Ecosystem photosynthetic characteristics are of utmost importance for the estimation of regional carbon budget, but such characteristics are not well understood in alpine regions. We collected CO2 flux data measured by eddy covariance technique over an alpine dwarf shrubland on the Qinghai-Tibetan Plateau during years 2003-2010; and we quantified the temporal patterns of ecosystem apparent quantum yield (a), saturated photosynthetic rate (Pmax), and ecosystem dark respiration (RDe). Results showed that the strong seasonality of a and RDe was driven mainly by air temperature (Ta), whereas that of Pmax was much more determined by leaf area index rather than abiotic factors. Diurnal thermal fluctuation inhibited significantly the daytime photosynthetic capacity. Stepwise regression revealed that the seasonal deviations of a, Pmax, and RDe were significantly controlled by Ta. The annual a was regulated mainly by annual growing season Ta, which indicated that the response of ecosystem a was instant. The annual variations of Pmax correlated positively with soil temperature 5 cm below ground (Ts) of the annual nongrowing season and those of RDe related negatively with the annual nongrowing season precipitation. We suggested that a lagged response regulated the annual Pmax and the annual RDe. Annual deviations of a and RDe were both significantly controlled by annual Ts, and those of Pmax were marginally determined by annual PPFD. Thus, the future warming scenario, especially significant for nongrowing seasonal warming in the Qinghai-Tibetan Plateau, would favor ecosystem photosynthetic capacity in the alpine dwarf shrubland., H. Q. Li, F. W. Zhang, Y. N. LI, G. M. Cao, L. Zhao, X. Q. Zhao., and Obsahuje bibliografii
Seasonal changes in leaf gas exchange, assimilation response to light and leaf area were monitored in bearing and nonbearing pistachio shoots. Shoot bearing status did not directly affect leaf photosynthetic rate. However, photosynthetic light-response curves strongly varied during the season demonstrating the dominant effect of the tree’s seasonal phenology on assimilation. Early in the season low photosynthetic rates were associated with high rates of dark respiration indicating limited photosynthesis in the young leaves. As leaves matured, dark respiration decreased and assimilation reached maximum values. Photosynthetic efficiency was strongly reduced late in the season due to leaf age and senescence. Fruit load precipitated an early leaf senescence and drop that resulted in a 53% decrease in leaf area in bearing vs. nonbearing shoots, strongly decreasing the seasonal photosynthetic performance of bearing shoots. Bearing shoots produced a 26% lower seasonal carbon gain compared to nonbearing shoots., G. Marino, M. La Mantia, T. Caruso, F. P. Marra., and Obsahuje bibliografii
Seasonal variations in photosynthesis of cassava cv. Rayong 9 (RY9) under irrigated and rain-fed conditions were evaluated at the age of three and six months after planting (MAP). Photosynthetic light-response (PN/I) curves revealed that cassava leaves attained the highest maximum net photosynthetic rates (PNmax) in the rainy season, followed by the hot one, while the lowest PNmax was found in the cool season. Photosynthetic potential of the 3-month-old plants was mostly higher than that of the 6-month-old plants, and the seasonal variation in photosynthetic capacity was also more apparent in the younger plants. PN/I curves were used to predict daily net photosynthetic rate (PN) for each season based on daily average solar radiation data. The predicted PN were considerably lower than the PNmax values. This indicated that solar radiation is a limiting factor for photosynthesis, particularly in the rainy season. The data provided basic information for breeding cassava genotypes with enhanced photosynthesis during the period of unfavorable environment. Furthermore, the data are potentially useful in modeling photosynthesis and crop growth as affected by environmental factors., K. Vongcharoen, S. Santanoo, P. Banterng, S. Jogloy, N. Vorasoot, P. Theerakulpisut., and Obsahuje bibliografii
Effect of selenium on leaf senescence was studied in oilseed rape plants treated with 10 μM Na2SeO4 at a rosette growth stage. In addition to developmental senescence, N deficiency and leaf detachment were used for induction of senescence. Nonphotochemical quenching declined in old leaves as senescence became more advancing but rose progressively in the plants supplied by Se. The total carbohydrate and protein pools decreased with leaf age, while increased by the Se treatment. However, during senescence induced by N deficiency, Se did not change remarkably the C and N metabolism, but delayed senescence mainly through protection of plants from photoinhibitory effects. After detachment, untreated leaves became chlorotic and necrotic, while the Se-treated ones remained fairly green. Our results demonstrated that Se delayed leaf senescence by a maintaining or even improving photochemical activities. During developmental senescence, the Se effect on the extending life span of the leaves was additionally linked to the metabolic regulation of senescence., S. Rahmat, R. Hajiboland, N. Sadeghzade., and Obsahuje bibliografii
The effects of selenium on photosynthesis and Chl fluorescence in pear, grape, and peach were analyzed. The foliar spray of amino acid-chelated selenium solution was performed soon after fruit setting, totally six times, with an interval of ten days. After seven days from the last spray, the leaves in the middle of shoots were examined. Foliar spray of selenium increased the net photosynthetic rate in pear, grape, and peach. In contrast, the treatment decreased stomatal conductance, transpiration rate, and substomatal CO2 concentration in all the three species. The selenium treatment improved the maximum quantum yield of PSII, effective quantum yield of PSII, and photochemical quenching in all three species. Conversely, the selenium treatment reduced nonphotochemical quenching in all three species. We suggested that selenium can improve photosynthesis and protect PSII in fruit crops., T. Feng, S. S. Chen, D. Q. Gao, G. Q. Liu, H. X. Bai, A. Li, L. X. Peng, Z. Y. Ren., and Obsahuje seznam literatury
Responses of drought-tolerant (DT) and drought-susceptible (DS) pot-grown groundnut (Arachis hypogaea L.) varieties to changes in leaf relative water content (RWC) were studied. Water stress (WS) was imposed on 30-day-old plants for 2 weeks. Leaf RWC decreased significantly under WS conditions with simultaneous decrease in net photosynthetic rate (PN) and stomatal conductance (gs). Even though no significant difference was observed between DT and DS varieties with regard to RWC, DT varieties were able to maintain significantly higher PN than DS varieties. Higher values of water use efficiency (WUE) were also observed in DT varieties during WS conditions. The decline in PN due to WS could be attributed to both reduction in g s (i.e. stomatal limitation) and to reduction in chlorophyll content (Chl). No significant difference in leaf area index (LAI) was found between DT and DS types and LAI was not reduced by WS. Significant differences were found among the studied groundnut varieties, but not between DT and DS types, in terms of root, aboveground, and total dry mass. These growth parameters significantly decreased under WS conditions. Based on the results, a sequence of physiological responses in groundnut crop subjected to WS was postulated. and P. R. Jeyaramraja, S. S. Thushara.
Wheat (Triticum aestivum L.) cv. Jimai22 was used to evaluate the effect of ethylene evolution rate (EER) and 1-aminocyclopropane-1-carboxylic acid (ACC) and their relations with photosynthesis and photochemical efficiency in plants well-watered (WW) and under a severe water deficit (SWD). SWD caused a noticeable reduction in the grain mass. The marked increases in both EER and the ACC concentration were observed under SWD; it was reversed effectively by exogenous spermidine (Spd) or amino-ethoxyvinylglycine (AVG). Thermal images indicated that SWD increased obviously the temperature of flag leaves, mainly due to the decrease in transpiration rate under SWD. Exogenous Spd or AVG decreased to some extent the temperature of the flag leaves. The strong decline in photosynthetic rate (PN) and stomatal conductance as well as the photodamage of PSII were also observed under SWD after 14 and 21 days after anthesis (DAA). Intercellular CO2 concentration was reduced at 7 DAA, but slightly increased at 14 and 21 DAA under SWD, indicating that the decreased PN at 7 DAA might result from stomatal limitations, while the decline after 14 and 21 DAA might be attributed to nonstomatal limitations. Correlation analysis suggested that EER and ACC showed negative relations to photosynthesis and photochemical efficiency. Data obtained suggested that the effects of SWD were mediated predominantly by the increase in EER and ACC concentration, which greatly decreased the leaf photosynthesis and photochemical efficiency, and, therefore, reduced the grain mass. Application of Spd or AVG reduced the EER and ACC, and thus positively influenced photosynthesis and photochemical efficiency under SWD., W. Yang, Y. Yin, W. Jiang, D. Peng, D. Yang, Y. Cui, Z. Wang., and Obsahuje bibliografii