Emission of volatile compounds by seeds under different environmental conditions

Small mammals locate buried wet seeds more efficiently than buried dry seed s. This may be attributable to emission of volatile compounds by the seeds. To test this hypothesis I measured emission of volatile compounds from see ds of three plant species (Pinus contorta, Purshia tridentata and Achnather um hymenoides) under wet and dry conditions using solid phase micro-extract ion, gas chromatography/mass spectrometry headspace analysis. Seeds respond ed in two ways: (1) wet seeds released different, generally greater, amount s of volatile gas than dry seeds and (2) wet seeds and dry seeds released d ifferent compounds. Pinus contorta seeds release greater amounts of three c ompounds when wet: Purshia tridentata seeds release two compounds when dry that are not released when wet, and release increased amounts of two compou nds when wet, and increased amounts of two compounds when dry; Achnatherum hymenoides releases at least 22 compounds, one of which is released in larg e concentrations when wet. These data suggested two mechanisms by which sma ll mammals locate buried seeds. First, small mammals may be sensitive to re lease of differing concentrations of volatile compounds by seeds. Second, s mall mammals may be sensitive to compounds released by wet seeds that are n ot released by dry seeds. Ability of seeds to survive depredation by graniv ores may be an adaptive trait influenced by natural selection.