The aim of this study was to investigate the effects of silicon in alleviating cadmium stress in maize plants grown in a nutrient solution and to evaluate the potential of the spectral emission parameters and the ratio of red fluorescence (Fr) to far-red fluorescence (Ffr) in assessing the beneficial effects of Si. An experiment was carried out using a nutrient solution with a toxic dose of Cd and six doses of Si; biomass, Cd, Si, and photosynthetic pigments of the plants were measured. Chlorophyll (Chl) a fluorescence analysis demonstrated that Si alleviated Cd toxicity in plants. Chl fluorescence measurements were sensitive in detecting such effects even when significant changes in biomass production and concentrations of photosynthetic pigments were not observed. The spectral emission and the Fr/Ffr ratio were sensitive to the effects of Si. Silicon caused a reduction in the translocation of Cd to the shoots of maize plants., A. J. Silva, C. W. A. Nascimento, A. S. Gouveia-Neto., and Obsahuje seznam literatury
Photosynthetic parameters including net photosynthetic rate (P N), transpiration rate (E), water-use efficiency (WUE), and stomatal conductance (g s) were studied in indoor C3 plants Philodendron domesticum (Pd), Dracaena fragans (Df), Peperomia obtussifolia (Po), Chlorophytum comosum (Cc), and in a CAM plant, Sansevieria trifasciata (St), exposed to various low temperatures (0, 5, 10, 15, 20, and 25°C). All studied plants survived up to 0°C, but only St and Cc endured, while other plants wilted, when the temperature increased back to room temperature (25°C). The P N declined rapidly with the decrease of temperature in all studied plants. St showed the maximum P N of 11.9 μmol m-2 s-1 at 25°C followed by Cc, Po, Pd, and Df. E also followed a trend almost similar to that of P N. St showed minimum E (0.1 mmol m-2 s-1) as compared to other studied C3 plants at 25°C. The E decreased up to ≈4-fold at 5 and 0°C. Furthermore, a considerable decline in WUE was observed under cold stress in all C3 plants, while St showed maximum WUE. Similarly, the g s also declined gradually with the decrease in the temperature in all plants. Among C3 plants, Pd and Po showed the maximum g s of 0.07 mol m-2 s-1 at 25°C followed by Df and Cc. However, St showed the minimum gs that further decreased up to -4-fold at 0°C. In addition, the content of photosynthetic pigments [chlorophyll a, b, (a+b), and carotenoids] was varying in all studied plants at 0°C. Our findings clearly indicated the best photosynthetic potential of St compared to other studied plants. This species might be recommended for improving air quality in high-altitude closed environments., S. M. Gupta, A. Agarwal, B. Dev, K. Kumar, O. Prakash, M. C. Arya, M. Nasim., and Obsahuje seznam literatury
Waterlogging is one of the critical factors controlling the distribution, regeneration, and survival of vegetation in wetlands. Here, we tested the hypothesis that Mitragyna parvifolia (Roxb.) Korth. and Syzygium cumini Keels, inhabiting the Keoladeo National Park, a Ramsar wetland (Bharatpur, India), are tolerant to waterlogging. The morphological and photosynthetic variables of four-month-old seedlings subjected to waterlogging, along with the concentrations of macroand micronutrients, were examined. After 35 days, treatment was halted due to high mortality of S. cumini seedlings in contrast to that of M. parvifolia seedlings. Significant declines in most of the studied variables were observed in both species when compared with their respective controls. In addition, M. parvifolia seedlings developed adventitious roots and lenticels and showed an increased root biomass. Based on the results, we concluded that adaptive traits displayed by M. parvifolia seedlings facilitate its tolerance to waterlogging in contrast to S. cumini seedlings., A. Bidalia, Z. Okram, M. Hanief, K. S. Rao., and Obsahuje bibliografii
The effect of water stress on the gas exchange (CO2, H2O), distribution, water potential (T*), membrane permeability and chlorophyll content was studied in two maize hybrids, of the high and low drought tolerance, in the vegetative phase of growth. Diťferences in the responses to drought between both hybrids were clearly marked. After 5 d of drought the decrease in the net photosynthetic rate uptake and losses, transpiration rate (E) and increase of stomata resistance (r^ were greater in the drought-resistant hybrid than in the drought-susceptible one. On the contrary, after 10 or 15 d of drought, the decrease of and 'P in whole seedlings was greater in the susceptible hybrid than in the resistant one. Significant differences between hybrids were also observed in the accumulation of *'^C, the membrane permeability and the chlorophyll content. For all treatments the amount of carbon accumulation in roots of the resistant hybrid increased, while that of the susceptible one decreased. In the drought-resistant hybrid we observed a greater chlorophyll stability and a smaller damage of cell membranes than in the sensitive one.
The effects of the atomic ratio of N to P (N:P) on the response of Alexandrium tamarense to UV radiation (UVR) were investigated in this study. Artificial sea water of 5 different N:P ratios for indoor culture and with 3 different N:P ratios for outdoor culture were used for a period of 14 and 9 d, respectively. The short-term response of cells to UVR was analyzed using a fluorometer. Cells that acclimated to nutrient conditions at the Redfield value (16:1) showed the fastest growth rate and highest pigment concentrations in both indoor and outdoor conditions, compared to those acclimated to the non-Redfield conditions. Moreover, these physiological parameters were functions of the N:P ratio according to a two-order equation (y = a + bx + cx2, R2>0.95). The fluorescence data of indoor cultures showed that A. tamarense grown at 16:1 (N:P) exhibited the greatest ratio of repair rate/damage rate (r/k) and minimum level of UVR-induced inhibition. among those grown at all of the N:P ratios following UVR exposure. Outdoor cultures had the same patterns of fluorescence as indoor cultures, but the less UVR-induced inhibitions were detected compared the former with the latter. The following three parameters, the r/k, level of inhibition caused by the two radiation treatments following 60 min of exposure (PAR and PAB, respectively), and level of UVR-induced inhibition, were also functions of the N:P ratio according to the two-order equation (R2>0.96). Further, there was a negative correlation between
UVR-induced inhibition and the r/k ratio. In summary, the Redfield value (16:1) was the optimal nutrient stoichiometry for the protection of A. tamarense against the deleterious effects of UVR. Results were not impacted by previous light history experienced by cells., W. C. Guan, L. Li., and Obsahuje bibliografii
To investigate the effects of atmospheric CO2 enrichment on physiology and autumnal leaf phenology, we exposed 3-year-old sugar maple (Acer saccharum Marsh.) seedlings to 800 (A8), 600 (A6), and 400 μL(CO2) L-1 (AA) in nine continuous stirred tank reactor (CSTR) chambers during the growing season of 2014. Leaf abscission timing, abscised leaf area percentages, leaf number, light-saturated net photosynthetic rate (PNmax), leaf area, accumulative growth rates, and biomass were determined and assessed. The results suggested the following: (1) no significant differences were found in the timing of leaf abscission in the three CO2-concentration treatments; (2) PNmax was continuously stimulated to the greatest extent in A8 at 319% and 160% in A6 until the end of the growing season, respectively; and (3) leaf number, leaf area, and accumulative height growth all significantly increased by elevated CO2, which led to a 323% increase in A8 biomass and 235% in A6 biomass after 156-d fumigation. In summary, the results suggest, the timing of leaf abscission of sugar maple in fall was not modified by CO2 enrichment, the increased carbon gain by elevated CO2 was mainly due to increased leaf area, more leaves, and the continuously enhanced high photosynthesis throughout the growing season instead of the leaf life span., L. Li, W. J. Manning, X. K. Wang., and Obsahuje bibliografii