Soil carbon dioxide effluxes from different vegetation environments in semi-arid Eastern Cape, South Africa

Abstract

Though important, CO2 effluxes from non-agricultural ecosystems are poorly characterised. Given that thicket vegetation is prevalent in Eastern Cape, South Africa, we monitored soil CO2 effluxes from an intact thicket, degraded thicket (DT) and grassland (G) over 10 months, as affected by temperature, moisture and penetration resistance (PR). High soil moisture (16%) reduced PR (4 kg cm−2), which raised winter effluxes (1.2 µmol m−2 s−1), while low moisture (2%) resulted in hard dry soil (14 kg cm−2) that suppressed spring effluxes (0.2 µmol m−2 s−1). There was good interaction between PR and moisture (r = −0.53), with seasonal effluxes increasing with increasing moisture (r = 0.9, p = 0.0001) and decreasing PR (r = −0.66, p = 0.02). Temperature effects were significant under unlimited moisture supply. Thus high summer temperature (40 °C) gave lower effluxes in DT and G (<1 µmol m−2 s−1) due to limited moisture (<10%), whereas high autumn temperature (48 °C) and good moisture (16%) accelerated CO2 emissions (averaging 2 µmol m−2 s−1) from all covers. Although semi-arid ecosystems are limited by low moisture and sandy soils, they contribute to CO2 emissions under high moisture and increasing temperature. Keywords: Eastern Cape, grassland, soil carbon dioxide effluxes, soil organic carbon, thicket