Direction of Alliaria petiolata (garlic mustard) leachate's effect on early litter mass loss is dependent upon saprotrophic community composition

Abstract

Differences between fungal and bacterial decomposition trajectories can be related to differences in sensitivity to nutrient input and to plant secondary metabolites. The invasive plant Alliaria petiolata (Beib. Cavara and Grande; garlic mustard) produces unique secondary metabolites (glucosinolates) capable of altering the functioning of root-associated communities. However, few studies explore whether these compounds can alter litter decomposition— a route for ecosystem-level impacts of garlic mustard invasion. This preliminary study investigated the potential for aqueous garlic mustard leachate to alter mass loss from tea litterbags in artificially fungal-dominant compared to intact soils (fungal and bacterial components) in laboratory microcosm incubations. Garlic mustard and native Acer saccharum (Marsh.; sugar maple) leachates stimulated fungal decomposition indistinguishably. In intact soils, garlic mustard suppressed mass loss relative to a water control and native leachate, though this later effect was only marginally significant. These results suggest the energetic benefit of labile carbon in garlic mustard leachate may exceed any negative effect of glucosinolates for fungal decomposers, but that bacteria were more sensitive to leachate toxicity and the inhibitory effects of high nutrient input. Overall, our results imply the direction of garlic mustard's effect on decomposition may depend on saprotrophic community composition and therefore the consequences for litter decay in garlic mustard invaded soils may be context-dependent.