Genetics, phosphorus availability, and herbivore-derived induction as sources of phenotypic variation of leaf volatile terpenes in a pine species

Abstract

Oleoresin produced and stored in pine tree leaves provides direct resistance to herbivores, while leaf volatile terpenes (LVT) in the resin are also powerful airborne infochemicals. Resin concentration and profile show considerable spatial and temporal phenotypic variation within and among pine populations. LVT biochemistry is known to be under genetic control, and although LVT should be plastic to diverse abiotic and biotic environmental factors such as nutrient availability and herbivore attack, little is known about their relative contributions and interactive effects. The aim of this paper was to clarify whether reduced phosphorus availability could increase the LVT concentration and affect the expression of herbivore-derived induced defences, and how plasticity would contribute to the phenotypic variation of LVT. The constitutive and methyl-jasmonate (MeJa) induced LVT concentration and profile were analysed in 17 half-sib Pinus pinaster families growing under two levels of P-availability (complete and P-limited fertilization). Individual terpene concentrations showed large additive genetic variation, which was more pronounced in the control than in MeJa-induced pines. MeJa application did not affect the LVT concentration, but significantly modified the LVT profile by depleting the α-pinene content and reducing the sesquiterpene fraction. Low P-availability strongly reduced plant growth and foliar nutrient concentrations, but did not affect LVT concentration and profile, and did not interact with MeJa-induction. Results indicate a strong homeostasis of LVT concentration to P-availability, and minor changes in the LVT profile due to MeJa-induction. Genetic variation appears to be the main source of phenotypic variation affecting the LVT concentration in this pine species.

Fig. 1.

Constitutive (white bars) and MeJa-induced (black bars) concentration of monoterpenes (a) and sesquiterpenes (b) in the needles of P. pinaster seedlings grown in two different phosphorus availabilities. Fertilization had no significant effect, and chemical induction with MeJa significantly reduced sesquiterpene concentration in the two P treatments. Error bar is s.e., n=72. Concentrations are expressed on a dry weight basis.

Fig. 2.

Family relationship between total concentration of sesquiterpenes and monoterpenes in the needles of P. pinaster seedlings under constitutive conditions and after defensive induction with MeJa. The relative contribution of mono- and sesqui-terpenes was similar among families presenting a broad range of terpene concentrations. MeJa induced a shift to lower sesquiterpene concentration, which was consistent among families. Analysis of covariance showed that intercepts were significantly different (F_1,31=15.1; P <0.001), and slopes were marginally different (F_1,30=4.17; P=0.050). Each point represents an open pollinated family (n=8 replicates). Concentrations are expressed on a dry weight basis.

Fig. 3.

Family relationships between concentration of β-pinene and α-pinene in the needles of P. pinaster seedlings under constitutive conditions and after defensive induction with MeJa. Both relationships were strong, positive, and consistent among families. Induction with MeJa shifted upwards the relationships. Analysis of covariance showed that intercepts were significantly different (F_1,31=33.87; P < 0.0001) but slopes were not different (F_1,30=3.56; P=0.069). Each point represents an open pollinated family, n=8. Concentrations are expressed on a dry weight basis.