Plant Secondary Compounds in Soil and Their Role in Belowground Species Interactions.

Knowledge of the effect of plant secondary compounds (PSCs) on belowground interactions in the more diffuse community of species living outside the rhizosphere is sparse compared with what we know about how PSCs affect aboveground interactions. We illustrate here that PSCs from foliar tissue, root exudates, and leaf litter effectively influence such belowground plant–plant, plant–microorganism, and plant–soil invertebrate interactions. Climatic factors can induce PSC production and select for different plant chemical types. Therefore, climate change can alter both quantitative and qualitative PSC production, and how these compounds move in the soil. This can change the soil chemical environment, with cascading effects on both the ecology and evolution of belowground species interactions and, ultimately, soil functioning. Plants produce a high diversity of secondary compounds that are released to their surroundings. The role of PSCs on aboveground interactions has been well studied, but less is known about the role of PSCs in mediating and determining the outcome of belowground interactions, especially interactions beyond the rhizosphere. PSCs enter the soil directly by excretion from belowground plant organs or indirectly by washing from the canopy and leaching from litter. Leaching of PSCs creates a heterogeneous soil chemical environment and mediates plant–plant interactions, plant–microbiome associations, and plant–soil invertebrate relationships. This also affects and shapes the diffuse community of species living in soil further away from the rhizosphere. Climate change can substantially alter the quantitative and qualitative production of PSCs released to the soil, which may change belowground species interactions and affect species composition, richness, and, ultimately, soil functioning. [ABSTRACT FROM AUTHOR]