Polley, H.W., Aspinwall, M.J.,
Collins, H.P., Gibson, A.E.,
Gill, R.A., Jackson, R.B., Jin, V.L.,
Khasanova, A.R., Reichmann, L.G.
and Fay, P.A.
2019
CO2 enrichment and soil type
additively regulate
grassland productivity.
New Phytologist 222: 183-192
NOTE:
Grasslands cover one-quarter
of the planet's land surface
and are an important component
of the global carbon balance.
SUMMARY:
Polley et al. report that
increasing the CO2 content
of the air from 280 to 480 ppm
resulted in an ANPP increase
( ANPP = aboveground net primary productivity )
of approximately 170 g m-2
that was realized across
all three soil types.
Elevated CO2 increased ANPP
by around +49%, +84% and +38%
in the sandy loam, silty clay
and clay soil type treatments,
respectively.
For comparison, Polley et al.
write that the observed 170 g m-2
enhancement is similar to that
resulting from a 290-mm increase
in mean annual precipitation
across grasslands in the
Central Plains of North America.
The researchers say that
"the predominant direct effect
of CO2 on ANPP is probably
explained by increased
photosynthetic water use
efficiency (assimilation rate
/transpiration rate),"
which increase
"probably arose
from increased
canopy-level C
assimilation rates"
observed in
previous
observations
during the
ten-year experiment.
DETAILS:
Working at the Lysimeter CO2
Gradient facility in central Texas,
the team of ten researchers
conducted a ten-year field
experiment to determine
the effects of soil type
and atmospheric CO2
concentration on the
aboveground net
primary productivity (ANPP)
of native Texas grasslands.
Native grass assemblages
were grown inside of transparent,
tunnel-shaped chambers
enclosed in a transparent
polyethylene film that included
a CO2 gradient from 250 ppm
to 500 ppm, with the CO2
only being maintained
during the growing season
of each year.
Three soil treatment types
were also included
in the experimental design:
clay, sandy loam and silty clay.
