Impact des métaux lourds sur les interactions plante/ver de terre ...

Partie C : Résultats – Chapitre C-I2.2. Biological materialtel-00486649, version 1 - 26 May 2010At the Phu An Ecomuseum, 200 seedlings were planted in plastic pots (V=5 L) in amixture of grey soil, manure and coconut fiber (1/3, 1/3, 1/3). After one month, seedlings ofsimilar size (40cm high, 20 cm diameter) were transferred to the microcosms. The plants weregrown on outside under a single set of conditions - day/night, temperature and water (300 mlin the morning and 200 ml in the evening). To remove variations due to lighting, the potswere covered by a bamboo roof and the pots were randomly distributed.Earthworms, P. corethrurus, were hand-collected from grassland in Bien Hoa, (DongNai Province) that had not been contaminated with heavy metals. The earthworms were keptin the Bien Hoa soil in plastic boxes for 1 week to monitor their health before starting theexperiments. Ten adult earthworms (±10g) were put into each pot to provide a density of100 g m -2 as for a previous experiment (unpublished results).2.3. Experimental designThe experiment was carried out using three processes combined with three levels oflead contamination in five replicates for each. The processes were soil + plant (P), soil +earthworm (E) and soil + plant + earthworm (PE). The levels of lead contamination werecontrol without lead (nPb), soil contaminated with 500 mg.kg -1 lead (lPb) and soilcontaminated with 1000 mg.kg -1 lead (hPb). The experiment was carried out for one month.2.4. Harvesting and soil samplingThe shoots were removed by cutting above the soil surface and the fresh biomass wasassayed immediately. For each replicate, the bamboo was individually harvested and theleaves and stems were collected separately. They were then put in paper bags and dried at60°C for one week. The contents of the pots were transferred onto a large plastic sheet. Theearthworms were removed, weighed and kept in 90% alcohol for further analysis. The soilfrom each pot was kept in laboratory conditions for separation of plant and earthwormaggregates (23). Before the aggregates were separated, dry roots were removed from the soil,washed twice in ultra-pure water, dried and weighed. The plant aggregates in the rhizosphereand the earthworm casts in the drilosphere were separated, sieved and kept for further analysis(biochemical and molecular) not presented in this paper.59