Effects of the invasive plant garlic mustard (Alliaria petiolata) on bacterial communities in a northern hardwood forest soil.

We compared the effects of the invasive plant Alliaria petiolata (garlic mustard) and 2 native plants on soil bacterial communities in a mature mesophytic forest. Soil samples were collected from plant patches containing either Alliaria or the native plants Allium tricoccum (wild leek) and Gallium triflorum (bedstraw). Since Alliaria litter contains secondary compounds that have reported antimicrobial properties, soil was collected outside the root zone of the plants but within the plant patches such that the soil would have been influenced by the litter of the respective plant species but not by plant roots. DNA was extracted from the soil samples and used to amplify the 16S rRNA gene region using bacterial specific primers. Terminal restriction fragment length polymorphism (TRFLP) profiles of each bacterial community were used to examine differences in bacterial communities among the plant species and between August and April sampling. Bacterial richness, evenness, and diversity were not significantly affected by plant species. Non-metric multidimensional scaling (NMS) suggested that differences existed between August and April sampling, but that plant species litter exerted a much weaker effect on soil bacterial communities. Soil physiochemical conditions were significantly correlated with soil bacterial communities and may underlie the observed seasonal changes in bacterial communities.

Vegetation and soil environment influence the spatial distribution of root-associated fungi in a mature beech-maple forest.

Although the level of diversity of root-associated fungi can be quite high, the effect of plant distribution and soil environment on root-associated fungal communities at fine spatial scales has received little attention. Here, we examine how soil environment and plant distribution affect the occurrence, diversity, and community structure of root-associated fungi at local patch scales within a mature forest. We used terminal restriction fragment length polymorphism and sequence analysis to detect 63 fungal species representing 28 different genera colonizing tree root tips. At least 32 species matched previously identified mycorrhizal fungi, with the remaining fungi including both saprotrophic and parasitic species. Root fungal communities were significantly different between June and September, suggesting a rapid temporal change in root fungal communities. Plant distribution affected root fungal communities, with some root fungi positively correlated with tree diameter and herbaceous-plant coverage. Some aspects of the soil environment were correlated with root fungal community structure, with the abundance of some root fungi positively correlated with soil pH and moisture content in June and with soil phosphorous (P) in September. Fungal distribution and community structure may be governed by plant-soil interactions at fine spatial scales within a mature forest. Soil P may play a role in structuring root fungal communities at certain times of the year.