Microbe-mediated plant-soil feedback in pioneer stages of secondary succession causes long-lasting historical contingency effects in plant community composition.

Soil microbes and soil fauna have been assumed to play a key role in interspecific plant competition and successional community development. It has been suggested that plants can influence their performance by changing the composition of their associated soil communities. Such feedback effects may be essential to explain temporal plant community dynamics. In a two-phase greenhouse feedback experiment we tested the hypothesis that in secondary succession on ex-arable land, species-specific plant-induced changes in soil microbial community composition reduces the competitive ability of early-successional plant species compared to mid-successional species. Plant-soil feedback was tested by growing early-successional plants in monocultures and in competition with mid-successional species in soils cultured by conspecifics and by heterospecifics. Subsequently, we tested the hypothesis that soil microbes are involved in these plant-soil feedbacks by isolating the microbial component from the soil community and re-inoculating these in a third phase of the experiment. Molecular techniques were used to characterize fungal and bacterial rhizosphere communities in order to determine the identity of the microbes involved in the observed effects. Our results show that plant-soil feedbacks significantly reduced the performance of early-successional plant species in mid-successional plant communities. Therefore, we propose that feedback between early-successional plants and the microbial component of the soil community may influence plant community dynamics during early stages of secondary succession following land abandonment. Our results also showed that the performance of mid succession plant species may depend on the plant colonization history during early secondary succession. When the soil has been colonized by early-successional grasses, mid-successional grasses will perform worse than mid-successional forbs. Therefore, plant-soil feedback may provide a biotic legacy effect to the soil community that influences the composition of mid-successional plant communities