Hanh Nguyen Hong, Rumpel C., Henry des Tureaux Thierry, Bardoux G., Billou D., Toan Tran Duc, Jouquet Pascal. (2011). How do earthworms influence organic matter quantity and quality in tropical soils ?. Soil Biology and Biochemistry, 43 (2), p. 223-230. ISSN 0038-0717.
Titre du document
How do earthworms influence organic matter quantity and quality in tropical soils ?
Hanh Nguyen Hong, Rumpel C., Henry des Tureaux Thierry, Bardoux G., Billou D., Toan Tran Duc, Jouquet Pascal
Source
Soil Biology and Biochemistry, 2011,
43 (2), p. 223-230 ISSN 0038-0717
Earthworms are important regulators of soil structure and soil organic matter (SUM) dynamics; however, quantifying their influence on SUM cycling in tropical ecosystems remains little studied. Simulated rainfall was used to disrupt casts produced by Amynthas khami and their surrounding soil (control) into a range of small sized aggregates (50-250, 250-500, 500-2000 and 2000-5000 mu m). To gain insight into how earthworms influence SUM biogeochemical composition in the aggregates, we carried out elemental and stable isotope analysis, and analytical pyrolysis (Py GC/MS). We also characterized their lignin component after oxidation with cupric oxide (CuO). The C content of smaller size fractions (<500 mu m) in the control soil was higher than in the larger fractions. Our study therefore suggests that the aggregate hierarchy concept, which is used to understand soil aggregates and SUM dynamics in temperate soils, may not be applicable to the tropical Acrisol studied here. Earthworms modified SUM organization in soil aggregates. Although the isotope analyses were useful for highlighting SUM enrichment in the earthworm casts, aggregate fractions could not be classified according to particle size. Molecular analyses were necessary to indicate that SUM in all size fractions of casts consisted of relatively undecomposed material. Protection of the most labile SUM structures occurred in the smallest aggregate size fraction (50-250 mu m). Py GC/MS showed that earthworm casts and control aggregates <2000 mu m could be clearly distinguished according to the molecular properties of their SOM. Aggregates larger than 2000 mu m, however, were most probably composed of all fractions and were not different. As a consequence, our results indicate that studies to determine the impact of earthworms on SUM turnover in soil are spatially dependant on the scale of observation.
