Monday, August 3, 2009

PS 17-143: Mycorrhizal colonization elicits limited plasticity in functional root traits of maple and oak

Mei-Ho Lee, Columbia University, Hilary S. Callahan, Barnard College, Columbia University, Matthew I. Palmer, Columbia University, Angelica E. Patterson, Barnard College, Columbia University, and Louise H. Comas, Penn State University.

Interactions between plant roots and symbiotic fungi are critical but poorly understood components of belowground ecology. To better understand how mycorrhizae affect tree roots, we experimentally investigated the effects of mycorrhizal colonization on Acer and Quercus fine root traits: diameter, tissue density, specific root length (SRL), tip frequency, and N content. The plasticity of root traits in the absence of mycorhizal fungi may be relevant to whether and how plants compensate in their absence. Roots of 16 Acer rubrum and 15 Quercus rubra seedlings were sterilized with 25% or 50% bleach solution before installation in a greenhouse paired-pot system containing soil with or without mycorrhizal fungi inoculation. After 70 days, newly grown fine roots were collected and their morphology, architecture and N concentrations measured.
Both bleach concentrations successfully maintained near-zero mycorrhizal fungi colonization levels in the non-inoculated roots and bleach concentrations had negligible effects on other traits. Inoculated roots had significantly greater root tissue density (~10-20%) but the correlation between colonization level and density was weak (r = 0.23, P < 0.08) and other effects of inoculation on root morphology and architecture were limited. Compared to Acer roots, roots of Quercus had greater mean SRL (+65%), smaller mean diameter (-50%), greater mean tip frequency (+12%) and less mean nitrogen content (-12%). These results were compared qualitatively to those from a similar experiment conducted in the field on A. saccharum and Q. rubra using 10% bleach solution. Field-grown roots displayed greater mean root diameter, tissue density and tip frequency but lesser mean SRL. Our techniques might be useful for studying wider range of arbuscular mycorrhizal- and ectomycorrhizal-forming trees and shrubs. A key question is whether the lack of plasticity found here is the general response among woody species.