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191.
Elevated CO2 enhances carbon uptake of a plant stand, but the magnitude of the increase varies among growth stages. We studied the relative
contribution of structural and physiological factors to the CO2 effect on the carbon balance during stand development. Stands of an annual herb Chenopodium album were established in open-top chambers at ambient and elevated CO2 concentrations (370 and 700 μmol mol−1). Plant biomass growth, canopy structural traits (leaf area, leaf nitrogen distribution, and light gradient in the canopy),
and physiological characteristics (leaf photosynthesis and respiration of organs) were studied through the growing season.
CO2 exchange of the stand was estimated with a canopy photosynthesis model. Rates of light-saturated photosynthesis and dark
respiration of leaves as related with nitrogen content per unit leaf area and time-dependent reduction in specific respiration
rates of stems and roots were incorporated into the model. Daily canopy carbon balance, calculated as an integration of leaf
photosynthesis minus stem and root respiration, well explained biomass growth determined by harvests (r
2 = 0.98). The increase of canopy photosynthesis with elevated CO2 was 80% at an early stage and decreased to 55% at flowering. Sensitivity analyses suggested that an alteration in leaf photosynthetic
traits enhanced canopy photosynthesis by 40–60% throughout the experiment period, whereas altered canopy structure contributed
to the increase at the early stage only. Thus, both physiological and structural factors are involved in the increase of carbon
balance and growth rate of C. album stands at elevated CO2. However, their contributions were not constant, but changed with stand development. 相似文献
192.
Question: Herb‐rich patches are biodiversity hotspots for vascular plants in boreal forests. We ask: Do species occurrences on herb‐rich patches show a non‐random, nested structure?; Does patch size relate to richness of edaphically demanding and red‐listed species?; Does a set of small patches support more edaphically demanding and red‐listed species than a few large patches of the equal area? Location: Eastern Finland (63°04′N, 29°52′E), boreal vegetation zone. Data: Vegetation mapping of 90 herb‐rich sites, varying from 0.05 to 6.93 ha in size and belonging to six different, predetermined forest site types. Results: Using the RANDNEST procedure, only one site type showed a significantly nested pattern, and patch area was not related to “nestedness” in any of the site types. The number of edaphically demanding and red‐listed plant species was positively correlated with a patch size in three forest site types. In all site types, a set of small patches had more edaphically demanding and red‐listed species than did a few large patches of the equal total area. Conclusions: For conservation, it is essential to protect representative sets of different herb‐rich forest site types because flora varies between the site types. Within herb‐rich forest site types, several small areas may support representative species composition. However, successful conservation requires thorough species inventories, because of the high level of heterogeneity between the herb‐rich patches. 相似文献
193.
? Premise of the study: Viola hondoensis is a perennial herb that inhabits the understory of temperate, deciduous forests. It is an evergreen plant with a leaf life span that is shorter than a year. Its summer leaves are produced in spring and shed in autumn; winter leaves are produced in autumn and shed in spring. Here we asked why the plant sheds its winter leaves in spring, though climate conditions improve from spring to summer. We proposed four hypotheses for the cause of shedding: (1) changes in seasonal environment such as day length or air temperature, (2) shading by canopy deciduous trees, (3) self-shading by taller summer leaves, and (4) competition for nutrients between summer and winter leaves. ? Methods: To test these hypotheses, we manipulated the environment of winter leaves: (1) plants were transplanted to the open site where there was no shading by canopy trees. (2) Petioles of summer leaves were anchored to the soil surface to avoid shading of winter leaves. (3) Sink organs were removed to eliminate nutrient competition. ? Key results: Longevity of winter leaves was extended when shading by summer leaves was eliminated and when sink organs were removed, but not when plants were transplanted to the open site. ? Conclusion: We conclude that the relative difference in light availability between summer and winter leaves is a critical factor for regulation of leaf shedding, consistent with the theory of maximization of the whole-plant photosynthesis. 相似文献
194.
Koide T Nishikawa Y Asada S Yamazaki CM Takahara Y Homma DL Otaka A Ohtani K Wakamiya N Nagata K Kitagawa K 《The Journal of biological chemistry》2006,281(16):11177-11185
The endoplasmic reticulum-resident chaperone heat-shock protein 47 (HSP47) plays an essential role in procollagen biosynthesis. The function of HSP47 relies on its specific interaction with correctly folded triple-helical regions comprised of Gly-Xaa-Yaa repeats, and Arg residues at Yaa positions have been shown to be important for this interaction. The amino acid at the Yaa position (Yaa(-3)) in the N-terminal-adjoining triplet containing the critical Arg (defined as Arg(0)) was also suggested to be directly recognized by HSP47 (Koide, T., Asada, S., Takahara, Y., Nishikawa, Y., Nagata, K., and Kitagawa, K. (2006) J. Biol. Chem. 281, 3432-3438). Based on this finding, we examined the relationship between the structure of Yaa(-3) and HSP47 binding using synthetic collagenous peptides. The results obtained indicated that the structure of Yaa(-3) determined the binding affinity for HSP47. Maximal binding was observed when Yaa(-3) was Thr. Moreover, the required relative spatial arrangement of these key residues in the triple helix was analyzed by taking advantage of heterotrimeric collagen-model peptides, each of which contains one Thr(-3) and one Arg(0). The results revealed that HSP47 recognizes the Yaa(-3) and Arg(0) residues only when they are on the same peptide strand. Taken together, the data obtained led us to define the HSP47-binding structural epitope in the collagen triple helix and also define the HSP47-binding motif in the primary structure. A motif search against human protein database predicted candidate clients for this molecular chaperone. The search result indicated that not all collagen family proteins require the chaperoning by HSP47. 相似文献
195.
Temperature acclimation of photosynthesis: mechanisms involved in the changes in temperature dependence of photosynthetic rate 总被引:17,自引:0,他引:17
Hikosaka K Ishikawa K Borjigidai A Muller O Onoda Y 《Journal of experimental botany》2006,57(2):291-302
Growth temperature alters temperature dependence of the photosynthetic rate (temperature acclimation). In many species, the optimal temperature that maximizes the photosynthetic rate increases with increasing growth temperature. In this minireview, mechanisms involved in changes in the photosynthesis-temperature curve are discussed. Based on the biochemical model of photosynthesis, change in the photosynthesis-temperature curve is attributable to four factors: intercellular CO2 concentration, activation energy of the maximum rate of RuBP (ribulose-1,5-bisphosphate) carboxylation (Vc max), activation energy of the rate of RuBP regeneration (Jmax), and the ratio of Jmax to Vc max. In the survey, every species increased the activation energy of Vc max with increasing growth temperature. Other factors changed with growth temperature, but their responses were different among species. Among these factors, activation energy of Vc max may be the most important for the shift of optimal temperature of photosynthesis at ambient CO2 concentrations. Physiological and biochemical causes for the change in these parameters are discussed. 相似文献
196.
197.
Thallus mechanical strength, as well as production of secondary metabolites as defensive compounds, of tropical macroalgae is often essential for protection from herbivory. In tropical macroalgae, thallus mechanical strength is negatively correlated with productivity — a trade‐off between productivity and thallus toughness. The tropical fucoids, Turbinaria ornata which has defensive morphological traits against herbivory and Sargassum ilicifolium which is expanding its distribution in Japanese waters, were examined to determine thallus traits related to mechanical strength and productivity and their pair‐wise relationships were also examined. These traits that are directly or indirectly related to the trade‐off between productivity and thallus toughness were compared to data for various other temperate macroalgae by regression analyses. We found two strong positive correlations between thallus mechanical strength and thallus mass or thallus thickness, confirming that higher levels of mechanical strength for tropical fucoids is associated with higher biomass or thallus thickness. Also, negative correlations between thallus toughness and productivity were found indicating structural and physiological trade‐offs. However, the tropical fucoids exhibited relatively high productivity regardless of their higher level of thallus toughness. These traits of the tropical fucoids slightly deviate from the typical conservative strategy with higher thallus toughness and lower productivity as a trade‐off between productivity and thallus toughness. 相似文献
198.
Saidi N Kouki S Mehri I Ben Rejeb A Belila A Hassen A Ouzari H 《Current microbiology》2011,63(4):337-340
The efficiency of ultraviolet (UV) light disinfection of wastewater effluent using a large-scale pilot system was studied.
The relationship between biofilm and siderophore production and UV doses received by Pseudomonas aeruginosa strain ATCC 15442 was determined. UV decreased pyoverdine production and enhanced biofilm production. Consequently external
factors conditioned by both pyoverdine and biofilm may affect the UV effect on bacterial disinfection. 相似文献
199.
The most appropriate strategy for preserving fragmented populations depends on a species’ ability to colonise distant habitat
patches. Insects associated with early decay stages of dead wood are expected to have a high capacity to colonise new habitat
patches. To study the dispersal ranges of beetles (Coleoptera) and flat bugs (Hemiptera: Aradidae) dependent on recently dead
aspen (Populus tremula) wood in Finland, we set out 58 piles of recently cut aspen logs at various distances up to 1.6 km from forests that contained
a high density of old aspen trees. We captured insects by trunk window-traps, and counted beetles’ exit holes. Habitat connectivity
was measured in terms of the amount of suitable aspen-wood in the surrounding environment, with the closest dead wood items
up-weighted by a negative-exponential function. The log-piles attracted many saproxylic insects including four red-listed
aspen-specialist species. The exposure of log-piles to the sun, and high levels of habitat connectivity increased the species
richness of aspen-specialists, whereas bark peeling by moose decreased richness. The spatial scale at which species richness
had its strongest response to habitat was 93 m. Among individual species there was a wide variability in spatial scale of
response. This study supports the view that conservation efforts in boreal forests should be concentrated on sites where colonisation
by target species is most likely. Restoration of habitat by re-locating logs may be useful at localities with a rich and specialised
fauna but which have too low rate of formation of dead wood by natural processes. 相似文献