Carbon sequestration in soils might offset part
of the increase of CO2 in the atmosphere. Two contrasting
subtropical grassland species, bahiagrass (BG), Paspalum notatum Flügge, and rhizoma perennial peanut (PP), Arachis glabrata Benth., a legume, were
grown at Gainesville, Florida, USA, in field soil plots in four temperature
zones (baseline-ambient, +1.5, +3.0, and +4.5 °C) in four temperature-gradient
greenhouses, two each at 360 and 700 ppm CO2. The soil had been in
continuous cultivation for more than 20 years before plant establishment. Samples
from the top 20 cm of each plot were collected before plant establishment and six
years later, after the study ended. Soil organic carbon (SOC) increases across
the six years were greater for BG than PP, 1.396 and 0.746 g/kg, respectively. Belowground
biomass was also greater for BG than PP. Mean SOC gains in BG plots at 700 and
360 ppm CO2 were 1.450 and 1.343 g/kg, respectively (no CO2
effect). Mean SOC increases in PP plots at 700 and 360 ppm CO2 were
0.949 g/kg and 0.544 g/kg, respectively (significant CO2 effect).
Overall, SOC increased only for the first temperature increment, and thereafter
declined. Soil organic nitrogen (SON) accumulation patterns were similar to SOC
increases. Mean annual SOC accumulation was 475 kg/ha per year, comparable with
other studies. We conclude that carbon can be accumulated in soils converted to
grassland species in humid, subtropical environments. The SOC accumulation will
be greatest for species that have greater belowground biomass accumulation.
Author: L.H. Allen, Jr, S.L. Albrecht, K.J. Boote, J.M.G. Thomas, and K.W. Skirvin (lhajr at mail dot ifas dot ufl dot edu)
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