This project was designed to better understand the roles of soil biota in (1) mediating native species to non-native invasive species (NIS) interactions; and (2) facilitating the recovery of degraded ecosystems. The associated Research Needs were listed as follows: (1) to quantify the functional diversity of soil biota and the role of key taxa in maintaining desired functional ecosystem attributes; (2) to identify processes by which desired soil properties and associated soil biotic communities are degraded by NIS invasion and test potential mechanisms to restore them; (3) to examine the role of disturbance in determining the functional attributes of the soil community; (4) to test how the soil community and nutrient cycling may be adversely impacted by regional and global change stressors; (5) to elucidate the role of soil in mediating interactions between native species and NIS; and (6) to provide innovative approaches to the study of soil ecology and their implications for management.
The general goals of this project were to examine the interactive effects of biological invasion and abiotic global change factors on the functional diversity of soil fungi of Northeastern forest habitats. The focus was on on management implications for forests disrupted by the invasive plant species Alliaria petiolata (garlic mustard).
The two main components of the project were: (1) experimental eradications of garlic mustard at multiple sites distributed across regional environmental gradients (climate and nitrogen (N) deposition) in the Northeastern US, taking advantage of Department of Defense (DoD) lands with active invasions; and (2) A controlled invasion of garlic mustard within an existing Long-termerm Ecological Research (LTER) site experiment to test how chronic N fertilization and soil warming interact with phytochemical disruption of the soil biota and the plant community. Following one season of experimental invasion, the researchers planned to eradicate garlic mustard and simulate restoration efforts by transplanting 240 seedlings of red maple and red oak, two dominant native tree species, from locally collected seed stock, which will will allow them to assess the impacts of their treatments on native plant-fungal interactions. The test eradications provide critical high-resolution data for developing NIS control strategies that can be adapted to individual sites, or more broadly across the landscape scale. The report states that the controlled invasion complements these regional observations by demonstrating the interactive impacts of invasion, N deposition, and warming under controlled experimental conditions, and would allow the researchers to disentangle the effects of each factor on plant and soil community response.
The researchers visited and sought permission to work at over fifteen candidate sites for this study and ultimately identified eight study sites in locations with active garlic mustard invasions, including the West Point DoD installation. These sites were strategically distributed across a climatic/N deposition gradient in New England and provided a unique opportunity to observe landscape-level variation in the soil ecological responses to invasion and eradication.
The researchers experimentally eradicated garlic mustard successfully from 2013-2018 and reported their findings related to above and below-ground responses to invasion. The results presented indicate a clear pattern of garlic mustard impacts on both soil microbes and vegetation that is consistently observed across several geographically distributed sites experiencing garlic mustard invasions.
The researchers found that forest patches invaded by garlic mustard consistently have floristic and soil communities that are distinct from nearby patches of forest not affected by the invasion. Invasion is associated with taxonomic and functional shifts in the microbial community that are correlated with biogeochemical processes. Further, the report states that the researchers demonstrated clear effects of garlic mustard on soil biota including fungi and earthworms and expect to publish additional work detailing the effects of eradication on (a) diversity, composition, and function of the soil fungal community; (b) soil carbon and nitrogen cycling; (c) native plant – soil biota feedbacks; and (d) lag times for a-c to recover to reference levels of soil biota structure/function in proximate un-invaded sites.
This is the first study to document impacts of garlic mustard on soil microbes with such high molecular resolution and at a broad landscape scale. The researchers had hoped to take advantage of their experimental invasion to also test how garlic mustard itself is affected by global change factors at no additional cost to the budget, but prioritized the original tasks outlined in the proposal and did not complete this endeavor. The multi-year datasets compiled indicate significant lag times for effective recovery of native vegetation and soil fungal communities, and species that are negatively correlated with invasion.
The researchers' garlic mustard invasion in a long-term global change experiment showed that garlic mustard invasion interacts with warming temperatures and anthropogenic N fertilization to alter the mycorrhizal colonization and growth of red maple seedlings, a key canopy species in the forests at their study sites. Two upcoming publications will detail how these treatments also alter the structure and function of soil fungal communities, fungal gene abundance, and associated carbon (C) & N cycling dynamics.
The researchers determined that warming has the potential to interact with garlic mustard invasion to affect tree seedling performance and thus the impact and success of further invasions, such that tree seedlings are suppressed in response to the combined effects of warming and invasion. They further showed that specific landscape drivers affect forest invasion by garlic mustard using survey data obtained during the site selection process.