Soil CO2 emission in Brazil

Abstract

The signficant increase in atmospheric CO2 in the last century is primarily due to fossil fuel combustion (36.6 Gt of CO2 in 2018) and landuse change/deforestation (5.5 Gt of CO2 per year from 2009 to 2018). In Brazil, agricultural activities account for 22% of total CO2 emission. Land use change, the main cause of CO2 emission in the country, accounts for 51%. These changes occur mainly in forests and savannas, because their soil and climate conditions are ideal for high-yield agricultural production. Changes in land cover significantly alter physical, biological, and chemical characteristics of soils. Soil CO2 emissions (FCO2) is a result of physical and biochemical processes that determine CO2 production and transport from soil to atmosphere. CO2 production is related to microorganism activity and plant root respiration, whereas CO2 transport is associated to the physical structure of the soil, especially its porosity, which affects soil gas flux. Based on pooled data from FCO2 research carried out in Brazil from 1990 to 2019 with IRGA (infra-red gas analyzer), this study aims to assess the effects of land use change on soil carbon flux in Brazil, in addition to contributing to the body of knowledge about carbon stock balance in tropical and subtropical domains. A bibliographical review was conducted and data from research done in the Amazon Forest, Atlantic Forest, Cerrado (South America savanna), and agricultural crops were pooled. FCO2 in the Amazon Forest ranged from 3.2 to 6.4 μmol CO2 m-2 s-1; several studies reported a significant linear correlation (p < 0.05) between FCO2 and soil moisture. FCO2 in the Atlantic Forest ranged from 0.51 to 3.86 mol CO2 m-2 s-1, indicating a significant linear correlation with soil moisture (r = 0.55, p < 0.0001). FCO2 in the Cerrado was 2.55 μmol and 0.86 μmol CO2 m-2 s-1 CO2 m-2 s-1 in the rainy and dry seasons, respectively. In agricultural crops in Brazil's southeast (São Paulo State), FCO2 ranged from 1.19 up 5.3 mol CO2 m-2 s-1. Most of these studies were conducted in sugarcane plantations using spatial variability analysis, while those carried out in natural areas focused on temporal variability. Studies in Brazil indicate that soil moisture has the most important temporal influence on FCO2 in forests and savannas. In agricultural crops, FCO2 values are affected by soil and agricultural management practices. The implications of the land cover change in Brazil need to be discussed.