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