Development of split-root assays for loblolly pine (Pinus taeda L.) seedlings to study ectomycorrhizal symbioses

Split-root techniques are valuable to investigate systemic vs. local plant responses to biotic and abiotic environmental factors, including interactions with soil microbes. Loblolly pine (Pinus taeda L.) is an economically important tree species that associates with many ectomycorrhizal fungi. However, a protocol for the establishment of split-roots experiments with loblolly pine has not been described so far. This method successfully establishes a split-root system in eight weeks following germination of loblolly pine seedlings. Rapid lateral root elongation is promoted by cutting the primary root tip and growing the seedlings in a hydroponic medium. Lateral roots can then be divided into two separated compartments and inoculated with ectomycorrhizal fungi. The method was validated by growth of split roots with or without inoculation. Root dry biomass was not significantly different between separated non-inoculated roots. Ectomycorrhizal colonization was not detected on the non-inoculated side of roots that were inoculated only on one side, demonstrating the success of the technique as a valuable method for split-root experiments in P. taeda. In addition to ectomycorrhizal fungi, researchers can use this method with loblolly pine to study systemic and local responses to a variety of other biotic or abiotic factors in the root environment. • We describe a protocol to produce split-roots in loblolly pine (Pinus taeda L.) in eight weeks. • This protocol uses hydroponics to promote the elongation of loblolly pine roots. • We validated this protocol by determining split-root biomass and inoculating the seedlings with the ectomycorrhizal fungi Paxillus ammoniavirescens or Hebeloma cylindrosporum.