Sc. Jeong et Dd. Myrold, Population size and diversity of Frankia in soils of Ceanothus velutinus and Douglas-fir stands, SOIL BIOL B, 33(7-8), 2001, pp. 931-941
The influence of host plants on Frankia populations was investigated using
soils from Ceanothus velutinus (Dougl.) and Douglas-fir (Pseudotsuga menzie
sii (Mirb.) Franco) stands. Population sizes of Ceanothus-infective Frankia
in the soils were measured using plant bioassays with C. velutinus. C. san
guineus (Pursh), and C. integerrimus (H. & A.) as trap plants. The Frankia
population in soil from the C. velutinus stand soil was about 10 times high
er than that from the Douglas-fir stand. This result supports previous repo
rts that, although the presence of host plants increases Frankia population
s. Frankia persist without host plants, Nodulation capacities of the three
trap plants were not significantly different. All nodules showed N-2 fixati
on activity using the acetylene reduction assay. The diversity of Frankia t
hat nodulated trap plants was examined using repetitive intergenic DNA and
the polymerase chain reaction (rep-PCR). A newly designed, direct repeat se
quence and a BOX sequence were used as rep-PCR primers. The results showed
that infective Frankia in the two soils contained a common group of Frankia
as well as some Frankia strains unique to each soil. The level of host spe
cificity of the infective Frankia was low; however, one group of Frankia no
dulated only C. integerrimus seedlings. Taken together, the results suggest
that the higher populations in the soil from the C. velutinus stand may be
due to preferential increases in particular groups of Frankia. (C) 2001 El
sevier Science Ltd. All rights reserved.