Physiological ecology of lodgepole pine (Pinuscontorta) in an enriched CO2 environment

Abstract

Relatively little work has been done to evaluate the effects of chronically high levels of CO2 on growth and physiology of woody plants. Seedlings of lodgepole pine were grown for 5-mo. periods at 330, 1000 or 2000 .mu.l CO2 .cntdot. l-1. Height growth; leaf area production; biomass of leaves, stems, and roots; and photosynthetic responses to changing light, moisture and CO2 concentration were measured. Significant differences between treatments were found in mean seedling height on all measurement dates. Seedlings grown at 1000 .mu.l CO2 .cntdot. l-1 were tallest, with seedlings grown in 2000 .mu.l .cntdot. l-1 intermediate between the control (330 .mu.l .cntdot. l-1) and 1000 .mu.l .cntdot. 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 CO2 up to 2000 .mu.l .cntdot. l-1 even if no increase in net photosynthesis is assumed. Biomass of stems, roots, and secondary leaves was increased in both elevated CO2 conditions, with root biomass approximately 15 times greater in seedlings grown at 1000 .mu.l .cntdot. l-1 than in those grown at 330 .mu.l CO2 .cntdot. l-1. Stomatal resistances were essentially the same for all treatments, indicating no CO2-induced stomatal closure to at least 2000 .mu.l .cntdot. l-1. Photosynthetic Vmax (milligrams per square decimeter per hour) for light response curves varied with CO2 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.