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

Abstract

Previous studies of the effects of growth at elevated CO 2 on energy partitioning in the photosynthetic apparatus have produced conflicting results. The hypothesis was developed and tested that elevated CO 2 increases photochemical energy use when there is a high demand for assimilates and decreases usage when demand is low. Modulated chlorophyll a fluorescence and leaf gas exchange were measured on needles at the top of a mature, 12-m loblolly pine (Pinus taeda L.) forest. Trees were exposed to ambient CO 2 or ambient plus 20 Pa CO 2 using free-air CO 2 enrichment. During April and August, periods of shoot growth, light-saturated photosynthesis and linear electron transport were increased by elevated CO 2 . In November, when growth had ceased but temperatures were still moderate, CO 2 treatment had no significant effect on linear electron transport. In February, when low temperatures were likely to inhibit translocation, CO 2 treatment caused a significant decrease in linear electron transport. This coincided with a slower recovery of the maximum photosystem II efficiency on transfer of needles to the shade, indicating that growth in elevated CO 2 induced a more persistent photoinhibition. Both the summer increase and the winter decrease in linear electron transport in elevated CO 2 resulted from a change in photochemical quenching, not in the efficiency of energy transfer within the photosystem II antenna. There was no evidence of any effect of CO 2 on photochemical energy sinks other than carbon metabolism. Our results suggest that elevated CO 2 may increase the effects of winter stress on evergreen foliage.Most previous studies of the effects of elevated pCO 2 on photosynthesis have focused on carbon assimilation and metabolism (for review, see Drake et al., 1997). Changes in carbon assimilation at elevated p CO 2 necessitate changes in the partitioning of absorbed energy between heat dissipation and photochemistry in the thylakoid membrane (Pammenter et al., 1993; Valentini et al., 1995;Drake et al., 1997). Modulated chlorophyll a fluorescence enables direct analysis of these processes (Ghashghaie and Cornic, 1994; Valentini et al., 1995). Previous fluorescence studies have shown contrasting effects of long-term elevation of p CO 2 on photochemistry.For instance, in young wheat plants exposed to elevated p CO 2 , a greater proportion of the absorbed light is used in photochemistry at high light (Habash et al., 1995). Such an increase in photochemical energy dissipation should diminish reversible photoinhibition, which would be evident as an increase in F v /F m . Consistent with this expectation, Jones et al. (1995) observed a higher midday F v /F m in the evergreen tree Arbutus unedo growing at elevated p CO 2 in the field under drought stress. In contrast, ScarasciaMugnozza et al. (1996) showed decreased photochemistry and increased photoinhibition in Quercus ilex at elevated p CO 2 under drought in the field. Similarly, Roden and Ball (1996) observed a lower F v /F m in Eucalyptus macrorhyncha grown ...

Photosynthesis of Scenedesmus obliquus in outdoor open thin-layer cascade system in high and low CO2 in Belgium

“…It has been shown that ΦPSII (or ETR) measured in the light was linearly correlated to the quantum yield of oxygen or CO 2 uptake in C3 higher plants when photorespiration was avoided (Genty et al, 1989;Krall and Edwards, 1990;Cornic and Ghashghaie, 1991;Genty and Meyer, 1995;Hymus et al, 1999). This finding permitted the use of simple fluorescence measurements to estimate the CO 2 uptake and the productivity of plants.…”

Growth in Elevated CO2 Can Both Increase and Decrease Photochemistry and Photoinhibition of Photosynthesis in a Predictable Manner. Dactylis glomerata Grown in Two Levels of Nitrogen Nutrition

“…In addition, J o will be competitively suppressed by increasing pCO 2 . Many studies have shown no effect of growth in elevated pCO 2 on sinks for J t , other than carbon metabolism (Epron et al, 1994;Habash et al, 1995; Bartak et al, 1996;Hymus et al, 1999). However, there is some evidence that growth in elevated pCO 2 decreases antioxidant activity (Polle et al, 1997), suggesting a possible change in potential electron flux to a Mehler reaction.…”

Chlorophyll fluorescence characteristics, performance and survival of freshly lifted and cold stored Douglas fir seedlings

“…Declines in Φ PSII, with little or no alteration in Fv' / Fm', indicates that these changes were largely associated with variations in the proportion of open PSII reaction centres (q p , or photochemical efficiency), rather than a decline in the photochemical efficiency of open reaction centres under steady state, light adapted, conditions (Fv' / Fm'), as Φ PSII = Fv' / Fm'⋅q p [15]. A similar conclusion has been suggested for changes in Φ PSII associated with the effects of low temperature, CO 2 enrichment or restricted "sink" activity [19,22]. This suggests that changes in field performance are linked to processes downstream of PSII that increasingly constrain light-driven electron flow.…”

“…One increasingly used method for assessing the "integrity" of a trees photosynthetic apparatus is via the use of chlorophyll fluorescence signals [40,41]. Although chlorophyll fluorescence assessments originally focused on measurements made on initially dark-adapted samples, there is now increasing evidence that these may not always give an accurate assessment of a plants actual photosynthetic status (under constant illuminated conditions), due to differences between light-and dark-adapted quenching processes [22]. The development of portable, pulse-modulated instruments (e.g.…”