Invasive alien plants can alter the ecosystem functions and soil health. Here, we investigate the impact of Rhododendron ponticum on the processes involved in the transformation of carbon in forest ecosystems. The hypotheses relating to its impacts are based on three pathways: (1) a modification of abiotic conditions leading to lower soil temperature and moisture, (2) the input of recalcitrant litter limiting microbial activity, and (3) an intensification of the impacts over time (12–63 year invasions). We assess this function using several indicators measuring degradation rates (k), stabilization factors (S), microbial activity (BR) and oxidizable carbon (POXC). We show that R. ponticum modifies the microclimate of invaded soils, but these changes have no direct effect on the carbon transformation function, which is more influenced by its litter input. The accumulation of recalcitrant litter leads to an average thickness increase twice as high in invaded sites. The magnitude of these impacts also depends on the context, in particular the duration of the invasion and the composition of the forest canopy composition. Organic matter decomposes more slowly in the early stages of invasion, but rates return to levels comparable to invaded sites after 30 years. Conversely, microbial activity increased at the beginning of the invasion and then declined as the invasion age progresses. These results suggest a long-term adaptation of microbial communities and underline the importance of integrating the temporal dimension into the assessment of the effects of invasive alien plants on soils.
Jeune et al. (Sat,) studied this question.