Cost-benefit analysis of foliar construction and maintenance costs and of carbon assimilation of leaves of differing life-span were conducted using two evergreen, three semi-deciduous, and three deciduous tree species of savannas of north Australia. Rates of radiant-energy-saturated CO2 assimilation (Pmax) and dark respiration were measured and leaves were analysed for total nitrogen, fat, and ash concentrations, and for heat of combustion. Specific leaf area, and leaf N and ash contents were significantly lower in longer-lived leaves (evergreen) than shorter-lived leaves (deciduous) species. Leaves of evergreen species also had significantly higher heat of combustion and lower crude fat content than leaves of deciduous species. On a leaf area basis, Pmax was highest in leaves of evergreen species, but on a leaf dry mass basis it was highest in leaves of deciduous species. Pmax and total Kieldahl N content were linearly correlated across all eight species, and foliar N content was higher in leaves of deciduous than evergreen species. Leaf construction cost was significantly higher and maintenance costs were lower for leaves of evergreen than deciduous species. Maintenance and construction costs were linearly related to each other across all species. Leaves of evergreen species had a higher cost-benefit ratio compared to leaves of deciduous species but with longer lived leaves, the payback interval was longer in evergreen than deciduous species. These results support the hypotheses that longer lived leaves are more expensive to construct than short-lived leaves, and that a higher investment of N into short-lived leaves occurs which supports a higher Pmax over a shorter payback interval. and D. Eamus ... [et al.].
Sulfur (S) is an essential nutrient element required in a large quantity by mustard. S regulates photosynthesis and plant growth through improving nitrogen (N) acquisition. Mustard cultivars Alankar, Varuna, Pusa Jai Kisan, and SS2 differing in S accumulation capacity calculated as sulfate transport index (STI) were tested for ATP-sulfurylase activity, S and N accumulation, photosynthesis, and shoot dry mass (DM) at 30 and 60 d after sowing (DAS). The activity of ATP-sulfurylase, shoot N content, net photosynthetic rate (PN), leaf area, and shoot DM of the cultivars were in the order: Pusa Jai Kisan>Alankar>Varuna>SS2. ATP-sulfurylase activity was strongly and positively correlated with PN and shoot DM in all the cultivars. Hence ATP-sulfurylase activity may be used as a physiological trait for augmenting photosynthesis and shoot DM. and R. Nazar, N. A. Khan, N. A. Anjum.
Photosynthetic traits of two-year-old Japanese larch seedlings (Larix kaempferi Carr.) grown at elevated CO2 concentrations were studied in relation to structural changes in the needles. Seedlings were grown at two CO2 concentrations, 360 (AC) and 720 (EC) μmol mol-1 at high and low nutrient supply rates, high N (HN) and low N (LN). The photosynthetic capacity fell significantly in EC+LN, but increased significantly in EC+HN. Since the mesophyll surface area exposed to intercellular space per unit leaf area (Ames/A) is correlated with the photosynthetic rate, we measured Ames/A for larch needles growing in EC. Changes of Ames/A in both EC+HN and EC+LN were very similar to the changes in photosynthetic capacity. This suggests that the changes of Ames/A in EC probably caused the changes in the photosynthetic capacity. The changes of Ames/A in EC were attributed to changes in the mesophyll cell size and mesophyll cell number. The photosynthetic capacity in EC can be explained by taking morphological and structural adaptations into account as well as biochemical factors. and N. Eguchi ... [et al.].
A field experiment was conducted to investigate the changes in chlorophyll (Chl) and nitrogen (N) contents, ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBPCO) and phosphoenolpyruvate carboxylase (PEPC) contents and PEPC activity, and the photon-saturated net photosynthetic rate (PNsat), and their relationships with leaf senescence in two maize hybrids with different senescent appearance. One stay-green (cv. P3845) and one earlier senescent (cv. Hokkou 55) hybrid were used in this study, and we found that Chl and N contents and the PNsat in individual leaves of P3845 were greater than those in corresponding leaves of Hokkou 55 at the successive growth stages. In addition, larger contents of RuBPCO and PEPC, and a greater activity of PEPC were observed in P3845. Due to the lower rates of decrease of Chl, RuBPCO, and PEPC amounts per unit of N, and the lower net C translocation rate per unit of N in the stay-green hybrid, leaf senescence was delayed in comparison to the earlier senescent hybrid. and Ping He ... [et al.].
From the beginning of olive leaf yellowing to leaf fall (1/3 months), there was a general trend from anabolism to catabolism. Rates of net photosynthesis (PN) and respiration, areal dry mass, and contents of pigments, particularly of chlorophyll (Chl) a, starch, and above all nitrogen (N) decreased. The detachment force decreased dramatically only in completely chlorotic leaves. Chl a : b ratio only declined in the last 10-20 d of senescence, when the total Chl contents diminished by about 70 %, after which the N content, PN, and efficiency of the photochemical energy conversion of the remaining Chl and N dramatically declined. Consequently, for most of the natural course of senescence PN remained relatively high. The reduction in PN was associated with the decreases in transpiration rate (E) and stomatal conductance (gs), but these probably did not cause the decline of PN. The recycling of saccharide compounds was low, while 50 % of the total N on a leaf area basis was relocated back before leaf abscission, changing the leaf from a carbon source to a mineral source. Therefore, considering that senescing leaves in olive trees contribute to carbon gain and allow the recycling of resources, it is essential to prevent the premature leaf abscission by avoiding deficits of water and mineral nutrients and by using pruning and training systems that allow good irradiation of all leaves in the crown.
Insect-infested (II) acorns germinated 3 d earlier than the healthy (H) ones. However, germination ratio of II-acorns was strongly decreased compared with H-acorns and there were great differences in activities of amylase. We found an apparently lower net photosynthetic rate and total chlorophyll contents of the first true leaf of II-acorns than of the H-ones. Maximal photochemical efficiency of photosystem 2 (PS2, Fv/Fm) decreased in seedlings germinated from II-acorns than from the H-ones. Infestation of insects, especially for weevil (Curculio spp.) had significantly negative effects on length of taproots, height of plants, dry mass (DM) of roots and the first fully expanded true leaf. Leaf area and total N content of the first true leaf declined due to limitation of resource reserves in cotyledons. Damage of cotyledons caused by weevil accounted much for poor development of seedlings germinated from II-acorns. A mutual relationship between seedling establishment and seed-infesting insects may exist due to high predation on H-acorns by small rodents. and X. F. Yi, Z. B. Zhang
Leaf mass per unit area (LMA), carbon and nitrogen contents, leaf construction cost, and photosynthetic capacity (Pmax) of Adiantum reniforme var. sinensis, an endangered fern endemic to the Three Gorges region in southwest China, were compared in five populations differing in habitat such as soil moisture and irradiance. The low soil moisture and high irradiance habitat population exhibited significantly higher LMA, area-based leaf construction (CCA), and carbon content (CA), but lower leaf nitrogen content per unit dry mass (NM) than the other habitat populations. The high soil moisture and low irradiance habitat populations had the lowest CCA, but their cost/benefic ratios of CCA/P max were similar to the medium soil moisture and irradiance habitat population due to their lower leaf Pmax. Hence A. reniforme var. sinensis prefers partially shaded, moist but well-drained, slope habitats. Due to human activities, however, its main habitats now are cliffs or steeply sloped bare rocks with poor and thin soil. The relatively high energy requirements and low photosynthetic capacity in these habitats could limit the capability of the species in extending population or interspecific competition and hence increase its endangerment. and J. X. Liao ... [et al.].