Relationships between stem CO2 efflux, substrate supply, and growth in young loblolly pine trees.

•We examined the relationships between stem CO₂ efflux ( E_s), diameter growth, and nonstructural carbohydrate concentration in loblolly pine trees. Carbohydrate supply was altered via stem girdling during rapid stem growth in the spring and after growth had ceased in the autumn. We hypothesized that substrate type and availability control the seasonal variation and temperature sensitivity of E_s. •The E_s increased and decreased above and below the girdle, respectively, within 24 h of treatment. Seasonal variation in E_s response to girdling corresponded to changes in stem soluble sugar and starch concentration. Relative to nongirdled trees, E_s increased 94% above the girdle and decreased 50% below in the autumn compared with a 60% and 20% response at similar positions in the spring. •The sensitivity of E_s to temperature decreased below the girdle in the autumn and spring and increased above the girdle but only in the autumn. Temperature-corrected E_s was linearly related to soluble sugar ( R² = 0.57) and starch ( R² = 0.62) concentration. •We conclude that carbohydrate supply, primarily recently fixed photosynthate, strongly influences E_s in Pinus taeda stems. Carbohydrate availability effects on E_s obviate the utility of applying short-term temperature response functions across seasons. [ABSTRACT FROM AUTHOR]