The mangroves Rhizophora lamarkii, Ceriops roxburghiana, Bruguiera gymnorrhiza, Aegiceras corniculatum, and Lumnitzera racemosa were screened for their carbon metabolic pathways by measuring net photosynthetic rate (PN), 13C discrimination rate, leaf anatomy, titratable acidity, and activities of phosphoenolpyruvate carboxylase, NADH-malate dehydrogenase, alanine aminotransferase, aspartate aminotransferase, and pyruvate phosphate dikinase. The tested mangroves had a well developed succulence, opening of stomata during day time and closure in the night hours, and absence of diurnal fluctuation of organic acids in their leaves which excludes the possibility of these species being CAM plants. Moreover, the leaf anatomy had not exhibited Kranz syndrome. The high values of discrimination against 13C, low PN, high CO2 compensation concentration, and the activities of aminotransferases in the direction of alanine formation suggest that the species may follow C3 mode of carbon metabolic pathway. and V. Venkatesalu ... [et al.].
Net photosynthetic (P^) and transpiration (£) rates and stomatal conductance (gj) were determined in cotton genotypes under drought during the growth cycle. A decrease in P^, E and gs was observed as soil water availability diminished. appeared dosely related to stomatal apertuře at low g^ levels. However, intercellular CO2 concentration was not so much affected by stomatal closure. An important inter- and intra-genotypic variation in g^ was found at the initial sampling dates. Inter-genotypic variation for increased with time, probably as a result of a higher capacity for water uptake in some genotypes.
Responses of stem net photosynthetic rate (P^) to irradiance (/), temperature, vapor pressure, CO2 concentration, nitrogen content, and water potential were studied during early spring (March) and mid summer (latě July) in field populations of two stem photosynthesizing species introduced into Coastal California sites. Stem in Spartium junceum was inhibited in the summer compared with the spring due to low water potential and low tissue nitrogen content. Quantum yield decreased from March to July, along with a decrease in the demand fimction of the C, response curves. Stem conductance was lower at all vapor pressure deficits during the summer, but Cj at a Cg of 350 pmol moE* increased for S. junceum from spring to summer. The thermal optimum for stem did not change between the two seasons, but that of S. junceum was 5 °C higher than that for Cytisus scoparius. The demand function for the Cj curves of C. scoparius also decreased from spring to summer, but the Cj at a Cg of 350 pmol moT* remained unchanged between the seasons. Thus, the water use efficiency of S. junceum decreased in the summer compared with that of the spring while that of C. scoparius remained unchanged between seasons. There was little evidence for compensatory acclimation of stem F^ to changes in climatic conditions in these species.
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
The relationship between soil water availability, physiological responses [leaf chlorophyll (Chl) fluorescence, leaf water potential (Ψ), and stomatal conductance (gs)] and plant stress was studied in Halimium halimifolium (L.) Willk, Cistaceae, in three sites with contrasted water regimes (Monte Blanco - MB, Monte Intermedio - MI, and Monte Negro - MN) of Doñana National Park (SW of Spain) along the day, in September (summer period) and December (winter period) 1994. In winter, differences among the areas were not significant, with Ψ, gs, and photochemical efficiency values of -1.5 MPa, 0.200 cm s-1, and 0.70, respectively. In summer, however, high declines of gs (0.014 cm s-1 in MI and 0.021 cm s-1 in MB), photochemical efficiency (0.65 Fv/Fp in MB and MI sites) and Ψ (-3.76 in MI and -3.04 MPa in MB) were recorded. Winter-summer differences were minimum in well-watered sites (MN) and maximum in MI. The Ψ and photosystem 2 (PS2) fluorescence were correlated and showed similar seasonal patterns in all three areas. and M. Zunzunegui ... [et al.].