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Kerstin Huss-danell – One of the best experts on this subject based on the ideXlab platform.

  • Local and systemic effects of phosphorus and nitrogen on nodulation and nodule function in Alnus incana
    Journal of experimental botany, 2003
    Co-Authors: Francesco G. Gentili, Kerstin Huss-danell

    Abstract:

    Phosphorus (P) and nitrogen (N) effects on nodulation, nitrogenase activity and plant growth were studied in the root-hair-infected actinorhizal plant Alnus incana (L.) Moench. A split-root experiment, as well as a short-term experiment with entire root systems and a broader range of P concentrations, showed that P effects were specific on nodulation and not a general stimulation via a plant growth effect. These results indicate that nodule initiation and nodule growth have a high P demand. The split-root assay, comprising seven combinations of two N and two P levels, showed that P could counteract systemic N inhibition of nodulation, but did not counteract N inhibition of nitrogenase activity.

  • Nitrogen, Phosphorus, and the Ratio Between them Affect Nodulation in Alnus incana and Trifolium pratense
    Symbiosis, 2000
    Co-Authors: Luis Gabriel Wall, Anna Hellsten, Kerstin Huss-danell

    Abstract:

    Nodulation of Alnus incana by Frankia was studied at three levels of N (ammonium nitrate, 0.071-7.1 mM N) combined with three levels of P (0.01-1.0 mM) in a factorial design. Nodulation of Trifolium pratense by Rhizobium leguminosarum bv. trifolii was studied in a partial factorial design. Plants were in growth pouches for 10.5 weeks. In general, the degree of N inhibition depended on the P level. In A. incana, high P level stimulated nodule number and nodule dry matter per plant and per plant dry matter or per root dry matter. High P also stimulated nodule size and nitrogenase activity. Effects on nodule number seemed to be largely explained by plant growth whereas P had more of a specific effect on nodule dry matter. The N/P ratio was important, and increased N levels inhibited nodulation at N/P ratios >7 but not at N/P ratios

  • Regulation of nodulation in Alnus incana‐Frankia symbiosis
    Physiologia Plantarum, 1997
    Co-Authors: Luis G. Wall, Kerstin Huss-danell

    Abstract:

    We have studied regulation of nodulation in Alnus incana (L.) Moench using double inoculations in plastic pouches and a slide technique to observe root hair deformation. Initially, the distribution of nodules between main and lateral roots appeared quite constant, independent of the concentration of inoculum (1 to 250 μg of crushed nodules plant−1). Susceptibility to infection after the second inoculation was restricted to lateral roots after the initial infections developed. When pre-existing nodules were excised before the second inoculation, subsequent nodules appeared to arise where infections had arrested at stages earlier than actual nodule emergence. We observed that root hairs formed postinoculation were very crowded and short with a pronounced deformation. No nodules were found later on this region of the root, suggesting a loss of susceptibility in this region. Split-root experiments with delays between inoculation of the first and second side of the root system showed irreversible, systemic inhibition of nodulation on the second side starting between 3 and 6 days after the inoculation of the first side. Only when compatible, infective strains were used in the first inoculation, was nodule formation inhibited after the second inoculation. We conclude that autoregulation of nodulation operates in Alnus incana and on a time scale similar to what is found in some legumes.

Kerstin Hussdanell – One of the best experts on this subject based on the ideXlab platform.

  • nitrogen phosphorus and the ratio between them affect nodulation in Alnus incana and trifolium pratense
    Symbiosis, 2000
    Co-Authors: Luis Gabriel Wall, Anna Hellsten, Kerstin Hussdanell

    Abstract:

    Nodulation of Alnus incana by Frankia was studied at three levels of N (ammonium nitrate, 0.071-7.1 mM N) combined with three levels of P (0.01-1.0 mM) in a factorial design. Nodulation of Trifolium pratense by Rhizobium leguminosarum bv. trifolii was studied in a partial factorial design. Plants were in growth pouches for 10.5 weeks. In general, the degree of N inhibition depended on the P level. In A. incana, high P level stimulated nodule number and nodule dry matter per plant and per plant dry matter or per root dry matter. High P also stimulated nodule size and nitrogenase activity. Effects on nodule number seemed to be largely explained by plant growth whereas P had more of a specific effect on nodule dry matter. The N/P ratio was important, and increased N levels inhibited nodulation at N/P ratios >7 but not at N/P ratios <7. In T. pratense, high P level counteracted the inhibition of high N on nodule number and nitrogenase activity. The fact that N effects on nodulation and nitrogenase activity depend on P level should encourage more detailed work on effects of nutrient interactions on nodulation, both in actinorhizal plants and in legumes.

  • regulation of nodulation in Alnus incana frankia symbiosis
    Physiologia Plantarum, 1997
    Co-Authors: Luis G. Wall, Kerstin Hussdanell

    Abstract:

    We have studied regulation of nodulation in Alnus incana (L.) Moench using double inoculations in plastic pouches and a slide technique to observe root hair deformation. Initially, the distribution of nodules between main and lateral roots appeared quite constant, independent of the concentration of inoculum (1 to 250 μg of crushed nodules plant−1). Susceptibility to infection after the second inoculation was restricted to lateral roots after the initial infections developed. When pre-existing nodules were excised before the second inoculation, subsequent nodules appeared to arise where infections had arrested at stages earlier than actual nodule emergence. We observed that root hairs formed postinoculation were very crowded and short with a pronounced deformation. No nodules were found later on this region of the root, suggesting a loss of susceptibility in this region. Split-root experiments with delays between inoculation of the first and second side of the root system showed irreversible, systemic inhibition of nodulation on the second side starting between 3 and 6 days after the inoculation of the first side. Only when compatible, infective strains were used in the first inoculation, was nodule formation inhibited after the second inoculation. We conclude that autoregulation of nodulation operates in Alnus incana and on a time scale similar to what is found in some legumes.

  • nitrogen fixation by Alnus incana and nitrogen transfer from a incana to pinus sylvestris influenced by macronutrients and ectomycorrhiza
    New Phytologist, 1995
    Co-Authors: Alf Ekblad, Kerstin Hussdanell

    Abstract:

    The aims of this study were to evaluate the effect of macronutrients on nitrogen fixation in mycorrhizal and non-mycorrhizal grey alder (Alnus incana (L.) Moench), and to evaluate the effect of ect …

Per-olof Lundquist – One of the best experts on this subject based on the ideXlab platform.

  • Carbon cost of nitrogenase activity in Frankia-Alnus incana root nodules
    Plant and Soil, 2005
    Co-Authors: Per-olof Lundquist

    Abstract:

    The carbon cost of nitrogenase activity was investigated to determine symbiotic efficiency of the actinorhizal root nodule symbiosis between the woody perennial Alnus incana and the soil bacterium Frankia. Respiration (CO2 production) and nitrogenase activity (H2 production) by intact nodulated root systems were continuously recorded in short-term assays in an open-flow gas exchange system. The assays were conducted in N2:O2, thus under N2-fixing conditions, in all experiments except for one. This avoided the declines in nitrogenase activity and respiration due to N2 deprivation that occur in acetylene reduction assays and during extended Ar:O2 exposures in H2 assays. Two approaches were used: (i) direct estimation of root and nodule respiration by removing nodules, and (ii) decreasing the partial pressure of O2 from 21 to 15% to use the strong relationship between respiration and nitrogenase activity to calculate CO2/H2. The electron allocation of nitrogenase was determined to be 0.6 and used to convert the results into moles of CO2 produced per 2e− transferred by nitrogenase to reduction of N2. The results ranged from 2.6 to 3.4 mol CO2 produced per 2e−. Carbon cost expressed as g C produced per g N reduced ranged from 4.5 to 5.8. The result for this actinorhizal tree symbiosis is in the low range of estimates for N2-fixing actinorhizal symbioses and crop legumes. Methodology and comparisons of root nodule physiology among actinorhizal and legume plants are discussed.

  • Nitrogenase activity in Alnus incana root nodules. Responses to O2 and short-term N2 deprivation.
    Plant physiology, 2000
    Co-Authors: Per-olof Lundquist

    Abstract:

    O 2 and host-microsymbiont interactions are key factors affecting the physiology of N 2 -fixing symbioses. To determine the relationship among nitrogenase activity of Frankia – Alnus incana root nodules, O 2 concentration, and short-term N 2 deprivation, intact nodulated roots were exposed to various O 2 pressures (pO 2 ) and Ar:O 2 in a continuous flow-through system. Nitrogenase activity (H 2 production) occurred at a maximal rate at 20% O 2 . Exposure to short-term N 2 deprivation in Ar:O 2 carried out at either 17%, 21%, or 25% O 2 caused a decline in the nitrogenase activity at 21% and 25% O 2 by 12% and 25%, respectively. At 21% O 2 , nitrogenase activity recovered to initial activity within 60 min. The decline rate was correlated with the degree of inhibition of N 2 fixation. Respiration (net CO 2 evolution) decreased in response to the N 2 deprivation at all pO 2 values and did not recover during the time in Ar:O 2 . Increasing the pO 2 from 21% to 25% and decreasing the pO 2 from 21% to 17% during the decline further decreased rather than stimulated nitrogenase activity, showing that the decline was not due to O 2 limitation. The decline was possibly due to a temporary disturbance in the supply of reductant to nitrogenase with a partial O 2 inhibition of nitrogenase at 25% O 2 . These results are consistent with a fixed O 2 diffusion barrier in A. incana root nodules, and show that A. incana nodules differ from legume nodules in the response of the nitrogenase activity to O 2 and N 2 deprivation.

  • N2 fixation in a young Alnus incana stand, based on seasonal and diurnal variation in whole plant nitrogenase activity
    Canadian Journal of Botany, 1992
    Co-Authors: Kerstin Huss-danell, Per-olof Lundquist, Helene Ohlsson

    Abstract:

    N2 fixation by grey alder, Alnus incana (L.) Moench, was studied in the field during two growing seasons in northern Sweden. Alders were planted in a nitrogen-poor soil. Each alder had its root system enclosed in an open-ended cylinder that was closed with a gas-tight lid around the stem base to serve as cuvette during nitrogenase activity (acetylene reducing activity) measurements. To follow the seasonal variation, nitrogenase activity was measured at noon on 15 occasions for each alder in 1987 and on 15 occasions in 1988. Diurnal variation in nitrogenase activity was studied at six occasions, but no obvious pattern in the diurnal variation was found. Nitrogenase activity began shortly after leaf emergence at the very end of May, increased in June, stayed high although with some variation through July and August, declined during September, and was zero in early October. Cumulative nitrogenase activity over the season was converted to cumulative N2 fixation after determination of molar ratio nitrogenase a…