Rhizosphere soil fungal communities vary by host genotype and influence host performance during drought

Background/Question/Methods: Models of vegetation response to climate change rarely incorporate intraspecific genetic variation in plants or the influence of plant associated micro-organisms. We used field, common garden and greenhouse studies of pinyon pine to examine how plant genetic variation affects drought tolerance, belowground fungal and bacterial species composition and their interaction. Previous studies have shown that mature pinyon pines vary markedly in growth and drought-related mortality and that these differences are also associated with variation in ectomycorrhizal fungal community composition. Here we report the results of studies of the offspring of these drought tolerant and drought intolerant trees planted in a common garden. We measured seedling mortality and growth and used Illumina sequencing of bacterial 16S V4 and fungal ITS2 amplicons to describe the rhizosphere fungal and bacterial community. We also conducted a greenhouse experiment to determine if variation in soil microbial community composition influenced seedling performance.   

Results/Conclusions: We found that: 1) the mortality and growth patterns of the offspring of drought tolerant and drought intolerant trees was similar to that of their mothers, suggesting a strong genetic basis to performance during drought. 2) Also similar to patterns observed in their mothers, seedlings of drought tolerant versus intolerant mothers had different ectomycorrhizal fungal communities as measured using Sanger sequencing of root tips and next generation sequencing of the surrounding soil. Similar results were observed for the entire fungal community, though differences were less strong. The most common taxa of ectomycorrhizal fungi belonged to three families, the Pyronemataceae, Thelephoraceae, and Rhizopogonaceae, two of which are known for their tolerance of drought. 3)  In contrast to our observations with fungi, rhizosphere bacterial communities were similar in both groups of seedlings. 4)  Greenhouse inoculation experiments showed that the soil communities associated with drought tolerant pinyons promote growth significantly more than those of drought intolerant pinyons under dry conditions. Taken together, these results show that soil fungal communities vary among host genotypes grown in a common environment and that this variation influences host plant performance. Our results also indicate that maintenance of forest genetic diversity will promote greater soil fungal diversity.