Characterization and analysis of the succession of endophytes in decaying leaves in Manistee National Forest, MI

Background/Question/Methods

Endophytes fill a niche within the fungal community which has not been thoroughly characterized. They usually live asymptomatically as symbionts within plant tissues. Upon senescence a leaf presents an ideal resource that many fungi compete for and exploit. Saprotrophic fungi can utilize this resource using a complex array of extracellular enzymes. Endophytes may be able to exploit this niche due to their pre-existing colonization of plant tissue. If endophytes indeed take advantage of the senesced leaf, they could effectively become saprotrophic. This study focuses on the characterization and analysis of the succession of endophytes isolated from living and decaying leaves in Manistee National Forest, MI. Leaves of Acer saccharum, Quercus rubra, Quercus velutina, Quercus alba and Tilia americana trees were collected at three successional stages: living, recently senesced and decayed. Subsamples of the leaveswere surface sterilized and used to inoculate nutrient plates. The fungal isolates growing off of the plates were then subcultured. From the many cultures obtained, ten isolates from living leaves, tentatively classified as endophytes, and twenty from decayed leaves, thought to be saprotrophs, were placed into individual microcosms of sterile leaf litter. Leaf litter sampled from each microcosm was taken for enzymatic characterization and biomass.

Results/Conclusions

Approximately 375 separate fungal colonies were grown from the inoculated plates.  These colonies were categorized into 68 distinct morphotypes, based upon visual observation. Morphotypes only isolated from decayed leaves made up 70%, 17% represent both living and decayed, and 10% represent isolates obtained from living leaves only. MANOVA analysis of data indicated that the presence or absence of fungal morphotypes was significantly affected by the decay stage (p-value<0.0001) and ecosystem of the leaves (p-value <0.0001). Enzymes generated by fungal isolates contained within microcosms after one week did not appear to show significant differences in the cellulose and lignin degrading enzyme activity. This study appears to show that several morphologically similar fungi can be found in fresh and decaying leaves. This gives some indication that endophytes may become saprotrophic under certain conditions. The enzyme data gives some evidence in this direction due to the lack of differences in cellulytic and lignonlytic activity.