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

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.