Dehydration affects the photosynthetic apparatus. The impact of dehydration on photosynthesis was assessed in twelve Mediterranean species representing different growth forms. Rapid and slow dehydration experiments were conducted to (1) compare the impact of water stress among species and growth forms, (2) rank species according to their drought tolerance. Rapid dehydration reduced the electron transport up to PSI, the reduction being linearly related to leaf relative water content (RWC), except for the deciduous species. Specific energy fluxes per reaction center and maximum photochemical activity of PSII remained relatively stable until 10-30% RWC. The modification pattern of the studied parameters was similar for all the growth forms. Slow rehydration increased specific energy fluxes and decreased quantum yields. The dehydration pattern was similar among growth forms, while the recovery pattern was species-specific. Drought tolerance ranking through drought factor index was relatively modified with the integrated biomarker response method.
Some reports indicate that mesophyll conductance (gm) to carbon dioxide varies greatly with the substomatal carbon dioxide concentration (Ci) during the measurement, while other reports indicate little or no change in g m with Ci. I used the oxygen sensitivity of photosynthesis to determine the response of gm to Ci over the range of about 100 to 300 μmol mol-1 Ci at constant temperature in common bean (Phaseolus vulgaris) and soybean (Glycine max) grown over a range of temperatures and photosynthetic photon flux densities (PPFD). In soybean grown and measured at high PPFD there was only a slight, approximately 15% decrease in gm with Ci over the range of 100 to 300 μmol mol-1. With lower PPFD during the measurement of gm, and especially with low PPFD during plant growth, there was a larger decrease in gm with Ci in soybean. In common bean, the same range in Ci resulted in about a 60% decrease in g m for plants grown and measured at high PPFD, with an even larger decrease for plants at low growth or measurement PPFD. Growth temperatures of 20 to 30°C had little influence on the response of gm to Ci or its absolute value in either species. It is concluded that these two species differed substantially in the sensitivity of gm to Ci, and that PPFD but not temperature during leaf development strongly affected the response of gm to Ci. and J. A. Bunce.
Carbonic anhydrase (CA) activity and net photosynthetic rate (/’N) in the leaves, and plant dry mass (DM) in twelve cultivars of mustard (Brassica juncea L.) were measured 50, 70 and 90 d after sowing. At different sampling stages CA was strongly associated with PN and DM.
Variations in leaf gas-exchange characteristics, leaf pigment content, and other important leaf traits were investigated in seven wild Oryza species, five hybrids, and five improved varieties. The significant variations were observed in photosynthetic pigment contents amongst different species of Oryza. The mean chlorophyll (Chl) content was higher in O. sativa (varieties and hybrids), while O. eichengeri showed the lowest Chl content. The mean carotenoid (Car) content in O. sativa (varieties and hybrids) was higher than in other wild rice species. O. eichengeri and O. barthii had significantly lower Car contents than other rice species. Significant differences were noticed in the rate of photosynthesis (PN), stomatal conductance (gs), transpiration rate (E), internal CO2 concentration (Ci), specific leaf mass (SLM), and leaf thickness amongst different Oryza species. The mean PN was the highest in O. nivara followed by O. eichengeri. The mean PN was the lowest in O. glumaepatula, which was lower than that of cultivated varieties and hybrids of O. sativa. High rates of photosynthesis were observed in O. nivara (ACC. No. CR 100097), O. rufipogon (ACC.No. CR 100267), and O. nivara (ACC.No. CR 100008). The O. nivara and O. rufipogon genotypes with high PN might be used in rice improvement programmes for an increase of leaf photosynthesis in rice. Multiple correlations performed between different gas-exchange characteristics and other physiological traits revealed that the rate of photosynthesis was not dependent on the leaf pigment content or the leaf thickness. A strong positive correlation between PN and the PN/Ci ratio, which represents the carboxylation efficiency, indicated that the observed variation in PN was not based on pigment content or other leaf traits. and T. V. Kiran ... [et al.].
Three genetically related Spathiphyllum cultivars, Claudia, Double Take, and Petite with similar initial sizes and biomass, were grown in a shaded greenhouse and fertilized with a constant supply of nitrogen at 200 g m-3 using an ebb-and-flow fertigation system. Seven months later, Claudia and Double Take had plant sizes and biomasses significantly greater than Petite. Stomatal conductances of Claudia and Double Take were 30 % greater, thus net photosynthetic rates (PN) were significantly higher than in Petite. In addition, the leaf areas (LA) of Claudia and Double Take were 60 % larger than of Petite. Since PN was expressed per leaf surface area, the greater the LA was, the more CO2 was fixed. Thus, the differences in plant size and biomass production of Claudia and Double Take compared to Petite are attributed to high PN and increased LA. and Qibing Wang, Jianjun Chen.