Survival of Native Arbuscular Mycorrhizal Inoculum Following Transplanting of Wyoming Big Sagebrush
Inoculation of seedlings with arbuscular mycorrhizal fungi (AMF) is a common practice aimed at improving seedling establishment. The success of this practice largely depends on the ability of the inoculum to multiply and colonize the growing root system after transplanting. These events were investigated in Wyoming big sagebrush (Artemisia tridentata ssp. wyomingensis) seedlings inoculated with native AMF. Seedlings were first grown in a greenhouse in 50 ml containers containing sterilized pot cultures (control seedlings) or pot cultures having a mixture of six mycorrhizal phylotypes (inoculated seedlings). In early spring, two-month old seedlings were transplanted to 24 L pots filled with soil collected from a sagebrush habitat and grown at the Idaho Botanical Gardens in Boise under natural climatic conditions. At the time of transplanting the percent colonization was 0.3 and 57% for control and inoculated seedlings, respectively. In mid-July, the roots had reached depths of 40 cm and by early October reached 80 cm. In July, there was a significant difference in colonization with average values of 18 and 42 % for control and inoculated seedlings, respectively. Similarly, in October inoculation had a significant effect on percent colonization, but there was a significant interaction between inoculation and root depth. The roots collected from the upper half of the pots showed significant differences in colonization with values of 18 and 48% for control and inoculated seedlings, respectively. In contrast, no significant difference in colonization was detected in roots collected from the lower half of the pots, which had average values of 22% for both treatments. Overall, our results indicate that the inoculum contributed to the colonization of the roots that developed after transplanting resulting in higher levels of colonization than those naturally occurring in the soil. These differences in colonization were associated with differences in seedling survival, which was 24% higher in inoculated than control seedlings.