Photosynthetic capacity of loblolly pine (Pinus taeda L.) trees during the first year of carbon dioxide enrichment in a forest ecosystem

Abstract

Our objective was to assess the photosynthetic responses of loblolly pine trees (Pinus taeda L.) during the first full growth season (1997) at the Brookhaven National Lab/Duke University Free Air CO 2 Enrichment (FACE) experiment. Gas exchange, fluorescence characteristics, and leaf biochemistry of ambient CO 2 (control) needles and ambient + 20 Pa CO 2 (elevated) needles were examined five times during the year. The enhancement of photosynthesis by elevated CO 2 in mature loblolly pine trees varied across the season and was influenced by abiotic and biotic factors. Photosynthetic enhancement by elevated CO 2 was strongly correlated with leaf temperature. The magnitude of photosynthetic enhancement was zero in March but was as great as 52% later in the season. In March, reduced sink demand and lower temperatures resulted in lower net photosynthesis, lower carboxylation rates and higher excess energy dissipation from the elevated CO 2 needles than from control needles. The greatest photosynthetic enhancement by CO 2 enrichment was observed in July during a period of high temperature and low precipitation, and in September during recovery from this period of low precipitation. In July, loblolly pine trees in the control rings exhibited lower net photosynthetic rates, lower maximum rates of photosynthesis at saturating CO 2 and light, lower values of carboxylation and electron transport rates (modelled from A-C i curves), lower total Rubisco activity, and lower photochemical quenching of fluorescence in comparison to other measurement periods. During this period of low precipitation trees in the elevated CO 2 rings exhibited reduced net photosynthesis and photochemical quenching of fluorescence, but there was little effect on light-and CO 2 -saturated rates of photosynthesis, modelled rates of carboxylation or electron transport, or Rubisco activity. These first-year data will be used to compare with similar measurements from subsequent years of the FACE experiment in order to determine whether photosynthetic acclimation to CO 2 occurs in these canopy loblolly pine trees growing in a forest ecosystem.

Sesquiterpene emissions from loblolly pine and their potential contribution to biogenic aerosol formation in the Southeastern US

“…Needle temperatures typically were $1-31 below the air temperatures inside the enclosure. The gas exchange measurements indicated that mid-day photosynthetic rates ranged from 4 to 5 mmol m À2 s À2 which is consistent with other lightsaturated measurements at the site (Myers et al, 1999). Results shown in Fig.…”

Does Free-Air Carbon Dioxide Enrichment Affect Photochemical Energy Use by Evergreen Trees in Different Seasons? A Chlorophyll Fluorescence Study of Mature Loblolly Pine1

“…As PPFD drops below the saturating level, a transition from limitation of Rubisco to RubP regeneration would be expected, eliminating any effect on J PSII . Responses of A to c i determined for these needles also indicated that in the absence of TPU limitation the amount of active Rubisco rather than the capacity for RubP regeneration is the major limitation to light-saturated photosynthesis (data not shown) (Myers et al, 1999). Fascicles excised under water around dawn during February and transferred to an illuminated, controlled-environment cuvette showed stimulation of both A and J PSII in elevated p CO 2 (Table III).…”

Modelling assimilation and intercellular CO2 from measured conductance: a synthesis of approaches

“…Our analysis uses the same parameters for trees grown in ambient and elevated CO 2 for 3 years, which reflects the analyses that have been conducted for Pinus taeda (Ellsworth 1999;Myers et al 1999). However, the analysis may apply for any species and environment so long as the physiological parameters in elevated CO 2 are known.…”

“…Separate experiments were conducted to estimate these model parameters, which are derived for ambient and elevated CO 2 measurements pooled together. For predictive purposes, we assume that elevated CO 2 itself has no direct effect on any of the parameters, which is generally consistent with Ellsworth (1999) and Myers, Thomas & DeLucia (1999). The model parameters were determined as follows:…”

“…4) perhaps indicating that assuming static parameters in these physiological models may not be appropriate for such a long time course (3 years). Unavoidable sampling error and spatial inhomogeneity within branches and age classes of needles may also contribute to variability in the data and parameters, along with the knowledge that parameters such as V c max , WUE and m have been shown to be dynamic with time (Myers et al 1999;Ellsworth 2000;Lai et al 2000b). Thus to highlight the overall model trends with minimal distortion from this intrinsic variability, Figs 4 and 5 also include the ensemble trends for model calculations and measurements.…”