Seasonal variation in mycorrhizal fungi colonizing roots of Allium tricoccum (wild leek) in a mature mixed hardwood forest.

The community of arbuscular mycorrhizal (AM) fungi colonizing roots of the forest herb Allium tricoccum Ait. (wild leek) was examined to assess whether colonization varied seasonally and spatially within the forest. Whole plants were collected to coincide with observed phenological stages, and the perennial tissue (i.e., the bulb) was used to analyze total C, N, and P over the growing season. AM fungal community composition, structure, and abundance were assessed in roots by terminal restriction fragment length polymorphism analysis and quantitative PCR. It was found that A. tricoccum rDNA co-amplified using the general AM primers NS31/AM1, and a new primer for qPCR was designed that discriminated against plant DNA to quantify AM colonization. Community structure of AM fungi did not vary seasonally, but did change spatially within the forest, and AM fungal communities were correlated with the presence of overstory tree species. Fungal colonization of roots, however, did change seasonally with a maximum observed in late winter and early spring following leaf emergence. Maximum AM fungal colonization was associated with declines in bulb N and P, suggesting that leaf emergence and growth were responsible for both declines in stored nutrients and increases in AM fungal colonization. Plant N and P contents increased between late summer and early spring while C contents remained unchanged. The observed increase in nutrient content during a time when A. tricoccum lacks leaves indicates that the roots or AM fungi are metabolically active and acquire nutrients during this time, despite an absence of photosynthesis and thus a direct supply of C from A. tricoccum.