The effect of differing environmental conditions on competition for resources was investigated by a comparison of net photosynthetic rate (PN) and vegetative production of Indiangrass [Sorghastrum nutans (L.) Nash.] at two strip mine sites with differing reclamation histories, and a railroad prairie site where this species occurs naturally. The treatment for a competition experiment consisted of tying back all species of neighboring plants around a target plant, and measuring its PN and vegetative performance during the growing season. Environmental variables at each site were also measured during the growing season. Soil bulk density and pH were higher at the two mine sites than at the prairie site, and soil texture, nutrients, and water potential were different at each of the three sites. PN of target plants compared closely among the three sites, and were lowest for plants at the railroad prairie. The competition experiment indicated that lower canopy leaves were most affected by competition for photosynthetically active radiation (PAR) at all sites. Significant differences in PN of upper canopy leaves were found between treatment and control plants at one of the mine sites. This site had higher soil water potentials and higher soil levels of P and K than the other mine site or the railroad prairie. Target plants at the other mine site experienced a low competition for PAR, likely due to lower soil moisture availability and therefore lower aboveground productivity. The largest differences in PN and irradiances between upper and lower canopy leaves occurred in target plants with neighbors at the railroad prairie, likely due to inter-specific competition. Vegetative production of the target plants also reflected the environment at each site, but did not reflect PN differences between treatments. S. nutans is well adapted to the varying environment at these three sites, and aboveground competition for radiant energy was probably not as limiting for this C4 grass as belowground competition. and V. A. Skeel, D. J. Gibson.
Quercus ilex plants grown on two different substrates, sand soil (C) and compost (CG), were exposed to photosynthetic photon flux densities (PPFD) at 390 and 800 µmol(CO2) mol-1 (C390 and C800). At C800 both C and CG plants showed a significant increase of net photosynthetic rate (PN) and electron transport rate (ETR) in response to PPFD increase as compared to C390. In addition, at C800 lower non-photochemical quenching (NPQ) values were observed. The differences between C390 and C800 were related to PPFD. The higher PN and ETR and the lower dissipative processes found in CG plants at both CO2 concentrations as compared to C plants suggest that substrate influences significantly photosynthetic response of Q. ilex plants. Moreover, short-term exposures at elevated CO2 decreased nitrate photo-assimilation in leaves independently from substrate of growth. and C. Arena, L. Vitale, A. Virzo De Santo.
The effects of shade on the gas exchange of four Hosta cultivars were determined under differing irradiances (5, 30, 50, and 100 % of full irradiance) within pots. Irradiance saturation ranged between 400-800 μmol m-2 s-1 among the four cultivars, of which H. sieboldiana cv. Elegans and H. plantagenea cv. Aphrodite exerted the lowest saturation and compensation irradiances. The maximal photosynthetic rate (Pmax) was significantly higher in shade than in full irradiance in Elegans and Aphrodite, and was at maximum in seedlings grown in 30 % of full irradiance. The best shade treatment for cvs. Antioch and Golden Edger was 50 % of full irradiance. The diurnal gas exchange patterns in four cultivars were greatly influenced by the irradiance. Single-peak patterns of net photosynthetic rate (PN) and stomatal conductance (gs) were observed under 5 and 30 % full irradiance for all the cultivars while Elegans and Aphrodite suffered from midday depression in 50 % of full irradiance. Under open sky, all four cultivars showed two-peak patters in their diurnal gas exchange, but the midday depression was less in Antioch and Golden Edger than in Elegans and Aphrodite. According to their photosynthetic responses to shade, the shade tolerance of the four cultivars was in the order: Elegans>Aphrodite>Antioch>Golden Edger. and J. Z. Zhang ... [et al.].
Infiltration of methyl viologen (MV, source of O2-) and Na-diethyldithiocarbamate (DDC, inhibitor of SOD) into wheat leaves resulted in the accumulation of active oxygen species and photo-oxidative damage to photosynthetic apparatus under both moderate and high irradiance. Exogenous antioxidants, ascorbate (ASA) and mannitol, scavenged active oxygen efficiently, protected the photosynthetic system from MV and DDC induced oxidative damage, and maintained high Fv/Fm [maximal photochemical efficiency of photosystem 2 (PS2) while all PS2 reaction centres are open], Fm/F0 (another expression for the maximal photochemical efficiency of PS2), ΦPS2 (actual quantum yield of PS2 under actinic irradiation), qP (photochemical quenching coefficient), PN (net photosynthetic rate), and lowered qNP (non-photochemical quenching coefficient) of the leaves kept under high irradiance and oxidative stress. Phenolic compounds used in these experiments, catechol (Cat), resorcinol (Res), and tannic acid (Tan), had similar anti-oxidative activity and protective effect on photosynthetic apparatus as ASA and mannitol. The anti-oxidative activity and the protective effect of phenolic compounds increased with increase in their concentration from 100 to 300 g m-3. The number and the position of hydroxyl group in phenolic molecules seemed to influence their antioxidative activity. and Hui Jie Zhao, Qi Zou.
On the basis of values from literature it was established that photosynthetically used radiation (PUR) amounts to 6 % of absorbed radiant energy in cabbage (producer of high yields), 3.5 % in sugar beet leaves, and 2.6 % in tobacco leaves. PUR of these species did not depend on irradiance in a wide range from 22 to 287 W m-2.
To assess photosynthesis and yield components' response of field-grown wheat to increasing ozone (O3) concentration (based on diurnal pattern of ambient O3) in China, winter wheat (Triticum aestivum L.) cv. Jia 403 was planted in open top chambers and exposed to three different O3 concentrations: O3-free air (CF), ambient air (NF), and O3-free air with additional O3 (CF+O3). Diurnal changes of gas exchange and net photosynthetic rate (PN) in response to photosynthetic photon flux density (PPFD) of flag leaves were measured at the filling grain stage, and yield components were investigated at harvest. High O3 concentration altered diurnal course of gas exchange [PN, stomatal conductance (gs), and intercellular CO2 concentration (Ci)] and decreased significantly their values except for Ci. Apparent quantum yield (AQY), compensation irradiance (CI), and saturation irradiance (SI) were significantly decreased, suggesting photosynthetic capacity was also altered, characterized as reduced photon-saturated photosynthetic rate (PNmax). The limit of photosynthetic activity was probably dominated by non-stomatal factors in combination with stomatal closure. The significant reduction in yield was observed in CF+O3 treatment as a result of a marked decrease in the ear length and the number of grains per ear, and a significant increase in the number of infertile florets per ear. Even though similar responses were also observed in plants exposed to ambient O3 concentration, no statistical difference was observed at current ambient O3 concentration in China. and Z.-Z. Feng ... [et al.].
a1_Chromolaena odorata is a widespread exotic weed in southern China and other regions of the world. To better understand its invasive strategies, we compared leaf pigment contents and gas-exchange traits of the invader with its two coexisting species (native Urena lobata and invasive Bidens pilosa) under combined conditions of irradiance (full, medium, and low) and nitrogen (full, medium, and low) supplies. The chlorophyll (Chl) a+b content of U. lobata was the highest and the Chl a/b ratio of C. odorata was the lowest among the three weed species. In most treatments, leaf pigment, light-saturated photosynthetic rate (P max), and light saturation point (LSP) of all the species increased, while their Chl a/b ratios decreased with the increasing nitrogen. The P max and LSP of U. lobata were greater than those of the coexisting weeds under full irradiance (FI), but significantly declined with the decreasing irradiance. The invasive weeds, especially C. odorata, showed lower P max and LSP under FI, but they showed slight decrease under low irradiance. Compared to U. lobata, C. odorata exhibited the lower light compensation point (LCP) in most treatments, higher LSP under low and medium irradiance, and lower dark respiration rate under FI. In addition, all the three species showed similar responses to different irradiance and nitrogen conditions, mean phenotypic plasticity index (MPPI) of most photosynthetic variables of the two invasive species was lower than that of U. lobata. These results suggested that C. odorata behaved as a facultative shadetolerant weed, being able to grow in moderately sheltered environments; the lower MPPI might be one of the important competitive strategies during its invasion. However, its invasion should be limited to some very shady habitats., a2_In the field, control should be mainly directed against populations growing in the open or nutrient-rich habitats, where its expansion speed could be much faster. Deep shade by intact canopies or luxuriant forests might be an effective barrier against its invasion., G. M. Quan, D. J. Mao, J. E. Zhang, J. F. Xie, H. Q. Xu, M. An., and Obsahuje seznam literatury
In the bark of Populus tremula L. photochemical efficiency of photosystem 2 (PS2) determined as Fv/Fm decreased during winter. The strongest reduction was found after cold periods. The degree of reduction depended on irradiance since the lowest levels of Fv/Fm were found on the sun-exposed side of the stem and below thin phellem. Therefore, photoinhibition was partly responsible for the reduction in Fv/Fm. The photochemical efficiency of PS2 recovered in late April about a month before the trees got leaves. In the laboratory, Fv/Fm recovered within about a week under low irradiance at 20 °C. Rapid recovery of photochemical efficiency of PS2 in the bark may be important to reduce respiratory loss of CO2 from the stem before the trees get leaves. and K. A. Solhaug, J. Haugen.
Nowadays, a quest for efficient greenhouse heating strategies, and their related effects on the plant's performance, exists. In this study, the effects of a combination of warm days and cool nights in autumn and spring on the photosynthetic activity and efficiency of Phalaenopsis were evaluated; the latter, being poorly characterised in plants with crassulacean acid metabolism (CAM) and, to our knowledge, not reported before in Phalaenopsis. 24-h CO2 flux measurements and chlorophyll (Chl) fluorescence analyses were performed in both seasons on Phalaenopsis 'Hercules' exposed to relatively constant temperature regimes, 25.5/24.0°C (autumn) and 30/27°C (spring) respectively, and distinctive warm day/cool night temperature regimes, 27/20°C (autumn) and 36/24°C (spring), respectively. Cumulated leaf net CO2 uptake of the distinctive warm day/cool night temperature regimes declined with 10-16% as compared to the more constant temperature regimes, while the efficiency of carbon fixation revealed no substantial differences in both seasons. Nevertheless, a distinctive warm day/cool night temperature regime seemed to induce photorespiration. Although photorespiration is expected not to occur in CAM, the suppression of the leaf net CO2 exchange during Phase II and Phase IV as well as the slightly lower efficiency of carbon fixation for the distinctive warm day/cool night temperature regimes confirms the involvement of photorespiration in CAM. A seasonal effect was reflected in the leaf net CO2 exchange rate with considerably higher rates in spring. In addition, sufficiently high levels of photosynthetically active radiation (PAR) in spring led to an efficiency of carbon fixation of 1.06-1.27% which is about twice as high than in autumn. As a result, only in the case where a net energy reduction between the temperature regimes compensates for the reduction in net CO2 uptake, warm day/cool night temperature regimes may be recommended as a practical sustainable alternative. and B. Pollet ... [et al.].
On the basis of literature and my calculations it was established that a chlorophyll (Chl) particle anchored with a phytol chain to the thylakoid membrane takes up about 1 nm2 of the surface area. At an irradiance of 287 W m-2 the leaves of cabbage seedlings become saturated with photosynthetically active radiation (PAR) thus reaching the maximum photosynthetic rate of 100 µg(C) m-2 s-1, that is 5 CO2 molecules per 1 nm2 per second, and the maximum power with which the Chl particle supplies the process of photosynthesis is 15 aJ.