Constitutive and Induced Defenses in Long-lived Pines Do Not Trade Off but Are Influenced by Climate

Increased whitebark pine (Pinus albicaulis) growth and defense under a warmer and regionally drier climate

“…Decreased precipitation (and presumably increased insolation due to less cloud cover) could also facilitate increased spring and autumn photosynthetic activity, promoting greater carbon sequestration annually, resulting in the observed increases in tree growth and resin duct defenses (Körner, 1998;Goldblum and Rigg, 2005). Our results align with Runyon et al (2022), one of the only other climate studies of pine defenses in highelevation systems, which found the highest concentration of both constitutive and induced terpene defenses in five-needle pines TABLE 1 Spearman correlation coefficients for raw, non-detrended whitebark pine tree size (diameter at breast height; DBH), tree growth (ring-width: mm), resin duct production (no. ducts year −1 ), duct size (mm 2 ), duct area (mm 2 year −1 ), and resin duct metrics that have been standardized to tree growth: duct density (no.…”

“…Sampling temporal variation in resin chemistry, viscosity, and flow is not possible in a retrospective analysis in this study; however, relatively small increases in resin duct area would lead to a greater capacity to deliver oleoresin to insect attack sites, as resin flow is proportional to the fourth power of resin duct diameter in accordance with Hagen-Poiseuille's law (Schopmeyer et al, 1954;Vázquez-González et al, 2020;Yi et al, 2021). Increasing temperatures also correlate with reduced resin viscosity and increased resin flow in some species, which may further enhance resin mobilization in whitebark pine under warmer conditions (Zas et al, 2020;Wermelinger et al, 2021), as well as increase terpene concentrations (Runyon et al, 2022). In addition, warming temperatures stimulate the production of ethylene, a phytohormone that stimulates the differentiation of resin duct epithelial cells from tracheid development in annual growth rings of trees (Yamamoto and Kozlowski, 1987;Franceschi et al, 2002;Hudgins and Franceschi, 2004;Vázquez-González et al, 2020).…”

“…The degree to which plants allocate resources toward defenses relative to growth remains an area of active debate with a number of competing models put forth to conceptualize these complex physiological processes (Stamp, 2003). While our study is not designed to test any of these hypotheses directly, the observed positive relationships between tree growth and resin duct defenses we found in whitebark pine, as well as enhanced resin chemistry reported for other high-elevation conifers (Runyon et al, 2022), suggest no apparent tradeoffs but rather increases in both growth and defense with warming conditions in these energy-limited systems. While we did detect negative relationships between tree growth and the resin duct metrics that have been standardized to tree growth (duct density and relative duct area), this is in agreement with other studies (Kane and Kolb, 2010;Ferrenberg et al, 2014;Moreira et al, 2015;Mason et al, 2019;Zhao and Erbilgin, 2019) and reflects a dilution effect, as the metrics standardized to tree growth geometrically decline with increased tree size, even if there is no actual decrease in resin duct production and/or total resin duct area.…”