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1.
The allocation and turnover of photosynthetically assimilated 14CO 2 in lipid and protein fractions of soybean ( Glycine max L. Clark) leaves and stem materials was measured. In whole plant labeling experiments, allocation of photosynthate from a pulse of 14CO 2 into polymeric compounds was: 25% to proteins in 4 days, 20% to metabolically inert cell wall products in 1 to 2 days, 10% to lipids in 4 days, and 4% to starch in 1 day. The amount of 14C labeled photosynthate that an actively growing leaf (leaf 4) used for its own lipid synthesis immediately following pulse labeling was about 25%. The 14C of labeled proteins turned over with half-lives of 3.8, 3.3, and 4.1 days in leaves 1, 2, and 3, respectively; and turnover of 14C in total shoot protein proceeded with a half-life of 5.2 days. Three kinetic 14C turnover patterns were observed in lipids: a rapid turnover fraction (within a day), an intermediate fraction (half-life about 5 days), and a slow turnover fraction. These results are discussed in terms of previously published accounts of translocation, carbon budgets, carbon use, and turnover in starch, lipid, protein, and cell wall materials of various plants including soybeans. 相似文献
2.
It is uncertain whether elevated atmospheric CO 2 will increase C storage in terrestrial ecosystems without concomitant increases in plant access to N. Elevated CO 2 may alter microbial activities that regulate soil N availability by changing the amount or composition of organic substrates
produced by roots. Our objective was to determine the potential for elevated CO 2 to change N availability in an experimental plant-soil system by affecting the acquisition of root-derived C by soil microbes.
We grew Populus tremuloides (trembling aspen) cuttings for 2 years under two levels of atmospheric CO 2 (36.7 and 71.5 Pa) and at two levels of soil N (210 and 970 μg N g –1). Ambient and twice-ambient CO 2 concentrations were applied using open-top chambers, and soil N availability was manipulated by mixing soils differing in
organic N content. From June to October of the second growing season, we measured midday rates of soil respiration. In August,
we pulse-labeled plants with 14CO 2 and measured soil 14CO 2 respiration and the 14C contents of plants, soils, and microorganisms after a 6-day chase period. In conjunction with the August radio-labeling
and again in October, we used 15N pool dilution techniques to measure in situ rates of gross N mineralization, N immobilization by microbes, and plant N uptake.
At both levels of soil N availability, elevated CO 2 significantly increased whole-plant and root biomass, and marginally increased whole-plant N capital. Significant increases
in soil respiration were closely linked to increases in root biomass under elevated CO 2. CO 2 enrichment had no significant effect on the allometric distribution of biomass or 14C among plant components, total 14C allocation belowground, or cumulative (6-day) 14CO 2 soil respiration. Elevated CO 2 significantly increased microbial 14C contents, indicating greater availability of microbial substrates derived from roots. The near doubling of microbial 14C contents at elevated CO 2 was a relatively small quantitative change in the belowground C cycle of our experimental system, but represents an ecologically
significant effect on the dynamics of microbial growth. Rates of plant N uptake during both 6-day periods in August and October
were significantly greater at elevated CO 2, and were closely related to fine-root biomass. Gross N mineralization was not affected by elevated CO 2. Despite significantly greater rates of N immobilization under elevated CO 2, standing pools of microbial N were not affected by elevated CO 2, suggesting that N was cycling through microbes more rapidly. Our results contained elements of both positive and negative
feedback hypotheses, and may be most relevant to young, aggrading ecosystems, where soil resources are not yet fully exploited
by plant roots. If the turnover of microbial N increases, higher rates of N immobilization may not decrease N availability
to plants under elevated CO 2.
Received: 12 February 1999 / Accepted: 2 March 2000 相似文献
3.
Young bean plants ( Phaseolus vulgaris L. var Saxa) were fed with three different types of inorganic nitrogen, after being grown on nitrogen-free nutrient solution for 8 days. The pattern of 14CO 2 fixation was investigated in photosynthesizing primary leaf discs of 11-day-old plants (3 days with nitrogen source) and in a pulse-chase experiment in 13-day-old plants (5 days with nitrogen source). Ammonium caused, in contrast to nitrate nutrition, a higher level of 14C incorporation into sugar phosphates but a lower incorporation of label into malate, glycolate, glycerate, aspartate, and alanine. The labeling kinetics of glycine and serine were little changed by the nitrogen source. Ammonium feeding also produced an increase in the ratio of extractable activities of ribulose-1,5-bisphosphate carboxylase to phosphoenolpyruvate carboxylase and an increase in dark respiration and the CO2 compensation concentration. Net photosynthesis was higher in plants assimilating nitrate. The results point to stimulated turnover of the photosynthetic carbon reduction cycle metabolites, reduced phosphoenolpyruvate carboxylation, and altered turnover rates within the photosynthetic carbon oxidation cycle in ammonium-fed plants. Mechanisms of the regulation of primary carbon metabolism are proposed and discussed. 相似文献
4.
To assess the influence of bacteria inoculation on carbon flow through maize plant and rhizosphere, 14C allocation after 14CO 2 application to shoots over a 5-day period was determined. Plants were grown on C- and N-free quartz sand in two-compartment
pots, separating root and shoot space. While one treatment remained uninoculated, treatments two and three were inoculated
with Pantoea agglomerans (D5/23) and Pseudomonas fluorescens (Ps I A12), respectively, five days after planting. Bacterial inoculation had profound impacts on carbon distribution within
the system. Root/rhizosphere respiration was increased and more carbon was allocated to roots of plants being inoculated.
After five days of 14CO 2 application, more ethanol-soluble substances were found in roots of inoculated treatments and lower rhizodeposition indicated
intensive C turnover in the rhizosphere. In both inoculated treatments the intensity of photosynthesis measured as net-CO 2-assimilation rates were increased when compared to the uninoculated plants. However, high C turnover in the rhizosphere reduced
shoot growth of D5/23 inoculated plants, with no effect on shoot growth of Ps I A12 inoculated plants. A separation of labeled
compounds in roots and rhizodeposition revealed that neutral substances (sugars) constituted the largest fraction. The relative
fractions of sugars, amino acids and organic acids in roots and rhizodeposition suggest that amino acid exudation was particularly
stimulated by bacterial inoculation and that turnover of this substance group is high in the rhizosphere. 相似文献
5.
14CO 2 uptake in leaves of wheat plants ( Triticum aestivum L.) fertilized by urea or Ca(NO 3) 2 (25 mol m -3) was investigated. The Warburg effect (inhibition of 14CO 2 uptake by oxygen) under 0.03 vol. % CO 2 concentration was observed only in non-fertilized plants. Under 0.03 vol. % CO 2, the Warburg antieffect (stimulation of 14CO 2 uptake by oxygen) was detected only in plants fertilized by Ca(NO 3) 2. Under saturating CO 2 concentration (0.30 vol. %), the Warburg antieffect was observed in all variants. Under limitation of ribulose-1,5-bisphosphate carboxylase/oxygenase activity (0.30 vol. % CO 2 + 1 vol. % O 2), the rate of synthesis of glycollate metabolism products decreased in control and urea-fertilized plants but was enhanced in nitrate-fed plants. Hence, there was an activation of glycollate formation via transketolase reaction in fertilized plants, and the products of nitrate reduction function were oxidants in nitrate-fertilized plants whereas the superoxide radical played this role in urea-fertilized plants. 相似文献
6.
Roots of Vitis vinifera L., were treated with benzyladenine when the plant shoots were 38 cm long. Seventy-two hours after benzyladenine treatment, apical or basal leaves on separate shoots were exposed to 14CO 2. Control shoots received 14CO 2 but no benzyladenine. Application of benzyladenine directed 14C-photosynthate to roots, but a small amount of radioactivity was detected in the shoot tip when 14CO 2 was administered to an apical leaf. Distribution of radioactivity among the sugar, organic acid, and amino acid fractions was altered by benzyladenine treatment. In all parts of plants with roots treated with benzyladenine and apical leaf fed 14CO 2, the percentage of the total label in the sugar fraction comprised of fructose was generally more than twice that in control plants. 相似文献
7.
The fates and the rates of metabolism of acetate, trimethylamine, methylamine, and methanol were examined to determine the significance of these compounds as in situ methane precursors in surface sediments of an intertidal zone in Maine. Concentrations of these potential methane precursors were generally <3 μM, with the exception of sediments containing fragments of the seaweed Ascophyllum nodosum, in which acetate was 96 μM. [2- 14C]acetate turnover in all samples was rapid (turnover time <2 h), with 14CO 2 as the primary product. [ 14C]trimethylamine and methylamine turnover times were slower (>8 h) and were characterized by formation of both 14CH 4 and 14CO 2. Ratios of 14CH 4/ 14CO 2 from [ 14C]trimethylamine and methylamine in uninhibited sediments indicated that a significant fraction of these substrates were catabolized via a non-methanogenic process. Data from inhibition experiments involving sodium molybdate and 2-bromoethanesulfonic acid supported this interpretation. [ 14C]methanol was oxidized relatively slowly compared with the other substrates and was catabolized mainly to 14CO 2. Results from experiments with molybdate and 2-bromoethanesulfonic acid suggested that methanol was oxidized primarily through sulfate reduction. In Lowes Cove sediments, trimethylamine accounted for 35.1 to 61.1% of total methane production. 相似文献
8.
The initial products of photosynthesis by the C 3 species Flaveria cronquistii, the C 4 species F. trinervia, and the C 3-C 4 intermediate species F. ramosissima were determined using a pulse-chase technique with 14CO 2- 12CO 2. The intermediate species F. ramosissima incorporated at least 42% of the total soluble 14C fixed into malate and aspartate after 10 seconds of photosynthesis in 14CO 2, as compared with 90% for the C 4 species F. trinervia and 5% for the C 3 species F. cronquistii. In both F. ramosissima and F. trinervia, turnover of labeled malate and aspartate occurred during a chase period in 12CO 2, although the rate of turnover was slower in the intermediate species. Relative to F. cronquistii, F. ramosissima showed a reduced incorporation of radioactivity into serine and glycine during the pulse period. These results indicate that a functional C 4 pathway of photosynthesis is operating in F. ramosissima which can account for its reduced level of photorespiration, and that this species is a true biochemical intermediate between C 3 and C 4 plants. 相似文献
9.
Dwarf french beans, Phaseolus vulgaris L., were grown with or without inoculation with rhizobia (strain 3644), and with or without a combined nitrogen source (nitrate or ammonium ions). The distribution of radioactivity into products of dark 14CO 2 assimilation was studied in roots or nodules from these plants. A detailed study was also made of the distribution and rates of excretion of nitrogen in xylem bleeding sap in 28 day old plants grown on the various sources of nitrogen. Whereas detached nodules accumulated radioactive glycine, serine and glutamate when incubated with 14CO 2, bleeding sap from plants root fed 14CO 2 contained low levels of radioactivity in these compounds but higher levels in allantoin. Chemical analysis showed allantoin to be the major compound transported in the xylem of nodulated plants, whether or not they were fed on combined nitrogen. In contrast uninoculated plants accumulated mainly amino acids in the bleeding sap, the amount and chemical composition of which depended on the combined nitrogen source.Abbreviations PEP
phosphoenol pyruvate
- OAA
oxaloacetate 相似文献
10.
The carbon and electron flow pathways and the bacterial populations responsible for the transformation of H 2-CO 2, formate, methanol, methylamine, acetate, ethanol, and lactate were examined in eutrophic sediments collected during summer stratification and fall turnover. The rate of methane formation averaged 1,130 μmol of CH 4 per liter of sediment per day during late-summer stratification versus 433 μmol of CH 4 per liter of sediment per day during the early portion of fall turnover, whereas the rate of sulfate reduction was 280 μmol of sulfate per liter of sediment per day versus 1,840 μmol of sulfate per liter of sediment per day during the same time periods, respectively. The sulfate-reducing population remained constant while the methanogenic population decreased by one to two orders of magnitude during turnover. The acetate concentration increased from 32 to 81 μmol per liter of sediment while the acetate transformation rate constant decreased from 3.22 to 0.70 per h, respectively, during stratification versus turnover. Acetate accounted for nearly 100% of total sedimentary methanogenesis during turnover versus 70% during stratification. The fraction of 14CO 2 produced from all 14C-labeled substrates examined was 10 to 40% higher during fall turnover than during stratification. The addition of sulfate, thiosulfate, or sulfur to stratified sediments mimicked fall turnover in that more CO 2 and CH 4 were produced. The addition of Desulfovibrio vulgaris to sulfate-amended sediments greatly enhanced the amount of CO 2 produced from either [ 14C]methanol or [2- 14C]acetate, suggesting that H 2 consumption by sulfate reducers can alter methanol or acetate transformation by sedimentary methanogens. These data imply that turnover dynamically altered carbon transformation in eutrophic sediments such that sulfate reduction dominated over methanogenesis principally as a consequence of altering hydrogen metabolism. 相似文献
11.
The rates, products, and controls of the metabolism of fermentation intermediates in the sediments of a eutrophic lake were examined. 14C-fatty acids were directly injected into sediment subcores for turnover rate measurements. The highest rates of acetate turnover were in surface sediments (0- to 2-cm depth). Methane was the dominant product of acetate metabolism at all depths. Simultaneous measurements of acetate, propionate, and lactate turnover in surface sediments gave turnover rates of 159, 20, and 3 μM/h, respectively. [2- 14C]propionate and [ U- 14C]lactate were metabolized to [ 14C]acetate, 14CO 2, and 14CH 4. [ 14C]formate was completely converted to 14CO 2 in less than 1 min. Inhibition of methanogenesis with chloroform resulted in an immediate accumulation of volatile fatty acids and hydrogen. Hydrogen inhibited the metabolism of C 3-C 5 volatile fatty acids. The rates of fatty acid production were estimated from the rates of fatty acid accumulation in the presence of chloroform or hydrogen. The mean molar rates of production were acetate, 82%; propionate, 13%; butyrates, 2%; and valerates, 3%. A working model for carbon and electron flow is presented which illustrates that fermentation and methanogenesis are the predominate steps in carbon flow and that there is a close interaction between fermentative bacteria, acetogenic hydrogen-producing bacteria, and methanogens. 相似文献
12.
The distribution of 14C in photosynthetic metabolites of two naturally occurring higher plants with reduced photorespiration, Moricandia arvensis and Panicum milioides, in pulse and pulse-chase 14CO 2 incorporation experiments was similar to that for the C 3 species, M. foetida and Glycine max. After 6 seconds of 14CO 2 incorporation, only about 6% of the total 14C fixed was in malate and aspartate in both M. arvensis and P. milioides. The apparent turnover of the C 4 acids was very slow, and malate accumulated during the day in M. arvensis. Thus, C 4 acid metabolism by M. arvensis and P. milioides had no significant role in photosynthetic carbon assimilation under the conditions of our experiments (310 microliters CO 2 per liter, 21% O 2, 1100 or 1900 micromoles photon per square meter per second, 27°C). After a 36-second chase period in air containing 270 microliters CO2 per liter, about 20% of the total 14C fixed was in glycine with M. arvensis, as compared to 15% with M. foetida, 14% with P. milioides, and 9% with G. max. After a 36-second chase period in 100 microliters CO2 per liter, the percentage in glycine was about twice that at 270 microliters CO2 per liter in the C3 species and P. milioides, but only 20% more 14C was in glycine in M. arvensis. These data suggest that either the photorespiratory glycine pool in M. arvensis is larger than in the other species examined or the apparent turnover rate of glycine and the flow of carbon into glycine during photorespiration are less in M. arvensis. An unusual glycine metabolism in M. arvensis may be linked to the mechanism of photorespiratory reduction in this crucifer. 相似文献
13.
The CO 2 compensation point of the submersed aquatic macrophyte Hydrilla verticillata varied from high (above 50 microliters per liter) to low (10 to 25 microliters per liter) values, depending on the growth conditions. Plants from the lake in winter or after incubation in an 11 C/9-hour photoperiod had high values, whereas summer plants or those incubated in a 27 C/14-hour photoperiod had low values. The plants with low CO 2 compensation points exhibited dark 14CO 2 fixation rates that were up to 30% of the light fixation rates. This fixation reduced respiratory CO 2 loss, but did not result in a net uptake of CO 2 at night. The low compensation point plants also showed diurnal fluctuations in titratable acid, such as occur in Crassulacean acid metabolism plants. However, dark fixation and diurnal acid fluctuations were negligible in Hydrilla plants with high CO 2 compensation points. 相似文献
14.
Radiocarbon signatures (Δ 14C) of carbon dioxide (CO 2) provide a measure of the age of C being decomposed by microbes or respired by living plants. Over a 2‐year period, we measured Δ 14C of soil respiration and soil CO 2 in boreal forest sites in Canada, which varied primarily in the amount of time since the last stand‐replacing fire. Comparing bulk respiration Δ 14C with Δ 14C of CO 2 evolved in incubations of heterotrophic (decomposing organic horizons) and autotrophic (root and moss) components allowed us to estimate the relative contributions of O horizon decomposition vs. plant sources. Although soil respiration fluxes did not vary greatly, differences in Δ 14C of respired CO 2 indicated marked variation in respiration sources in space and time. The 14C signature of respired CO 2 respired from O horizon decomposition depended on the age of C substrates. These varied with time since fire, but consistently had Δ 14C greater (averaging ~120‰) than autotrophic respiration. The Δ 14C of autotrophically respired CO 2 in young stands equaled those expected for recent photosynthetic products (70‰ in 2003, 64‰ in 2004). CO 2 respired by black spruce roots in stands >40 years old had Δ 14C up to 30‰ higher than recent photosynthates, indicating a significant contribution of C stored at least several years in plants. Decomposition of O horizon organic matter made up 20% or less of soil respiration in the younger (<40 years since fire) stands, increasing to ~50% in mature stands. This is a minimum for total heterotrophic contribution, since mineral soil CO 2 had Δ 14C close to or less than those we have assigned to autotrophic respiration. Decomposition of old organic matter in mineral soils clearly contributed to soil respiration in younger stands in 2003, a very dry year, when Δ 14C of soil respiration in younger successional stands dropped below those of the atmospheric CO 2. 相似文献
15.
Photosynthetic carboxylating enzymes and the effects of light and temperature on 14CO 2 efflux in two species of gymnosperm leaves were studied. The activity of RuBP carboxylase was high and that of PEP carboxylase was very low when compared to C 4 plants. The CO 2 compensation point was high. 14CO 2 efflux was greater in light than in darkness and the ratio (L/D) increased with increase in temperature and light intensity. The inhibitors of glycolate metabolism showed decreased 14CO 2 evolution in light while dark respiration was unaffected. It is concluded that both Cycas circinalis, L. and Cycas beddomei Dyer are C 3 plants. 相似文献
16.
Transformed plants of Nicotiana plumbaginifolia Viv. constitutively expressing nitrate reductase (35S-NR) or β-glucuronidase (35S-GUS) and untransformed controls were grown
for two weeks in a CO 2-enriched atmosphere. Whereas CO 2 enrichment (1000 μl · l −1) resulted in an increase in the carbon (C) to nitrogen (N) ratio of both the tobacco lines grown in pots with vermiculite,
the C/N ratio was only slightly modified when plants were grown in hydroponic culture in high CO 2 compared to those grown in air. Constitutive nitrate reductase (NR) expression per se did not change the C/N ratio of the
shoots or roots. Biomass accumulation was similar in both types of plant when hydroponic or pot-grown material, grown in air
or high CO 2, were compared. Shoot dry matter accumulation was primarily related to the presence of stored carbohydrate (starch and sucrose)
in the leaves. In the pot-grown tobacco, growth at elevated CO 2 levels caused a concomitant decrease in the N content of the leaves involving losses in NO −
3 and amino acid levels. In contrast, the N content and composition were similar in all plants grown in hydroponic culture.
The 35S-NR plants grown in air had higher foliar maximum extractable NR activities and increased glutamine levels (on a chlorophyll
or protein basis) than the untransformed controls. These increases were maintained following CO 2 enrichment when the plants were grown in hydroponic culture, suggesting that an increased flux through nitrogen assimilation
was possible in the 35S-NR plants. Under CO 2 enrichment the NR activation state in the leaves was similar in all plants. When the 35S-NR plants were grown in pots, however,
foliar NR activity and glutamine content fell in the 35S-NR transformants to levels similar to those of the untransformed
controls. The differences in NR activity between untransformed and 35S-NR leaves were much less pronounced in the hydroponic
than in the pot-grown material but the difference in total extractable NR activity was more marked following CO 2 enrichment. Foliar NR message levels were decreased by CO 2 enrichment in all growth conditions but this was much more pronounced in pot-grown material than in that grown hydroponically.
Since β-glucuronidase (GUS) activity and message levels in 35S-GUS plants grown under the same conditions of CO 2 enrichment (to test the effects of CO 2 enrichment on the activity of the 35S promoter) were found to be constant, we conclude that NR message turnover was specifically
accelerated in the 35S-NR plants as well as in the untransformed controls as a result of CO 2 enrichment. The molecular and metabolic signals involved in increased NR message and protein turnover are not known but possible
effectors include NO 3
−, glutamine and asparagine. We conclude that plants grown in hydroponic culture have greater access to N than those grown
in pots. Regardless of the culture method, CO 2 enrichment has a direct effect on NR mRNA stability.
Received: 17 October 1996 / Accepted: 11 February 1997 相似文献
17.
3,4-Dichloropropionanilide- 14C (propanil) labeled in either the C-1 or C-3 carbon atoms of the propionic acid moiety was applied to the roots of pea ( Pisum sativum L.) and rice ( Oryza sativa L.) plants in nutrient solution (0.1 m m-0.28 m m). Radioactivity was detected throughout the treated plants, but the greatest labeling was found in the roots. None of the products that contained aniline were radioactive, suggesting that the plants split the propionic acid moiety from propanil. The fate of the propionate moiety of propanil was determined by recovery of 14CO 2 from plants exposed to propanil- 14C. The time-course of the 14CO 2 production demonstrated that the intact propionic acid was cleaved from the propanil and subsequently catabolized by the β-oxidation catabolic sequence. The appearance of radioactivity in the shoots was attributed to the incorporation of products of propionate metabolism. Both the susceptible pea plants and the tolerant rice plants converted a high percentage of the administered propanil- 14C to 14CO 2. 相似文献
18.
A normal appearing plant with a low rate of photorespiration (ratio of 14CO 2 released light/dark = 1.6) was found in an unselected tobacco ( Nicotiana tabacum) cultivar. The plant was self-pollinated, and further selections were made on several successive generations. Excised leaves from the progeny of the selections were examined for photorespiration and net CO 2 assimilation in normal air during photosynthesis. Similar measurements were made of plants derived from selfed parents with high rates of photorespiration (ratio of 14CO 2 released light/dark = 3.0 or greater). Efficient photosynthetic plants (greater than 22.0 mg of CO 2 dm −2 hr −1) with low rates of photorespiration produced a larger proportion of efficient progeny (about 25%) than did selfing inefficient plants (about 6%), but this proportion did not increase in successive generations. 相似文献
19.
Rice ( Oryza sativa[L.] cv. IR-72) was grown for a season in sunlit, controlled-environment chambers at 350 or 700 µmol CO 2 mol ?1 under continuously flooded (unstressed) or drought-imposed periods at panicle initiation (stressed). The midday canopy photosynthetic rates (P n), measured at the CO 2 concentration ([CO 2]) used for growth, were enhanced by high [CO 2] but reduced by drought. High [CO 2] increased P n by 18 to 34% for the unstressed plants, and 6 to 12% for the stressed plants. In the unstressed plants, CO 2 enrichment increased water-use efficiency (WUE) by 26%, and reduced evapotranspiration (ET) by 8 to 14%. Both high [CO 2] and severe drought decreased the activity and content of ribulose bisphosphate carboxylase-oxygenase (Rubisco). High-CO 2-unstressed plants had 6 to 22% smaller content and 5 to 25%, lower activity of Rubisco than ambient-CO 2-unstressed plants. Under severe drought, reductions of Rubisco were 53 and 27% in activity and 40 and 12% in content, respectively, for ambient- and high-CO 2 treatments. The apparent catalytic turnover rate (K cat) of midday fully activated Rubisco was not altered by high [CO 2], but severe drought reduced K cat by 17 to 23%. Chloroplasts of the high-CO 2 leaves contained more, and larger starch grains than those of the ambient CO 2 leaves. High [CO 2] did not affect the leaf sucrose content of unstressed plants. In contrast, severe drought reduced the leaf starch and increased the sucrose content in both CO 2 treatments. The activity of leaf sucrose phosphate synthase of unstressed plants was not affected by high [CO 2], whereas that of ambient-CO 2-grown plants was reduced 45% by severe drought. Reduction in ET and enhancements in both P n and WUE for rice grown under high [CO 2] helped to delay the adverse effects of severe drought and allowed the stressed plants to assimilate CO 2 for an extra day. Thus, rice grown in the next century may utilize less water, use water more efficiently, and be able to tolerate drought better under some situations. 相似文献
20.
The effects of different shading periods of maize plants on rhizosphere respiration and soil organic matter decomposition were investigated by using a 13C natural abundance and 14C pulse labeling simultaneously. 13C was a tracer for total C assimilated by maize during the whole growth period, and 14C was a tracer for recently assimilated C. CO 2 efflux from bare soil was 4 times less than the total CO 2 efflux from planted soil under normal lighting. Comparing to the normal lighting control (12/12 h day/night), eight days with reduced photosynthesis (12/36 h day/night period) and strongly reduced photosynthesis (12/84 h day/night period) resulted in 39% and 68% decrease of the total CO 2 efflux from soil, respectively. The analysis of 13C natural abundance showed that root-derived CO 2 efflux accounted for 82%, 68% and 56% of total CO 2 efflux from the planted soil with normal, prolonged and strongly prolonged night periods, respectively. Clear diurnal dynamics of the total CO 2 efflux from soil with normal day-night period as well as its strong reduction by prolonged night period indicated tight coupling with plant photosynthetic activity. The light-on events after prolonged dark periods led to increases of root-derived and therefore of total CO 2 efflux from soil. Any factor affecting photosynthesis, or substrate supply to roots and rhizosphere microorganisms, is an important determinant of root-derived CO 2 efflux, and thereby, total CO 2 efflux from soils. 14C labeling of plants before the first light treatment did not show any significant differences in the 14CO 2 respired in the rhizosphere between different dark periods because the assimilate level in the plants was high. Second labeling, conducted after prolonged night phases, showed higher contribution of recently assimilated C ( 14C) to the root-derived CO 2 efflux by shaded plants. Results from 13C natural abundance showed that the cultivation of maize on Chromic Luvisol decreased soil organic matter (SOM) mineralization compared to unplanted soil (negative priming effect). A more important finding is the observed tight coupling of the negative rhizosphere effect on SOM decomposition with photosynthesis. 相似文献
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