Effects Of Soil Temperature And Moisture On Population Growth Of Exotic Earthworm Pontoscolex Corethrurus

Laboratory experiments were conducted to examine the effects of soil temperature and moisture on the population growth of the exotic and native earthworm: Pontoscolex corethrurus and Amynthas sp.under controlled conditions. The study was carried out by setting up 9 combinations of soil temperature and moisture with split—plot block design. Monoculture of each species and mixed-culture of both species were included. After recording and measuring the number and biomass of earthworms as well as cocoons regularly(30d interval), we found :(1) Regardless of soil temperature, P.corethrurus grew fast at soil moisture of 25% and 35% in both monoculture and mixed-culture. Maximum of growth rate were 6.15mg·day-1(monoculture) and 5.44mg·day-1(mixed-culture)respectively at 35% soil moisture. The native earthworm Amynthas sp. also grew very fast just during the first 60 days, then lost weight. The maximum of growth rate were 4.73mg·day-1 (monoculture) and 10.5mg·day-1(mixed-culture).(2) Consecutive cocoon production and hatching took place at all the three soil temperatures and the two higher soil moistures. Cultivation time, soil moisture and temperature had significant effects on cocoon production and hatching of P. corethrurus. When soil moisture was preferable (e.g. 35%), cocoon production increased with the elevation of soil temperature. Hatching ability increased with soil temperature if soil moisture is agreeable, however it was restrained if temperature is too high or too low, the greatest hatching ability only occurred at the combination of 25℃*35%. (3) In monoculture, P. corethrurus possessed a logistic population growth if condition is adaptive. Earthworms suffered a diapause or even died when reared in soil of 20% moisture. Soil temperature and moisture affected the population growth rate, with a maximum at 25℃*35% (r=0.634). For the native earthworm Amynthas sp., population didn't increase in most cases, and just increased in a narrow range at the combination of 25℃*35% .(4) Competition between the native and exotic earthworm made the population of native earthworm Amynthas sp. not maintainable. In mixed-culture, P. corethrurs could still gain body weight, deposit cocoons and hatching, but in a narrower range of climate condition could population increase logistically. The native earthworm Amynthas sp. could not maintain its population in any case, it went towards death.(5) The exotic earthworm P. corethrurus was found to be more tolerant of temperature stress than the native earthworm Amynthas sp.. P.corethrurus could survive in the range of 15-35℃soil tempeature, while Amynthas sp. of 17.5-32.5℃in the same time period.(6) The lowest temperature at which P. corethrurus can hatch is higher than 17.5℃, lower than or equal to 20℃, cocoons become nonviable if temperature is lower than that.(7) In the present study, we demonstrated that soil moisture is the primary factor limiting the reproduction of P.corethrurus, but the effects of soil temperature on earthworm reproduction are modified by soil moisture.