Variation in resin flow among Maritime pine populations: Relationship with growth potential and climatic responses

Abstract

Pine trees produce large amounts of oleoresin to defend against biotic threats. Resin is highly costly to produce and investment in its production must be accurately optimized in relation to allocation to other life functions such growth. As a result of these costs, resin production is highly variable both genetically (among and within species) and plastically (across temporal and spatial environmental heterogeneity). The relative contribution of these sources of variation is, however, far from being completely understood. Besides being a main defensive mechanism, pine resin is also a valuable non-timber forest product that is regaining attention as a renewable resource for different industrial sectors. Improving our knowledge on the main drivers of resin production is vital to fine-tune resin-tapping management, especially in regions with little tradition in resin-tapping such are the Atlantic areas of the Iberian Peninsula. Here, we assessed resin flow and growth in a network of seven Maritime pine (Pinus pinaster) provenance tests established in North West Spain to explore the within species variation in resin flow, the plasticity of resin flow across sites and across the season and the (phenotypic and genotypic) relationships between resin flow and tree growth. Resin flow was assessed in three contrasting Maritime pine populations at three times within the season using a micro-tapping procedure that predicts well the resin yield potential for exploitation purposes. Results supported the theoretical predictions as resin flow significantly varied among populations, with populations from more favorable environmental conditions producing less resin than those from harsher conditions. Resin flow was positively correlated with tree size at the phenotypic level. However, the genetically-based relationship between growth potential and resin flow was markedly negative. Fast growing populations produced less resin than slow growing origins. Resin flow was also highly plastic across sites and across seasons, with resin flow consistently increasing towards the end of the growing season. Temperature and water deficit immediately before sampling emerged as main drivers of the observed variation in resin flow across sites and seasons. Results are valuable to understand the extremely large variation in defensive investment on resin-based defenses in conifer species, to model the potential of Atlantic Maritime pine forest for resin tapping, and to fine-tune the resin-tapping management of these forests.