Limitation of photosynthetic activity by CO₂ availability in the chloroplasts of oak leaves from different species and during drought

Abstract

Summary — It has recently been suggested that the low photosynthesis rates in tree species as compared to highly productive crops is at least partly due to resistances opposing the CO 2 fluxes in the mesophyll of tree leaves. To validate this assertion, values of CO 2 mole fractions in the chloroplasts of leaves from Quercus petraea, Q robur, Q ilex and Populus sp were estimated on the basis of the analysis of the partitioning of light driven electron flow between fractions used for the carboxylation or the oxygenation of RuBP by Rubisco. The procedure used included: i) a measure of total light driven electron flows derived from the chlorophyll a fluorescence ratio ΔF/F m ', which is proportional to the photochemical efficiency of PS II, multiplied by incident irradiance and a calibration coefficient; ii) an estimation of the electron flux devoted to carboxylation obtained from net CO 2 assimilation and respiration rate measurement, and using the known electron requirements (four electrons for CO 2 or O 2 fixation); iii) the derivation of the CO 2 mole fraction in the chloroplasts from the specificity factor of Rubisco, and the ratio of carboxylation/oxygenation of RuBP. Results showed that in the absence of drought stress, the mole fraction of CO 2 in the chloroplasts (35-45% of the atmospheric one) was much lower than the calculated substomatal one (60-70% of the atmospheric) in all species. Moreover, lowest values were * Correspondence and reprints: dreyer@nancy.inra.for Abbreviations: A: net CO 2 assimilation rate (μmol m -2 s -1 ); A 1% : net CO 2 assimilation under nonphotorespiratory (1% O 2 ) conditions; R d : nonphotorespiratory respiration (μmol m -2 s -1 ); g s+b : leaf conductance to CO 2 (mmol m -2 s -1 ); g s : stomatal conductance to CO 2 (mmol m -2 s -1 ); c a , c i , c c : mole fractions of CO 2 in the free atmosphere, in the substomatal spaces and in the chloroplast stroma, respectively (μmol mol -1 ); c cl and o cl : liquid phase concentrations of CO 2 and O 2 in the chloroplast stroma (μmol l -1 ); g m : mesophyll conductance to CO 2 (ie, from the substomatal spaces to the chloroplast stroma, mmol m -2 s -1 ); F m ' and F: maximal and steady-state fluorescence in the presence of actinic light; Φ II : photochemical efficiency of PS II; Φ e-: apparent quantum yield of light-driven electron flow; PFD: incident photosynthetic photon flux density (μmol m -2 s -1 ); J T : total light driven electron flow (μmol m -2 s -1 ); J C and J O : electron flows devoted to RuBP carboxylation and oxygenation, respectively (μmol m -2 s -1 ); S: specificity factor of Rubisco; α and α c : leaf absorptance in the PAR (adaxial surface) measured with an integrating sphere or computed from fluorescence data, respectively. recorded in the species with lowest assimilation rates, suggesting that the differences in the net CO 2 assimilation rate between species are linked to the CO 2 availability in the chloroplasts. Finally, the CO 2 availability decreased with increa...

Responses to water stress in an ABA‐unresponsive hybrid poplar (Populus koreana×trichocarpa cv. Peace) III. Consequences for photosynthetic carbon assimilation

“…Roupsard et al (1996). Fluorescence signals were used to compute: (i) before switching on the illumination, the photochemical efficiency of PS II of dark-adapted leaves: Oi,,, = i^^,//?_^ = (i?^ _7?_)/r^_ (Butler, 1978) and (ii) the photochemical efficiency of leaves when they had reached steady-state photosynthesis under a PPFR of 500//mol m"'" s"', as <^,,=^F|F'", = {F\,,-F)/F'"^ (Genty et al, 1989).…”

“…was calculated as: CD,,-X PPFR with k and /;, slope and ^'-intercept of the calibration curve, respectively. J.^ was partitioned into the tractions devoted either to RuBP regeneration for carboxylation {J^) or for oxygenation {J^) (Peterson, 1989) according to the equations presented by Epron et al (1995), Valentini et al (1995) and Roupsard et al (1996):…”

“…This decline is thought to result mainly from a stomatal limitation of CO., diffusion from the atmosphere to intercellular air spaces (Kaiser, 1987;Cornic et al, 1989;Epron & Dreyer, 1993). Recent developments, based on the use of chlorophyll a fluorescence signals to monitor light-dri\en electron fluxes (Genty, Briantais & Baker, 1989), yielded a useful tool to quantify carboxylation and photorespiration rates in situ (Peterson, 1989;Di Marco et al, 1990;Cornic & Briantais, 1991, Valentini et aL, 1995 and to compute COj availability in the chloroplasts (Roupsard, Gross & Dreyer, 1996). Thus a drought-induced decrease in chloroplastic CO, concentration (C(,) was recently reported with apparently constant CO.2 mole fractions in the substomatal spaces (c,) (Renou et al, 1990;Tourneux & Peltier, 1994;Roupsard et al, 1996).…”

“…Recent developments, based on the use of chlorophyll a fluorescence signals to monitor light-dri\en electron fluxes (Genty, Briantais & Baker, 1989), yielded a useful tool to quantify carboxylation and photorespiration rates in situ (Peterson, 1989;Di Marco et al, 1990;Cornic & Briantais, 1991, Valentini et aL, 1995 and to compute COj availability in the chloroplasts (Roupsard, Gross & Dreyer, 1996). Thus a drought-induced decrease in chloroplastic CO, concentration (C(,) was recently reported with apparently constant CO.2 mole fractions in the substomatal spaces (c,) (Renou et al, 1990;Tourneux & Peltier, 1994;Roupsard et al, 1996). These techniques, together with on-line measurements of carhon isotope discrimination in gas exchange systems (Evans et al, 1986;Lloyd et al, 1992) also underlined that CO.â vailabihty in the chloroplasts of well watered plants was much lower than that computed for the substomata!…”

Leaf anatomy enables more equal access to light and CO2 between chloroplasts

“…The data have been separated into two groups : mesophytic leaves which are short-lived, herbaceous or deciduous species ; and sclerophytic leaves which either are evergreen or have a low specific leaf area. As the fluorescence method becomes unreliable when internal conductances exceed 0.3 mol m −# s −" , only data collected using the isotopic method were used Lloyd et al, 1992 ;Loreto et al, 1992 ;Evans et al, 1994 ;Epron et al, 1995 ;Syvertsen et al, 1995 ;Evans & Vellen, 1996 ;Roupsard et al, 1996 ;Lauteri et al, 1997. Solid lines from the origin indicate mean drawdown in CO # mole fraction (µmol mol −" ) across stomata (C a -C i ), or from substomatal cavities to the sites of carboxylation (C i -C c ).…”