Sustained photosynthetic performance of Coffea spp. under long-term enhanced [CO2].

Coffee is one of the world's most traded agricultural products. Modeling studies have predicted that climate change will have a strong impact on the suitability of current cultivation areas, but these studies have not anticipated possible mitigating effects of the elevated atmospheric [CO2] because no information exists for the coffee plant. Potted plants from two genotypes of Coffea arabica and one of C. canephora were grown under controlled conditions of irradiance (800 μmol m(-2) s(-1)), RH (75%) and 380 or 700 μL CO2 L(-1) for 1 year, without water, nutrient or root development restrictions. In all genotypes, the high [CO2] treatment promoted opposite trends for stomatal density and size, which decreased and increased, respectively. Regardless of the genotype or the growth [CO2], the net rate of CO2 assimilation increased (34-49%) when measured at 700 than at 380 μL CO2 L(-1). This result, together with the almost unchanged stomatal conductance, led to an instantaneous water use efficiency increase. The results also showed a reinforcement of photosynthetic (and respiratory) components, namely thylakoid electron transport and the activities of RuBisCo, ribulose 5-phosphate kinase, malate dehydrogenase and pyruvate kinase, what may have contributed to the enhancements in the maximum rates of electron transport, carboxylation and photosynthetic capacity under elevated [CO2], although these responses were genotype dependent. The photosystem II efficiency, energy driven to photochemical events, non-structural carbohydrates, photosynthetic pigment and membrane permeability did not respond to [CO2] supply. Some alterations in total fatty acid content and the unsaturation level of the chloroplast membranes were noted but, apparently, did not affect photosynthetic functioning. Despite some differences among the genotypes, no clear species-dependent responses to elevated [CO2] were observed. Overall, as no apparent sign of photosynthetic down-regulation was found, our data suggest that Coffea spp. plants may successfully cope with high [CO2] under the present experimental conditions

Maximal activities of some respiratory enzymes.

<p>Variation of the total activities of malate dehydrogenase (MDH) and pyruvate kinase (PK) in the leaves of <i>C. arabica</i> (Icatu and IPR 108) and <i>C. canephora</i> (Conilon CL 153) grown under 380 (white bar) and 700 (black bar) μL CO₂ L^-1. For each enzyme, the mean values + SE (n = 4) followed by different letters express significant differences between cultivars for the same CO₂ treatment (a, b) or between CO₂ treatments within the same cultivar (r, s). The ANOVAs for MDH and PK showed significant differences between the cultivars for the same CO₂ treatment and between CO₂ treatments within the same cultivar.</p

Cellular membranes selectivity stability.

<p>Evaluation of membrane permeability in the leaves of <i>C. arabica</i> (Icatu and IPR 108) and <i>C. canephora</i> (Conilon CL 153) grown under 380 (white bar) and 700 (black bar) μL CO₂ L^-1. The mean values + SE (n = 5) followed by different letters express significant differences between cultivars for the same CO₂ treatment (a, b) or between CO₂ treatments within the same cultivar (r, s). The ANOVA for leakage showed significant differences between cultivars for the same CO₂ treatment, between CO₂ treatments within the same cultivar and for the interaction.</p

Thylakoid electron transport potential.

<p>Changes in the thylakoid electron transport rates associated with PSII (with and without the inclusion of OEC) and PSI in the leaves of <i>C. arabica</i> (Icatu and IPR 108) and <i>C. canephora</i> (Conilon CL 153) grown under 380 (white bar) and 700 (black bar) μL CO₂ L^-1. For each parameter, the mean values + SE (n = 4) followed by different letters express significant differences between cultivars for the same CO₂ treatment (a, b) or between CO₂ treatments within the same cultivar (r, s). The ANOVAs for PSII+OEC, PSII-OEC and PSI showed significant differences between cultivars for the same CO₂ treatment and between CO₂ treatments within the same cultivar, as well for the interaction between genotype and growth CO₂ (except in PSI for the interaction).</p

Dynamics of the lipid matrix from chloroplast membranes.

<p>Changes in the total fatty acid (TFA) content and unsaturation level (DBI) of the chloroplast membranes of leaves of <i>C. arabica</i> (Icatu and IPR 108) and <i>C. canephora</i> (Conilon CL 153) grown under 380 (white bar) and 700 (black bar) μL CO₂ L^-1. For each fatty acid, the mean values + SE (n = 4) followed by different letters express significant differences between cultivars for the same CO₂ treatment (a, b) or between CO₂ treatments within the same cultivar (r, s). The ANOVAs for TFA and DBI showed significant differences between cultivars for the same CO₂ treatment, between CO₂ treatments within the same cultivar, and for the interaction between genotype and growth CO₂.</p

Photosynthetic pigment stability.

<p>Changes in the content of total chlorophylls (Chl <i>a</i>+<i>b</i>) and total carotenoids (Tot. Carot.), as well as their ratio (Tot Chl/Tot Carot), in the leaves of <i>C. arabica</i> (Icatu and IPR 108) and <i>C. canephora</i> (Conilon CL 153) grown under 380 (white bar) and 700 (black bar) μL CO₂ L^-1. For each parameter, the mean values + SE (n = 6-8) followed by different letters express significant differences between cultivars for the same CO₂ treatment (a, b) or between CO₂ treatments within the same cultivar (r, s).</p

Maximal activities of some photosynthetic enzymes.

<p>Variation of the total activities of ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBisCo) and ribulose 5-phosphate kinase (Ru5PK) in the leaves of <i>C. arabica</i> (Icatu and IPR 108) and <i>C. canephora</i> (Conilon CL 153) grown under 380 (white bar) and 700 (black bar) μL CO₂ L^-1. For each enzyme, the mean values + SE (n = 4) followed by different letters express significant differences between cultivars for the same CO₂ treatment (a, b) or between CO₂ treatments within the same cultivar (r, s). The ANOVA for RuBisCo showed significant differences only between CO₂ treatments within the same cultivar, whereas that for Ru5PK showed significant differences between cultivars for the same CO₂ treatment and between CO₂ treatments within the same cultivar.</p

Gas exchanges under ambient [CO₂].

<p>Changes in leaf net photosynthesis (P_n), stomatal conductance to water vapor (g_s) and instantaneous water use efficiency (iWUE) in <i>C. arabica</i> (Icatu and IPR 108) and <i>C. canephora</i> (Conilon CL 153) measured at their growth [CO₂]: 380 (white bars) and 700 (black bars) μL CO₂ L^-1. For each parameter, the mean values + SE (n = 6-8) followed by different letters express significant differences between cultivars for the same CO₂ treatment (a, b) or between CO₂ treatments within the same cultivar (r, s). The ANOVA for P_n, showed significant differences between cultivars for the same growth CO₂ treatment and between CO₂ treatments within the same cultivar; that for iWUE showed significant differences between CO₂ treatments within the same cultivar; that for g_s did not show any significant difference,.</p

Potential photosynthesis.

<p>Changes in photosynthetic capacity (A_max) in the leaves of <i>C. arabica</i> (Icatu and IPR 108) and <i>C. canephora</i> (Conilon CL 153) grown under 380 (white bar) and 700 (black bar) μL CO₂ L^-1. The mean values + SE (n = 6) followed by different letters express significant differences between cultivars for the same CO₂ treatment (a, b) or between CO₂ treatments within the same cultivar (r, s). The ANOVA for A_max showed significant differences between cultivars for the same growth CO₂ treatment.</p