Patterns and controls of carbon dioxide and water vapor fluxes in a dry forest of central Argentina

DI BELLA, CARLOS M.; JOBBÁGY, ESTEBAN G.; NOSETTO, MARCELO D.; HOUSPANOSSIAN, JAVIER; POSSE, GABRIELA; GARCÍA, ALFREDO G.; MAGLIANO, PATRICIO N.; FERNÁNDEZ, ROBERTO J.

AGRICULTURAL AND FOREST METEOROLOGY

ELSEVIER SCIENCE BV

Lugar: Amsterdam; Año: 2017 vol. 247 p. 520 - 532

0168-1923

Covering 16% of global land surface, dry forests play a key role in the global carbon budget. The SouthernHemisphere still preserves a high proportion of its native dry forest cover, but deforestation rates have increaseddramatically in the last decades. In this paper, we quantified for the first time the magnitude and temporalvariability of carbon dioxide and water vapor fluxes and their environmental controls based on eddy covariancemeasurements in a dry forest site of central Argentina. Continuous measurements of CO2 and water vapor exchangesspanning a 15-month period (Dec. 2009 ? March 2011) showed that the studied dry forest was a net sinkof carbon, with an overall integrated net ecosystem exchange (NEE) of−172 g C m−2 (−132.8 g C m−2 for year2010). The cool dry season (May?Sept.) accounted for a quarter of the total annual NEE of year 2010 with lowbut steady CO2 uptake rates (1 g C m−2 d−1 on average) that were more strongly associated with temperaturethan with soil moisture. By contrast, in the warm wet season (Oct.?April), almost three times greater CO2 uptakerates (2.7 g C m−2 d−1 on average) resulted from a highly pulsed behavior in which CO2 uptake showed sharpincreases followed by rapid declines after rainfall events. Cumulative evapotranspiration (ET) during the wholestudy (595 mm) accounted for most of the rainfall inputs (674 mm), with daily water vapor fluxes during the wetseason being four times greater compared to those observed during the dry season (1.7 mm d−1 vs.0.45 mm d−1). Modeling of the partition of all evaporative water losses suggested that transpiration was thedominant vapor flux (67% of ET), followed by interception (20%) and soil evaporation (13%). The influence ofair temperature on half-hourly CO2 fluxes was notably different for the dry and wet seasons. In the 11?34 °C airtemperature range, CO2 uptake rates were higher in the warm wet rather than the cool dry season, yet thisdifference narrowed with temperatures>26 °C. The dry forest became a net CO2 source at 40 °C. Our studyprovides new insights about the functioning of dry forests and the likely response of their CO2 and water vaporexchange with the atmosphere under future climate and land use/cover changes.