Effects of pasture introduction on soil CO2 emissions during the dry season in the state of Rond�nia, Brazil

Abstract

Soil CO2 evolution rates, soil temperatures and moisture were measured during the dry season in two forest-to-pasture chronosequences in Rondonia, Brazil. The study included pastures ranging from 3 to 80 years-old. Mean dry-season CO2 evolution from the forest in chronosequence 1, 88.8 mg CO2-C m−2h−1 was lower than from the pastures which ranged from 111 to 158 mg CO2-C m−2h−1. We found that temperature was not a good predictor of CO2 emissions from pasture but that there was a significant relationship (r = 0.72,p < 0.05) between soil moisture and pasture emissions. The δ13C of the soil CO2 emissions also was measured on chronosequence I; δ13C of the CO2 emitted from the C3 forest was −29.43%. Pasture13CO2 δ values increased from −17.91%. in the 3 year-old pasture to −12.86% in the 80 year-old, reflecting the increasing C4 inputs with pasture age. Even in the youngest (3 year-old) pasture, 70 percent of the CO2 evolved originated from C4 pasture-derived carbon.