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1.
Wheat (cv. Gutha) and barley (cv. O'Connor) were grown as field crops on a shallow duplex soil (sand over clay) in Western Australia with their root systems contained within pvc columns. At four stages during growth, the shoots were pulse-labelled for 1.5h with 14CO 2; immediately prior to labelling, the soil was isolated from the shoot atmosphere by pvc sheets. After labelling, the soil atmosphere was pumped through NaOH to trap respired CO 2 and after 2.5, 5, 7.5 and 24 h from the start of labelling, columns were destructively sampled to recover 14C from the roots, soil and shoot.Both species showed similar patterns of 14C distribution and changes in distribution through the growing season. During early tillering, 15–25% of the 14C recovered after 24 h had been respired by the roots and rhizosphere, 17–27% was retained in the roots, 0.4–1.8% was recovered as water-soluble 14C in the soil and the remainder (45–67%) was present in the shoot. These percentages changed during growth so that during grain filling only 2–3% of the 14C recovered after 24 h was as respired CO 2, 2–6% was in the roots, 0.2% was in the soil and over 90% was in the shoot.The distribution of 14C in components of the soil-plant system changed during the 24 h after labelling with the most rapid changes occurring generally during the first 7.5 h after labelling.Using growth measurements from adjacent plots, the amounts of C added to the soil were estimated for the whole season. Carbon input to the soil was about 48 gC m –2 for wheat and 58 gC m –2 for barley; the crops produced total shoot dry matter of 494 (wheat) and 735 g m –2 (barley). Of the C input to the soil, 27.8% (wheat) and 40.3% (barley) was as respired C and only 3.3 (wheat) and 4.1% (barley) was collected as exudate (water-soluble material). 相似文献
2.
The results of a simultaneous 13C and 15N labelling experiment with two different durum wheat cultivars, Blanqueta (a traditional wheat) and Sula (modern), are presented. Plants were grown from the seedling stage in three fully controllable plant growth chambers for one growing season and at three different CO 2 levels ( i.e. 260, 400 and 700 ppm). Short‐term isotopic labelling (ca. 3 days) was performed at the anthesis stage using 13CO 2 supplied with the chamber air and 15NH 4‐ 15NO 3 applied with the nutrient solution, thereby making it possible to track the allocation and partitioning of 13C and 15N in the different plant organs. We found that photosynthesis was up‐regulated at pre‐industrial CO 2 levels, whereas down‐regulation occurred under future CO 2 conditions. 13C labelling revealed that at pre‐industrial CO 2 carbon investment by plants was higher in shoots, whereas at future CO 2 levels more C was invested in roots. Furthermore, the modern genotype invested more C in spikes than did the traditional genotype, which in turn invested more in non‐reproductive shoot tissue. 15N labelling revealed that the modern genotype was better adapted to assimilating N at higher CO 2 levels, whereas the traditional genotype was able to assimilate N more efficiently at lower CO 2 levels. 相似文献
3.
The effect of varying CO 2 concentrations on the growth of beet and safflower hairy roots was measured for tissues cultured in nutrient mists and on solid media in chambers fed mixtures of humidified air supplemented with different CO 2 concentrations. Hairy root tissue grown on solid media in air enriched with CO 2 showed increased growth, as measured by dry weight increases vs air-fed controls. Growth increased with CO 2 enrichment as much as 2.5 times more than the air-fed control for safflower at 1.0% CO 2 and 1.4 times more than the air-fed control for beets at 1.5% CO 2 over a 12-day period. Beet hairy root tissue was also cultured aeroponically in nutrient mists. Beet hairy root cultured aeroponically in nutrient mists enriched with 1.0% CO 2 showed a 15% increase in biomass over a 7-day period vs tissue cultured in nutrient mists (with ambient air) or in shake flasks. The stimulation of root growth via CO 2 enrichment reduced the time required for biomass accumulation.
Correspondence to: A. A. DiIorio 相似文献
4.
Respiratory characteristics of wheat ( Triticum aestivum L. cvs Gabo and WW15), mung bean ( Vigna radiata L. Wilczek cv. Celera) and sunflower ( Helianthus annuus L. cv. Sunfola) were studied in plants grown under a normal CO 2 concentration and in air containing an additional 340 (or 250) μl l ?1 CO 2. Such an increase in global atmospheric CO 2 concentration has been forecast for about the middle of the next century. The aim was to measure the effect of high CO 2 on respiration and its components. Polarographic and, with wheat, CO 2 exchange techniques were used. The capacity of the alternative pathway of respiration in roots was determined polarographically in the presence of 0.1 m M KCN. The actual rate of alternative pathway respiration was assessed by reduction in oxygen consumption caused by 10 m M salicylhydroxamic acid. Each species responded differently. In wheat, growth in high atmospheric CO 2 was associated with up to 45% reduction in respiration by both roots and whole plants. Use of respiratory inhibitors in polarographic measurements on wheat roots implicated reduction in the degree of engagement of the alternative pathway as a major contributor to this reduced respiratory activity of high-CO 2 plants. No change was found in the total sugar content per unit wheat root dry weight as a result of high CO 2. In none of the species was there an increase in the absolute, or relative, contribution by the alternative pathway to total respiration of the root systems. Thus the improved photosynthetic assimilate supply of plants grown in high CO 2 did not lead to increased diversion of carbon through the non-phosphorylating alternative pathway of respiration in the root. On the contrary, in wheat grown in high CO 2 the reduced loss of carbon through that route must have contributed to their larger dry weight. 相似文献
5.
The effects of elevated CO 2 (eCO 2) on the relative uptake of inorganic and organic nitrogen (N) are unclear. The uptake of different N sources by pak choi ( Brassica chinensis L.) seedlings supplied with a mixture of nitrate, glycine and ammonium was studied using 15N‐labelling under ambient CO 2 (aCO 2) (350 ppm) or eCO 2 (650 ppm) conditions. 15N‐labelled short‐term uptake and 15N‐gas chromatography mass spectrometry (GC–MS) were applied to measure the effects of eCO 2 on glycine uptake and metabolism. Elevated CO 2 increased the shoot biomass by 36% over 15 days, but had little effect on root growth. Over the same period, the N concentrations of shoots and roots were decreased by 30 and 2%, respectively. Elevated CO 2 enhanced the uptake and N contribution of glycine, which accounted for 38–44% and 21–40% of total N uptake in roots and shoots, respectively, while the uptake of nitrate and ammonium was reduced. The increased glycine uptake resulted from the enhanced active uptake and enhanced metabolism in the roots. We conclude that eCO 2 may increase the uptake and contribution of organic N forms to total plant N nutrition. Our findings provide new insights into plant N regulation under eCO 2 conditions. 相似文献
6.
The aim of this work was to examine the response of wheat plants to a doubling of the atmospheric CO 2 concentration on: (1) carbon and nitrogen partitioning in the plant; (2) carbon release by the roots; and (3) the subsequent N uptake by the plants. The experiment was performed in controlled laboratory conditions by exposing fast-growing spring wheat plants, during 28 days, to a 14CO 2 concentration of 350 or 700 L L –1 at two levels of soil nitrogen fertilization. Doubling CO 2 availability increased total plant production by 34% for both N treatment. In the N-fertilized soil, the CO 2 enrichment resulted in an increase in dry mass production of 41% in the shoots and 23% in the roots; without N fertilization this figure was 33% and 37%, respectively. In the N-fertilized soil, the CO 2 increase enhanced the total N uptake by 14% and lowered the N concentration in the shoots by 23%. The N concentration in the roots was unchanged. In the N-fertilized soil, doubling CO 2 availability increased N uptake by 32% but did not change the N concentrations, in either shoots or roots. The CO 2 enrichment increased total root-derived carbon by 12% with N fertilization, and by 24% without N fertilization. Between 85 and 90% of the total root derived- 14C came from respiration, leaving only 10 to 15% in the soil as organic 14C. However, when total root-derived 14C was expressed as a function of root dry weight, these differences were only slightly significant. Thus, it appears that the enhanced carbon release from the living roots in response to increased atmospheric CO 2, is not due to a modification of the activity of the roots, but is a result of the increased size of the root system. The increase of root dry mass also resulted in a stimulation of the soil N mineralization related to the doubling atmospheric CO 2 concentration. The discussion is focused on the interactions between the carbon and nitrogen allocation, especially to the root system, and the implications for the acquisition of nutrients by plants in response to CO 2 increase.Abbreviations N
soil fertilization without nitrogen
- N
soil fertilization with nitrogen 相似文献
7.
Experiments were designed to determine the significance of dark CO 2 fixation in excised maize roots, carrot slices and excised tomato roots grown in tissue culture. Bicarbonate- 14C was used to determine the pathway and amounts of CO 2 fixation, while leucine- 14C was used to estimate protein synthesis in tissues aerated with various levels of CO 2. Organic acids were labeled from bicarbonate-14C, with malate being the major labeled acid. Only glutamate and aspartate were labeled in the amino acid fraction and these 2 amino acids comprised over 90% of the 14C label in the ethanol-water insoluble residue. Studies with leucine-14C as an indicator of protein synthesis in carrot slices and tomato roots showed that those tissues aerated with air incorporated 33% more leucine-14C into protein than those aerated with CO2-free air. Growth of excised tomato roots aerated with air was 50% more than growth of tissue aerated with CO2-free air. These studies are consistent with the suggestion that dark fixation of CO2 is involved in the growth of plant tissues. 相似文献
8.
Summary Methods for labelling growing plants by exposing them to C 14O 2 under a cellulose acetate-butyrate canopy have been developed for laboratory and field use. The length of labelling ranged from 2 to 33 days and the C 14O 2 content of the atmosphere was automatically controlled. This made it possible to measure carbon assimilation by the plants, transfer of photosynthates beneath ground and respiration of the roots.In the laboratory, root respiration of wheat plants was measured by separating the above and beneath ground plant parts using a RTV rubber partition. Half to two thirds of the assimilated carbon was found above ground, 15 to 25 per cent in the roots and shoot bases below the partition and 17 to 25 per cent was lost by underground respiration. The variability of these proportions was related to the stage of maturity of the plants.On native grassland, the relative above and beneath ground productivity was 50 per cent. The time required for the photosynthates to reach the roots at various depths ranged from 1 to 5 days and the amount of material deposited in the roots changed with time and soil moisture content. The use of tubes inserted at various depths beneath the canopy permitted sampling of soil air for C 14 and CO 2 measurements. The soil C 14O 2 flux indicated that root respiration during 8 days accounted for 24 per cent of the labelled carbon translocated to the roots after a two days labelling period. 相似文献
9.
Summary Plantlets of Nicotiana tabacum (var. Samsun) were grown under CO 2 enriched air supplied by a Warburg buffer. Growth of all plant parts was enhanced. The maximum growth increase was found for roots (120%).Addition of 30 g.l -1 sucrose in the medium resulted in a three time faster growth. However, the effect of CO 2 enrichment was still positive in these conditions, although less pronounced than in autotrophic cultures. 相似文献
10.
Gas exchange and dry-weight production in Opuntia ficus-indica, a CAM species cultivated worldwide for its fruit and cladodes, were studied in 370 and 750 μmol mol −1 CO 2 at three photosynthetic photon flux densities (PPFD: 5, 13 and 20 mol m −2 d −1). Elevated CO 2 and PPFD enhanced the growth of basal cladodes and roots during the 12-week study. A rise in the PPFD increased the growth of daughter cladodes; elevated CO 2 enhanced the growth of first-daughter cladodes but decreased the growth of the second-daughter cladodes produced on them. CO 2 enrichment enhanced daily net CO 2 uptake during the initial 8 weeks after planting for both basal and first-daughter cladodes. Water vapour conductance was 9 to 15% lower in 750 than in 370 μmol mol −1 CO 2. Cladode chlorophyll content was lower in elevated CO 2 and at higher PPFD. Soluble sugar and starch contents increased with time and were higher in elevated CO 2 and at higher PPFD. The total plant nitrogen content was lower in elevated CO 2. The effect of elevated CO 2 on net CO 2 uptake disappeared at 12 weeks after planting, possibly due to acclimation or feedback inhibition, which in turn could reflect decreases in the sink strength of roots. Despite this decreased effect on net CO 2 uptake, the total plant dry weight at 12 weeks averaged 32% higher in 750 than in 370 μmol mol −1 CO 2. Averaged for the two CO 2 treatments, the total plant dry weight increased by 66% from low to medium PPFD and by 37% from medium to high PPFD. 相似文献
11.
The red seaweed Hypnea spinella (Gigartinales, Rhodophyta), was cultured at laboratory scale under three different CO 2 conditions, non-enriched air (360?ppm CO 2) and CO 2-enriched air at two final concentrations (750 and 1,600?ppm CO 2), in order to evaluate the influence of increased CO 2 concentrations on growth, photosynthetic capacity, nitrogen removal efficiency, and chemical cellular composition. Average specific growth rates of H. spinella treated with 750 and 1,600?ppm CO 2-enriched air increased by 85.6% and 63.2% compared with non-enriched air cultures. CO 2 reduction percentages close to 12% were measured at 750?ppm CO 2 with respect to 5% and 7% for cultures treated with air and 1,600?ppm CO 2, respectively. Maximum photosynthetic rates were enhanced significantly for high CO 2 treatments, showing P max values 1.5-fold higher than that for air-treated cultures. N–NH 4 + consumption rates were also faster for algae growing at 750 and 1,600?ppm CO 2 than that for non-enriched air cultures. As a consequence of these experimental conditions, soluble carbohydrates increased and soluble protein contents decreased in algae treated with CO 2-enriched air. However, internal C and N contents remained constant at the different CO 2 concentrations. No significant differences in data obtained with both elevated CO 2 treatments, under the assayed conditions, indicate that H. spinella is saturated at dissolved inorganic carbon concentrations close by twice the actual atmospheric levels. The results show that increased CO 2 concentrations might be considered a key factor in order to improve intensively cultured H. spinella production yields and carbon and nitrogen bioremediation efficiencies. 相似文献
12.
Pedunculate oak ( Quercus robur L.) was germinated and grown at ambient CO 2 concentration and 650 μmol mol ?1 CO 2 in the presence and absence of the ectomycorrhizal fungus Laccaria laccata for a total of 22 weeks under nonlimiting nutrient conditions. Sulphate uptake, xylem loading and exudation were analysed in excised roots. Despite a relatively high affinity for sulphate ( KM= 1.6 mmol m ?3), the rates of sulphate uptake by excised lateral roots of mycorrhizal oak trees were low as compared to herbaceous plants. Rates of sulphate uptake were similar in mycorrhizal and non-mycorrhizal roots and were not affected by growth of the trees at elevated CO 2. However, the total uptake of sulphate per plant was enhanced by elevated CO 2 and further enhanced by elevated CO 2 and mycorrhization. Sulphate uptake seemed to be closely correlated with biomass accumulation under the conditions applied. The percentage of the sulphate taken up by mycorrhizal oak roots that was loaded into the xylem was an order of magnitude lower than previously observed for herbaceous plants. The rate of xylem loading was enhanced by mycorrhization and, in roots of mycorrhizal trees only, by growth at elevated CO 2. On a whole-plant basis this increase in xylem loading could only partially be explained by the increased growth of the trees. Elevated CO 2 and mycorrhization appeared to increase greatly the sulphate supply of the shoot at the level of xylem loading. For all treatments, calculated rates of sulphate exudation were significantly lower than the corresponding rates of xylem loading of sulphate. Radiolabelled sulphate loaded into the xylem therefore seems to be readily diluted by unlabelled sulphate during xylem transport. Allocation of reduced sulphur from oak leaves was studied by flap-feeding radiolabelled GSH to mature oak leaves. The rate of export of radioactivity from the fed leaves was 4–5 times higher in mycorrhizal oak trees grown at elevated CO 2 than in those grown at ambient CO 2. Export of radiolabel proceeded almost exclusively in a basipetal direction to the roots. From these experiments it can be concluded that, in mycorrhizal oak trees grown at elevated CO 2, the transport of sulphate to the shoot is increased at the level of xylem loading to enable increased sulphate reduction in the leaves. Increased sulphate reduction seems to be required for the enhanced allocation of reduced sulphur to the roots which is observed in trees grown at elevated CO 2. These changes in sulphate and reduced sulphur allocation may be a prerequisite for the positive effect of elevated CO 2 on growth of oak trees previously observed. 相似文献
13.
Carbon rhizodeposition and root respiration during eight development stages of Lolium perenne were studied on a loamy Gleyic
Cambisol by 14CO 2 pulse labelling of shoots in a two compartment chamber under controlled laboratory conditions. Total 14CO 2 efflux from the soil (root respiration, microbial respiration of exudates and dead roots) in the first 8 days after 14C pulse labelling decreased during plant development from 14 to 6.5% of the total 14C input. Root respiration accounted for was between 1.5 and 6.5% while microbial respiration of easily available rhizodeposits
and dead root remains were between 2 and 8% of the 14C input. Both respiration processes were found to decline during plant development, but only the decrease in root respiration
was significant. The average contribution of root respiration to total 14CO 2 efflux from the soil was approximately 41%. Close correlation was found between cumulative 14CO 2 efflux from the soil and the time when maximum 14CO 2 efflux occurred (r=0.97). The average total of CO 2 Defflux from the soil with Lolium perenne was approximately 21 μg C-CO 2 d −1 g −1. It increased slightly during plant development. The contribution of plant roots to total CO 2 efflux from the soil, calculated as the remainder from respiration of bare soil, was about 51%. The total 14C content after 8 days in the soil with roots ranged from 8.2 to 27.7% of assimilated carbon. This corresponds to an underground
carbon transfer by Lolium perenne of 6–10 g C m −2 at the beginning of the growth period and 50–65 g C m −2 towards the end of the growth period. The conventional root washing procedure was found to be inadequate for the determination
of total carbon input in the soil because 90% of the young fine roots can be lost.
This revised version was published online in June 2006 with corrections to the Cover Date.
This revised version was published online in June 2006 with corrections to the Cover Date.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
14.
In vivo experiments in mice demonstrated that 5% CO 2 content in the air inhaled did not change the labelling in autoradiograms from animals injected with [ 3H]uridine, [ 3H]orotic acid, [ 3H]hypoxanthine, [ 3H]lysine or [ 3H]cytidine. At 20% CO 2 content there was a significant decrease in labelling of brain cells with [ 3H]uridine and [ 3H]cytidine, but not following [ 3H]lysine; there was no labelling of nerve cells with [ 3H]orotic acid or [ 3H]hypoxanthine, but a control group was not included. The labelling of choroid plexus and hepatocytes was independent of the CO 2 concentration. A comparison of in vivo and in vitro experiments at 20% CO 2 content showed a similar significant decrease in labelling of brain cells with [ 3H]uridine and [ 3H]cytidine. It is concluded that a metabolic change is the most appropriate explanation of the CO 2 effect. 相似文献
15.
Barley roots contain a CO 2 sensitive respiratory fraction which is inhibited in 50 per cent CO 2 and is partially restored upon subsequent exposure to air. The residual O 2 consumption occurring at CO 2 concentrations between 50 per cent and 95 per cent amounts to about 40 per cent of the O 2 uptake in air and can support K + uptake for a limited time at a rate equal to or higher than occurs in air. Above 95 per cent CO 2 both O 2 and K + uptakes decrease rapidly. 2,4-dinitrophenol (DNP), in the range of 10 ?6 to 10 ?5M, stimulates O 2 uptake by the roots in air. The stimulation is absent when roots are treated with DNP in 80 per cent CO 2, presumably because of the reduced demand for inorganic phosphate and phosphate acceptor at the lower respiratory level in high CO 2. In either air or CO 2, K + uptake is strongly inhibited by DNP. A comparison of the respiratory and K + uptake data indicates that O 2 consumption is a necessary requirement for the uptake process in high CO 2. Protoplasmic streaming in the root cells is rapidly stopped by high CO 2 although K + uptake and O 2 consumption continue. The cation uptake mechanism in high CO 2 appears to be limited to the stationary cytoplasm. It is also possible that a similar mechanism may be involved in cation uptake in air. 相似文献
16.
Summary The relationships between root exudation, root disease and anaerobic root stresses were investigated. Sand culture and mist
chamber studies demonstrated that low O 2 and high CO 2 reduced plant growth and increased the exudation of ethanol, amino acids, and sugars by pea roots. The relative loss of ethanol
by roots was much greater in treatments with atmospheres of N 2 containing 30% CO 2 than in treatments of air containing 30% CO 2 or N 2. Ethanol was not detected in the nutrient solution of aerated plant roots. Atmospheres of N 2 plus 30% CO 2 caused 500% greater mycelial growth of Fusarium solani f. sp. pisi and 400% more disease of inoculated pea roots. Relative losses of four amino acids and four sugars were much greater in atmospheres
of N 2 plus 30% CO 2 than in N 2 or air. 相似文献
17.
We assessed the effects of doubling atmospheric CO 2 concentration, [CO 2], on C and N allocation within pedunculate oak plants ( Quercus robur L.) grown in containers under optimal water supply. A short-term dual 13CO 2 and 15NO 3? labelling experiment was carried out when the plants had formed their third growing flush. The 22-week exposure to 700 μl l ?1 [CO 2] stimulated plant growth and biomass accumulation (+53% as compared with the 350 μl l ?1 [CO 2] treatment) but decreased the root/shoot biomass ratio (-23%) and specific leaf area (-18%). Moreover, there was an increase in net CO 2 assimilation rate (+37% on a leaf dry weight basis; +71% on a leaf area basis), and a decrease in both above- and below-ground CO 2 respiration rates (-32 and -26%, respectively, on a dry mass basis) under elevated [CO 2]. 13C acquisition, expressed on a plant mass basis or on a plant leaf area basis, was also markedly stimulated under elevated [CO 2] both after the 12-h 13CO 2 pulse phase and after the 60-h chase phase. Plant N content was increased under elevated CO 2 (+36%), but not enough to compensate for the increase in plant C content (+53%). Thus, the plant C/N ratio was increased (+13%) and plant N concentration was decreased (-11%). There was no effect of elevated [CO 2] on fine root-specific 15N uptake (amount of recently assimilated 15N per unit fine root dry mass), suggesting that modifications of plant N pools were merely linked to root size and not to root function. N concentration was decreased in the leaves of the first and second growing flushes and in the coarse roots, whereas it was unaffected by [CO 2] in the stem and in the actively growing organs (fine roots and leaves of the third growth flush). Furthermore, leaf N content per unit area was unaffected by [CO 2]. These results are consistent with the short-term optimization of N distribution within the plants with respect to growth and photosynthesis. Such an optimization might be achieved at the expense of the N pools in storage compartments (coarse roots, leaves of the first and second growth flushes). After the 60-h 13C chase phase, leaves of the first and second growth flushes were almost completely depleted in recent 13C under ambient [CO 2], whereas these leaves retained important amounts of recently assimilated 13C (carbohydrate reserves?) under elevated [CO 2]. 相似文献
18.
Pedunculate oak ( Quercus robur L.) was germinated and grown under nutrient non-limiting conditions for a total of 10–15 weeks at ambient CO 2 concentration and 1100 μmol mol –1 CO 2 either in the presence or the absence of the mycorrhizal fungus Laccaria laccata. Half of the oak trees of these treatments were exposed to drought during final growth by suspending the water supply for 21 d. Mycorrhization and elevated atmospheric CO 2 each enhanced total plant biomass per tree. Whereas additional biomass accumulation of trees grown under elevated CO 2 was mainly attributed to increased growth of lateral roots, mycorrhization promoted shoot growth. Water deficiency reduced biomass accumulation without affecting relative water content, but this effect was more pronounced in mycorrhizal as compared to non-mycorrhizal trees. Elevated CO 2 partially prevented the development of drought stress, as indicated by leaf water potential, but did not counteract the negative effects of water deficiency on growth during the time studied. Enhanced biomass accumulation requires adaption in protein synthesis and, as a consequence, enhanced allocation of reduced sulphur produced in the leaves to growing tissues. Therefore, allocation of reduced sulphur from oak leaves was studied by flap-feeding radiolabelled GSH, the main long-distance transport form of reduced sulphur, to mature oak leaves. Export of radiolabel proceeded almost exclusively in basipetal direction to the roots. The rate of export of radioactivity out of the fed leaves was significantly enhanced under elevated CO 2, irrespective of mycorrhization. A higher proportion of the exported GSH was transported to the roots than to basipetal stem sections under elevated CO 2 as compared to ambient CO 2. Mycorrhization did not affect 35S export out of the fed leaves, but the distribution of radiolabel between stem and roots was altered in preference of the stem. Trees exposed to drought did not show appreciable export of the 35S radioactivity fed to the leaves when grown under ambient CO 2. Apparently, drought inhibited basipetal transport of reduced sulphur at the level of phloem loading and/or phloem transport. Elevated CO 2 seemed to counteract this effect of drought stress to some extent, since higher leaf water potentials and improved 35S export out of the fed leaves was observed in oak trees exposed to drought and elevated CO 2 as compared to trees exposed to drought and ambient CO 2. 相似文献
19.
The effect of elevated [CO 2] on the productivity of spring wheat, winter wheat and faba bean was studied in experiments in climatized crop enclosures in the Wageningen Rhizolab in 1991–93. Simulation models for crop growth were used to explore possible causes for the observed differences in the CO 2 response. Measurements of the canopy gas exchange (CO 2 and water vapour) were made continuously from emergence until harvest. At an external [CO 2] of 700 μmol mol ?1 Maximum Canopy CO 2 Exchange Rate (CCERmax) at canopy closure was stimulated by 51% for spring wheat and by 71% for faba bean. At the end of the growing season, above ground biomass increase at 700 μmol mol ?1 was 58% (faba bean), 35% (spring wheat) and 19% (winter wheat) and the harvest index did not change. For model exploration, weather data sets for the period 1975-88 and 1991–93 were used, assuming adequate water supply and [CO 2] at 350 and 700 μmol mol ?1. For spring wheat the simulated responses (35–50%) were at the upper end of the experimental results. In agreement with experiments, simulations showed smaller responses for winter wheat and larger responses for faba bean. Further model explorations showed that this differential effect in the CO 2 response may not be primarily due to fundamental physiological differences between the crops, but may be at least partly due to differences in the daily air temperatures during comparable stages of growth of these crops. Simulations also showed that variations between years in CO 2 response can be largely explained by differences in weather conditions (especially temperature) between growing seasons. 相似文献
20.
Roots of annual crop plants are a major sink for carbon particularly during early, vegetative growth when up to one-half of all assimilated carbon may be translocated belowground. Flowering marks a particularly important change in resource allocation, especially in determinate species, with considerably less allocation to roots and, depending on environmental conditions, there may be insufficient for maintenance. Studies with 14C indicate the rapid transfer belowground of assimilates with typically 50% translocated in young cereal plants of which 50% is respired; exudation/rhizodeposition is generally <5% of the fixed carbon. Root: total plant mass decreases through the season and is affected by soil and atmospheric conditions. Limited water availability increased the allocation of 13C to roots of wheat grown in columns so that at booting 0.38 of shoot C (ignoring shoot respiration) was belowground compared to 0.31 in well-watered plants. Elevated CO 2 (700 mol CO 2 mol –1 air) increased the proportion of root:total mass by 55% compared with normal concentration, while increasing the air temperature by a mean of 3 °C decreased the proportion from 0.093 in the cool treatment to 0.055 in the warm treatment. 相似文献
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