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1.
Seasonal information on photosynthetic-capacity parameters (maximum carboxylation velocity, Vcmax; and maximum rate of electron transport, Jmax) plays an important role in accurate simulation of carbon fixation in gas-exchange models. Exact inclusion of seasonal information on photosynthetic-capacity parameters into the models has been an irresolvable challenge. This paper investigated the relationships between vegetation indices (from multiple sources) and photosynthetic-capacity parameters of three beech forest stands (Fagus crenata) along an elevation gradient in the cold-temperate zone of Japan, over the entire growing season of 2006. Diverse vegetation indices were examined in terms of spectral, spatial and temporal scales; ranging from meteorological sensor-based broadband indices to hyperspectral data-based narrowband indices, to simulated MODIS (MODerate-resolution Imaging Spectroradiometer) indices based on hyperspectral data, and finally satellite-borne MODIS vegetation indices. Regression analysis revealed that all examined indices, with the exception of the downloaded MODIS products, had significant regression relationships with photosynthetic parameters (P < 0.001) when all data were pooled. Among the different indices, the simulated MODIS NDVI (Normalized Difference Vegetation Index) performed the best for both Vcmax and Jmax (R2 = 0.81 and 0.73, respectively). Site differences were apparent, as the simulated MODIS NDVI performed the best in exponential regressions for the 550 m site, while broadband NDVI performed best in exponential regression models for the 900 m site. The broadband SR (Simple Ratio) in relation to Vcmax performed best with respect to a linear model, whereas the broadband NDVI with Jmax performed the best in an exponential model for the 1500 m site. The results reveal that vegetation indices which are obtained across different scales nevertheless retain tight relationships with canopy-scale photosynthetic-capacity parameters. The established relationships were inversely applicable to derive seasonal trajectories of photosynthetic-capacity parameters. Thus, new insight and confidence is gained for using remotely estimated photosynthetic parameters, even though most previous research works were limited on linking of vegetation indices with biophysical parameters. The control effect of physiological capacity on reflectance and further on vegetation indices has not been adequately established and thus needs further orientation for rigorous research work. 相似文献
2.
The role of fitness on VO2 and VCO2 kinetics in response to proportional step increases in work rate
Yong-Yu Zhang Martin C. Johnson Norman Chow Karlman Wasserman 《European journal of applied physiology and occupational physiology》1991,63(2):94-100
The purpose of this study was to determine the effect of fitness and work level on the O2 uptake and CO2 output kinetics when the increase in work rate step is adjusted to the subject's maximum work capacity. Nine normal male subjects performed progressive incremental cycle ergometer exercise tests in 3-min steps to their maximum tolerance. The work rate step size was selected so that the symptom-limited maximum work rate would be reached in four steps at 12 min in all subjects. Oxygen consumption (VO2) and carbon dioxide production (VCO2) were calculated breath by breath. For the group, the time (mean, SEM) to reach 75% of the 3-min response (T0.75) for VO2 increased significantly (P less than 0.01) at progressively higher work rate steps, being 53.3 (5.5) s, 63.5 (4.6) s, 79.5 (5.0) s, and 94.5 (5.8) s, respectively. In contrast, T0.75 for VCO2 did not change significantly [74.9 (7.4) s, 75.6 (5.0) s, 85.1 (5.3) s, and 89.4 (6.3) s, respectively]. VCO2 kinetics were slower than VO2 kinetics at the low fractions of the subjects' work capacities but were the same or faster at the high fractions because of the slowing of VO2 kinetics. The first step showed the fastest rise in VO2. While VO2 kinetics slowed at each step, they were faster at each fraction of the work capacity in the fitter subjects. The step pattern in VO2 disappeared at high work rates for the less fit subjects.(ABSTRACT TRUNCATED AT 250 WORDS) 相似文献
3.
Tobias O. Bickel Carsten A. Brühl Jürgen R. Gadau Bert Hölldobler K. Eduard Linsenmair 《Biodiversity and Conservation》2006,15(1):157-175
Two ant species, Odontomachus rixosus and Pheidole annexus, were studied in the tropical rainforests of Sabah, Malaysia, North Borneo, to analyze the impact of habitat fragmentation
on the genetic diversity and population structure of ant populations using RAPD-fingerprinting. Ants were sampled in a contiguous
(43,800 ha) and three patches of primary rainforests of varying size (4294, 146 and 20 ha) that were fragmented about 40 years
ago. We found a decrease in genetic variability for both species in the fragmented populations compared to the contiguous.
Genetic distances between populations resembled the geographical arrangement of populations and can be explained by an effect
of isolation by distance. A high degree in population subdivision suggests a lack of meta-population dynamics due to a shortage
of gene flow between populations, possibly the result of the high degree of habitat isolation by oil palm plantations. Although
the results of this study are limited due to low replication this is the first data on genetic patterns of insect populations
in fragmented rainforests and should be seen as starting point for future research. The value of small to medium sized protection
areas for conservation needs to be carefully evaluated in the context of this study, as even relatively large areas (4294 ha)
may not prevent the critical loss of genetic variability and guarantee long-term survival of organisms. 相似文献
4.
Genotypic variation in the photosynthetic competence of Sorghum bicolor seedlings subjected to polyethylene glycol-mediated drought stress 总被引:3,自引:0,他引:3
Eleven varieties of Sorghum bicolor, subjected to PEG-mediated drought stress were compared for their photosynthetic performance. The varieties differed in their relative water content over a range of PEG concentrations (0-25%). CO2 assimilation, stomatal conductance and the quantum yield of PSII electron transport decreased with increasing PEG concentrations in all varieties. However the intercellular CO2 concentration showed a nonlinear PEG concentration-dependent change. At lower PEG concentrations there was a decrease in the levels of intercellular CO2 concentration in all varieties that could be attributed to stomatal closure. At higher PEG concentrations, some varieties showed an increase in the intercellular CO2 concentration, indicating an inhibition of photosynthetic activity due to non-stomatal effects, while others did not. It was seen that the varieties differed in the stress thresholds at which stomatal and metabolic limitations to photosynthesis occur. These differences in the photosynthetic adaptation of Sorghum varieties could be useful in identifying genotypes showing large differences in photosynthetic adaptation, which could be useful in mapping photosynthetic traits for drought stress tolerance. 相似文献
5.
Summary Gas exchange characteristics of droughted and rewatered Portulacaria afra were studied during the seasonal shift from CAM to C3 photosynthesis. 14CO2 uptake, stomatal conductance, and total titratable acidity were determined for both irrigated and 2, 4, and 7.5 month waterstressed plants from summer 1984 to summer 1985. Irrigated P. afra plants were utilizing the CAM pathway throughout the summer and shifted to C3 during the winter and spring. Beginning in September, P. afra plants shifted from CAM to CAM-idling after 2 months of water-stress. When water-stress was initiated later in the fall, exogenous CO2 uptake was still measurable after 4 months of drought. After 7.5 months of stress, exogenous CO2 uptake was absent. The shift from CAM to CAM-idling or C3 in the fall and winter was related to when water stress was initiated and not to the duration of the stress. Gas exchange resumed within 24 h of rewatering regardless of the duration of the drought. In the winter and spring, rewatering resulted in a full resumption of daytime CO2 uptake. Whereas during the summer, rewatering quickly resulted in early morning CO2 uptake, but nocturnal CO2 uptake through the CAM pathway was observed after 7 days. Gas exchange measurements, rewatering characteristics, and transpirational water loss support the hypothesis that the C3 pathway was favored during the winter and spring. The CAM pathway was functional during the summer when potential for water loss was greater. Our investigations indicate that P. afra has a flexible photosynthetic system that can withstand long-term drought and has a rapid response to rewatering. 相似文献
6.
Climate change may affect ecosystem functioning through increased temperatures or changes in precipitation patterns. Temperature and water availability are important drivers for ecosystem processes such as photosynthesis, carbon translocation, and organic matter decomposition. These climate changes may affect the supply of carbon and energy to the soil microbial population and subsequently alter decomposition and mineralization, important ecosystem processes in carbon and nutrient cycling. In this study, carried out within the cross-European research project CLIMOOR, the effect of climate change, resulting from imposed manipulations, on carbon dynamics in shrubland ecosystems was examined. We performed a 14C-labeling experiment to probe changes in net carbon uptake and allocation to the roots and soil compartments as affected by a higher temperature during the year and a drought period in the growing season. Differences in climate, soil, and plant characteristics resulted in a gradient in the severity of the drought effects on net carbon uptake by plants with the impact being most severe in Spain, followed by Denmark, with the UK showing few negative effects at significance levels of p 0.10. Drought clearly reduced carbon flow from the roots to the soil compartments. The fraction of the 14C fixed by the plants and allocated into the soluble carbon fraction in the soil and to soil microbial biomass in Denmark and the UK decreased by more than 60%. The effects of warming were not significant, but, as with the drought treatment, a negative effect on carbon allocation to soil microbial biomass was found. The changes in carbon allocation to soil microbial biomass at the northern sites in this study indicate that soil microbial biomass is a sensitive, early indicator of drought- or temperature-initiated changes in these shrubland ecosystems. The reduced supply of substrate to the soil and the response of the soil microbial biomass may help to explain the observed acclimation of CO2 exchange in other ecosystems. 相似文献
7.
Seasonal correlations of specific leaf weight to net photosynthesis and dark respiration of apple leaves 总被引:2,自引:0,他引:2
Specific leaf weight (SLW), net photosynthesis (Pn), and dark respiration (Rd) of apple leaves were monitored for an entire growing season. Leaves were sampled from the canopy interior and periphery to provide a range of SLW. Leaf Pnwas linearly correlated with SLW until mid-August, when Pnbegan to decline. During September the relationship between SLW and Pnwas a quadratic. Leaf Rdand SLW were linearly correlated throughout the season. Leaf Pnand Rdwere significantly correlated through most of the season, but the relationship was not always linear. Specific leaf weight appears to be a reliable index of the previous light environment of a leaf, but use to estimate Pnis probably limited to the first half of the season, because of increased variation after mid-August.Former Graduate Research Assistant (presently Assistant Professor, Department of Horticulture and Forestry, Rutgers University, Cook College, New Brunswick, NJ 08903, USA) and Associate Professor, respectively. 相似文献
8.
Single leaf photosynthesis (Pn) and stomatal conductance (Cg) of drought stressed and nonstressed pearl millet [Pennisetum americanum (L.) Leeke] were measured across growth stages to determine if a pattern exists in Pn and Cg during the growing season and to evaluate the influence of air vapor pressure deficit (VPDa) on the seasonal variations of Pn and Cg. Leaf photosynthesis and Cg were measured independently on pearl millet plants grown at the driest (drought stressed) and wettest (nonstressed) ends of a line-source irrigation gradient system. Well defined and predictable variations in both Pn and Cg were found across two growing seasons. Leaf photosynthesis of the nonstressed plants declined from a maximumof 25.8 mol m–2 s–1 at the flag leaf emergence (48 days after planting, DAP) to a minimum of 14.5 mol m–2 s–1 at physiological maturity. Stomatal conductance of the nonstressed plants peaked at the flowering and early grain fill stages and declined as plants approached maturity. In contrast, Pn and Cg of the stressed plants declined from a maximum at flag leaf emergence to a minimum at flowering and increased as plants approached maturity. High VPDa during the flowering and grain fill stages induced stomatal closure and decreased Pn in the stressed plants. High mid-season VPDa did not induce stomatal closure and did not reduce leaf photosynthesis in nonstressed plants. The lack of sensitivity of Pn to VPDa in the nonstressed treatment suggests large air VPD such as that prevalent in southern Arizona does not limit the growth of irrigated pearl millet by limiting CO2 assimilation.Abbreviations Cg
stomatal conductance
- DAP
days after planting
- Pn
leaf photosynthesis
- VPDa
air vapor pressure deficit
- VPD1-a
leaf to air vapor pressure deficit
Contribution of the Arizona Agricultural Experimental Station. Research supported in part by INTSORMIL/USAID. 相似文献
9.
J. Dušek 《Biologia Plantarum》2002,45(3):383-387
Seasonal dynamic of total nonstructural saccharides (TNS) and individual saccharides (starch, sucrose, glucose, fructose, fructans) was followed in rhizomes and stem bases of Calamagrostis epigeios (L.) Roth at two types of meadows communities in the South Moravia (Czech Republic): cnidion and molinion alliances, which differ in their water regime. The TNS were formed mainly by fructans and starch, while glucose, sucrose and fructose were low. The amount of TNS in rhizomes and stem bases of plants from wet cnidion site was higher than in plants from drier molinion site. The seasonal trends of all saccharides were similar in the both sites. During growing season (June to October) the main storage sugar was fructan (18 – 21 % of dry biomass). At the beginning of September the content of fructan decreased to 10 – 12 % and simultaneously the content of sucrose increased from 1 to 3 %. This may increase frost resistance. The content of TNS in the stem bases was lower than in the rhizomes. During winter time the stem bases contained 2 to 2.5 % of sucrose. Plant height and aboveground biomass were also higher in molinion site. 相似文献
10.
Characterization of glutathione reductase and catalase in the fronds of two Pteris ferns upon arsenic exposure 总被引:1,自引:0,他引:1
Gina M. Kertulis-Tartar Bala Rathinasabapathi Lena Q. Ma 《Plant Physiology and Biochemistry》2009,47(10):960-965
To better understand the mechanisms of plant tolerance to high concentration of arsenic, we characterized two antioxidant enzymes, glutathione reductase (GR) and catalase (CAT), in the fronds of Pteris vittata, an arsenic-hyperaccumulating fern, and Pteris ensiformis, an arsenic-sensitive fern. The induction, activation and apparent kinetics of GR and CAT in the plants upon arsenic exposure were investigated. Under arsenic exposure (sodium arsenate), CAT activity in P. vittata was increased by 1.5-fold, but GR activity was unchanged. Further, GR was not inhibited or activated by the arsenic in assays. No significant differences in Km and Vmax values of GR or CAT were observed between the two ferns. However, CAT activity in P. vittata was activated by 200 μM arsenate up to 300% compared to the control. Similar but much smaller increases were observed for P. ensiformis and purified bovine liver catalase (133% and 120%, respectively). This research reports, for the first time, the activation of CAT by arsenic in P. vittata. The increased CAT activities may allow P. vittata to more efficiently mediate arsenic-induced stress by preparing the fern for the impeding production of reactive oxygen species resulting from arsenate reduction to arsenite in the fronds. 相似文献
11.
Heterotrophic Soil Respiration in Relation to Environmental Factors and Microbial Biomass in Two Wet Tropical Forests 总被引:2,自引:0,他引:2
We examined the correlation between fungal and bacterial biomass, abiotic factors such as soil moisture, carbon in the light soil fraction and soil nitrogen to a depth of 0–25 cm and heterotrophic soil respiration using a trenching technique – in a secondary forest (Myrcia splendens, Miconia prasina and Casearia arborea) and a pine (Pinus caribeae) plantation in the Luquillo Experimental Forest in Puerto Rico. Soil respiration was significantly reduced where roots were excluded for 7 years in both the secondary forest and the pine plantation. Microbial biomass was also significantly reduced in the root exclusion plots. In root exclusion treatment, total fungal biomass was on average 31 and 65% lower than the control plots in the pine plantation and the secondary forest, respectively, but the total bacterial biomass was 24 and 8.3% lower than the control plots in the pine plantation and the secondary forest, respectively. Heterotrophic soil respiration was positively correlated with fungal biomass (R2=0.63, R2=0.39), bacterial biomass (R2=0.16, R2=0.45), soil moisture (R2=0.41, R2=0.56), carbon in light fraction (R2=0.45, R2=0.39) and total nitrogen (R2=0.69, R2=0.67) in the pine plantation and the secondary forest, respectively. The regression analysis suggested that fungal biomass might have a greater influence on heterotrophic soil respiration in the pine plantation, while the bacterial biomass might have a greater influence in the secondary forest. Heterotrophic soil respiration was more sensitive to total N than to carbon in the light fraction, and soil moisture was a major factor influencing heterotrophic soil respiration in these forests where temperature is high and relatively invariable. 相似文献
12.
Dry weight and Relative Growth Rate of Lemna gibba were significantly increased by CO2 enrichment up to 6000 l CO2 l–1. This high CO2 optimum for growth is probably due to the presence of nonfunctional stomata. The response to high CO2 was less or absent following four days growth in 2% O2. The Leaf Area Ratio decreased in response to CO2 enrichment as a result of an increase in dry weight per frond. Photosynthetic rate was increased by CO2 enrichment up to 1500 l CO2 l–1 during measurement, showing only small increases with further CO2 enrichment up to 5000 l CO2 l–1 at a photon flux density of 210 mol m–2 s–1 and small decreases at 2000 mol m–1 s–1. The actual rate of photosynthesis of those plants cultivated at high CO2 levels, however, was less than the air grown plants. The response of photosynthesis to O2 indicated that the enhancement of growth and photosynthesis by CO2 enrichment was a result of decreased photorespiration. Plants cultivated in low O2 produced abnormal morphological features and after a short time showed a reduction in growth. 相似文献
13.
Phosphoenolpyruvate carboxylase (PEPCase, EC 4.1.1.3) is a key enzyme of C4 photosynthesis. It has evolved from ancestral non-photosynthetic (C3) isoforms and thereby changed its kinetic and regulatory properties. We are interested in understanding the molecular changes,
as the C4 PEPCases were adapted to their new function in C4 photosynthesis and have therefore analysed the PEPCase genes of various Alternanthera species. We isolated PEPCase cDNAs from the C4 plant Alternanthera pungens H.B.K., the C3/C4 intermediate plant A. tenella Colla, and the C3 plant A. sessilis (L.) R.Br. and investigated the kinetic properties of the corresponding recombinant PEPCase proteins and their phylogenetic
relationships. The three PEPCases are most likely derived from orthologous gene classes named ppcA. The affinity constant for the substrate phosphoenolpyruvate (K
0.5 PEP) and the degree of activation by glucose-6-phosphate classified the enzyme from A. pungens (C4) as a C4 PEPCase isoform. In contrast, both the PEPCases from A. sessilis (C3) and A. tenella (C3/C4) were found to be typical C3 PEPCase isozymes. The C4 characteristics of the PEPCase of A. pungens were accompanied by the presence of the C4-invariant serine residue at position 775 reinforcing that a serine at this position is essential for being a C4 PEPCase (Svensson et al. 2003). Genomic Southern blot experiments and sequence analysis of the 3′ untranslated regions of these genes indicated the existence
of PEPCase multigene family in all three plants which can be grouped into three classes named ppcA, ppcB and ppcC. 相似文献
14.
Summary The biological nature of soil H2-consumption has been investigated. Soil microorganisms were capable to remove H2 present in the gas phase at concentrations in the range of 200 ppm at rates varying between 0.2 and 1.0 l.min–1. 100 g–1. Free soil enzymes did not contribute significantly at the H2 concentrations tested. Oxygen seemed to be the predominant electron acceptor. The influence of microbiological and physical soil properties on the H2-uptake activity was examined for 38 soils.A highly significant correlation between biomass-C and H2-uptake rate of the soil was noted, suggesting that the latter parameter might be useful as an indirect estimation of soil microbial biomass. The correlation was however not applicable for soils recently grown with legumes. Indeed, soya plants nodulated with aRhizobium strain with a weak hydrogen uptake capability, strongly increased the hydrogen oxidizing capability of the surrounding soil. 相似文献
15.
Schäfer I Rössle M Biuković G Müller V Grüber G 《Journal of bioenergetics and biomembranes》2006,38(2):83-92
The first low-resolution shape of subunit F of the A1AO ATP synthase from the archaeon Methanosarcina mazei Gö1 in solution was determined by small angle X-ray scattering. Independent to the concentration used, the protein is monomeric and has an elongated shape, divided in a main globular part with a length of about 4.5 nm, and a hook-like domain of about 3.0 nm in length. The subunit-subunit interaction of subunit F inside the A1AO ATP synthase in the presence of 1-ethyl-3-(dimethylaminopropyl)-carbodiimide EDC was studied as a function of nucleotide binding, demonstrating movements of subunits F relative to the nucleotide-binding subunit B. Furthermore, in the intact A1AO complex, crosslinking of subunits D-E, A-H and A-B-D was obtained and the peptides, involved, were analyzed by MALDI-TOF mass spectrometry. Based on these data the surface of contact of B-F could be mapped in the high-resolution structure of subunit B of the A1AO ATP synthase. 相似文献
16.
The low resolution structure of subunit d (Vma6p) of the Saccharomyces cerevisiae V-ATPase was determined from solution X-ray scattering data. The protein is a boxing glove-shaped molecule consisting of
two distinct domains, with a width of about 6.5 nm and 3.5 nm, respectively. To understand the importance of the N- and C-termini
inside the protein, four truncated forms of subunit d (d
11–345, d
38–345, d
1–328 and d
1–298) and mutant subunit d, with a substitution of Cys329 against Ser, were expressed, and only d
11–345, containing all six cysteine residues was soluble. The structural properties of d depends strongly on the presence of a disulfide bond. Changes in response to disulfide formation have been studied by fluorescence-
and CD spectroscopy, and biochemical approaches. Cysteins, involved in disulfide bridges, were analyzed by MALDI-TOF mass
spectrometry. Finally, the solution structure of subunit d will be discussed in terms of the topological arrangement of the V1VO ATPase. 相似文献
17.
The effects of short-term exposure to chilling temperature (10 °C) on sucrose synthesis in leaves of the cold-tolerant sugarcane cultivars Saccharum sinense R. cv. Yomitanzan and Saccharum sp. cv. NiF4, and the cold-sensitive cultivar S. officinarum L. cv. Badila were studied. Plants were grown at day/night temperatures of 30/25 °C, and then shifted to a constant day/night temperature of 10 °C. After 52-h exposure to the chilling temperature, sucrose content in the leaves of NiF4 and Yomitanzan showed a 2.5- to 3.5-fold increase relative to that of the control plants that had been left on day/night temperatures of 30/25 °C. No such increase was observed in Badila leaves. Similarly, starch content in the leaves of NiF4 and Yomitanzan was maintained high, but starch was depleted in Badila leaves after the 52-h exposure. During the chilling temperature, sucrose phosphate synthase (SPS; E.C.2.4.1.14) activity was relatively stable in the leaves of NiF4 and Yomitanzan, whereas in Badila leaves SPS activity significantly decreased. There was no significant change in cytosolic fructose-1,6-bisphosphatase activity for the three cultivars at the chilling temperature. This supports the hypothesis that: (1) on exposure to chilling temperature, sucrose content in sugarcane leaves is determined by the photosynthetic rate in the leaves, and is not related to SPS activity; (2) SPS activity in sugarcane leaves at chilling temperature is to be determined by sugar concentration in the leaves. 相似文献
18.
Desjardins AE Li YX Reinker S Miura RM Neuman RS 《Journal of computational neuroscience》2003,15(2):131-142
Recent experimental and theoretical studies have found that active dendritic ionic currents can compensate for the effects of electrotonic attenuation. In particular, temporal summation, the percentage increase in peak somatic voltage responses invoked by a synaptic input train, is independent of location of the synaptic input in hippocampal CA1 pyramidal neurons under normal conditions. This independence, known as normalization of temporal summation, is destroyed when the hyperpolarization-activated current, I
h, is blocked [Magee JC (1999a), Nature Neurosci. 2: 508–514]. Using a compartmental model derived from morphological recordings of hippocampal CA1 pyramidal neurons, we examined the hypothesis that I
h was primarily responsible for normalization of temporal summation. We concluded that this hypothesis was incomplete. With a model that included I
h, the persistent Na+ current (I
NaP), and the transient A-type K+ current (I
A), however, we observed normalization of temporal summation across a wide range of synaptic input frequencies, in keeping with experimental observations. 相似文献
19.
Sensitivity of CO<Subscript>2</Subscript> Exchange of Fen Ecosystem Components to Water Level Variation 总被引:1,自引:0,他引:1
Abstract
Climate change is predicted to bring about a water level (WL) draw-down in boreal peatlands. This study aimed to assess the
effect of WL on the carbon dioxide (CO2) dynamics of a boreal oligotrophic fen ecosystem and its components; Sphagnum mosses, sedges, dwarf shrubs and the underlying peat. We measured CO2 exchange with closed chambers during four growing seasons in a study site that comprised different vegetation treatments.
WL gradient in the site was broadened by surrounding half of the site with a shallow ditch that lowered the WL by 10–25 cm.
We modeled gross photosynthesis (P
G) and ecosystem respiration (R
ECO) and simulated the CO2 exchange in three WL conditions: prevailing and WL draw-down scenarios of 14 and 22 cm. WL draw-down both reduced the P
G and increased the R
ECO, thus leading to a smaller net CO2 uptake in the ecosystem. Of the different components, Sphagnum mosses were most sensitive to WL draw-down and their physiological activities almost ceased. Vascular plant CO2 exchange, en bloc, hardly changed but whereas sedges contributed twice as much to the CO2 exchange as shrubs in the prevailing conditions, the situation was reversed in the WL draw-down scenarios. Peat respiration
was the biggest component in R
ECO in all WL conditions and the increase in R
ECO following the WL draw-down was due to the increase in peat respiration. The results imply that functional diversity buffers
the ecosystem against environmental variability and that in the long term, WL draw-down changes the vegetation composition
of boreal fens. 相似文献
20.
Superoxide production by thylakoids during chilling and its implication in the susceptibility of plants to chilling-induced photoinhibition 总被引:9,自引:0,他引:9
Factors influencing the rate of superoxide (O
2
-
) production by thylakoids were investigated to determine if increased production of the radical was related to injury induced by chilling at a moderate photon flux density (PFD). Plants used were Spinacia oleracea L., Cucumis sativus L. and Nerium oleander L. grown at either 200° C or 45° C. Superoxide production was determined by electron-spin-resonance spectroscopy of the (O
2
-
)-dependent rate of oxidation of 2-ethyl-1-hydroxy-2,5,5-trimethyl-3-oxazolidine (OXANOH) to the corresponding oxazolidinoxyl radical, OXANO ·. For all plants, the steady-state rate of O
2
-
production by thylakoids, incubated at 25° C and 350 mol photon · m–2 · s–1 (moderate PFD) with added ferredoxin and NADP, was between 7.5 and 12.5 mol · (mg chlorophyll)–1 · h–1. Incubation at 5° C and a moderate PFD, decreased the rate of O
2
-
production 40% and 15% by thylakoids from S. oleracea and 20° C-grown N. oleander, chillinginsensitive plants, but increased the rate by 56% and 5% by thylakoids from C. sativus and 45° C-grown N. oleander, chilling-sensitive plants. For all plants, the addition of either ferredoxin or methyl viologen increased the rate of O
2
-
-production at 25° C by 75–100%. With these electron acceptors, lowering the temperature to 5° C caused only a slight decrease in O
2
-
production. In the absence of added electron acceptors, thylakoids produced O
2
-
at a rate which was about 45% greater than that when ferredoxin and NADP were present. The addition of 3-(3,4-dichlorophenyl)-1,1-dimethylurea reduced O
2
-
production under all conditions tested. The results show that the rate of O
2
-
production increases in thylakoids when the rate of electron transfer to NADP is reduced. This could explain differences in the susceptibility of thylakoids from chilling-sensitive and chilling-insensitive plants to chilling at a moderate PFD, and is consistent with the proposal that O
2
-
production is involved in the injury leading to the inhibition of photosynthesis induced under these conditions.Abbreviations Chl
chlorophyll
- DCMU
3-(3,4-dichlorophen-yl)-1,1-dimethylurea
- Fd
ferredoxin
- MV
methyl viologen
- 20°oleander
Nerium oleander grown at 20° C
- 45°-oleander
N. oleander grown at 45° C
- OXANOH
2-ethyl-1-hydroxy-2,5,5-tri-methyl-3-oxazolidine
- PFD
photon flux density (photon fluence rate)
- TEMED
tetramethyl ethylenediamine
We would like to thank R.T. Furbank, R.S.B.S., Australian National University, Canberra, A.C.T., and C.B. Osmond, now of Duke University, Durham, N.C., USA, for the gift of ferredoxin, R.A.J.H. was supported by a Commonwealth Postgraduate Research Award. 相似文献