The current laboratory study was designed to evaluate the effect of abiotic and biotic factors such as temperature, light intensity, relative humidity and host age on biological and ecological characteristics of Aphelinus asychis (Walker) parasitizing Aphis gossypii (Glover). The traits studied were developmental duration, mortality, sex ratio, longevity, fecundity and host feeding. A. asychis can completely develop and reproduce at temperatures 18°C and 30°C, light intensities of 1000 and 7000 lux and relative humidities of 30% and 60%. Temperature had a significant effect on the developmental duration as well as on the percentage and longevity of females, while mortality from mummification to emergence, fecundity and host feeding were only slightly affected. Relative humidity only affected the developmental duration of A. asychis. Light intensity had mostly affected the biological and ecological traits of A. asychis. High light intensity resulted in a shorter developmental duration, higher incidence of females and longer life span of the female parasitoid. A high tolerance to climatic variations and life cycle well adapted to this aphid host are properties that make it likely that A. asychis could be used for the biological control of the cotton aphid in greenhouses.
This work aimed to evaluate if gas exchange and PSII photochemical activity in maize are affected by different irradiance levels during short-term exposure to elevated CO2. For this purpose gas exchange and chlorophyll a fluorescence were measured on maize plants grown at ambient CO2 concentration (control CO2) and exposed for 4 h to short-term treatments at 800 μmol(CO2) mol-1 (high CO2) at a photosynthetic photon flux density (PPFD) of either 1,000 μmol m-2 s-1 (control light) or 1,900 μmol m-2 s-1 (high light). At control light, high-CO2 leaves showed a significant decrease of net photosynthetic rate (PN) and a rise in the ratio of intercellular to ambient CO2 concentration (Ci/Ca) and water-use efficiency (WUE) compared to control CO2 leaves. No difference between CO2 concentrations for PSII effective photochemistry (ΦPSII), photochemical quenching (qp) and nonphotochemical quenching (NPQ) was detected. Under high light, high-CO2 leaves did not differ in PN, Ci/Ca, ΦPSII and NPQ, but showed an increase of WUE. These results suggest that at control light photosynthetic apparatus is negatively affected by high CO2 concentration in terms of carbon gain by limitations in photosynthetic dark reaction rather than in photochemistry. At high light, the elevated CO2 concentration did not promote an increase of photosynthesis and photochemistry but only an improvement of water balance due to increased WUE. and C. Arena, L. Vitale, A. Virzo de Santo.
This study aimed to determine the photosynthetic performance and differences in chlorophyll fluorescence (ChlF) parameters between Eulophia dentata and its companion species Bletilla formosana and Saccharum spontaneum when subjected to different photosynthetic photon flux density (PPFDs). Leaf surfaces were then illuminated with 50, 100 (low PPFDs), 300, 500, 800 (moderate PPFDs); 1,000; 1,500; and 2,000 (high PPFDs) μmol m-2.s-1, and the ChlF parameters were measured during the whole process. Increasing nonphotochemical quenching of ChlF and decreasing potential quantum efficiency of PSII, actual quantum efficiency of PSII, and quantum efficiency ratio of PSII in dark recovery from 0-60 min were observed in all leaves. A significant and negative relationship was detected between energy-dependent quenching (qE) and photoinhibition percent in three species under specific PPFD conditions, whereas a significant and positive relationship was detected between photoinhibitory quenching (qI) and photoinhibition percent. The qE and qI can be easily measured in the field and provide useful ecological indexes for E. dentata species restoration, habitat creation, and monitoring.
We have studied the effect of different light gradient regimes on host-plant selection of the carrot psyllid, Trioza apicalis Förster. In both a strong and a weak light gradient, carrot psyllids preferred a carrot leaf placed in higher light intensity. When the choice was between the host (carrot Daucus carota L.) and a non-host (barley Hordeum vulgare L.) virgin adults settled significantly more often on non-host in higher light intensity than on carrot in lower light intensity. In a weak light gradient, none of the gravid females settled on a non-host. In an experiment without light gradient, gravid females showed a preference for carrot, whereas virgin females settled approximately equally on Norway spruce Picea abies Karst. (winter shelter plant) and carrot. Our results show that virgin and gravid individuals have different host-plant selection behaviour, and that they are sensitive to small differences in light intensity. Both factors can create a source of variation in behavioural assays, and should be taken into consideration in future experiments with this and probably also related species. Our results suggest that carrot psyllids can utilize visual cues (light intensity or wavelength) in host-plant selection, and the role of visual cues should be more thoroughly studied.
One broad-leaved pioneer tree, Alnus formosana, two broad-leaved understory shrubs, Ardisia crenata and Ardisia cornudentata, and four ferns with different light adaptation capabilities (ranked from high to low, Pyrrosia lingus, Asplenium antiquum, Diplazium donianum, Archangiopteris somai) were used to elucidate the light responses of photosynthetic rate and electron transport rate (ETR). Pot-grown materials received up to 3 levels of light intensity, i.e., 100%, 50% and 10% sunlight. Both gas exchange and chlorophyll (Chl) fluorescence were measured simultaneously by an equipment under constant temperature and 7 levels (0-2,000 μmol m-2 s-1) of photosynthetic photon flux density (PPFD). Plants adapted to-or acclimated to high light always had higher
light-saturation point and maximal photosynthetic rate. Even materials had a broad range of photosynthetic capacity [maximal photosynthetic rate ranging from 2 to 23 μmol(CO2) m-2 s-1], the ratio of ETR to gross photosynthetic rate (PG) was close for A. formosana and the 4 fern species when measured under constant temperature, but the PPFD varied. In addition, P. lingus and A. formosana grown under 100% sunlight and measured at different seasonal temperatures (15, 20, 25, and 30°C) showed increased ETR/P G ratio with increasing temperature and could be fitted by first- and second-order equations, respectively. With this equation, estimated and measured PG were closely correlated (r2 = 0.916 and r2 = 0.964 for P. lingus and A. formosana, respectively, p<0.001). These equations contain only the 2 easily obtained dynamic indicators, ETR and leaf temperature. Therefore, for some species with near ETR/PG ratio in differential levels of PPFD, these equations could be used to simulate dynamic variation of leaf scale photosynthetic rate under different temperature and PPFD conditions., S.-L.. Wong ... [et al.]., and Obsahuje bibliografii