Alkalies are important agricultural contaminants complexly affecting plant metabolism. In this study, rice seedlings were subjected to alkaline stress (NaHCO3:Na2CO3 = 9:1; pH 8.9) for 30 days. The results showed that stress mightily reduced net photosynthetic rate (PN), but slightly decreased transpiration rate and stomatal conductance. This indicated that decline of PN might be a result of nonstomatal factors. Alkaline stress caused a large accumulation of Na+ in leaves up to toxic concentration, which possibly affected chloroplast ultrastructure and photosynthesis. We found that alkaline stress reduced chlorophyll fluorescence parameters, such as ratios of Fv′/Fm′, Fv/Fm, photosystem (PS) II efficiency, and electron transport rates in rice plants, i.e. it influenced the efficiencies of photon capture and electron transport by PSII. This might be a main reason for the decrease of PN under such conditions. Deficiency of minerals could be another reason for the decline of PN. Alkaline stress lowered contents of N, K, Cu, Zn, P, and Fe in rice plants. In addition, the stress strongly affected metabolism of amino acids. This might be caused by imbalance in carbon metabolism as a result of photosynthesis reduction., Z.-H. Wu, C.-W. Yang, M.-Y. Yang., and Obsahuje bibliografii
The net photosynthetic rate (PN), transpiration rate (E), and water use efficiency (WUE) of two divergent Leymus chinensis populations from the grassland region of Northeast China were compared. The two populations experienced the similar habitats, but differed in leaf colour, stomata numbers, and chlorophyll contents. The leaf PN for the grey-green (GG) population was greater than that for the yellow-green (YG) population, while the leaf E for GG population was lower than that for the YG population. The greater WUE for the GG population suggests that this type is more able to maintain higher PN under drought and is more fit for the rangeland use in this climate region. and R. Z. Wang, Q. Gao.
In the order C. microphylla - C. intermedia - C. korshinskii, compensation irradiance, saturation irradiance, and optimum temperature for photosynthesis increased, net photosynthetic rate (PN) at low irradiance and low temperature decreased, optimum air humidity decreased, and PN at low air humidity increased. Daily cumulative value of PN increased while daily cumulative value of transpiration (E) decreased, and hence water use efficiency (WUE =PN/E) increased. Diurnal course of PN of C. microphylla was a double-peak curve, but the second peak in the curves of C. intermedia and C. korshinskii was not visible. These physiological characteristics are biological basis for the geographical distribution of these three Caragana species, and are in relation to water conditions of their habitats and distinctiveness in leaf hair of plant. and C. C. Ma ... [et al.].
Net photosynthetic rate (PN), transpiration rate (E), and stomatal conductance (gs) declined from upper leaves to the lower ones during dry and rainy seasons, indicating that long-term carbon budget should take into account PN variations for different leaf types. Relatively greater PN in the dry season suggested that this species is more able to maintain higher PN under drought, but the relatively higher E in the dry season might reduce water use efficiency (PN/E) for the species. Significant correlations between PN and gs indicated that gs may be the critical factor for PN variability in the desert region. and R. Z. Wang ... [et al.].
The intra- and inter-specific variations in net photosynthetic (PN) and transpiration (E) rates and water use efficiency (WUE) of Puccinellia tenuiflora and Puccinellia chinampoensis leaves were compared. The two species experienced a similar habitat, but differed in leaf area, leaf colour, and nitrogen contents. Leaf PN and E for both reproductive and vegetative shoots of the two species declined with leaf age. PN for reproductive shoots was less than for vegetative shoots, but their E was greater than that of vegetative shoots in the dry season. The average PN and E for reproductive shoots of P. tenuiflora were lower than those of P. chinampoensis, but higher for vegetative shoots. and R. Z. Wang, Y. Q. Yuan.
The differences in net photosynthetic rate (PN), transpiration rate (E), and water use efficiency (WUE) between the vegetative and reproductive shoots of three native grass species from the grassland of northeastern China [grey-green and yellow green populations of Leymus chinensis (Trin.) Tzvel., Puccinellia tenuiflora (Griseb) Scrib & Merr, Puccinellia chinampoensis Ohwi] were compared. The two type shoots experienced similar habitats, but differed in leaf life-span and leaf area. The leaf PN and WUE for the vegetative shoots were significantly higher than those for the reproductive shoots in the grasses, while their E were remarked lower in the dry season. Relative lower leaf PN and WUE for the reproductive shoots of grassland grasses may explain the facts of lower seed production and the subordinate role of seed in the grassland renewal in north-eastern China.
The effects of water deficit and re-irrigation were studied in glasshouse-grown rice plants (cvs. Cimarrón and Fonaiap 2000) which differ in their susceptibility to water deficit. Relative water content decreased from >90 to 67-69 % and recovered to pre-stress values within 24 h after re-irrigation. The irradiance-saturated rate of photosynthesis (Psat), transpiration rate (E), and stomatal conductance (gs) decreased with water deficit. E and gs decreased similarly in both cultivars, but Psat was more strongly inhibited in Cimarrón than in Fonaiap 2000. Water deficit increased water use efficiency (WUET) over 2-fold in Fonaiap 2000 and by 1.5-fold in Cimarrón. The ratio of intercellular to ambient CO2 concentration (Ci/Ca) decreased in Fonaiap 2000 during mild stress but increased at severe stress. Contrarily, Cimarrón did not change Ci/Ca with water deficit. After re-irrigation Fonaiap 2000 recovered Psat to ca. 80 % of control values 24 h after re-irrigation, whereas Cimarrón recovered to 60 % of control values 48 h after re-irrigation. E and gs recovered to a lesser extent (50 %) than
Psat, after 48 h of re-irrigation in both cultivars. Total aboveground and green (live) biomass were unaffected by water deficit in Fonaiap 2000 but were reduced by 21 and 40 % in Cimarrón, respectively. Dead biomass increased in stressed plants of both cultivars but to a larger extent in Cimarrón than in Fonaiap 2000. Water deficit increased δ13C in Fonaiap 2000, whereas Cimarrón was unaffected by water deficit showing lower values than those of Fonaiap 2000. δ13C was highly and linearly correlated to the ratio
Ci/Ca. WUET was also significantly correlated to δ13C. and A. J. Pieters, M. Núñez.
A field experiment involving two planting densities (83,333 and 166,666 plants per ha), two cropping systems (monoculture and mixed culture) and five cowpea [Vigna unguiculata L. (Walp.)] genotypes was conducted at Nietvoorbij (33°54S, 18°14E), Stellenbosch, South Africa, to select cowpea material with superior growth and water-use efficiency (WUE). The results showed significantly higher photosynthetic rates, stomatal conductance and transpiration in leaves of plants at low density and in monoculture due to greater chlorophyll (Chl) levels relative to those at high density and in mixed culture. As a result, C concentration in leaves and the amount of C, P, K, Ca, Mg, Fe, Cu, Zn, Mn, and B accumulated in shoots at low density and under monoculture were also much higher. Even though no marked differences in photosynthetic rates were found between and among the five cowpea genotypes, leaf C concentration and shoot C, P, K, Ca, Mg, Fe, Cu, Zn, Mn, and B contents differed considerably, with Sanzie exhibiting the highest C concentration and C, P, K, Ca, Mg, Fe, Cu, Zn, Mn, and B contents in shoots, followed by Bensogla and Omondaw, while ITH98-46 and TVu1509 had the lowest shoot concentration and contents of C, P, K, Ca, Mg, Fe, Cu, Zn, Mn, and B. WUE (calculated as photosynthate produced per unit water molecule transpired) was significantly greater in plants at low density and monoculture relative to those at high density and in mixed culture. Isotopic analysis revealed significant differences in δ13C values of sorghum [Sorghum bicolor L. (Moench.)] and cowpea, with higher δ13C values being obtained for plants at low density and in monoculture relative to those at high density or in mixed culture. The five cowpea genotypes also showed significant differences in δ13C values, with Sanzie exhibiting the most negative value (i.e. low WUE) and ITH98-46, the least negative δ13C value (i.e. high WUE). Whether measured isotopically or from gas-exchange studies, sorghum (a C4 species) exhibited much higher WUE relative to cowpea (a C3 species). Both correlation and regression analyses revealed a positive relationship between WUE from gas-exchange studies and δ13C values from isotopic analysis of cowpea and sorghum shoots. and J. H. J. R. Makoi, S. B. M. Chimphango, F. D. Dakora
The relationship between light-saturated photosynthetic capacity
(Pmax) and leaf nitrogen (N) content was investigated for one year in a 15-year-old Chamaecyparis obtusa canopy and was compared with a Cryptomeria japonica canopy previously described. The linear regression between P max and leaf N content tended to converge toward a single line segment from July to January and in May for C. obtusa. The slope of the linear regression between Pmax and leaf N content of C. obtusa was gentler than that of C. japonica. The smaller regression coefficient of C. obtusa may reflect species differences in nitrogen nutrition requirements between C. obtusa and C. japonica. A pronounced decrease in the slope of the linear regression lines due to low temperature was observed in February and March. During this period, P max of C. obtusa declined more than that of C. japonica suggesting that C. obtusa is less tolerant to low temperatures than C. japonica., H. Kobayashi, S. Inoue, and K. Gyokusen., and Obsahuje bibliografii
Tropical forest disturbances lead to the establishment of secondary successional plant communities constituted by light demanding species with high relative growth rate that conduct to rapid canopy closure. Two main strategies for N nutrition are: (a) mineral N acquisition in the form of NH4 and NO3, and (b) symbiotic atmospheric N2 fixation. Given the high N requirement for maximization of leaf area and radiant energy absorption, we hypothesize that contrasting strategies of N nutrition in these environments are reflected in leaf photosynthetic characteristics. We compared the N-photosynthesis relationships and carbon balance parameters per unit leaf area as they vary with age in two species with contrasting N acquisition strategies: a N2-fixer Crotalaria anagyroides HBK (Papilionoideae), and a mineral-N user Verbesina turbacensis HBK (Asteraceae). N2 fixation capacity was associated to higher specific leaf area (SLA), higher photosynthetic capacity (Pmax) per unit leaf area and leaf mass, and higher N content per unit leaf mass. The N2-fixer species showed higher slope in the relationship Pmax-N per unit leaf mass and area when compared to the leaves of non-fixer species. Moreover, the intrinsic photosynthetic N use efficiency (Pmax/N) was higher in the N2 fixer than in leaves of the non-fixer species. Changes in N due to leaf age resulted in larger changes in CO2 flux density at the leaf level in the N2-fixer species. The higher photosynthetic capacity of the N2-fixer species was mechanistically related to higher stomatal conductance, internal CO2 concentration (ci) values closer to atmospheric CO2 concentration (ca), and lower intrinsic water use efficiency than the mineral N-user species. Despite their higher Pmax per unit leaf area, total non-structural saccharides concentration was lower in mature leaves of the N2-fixer plant as compared to the non-fixer counterpart. This might be caused by the presence of a larger root sink (symbionts) stimulating saccharides export and higher diurnal respiration rates. and A. Quilici, E. Medina.