Frankia strains of soil under Betula pendula : Behaviour in soil and in pure culture

Plant and Soil (Impact Factor: 3.24). 02/1990; 122(1):129-136. DOI: 10.1007/BF02851920

ABSTRACT The development of the nativeFrankia population was studied in a pot experiment in two types of soil; one from aBetula pendula Roth stand, with a high nodulation capacity, and one with a low nodulation capacity from aPinus sylvestris L. stand. The soils were kept at 22°C and 80% WHC. The capacity of the soils to form root nodules onAlnus incana (L.) Moench seedlings was followed over time. An increase in nodulation capacity was observed in the birch soil at pH 6 (attained
by liming). The increase was most pronounced when the soil was planted withBetula pendula seedlings. Nodulation capacity decreased in the birch soil at its original pH of 4.2, and in the pine soil (original pH 3.7),
irrespective of whether it was limed or planted.

Frankia strains were isolated fromAlnus incana root nodules, induced by soil samples from twoBetula pendula stands devoid of actinorhizal plants but showing a high nodulation capacity. The effect of various aqueous soil extracts
on the growth of the strains in propionate medium was studied. Extracts either inhibited or did not affect the growth of the
strains. No adaptation to normal soil pH and temperature conditions was found.

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    ABSTRACT: The actinobacterial genus Frankia encompasses sporulating filamentous bacteria (actinomycetes) that fix N 2 ; they are defined by their ability to induce N 2 -fixing root nodules on a broad range of 'actinorhizal plants'. Actinorhizal plants, in turn, are defined by their ability to form root nodules when in symbiosis with Frankia. Within the root nodule, Frankia fixes nitrogen that is transported to the host plant in amounts sufficient to supply most of the plant's nitrogen require-ments. This symbiosis allows actinorhizal plants to invade and proliferate in soils that are low in combined nitrogen. Although similar in outcome, the symbiosis differs markedly from the rhizobium–legume symbiosis. The overall nodule architecture more closely resembles a foreshortened lateral root rather than a unique plant organ, and the plants have evolved a variety of mechanisms to modulate the levels of free O 2 that would otherwise inactivate nitrogenase (Benson and Silvester, 1993). In common with legumes, however, the plants belong to the 'nitrogen-fixing Clade' within the Rosid I lineage initially described by Soltis et al. (1995). Since the first successful and confirmed isolation of a Frankia strain in 1978 (Callaham et al., 1978), many studies have addressed the diversity and distribution of Frankia strains in root nodules, and some have dealt with the biogeographic distribution of strains and plants. It has become clear that the existing biogeo-graphic patterns of Frankia strain distribution can be viewed as resulting from adaptation by both plants and Frankia strains within a geographic mosaic of envi-ronments developed over millions of years. To sort out factors that control the distribution of frankiae, one must know the host ranges of strain groups, the richness (number of unique strains) and evenness (representation of each unique strain) components of strain diversity in nodules in nature and the geographical distribution of both plants and frankiae. This chapter focuses on the broad patterns of Frankia strain distribution and diversity as they relate to host plant distribution across a geographical mosaic of environments. It begins with some of the issues that arise in studying the biogeog-raphy of the symbiosis, followed by a brief overview of the phylogenetic relation-ships among actinorhizal plants and among Frankia strains. Finally, information will be presented concerning the biogeography of the symbioses, and the diversity of Frankia strains that participate in symbiosis in each plant family. The chapter will conclude with a discussion of basic principles that are emerging.
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    ABSTRACT: Fallen trees, recruited by natural catastrophic events, are abundant on the forest floor of many natural forests. They pass through recognizable classes of decomposition, forming a major structural diversity with many ecological functions, and providing habitats for plants, animals, and microorganisms. In greenhouse studies, wood samples collected from within fallen trees decades-old, partially decomposed under both conifer and red alder stands induced effective nodule formation in Alnus rubra, indicating that the fallen trees, devoid of soil and actinorhizal host roots, contained infectious and effective Frankia. Nodule development, growth, and nitrogen fixation were greatest in wood from fallen trees in the alder stand. Frankia is apparently able to live saprophytically or exists in spores in partially decomposed wood.
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