Carbon uptake and water vapor exchange in a pasture site in the Brazilian Cerrado

Abstract

As Brazil becomes one of the largest agricultural and livestock producers, the expansion of cultivated pasture and crop areas in the Cerrado region is expected to cause significant changes in carbon and water vapor fluxes. While this change in land use promotes modifications in regional carbon uptake and water cycle, eddy covariance studies carried out in pasture areas in the Brazilian Cerrado remain scarce. The present study aimed to quantify the carbon uptake and water vapor exchange of these areas in the Brazilian Cerrado. The experimental site was installed in an area covered by Brachiaria sp. in Três Lagoas – MS, Brazil. Data were collected during two hydrological years (2016–2017 and 2017–2018). Pasture strongly acted as a carbon sink; its total accumulation reached −208.9 (±9.6) and −171.8 (±15.8) g C m−2 in the first and second hydrological years, respectively. Average evapotranspiration of 2.0 (±1.1) mm d−1 was observed in the two hydrological years. There was significant reduction in evapotranspiration at the pasture site during the driest months of the year (June and July), mainly in the second hydrological year, which recorded an average of 0.4 (±0.1) mm d−1. The lower recorded water availability in the soil led to the release of 86.7 g C m−2 (over 85 days) in the dry season of the second hydrological year. Ecosystem-level water use efficiency observed during the higher soil water deficit facilitated the survival of the grass. This information is the basis for further studies about the impact of climate change on carbon uptake and water vapor flux by cultivated and natural pasture; additionally, the present research will allow comparisons of carbon storage results to other ecosystems and to support studies of agrometeorological modeling.