Radial growth and non-structural carbohydrate partitioning response to resin tapping of slash pine (Pinus elliottii Engelm. var. elliottii)

Slash pine (Pinus elliottii Engelm. var. elliottii) is a resin-producing species grown worldwide for significant economic benefits for wood production. Resin tapping creates a carbon sink at the expense of carbon allocation for growth and consequently, wood production may be reduced. Non-structural carbohydrates comprising starch and sugars stored in plant organs, may serve as intermediate pools between assimilation and utilisation. However, the effect of resin tapping between tree growth and non-structural carbohydrates is not well understood. This study investigated (1) the effects of resin tapping on radial growth, (2) the effects of resin tapping on non-structural carbohydrate pools in different compartments, and (3) the feasibility of resin production without disruption of tree growth. Twenty one-year-old slash pines were subjected to resin tapping over two successive years. Non-structural carbohydrate concentrations in needles, branches, stem phloem, and roots of tapped and untapped trees in summer and winter were determined after the second year of resin harvest. The results showed that tapping had no significant effects on annual increments. Starch was the dominant non-structural carbohydrate fraction, regardless of tissues and season, and constituted up to 99% of the total non-structural carbohydrates in the phloem and roots. Glucose and fructose were the dominant sugars; sucrose was negligible. Compared with the controls, tapped trees showed 26% lower non-structural carbohydrate concentration in the phloem above the tapping wound in summer, which was attributable to the decreased abundance of starch, glucose, fructose, and sucrose. In winter, the altered non-structural carbohydrate profiles in the phloem above the tapping wounding were minimised as a result of recovery of the sugar concentrations. In contrast to free sugars, which accumulated substantially in needles and branches during winter, starch was enriched in the phloem, roots, and current-year needles. The results provide evidence for a localised effect of resin tapping, and highlight the observation that resin extraction does not always cause a sacrifice in wood growth under a moderate resin-tapping intensity in slash pine plantations.