Abstract:
Associative nitrogen (N2)-fixation (ANF) by bacteria in the root-zone of perennial
bioenergy grasses has the potential to replace or supplement N fertilizer and sup port sustainable production of biomass, but its application in marginal ecosystems
requires further evaluation. In this study, we first combined both greenhouse and
field experiments, to explore the N2 fixation effects of three temperate feedstocks
Miscanthus × giganteus (giant miscanthus, Freedom), Panicum virgatum (switch grass, Alamo), and Saccharum sp. (energycane, Ho 02-147). In field studies across
three growing seasons, plant and soil pools of candidate feedstocks were partially
composed of N derived from the atmosphere (Ndfa). Energycane, giant miscanthus,
and switchgrass were estimated to derive >30%, %Ndfa. Greenhouse studies were
also performed to trace isotopically labeled 15N2 into plant biomass and soil pools.
Evidence for Ndfa was detected in all three feedstock grasses (using reference 15N
of soil, chicory, and sorghum, δ15N~+7.0). Isotopically labeled 15N2 was traced
into biomass (during grass elongation stage) and soil pools. Extrapolation of rates
during the 24 hr labeling period to 50 days estimated 30%–55% of plant Ndfa, with
the greatest Ndfa for energycane. The findings of the field natural abundance and
greenhouse 15N2 feeding experiments provided complementary evidence that peren nial bioenergy grasses have the potential to support relatively high rates of ANF,
and accumulate diazotroph-derived N into biomass when grown on non-fertilized
soil.
