Evaluating alder-endophyte (Alnus acuminata-Frankia-Mycorrhizae) interactions

The objective of this study was to compare the interaction betweenFrankia and vesicular-arbuscular mycorrhizae (VAM) on the growth and N-fixing response ofAlnus acuminata seedlings under three different phosphorus levels.A. acuminata is an actinorhizal tree, commonly associated with pastures on upland areas. Seedlings were grown in sterile vermiculite, and inoculated withFrankia strain ArI3 and/or VAM (asGlomus intra-radices) under three phosphorus levels (10, 50 and 100 ppm). After 120 days differences in growth were observed at the 50 ppm P level between nodulated and non-nodulated plants; either if inoculated withFrankia+VAM or just with VAM. Interaction betweenFrankia and VAM was positive on nodule weight at 50 ppm P level. Differences in acetylene reduction, per gram of fresh nodule, were observed between and within both groups:Frankia inoculated andFrankia+VAM inoculated seedlings. InFrankia inoculated seedlings differences were observed between seedlings receiving 50 ppm P which showed higher nitrogenase activity than seedlings treated with 100 ppm P. Plants inoculated withFrankia andGlomus intra-radices at low P level (10 ppm) showed the highest acetylene reduction. It was 150% higher than the mean of the other treatments within the group, and 87% higher than the general mean of the onlyFrankia inoculated plants.