This component of the project will:

• Analyse the monoterpene and other phytochemicals among individual Scots pines
  
  
• Quantify variation in these chemical parameters
  across key stage of the Scots pine life cycle
  across a range of temporal scales
  across a range of spatial scales, from plant tissues upwards between above and below ground components of the ecosystem

The genetic basis for chemical diversity of Scots pine

Genetic data is already available on the population structure of Scots pine in Scotland. Isozyme markers (Kinloch et al., 1986), cpSSRs (developed via a previous SERAD Flexible fund initiative, commission no: SCR/461/95; Provan et al., 1998) and mt DNA RFLPs (Sinclair, 1998) have all shown little evidence of population differentiation in Scotland, except that some western populations possess markers consistent with origins from a separate glacial refugium to other Scottish populations. However, the overriding picture from neutral markers is one of high levels of within-, and low levels of between-population variability (nuclear DNA FST = 0.028; cpDNA FST = 0.032; mtDNA FST =0.37) (Kinloch et al., 1986; Provan et al., 1998; Sinclair et al., 1998, 1999). This is consistent with xenogamous reproduction via copious quantities of highly dispersed pollen, along with relatively efficient seed dispersal (pollen-to-seed flow ratio 18:1; Ennos et al., 1999). While this virtual panmixia for neutral markers need not reflect the distribution of adaptive traits (Karhu et al., 1996; Ennos et al., 1998), it clearly demonstrates the high degree of genetic variability among individual trees within populations. This study will build on this previous work and investigate the within-population, between-individual, spatial distribution of genetically determined monoterpene variation, an expressed, ecologically relevant biochemical marker.

Biochemical variation

Genetic differences in coniferous trees have been studied using monoterpenes and phenolics as biochemical markers (Yadzani & LeBreton, 1991). It is conventionally thought that monoterpenes are under genetic and environmental control; ratios of individual compounds remaining constant, whilst overall levels vary with season and phenology (Langenheim, 1994). However, such a generality across species appears unlikely (Hartley et al., 2000). Some studies confirm the responsiveness of monoterpenes to environmental manipulation (Muzika et al., 1989), but several studies have failed to confirm it in conifers including Scots pine. Monoterpene concentrations and ratios vary very little under manipulated nutrient, light and CO2 conditions, in comparison to the very high genetically-based variability between individuals of the same provenance (Duncan et al., 1994; Iason et al., 1996; Heyworth et al., 1998). Responses in monoterpenes induced by herbivory are also slight and localised to the area of damage, particularly in mature trees, which contribute most to the litterfall (Trewhella et al., 1997). While phenolics can show environmentally induced variation, due to light and soil nutrient concentrations in conifers including Scots pine (Iason et al., 1996, Heyworth et al., 1998), an underlying genetic base has been documented. The large magnitude of genetically determined differences among individuals in phytochemical composition, and the residual environmentally-induced variability, is likely to result in much spatial heterogeneity in phytochemistry. This in turn is hypothesised to confer spatial heterogeneity in ecosystem functioning via the broad range of allelochemic processes in which the secondary metabolites are involved.

Contact: Vera Thoss