Much evidence in the past 20 years has pointed to plant-soil feedbacks (PSF) as a driver of plant performance, population, and community dynamics. For example, PSFs have been shown to alter competitive dynamics among hosts, contribute to coexistence of plants in the community, and explain patterns of plant species commonness and rarity. Less is known, however, about how PSFs alter temporal plant community dynamics such as turnover and stability, and no study has yet demonstrated these relationships in the field, across different life stages of the host plant. We conducted a field experiment to link the strength of PSF to plant community stability. We first quantified long-term dynamics of two dominant desert grasses along a 400m transect, and identified areas that showed spatial variability in the rates of vegetation composition change. Regions of dynamic vegetation history show frequent changes in species relative abundances, whereas static regions show stable coexistence through time. Then, we measured the strength of PSF in dynamic and static regions in the field using experimental transplants. We asked: 1) Do the strength and direction of PSF differ between regions of static and dynamic vegetation history? 2) If so, does the relationship change with plant ontogeny?
Results/Conclusions
PSF was more negative in regions of static vegetation history than dynamic. B. gracilis experienced significantly positive feedback in dynamic regions, and significantly negative feedbacks in static regions. This was explained by B. gracilis plants experiencing “away” soils being 90% larger than seedlings in “home” soils, and 87% larger than seedlings in “sterile” soils in static regions. In dynamic regions, B. gracilis plants experiencing “away” soils were 21% smaller than “home” soil counterparts, and 10% smaller than those in “sterile” soils. This suggests increased fungal mutualists when B. gracilis leave their home environment in static regions, compared to increased pathogens in dynamic regions. B. eriopoda feedbacks on average were not significantly different from neutral in either vegetation history type. Survival was 65% higher for B. gracilis seedlings than B. eriopoda seedlings, and 34% higher in static regions compared to dynamic region for both species, but did not differ among PSF treatments. Germination was also higher for B. gracilis seedlings, but contrary to survival, was higher in dynamic regions for B. gracilis. We found no differences in soil nutrients, texture, temperature, or moisture in regions of different vegetation history that could explain the different patterns of long-term community stability dynamics.