Jd. Vonderwell et Sa. Enebak, Differential effects of rhizobacterial strain and dose on the ectomycorrhizal colonization of loblolly pine seedlings, FOREST SCI, 46(3), 2000, pp. 437-441
Loblolly pine seed were inoculated at sowing with one of four plant growth-
promoting rhizobacteria (PGPR) strains at four different rates both in the
nursery and in the greenhouse. Seedlings were harvested at 4, 8, and 12 wk
after sowing in the greenhouse and at 5, 10, and 15 wk after sowing in the
nursery. Ectomycorrhizae colonization, estimated as the total number ectomy
corrhizal roots per seedling and averaging by gram root biomass, were not e
vident on any treatment at either 5 wk in the nursery or 4 wk in the greenh
ouse. However, by 8 wk after sowing, many treatments significantly (P < 0.0
001) inhibited ectomycorrhizal root formation. Generally, increasing the ra
te of all bacteria applied in the greenhouse decreased ectomycorrhizal root
formation. Conversely, strain LS212 at 10(11) cfu resulted in an increase
in ectomycorrhizal roots in the nursery. Increases in seedling root growth
were also dependent on bacterial strain and rate, whereas shoot biomass was
not effected. Decreases in ectomycorrhizae colonization accounted for 61%
of the variation in increases in root biomass, suggesting high metabolic co
sts of mycorrhizal maintenance in the presence of some rhizobacteria. Howev
er, differences in shoot height and survival after outplanting could not be
attributed to the mycorrhizae colonization effect. These studies demonstra
te that mycorrhizae may serve as a carbon sink early in seedling developmen
t and indicate a complex interaction between soil microflora and bacterium
in nursery and greenhouse settings.