Photosynthetic acclimation to long‐term exposure to elevated CO₂ concentration in Pinus radiata D. Don. is related to age of needles

Abstract

The effects of CO 2 enrichment on photosynthesis and ribulose-1,5-bisphosphate carboxylase / oxygenase (Rubisco) in current year and 1-year-old needles on the same branch were studied on Pinus radiata D. Don. trees growing for 4 years in large, open-top chambers at ambient (36 Pa) and elevated (65 Pa) CO 2 partial pressures. At this age trees were 3·5-4 m tall. Measurements made late in the growing cycle (March) showed that photosynthetic rates at the growth CO 2 concentration [(pCO 2 ) a ] were lower in 1-year-old needles of trees grown at elevated CO 2 concentrations than in those of trees grown at ambient (pCO 2 ) a . At elevated CO 2 concentrations V cmax (maximum carboxylation rate) was reduced by 13% and J max (RuBP regeneration capacity mediated by maximum electron transport rate) by 17%. This corresponded with photosynthetic rates at the growth (pCO 2 ) a of 4·68 ± 0·41 µmol m -2 s -1 and 6·15 ± 0·46 µmol m -2 s -1 at 36 and 65 Pa, respectively (an enhancement of 31%). In current year needles photosynthetic rates at the growth (pCO 2 ) a were 6·2 ± 0·72 µmol m -2 s -1 at 36 Pa and 10·15 ± 0·64 µmol m -2 s -1 at 65 Pa (an enhancement of 63%). The smaller enhancement of photosynthesis in 1-year-old needles at 65 Pa was accompanied by a reduction in Rubisco activity (39%) and content (40%) compared with that at 36 Pa. Starch and sugar concentrations in 1-year-old needles were not significantly different in the CO 2 treatments. There was no evidence in biochemical parameters for down-regulation at elevated (pCO 2 ) a in fully fexpanded needles of the current year cohort. These data show that enhancement of photosynthesis continues to occur in needles after 4 years' exposure to elevated CO 2 concentrations. Photosynthetic acclimation reduces the degree of this enhancement, but only in needles after 1 year of growth. Thus, responses to elevated CO 2 concentration change during the lifetime of needles, and acclimation may not be apparent in current year needles. This transitory effect is most probably attributable to the effects of developmental stage and proximity to actively growing shoots on sink strength for carbohydrates. The implications of such age-dependent responses are that older trees, in which the contribution of older needles to the photosynthetic biomass is greater than in younger trees, may become progressively more acclimated to elevated CO 2 concentration.

Effects of lifelong [CO2] enrichment on carboxylation and light utilization of Quercus pubescens Willd. examined with gas exchange, biochemistry and optical techniques

“…The absence of photosynthetic downregulation in current-year leaves has been observed in other studies of trees with unlimited rooting volume that were exposed to elevated [CO 2 ] (e.g. Idso et al 1991Idso et al , 1995Gunderson et al 1993;Teskey 1995;Scarascia-Mugnozza et al 1996;Hogan et al 1997;Turnbull et al 1998). These studies include initial investigations at the Bossoleto spring and control sites, which found no difference in photosynthetic capacity in early summer for Q. pubescens (van Gardingen et al 1997;Tognetti et al 1998).…”

“…Mousseau 1993;Tissue et al 1993Tissue et al , 1999Lewis et al 1996;Tissue, Thomas & Strain 1997, Rey & Jarvis 1998Spunda et al 1998;Turnbull et al 1998; also see review by Medlyn et al 1999). For example, A max did not differ for new Q. ilex leaves but was downregulated for 1-year-old leaves at the Laiatico CO 2 spring compared to a control site (C. Cario et al unpublished results).…”

“…Quercus pubescens is a winter-deciduous species that can produce multiple leaf flushes. Leaf ontogeny and age can affect physiological responses to elevated [CO 2 ] (Griffin & Seemann 1996;Turnbull et al 1998). To minimize these effects, measurements of the oldest cohort were made on leaves approximately 1-1·5 m above the ground.…”

The effects of lifting on mobilisation and new assimilation of C and N during regrowth of transplanted Corsican pine seedlings. A dual 13C and 15N labelling approach

“…The photosynthetic activity in plants is generally strongly correlated with their N concentration even if the relationship between N concentration and CO 2 assimilation capacity is weaker in conifers than in other species due to lower rates of photosynthesis and a smaller range of N concentration than in non-coniferous species [25,32]. The proportion of leaf N found in Rubisco is known to vary between 6-20% in evergreen conifers [12,28] but, in tree seedlings the proportion of N allocated to Rubisco has been found to be independent of N supply [33]. In our experiment, newly assimilated N increased less in lifted versus control seedlings.…”

Long-Term Response of Photosynthesis to Elevated Carbon Dioxide in a Florida Scrub-Oak Ecosystem

“…Studies of mixed-grassland species have predicted that species composition in natural plant communities is likely to change at elevated [CO 2 ] (Jongen andJones 1998, Lü scher et al 1998); however, similar studies have not been performed in forest ecosystems. Cur- (Bazzaz et al 1995, Lee and Jarvis 1995, Lewis et al 1996, Turnbull et al 1998, Jach and Ceulemans 2000, Li et al 2000 This study tests the hypothesis that there is significant interspecific and seasonal variation in three scruboak species in the ability of photosynthesis to respond to rising [CO 2 ] at canopy closure. Photosynthetic acclimation, a change in photosynthetic capacity with growth in elevated [CO 2 ], was evaluated by measuring the response of light-saturated photosynthesis to changes in intercellular CO 2 concentration in the three dominant Florida scrub-oak species.…”