University of Vermont Burlington, VT, United States
Ericoid mycorrhizal fungi (EMF) form symbiotic relationships with ericaceous plants such as Vaccinium corymbosum, or highbush blueberry and assist in nutrient acquisition. EMF provide nutrients to plants in environments where nutrients are lacking. In plant-mycorrhizal symbioses, nutrient uptake kinetics may be dependent on the identity of the fungal partner. Therefore, differently sourced mycorrhizal fungi could show differences in nutrient uptake ability. Here, I hypothesized that inoculation of V. corymbosum plants with EMF would allow plants to compensate for low nutrient conditions, but the degree of compensation would depend on soil nutrient conditions. To test this, I used 135 potted highbush blueberry plants that were inoculated at planting with either 1) commercial inoculum, 2) local inoculum, or 3) uninoculated control. Within these, I haphazardly assigned 15 plants to one of three fertilizer treatments: i) the recommended amount of fertilizer added (10 ml), ii) half the recommended amount of fertilizer (5 ml), and iii) no fertilizer. I predicted that plants inoculated with EMF from local soils would be better able to access scarce nutrients than those inoculated with commercial inoculum or non-inoculated controls, and the effects would be measurable through increased plant growth and reproduction.
Plants inoculated with local and commercial EMF that were not fertilized did not differ in plant size from non-inoculated fertilized plants. However, plants with the local soil inoculum produced significantly more flowers (F2,108=11.315; P< 0.0001) and berries (F2,106=11.80; P< 0.0001) than both the commercial inoculum and control treatments. However, plants inoculated with the commercial inoculum produced significantly larger berries (F2,83=3.407; P=0.0378) than those with the local soil inoculum, suggesting a size-number tradeoff. Plants inoculated with local soil and given the recommended amount of fertilizer showed the greatest effect on reproduction compared to the control. These results add to growing evidence that the outcome of interactions among mycorrhizal fungi and their plant hosts depend on fungal identity, and EMF have the potential to act as a biofertilizer complement in combination with soil nutrients to achieve greater reproductive success, or yield.