Toxicity of Artemisia californica to Four Associated Herb Species

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Abstract
Natural and artificial rain drip, soil and leaf volatiles from A. californica are toxic to Hypochoeris glabra and Madia sativa but not nearly as toxic to Bromus rigidus and Festuca megalura. This supports the hypothesis, based on distributional patterns and animal exclosure experiments, that the former 2 spp. are allelopathically excluded from thickets of A. californica, but that the latter 2 are not. Volatile toxins are adsorbed by the soil during the dry season and released into the soil solution with the 1st rains. Toxins also come from litterfall and rain drip. Toxicity exists only at the very beginning of the wet season, after which the soil, leaves and rain drip become relatively innocuous.