Diurnal changes in chlorophyll a fluorescence, CO2-exchange and organic acid decarboxylation in the tropical CAM tree Clusia hilariana

Abstract

Crassulacean acid metabolism (CAM) plants are dependent on the organic acids that accumulate overnight in the vacuoles as a source of CO(2) during the daylight deacidification period, when stomata are closed and high irradiances generally prevail. We performed an integrative analysis of diurnal changes in gas exchange, chlorophyll fluorescence parameters and organic acid decarboxylation to understand the adjustments in photochemical and non-photochemical processes during the different CAM phases in Clusia hilariana Schlecht., a dominant tree species in the sandy coastal plains of southeastern Brazil. A linear relationship was obtained between the quantum yields of photochemical and non-photochemical quenching, irrespective of the CAM phase and prevailing irradiance. Degradation of malic and citric acids during the midday stomatal closure period could lead to potential CO(2) fixation rates of 23 &mgr;mol m(-2) s(-1), whereas CO(2) losses, measured as CO(2) evolution, corresponded to about 3% of this value. Thus, decarboxylation of malate and citrate provided high internal CO(2) concentrations during phase III of CAM, even though the stomata were closed, allowing optimal utilization of light energy, as indicated by the non-saturating electron transport rates (ETR) in the light response curves, with highest rates of ETR occurring at midday in the diurnal curves. At the transition from phase III to IV of CAM, depletion of internal CO(2) sources and low stomatal conductances, which restricted the supply of exogenous CO(2), reduced the demand for photochemical energy to drive carbon assimilation. This was compensated by increases in thermal energy dissipation as indicated by higher rates of non-photochemical quenching, while high irradiances still prevailed. Shifts in the CAM phases and changes in protective thermal dissipation potential allowed C. hilariana to match changes in PPFD patterns for leaves of different orientations. Evidence that most of the decline in photochemical efficiency was probably related to the fast-relaxing component of non-photochemical quenching is provided by the high values of the quantum yield of photosystem II after 20 min of relaxation in darkness, and an almost complete recovery after sunset. These adjustments in photosynthetic machinery minimized the danger of photo-inhibition in C. hilariana, which is commonly found in fully exposed habitats.

Midday depression in savanna trees: coordinated adjustments in photochemical efficiency, photorespiration, CO2 assimilation and water use efficiency

“…Thus, if decreases in the efficiency of PSII photochemistry are compensated by proportional increases in non-photochemical processes related to photoprotection, the sum of Y P +Y N would be about 0.8 (Laisk et al 1997;Franco et al 1999). There was a tight linear relationship between the quantum yields of photochemical and non-photochemical quenching irrespective of the species and hour of the day (Fig.…”

Effect of low irradiance on the photosynthetic performance and spiking of Phalaenopsis

“…2A). In fact, this distinct day-night and reciprocal fluctuation between  PSII and NPQ was also manifested in C 3 plants, such as Helianthus annuus, Vinca major (Demmig-Adams et al 1996), Phaseolus radiates (Yang et al 2004), C 4 plant, such as Setaria italic (Yang et al 2004), and CAM plants, such as Clusia hilariana (Franco et al 1999) and Phalaenopsis (Pollet et al 2009). Pollet et al (2009) explained that low  PSII and high NPQ at the transition from day to night was closely associated with the inactivation of the Calvin cycle.…”

Evaluation of instant light‐response curves of chlorophyll fluorescence parameters obtained with a portable chlorophyll fluorometer on site in the field

“…To encounter these methodological problems, most of the miniaturized fluorometers offer the possibility of measuring so-called instant lightresponse curves, where actinic light intensity is changed in rather short intervals. Although in this way no steady-state conditions are applied during light-curve runs, comparisons of different plants measured under the same environmental conditions are possible, and this has been widely used in the literature (de Mattos et al 1997;Lüttge et al 1998;Franco et al 1999). Nevertheless, this remains somewhat problematic and the approach of the instant light-response curves needs to be checked more stringently.…”