Net primary production and ecosystem carbon flux of Brazilian tropical
savanna ecosystems from eddy covariance and inventory methods
Abstract
Estimates of net primary (NPP) and ecosystem production (NEP) are needed
for tropical savanna, which is structurally diverse but understudied
compared to tropical rainforest. Estimates of NPP and NEP are available
from eddy covariance and inventory methods, but both approaches have
errors and uncertainties. We used both methods to estimate carbon (C)
fluxes for an upland mixed grassland and a seasonally flooded forest to
determine the correspondence in C cycling components derived from these
methods and assess the contribution of the various C cycling components
to the overall NEP. Both techniques provided similar estimates of NPP,
NEP, and gross primary production (GPP). Belowground NPP accounted for
49-53% of the total NPP for both ecosystems, followed by aboveground
litter (26-27%) and wood (16-17%) production. Increases in water
availability increased the potential for C storage, but the mechanism
was different in the savanna types with an increase in soil moisture
causing higher NPP in the mixed grassland but lower ecosystem
respiration (Reco) in the Cerrado forest. Compared to
other savanna ecosystems, the mixed grassland had a similar rate of
Reco but lower productivity and C use efficiency (CUE =
NPP/GPP = 0.28). The Cerrado forest had a high CUE (0.58) and similar C
flux rates to other tropical savanna forests and woodlands. While our
measurements are spatially and temporally limited, the agreement in C
fluxes estimated using inventory and eddy covariance methods suggest
that the C cycle estimates for these savanna ecosystems are robust.