Plant landscape abundance and soil fungi modulate drought effects on plant-soil feedbacks

Plant-soil feedbacks (PSF) play an important role in determining plant
community structure and dynamics. However, previous studies have provided
mixed results for the relationship between PSF and plant landscape
abundance (i.e., abundance across local communities). This may reflect the
mediation of climate factors on PSF. Here, we tested how PSF of tree
species varied with local abundances by growing seedlings in conspecific
versus heterospecific soil and how simulated drought altered PSF-plant
abundance relationships. Six tree species were selected and half of the
seedlings were grown under ambient moisture conditions, while the others
experienced a 2-month period of drought following 3-months of growth under
ambient moisture conditions. Fungal communities in the rhizosphere soil
were analysed using DNA amplicon sequencing to link shifts in soil fungi
to the observed PSF. We found that drought reduced negative PSF for all
plant species except one species (Lithocarpus lohangwu). In the drought
treatments, PSF were positively correlated with the relative abundance of
total putative pathogens, but negatively correlated with the proportion of
unique pathogens (those pathogens that were present in conspecific soil
rather than heterospecific soil, thereby potentially species-specific). In
addition, we found that PSF only significantly predicted plant relative
abundance in the drought treatment, indicating that abiotic stress made
PSF a stronger predictor of plant landscape abundance. This finding also
implies that future extreme drought events could promote the dominance of
the abundant plant species, thereby leading to the loss of biodiversity.
Collectively, our results provide evidence for microbial mechanisms of PSF
and suggest that accounting for abiotic stress can make PSF a stronger
predictor of plant landscape abundance due to the omnipresence of stress
under natural conditions.