Soil oxygen status and dehydrogenase activity

Soils obtained from Ap horizons of 11 Orthic Luvisols and 10 Haplic Phaeozems developed from loess were subjected to 14 d conditioning on soil water tension plates at 10, 20 and 30°C in 30 cm3 plastic cylinders at a bulk density of 1.3 Mg m−3 and soil water tensions of 0 or 5 or 15.9 kPa. After conditioning, the dehydrogenase activity and reduced Fe content as well as the values of such aeration indicators as O2 diffusion rate and redox potential were measured. The activity of soil dehydrogenases increased with increases of soil water content and the conditioning temperature. An increase of temperature by 10°C increased the dehydrogenase activity on average 2.6 and 4.6 times for the 15.9 kPa and for the flooded treatment, respectively. Flooding caused in turn an increase of the dehydrogenase activity on average 18 times with respect to the 15.9 kPa treatment; the increase being much higher for 30°C (24.8-fold) and lower for 10°C (11-fold). The combined effect of flooding and temperature increase to 30°C caused an increase of dehydrogenase activity on average 129-fold as compared with the 15.9 kPa at 10°C treatment. Flooding and temperature increase caused a decrease of redox potential and of O2 diffusion rate indicating a reduction of soil aeration. Soil dehydrogenase activity was highly correlated with redox potential (for all the soils together r=−0.81) and with oxygen diffusion rate (r=−0.71). It is suggested that soil water content and temperature influence the dehydrogenase activity indirectly by affecting the soil oxidation–reduction status.