Plant-soil microbe feedbacks depend on distance and ploidy in a mixed cytotype population of Larrea tridentata

Premise of the study

Theory predicts that mixed ploidy populations should be short-lived due to strong fitness disadvantages for the rare ploidy. However, mixed ploidy populations are common, suggesting that the fitness costs for rare ploidies are counterbalanced by ecological benefits that emerge when rare. We investigated whether differences in ecological interactions with soil microbes help to maintain a tetraploid-hexaploid population of Larrea tridentata (creosote bush) in the Sonoran Desert, California, USA, where prior work documented ploidy-specific root-associated microbes.

Methods

We used a plant-soil feedback (PSF) experiment to test whether host-specific soil microbes can alter the outcomes of intra-ploidy vs. inter-ploidy competition. Host-specific soil microbes can build up over time; thus, distance from a host plant can affect the fitness of nearby plants.

Key results

Seedlings grown in soils from near plants of a different ploidy produced greater biomass relative to seedlings grown in soils from near plants of the same ploidy. Moreover, seedlings grown in soils from near plants of a different ploidy produced greater biomass than those grown in soils from further away from plants of a different ploidy. This suggests the ecological consequences of PSF may facilitate the persistence of mixed ploidy populations.

Conclusions

This is the first evidence, to our knowledge, consistent with plant-soil microbe feedback as a viable mechanism to maintain the coexistence of multiple ploidy levels in a single population.