PARENT SESSION
Oral Session #91: Mutualisms -- Facultative, conditional, and complex.
Presiding: W. Wilson
Thursday, August 8. 1:00 PM to 3:45 PM. Cochise Meeting Room, TCC.

Effects of mycorrhizae and light on plant performance and community structure of understory shrubs.

Kyllo, Damond^*,1, ¹ University Missouri-St Louis, St Louis, MO

ABSTRACT- Evidence from temperate grasslands demonstrates that arbuscular mycorrhizae (AM) influence plant community structure, species diversity, and belowground ecosystem processes. I used experimental microcosms to examine the interactive effects of light(high/low; 30 and 3.5% of full sun), AM(+/–), and nutrient movement through a common mycorrhizal network (CMN) on growth and community structure of common tropical understory shrubs, Piper and Psychotria. Results show that AM increased individual leaf area (Psychotria: 46-118%, Piper: 111-185%) by day 70 for all species with little or no effect of light. Overall RGR was significantly improved by both light and AM (at 6 months) and was highly correlated with a plant's physiology, whereas plant morphology was minimally altered. The biomass structure of the shrub community was strongly affected by both AM and light, but changes were generally unrelated to a species' AM dependence. Resource distribution through a CMN between light levels enhanced the dominance of the more light-demanding Piper species in high light, whereas the understory specialist, Piper cordulatum, benefited in low light. Psychotriaspecies were not affected. Using 32P, phosphorus was dispersed throughout the system regardless of direction across light levels with greater uptake by Psychotriathan Piper species. The results demonstrate the differential effects of AM and light on plant species growth and community structure and indicate the potential importance of belowground distribution of nutrients and carbon through a CMN.

KEY WORDS: arbuscular mycorrhizae, Piper, Psychotria, plant community