Nitrogen Fixation and Vegetative Regrowth of Alfalfa and Birdsfoot Trefoil after Successive Harvests or Floral Debudding

Cralle, Harry T.; Heichel, G. H.

doi:10.1104/pp.67.5.898

Cited by 57 publications

(26 citation statements)

References 17 publications

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“…The second harvest, however, may have led to the loss of other forms ofN. Cralle and Heichel (1979) and Vance et al (1979) reported temporary senescence of root and nodule tissue of alfalfa after herbage removal. Such senescence could have contributed to increased N loss after both the first and second harvests (Fig.…”

Section: Relationship To Other Researchmentioning

confidence: 95%

Nitrogen release from roots of alfalfa and soybean grown in sand culture

1989

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An enclosed root chamber containing sterile sand medium was used to study net nitrogen (N) release from actively growing root systems of'Saranac' alfalfa (Medicago sativa L.) and 'Fiskeby V' soybean (Glycine max L. Merr.). Plants were inoculated with a rhizobial strain appropriate to each host, irrigated with N-free nutrient solution, and grown either to 85 or to 173 d after germination (alfalfa) or to physiological maturity (soybean). Alfalfa released 4.5% of symbiotically-fixed plant N into the root zone over its growth period; soybean released 10.4% of plant N. Root zone leachates were analyzed for total N and for amino acid and ammonium content. Significant ammonium-N release occurred from the alfalfa but not the soybean root system; little amino-N was released by root systems of either species. Shoot harvest and water deficit caused increased release of N from alfalfa roots. The results provide evidence that alfalfa and soybean released significant proportions of their N into the root zone, and indicate that while substantial ammonium-N was released from alfalfa roots, passive leakage of amino-N was not a primary mechanism for N release from root systems of either species.

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Section: Relationship To Other Researchmentioning

confidence: 95%

Nitrogen release from roots of alfalfa and soybean grown in sand culture

1989

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“…The persistence of forage legumes may depend in part on the sensitivity of N2 fixation to defoliation (1). It was previously assumed that the principal effect of defoliation on N2 fixation was a reduction in photosynthate supply.…”

mentioning

confidence: 99%

“…N2 fixation is reportedly more sensitive to defoliation in birdsfoot trefoil than in alfalfa, possibly because ofgreater nonstructural carbohydrate reserves in alfalfa (1). We also used nodule respiration data to test the hypothesis that nodule permeability changes are triggered by decreased availability of carbon substrates for respiration.…”

mentioning

confidence: 99%

Nitrogenase Activity, Nodule Respiration, and O₂ Permeability Following Detopping of Alfalfa and Birdsfoot Trefoil

Denison¹,

Hunt²,

Layzell³

1992

Plant Physiol.

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Gas exchange measurements and noninvasive leghemoglobin (Lb) spectrophotometry (nodule oximetry) were used to monitor nodule responses to shoot removal in alfalfa (Medicago sativa L. cv Weevichek) and birdsfoot trefoil (Lotus corniculatus L. cv Fergus). In each species, total nitrogenase activity, measured as H2 evolution in Ar:02 (80:20), decreased to <50% of the initial rate within 1 hour after detopping, and net CO2 production decreased to about 65% of the initial value. In a separate experiment in which nodule oximetry was used, nodule 02 permeability decreased 50% within 5 hours in each species. A similar decrease in the 02-saturated respiration rate (V,,,) for the nodule central zone occurred within 5 hours in birdsfoot trefoil, but only after 24 hours in alfalfa. Lb concentration, also measured by oximetry, decreased after 48 to 72 hours. The decrease in permeability preceded the decrease in Vmax in each species. V,,,x may depend mainly on carbohydrate availability in the nodule. If so, then the decrease in permeability could not have been triggered by decreasing carbohydrate availability. Both oximetry and gas exchange data were consistent with the hypothesis that, for the cultivars tested, carbohydrate availability decreased more rapidly in birdsfoot trefoil than in alfalfa nodules. Fractional Lb oxygenation (initially about 0.15) decreased during the first 24 hours after detopping but subsequently increased to >0.65 for a majority of nodules of each species. This increase could lead to 02 inactivation of nitrogenase.The persistence of forage legumes may depend in part on the sensitivity of N2 fixation to defoliation (1). It was previously assumed that the principal effect of defoliation on N2 fixation was a reduction in photosynthate supply. Indeed, a decrease in acetylene reduction following defoliation was used as evidence that carbohydrate availability was the major factor limiting N2 fixation (8, 13). Although photosynthate supply may set an upper limit on potential N2 fixation rate, oxygen supply often sets a more stringent limit. Denison et al. (7) reviewed the evidence that specific nodule activity is usually limited more directly by 02 supply than by photosynthate supply.The 02 flux into nodules is restricted by a barrier to gaseous diffusion in the nodule cortex (20). Restricted diffusion maintains low 02 concentrations in the nodule central zone, thereby protecting nitrogenase from inactivation by 2. However, low 02 concentrations may also limit nodule respiration in support of N2 fixation. The O2 permeability of the nodule diffusion barrier is under physiological control. Decreases in nodule permeability have been reported in response to drought (6, 25), increased external PO2 (4, 26, 27), and exposure to acetylene (17) or nitrate (19, 23).The first evidence for permeability decreases following defoliation came from experiments by Hartwig et al. (9). Using two Trifolium species, they showed that exposure of root systems to elevated PO2 restored most of the acetylene reduction activi...

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“…This result could be closely related to lowered activities of enzymes such as nitrate reductase or nitrogenase (Cralle and Heichel, 1981;Macdowall 1983;Vance and Heichel, 1981), and to the decline in photosynthesis and carbohydrate reserves (Davidson et al, 1990;Gonzalez et al, 1989;Hodgkinson, 1969;Smith and Silva, 1969) after defoliation. On the other hand, shoot removal induced higher levels of N outflow from N reserves of roots and remaining parts of shoots (both acting as source organs).…”

Section: Discussionmentioning

confidence: 99%

Amino acid content in xylem sap of regrowing alfalfa (Medicago sativa L.): Relations with N uptake, N2 fixation and N remobilization

et al. 1993

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During vegetative regrowth of Medicago sativa L., soil N, symbiotically fixed N 2 and N reserves meet the nitrogen requirements for shoot regrowth. Experiments with nodulated or non-nodulated plants were carried out to investigate the changes in N flows originating from the different N sources and in xylem transport of amino acids during regrowth. Exogenous N uptake, N 2 fixation and endogenous N remobilization were estimated by 15N labelling and amino acids in xylem sap were analysed. Removal of shoots resulted in great declines of exogenous N flows derived either from N 2 or from NHnNO 3 during the first week of regrowth, thereafter recovery increased linearly. Mineral N uptake as well as N 2 fixation occurred mainly between the 10th and 18th day after removal of shoots while exogenous N assimilation in intact plants remained at a steady level. Nitrogen remobilization rates in defoliated plants increased by at least three to five-fold, especially during the first 10 days following shoot removal. Compared to control plants, contents of amino acids in xylem sap, during the first 10 days of regrowth, were reduced by about 72% and 82% in NH4NO 3 grown and in N z fixing plants, respectively. Asparagine was the main amino acid transported in xylem sap of both treated plants. Its relative contents during this period significantly decreased from 75% to 59% and from 67% to 36% respectively in non-nodulated plants and in nodulated ones. This decline was accompanied by compensatory increase in the relative contents of aspartate and glutamine.

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Nitrogen Fixation and Vegetative Regrowth of Alfalfa and Birdsfoot Trefoil after Successive Harvests or Floral Debudding

Cited by 57 publications

References 17 publications

Nitrogen release from roots of alfalfa and soybean grown in sand culture

Nitrogen release from roots of alfalfa and soybean grown in sand culture

Nitrogenase Activity, Nodule Respiration, and O₂ Permeability Following Detopping of Alfalfa and Birdsfoot Trefoil

Amino acid content in xylem sap of regrowing alfalfa (Medicago sativa L.): Relations with N uptake, N2 fixation and N remobilization

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Nitrogen Fixation and Vegetative Regrowth of Alfalfa and Birdsfoot Trefoil after Successive Harvests or Floral Debudding

Cited by 57 publications

References 17 publications

Nitrogen release from roots of alfalfa and soybean grown in sand culture

Nitrogen release from roots of alfalfa and soybean grown in sand culture

Nitrogenase Activity, Nodule Respiration, and O2 Permeability Following Detopping of Alfalfa and Birdsfoot Trefoil

Amino acid content in xylem sap of regrowing alfalfa (Medicago sativa L.): Relations with N uptake, N2 fixation and N remobilization

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Nitrogenase Activity, Nodule Respiration, and O₂ Permeability Following Detopping of Alfalfa and Birdsfoot Trefoil