Biologie du chénopode blanc (Chenopodium album): influence du travail du sol sur la levée et de la densité du peuplement sur la croissance

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Abstract
The emergence pattern and the effects of density on population growth of lamb's-quarters (Chenopodium album L.) were studied in field and greenhouse experiments. Seedling emergence occurred from May to July but reached a maximum during the last 2 weeks of June. Harrowing, performed from the middle of May to the beginning of June, increased considerably the emergence of the species. According to the time of their emergence, the seedlings of each population of lamb's-quarters were grouped into different cohorts. Most plants (87% in 1981 and 42% in 1982) belonged to the first cohort. Those early emerging plants produced 90% of the total biomass and were least subject to mortality. Plants of the late cohorts were few, produced little biomass, and tended to die younger. Populations of lamb's-quarters reacted to density stress mostly through phenotypic plasticity. Mortality occurred mainly in high density populations. Average dry weight per plant was inversely related to density. Height and weight distribution of mature populations followed a hierarchical pattern. Most individuals were of low height and weight, while a few plants dominated the canopy.