The adaptation of barley (Hordeum vulgare L. cv. Akcent) plants to low (LI, 50 µmol m-2 s-1) and high (HI, 1000 µmol m-2 s-1) growth irradiances was studied using the simultaneous measurements of the photosynthetic oxygen evolution and chlorophyll a (Chl a) fluorescence at room temperature. If measured under ambient CO2 concentration, neither increase of the oxygen evolution rate (P) nor enhancement of non-radiative dissipation of the absorbed excitation energy within photosystem 2 (PS2) (determined as non-photochemical quenching of Chl a fluorescence, NPQ) were observed for HI plants compared with LI plants. Nevertheless, the HI plants exhibited a significantly higher proportion of QA in oxidised state (estimated from photochemical quenching of Chl a fluorescence, qP), by 49-102 % at irradiances above 200 µmol m-2 s-1 and an about 1.5 fold increase of irradiance-saturated PS2 electron transport rate (ETR) as compared to LI plants. At high CO2 concentration the degree of P stimulation was approximately three times higher for HI than for LI plants, and the irradiance-saturated P values at irradiances of 2 440 and 2 900 µmol m-2 s-1 were by 130 and 150 % higher for HI plants than for LI plants. We suggest that non-assimilatory electron transport dominates in the adaptation of the photosynthetic apparatus of barley grown at high irradiances under ambient CO2 rather than an increased NPQ or an enhancement of irradiance-saturated photosynthesis. and I. Kurasová ... [et al.].
Spectral absoiptance of greenhouse tomato (Lycopersicon esculentum Milí.) canopy (sunny day, LAI = 2.54) varied between 87-89 %. Absoiptance of smáli tomato fruits was 77 % of PAR energy (spectral reflectance was 22 % and transmittance 1 %). The difíusion resistance to COj of the parenchyma extemal layer with epidermis in smáli fruits reached 25 s cm‘i and in large green fruits 75 s cm-i. At the atmospheric CO2 concentration (330 cm^ m*^) and the quantum flux density of PAR 800 pmol m'2 s'* the steady statě CO2 evolution rate was found to be slightly below its compensation value [-0.06 mg(C02) kg-i(d.m.) s-i]. The net photosynthetic rate in smail tomato fruits was 0.3 mg(C02) kg-i(d.m.) s'*, whereas in a large green tomato it reached 0.16 mg(C02) kg-i(d.m.) s’T Intemal CO2 concentration in smáli tomato frnits by the light was 2 300 cm3(C02) m-3 and in the dark 2 900 cm3(C02) m*3. Even under the optimal irradiance CO2 difíusion proceeded always from fruits to the environment.