Monoterpene persistence in the sapwood and heartwood of longleaf pine stumps: assessment of differences in composition and stability under field conditions
Monoterpenes in exudates, phloem and sapwood have received considerable attention relative to the active defenses of pine trees. However, little is known about the composition and function of the heartwood monoterpenes. To address this deficiency, monoterpene contents and relative compositions were determined for sapwood and heartwood samples from longleaf pine (Pinus palustris Mill.) stumps monitored in the field for a one-year period post-harvest. Gas chromatography – mass spectrometry analysis of sapwood and heartwood sample extracts showed the total monoterpene contents for both declined at essentially the same rate. For sapwood, a-pinene continued to comprise about 75% of all compounds detected, while the proportion of b-pinene declined with time (15% to 7%). For the heartwood, lower proportions of both a- and b-pinenes (64 and 10%, respectively) were offset by higher proportions of other monoterpenes (e.g., limonene, a-terpineol, borneol). The low proportion of b-pinene in very old turpentine and lightwood stump samples further suggested the lower stability of this particular monoterpene. While it has not been specifically demonstrated that the monoterpenes have an active role in the decay resistance of longleaf pine stump heartwood, these compounds do persist for a very long time and thus are available should they serve this function.