RESPONSE OF THE FAUNA OF A GRASSLAND SOIL TO DOUBLING OF ATMOSPHERIC CARBON-DIOXIDE CONCENTRATION

The effects of elevated CO2 on rhizosphere processes, including the re sponse of soil faunal populations and community structure, have so far received little attention. We report on significant responses in the soil fauna of ryegrass/white clover swards to both increasing CO2 from 350 to 750 mu l . l(-1) and, to a period of 60 days when some of the turves were subject to drought, in a controlled climate growth room ex periment. The nematodes which increased were predominantly Enoplia, in cluding dorylaimids, alaimids and trichodorids. This accords with both the doubling of Alaimus under elevated CO2 conditions reported in a s imilar experiment and with the common association of Enoplia with less disturbed habitats. The most marked decrease was in the bacterial-fee ding Rhabditis (Secernentea). The increase in omnivorous and predaciou s nematodes may have been responsible for the decrease in populations of bacterial-feeding nematodes. However, in contrast to their standing crops, the turnover rate of bacterial-feeding nematodes and soil micr obial biomass probably increased as a result of increased grazing by t hese omnivorous and predacious nematodes. Increases in earthworm and e nchytraeid populations were related to increased below-ground producti vity reported for the same trial.