Author (Your Name)

Shayla R. WilliamsFollow

Date of Award


Document Type

Honors Thesis (Open Access)


Colby College. Biology Dept.


Cathy Collins

Second Advisor

Judy Stone

Third Advisor

Russell Johnson


Purple loosestrife (Lythrum salicaria) is a highly invasive species able to quickly take over entire wetlands, especially after disturbances. Bountiful seed production and a persistent and prolific seed bank play a key role in loosestrife’s ability to invade. However, some competing native species, such as cattails (Typha spp.) have comparable seed production rates but less abundant seed banks, suggesting that there may be a difference in belowground seed survival. I investigated the abundance of loosestrife and cattail seeds in soils at roadside sites relative to above-ground stem densities. Given the importance of fungal pathogens to seed viability, I asked whether soil fungi differentially affect seed germination rates of purple loosestrife and cattail species under a variety of soil moisture conditions (dry, well-watered, and saturated). I also examined the proportion of seeds with microbial infections. I found that purple loosestrife is ~20 times more abundant in the soil than cattail in sites with varying aboveground dominance. Fungicide provided a protective effect (i.e. yielded more germinants) for both purple loosestrife and cattail in moist soils, but benefitted only cattails in saturated soils. When I examined the microbes that infected seeds, I found a diverse array of fungi and bacteria, which may explain some of the trends in the fungal/seed bank interactions. Overall, this study indicates that fungal interactions with the seed bank vary between species and are contingent on soil moisture. The results are consistent with the idea that under some environmental conditions, soil-fungi may influence competitive outcomes between invasive loosestrife and native cattails.


Lythrum salicaria, Typha, seed bank, fungi, pathogens, soil moisture