Temperature effects on leaf properties, resin content, and composition in Grindelia chiloensis (Asteraceae)

Grindelia chiloensis (Asteraceae) is a shrub native to the Patagonia and Monte regions of Argentina, presently under investigation as a resin crop. The rate of production of diterpene resin-acids is, in part, determined by environmental conditions and can be manipulated changing water, nitrogen, and radiation availability. Although the theory predicts that resin content should increase with low temperature, this response has not been tested, yet. The objective of this work was to test whether the response of resin production to temperature predicted by the Growth-Differentiation-Balance Hypothesis (GDBH) is found in G. chiloensis. Cloned plants of G. chiloensis were grown in greenhouses under different temperature regimes. Structural and functional characters were measured. Leaf resin and stem total non-structural carbohydrate content (TNC) were higher in plants grown at sub-optimal temperature (low temperature) for growth, whereas assimilation rate was not affected, in accordance with predictions. Under low temperature, specific leaf weight (SLW) and leaf-stem ratio were higher due to reductions in leaf expansion and stem growth, whereas individual leaf mass was not affected. Resin composition was slightly affected by temperature, suggesting that it is under strong genetic control. The stimulant effect of restrictive environmental conditions (low temperature in our study) required to compensate for the short growing season found in cooler environments such as Patagonia, appears insufficient to compensate for the reductions in aboveground biomass, thus resulting in lower resin production per plant.