Understanding belowground community regulation in an invaded forest
Doctor of Philosophy
Soil organisms have the potential to strongly influence plant species performance and survival and are in turn influenced by interactions with plants. These interactions can cause changes in the soil biota that influence the performance and survival of plant species and affect plant species composition, biodiversity, and exotic invasion potential. These plant-soil feedbacks are especially important in plant communities because plants are immobile. Yet, little is known about plant species feedbacks in temperate forest communities or the differences between native and non-native plant species in their soil feedbacks. These differences in soil feedbacks between non-natives and natives are important because they may influence successful invasions into plant communities. I utilized laboratory and field experiments in Big Thicket National Preserve to evaluate the role of plant-soil feedbacks on the community structure and invasion potential of temperate forests. Sapium sebiferum (Chinese Tallow tree) experiences unusual benefits from interactions with belowground biota in fertilized environments, particularly mycorrhizae, when establishing in newly invaded areas. This may provide Sapium with a performance advantage over natives in the forest understory and facilitate its invasion into temperate forest communities currently experiencing increased anthropogenic nutrient inputs. Fertilization also causes changes in mycorrhizal investment patterns, favoring internal fungal growth and storage instead of nutrient gathering and exchange. These belowground shifts in mycorrhizal composition may be one factor favoring the success of woody dominants, including Sapium , over obligately mycorrhizal grassland species in coastal prairies. However, Sapium , unlike native trees, experiences extremely negative plant-soil feedbacks in just one generation beneath Sapium adults from the accumulation of host-specific pathogenic soil fungi. This negative soil feedback may reduce Sapium seedling recruitment and will likely reduce Sapium persistence in heavily invaded areas and allow for replacement by native species. These results suggest that feedbacks exerted by native soil communities on non-native species can have important consequences for the establishment and persistence of invading species.