Department of Renewable Resources, University of Alberta, 442 Earth Sciences Bldg, Edmonton, AB T6G2E3, Canada.
Tree Physiol. 2011 Nov;31(11):1238-50. doi: 10.1093/treephys/tpr104. Epub 2011 Oct 18.
This study examined the role of ectomycorrhizal associations in nitrogen assimilation of Populus tremuloides seedlings. Seedlings were inoculated with Hebeloma crustuliniforme and compared with non-inoculated plants. Nitrogen-metabolizing enzymatic properties were also determined in H. crustuliniforme grown in sterile culture. The seedlings and fungal cultures were subjected to nitrogen treatments (including NO₃⁻, NH₄⁺ and a combination of NO₃⁻ + NH₄⁺) for 2 months to examine the effects on growth, nitrogen-assimilating enzyme activities and xylem sap concentrations of NH₄⁺ and NO₃⁻. Seedlings were also provided for 3 days with ¹⁵N-labeled NH₄⁺ and NO₃⁻, and leaf and root ¹⁵N content relative to total nitrogen was measured. Both NO₃⁻ and NH₄⁺ were effective in supporting seedling growth when either form was provided separately. When NO₃⁻ and NH₄⁺ were provided together, seedling growth decreased while enzymatic assimilation of NH₄⁺ increased. Additionally, nitrogen assimilation in inoculated seedlings was less affected by the form of nitrogen compared with non-inoculated plants. Fungal ability to enzymatically respond to and assimilate NH₄⁺ combined with aspen's enzymatic responsiveness to NO₃⁻ was likely the reason for efficient assimilation of both nitrogen forms by mycorrhizal plants.
本研究探讨了外生菌根共生体在颤杨幼苗氮素同化中的作用。将幼苗接种栓菌（Hebeloma crustuliniforme）并与未接种的植物进行比较。还在无菌培养中测定了栓菌中氮代谢酶的特性。将幼苗和真菌培养物进行氮处理（包括 NO₃⁻、NH₄⁺和 NO₃⁻+NH₄⁺的组合）2 个月，以研究其对生长、氮同化酶活性和木质部汁液中 NH₄⁺和 NO₃⁻浓度的影响。还为幼苗提供了 3 天的 ¹⁵N 标记的 NH₄⁺和 NO₃⁻，并测量了叶片和根中相对于总氮的 ¹⁵N 含量。当分别提供这两种形式时，NO₃⁻和 NH₄⁺都能有效地支持幼苗生长。当同时提供 NO₃⁻和 NH₄⁺时，幼苗生长减少，而 NH₄⁺的酶同化增加。此外，与未接种植物相比，接种幼苗的氮同化受氮形式的影响较小。真菌酶对 NH₄⁺的响应和同化能力以及白杨对 NO₃⁻的酶响应能力可能是菌根植物有效同化两种氮形式的原因。
