Lowering irradiance can delay the flower stalk, i.e., spike development, in order to schedule flowering time of Phalaenopsis; however, the effect on photosynthetic performance and spiking inhibition remains poorly understood. We compared light and shade treatments of Phalaenopsis aphrodite subsp. formosana in order to determine how limiting light affects day-night changes in the photosynthetic capacity of leaves and the carbon pool of leaves and stems resulting in delayed spiking. The low irradiance treatment [20 μmol(photon) m-2 s-1] for six weeks did not affect potential functions of photosynthetic apparatus estimated by chlorophyll a fluorescence analysis, but it significantly reduced the net CO2 uptake and O2 evolution rates, carbohydrate and organic acid concentrations, and amplitudes of CAM activity in new and fully expanded leaves of Phalaenopsis and delayed the spiking compared with the control kept at 150 μmol(photon) m-2 s-1. The shortened stem contained a remarkably high sucrose concentration, accounting for more than 80% of total soluble sugars for both treatments throughout the day. Moreover, the sucrose concentration was unaffected by the lowering of irradiance. The relationship between the sucrose content and spiking seemed to be loose; the major factor(s) for spiking in Phalaenopsis remained to be ascertained as the flower stalk bud is attached to the shortened stem., Y.-C. Liu, C.-H. Liu, Y.-C. Lin, C.-H. Lu, W.-H. Chen, H.-L. Wang., and Obsahuje seznam literatury
The effects of NaCl (200 mM) and osmotic stress generated by polyethylene glycol (PEG) on PSII maximal quantum efficiency, photosynthetic CO2/H2O gas exchange at two CO2 concentrations, content of chlorophyll, proline, and malondialdehyde were investigated in shoots of C4 xerohalophyte Haloxylon aphyllum (Chenopodiaceae). The PEG treatment induced a low water osmotic potential (-0.4 MPa) and inhibited photosynthesis (by a factor of 2) and transpiration (by a factor of 4). The NaCl treatment, at equal osmoticity conditions, reduced transpiration (by a factor of 2) and stimulated photosynthesis (by a factor of 2.5). Only the
PEG-treated plants showed osmotic stress effects, which were demonstrated by an increase in proline and malondialdehyde contents in the shoot tissue. The data indicated that the halophilic character of this species was essential for maintaining the plant water status and photosynthesis under osmoticity induced by NaCl treatment. Herewith, the presence of C4-type photosynthesis appeared to be just an auxiliary mechanism, because this xerohalophyte did not reveal the efficiency in water use typical for C4 plants under osmotic stress, in the absence of a saline substrate., Z. F. Rakhmankulova, P. Yu. Voronin, E. V. Shuyskaya, N .A. Kuznetsova, N. V. Zhukovskaya, K. N. Toderich., and Obsahuje bibliografii
Nitrogen (N) availability is a critical factor affecting photosynthetic acclimation of C3 plants under elevated atmospheric CO2 concentration ([CO2]e). However, current understanding of N effects on photosynthetic electron transport rate and partitioning, as well as its impact on photosynthesis under [CO2]e, is inadequate. Using controlled environment open-top chambers, wheat (Triticum aestivum L.) was grown at two N levels (0 and 200 mg(N) kg-1 soil) and two atmospheric CO2 concentrations of 400 ([CO2]a) and 760 μmol mol-1([CO2]e) during 2009 and 2010. Under [CO2]e high N availability increased stomatal conductance and transpiration rate, reduced limitations on the activity of triose phosphate isomerase, a Calvin cycle enzyme, and increased the rate of net photosynthesis (PN). Considering photosynthetic electron transport rate and partitioning aspects, we suggest that greater N availability increased PN under [CO2]e due to four following reasons: (1) higher N availability enhanced foliar N and chlorophyll concentrations, and the actual photochemical efficiency of photosystem (PS) II reaction centers under irradiance increased, (2) increase of total electron transport rate and proportion of open PSII reaction centers, (3) enhancement of the electron transport rate of the photochemical and carboxylation processes, and (4) reduced limitations of the Calvin cycle enzymes on the photosynthetic electron transport rate. Consequently, sufficient N improved light energy utilization in wheat flag leaves under [CO2]e, thus benefiting to photosynthetic assimilation. and X. C. Zhang, X. F. Yu, Y. F. Ma.
In order to understand the physiological traits important in conferring salt tolerance in three barley genotypes, this study was performed under field conditions with three water salinity levels (2, 10, and 18 dS m-1). High salinity decreased net photosynthetic rate, transpiration rate, and stomatal conductance, K+ concentration, K+:Na+ ratio, and grain yield, but increased electrolyte leakage and Na+ content. Under 10 and 18 dS m-1 salinity, Khatam (salt-tolerant) had the maximum stomatal conductance, K+, K+:Na+ ratio, and the grain yield, and a minimum Na+ content and electrolyte leakage, whereas Morocco (salt-sensitive) had the lowest net photosynthetic rate, stomatal conductance, K+ content, K+:Na+ ratio, and grain yield, and the highest Na+ content and electrolyte leakage. This study showed that tolerant genotypes of barley may avoid Na+ accumulation in aboveground parts, facilitating a higher photosynthetic rate and higher grain yield., M. Mahlooji, R. Seyed Sharifi, J. Razmjoo, M. R. Sabzalian, M. Sedghi., and Obsahuje bibliografii
In order to study the mechanisms of Se-mediated growth improvement as related to carbon (C) and nitrogen (N) metabolism, wheat plants were cultivated hydroponically with adequate (4 mM, Na) or low (1 mM, Nd) N supply and treated with 10 and 50 μM Na2SeO4 for six weeks. The Se supplementation enhanced plant biomass; it was significant for shoots of Na plants at 50 μM Se. Chlorophyll fluorescence parameters were significantly lowered under Nd conditions but restored completely by Se addition reaching values of those in Na plants. Net CO2 assimilation rate (PN) decreased only slightly by limited N availability, but it enhanced significantly in both Nd and Na plants equally by 10 and 50 μM Se. Effect of Se on PN in the Na plants occurred mainly due to the stomata opening, while it was related to both stomatal and nonstomatal mechanisms in the Nd plants. The Se treatment resulted in enhancement of nitrate reductase (NR) activity in both Na and Nd plants with an optimal response at 10 μM Se. Negative correlations between nitrate concentration and NR activity indicated a partial nitrate depletion in the roots following by elevated NR activity in Nd plants. In contrast, nitrite concentrations were higher in the Se treated plants. Higher amino acids and protein concentrations in the Se-treated plants might be an indication of a general upregulation of N metabolism. However, in Na plants, the stimulation of N metabolism was not observed at 50 μM Se which could not be attributed to lesser availability of C skeletons because of maintaning higher CO2 fixation under these conditions. It implies the function of some regulatory mechanisms that are responsible for coordination of C and N metabolism in whole plant., R. Hajiboland, N. Sadeghzade., and Obsahuje bibliografii
The objective of this study was to investigate a response to low-light environments in hybrids and commercial cultivars of Boehmeria nivea L. Two hybrids (Chuanzhu 11 and Chuanzhu 8) and two commercial cultivars (Chuanzhu 12 and Chuanzhu 6) of ramie were subjected to a shade treatment for 6, 12, and 18 days. The shade treatment led to a significant decrease in some plant traits and fiber yield in four ramie cultivars, whereas their leaf area and plant height increased. In addition, net photosynthesis and stomatal conductance significantly declined in response to shade, while transpiration rate and intercellular CO2 did not significantly change. Moreover, chlorophyll (Chl) and carotenoid (Car) concentration, Chl/Car, and Chl (a+b) per leaf dry mass significantly increased in the response to shade, while the Chl a/b ratio decreased. Furthermore, Chuanzhu 6 and Chuanzhu 11 were more tolerant to shade than Chuanzhu 12 and Chuanzhu 8, thus, they could be potentially used for management practices and breeding programs., C.-J. Huang, G. Wei, Y.-C. Jie, J.-J. Xu, S. A. Anjum, M. Tanveer., and Seznam literatury
a1_The photosynthetic and chlorophyll fluorescence parameters were studied in Ziziphus jujuba var. spinosus under different soil water gradients obtained by irrigation and natural water consumption. We used the rectangular hyperbola model, the nonrectangular hyperbola model, the exponential model, and the modified rectangular hyperbola model to fit our data and evaluate them quantitatively. Based on the relationship among the parameters, the effects of the availability of soil water on photosynthesis were elucidated. The results showed that: (1) The relationship between water content and photosynthetic parameters were fitted best by the modified rectangular hyperbola model, followed by the nonrectangular hyperbola model, the exponential model, and the rectangular hyperbola model. The modified rectangular hyperbola model fitted best the maximum net photosynthetic rate (PNmax) and the light-saturation point (LSP), while the nonrectangular hyperbola model fitted best the dark respiration rate (RD), the apparent quantum yield (AQY), and the light-compensation point (LCP)., a2_(2) The main reason for the net photosynthetic rate (PN) decline was that it reached a stomatal limit when the soil relative water content (RWC) was greater than 25% and it reached a nonstomatal limit when the RWC was lesser than 25%. Under these conditions, the photosynthetic apparatus of Z. jujuba was irreversibly damaged. (3) Pmax, RD, AQY, and LSP increased first and then decreased, while LCP increased contrary to the RWC. The P N light-response parameters reached optimum when the RWC was 56-73%. (4) The quantum yield of PSII photochemistry reached a maximum when RWC was 80%. Nonphotochemical quenching decreased rapidly, and the minimum fluorescence in the dark-adapted state increased rapidly when RWC was lesser than 25%. Under these conditions, PSII was irreversibly damaged. (5) The RWC range of 11-25% resulted in low productivity and low water use efficiency (WUE). The RWC range of 25-56% resulted in moderate productivity and moderate WUE, and the RWC range of 56-80% resulted in high productivity and high WUE. The RWC range of 80-95% resulted in moderate productivity and low WUE. In summary, photosynthesis of Z. jujuba was physiologically adaptable in response to water stress in sand formed from seashells. The photosynthetic and physiological activity was maintained relatively high when the RWC was between 56 and 80%; Z. jujuba seedlings grew well under these conditions., J. B. Xia, G. C. Zhang, R. R. Wang, S. Y. Zhang., and Obsahuje bibliografii
In the Orinoco lowlands, savannas have been often replaced by pastures composed of the C4 grass, Brachiaria decumbens Stapf. We addressed following questions: (1) How does the replacement of the native vegetation affect CO2 exchange on seasonal and annual scales? (2) How do biophysical constraints change when the landscape is transformed? To assess how these changes affect carbon exchange, we determined simultaneously the CO2 fluxes by eddy covariance, and the soil CO2 efflux by a chamber-based system in B. decumbens and herbaceous savanna stands. Measurements covered a one-year period from the beginning of the dry season (November 2008) to the end of the wet season (November 2009). During the wet season, the net ecosystem CO2 exchange reached maximum values of 23 and 10 μmol(CO2) m-2 s-1 in the B. decumbens field and in the herbaceous savanna stand, respectively. The soil CO2 efflux for both stands followed a temperature variation during the dry and wet seasons, when the soil water content (SWC) increased above 0.087 m3 m-3 in the latter case. Bursts of CO2 emissions were evident when the dry soil experienced rehydration. The carbon source/sink dynamics over the two canopies differed markedly. Annual measurements of the net ecosystem production indicated that the B. decumbens field constituted a strong carbon sink of 216 g(C) m-2 y-1. By contrast, the herbaceous savanna stand was found to be only a weak sink [36 g(C) m-2 y-1]. About 53% of the gross primary production was lost as the ecosystem respiration. Carbon uptake was limited by SWC in the herbaceous savanna stand as evident from the pattern of water-use efficiency (WUE). At the B. decumbens stand, WUE was relatively insensitive to SWC. Although these results were specific to the studied site, the effect of land use changes and the physiological response of the studied stands might be applicable to other savannas., J. San José, R. Montes, N. Nikonova, J. Grace, C. Buendía., and Obsahuje bibliografii
Water availability is an important factor for plant growth in arid environments. In recent decades, vermicompost (VC) fertilizer has been used in agriculture as a safe and effective fertilizer with high water-holding capacity. The aim of the present study was to characterize effects of VC fertilizer on photosynthetic activity of chickpea (Cicer arietinum L. cv. Karaj) under drought conditions at three different growth stages. Tests were carried out with four volumetric ratios of VC to soil, i.e., 0:100, 10:90, 20:80, and 30:70, and three levels of drought stress, i.e., no stress (NS), moderate drought (MS), and severe drought (SS) (100, 75, and 25% of field capacity, respectively). Evaluations were performed at the seedling, flowering, and podding stage. We found that the VC treatment under NS conditions significantly increased total chlorophyll content [Chl (a+b)], intercellular CO2 concentration (C i), net photosynthetic rate (P N), transpiration rate (E), and maximal quantum yield of PSII photochemistry (Fv/Fm) at all three stages. The VC addition of 10 and 20% significantly enhanced the Chl content and Fv/Fm under MS and Fv/Fm, C i, and P N under SS at the flowering stage. In conclusion, our results proved a positive effect of the VC fertilizer on photosynthesis of chickpea under NS conditions, but it was not found under MS and SS., S. R. Hosseinzadeh, H. Amiri, A. Ismaili., and Obsahuje seznam literatury
Photosynthetic electron flux allocation, stomatal conductance, and the activities of key enzymes involved in photosynthesis were investigated in Rumex K-1 leaves to better understand the role of nitric oxide (NO) in photoprotection under osmotic stress caused by polyethylene glycol. Gas exchange and chlorophyll fluorescence were measured simultaneously with a portable photosynthesis system integrated with a pulse modulated fluorometer to calculate allocation of photosynthetic electron fluxes. Osmotic stress decreased stomatal conductance, photosynthetic carbon assimilation, and nitrate assimilation, increased Mehler reaction, and resulted in photoinhibition. Addition of external NO enhanced the stomatal conductance, photosynthetic rate, activities of glutamine synthetase and nitrate reductase, and reduced Mehler reaction and photoinhibition. These results demonstrated that osmotic stress reduced CO2 assimilation, decreasing the use of excited energy via CO2 assimilation which caused significant photoinhibition. Improving stomatal conductance by the addition of external NO enhanced the use of excited energy via CO2 assimilation. As a result, less excited energy was allocated to Mehler reaction, which reduced production of reactive oxygen species via this pathway. We suppose that Mehler reaction is not promoted unless photosynthesis and nitrogen metabolism are prominently inhibited. and H. D. Li ... [et al.].