Plant-soil feedbacks contribute to coexistence when considering multispecies assemblages over a soil depth gradient

Area of Science:

• Ecology
• Plant Ecology
• Community Ecology

Background:

• Plant-soil feedbacks (PSFs) are crucial for plant species coexistence, but their effects can be context-dependent, often destabilizing coexistence by increasing fitness differences.
• Most research on PSFs has utilized simplified pairwise models in controlled greenhouse environments, leaving their role in complex, multispecies field communities largely unexplored.

Purpose of the Study:

• To investigate the role of plant-soil feedbacks (PSFs) in determining plant species coexistence within a semiarid grassland ecosystem across a hydric gradient.
• To analyze how PSFs influence pairwise and multispecies community stability and fitness differences under natural field conditions.
• To determine the contribution of PSFs to overall diversity maintenance in relation to environmental conditions and species richness.

Main Methods:

• Estimated PSF strengths for 17 plant species and analyzed pairwise and multispecies coexistence dynamics over a hydric gradient.
• Quantified species stability and fitness differences, and computationally modeled multispecies communities to assess PSF-driven stabilization.
• Examined the relationship between PSF type (positive/negative), species richness, and environmental conditions (hydric gradient).

Main Results:

• Strong PSFs increased fitness differences, hindering pairwise coexistence, while negative PSFs predominated in species-rich communities, suggesting indirect facilitation.
• Community stability decreased with increasing species richness, with the largest stable community comprising 12 of 17 species.
• Predicted species density changes based on PSF-stabilized communities aligned with observed patterns along the hydric gradient, indicating PSFs drive species turnover and coexistence.

Conclusions:

• Multispecies analyses are essential, as indirect interactions significantly influence coexistence dynamics, often overlooked in pairwise models.
• The interplay between environmental conditions and PSFs is a key driver of plant diversity and community structure in natural ecosystems.
• Negative PSFs, potentially mediated by indirect positive interactions, play a critical role in maintaining diversity in species-rich plant communities.