Role of soil animals in C and N mineralisation

Addition of single species of soil animals to animal-free microcosms often increases total heterotrophic respiration, but sometimes additions of microarthropods have been reported not to increase or even decrease CO2 evolution rates. Most studies indicate that addition of soil animals increases net N mineralisation. In a study with F/H layer materials from a spruce stand in central Sweden kept at two temperatures (5 and 15°C) and three moisture levels (15, 30 and 60% of WHC), addition of a mixed fauna of soil arthropods, mainly microarthropods, could not be shown to change the CO2 evolution rates in comparison with materials where arthropods were absent. However, addition of the arthropods significantly increased net N mineralisation for each of the temperature and moisture combinations. The increase due to the arthropods was dependent on soil temperature but not on soil moisture. Because the total net N mineralisation decreased with decreasing soil moisture, the soil arthropods had a much larger relative effect on net N mineralisation under dry than under moist conditions. It is concluded that soil arthropods are important in maintaining net N mineralisation under dry conditions when the microflora is largely inactive. The microbial/faunal release of mineral N is discussed in relation to the C∶N of the substrate.