首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献,搜索用时 15 毫秒
1.
The CO2-exchange rate required to make full use of available N2-fixation capacity, measured as acetylene reduction, was determined in soybean and alfalfa. Carbohydrates of root systems were depleted during a 40-hour dark treatment; then plants were exposed to a 24-hour light period during which different CO2-exchange rates were maintained with various CO2 concentrations. In three- and four-week-old soybeans and four-week-old alfalfa plants, acetylene-reduction capacity was used fully with CO2-exchange rates as low as 10 milligrams CO2 per plant per hour. In six-week-old alfalfa plants, however, acetylene reduction rates increased linearly, and apparent N2-fixation capacity was not used fully when CO2-exchange rates were higher than 40 milligrams CO2 per plant per hour. Under the conditions established, the energy cost of N2 fixation, measured as Δ(respiration of roots + nodules)/Δacetylene reduction over dark-treatment values, was 0.453 milligrams CO2 per micromole C2H4 for all rates of acetylene reduction and for both ages of soybean and alfalfa plants. Thus, root-plus-nodule respiration was not promoted by higher rates of apparent photosynthesis after C2H2-reduction capacity became saturated, and all available capacity for apparent N2 fixation had the same energy requirement.  相似文献   

2.
Summary Lucerne, red clover and white clover were grown at two atmospheric concentrations of CO2 (300 and 1000 μl l−1) and the effects on N2 fixation, nodule mass/number and root/shoot dry matter production determined. Pea plants were similarly evaluated as a comparison with grain legumes. CO2 enrichment increased N2 fixation activity in all cases but activity/unit nodule mass was significantly increased only in the pea. The enhancement of N2 fixation in herbage legumes by CO2 enrichment reflected an increase in nodule mass which in turn was attributed to increased nodule number, and results show that under the experimental conditions obtaining here photosynthate supply did not limit nodule N2 fixation in these plants though it was limiting in the case of peas. White clover growing in a 6 and 14 hour photoperiod was studied for response of the N2 fixing system to light. Long photoperiod (14 hour) plants assayed at constant temperature (20°C) did not show a significant response to light at the end of the dark period either in terms of fixation per plant or per unit nodule mass, in contrast with short photoperiod (6 hour) plants which showed significant responses. Short photoperiod plants compensated for reduced photosynthates by maintaining only half the root nodule mass and fixation activity of 14 hour photoperiod plants though plants in both systems supported similar rates of N2 fixation per unit mass of nodule during the photoperiod. Comparison of N2 fixation activities in whole and decapitated plant systems indicates the importance of shoot reserves for sustaining nitrogenase activity in white clover during short-term interruption of photosynthesis. These results support the conclusion of the CO2 enrichment studies, that herbage legumes have the potential for supplying their nodule photosynthate requirements for sustaining optimum rates of N2 fixation and excess carbon supply is used solely to promote further nodulation. Nodules of short photoperiod white clover plants were less efficient in N2 fixation in that they evolved more H2 relative to N2 (C2H2) reduced than did long photoperiod plants.  相似文献   

3.
An apparatus was designed that permitted acetylene reduction (N2 fixation) by root nodules to be measured in situ simultaneously with net photosynthesis, dark respiration, and transpiration of the shoot in soybean plants (Glycine max [L.] Merr. var. Beeson). Tests showed that acetylene reduction was linear with time for at least 5 hours, except for the first 30 to 60 minutes. Endogenous ethylene production did not affect the measurements. Successive determinations of acetylene reduction could be made without apparent aftereffects on the plant.  相似文献   

4.
The dependence of alfalfa (Medicago sativa L.) root and nodule nonphotosynthetic CO2 fixation on the supply of currently produced photosynthate and nodule nitrogenase activity was examined at various times after phloem-girdling and exposure of nodules to Ar:O2. Phloemgirdling was effected 20 hours and exposure to Ar:O2 was effected 2 to 3 hours before initiation of experiments. Nodule and root CO2 fixation rates of phloem-girdled plants were reduced to 38 and 50%, respectively, of those of control plants. Exposure to Ar:O2 decreased nodule CO2 fixation rates to 45%, respiration rates to 55%, and nitrogenase activities to 51% of those of the controls. The products of nodule CO2 fixation were exported through the xylem to the shoot mainly as amino acids within 30 to 60 minutes after exposure to 14CO2. In contrast to nodules, roots exported very little radioactivity, and most of the 14C was exported as organic acids. The nonphotosynthetic CO2 fixation rate of roots and nodules averaged 26% of the gross respiration rate, i.e. the sum of net respiration and nonphotosynthetic CO2 assimilation. Nodules fixed CO2 at a rate 5.6 times that of roots, but since nodules comprised a small portion of root system mass, roots accounted for 76% of the nodulated root system CO2 fixation. The results of this study showed that exposure of nodules to Ar:O2 reduced nodule-specific respiration and nitrogenase activity by similar amounts, and that phloem-girdling significantly reduced nodule CO2 fixation, nitrogenase activity, nodule-specific respiration, and transport of 14C photoassimilate to nodules. These results indicate that nodule CO2 fixation in alfalfa is associated with N assimilation.  相似文献   

5.
Root respiration associated with symbiotic fixation in soybean (Glycine max [L.] Merr.) was estimated by four methods.

Averaged over the life of the plant, the root respires 5.8 milligrams C per milligram N accumulated from fixation. When nitrogenase (C2H2) activity and root respiration were decreased by treating roots briefly with 1.0 atmosphere O2, the respiration associated with nitrogenase was estimated as 2.10 micromoles CO2 per micromole C2H4.

When nitrogenase activity and respiration were decreased by addition of nitrate, the respiration associated with fixation was calculated as 2.90 micromoles CO2 per micromole C2H4. Removing nodules from roots decreased fixation and root respiration, and the ratio was 4.08 micromoles CO2 per micromole C2H4. When soybean plants were kept in prolonged darkness, then returned to light, the associated drop and recovery of respiration and nitrogenase activity had a ratio of 4.36 micromoles CO2 per micromole C2H2.

  相似文献   

6.
Partitioning and utilization of assimilated C and N were compared in nonnodulated, NO3-fed and nodulated, N2-fed plants of white lupin (Lupinus albus L.). The NO3 regime used (5 millimolar NO3) promoted closely similar rates of growth and N assimilation as in the symbiotic plants. Over 90% of the N absorbed by the NO3-fed plants was judged to be reduced in roots. Empirically based models of C and N flow demonstrated that patterns of incorporation of C and N into dry matter and exchange of C and N among plant parts were essentially similar in the two forms of nutrition. NO3-fed and N2-fed plants transported similar types and proportions of organic solutes in xylem and phloem. Withdrawal of NO3 supply from NO3-fed plants led to substantial changes in assimilate partitioning, particularly in increased translocation of N from shoot to root. Nodulated plants showed a lower (57%) conversion of C or net photosynthate to dry matter than did NO3-fed plants (69%), and their stems were only half as effective as those of NO3-fed plants in xylem to phloem transfer of N supplied from the root. Below-ground parts of symbiotic plants consumed a larger share (58%) of the plants' net photosynthate than did NO3-fed roots (50%), thus reflecting a higher CO2 loss per unit of N assimilated (10.2 milligrams C/milligram N) by the nodulated root than by the root of the NO3-fed plant (8.1 milligrams C/milligram N). Theoretical considerations indicated that the greater CO2 output of the nodulated root involved a slightly greater expenditure for N2 than for NO3 assimilation, a small extra cost due to growth and maintenance of nodule tissue, and a considerably greater nonassimilatory component of respiration in root tissue of the symbiotic plant than in the root of the NO3-fed plant.  相似文献   

7.
The relationship between ureide N and N2 fixation was evaluated in greenhouse-grown soybean (Glycine max L. Merr.) and lima bean (Phaseolus lunatus L.) and in field studies with soybean. In the greenhouse, plant N accumulation from N2 fixation in soybean and lima bean correlated with ureide N. In soybean, N2 fixation, ureide N, acetylene reduction, and nodule mass were correlated when N2 fixation was inhibited by applying KNO3 solutions to the plants. The ureide-N concentrations of different plant tissues and of total plant ureide N varied according to the effectiveness of the strain of Bradyrhizobium japonicum used to inoculate plants. The ureide-N concentrations in the different plant tissues correlated with N2 fixation. Ureide N determinations in field studies with soybean correlated with N2 fixation, aboveground N accumulation, nodule weight, and acetylene reduction. N2 fixation was estimated by 15N isotope dilution with nine and ten soybean genotypes in 1979 and 1980, respectively, at the V9, R2, and R5 growth stages. In 1981, we investigated the relationship between ureide N, aboveground N accumulation, acetylene reduction, and nodule mass using four soybean genotypes harvested at the V4, V6, R2, R4, R5, and R6 growth stages. Ureide N concentrations of young stem tissues or plants or aboveground ureide N content of the four soybean genotypes varied throughout growth correlating with acetylene reduction, nodule mass, and aboveground N accumulation. The ureide-N concentrations of young stem tissues or plants or aboveground ureide-N content in three soybean genotypes varied across inoculation treatments of 14 and 13 strains of Bradyrhizobium japonicum in 1981 and 1982, respectively, and correlated with nodule mass and acetylene reduction. In the greenhouse, results correlating nodule mass with N2 fixation and ureide N across strains were variable. Acetylene reduction in soybean across host-strain combinations did not correlate with N2 fixation and ureide N. N2 fixation, ureide N, acetylene reduction, and nodule mass correlated across inoculation treatments with strains of Bradyrhizobium spp. varying in effectiveness on lima beans. Our data indicate that ureide-N determinations may be used as an additional method to acetylene reduction in studies of the physiology of N2 fixation in soybean. Ureide-N measurements also may be useful to rank strains of B. japonicum for effectiveness of N2 fixation.  相似文献   

8.
The relationship between photosynthesis of soybean and nitrogen fixation of the nodules by symbiotic Rhizobium was studied. The contents of total nitrogen and chlorophyll, the net photosynthetic rate and seed yield of soybean were much higher in either hydroponically cultivated or field-grown plants inoculated with Rhizobium B16–11C (or Clark nodulating strain) than in control without inoculation (or Clark non-nodulating strain). These results show that the symbiotic nitrogen fixation has a beneficial effect on photosynthesis. However, the effect was indirect and slow so that there was no change in the net photosynthetic rate of the soybean leaves until three clays after removing nodules from the soybean roots. On the other hand, decreasing the photosynthate supply to nodule by shade, defoliation or shoot removal of the soybean, the nodule activity declined significantly. It seems that the supply of photosynthate to root nodule is a limiting factor for symbiotic nitrogen fixation. However, the diurnal variation of the nodule activity could not be explained by change neither in the contents of sucrose and starch of the root nodules nor in the ambient temperature. The factor controlling the diurnal variation deserves further study.  相似文献   

9.
水培大豆和田间生长的大豆,接种根瘤菌 Rhizobium B16-11C 后植株全氮含量、叶片叶绿素含量和净光合速率及种子产量都明显增加。比较 Clark 大豆的结瘤品系和不结瘤品系获类似结果。摘除根瘤后3天内叶片净光合速率无明显变化。大豆植株遮阴、去叶或切掉地上部导致根瘤活性明显下降。但去豆荚不能提高根瘤固氮的比活性。根瘤活性的日变化不能用根瘤蔗糖、淀粉含量或周围温度的变化来解释,其控制因子尚待深入研究。  相似文献   

10.
Carbon and nitrogen limitations on soybean seedling development   总被引:2,自引:2,他引:0       下载免费PDF全文
Carbon and nitrogen limitations on symbiotically grown soybean seedlings (Glycine max [L.] Merr.) were assessed by providing 0.0, 1.0, or 8.0 millimolar NH4NO3 and 320 or 1,000 microliters CO2/liter for 22 days after planting. Maximum development of the Rhizobium-soybean symbiosis, as determined by acetylene reduction, was measured in the presence of 1.0 millimolar NH4NO3 under both levels of CO2. Raising NH4NO3 from 0.0 to 8.0 millimolar under 320 microliters CO2/liter increased plant dry weight by 251% and Kjeldahl N content by 287% at 22 days after planting. Increasing NH4NO3 from 1.0 to 8.0 millimolar under 320 microliters CO2/liter increased total dry weight and Kjeldahl N by 100 and 168%, respectively, on day 22. Raising CO2 from 320 to 1,000 microliters CO2/liter during the same period had no significant effect on Kjeldahl N content of plants grown with 0.0 or 1.0 millimolar NH4NO3. The maximum CO2 treatment effects were observed in plants supplied with 8.0 millimolar NH4NO3, where dry weight and Kjeldahl N content were increased 64% and 20%, respectively. An increase in shoot CO2-exchange rate associated with the CO2-enrichment treatment was reflected in a significant increase in leaf dry weight and starch content for plants grown with 1,000 microliters CO2/liter under all combined N treatments. These data show directly that seedling growth in symbiotically grown soybeans was limited primarily by N availability. The failure of the CO2-enrichment treatment to increase total plant N significantly in Rhizobium-dependent plants indicates that root nodule development and functioning in such plants was not limited by photosynthate production.  相似文献   

11.
The role of photosynthesis and transpiration in the desiccation-induced inhibition of acetylene reduction (nitrogen fixation) was investigated in soybean (Glycine max [L.] Merr. var. Beeson) using an apparatus that permitted simultaneous measurements of acetylene reduction, net photosynthesis, and transpiration. The inhibition of acetylene reduction caused by low water potentials and their aftereffects could be reproduced by depriving shoots of atmospheric CO2 even though the soil remained at water potentials that should have favored rapid acetylene reduction. The inhibition of acetylene reduction at low water potentials could be partially reversed by exposing the shoots to high CO2 concentrations. When transpiration was varied independently of photosynthesis and dark respiration in plants having high water potentials, no effects on acetylene reduction could be observed. There was no correlation between transpiration and acetylene reduction in the CO2 experiments. Therefore, the correlation that was observed between transpiration and acetylene reduction during desiccation was fortuitous. We conclude that the inhibition of shoot photosynthesis accounted for the inhibition of nodule acetylene reduction at low water potentials.  相似文献   

12.
Four consecutive trifoliate leaves of 56-day-old symbiotic or nonsymbiotic soybean plants were evaluated individually for CO2 exchange rates (CER), leaf area and dry weight, and leaf N, P, and starch concentrations. Plants had been inoculated with the vesicular-arbuscular mycorrhizal (VAM) fungus Glomus mosseae and Rhizobium japonicum, with either of the endophytes alone, or with neither at time of planting. Plants lacking one or both endophytes received N and/or P fertilizers to produce plants of equal total leaf dry weight in all four treatments. Photosynthetic P-use efficiency (CER per unit leaf P) was higher in the leaves of VAM plants than in P-fertilized plants regardless of the N source (N2 fixation or combined N). Photosynthetic N-use efficiency was also higher in VAM than in non-VAM plants, but it was affected by the N source, with higher CER in the nodulated plants. The greatest differences in CER, starch accumulation and leaf area were found between the nonsymbiotic plants and those with both endophytes. Statistical evaluations of leaf parameters for treatment or nutrient concentration (N and P) effects between the tri-partite and the nonsymbiotic treatments showed significant changes in concentration of P, but not N, with decreasing leaf age. Both endophytes apparently enhance CO2 fixation at N and/or P concentrations lower than those of the nonsymbiotic plants. The effects of the endophytes on CO2 fixation were additive.  相似文献   

13.
Direct, continuous measurements of the CO2 evolution of rootnodules, calibrated by direct measurements of rate of ethyleneproduction, were utilized to determine the short-term responseof nitrogenase activity to defoliation and photosynthesis inwhite clover. Defoliation (removal of all expanded leaflets) generally resultedin a fall in nodulated root respiration within 10 min; mostrespiration associated with nitrogenase activity ceased within1–2 h. Darkening of the shoot also reduced nodulated root respirationwithin 10 min, but the subsequent fall in respiration, althoughof the same magnitude, was slower. The re-illumination of shootslargely reversed these effects. The inhibition of photosynthesisby DCMU largely simulated the effects of darkening the shoots. It is concluded that, in these white clover plants of 100 mgto 2.0 g total weight, current photosynthate provides the primarysource of energy for N2 fixation. The mobilization of reserveenergy substrate appeared to play only a small role. The minimumtime interval of 10 min between onset of treatment and fallin nodule respiration probably reflects the time taken to exhaustthe assimilate in transit between leaf and nodule. Key words: White clover, N2 fixation, Defoliation, Photosynthesis  相似文献   

14.
Single plants of white clover, grown in a controlled environmentand dependent for nitrogen on fixation in their root nodules,were defoliated once by removing approximately half their shoottissue. Their regrowth was compared with the growth of comparableundefoliated plants. Two similar experiments were carried out:in the first, plants were defoliated at 2.5 g, and in the secondat 1.2 g total plant d. wt. Defoliation reduced rate of N2 fixation by > 70 per cent,rate of photosynthesis by 83–96 per cent, and rate ofplant respiration by 30–40 per cent. Nodule weights initiallydeclined following defoliation as a result of loss of carbohydratesand other unidentified components. No immediate shedding ofnodules was observed but nodules on the most severely defoliatedplants exhibited accelerated senescence. The original rates of N2 fixation were re-attained after 5–6or 9 d regrowth, with increase in plant size at defoliation.In general, the rate of recovery of N2 fixation was relatedto the re-establishment and increase of the plant's photosyntheticcapacity. Throughout the growth of both defoliated and undefoliatedplants nodule respiration (metabolism) accounted for at least23 ± 2 per cent of gross photosynthesis. The unit ‘cost’of fixing N2 in root nodules, in terms of photosynthate, appearedto be unaffected by defoliation, except perhaps for plants veryrecently defoliated. Similarly, the percentage nitrogen contentsof shoot, root and nodules of defoliated plants became adaptedwithin a few days to those characteristic of undefoliated plants. Trifolium repens, white clover, N2 fixation, defoliation, photosynthesis, respiration  相似文献   

15.
Finn GA  Brun WA 《Plant physiology》1982,69(2):327-331
The objective of this study was to determine whether the supply of current photosynthate was limiting root nodule activity. Both short-term (36 hours) and long-term (16 days) periods of CO2 enrichment were imposed on vegetative, growth chamber-grown soybean plants (Glycine max. [L.] Merr. cv. `Clay') to increase the supply of current photosynthate and to observe the effects on photosynthate partitioning in the plants, plant growth, and root nodule activity.  相似文献   

16.
The total metabolic cost of soybean (Glycine max L. Mer Clark) nodule nitrogen fixation was empirically separated into respiration associated with electron flow through nitrogenase and respiration associated with maintenance of nodule function.

Rates of CO2 evolution and H2 evolution from intact, nodulated root systems under Ar:O2 atmospheres decreased in parallel when plants were maintained in an extended dark period. While H2 evolution approached zero after 36 hours of darkness at 22°C, CO2 evolution rate remained at 38° of the rate measured in light. Of the remaining CO2 evolution, 62% was estimated to originate from the nodules and represents a measure of nodule maintenance respiration. The nodule maintenance requirement was temperature dependent and was estimated at 79 and 137 micromoles CO2 (per gram dry weight nodule) per hour at 22°C and 30°C, respectively.

The cost of N2 fixation in terms of CO2 evolved per electron pair utilized by nitrogenase was estimated from the slope of H2 evolution rate versus CO2 evolution rate. The cost was 2 moles CO2 evolved per mole H2 evolved and was independent of temperature.

In this symbiosis, nodule maintenance consumed 22% of total respiratory energy while the functioning of nitrogenase consumed a further 52%. The remaining respiratory energy was calculated to be associated with ammonia assimilation, transport of reduced N, and H2 evolution.

  相似文献   

17.
Waterlogging of soybean plants (Glycine max L.) led to impaired symbiotic N2 fixation and a marked decline in glutamine (Gln) concentration in xylem bleeding sap. Xylem Gln concentration increased during the growth cycle of the plant and was correlated with nodule formation. Treatments known to impair N2 fixation, such as exposing the root system to pure N2 gas or a mixture of Ar and O2 (80:20; v/v), led to specific declines in xylem sap Gln. The decrease in Gln observed during waterlogging was also seen on transfer of nodulated plants to aerated hydroponics, where the decline was highly correlated with ureide content in the xylem sap. Upon flooding the nodulated root system, the specific decline in xylem sap Gln could be detected within 10 min and reached a minimum within 60 min, indicating that waterlogging has an immediate effect on N2 fixation. It is concluded that xylem Gln arises directly from N2-fixation and is a useful indicator of N2 fixation activity of symbiotic soybean plants.  相似文献   

18.
The effects of water stress and CO2 enrichment on photosynthesis, assimilate export, and sucrose-P synthase activity were examined in field grown soybean plants. In general, leaves of plants grown in CO2-enriched atmospheres (300 microliters per liter above unenriched control, which was 349 ± 12 microliters per liter between 0500 and 1900 hours EST over the entire season) had higher carbon exchange rates (CER) compared to plants grown at ambient CO2, but similar rates of export and similar activities of sucrose-P synthase. On most sample dates, essentially all of the extra carbon fixed as a result of CO2 enrichment was partitioned into starch. CO2-enriched plants had lower transpiration rates and therefore had a higher water use efficiency (milligrams CO2 fixed per gram H2O transpired) per unit leaf area compared to nonenriched plants. Water stress reduced CER in nonenriched plants to a greater extent than in CO2-enriched plants. As CER declined, stomatal resistance increased, but this was not the primary cause of the decrease in assimilation because internal CO2 concentration remained relatively constant. Export of assimilates was less affected by water stress than was CER. When CERs were low as a result of the imposed stress, export was supported by mobilization of reserves (mainly starch). Export rate and leaf sucrose concentration were related in a curvilinear manner. When sucrose concentration was above about 12 milligrams per square decimeter, obtained with nonstressed plants at high CO2, there was no significant increase in export rate. Assimilate export rate was also correlated positively with SPS activity and the quantitative relationship varied with CER. Thus, export rate was a function of both CER and carbon partitioning.  相似文献   

19.
When arrival of shoot supplied carbohydrate to the nodulated root system of soybean was interrupted by stem girdling, stem chilling, or leaf removal, nodule carbohydrate pools were utilized, and a marked decline in the rates of CO2 and H2 evolution was observed within approximately 30 minutes of treatment. Nodule excision studies demonstrated that the decline in nodulated root respiration was associated with nodule rather than root metabolism, since within 3.5 hours of treatment, nodules respired at less than 10% of the initial rates. Apparently, a continuous supply of carbohydrate from the shoot is required to support nodule, but not root, function. Depletion of nodular carbohydrate pools was sufficient to account for the (diminishing) nodule respiration of girdled plants. Of starch and soluble sugar pools within the whole plant, only leaf starch exhibited a diurnal variation which was sufficient to account for the respiratory carbon loss of nodules over an 8 hour night. Under 16 hour nights, or in continuous dark, first the leaf starch pools were depleted, and then nodule starch reserves declined concomitant with a decrease in the rates of CO2 and H2 evolution from the nodules. Nodule soluble sugar levels were maintained in dark treated plants but declined in girdled plants. The depletion of starch in root nodules is an indicator of carbohydrate limitation of nodule function.  相似文献   

20.
The role of lateral root nodules in N2 fixation and the relationships between total shoot N and several traits which influence or control N2 fixation in common bean (Phaseolus vulgaris L.)i.e., acetylene reduction value, specific nodule activity, leghemoglobin concentration, total leghemoglobin and nodule mass, were investigated in field studies. Significant variation among bean lines was observed for all the traits measured. Lines varied for the proportion of total N accumulated up to the R3 growth state, thus measurements of total shoot N near maturity (e.g., R7) provided a better estimate of total N2 fixation than measurements taken at an early growth stage. Nodule mass was correlated with acetylene reduction and total leghemoglobin, and total leghemoglobin was correlated with acetylene reduction value. Total shoot N at R7 was correlated with seasonal means of nodule mass and number, acetylene reduction value and total leghemoglobin. For all traits except total leghemoglobin, values for lateral roots were more highly correlated with total shoot N than were values for either crown roots or the whole root system. Seed yield was most highly correlated with nodule mass of the lateral roots. These results will be useful in devising breeding strategies for improved N2 fixation of the host plant.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号