Location: Water Management and Systems ResearchTitle: Experimentally reduced root–microbe interactions reveal limited plasticity in functional root traits in Acer and Quercus Author
Submitted to: Annals Of Botany
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/14/2013
Publication Date: 12/19/2013
Publication URL: http://handle.nal.usda.gov/10113/59429
Citation: Lee, M., Comas, L.H., Callahan, H.S. 2013. Experimentally prevention of natural root-microbe interactions reveals limited plasticity in functional root traits of Acer and Quercus. Annals Of Botany. 113:513-521. doi:10.1093/aob/mct276 Interpretive Summary: Breeding plant roots to more effectively take up water and nutrients from the soil is critical for increasing crop productivity. Roots are not well understood and their effectiveness is complicated by root interactions with soil microbes. We sought to determine whether plants can adjust root traits in the absence of beneficial soil microbes. We grew seedlings of maple and oak trees with the root sections divided into multiple satellite pots filled with natural soil on one side and sterilized soil on the other side, and assessed how root traits responded to colonization by symbiotic fungi. We found that roots grown in sterilized soil with no symbiotic fungi had less tissue density and increased specific root length (length per unit dry mass) but negligible change in root diameter, branching intensity and nitrogen concentration compared to roots grown in natural soil with symbiotic fungi. Root responses to these treatments and growing conditions were less than the differences between the species. Our data suggest that root traits are largely species dependent, but as such, are inheritable.
Technical Abstract: Abstract. Background and Aims Interactions between roots and soil microbes are critical components of below-ground ecology. It is essential to quantify the magnitude of root trait variation both among and within species, including variation due to plasticity. In addition to contextualizing the magnitude of plasticity relative to differences between species, studies of plasticity can ascertain if plasticity is predictable and whether an environmental factor elicits changes in traits that are functionally advantageous. † Methods To compare functional traits and trait plasticities in fine root tissues with natural and reduced levels of colonization by microbial symbionts, trimmed and surface-sterilized root segments of 2-year-old Acer rubrum and Quercus rubra seedlings were manipulated. Segments were then replanted into satellite pots filled with control or heat-treated soil, both originally derived from a natural forest. Mycorrhizal colonization was near zero in roots grown in heat-treated soil; roots grown in control soil matched the higher colonization levels observed in unmanipulated root samples collected from field locations. † Key Results Between-treatment comparisons revealed negligible plasticity for root diameter, branching intensity and nitrogen concentration across both species. Roots from treated soils had decreased tissue density (approx. 10–20 %) and increased specific root length (approx. 10–30 %). In contrast, species differences were significant and greater than treatment effects in traits other than tissue density. Interspecific trait differenceswere also significant in field samples, which generally resembled greenhouse samples. †Conclusions The combination of experimental and field approacheswas useful for contextualizing trait plasticity in comparison with inter- and intra-specific trait variation. Findings that root traits are largely species dependent, with the exception of root tissue density, are discussed in the context of current literature on root trait variation, interactions with symbionts and recent progress in standardization of methods for quantifying root traits.