Effect of the endogeic earthworm Pontoscolex corethrurus on the microbial structure and activity related to CO2 and N2O fluxes from a tropical soil (Madagascar)

2010

Article référencé dans le Web of Science WOS:000280541700012

Chapuis Lardy Lydie, Brauman Alain, Bernard Laetitia, Pablo Anne-Laure, Toucet Joële, Mano M. J., Weber L., Brunet Didier, Razafimbelo T., Chotte Jean-Luc, Blanchart Eric

Applied Soil Ecology, 2010, 45 (3), p. 201-208 ISSN 0929-1393

The objective of this laboratory study was to determine the influence of a tropical endogeic earthworm, Pontoscolex corethrurus, on CO2 and N2O fluxes from a tropical Ferralsol and microorganisms potentially involved in these gases emissions. CO2 and N2O fluxes were measured during 35 days from soil mesocosms with and without earthworms. At the end of the incubation, 7% of soil was egested as cast in the earthworm treatment. Then, casts which may be aged from few hours to 35 clays old were isolated from non-ingested soil. Different descriptive parameters (activity, density, and structure) of the microbial communities were investigated in the control, the non-ingested soils, and the casts. Quantitative PCR of denitrification genes encoding the nitrite (nirK) anti nitrous oxide (nosZ) reductases was used to study denitrifier density in the earthworm casts. The presence of P. corethrurus induced a significant increase in CO2 emissions but did not affect N2O fluxes when measured at mesocosm level. Despite the absence of significant differences in C and N contents between soils and casts, the near infra-red spectra analysis clearly underlined a specific organic signature for the casts. Fungal and bacterial biomass significantly decreased (similar to 2-fold) in casts compared to parent soil, but the fungal-to-bacterial ratio was not modified by the earthworm casting activity. Data suggested that bacterial communities, especially denitrifiers, were modified in casts. The relative abundance of nirK and nosZ genes increased in the casts while the genetic structures of total bacteria and denitrifying communities were slightly modified in the casts. This study highlighted the importance of earthworm casts as a specific soil habitat where a subset of soil functional bacterial communities (such as denitrifiers) found favourable condition for their growth. However the effect of P. corethrurus was less evident when up-scaling from casts to mesocosm level.

Biologie du sol [074]

Fonds IRD [F B010049688]

fdi:010049688