COS 15-3
The effect of plant neighbors on root profiles of a common desert shrub, Larrea tridentata

Monday, August 11, 2014: 2:10 PM
314, Sacramento Convention Center
Heather A. Kropp, School of Life Sciences, Arizona State University, Tempe, AZ
Kiona Ogle, School of Life Sciences, Arizona State University, Tempe, AZ
Martin F. Wojciechowski, School of Life Sciences, Arizona State University, Tempe, AZ

In arid systems, the plant root profile indicates a plant’s potential to utilize different sources of water (e.g. deep vs shallow soil water) and is useful for understanding water use strategies. Interactions between plant neighbors may affect root profiles directly through allelopathy or indirectly by altering soil water availability through competition or facilitation. Larrea tridentata (creosote bush) is a dominant, evergreen species throughout the arid, southwestern United States. This project will focus on better understanding Larrea vertical root profiles, addressing two questions: 1.) How are root biomass profiles affected by plant neighbors? 2.) How is the probability of a species rooting across soil depths affected by plant neighbors? Root profiles were assessed beneath four neighbor associations: 1) Larrea growing “alone” (e.g. more than 1.5m from neighboring species) and Larrea growing in close proximity (overlapping canopies) with 2) Prosopis velutina (mesquite), 3) Olneya tesota (ironwood), and 4) Ambrosia deltoidea (bursage). Root biomass was collected in soil cores from 0-60cm in August of 2012 and 2013, and the presence of each species was assessed on 2012 root mixtures using genetic techniques. The data was analyzed using an occupancy model implemented in a Bayesian framework to assess the probability of species presence.


Larrea growing alone had the highest average root biomass of 3.21mg root per g soil in the shallowest soil layer from 0-10cm, but sharply declined at all other depths with the lowest biomass compared to all other neighbor associations. The highest root biomass from 10-20cm was found below Prosopis and Larrea canopies (1.51mg root per g soil). Larrea and Ambrosia canopies had the highest root biomass of 1.93mg root per g soil from 20-30cm. Model results indicate that Larrea roots had a high probability of being present across all depths from 0-60 cm, ranging from 0.8-0.95 regardless of neighbor association. Prosopis roots had the lowest probability of presence across all depths (0.1-0.3). Olneya and Ambrosia roots had similar probabilities of being present across the soil profile that were highly variable ranging from 0.4-0.9. The results indicate that shallow root biomass from 0-60cm varies significantly between neighbor associations. The results also show that Larrea roots have a high probability of presence regardless of surronding plant neighbors and depth, but the probability of other species being present is much more variable than Larrea.