Consideration of “mycorrhizal type” as a plant functional trait (i.e. which broad groups of mycorrhizal fungi a plant associates with, if any) has led to several recent advances in the fields of plant ecology and biogeography. Although studies of plant roots that consider mycorrhizal fungi are now reasonably common there are many other plant-fungal interactions taking place both within the rhizosphere, and within plant roots. Even species which are considered to have a specific mycorrhizal type may still interact with other mycorrhizal fungi. The interactions within and between mycorrhizal, endophytic, saprotrophic, and pathogenic fungi are likely to have important consequences for plant growth and health, which may be reflected in their fine root traits. Here we asked whether there was any evidence that the whole community of root or rhizosphere fungi corresponded to differences in seedling root traits along a disturbance gradient. We examined the fungal communities associated with seedling roots in an oak habitat restoration project on the Edwards Plateau in Central Texas. Entire seedlings were excavated from six replicate plots of three habitat treatments along a disturbance gradient (living canopy, dead canopy, open canopy). Fine root traits were quantified, including ectomycorrhizal root tip density, and Illumina MiSeq sequencing of fine root and rhizosphere soil fungal communities was applied.
Results/Conclusions
Oak seedlings grown from acorns under living canopy had a significantly greater density of fine root tips per unit biomass than those grown under dead canopy. We observed that seedling fine root density in general appeared to be influenced by the proximity of living mature oak fine roots. This was even the case for surviving seedlings in open patches, which were influenced by nearby roots attached to trees that were in some cases more than 11m away. Approximately 92 million fungal ITS sequences were obtained across all root and soil samples. As expected, endophytic and mycorrhizal fungi were the most abundant in terms of sequence numbers in root samples, whereas mycorrhizal and saprotrophic fungi were most abundant in associated soils, reflecting the lifestyle and hyphal distribution of these trophic groups. While ectomycorrhizal fungi appeared responsible for much of the variance in fine root traits, other groups of fungi varied in their contributions. However, the sequence abundance of ectomycorrhizal fungi was not well correlated with the abundance of observed ectomycorrhizal root tips, supporting caution when using fungal sequence abundance in studies of fine root traits.