title: Differentiation of persistent anatomical defensive structures is costly and determined by nutrient availability and genetic growth-defence constraints.
abstract: Conifers exhibit a number of chemical and anatomical mechanisms to defend against pests and pathogens. Theory predicts an increased investment in plant defences under limited nutrient availability, but while this has been demonstrated for chemical defences, it has rarely been shown for anatomical defensive structures. In a long-lived woody plant, we tested the hypothesis that limited nutrient availability may promote an improved differentiation of persistent anatomical defences. We also hypothesized that the costs of differentiation of those long-term anatomical structures may be determined by genetic constraints on early growth potential. Using Pinus pinaster Ait. juveniles, we performed a greenhouse study with 15 half-sib families subjected to experimental manipulation of phosphorus (P) availability and herbivory-related induced responses. When plants were ∼30 cm high, half of the plant material was treated with methyl jasmonate to induce defences, and 2 weeks later plants were harvested and the abundance of resin canals in the cortex and xylem was assessed. Density of constitutive resin canals in the cortex and the total canal system was ∼1.5-fold higher in plants under limited P availability than in fully fertilized plants. Availability of P did not significantly influence the inducibility of resin canal traits. We found negative genetic correlations between plant growth and the density of constitutive canals in the xylem and total canal system, but only under conditions of limited nutrition. These results demonstrate for the first time that differentiation of constitutive anatomical-based defences is affected by P limitation. Moreover, results also evidence the existence of genetic constraints between plant growth and constitutive defensive investment, where lineages with the highest growth potential showed the lowest investment in constitutive resin canals.
authors.affiliation: Institute of Biology, Laboratory of Evolutive Entomology, University of Neuchâtel, Rue Emile-Argand 11, 2000 Neuchâtel, Switzerland xmoreira1@gmail.com.
authors.forename: Xoaquín
authors.initials: X
authors.lastname: Moreira
authors.affiliation: Misión Biológica de Galicia (MBG-CSIC), Apdo 28, 36080 Pontevedra, Galicia, Spain.
authors.forename: Rafael
authors.initials: R
authors.lastname: Zas
authors.affiliation: Ingeniería Forestal y del Medio Natural, Universidad de Extremadura, Avenida Virgen del Puerto 2, 10600 Plasencia, Spain.
authors.forename: Alejandro
authors.initials: A
authors.lastname: Solla
authors.affiliation: Misión Biológica de Galicia (MBG-CSIC), Apdo 28, 36080 Pontevedra, Galicia, Spain.
authors.forename: Luis
authors.initials: L
authors.lastname: Sampedro
mesh_terms: D000222:Adaptation, Physiological; D005308:Fertilizers; D060434:Herbivory; D010758:Phosphorus / Q000378:metabolism*; D028223:Pinus / Q000033:anatomy & histology / Q000235:genetics / Q000502:physiology*; D010935:Plant Diseases; D012116:Resins, Plant; D036226:Seedlings; D013312:Stress, Physiological; D052584:Xylem / Q000033:anatomy & histology*
chemical_list: D005308:Fertilizers; D012116:Resins, Plant; D010758:Phosphorus
keywords: Pinus pinaster; growth-defence trade-offs; growth-differentiation balance hypothesis; maritime pine; resource allocation; resource availability hypothesis; traumatic resin ducts