Branch growth and gas exchange in 13-year-old loblolly pine (Pinus taeda) trees in response to elevated carbon dioxide concentration and fertilization

Abstract

Summary We used whole-tree, open-top chambers to expose 13-year-old loblolly pine (Pinus taeda L.) trees, growing in soil with high or low nutrient availability, to either ambient or elevated (ambient + 200 µmol mol^-1 ) carbon dioxide concentration ([CO₂]) for 28 months. Branch growth and morphology, foliar chemistry and gas exchange characteristics were measured periodically in the upper, middle and lower crown during the 2 years of exposure. Fertilization and elevated [CO₂] increased branch leaf area by 38 and 13%, respectively, and the combined effects were additive. Fertilization and elevated [CO₂] differentially altered needle lengths, number of fascicles and flush length such that flush density (leaf area/flush length) increased with improved nutrition but decreased in response to elevated [CO₂]. These results suggest that changes in nitrogen availability and atmospheric [CO₂] may alter canopy structure, resulting in greater foliage retention and deeper crowns in loblolly pine forests. Fertilization increased foliar nitrogen concentration (N_M), but had no consistent effect on foliar leaf mass (W_A) or light-saturated net photosynthesis (A_sat). However, the correlation between Asat and leaf nitrogen per unit area (N_A = W_AN_M) ranged from strong to weak depending on the time of year, possibly reflecting seasonal shifts in the form and pools of leaf nitrogen. Elevated [CO₂] had no effect on W_A, N_M or N_A, but increased Asat on average by 82%. Elevated [CO₂] also increased photosynthetic quantum efficiency and lowered the light compensation point, but had no effect on the photosynthetic response to intercellular [CO₂], hence there was no acclimation to elevated [CO₂]. Daily photosynthetic photon flux density at the upper, middle and lower canopy position was 60, 54 and 33%, respectively, of full sun incident to the top of the canopy. Despite the relatively high light penetration, W_A, N_A, A_sat and R_d decreased with crown depth. Although growth enhancement in response to elevated [CO₂] was dependent on fertilization, [CO₂] by fertilization interactions and treatment by canopy position interactions generally had little effect on the physiological parameters measured.

Citation

Maier, Chris A.; Johnsen, Kurt H.; Butnor, John; Kress, Lance W.; Anderson, Peter H. 2002. Branch growth and gas exchange in 13-year-old loblolly pine (Pinus taeda) trees in response to elevated carbon dioxide concentration and fertilization. Tree Physiology 22, 1093-1106