Plant-soil feedbacks (PSF), i.e., the reciprocal effects between a plant and the microbiome of the soil it grows in, can alter tree performance and thus species’ local abundance and diversity. PSF have been shown to affect grassland succession, yet their role in the recovery of tropical rainforest remains unknown.
PSF could drive a directional tree species turnover if they affect fast-growing, less well-defended species that are associated with early stages of succession more negatively than better-defended, late-successional species. Host-specific pathogens could moreover favor the recruitment of phylogenetically unrelated successor species and drive diversification. The rate of turnover could be affected by two opposing processes. Increasing microbial diversity could dilute the effect of individual microbial species and reduce the overall community-level strength of PSF with successional time, while decreasing light levels may create temperature and moisture conditions that favour microbial growth in late-successional soils.
In a two-phase greenhouse experiment in Panama, we assessed the interactive effects of successional age of the soil (0, 15, 25 and 115 years of forest recovery) and light level (high vs low) on PSF effects on germination, survival, and biomass of seven tree species that vary in their association from early- to late-successional forests. Subsequently, we inoculated seedlings of three successor species with the soils conditioned in phase one. We compared conspecific vs heterospecific PSF and quantified PSF variation with phylogenetic distance between conditioning and successor species.
We found positive, negative, and neutral PSF. PSF strength and direction varied strongly among species with late-successional species being least susceptible. Overall, species experienced more positive PSF in soils from forests of successional ages that they naturally occur in. Light level strongly, yet inconsistently, modulated PSF. Negative PSF on successor species decreased with phylogenetic distance to conditioning species.
Our results suggest that PSF affect most tree species during secondary succession. Lower susceptibility in late-successional species indicates declining community-level importance of PSF with succession. Positive, species- and soil-age-specific, PSF indicate a higher specificity of mutualistic microbes than historically assumed. This may promote establishment of certain tree species at their associated successional stage and thereby contribute to plant niche differentiation. PSF favoring phylogenetically unrelated successors suggest that PSF can accelerate tree species turnover and diversification. We present evidence that microbial-mediated PSF have a pervasive influence on secondary succession of tropical rainforests by enhancing tree species’ niche differentiation and favoring phylogenetic diversification over time.
fungi, mycorrhizae, forest regeneration, community assembly, tree species turnover