CO2 and soil water potential as regulators of the growth and N fraction derived from fixation of a legume in tallgrass prairie communities
Polley, H. W., H. P. Collins, L. G. Reichmann and P. A. Fay . 2016.
Abstract
Background and Aims CO2 enrichment may increase N
input to ecosystems by increasing N2 fixation, but the
fixation-CO2 response depends on factors such as soil
water availability that are influenced by soil properties.
Methods We used the δ15
N natural abundance method to
estimate the proportion of N in the legume Desmanthus
illinoensis that was derived from N2 fixation following
2-8 years of growth along a subambient to elevated CO2
gradient. Desmanthus was grown in tallgrass prairie
communities on each of three soils of differing texture.
Results Only on a clay soil was it possible to calculate
fixation (Nfix ; g N m-2 ). The fraction of legume N
derived from fixation (Ndfa) decreased by 20 % as CO2
increased from subambient to elevated concentrations.
The negative effect of reduced Ndfa on Nfix was obscured
by variation in Desmanthus production along the CO2
gradient that was positively linked to the ANPP-CO2
response of communities. Across soils, legume production was negatively correlated with soil water potential
to 0.3 m depth (Ψsoil). Conclusions Nfix in grasslands may depend primarily
on Ψsoil as influenced by soil hydrological properties.
CO2 enrichment may reduce Nfix during years in which
the legume-CO2 and related ANPP-CO 2 response is
small by depressing Ndfa.
Key Words
δ15 N natural abundance . Desmanthus illinoensis . Essential elements . Soil texture . Soil water potential . Subambient CO2
