Plant invasions not only pose major threats to the native biodiversity, but also potentially impact ecosystem stability and functions such as soil carbon (C) storage and cycling. Although much research has explored the effect of plant invasion on the quantity of soil C pools, questions remain as to whether the chemical components of soil organic C (SOC) will be influenced by the invasion of exotic plant species. Meanwhile, elevated nitrogen (N) associated with global change is predicted to promote plant invasion. However, how N availability modulates the effects of plant invasion on the accrual, composition, and stability of SOC remains largely unexplored.
We addressed these two questions by conducting a 10-year mesocosm experiment simulating the invasion of Polygonum cuspidatum (Japanese knotweed) into a fallow soil, coupled with a contemporary N fertilization scheme for the invasive plants. Using paired invaded and noninvaded plots as well as paired invaded and invaded + fertilized plots, we investigated the invasion effects on the chemical composition of various SOC components (i.e., plant- and microbial-derived C) at the molecular level. We further examined how these effects of plant invasion responded to altered soil N availability. We also quantified the soil microbial biomass, community composition, and enzyme activities to elucidate potential mechanisms driving the variation of SOC compositions.
Results/Conclusions
Compared with noninvaded soils, knotweed-invaded soils exhibited a 17% increase in the microbial-derived C, mainly through the accumulation of fungal residue in the form of amino sugars. Despite receiving leaf litter which was abundant in polyphenolic compounds, knotweed-invaded soils did not show a significant difference in the abundance of plant-derived compounds (plant lipids and lignin monomers) compared to noninvaded soils inhabited by grasses. N fertilization increased the retention of plant-derived recalcitrant structures in knotweed-invaded soils, but also stimulated the degradation of lignin monomers. Moreover, knotweed-invaded soils accumulated 46% more microbial-derived C under N enrichment, primarily due to the altered microbial biomass and community composition. Collectively, our findings suggest that plant invasion has the potential to influence SOC chemical composition, with microbial-derived C fractions showing a higher sensitivity relative to plant-derived C. Furthermore, N fertilization could modulate the invasion effects on molecular composition and accrual of SOC. Our results also highlight the need to understand the impacts of biological invasion in the context of other global change drivers that both affect invasions and modulate their effects.