Abstract
The impacts of invasive species on biodiversity may be mitigated or exacerbated by abiotic environmental changes. Invasive plants can restructure soil fungal communities with important implications for native biodiversity and nutrient cycling, yet fungal responses to invasion may depend on numerous anthropogenic stressors. In this study, we experimentally invaded a long-term soil warming and simulated nitrogen deposition experiment with the widespread invasive plant Alliaria petiolata (garlic mustard) and tested the responses of soil fungal communities to invasion, abiotic factors, and their interaction. We focused on the phytotoxic garlic mustard because it suppresses native mycorrhizae across forests of North America. We found that invasion in combination with warming, but not under ambient conditions or elevated nitrogen, significantly reduced soil fungal biomass and ectomycorrhizal relative abundances and increased relative abundances of general soil saprotrophs and fungal genes encoding for hydrolytic enzymes. These results suggest that warming potentially exacerbates fungal responses to plant invasion. Soils collected from uninvaded and invaded plots across eight forests spanning a 4 °C temperature gradient further demonstrated that the magnitude of fungal responses to invasion was positively correlated with mean annual temperature. Our study is one of the first empirical tests to show that the impacts of invasion on fungal communities depends on additional anthropogenic pressures and were greater in concert with warming than under elevated nitrogen or ambient conditions.
Highlights
Plant invasions are increasing at historically unprecedented rates (Seebens et al 2018), and interactions with abiotic global changes may further promote establishment and spread of non-native species beyond their home ranges (Milchunas and Lauenroth 1995; Howard et al 2004)
Fungal biomass was reduced by 43% in the two-factor warming × invasion plots in the organic horizon relative to control plots (Table 1)
Our study demonstrates that soil warming was Warming altered fungal community structure and increased invasibility to garlic mustard Garlic mustard invasion profoundly restructures temperate forest understories
Summary
Plant invasions are increasing at historically unprecedented rates (Seebens et al 2018), and interactions with abiotic global changes may further promote establishment and spread of non-native species beyond their home ranges (Milchunas and Lauenroth 1995; Howard et al 2004). The interactive effects of multiple anthropogenic global change drivers are widely recognized as important in determining future ecosystem functioning; less than 1% of all global change studies in soil ecology have tested interactions between biotic invasion (plant, animal, or microbes) and other global change factors (Rillig et al 2019). We currently lack an empirical assessment of how belowground ecosystem structure and function respond to simultaneous invasion and abiotic global changes. Most terrestrial plants host a belowground consortium of microorganisms, including fungi, which affect how ecosystems respond to invasion (Inderjit and van der Putten 2010). How fungi respond to invasion can feed-back to impact native plant communities (Stinson et al 2006), soil carbon (C) storage (Ehrenfeld 2003; Tamura and Tharayil 2014), and ecosystem restoration efforts (Lankau et al 2014; Anthony et al 2019). Fungi are highly sensitive to abiotic stressors such as warming and nitrogen deposition (Lilleskov et al 2011; Geml et al 2015; Morrison et al 2016; Fernandez et al 2017), but the interactive effects of invasion and concurrent abiotic global changes on soil fungi are rarely investigated (Wheeler et al 2017)
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