a1_This study evaluated the relationship between photosynthetic carbon accumulation and symbiotic nitrogen nutrition in young fully expanded leaves of 30 nodulated cowpea genotypes grown in the field at Manga, Ghana, in 2005 and 2006. Estimates of fixed-N in photosynthetic leaves revealed greater symbiotic N in genotypes with higher photosynthetic rates and increased leaf transpiration rate/efficiency. There was also greater C accumulation in genotypes with higher symbiotic N and/or total N. Additionally, genotypes with high contents of C per unit of leaf total N exhibited greater C per unit of leaf N-fixed. The C/N and C/Rubisco-N ratios were generally similar in their magnitude when compared to the C/N-fixed ratio due possibly to the fact that Rubisco accounts for a high proportion of photosynthetic leaf N, irrespective of whether the enzyme was formed from soil N or symbiotic N. Cowpea genotypes that relied heavily on soil N for their N nutrition exhibited much higher C/N-fixed ratios, while conversely those that depended more on symbiosis for meeting their N demands showed markedly lower C/N-fixed values. For example, genotypes Omondaw, Bensogla, IT93K-2045-29, and Sanzie, which respectively derived 83.9, 83.1, 82.9, and 76.3% N from fixation, recorded lower C/N-fixed ratios of 10.7, 12.2, 12.1, and 13.0 mg mg-1 in that order in 2005. In contrast, genotypes Botswana White, IT94D-437-1, TVu1509, and Apagbaala, which obtained 14.8, 15.0, 26.4, and 26.0% of their N nutrition from fixation, showed high C/N-fixed values of 84.0, 69.0, 35.2, and 40.6 mg.mg-1, respectively, in 2005., a2_This clearly indicates that genotypes that obtained less N from symbiosis and more N from soil revealed very high C/N-fixed values, an argument that was reinforced by the negative correlations obtained between the three C/N ratios (i.e. C/N, C/Rubisco-N, and C/N-fixed) and leaf N concentration, percentage nitrogen derived from fixation, total N content, amount of N-fixed, and Rubisco N. These data suggest a direct link between photosynthetic C accumulation and symbiotic N assimilation in leaves of nodulated cowpea, and where genotypes derived a large proportion of their N from fixation, photosynthetic C yield substantially increased., A. K. Belane, F. D. Dakora., and Obsahuje seznam literatury
The relationship between ash content and carbon isotope discrimination (Δ) was studied in durum wheat (Triticum durum Desf.) grown in a Mediterranean region (Northwest Syria) under three different water regimes (hereafter referred to as environments). In two of these environments, 144 genotypes were cultivated under rain-fed conditions. In the third environment, 125 genotypes were cultivated under irrigation. Ash content was measured in the flag leaf about 3 weeks after anthesis, whereas Δ was analysed in mature kernels. Total transpiration of the photosynthetic tissues of the culm contributing, from heading to maturity, to the filling of kernels was also estimated. Leaf ash content, expressed either on dry matter or leaf area basis or as total ash per blade, correlated positively (p< 0.001) with Δ in the three environments. However, this relationship was not the result of a positive correlation across genotypes between Δ and tissue water content. Moreover, only a small part of the variation in Δ across genotypes was explained by concomitant changes in ash content. When all genotypes across the three environments were plotted, Δ and ash content followed a non-linear relationship (r2 = 74), with Δ tending to a plateau as the ash content increased. However, for the set of genotypes and environments combined, total ash content per leaf blade was positively and linearly related (r2 = 0.76) with the accumulated culm transpiration. The non-linear nature of the relationship between ash content and Δ is sustained by the fact that culm transpiration also showed a non-linear relationship with kernel Δ. Therefore, differences in leaf ash content between environments, and to a lesser extent between genotypes, seem to be brought about by variations in accumulated transpiration during grain formation. and J. L. Araus ... [et al.].
The combined effects of water status, vapour pressure deficit (VPD), and elevated temperature from heading to maturity were studied in barley. Plants growing at high VPD, either under well-watered or water deficit conditions, had higher grain yield and grain filling rate than plants growing at low VPD. By contrast, water stress decreased grain yield and individual grain dry matter at any VPD. Water regime and to a lesser extent VPD affected δ13C of plant parts sampled at mid-grain filling and maturity. The differences between treatments were maximal in mature grains, where high VPD increased δ13C for both water regimes. However, the total amount of water used by the plant during grain filling did not change as response to a higher VPD whereas transpiration efficiency (TE) decreased. The net photosynthetic rate (PN) of the flag leaves decreased significantly under water stress at both VPD regimes. However, PN of the ears was higher at high VPD than at low VPD, and did not decrease as response to water stress. The higher correlation of grain yield with PN of the ear compared with that of the flag leaf support the role of ear as the main photosynthetic organ during grain filling under water deficit and high VPD. The deleterious effects of combined moderately high temperature and drought on yield were attenuated at high VPD. and M. Sánchez-Díaz ... [et al.].
Five-year-old plants of two olive cultivars (Frantoio and Moraiolo) grown in large pots were exposed for 7 to 8 months to ambient (AC) or elevated (EC) CO2 concentration in a free-air CO2 enrichment (FACE) facility. Exposure to EC enhanced net photosynthetic rate (PN) and decreased stomatal conductance, leading to greater instantaneous transpiration efficiency. Stomata density also decreased under EC, while the ratio of intercellular (Ci) to atmospheric CO2 concentration and chlorophyll content did not differ, except for the cv. Moraiolo after seven months of exposure to EC. Analysis of the relationship between photosynthesis and Ci indicated no significant change in carboxylation efficiency of ribulose-1,5-bisphosphate carboxylase/oxygenase after five months of exposure to EC. Based on estimates derived from the PN-Ci relationship, there were no apparent treatment differences in daytime respiration, CO2 compensation concentration, CO2-saturated photosynthetic rate, or photosynthetic rate at the mean Ci, but there was a reduction in stomata limitation to PN at EC. Thus 5-year-old olive trees did not exhibit down regulation of leaf-level photosynthesis in their response to EC, though some indication of adjustment was evident for the cv. Frantoio with respect to the cv. Moraiolo. and R. Tognetti ... [et al.].