Carbon Dioxide and Temperature Gradielits in Baermann Funnel Extraction of Rotylenchulus reniformis

Abstract

Vermiform Rotylenchulus reniformis were anesthetized in water by 10-40% CO[sub2] but were fully motile for 24 hours in water below 5% CO[sub2]. When air containing 2.5% CO[sub2] was blown onto agar, nematodes accumulated at the point of highest CO[sub2] concentration. Nematodes also accumulated when chilling (0.2-1 C) of agar by the gas flow at the accumulation point was offset with heat from a fiber optic. In Baermann funnels containing R. reniformis in silt loam and sandy clay loam soils, CO[sub2] in funnel water increased during 24 hours from 0 to ca. 1%; more CO[sub2] accumulated below the soil layer than above. Bubbling air with 2.5% CO[sub2] into water below soil in covered funnels increased the CO[sub2] gradient and increased nematode extraction, whereas bubbling air without CO[sub2] below soil purged CO[sub2] from the water and decreased nematode extraction. Manipulation of CO[sub2] within funnels usually increased extraction by only 30% and never by more than 3-fold. Controlling temperature gradients consistently increased extraction by 2-30-fold. Key words: Baermann funnel, carbon dioxide, nematode behavior, nematode extraction, Rotylenchulus reniformis, temperature gradient.