The organization of plant communities: negative plant-soil feedbacks and semiarid grasslands.

Understanding how plant communities are organized requires uncovering the mechanism(s) regulating plant species coexistence and relative abundance. Negative soil feedbacks may affect plant communities by suppressing dominant species, causing rarity of most plants, or reducing the competitive abilities of all species. Here, three soil feedback experiments were used to differentiate the effects of soil feedbacks on mid- to late-successional and semiarid grasslands. Then I tested whether the direction and degree of soil feedback accounts for variation in relative abundance among species that coexist within each plant community. Negative soil feedbacks predominated across all species and sites and were individually discernible for 40% of plant species. Negative soil feedbacks affected rare to dominant plant species. Negative soil feedbacks, capable of having negative frequency-dependent effects, have the potential to act as a fundamental driver of species coexistence.