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.

Nurse shrub nutrient enrichment facilitates pinyon pine development differentially across an edaphic stress gradient.

SCHOWALTER, RACHEL^*,1, HORVATH, SABINE¹, COBB, NEIL¹, ¹ Northern Arizona University, Flagstaff, AZ

ABSTRACT- Shrubs can significantly increase seedling survival of trees by acting as nurse plants to increase the quality of the seedling's microhabitat. In this study we examined how shrub nurse plants could change soil conditioning to increase pinyon (Pinus edulis) seedling survival. Furthermore, we tested the relative importance of shrubs as fertile islands between two habitats that represent ends of a spectrum in soil fertility; a high-stress nutrient-poor cinder soil site and a nearby low-stress sandy-loam site. We collected soil from under shrub canopies and in the open at both sites to grow pinyon from seed in a controlled greenhouse experiment. We germinated seeds collected from each site in their natal soil. This allowed us to test for main effects of site (high-stress vs. low stress) and nurse effects (under shrub vs. open) and interaction effects on seedling mortality and performance. Our results showed that 1) mortality was greater for seedlings grown in the cinder soil regardless of whether the soil source was under shrubs or in the open, 2) nurse effects on shoot and root biomass production was only significant for sandy-loam soil, and 3) soil nitrogen content was significantly greater under nurse shrubs than in the open space, especially in the low-stress environment. Thus, nurse shrubs significantly increase soil quality, especially in "low stress" versus "high stress" habitats.

KEY WORDS: pinyon pine, nurse plant, edaphic