were not limited by N assimilation under P deficiency. The same conclusion for plant growth at ambient pCO2 has been reached by other authors (Robson et al., 1981; Jakobsen, 1985; Israel, 1987). In this experiment, the higher concentration of N in the lowest P treatment was not a developmental effect linked to the smaller plants (Farrar and Williams, 1991). This is evident from the fact that, at the lowest P supply, the concentration of N at 55 DAP was higher than that of the younger and smaller plants harvested at 25 DAP. Under severe P deficiency, N assimilation from the mineral and symbiotic sources obviously exceeded the amount of N required for plant growth during the experimental period in both pCO2 treatments; it was the capacity of the plant to use the total assimilated N that was limited. This is strongly supported by the N/P ratio in the plants (Fig. 4), indicating that the plants in the 0.075 mM P treatment were slightly limited, whereas those in the 0.0027 mM P treatment were severely limited by P nutrition (Dunlop and Hart, 1987). Accordingly, P concentration in the leaves increased strongly with increasing P supply (Almeida et al., 1999). Therefore, the fact that P limited plant growth and the plant's response to elevated pCO2 (Fig. 1A; Almeida et al., 1999) was not due to a limiting effect of low P on the assimilation of N.
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Supply of photoassimilates did not limit growth and functioning of nodules
The decrease in the rates of leaf photosynthesis with decreasing P supply (Almeida et al., 1999) was due to a decrease in the Rubisco activity (decline of Vc,max) and a simultaneous reduction in the regeneration of RubP (decline of Jmax) (Brooks, 1986; Rao, 1997). The lower Vc,max may have been due to a decrease in the activation state of Rubisco rather than to a decrease in the total concentration of Rubisco, since the concentration of N in the leaves increased with decreasing P supply. Indeed, P-deficient tobacco does not show lower levels of protein or lower concentrations of Rubisco (Paul and Stitt, 1993). The mechanisms that reduce Vc,max are unclear, because low P limits growth directly and the expression of photosynthetic genes usually responds to N nutrition (Paul and Stitt, 1993).
The lower Vc,max under elevated pCO2 at medium P supply suggests an adaptive response of the photosynthetic apparatus to elevated pCO2. The balance between the C source and the C sink was probably maintained even when N was allocated for other processes (Stitt, 1991; Long and Drake, 1992), as suggested by the concomitant decrease in the starch-corrected concentration of N in the leaves under elevated pCO2. It is likely that the reduction in Vc,max, observed at the lower P concentration in the nutrient solution or under elevated pCO2, was due to a C sink limitation (Rao, 1997), as suggested by the high starch contents in the leaves and the lower growth rate of the plants. This interpretation is further supported by the fact that photosynthesis in these leaves was stimulated by CO2 only in the morning (Almeida et al., 1999). This increased photosynthetic performance at elevated pCO2, however, had no effect on the growth and functioning of the nodules.
Assuming that the root buffers the supply of water soluble carbohydrate (WSC) to nodules, the higher concentration of WSC in the roots than in the nodules suggests that a large source of WSC is available for the nodules in all treatments. Furthermore, when the concentration of P was low in the nutrient solution, the concentration of WSC in the nodules was highest compared with the other P treatments (Fig. 3D), indicating that P-deficient nodules were the weakest sink for WSC. With increasing P supply, the concentration of WSC in the nodule decreased, indicating a stronger sink which may have resulted in the increase in the concentration of starch to the initial value (Fig. 3, at 25 DAP). Hence, poor growth or performance of the nodules in our experiment did not appear to be due to a limited supply of C.
Low P inhibits nodulation and N2fixation to a greater extent than plant growth
Nodulation of clover roots did not occur when roots were inoculated with rhizobia under severe P deficiency (Table 1). As far as is known, this is the first time that such an absolute response of nodulation to P deficiency has been reported. In nodulated plants subjected to severe P deficiency, the further growth of already established nodules apparently stopped (Fig. 1B). The extent of this effect compared to that reported in other studies might be due to the very low concentration of P that it was found possible to maintain since pure silica sand was used. In experiments with soil, an uncontrolled supply of P from the soil probably affects test results. Similarly, other environmental stresses appear to prevent nodulation: K deficiency (Sangakkara et al., 1996a, b), high temperatures (Purwantari et al., 1995; Sangakkara et al., 1996b), and high salt concentration (Banet et al., 1996).
Under P deficiency, nodulation and nodule growth were inhibited to a greater extent than plant growth; this confirms the results of studies of other plant species (Drevon and Hartwig, 1997). Thus, when the external P supply is low, nodules might not receive sufficient P to sustain growth. However, under severe P deficiency, the concentration of P in the nodule is generally much higher than in the host plant (Jakobsen, 1985; Israel, 1987, 1993; Sa and Israel, 1991; Drevon and Hartwig, 1997), and nodules appear to take up P directly from the nutrient solution (Al-Niemi et al., 1998). This may explain why a relatively high concentration of P is maintained in the nodule. Thus, it is unlikely that the concentration of P in the nodules directly limits nodule growth and functioning. In fact, specific N2 fixation increased strongly under P deficiency (Fig. 1D), indicating that the nodule continued to function even when P supply was very low.
Even though the nodules did not grow under severe P deficiency, approximately 30% of the total N assimilated by these plants was due to symbiotic N2 fixation (Fig. 1C). Specific N2 fixation increased (Fig. 1D), consistent with the increased apparent O2 permeability of the nodule under P deficiency (Ribet and Drevon, 1995a, b; Drevon and Hartwig, 1997). Similar increases in specific N2 fixation under conditions that hindered the development of nodules to a greater extent than plant growth are found in white clover under high mineral N supply (Zanetti et al., 1998) and in faba bean and common bean under K deficiency (Sangakkara et al., 1996a).
Nodulation and N2fixation are regulated by an N feedback mechanism induced by low P
The proportion of N derived from symbiosis (%Nsym) decreased as the N/P mass ratio in the plant increased due to the reduced P concentration in the nutrient solution (Fig. 4), suggesting that the plant's N demand had decreased. Indeed, as the concentration of P in the nutrient solution decreased, the plant mass decreased by a factor of four (Fig. 1A), leading to a very low apparent demand for N by the plant at P deficiency. However, when the requirement for N was low due to cutting (Seresinhe et al., 1994), potassium deficiency (Sangakkara et al., 1996a), high temperature (Sangakkara et al., 1996b), or low pCO2 (Zanetti et al., 1998; Fig. 1C), then a simultaneous reduction in the assimilation of N from symbiosis and mineral sources was observed, i.e. %Nsym remained stable. The decrease in %Nsym under P deficiency (Figs 1C, 4; Cadisch et al., 1993) indicates that, in this case, N from mineral sources was preferred; the mechanistic understanding of the regulation of N uptake from the different sources has yet to be established.
There are two possible explanations for this behaviour. As plants grow faster under sufficient P, the gap between the mineral N uptake from the growth substrate and the plant's N demand increases, resulting in an increase in %Nsym because of a depletion of mineral N in the growth substrate. Since, however, plants were supplied with nutrient solution twice a day, the more plausible explanation is that a poor P supply leads more directly to a specific reduction of symbiotic N2 fixation. In this case, the high plant N concentration (Fig. 2B, C) and the fast senescence of leaves (Almeida et al., 1999) would result in high concentrations of amino acids in the vascular tissues. Such a dramatic increase was observed in the asparagine concentration in roots and nodules (Table 4) at low P supply. Rabe and Lovatt and Rufty et al. also found a strong increase in the concentration of amino acids in P-deficient plants (Rabe and Lovatt, 1986; Rufty et al., 1993). Fixation of N2 is believed to be regulated by an N feedback mechanism (Hartwig, 1998). Thus both nodulation (Parsons et al., 1993) and nodule performance (Heim et al., 1993; Hartwig et al., 1994; Neo and Layzell, 1997) are considered to be controlled by a signal of organic N from the vascular tissue.
It is reported here for the first time that there is an increase in the asparagine concentration and a concomitant reduction in %Nsym under P deficiency. Although it is assumed that the assimilation of mineral N is also regulated by an N feedback mechanism (Rufty et al., 1990, 1993; Imsande and Touraine, 1994; Marschner et al., 1996; Jeschke et al., 1996, 1997), this process may have a stronger effect on symbiotic N2 fixation compared to its effect on nitrate assimilation. It is proposed that, at low P supply, an N feedback mechanism, related to increased organic N compounds in the vascular tissues, is induced, which down-regulates or even prevents nodulation and nodule growth, thus leading to a decrease in the %Nsym even if the specific N2 fixation rate of the nodules is increased.
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Acknowledgments |
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We thank the Calouste Gulbenkian Foundation (Lisbon, Portugal) for funding this study, E Frossard for the use of laboratory facilities, R Sangakkara for helpful discussions and for his critical reading of the manuscript, B Fischer for the software program to fit A/Ci response curves to the biochemical models, T Flura for helping with the chemical analyses, and D Huber for helping with the nodulation experiment. We are grateful to M Schoenberg for checking the English.
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Notes |
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3 To whom correspondence should be addressed. Fax: +41 1 632 11 53. E-mail address: andreas.luescher{at}ipw.agrl.ethz.ch
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Abbreviations |
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DAP, days after planting; DM, dry mass; Jmax, apparent potential rate of electron transport at saturated light; %Nsym, relative contribution of symbiotically fixed N to total plant N; pCO2, partial pressure of atmospheric CO2; Rubisco, ribulose 1,5-bisphosphate carboxylase/oxygenase; RubP, ribulose 1,5-bisphosphate; Vc,max, apparent maximum rate of carboxylation with non-limiting ribulose-1,5-bisphosphate; WSC, water-soluble carbohydrate..
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References |
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Almeida JPF, Lüscher A, Frehner M, Oberson A, Nösberger J.1999. Partitioning of P and the activity of root acid phosphatase in white clover (Trifolium repens L.) are modified by increased atmospheric CO2 and P fertilization. Plant and Soil 210, 159–166.
Al-Niemi TS, Kahn ML, McDermott TR.1998. Phosphorus uptake by bean nodules. Plant and Soil 198, 71–78.
Banet G, Wininger S, Badani H, Ben-Dor B, Friedman Y, Kapulnik Y.1996. Toxic and osmotic effects of salinity on growth and nodulation of Medicago sativa. Symbiosis 21, 209–222.
Brooks A.1986. Effects of phosphorus nutrition on ribulose-1,5-biphosphate carboxylase activation, photosynthetic quantum yield and amounts of some Calvin-cycle metabolites in spinach leaves. Australian Journal of Plant Physiology 13, 221–237.
Cadisch G, Sylvester-Bradley R, Nösberger J.1989. 15N-based estimation of nitrogen fixation by eight tropical forage-legumes at two levels of P:K supply. Field Crops Research 22, 181–194.
Cadisch G, Sylvester-Bradley R, Boller BC, Nösberger J.1993. Effect of phosphorus and potassium on N2 fixation (15N-dilution) of field-grown Centrosema acutifolium and C. macrocarpum. Field Crops Research 31, 329–340.
Curioni PMG, Hartwig UA, Nösberger J, Schuller KA.1999. Glycolytic flux is adjusted to nitrogenase activity in nodules of detopped and argon-treated alfalfa plants. Plant Physiology 119, 445–453.
Daepp M, Suter D, Almeida JPF, Isopp H, Hartwig UA, Frehner M, Blum H, Nösberger J, Lüscher A.2000. Yield response of Lolium perenne swards to free air CO2 enrichment increased over six years in a high N input system on fertile soil. Global Change Biology (in press).
Drevon JJ, Hartwig UA.1997. Phosphorus deficiency increases the argon-induced decline of nodule nitrogenase activity in soybean and alfalfa. Planta 201, 463–469.
Dunlop J, Hart AD.1987. Mineral nutrition. In: Baker MJ, Williams WM, eds. White clover. Wallingford: CAB International, 1–30.
Farquhar GD, von Caemmerer S.1982. Modelling of photosynthetic response to environmental conditions. In: Lange OL, Nobel PS, Osmond CB, Ziegler H, eds. Physiological plant ecology. II. Water relations and carbon assimilation. Encyclopedia of plant physiology. Berlin&: Springer Verlag, 549–588.
Farrar JF, Williams ML.1991. The effect of increased carbon dioxide and temperature on carbon partitioning, source-sink relations and respiration. Plant, Cell and Environment 14, 819–830.
Fischer BU, Frehner M, Hebeisen T, Zanetti S, Stadelmann F, Lüscher A, Hartwig UA, Hendrey GR, Blum H, Nösberger J.1997. Source-sink relations in Lolium perenne L. as reflected by carbohydrate concentrations in leaves and pseudo-stems during regrowth in a free air carbon dioxide enrichment (FACE) experiment. Plant, Cell and Environment 20, 945–952.
Gordon AJ, Minchin FR, Skot L, James CL.1997. Stress-induced decline in soybean N2 fixation are related to nodule sucrose synthase activity. Plant Physiology 114, 937–946.[Abstract]
Hartwig UA.1998. The regulation of symbiotic N2 fixation: a conceptual model of N feedback from the ecosystem to the gene expression level. Perspectives in Plant Ecology Evolution and Systematics 1, 92–120.
Hartwig UA, Boller BC, Baur-Höch B, Nösberger J.1990. The influence of carbohydrate reserves on the response of nodulated white clover to defoliation. Annals of Botany 65, 97–105.
Hartwig UA, Heim I, Lüscher A, Nösberger J.1994. The nitrogen-sink is involved in the regulation of nitrogenase activity in white clover after defoliation. Physiologia Plantarum 92, 375–382.
Hartwig UA, Zanetti S, Hebeisen T, Lüscher A, Frehner M, Fischer B, van Kessel C, Hendrey GR, Blum H, Nösberger J.1996. Symbiotic nitrogen fixation: one key to understand the response of temperate grassland ecosystems to elevated CO2? In: Körner C, Bazzaz F, eds. Carbon dioxide, populations and communities. San Diego: Academic Press, 253–264.
Hebeisen T, Lüscher A, Zanetti S, Fischer BU, Hartwig UA, Frehner M, Hendrey R, Blum H, Nösberger J.1997. Growth response of Trifolium repens L. and Lolium perenne L. as monocultures and bi-species mixture to free air CO2 enrichment and management. Global Change Biology 3, 149–160.
Heim I, Hartwig UA, Nösberger J.1993. Current nitrogen fixation is involved in the regulation of nitrogenase activity in white clover (Trifolium repens L.). Plant Physiology 103, 1009–1014.[Abstract]
Imsande J, Touraine B.1994. N demand and the regulation of nitrate uptake. Plant Physiology 105, 3–7.[Web of Science][Medline]
Israel DW.1987. Investigation of the role of phosphorus in symbiotic dinitrogen fixation. Plant Physiology 84, 835–840.
Israel DW.1993. Symbiotic dinitrogen fixation and host-plant growth during development of and recovery from phosphorus deficiency. Physiologia Plantarum 88, 294–300.
Jakobsen I.1985. The role of phosphorus in the nitrogen fixation by young pea plants (Pisum sativum). Physiologia Plantarum 64, 190–196.
Jeschke DW, Peuke A, Kirkby A, Pate JS, Hartung W.1996. Effects of P deficiency on the uptake, flows of C, N and H2O within intact plants of Ricinus communis L. Journal of Experimental Botany 47, 1737–1754.
Jeschke DW, Kirkby A, Peuke A, Pate JS, Hartung W.1997. Effects of P deficiency on assimilation and transport of nitrate and phosphate in intact plants of castor bean (Ricinus communis L.). Journal of Experimental Botany 48, 75–91.
Kirschbaum MUF, Farquhar GD.1984. Temperature dependence of whole-leaf photosynthesis in Eucalyptus pauciflora Sieb. ex Spreng. Australian Journal of Plant Physiology 11, 519–538.
Long SP, Drake BG.1992. Photosynthetic CO2 assimilation and rising atmospheric CO2 concentrations. In: Baker NR, Thomas H, eds. Crop photosynthesis: spatial and temporal determinants. Amsterdam: Elsevier Science Publishers, 69–103.
Lüscher A, Hartwig UA, Suter D, Nösberger J.2000. Direct evidence that symbiotic N2 fixation in fertile grassland is an important trait for a strong response of plants to elevated atmospheric CO2. Global Change Biology (in press).
Lüscher A, Hebeisen T, Zanetti S, Hartwig UA, Blum H, Hendrey GR, Nösberger J.1996. Differences between legumes and nonlegumes of permanent grassland in their responses to free-air carbon dioxide enrichment: its effect on competition in a multispecies mixture. In: Körner C, Bazzaz F, eds. Carbon dioxide, populations and communities. San Diego: Academic Press, 287–299.
Lüscher A, Hendrey GR, Nösberger J.1998. Long-term responsiveness to free air CO2 enrichment of functional types, species and genotypes of plants from fertile permanent grassland. Oecologia 113, 37–45.
Marschner H, Kirkby EA, Cakmak I.1996. Effect of mineral nutritional status on shoot-root partitioning of photoassimilates and cycling of mineral nutrients. Journal of Experimental Botany 47, 1255–1263.
Minchin FR, Pate JS.1973. The carbon balance of a legume and the functional economy of its root nodules. Journal of Experimental Botany 24, 259–271.
Neo HH, Layzell DB.1997. Phloem glutamine and the regulation of O2 diffusion in legume nodules. Plant Physiology 113, 259–267.[Abstract]
Parsons R, Stanforth A, Raven JA, Sprent JI.1993. Nodule growth and activity may be regulated by a feedback mechanism involving phloem nitrogen. Plant, Cell and Environment 16, 125–136.
Paul MJ, Stitt M.1993. Effects of nitrogen and phosphorus deficiencies on levels of carbohydrates, respiratory enzymes and metabolites in seedlings of tobacco and their response to exogenous sucrose. Plant, Cell and Environment 16, 1047–1057.
Purwantari ND, Date RA, Dart PJ.1995. Nodulation and N2 fixation by Calliandra calothyrsus and Sesbania sesban grown at different root temperatures. Soil Biology and Biochemistry 27, 421–425.
Rabe E, Lovatt CJ.1986. Increased arginine biosynthesis during phosphorus deficiency. Plant Physiology 81, 774–779.
Rao IM.1997. The role of phosphorus in photosynthesis. In: Pessarakli M, ed. Handbook of photosynthesis. New York: Marcel Dekker Incorporation, 173–194.
Ribet J, Drevon JJ.1995a. Increase of permeability to oxygen and in oxygen uptake of soybean nodules under limiting phosphorus nutrition. Physiologia Plantarum 94, 298–304.
Ribet J, Drevon JJ.1995b. Phosphorus deficiency increases the acetylene-induced decline in nitrogenase activity in soybean (Glycine max (L.) Merr.). Journal of Experimental Botany 46, 1479–1486.
Robson AD, O'Hara GW, Abbott LK.1981. Involvement of phosphorus in nitrogen fixation by subterranean clover (Trifolium subterraneum L.). Australian Journal of Plant Physiology 8, 427–436.
Rogers A, Fischer BU, Bryant J, Frehner M, Blum H, Raines CA, Long SP.1998. Acclimation of photosynthesis to elevated CO2 under low-nitrogen nutrition is affected by the capacity for assimilate utilization. Perennial ryegrass under free-air CO2 enrichment. Plant Physiology 118, 683–689.
Rufty Jr TW, MacKown CT, Israel DW.1990. Phosphorus stress effects on assimilation of nitrate. Plant Physiology 94, 328–333.
Rufty Jr TW, Israel DW, Volk RJ, Qiu J, Sa TM.1993. Phosphate regulation of nitrate assimilation in soybean. Journal of Experimental Botany 44, 879–891.
Sa TM, Israel DW.1991. Energy status and functioning of phosphorus-deficient soybean nodules. Plant Physiology 97, 928–935.
Sa TM, Israel DW.1998. Phosphorus-deficiency effects on response of symbiotic N2 fixation and carbohydrate status in soybean to atmospheric CO2 enrichment. Journal of Plant Nutrition 21, 2207–2218.
Sangakkara UR, Hartwig UA, Nösberger J.1996a. Soil moisture and potassium affect the performance of symbiotic nitrogen fixation in faba bean and common bean. Plant and Soil 184, 123–130.
Sangakkara UR, Hartwig UA, Nösberger J.1996b. Growth and symbiotic nitrogen fixation of Vicia faba and Phaseolus vulgaris as affected by fertilizer potassium and temperature. Journal of the Science of Food and Agriculture 70, 315–320.
Seresinhe T, Hartwig UA, Kessler W, Nösberger J.1994. Symbiotic nitrogen fixation of white clover in mixed sward is not limited by height of repeated cutting. Journal of Agronomy and Crop Science 172, 279–288.
Stitt M.1991. Rising CO2 levels and their potential significance for carbon flow in photosynthetic cells. Plant, Cell and Environment 14, 741–762.
Stöcklin J, Schweizer K, Körner C.1998. Effects of elevated CO2 and phosphorus addition on productivity and community composition of intact monoliths from calcareous grassland. Oecologia 116, 50–56.
Warembourg FR, Roumet C.1989. Why and how to estimate the cost of symbiotic N2 fixation? A progressive approach based on the use of 14C and 15N isotopes. Plant and Soil 115, 167–177.
Weisbach C, Hartwig UA, Heim I, Nösberger J.1996. Whole nodule carbon metabolites are not involved in the regulation of the oxygen permeability and nitrogenase activity in white clover nodules. Plant Physiology 110, 539–545.[Abstract]
Zanetti S, Hartwig UA, Lüscher A, Hebeisen T, Frehner M, Fischer BU, Hendrey GR, Blum H, Nösberger J.1996. Stimulation of symbiotic N2 fixation in Trifolium repens L. under elevated atmospheric pCO2 in a grassland ecosystem. Plant Physiology 112, 575–583.[Abstract]
Zanetti S, Hartwig UA, van Kessel C, Lüscher A, Hebeisen T, Frehner M, Fischer BU, Hendrey GR, Blum H, Nösberger J.1997. Does nitrogen nutrition restrict the CO2 response of fertile grassland lacking legumes? Oecologia 112, 17–22.
Zanetti S, Hartwig UA, Nösberger J.1998. Elevated atmospheric CO2 does not affect per se the preference for symbiotic nitrogen as opposed to mineral nitrogen of Trifolium repens L. Plant, Cell and Environment 21, 623–630.
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