Abstract
CO2 fluxes were measured in a soybean field in the Province of Buenos Aires, Argentina, with an eddy covariance system consisting of a CO2/H2O infrared gas analyzer and a sonic anemometer. The measurements were carried out between 24th December 2008 and 31st March 2009. The measurements continued to be carried out even after the growing season, in order to capture data on the CO2 fluxes of dying plants and weed plants established after it. Changes in phenology and botanical composition were accompanied with important changes in CO2 flux values and on the relative importance exercised by three meteorological variables selected to describe the environmental condition: solar radiation, air temperature and vapor pressure deficit (VPD). The maximum CO2 fluxes were recorded before noon and reached values up to approximately 1.0 mg CO2 m-2 s-1, having a relation with the global radiation and VPD values. This low value was probably associated with the few rain registered during the spring. When senescence took place, respiration processes became more important and the field acted as a source of CO2. A weak relation was found then with the environmental conditions. Carbon dioxide uptake was reestablished when the soil was covered by weeds but at a much lower rate. The maximum flux value was then around 0.3 mg m-2 s-1. Carbon dioxide flux was strongly associated with global radiation, which explained 80% of the variance.
Highlights
The imbalance between anthropogenic emissions of CO2 and the sequestration of CO2 from the atmosphere by ecosystems has led to an increase in the average concentration of this greenhouse gas (GHG) in the atmosphere [1]
Three contrasting periods were selected to compare available measurement data at different stages of the status of the soybean field: in the first one, the soybean plants were in their growth peak, the soil was not completely covered; in the second period, plants were in the senescence stage; during the third period, natural succession took place in the abandoned field and weed species were established
There was a positive relationship with global radiation and a negative relationship with vapor pressure deficit (VPD) and with air temperature
Summary
The imbalance between anthropogenic emissions of CO2 and the sequestration of CO2 from the atmosphere by ecosystems has led to an increase in the average concentration of this greenhouse gas (GHG) in the atmosphere [1]. Industrial activities are mainly responsible for the emission of GHGs, changes in agriculture and land-use have an important influence on GHG emissions and global warming [2]. In this context, terrestrial ecosystems play a key role in the global carbon cycle because of their function as a potential CO2 sink. There are different methods to investigate the temporal variability of CO2 assimilation and its dependence on the phenological state of the plants or on meteorological parameters [6] Several of these methods use satellite-based remote
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