Effects on heterotrophic respiration and temperature sensitivity in soils of sub-Saharan Africa
This study investigates heterotrophic respiration (Rsh) and temperature sensitivity (Q10) under conservation and intensification in the Zambezi region, Namibia. We hypothesized that Rsh would be negatively affected by intensification and positively affected by conservation measures. In addition, habitat types (subcanopy, grass, bare soil) may modulate Rsh and Q10, whereby microbial abundance could partially explain these differences. We selected plots with high and low elephant densities and plots in croplands and rangelands. The heterotrophic Rsh was quantified by measuring the amounts of CO2 per hour while incubating the soil in a Respicond® apparatus at five different temperatures (20°C - 40°C; 5° steps). We also measured the pulse-like increase of Rsh after rewetting (Birch-effect) In addition, we separated soil samples by habitat types (subcanopy, grass, bare soil). We calculated different Q10 values for 20-40°C, but also for mean growing season temperature (Q10-G). 16S rRNA gene analyses were performed for selected soil samples exemplifying different land use and habitat types. Indeed, our results showed the highest Rsh values in soils with high elephant density, and here especially under canopy. In contrast, the lowest values were measured in areas with low elephant density, followed by cropland and rangeland. Q10 differed not significantly between land use types, with 1.8>1.7>1.6=1.6 for rangeland, high elephant density, cropland and low elephant density, respectively. Q10-G were higher in all land use types, but sensitivity was greater for rangeland and cropland (2.96; 2.4) than for plots with high and low elephant density (2.3; 1.7). Corresponding to the Rsh values, the microbial community in Namibia also differed across land uses, with high elephant density plots being the most conspicuous. This was also true for microbial abundance, biodiversity, and evenness, which showed higher values especially at sites with high elephant density.