Nutrient conditions mediate mycorrhizal effects on biomass production and cell wall chemistry in poplar

Abstract

Large-scale biofuel production from lignocellulosic feedstock is limited by the financial and environmental costs associated with growing and processing lignocellulosic material and the resilience of these plants to environmental stress. Symbiotic associations with arbuscular (AM) and ectomycorrhizal (EM) fungi represent a potential strategy for expanding feedstock production while reducing nutrient inputs. Comparing AM and EM effects on wood production and chemical composition is a necessary step in developing biofuel feedstocks. Here, we assessed the productivity, biomass allocation and secondary cell wall (SCW) composition of greenhouse-grown Populus tremuloidesMichx. inoculated with either AM or EM fungi. Given the long-term goal of reducing nutrient inputs for biofuel production, we further tested the effects of nutrient availability and nitrogen:phosphorus stoichiometry on mycorrhizal responses. Associations with both AM and EM fungi increased plant biomass by 14-74% depending on the nutrient conditions but had minimal effects on SCW composition. Mycorrhizal plants, especially those inoculated with EM fungi, also allocated a greater portion of their biomass to roots, which could be beneficial in the field where plants are likely to experience both water and nutrient stress. Leaf nutrient content was weakly but positively correlated with wood production in mycorrhizal plants. Surprisingly, phosphorus played a larger role in EM plants compared with AM plants. Relative nitrogen and phosphorus availability were correlated with shifts in SCW composition. For AM associations, the benefit of increased wood biomass may be partially offset by increased lignin content, a trait that affects downstream processing of lignocellulosic tissue for biofuels. By comparing AM and EM effects on the productivity and chemical composition of lignocellulosic tissue, this work links broad functional diversity in mycorrhizal associations to key biofuel traits and highlights the importance of considering both biotic and abiotic factors when developing strategies for sustainable biofuel production.

Keywords: Populus; biofuels; cellulose; lignin; mycorrhizal fungi; secondary cell wall; stoichiometry.