Physiological ecology of lodgepole pine (<i>Pinus</i><i>contorta</i>) in an enriched CO₂ environment

Abstract

Relatively little work has been done to evaluate the effects of chronically high levels of carbon dioxide on growth and physiology of woody plants. In this study, seedlings of lodgepole pine (Pinuscontorta Dougl. var. latifoliaEngelm.) were grown for 5-month periods at 330, 1000, or 2000 μL CO 2 •L −1 . Height growth; leaf area production; biomass of leaves, stems, and roots; and photosynthetic responses to changing light, moisture, and CO 2 concentration were measured. Significant differences between treatments were found in mean seedling height on all measurement dates. Seedlings grown at 1000 μL CO 2 •L −1 were tallest, with seedlings grown in 2000 μL•L −1 intermediate between the control (330 μL•L −1 ) and 1000 μL•L −1 treatments. The same relationship was found in production of total leaf surface area. Increased leaf surface area yields a productive advantage to seedlings grown at concentrations of CO 2 up to 2000 μL•L −1 even if no increase in net photosynthesis is assumed. Biomass of stems, roots, and secondary leaves was increased in both elevated CO 2 conditions, with root biomass approximately 15 times greater in seedlings grown at 1000 μL•L −1 than in those grown at 330 μL•CO 2 •L −1 . Stomatal resistances were essentially the same for all treatments, indicating no CO 2 -induced stomatal closure to at least 2000 μL•L −1 . Photosynthetic V max (milligrams per square decimetre per hour) for light response curves varied with CO 2 concentration. If results are extrapolated beyond a 5-month period and into field conditions, it appears that size of trees, interactions with competitors, and ecological role of the species might be altered.