Abstract
Soil resources derived from mutualistic arbuscular mycorrhizal fungi (AMF) play a critical role in the physiological function of many native plant species. Allelopathic plant invasion studies have revealed declines in AMF inoculation potential of invaded soils, and lost opportunities for plants to form new AMF associations. Yet, if allelochemicals also kill AMF external hyphae already associated with plant roots, this mutualism disruption should result in physiological stress for native plants. We previously demonstrated that forest soils infested with garlic mustard (Alliaria petiolata), an allelopathic invader, exhibit reduced fungal hyphal abundance. Here, we demonstrate for the first time that treatment with garlic mustard tissue reduces soil respiration rates and diminishes physiological function of false Solomon's seal (Maianthemum racemosum), an AMF-dependant forest understory native. Treated plants exhibited reduced stomatal conductance and photosynthesis relative to controls, consistent with the proposed loss of AMF function. Such physiological declines, if sustained over several growing seasons, could decrease native understory perennials' growth rates and increase their susceptibility to environmental stresses. These data provide an explicit mechanism that can help explain the loss of established native perennials from invaded mature forests. We propose that the physiological costs of mutualism disruption may be a widespread but previously untested mechanism enhancing the invasion of undisturbed ecosystems by allelopathic species.
Highlights
Plants rely on mutualistic interactions for a number of services that are vital for reproduction, defense, dispersal, and nutrient acquisition
Our field experimental data clearly demonstrate that short-term exposure to garlic mustard tissue, an allelopathic invasive species, can significantly reduce the physiological function of a native understory herb, false Solomon’s seal
Stomatal conductance in garlic mustardtreated false Solomon’s seal adults was reduced by 36%, with concomitant reductions in transpiration (E; 25%) and photosynthesis (An; 17%) compared to controls (Fig. 4A–C)
Summary
Plants rely on mutualistic interactions for a number of services that are vital for reproduction, defense, dispersal, and nutrient acquisition. Up to 20% of a plant’s carbon is shunted to the obligately symbiotic AMF, while AMF improve the supply of water, phosphorus and nitrogen to the plant (Smith and Read 2008). As a result of the numerous benefits that plants derive from AMF, these belowground mutualists can strongly influence the physiology (Fig. 1), overall carbon gain, and likely the competitive ability of their host plants. Disruption of this key plant mutualism is hypothesized to facilitate invasion (Mitchell et al 2006, Reinhart and Callaway 2006 )
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