In this study, cotton seedlings were subjected to osmotic-, salt- and alkali stresses. The growth, photosynthesis, inorganic ions, and organic acids in the stressed seedlings were measured, to compare the mechanisms by which plants adapt to these stresses and attempt to probe the mechanisms by which plants adapt to high pH stress. Our results indicated that, at high stress intensity, both osmotic and alkali stresses showed a stronger injurious effect on growth and photosynthesis than salt stress. Cotton accumulated large amount of Na+ under salt and alkali stresses, but not under osmotic stress. In addition, the reductions of K+, NO3 -, and H2PO4 - under osmotic stress were much greater than those under salt stress with increasing stress intensity. The lack of inorganic ions limited water uptake and was the main reason for the higher injury from osmotic-compared to salt stress on cotton. Compared with salt- and alkali stresses, the most dramatic response to osmotic stress was the accumulation of soluble sugars as the main organic osmolytes. In addition, we found that organic acid metabolism adjustment may play different roles under different types of stress. Under alkali stress, organic acids might play an important role in maintaining ion balance of cotton; however, under osmotic stress, malate might play an important osmotic role. and W. Chen ... [et al.].
Field trials under rain-fed conditions at the International Center for Tropical Agriculture (CIAT) in Colombia were conducted to study the comparative leaf photosynthesis, growth, yield, and nutrient use efficiency in two groups of cassava cultivars representing tall (large leaf canopy and shoot biomass) and short (small leaf canopy and shoot biomass) plant types. Using the standard plant density (10,000 plants ha-1), tall cultivars produced higher shoot biomass, larger seasonal leaf area indices (LAIs) and greater final storage root yields than the short cultivars. At six months after planting, yields were similar in both plant types with the short ones tending to form and fill storage roots at a much earlier time in their growth stage. Root yield, shoot and total biomass in all cultivars were significantly correlated with seasonal average LAI. Short cultivars maintained lower than optimal LAI for yield. Seasonal PN, across cultivars, was 12% greater in short types, with maximum values obtained in Brazilian genotypes. This difference in PN was attributed to nonstomatal factors (i.e., anatomical/biochemical mesophyll characteristics). Compared with tall cultivars, short ones had 14 to 24 % greater nutrient use efficiency (NUE) in terms of storage root production. The lesser NUE in tall plants was attributed mainly to more total nutrient uptake than in short cultivars. It was concluded that short-stemmed cultivars are superior in producing dry matter in their storage roots per unit nutrient absorbed, making them advantageous for soil fertility conservation while their yields approach those in tall types. It was recommended that breeding programs should focus on selection for more efficient short- to medium-stemmed genotypes since resource-limited cassava farmers rarely apply agrochemicals nor recycle residual parts of the crop back to the soil. Such improved short types were expected to surpass tall types in yields when grown at higher than standard plant population densities (>10,000 plants ha-1) in order to maximize irradiance interception. Below a certain population density (<10,000 plants ha-1), tall cultivars should be planted. Findings were discussed in relation to cultivation and cropping systems strategies for water and nutrient conservation and use efficiencies under stressful environments as well as under predicted water deficits in the tropics caused by trends in global climate change. Cassava is expected to play a major role in food and biofuel production due to its high photosynthetic capacity and its ability to conserve water as compared to major cereal grain crops. The interdisciplinary/interinstitutions research reported here, including, an associated release of a drought-tolerant, short-stem cultivar that was eagerly accepted by cassava farmers, reflects well on the productivity of the CIAT international research in Cali, Colombia., and M. A. El-Sharkawy, S. M. de Tafur
The effects of potassium (K) deficiency on chlorophyll (Chl) content, photosynthetic gas exchange, and photosystem II (PSII) photochemistry during the seedling stage were investigated in two soybean [Glycine max (L.) Merr.] cultivars, low-K sensitive Tiefeng31 and low-K tolerant Shennong6. The cultivars were grown hydroponically in K-sufficient (KS) and K-deficient (KD) solutions. Photosynthetic gas exchange and Chl content in Tiefeng31 were severely affected by the low K condition, but were almost unaffected in Shennong6. This difference is in accordance with the PSII photochemistry in the plants, indicating that the photosynthetic apparatus of Shennong6 is more tolerant to low-K stress than that of Tiefeng31. and X.-T. Li ... [et al.].
The parameters estimated from traditional A/Ci curve analysis are dependent upon some underlying assumptions that substomatal CO2 concentration (Ci) equals the chloroplast CO2 concentration (Cc) and the Ci value at which the A/Ci curve switches between Rubisco- and electron transport-limited portions of the curve (Ci-t) is set to a constant. However, the assumptions reduced the accuracy of parameter estimation significantly without taking the influence of Ci-t value and mesophyll conductance (gm) on parameters into account. Based on the analysis of Larix gmelinii's A/Ci curves, it showed the Ci-t value varied significantly, ranging from 24 Pa to 72 Pa and averaging 38 Pa. t-test demonstrated there were significant differences in parameters respectively estimated from A/Ci and A/Cc curve analysis (p<0.01). Compared with the maximum ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) carboxylation rate (Vcmax), the maximum electron transport rate (Jmax) and Jmax/Vcmax estimated from A/Cc curve analysis which considers the effects of gm limit and simultaneously fits parameters with the whole A/Cc curve, mean Vcmax estimated from A/Ci curve analysis (Vcmax-Ci) was underestimated by 37.49%; mean Jmax estimated from A/Ci curve analysis (Jmax-Ci) was overestimated by 17.8% and (Jmax-Ci)/(Vcmax-Ci) was overestimated by 24.2%. However, there was a significant linear relationship between Vcmax estimated from A/Ci curve analysis and Vcmax estimated from A/Cc curve analysis, so was it Jmax (p<0.05). and W. Zeng ... [et al.].
a1_Photosynthetic gas exchange, dry mass production, water relations and inducibility of crassulacean acid metabolism (CAM) pathway as well as antioxidative protection during the C3-CAM shift were investigated in Sedum album and Sedum stoloniferum from Crassulaceae under water stress for 20 days. Leaf relative water content (RWC), leaf osmotic and water potential decreased with increasing water stress in both studied species. Significant reduction in dry matter production and leaf thickness was detected only in S. stoloniferum after 20-d water stress. Δtitratable acidity and phosphoenolpyruvate carboxylase (PEPC) activity in S. album responded to drought at early stages of stress treatment, continued to increase throughout the entire stress period and reached levels 15 times higher than those in well-watered plants. In S. stoloniferum, however, both parameters responded later and after a transient increase declined again. In S. stoloniferum, in spite of increase by drought stress, net night-time CO2 assimilation was negative resembling a C3-like pattern of gas exchange. Catalase (CAT), ascorbate peroxidase (APX), and superoxide dismutase (SOD) activities increased in plants subjected to mild water stress while declined as the stress became severe. Although malondialdehyde (MDA) content was higher in drought-stressed S. stoloniferum, the increase in the concentration of hydrogen peroxide (H2O2) that may act as a signal for C3-CAM transition was higher in S. album compared with S. stoloniferum. In drought-stressed plants, SOD activity showed a clear diurnal fluctuation that was more steadily expressed in S. album. In addition, such pattern was observed for CAT only in S. album. We concluded that temporal and diurnal fluctuation patterns in the activity of antioxidant enzymes depended on duration of drought stress and was related to the mode of photosynthesis and degree of CAM induction., a2_According to our results, S. stoloniferum developed a low degree of CAM activity, e.g. CAM-cycling metabolism, under drought conditions., G. Habibi, R. Hajiboland., and Obsahuje bibliografii
The diurnal trends of gas exchange and chlorophyll fluorescence parameters in four Lycoris species (L. houdyshelii, L. aurea, L. radiata var. pumila and L. albiflora) were determined and compared with a portable photosynthesis analysis system. Our study revealed that L. houdyshelii had the lowest light compensation point (LCP), while the other three species had higher LCP (12.37-14.99 μmol m-2 s-1); L. aurea had the highest light saturation point (LSP) (1,189 μmol m-2 s-1), and L. houdyshelii and L. albiflora had lower LSP with the values being 322 and 345 μmol m-2 s-1, respectively, and L. radiata var. pumila showed the intermediate LSP. Both the species L. houdyshelii and L. albiflora exhibited a typical and obvious decline in net photosynthetic rate (PN) during midday, which was not observed in L. aurea. This indicated a possible photoinhibition in L. houdyshelii and L. albiflora as the ratio of variable to maximum fluorescence (Fv/Fm) values were higher in these two species. The minimal fluorescence (F0) values were lower in L. aurea and L. radiata var. pumila. The diurnal changes of transpiration rate (E) in all four species presented only one peak, appearing between 11:00 h or 13:00 h. By using simple correlation analyses, it was observed that the environmental factors affecting
PN were different among four species and the main factors were photosynthetic photon flux density (PPFD) and relative humidity especially for L. aurea and L. radiata. The results of studying indicated that the four species could be divided into two groups. The species L. radiata var. pumila and L. aurea were more adapted to a relatively high irradiance, and L. houdyshelii and L. albiflora could be grown in moderate-shade environment in order to scale up their growth and productivity., K. Liu ... [et al.]., and Obsahuje bibliografii
Leaf tissue damaging to seedlings can limit their subsequent growth, and the effects may be more extensive. Compensatory photosynthesis responses of the remnant cotyledon and primary leaf of Pharbitis purpurea to clipping and the effect of clipping on seedling growth were evaluated in a pot-cultivated experiment. Three treatments were conducted in the experiment, which were clipped cotyledon (CC), clipped second leaf (CL), and control group (CG). The area, thickness, mass, and longevity of the remaining cotyledon of CC exhibited over-compensatory growth. In contrast, seedlings of CC had under-compensatory growth in seedling height, root length, seedling mass, and root to shoot ratio. However, the traits of remnant cotyledon and seedling in CL treatment exhibited equal-compensatory growth. Net photosynthetic rate of the cotyledon of CC was significantly higher than those of CL and CG treatments, and the diurnal changes in photosynthetic rates showed significantly different patterns which were unimodal curve (CC) and bimodal curve (CL and CG), respectively. There was no significant difference between CL and CG treatment. Net photosynthetic rate of the primary leaf of CL was significantly higher than that of CG treatment. However, the photosynthetic rates of primary leaves of CL and CG treatments showed similar photosynthetic patterns characterized by a bimodal curve. P. purpurea seedlings used a compensatory growth strategy in the remaining cotyledon or the primary leaf to resist leaf loss and minimize any adverse effects. and W. Zheng ... [et al.].
The proportional light absorptance by photosynthetic tissue (α) is used with chlorophyll (Chl) fluorescence methods to calculate electron transport rate (ETR). Although a value of α of 0.84 is often used as a standard for calculating ETR, many succulent plant species and species with crassulacean acid metabolism (CAM) have photosynthetic tissues that vary greatly in color or are highly reflective, and could have values of α that differ from 0.84, thus affecting the calculation of ETR. We measured ETR using Chl fluorescence and α using an integrating sphere in 58 plant species to determine the importance of applying a measured value of α when calculating ETR. Values of α varied from 0.55-0.92 with a mean of 0.82 across species. Differences between ETR values calculated with measured α values ranged from 53% lower to 12% greater than ETR values calculated with a standard α value of 0.84 and were significantly different in 39 out of 58 species. While measurements of ETR using Chl fluorescence represent a rapid and effective assessment of physiological performance, the value of α needs to be considered. Measurements of α, especially on species with light-colored or reflective photosynthetic tissue, will allow more accurate determination of photosynthesis in succulent and CAM species. and J. A. Stemke, L. S. Santiago
We compared variation in sun-canopy leaf anatomy, morphology and photosynthetic rates of coexisting woody species (trees and lianas) in an 8-year-old secondary forest (SF) and mature forest (MF) in the wet season in Xishuangbanna, SW China. Variability of leaf traits of 66 species within growth-form groups in each forest was quantified using coefficients of variation (CV). For the mean values, the woody species in the SF had significantly higher leaf thickness and stomatal density, but lower nonmesophyll/mesophyll ratios than those in the MF. The average leaf area and leaf mass area (LMA) in the studied woody species did not change greatly during the successional process, but differed significantly between the growth forms, with trees having higher values than lianas. The light-saturated photosynthetic rate per unit leaf area (Aa) of the woody species in the SF ranged from 11.2 to 34.5 μmol m-2 s-1, similarly to pioneer tree species from literature data in southeast Asia. The Aa and photosynthetic nitrogen-use efficiency (PNUE) were significantly higher than those in the MF; whereas Aa in the MF ranged between 9 to 21 μmol m-2 s-1, with similar values between lianas and trees. For all woody species in both SF and MF, there were no significant differences in the average values of the CV of all measured variables for both lianas and trees. However, considerable variation in leaf anatomy, morphology, and photosynthetic rates within both growth forms and forests existed, as well as substantial variation in leaf size and stomatal density. We concluded that the tropical woody species formed a heterogeneous functional group in terms of leaf morphology and physiology in both secondary and mature forests. and L. Han ... [et al.].
Photosynthetic parameters and leaf carbon isotope composition (δ13C) in contrasting rice genotypes in relation to supplemental nitrogen (N) application and water management during the grain-filling period were compared. The changes in stomatal conductance (gs) and ratio of intercellular to ambient CO2 mole fraction (Ci/Ca) depended on the leaf nitrogen concentration (leaf N) in both ‘Hinohikari’ (temperate japonica genotype) and ‘IR36’ (indica genotype). In ‘Hinohikari’, δ13C reflects photosynthetic gas exchange during the grain-filling period, which is indicated by the significant response of δ13C to leaf N. In contrast, in ‘IR36’ δ13C did not depend on leaf N. This varietal difference in δ13C to leaf N can be attributed to a difference in the timing of leaf senescence. In ‘IR36’, leaf N and photosynthetic parameters decreased more rapidly, indicating earlier senescence and a shorter grain-filling period in comparison with ‘Hinohikari’. The significant increase in shoot dry mass in ‘Hinohikari’ resulting from supplemental N application, compared with nonsignificant effect observed in ‘IR36’, suggests that the timing of senescence in relation to the grainfilling period has a preponderant influence on productivity., S. Shimoda., and Obsahuje bibliografii