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1.
T. E. Huxman E. P. Hamerlynck B. D. Moore S. D. Smith D. N. Jordan S. F. Zitzer R. S. Nowak J. S. Coleman & J. R. Seemann 《Plant, cell & environment》1998,21(11):1153-1161
The photosynthetic response of Larrea tridentata Cav., an evergreen Mojave Desert shrub, to elevated atmospheric CO2 and drought was examined to assist in the understanding of how plants from water-limited ecosystems will respond to rising CO2. We hypothesized that photosynthetic down-regulation would disappear during periods of water limitation, and would, therefore, likely be a seasonally transient event. To test this we measured photosynthetic, water relations and fluorescence responses during periods of increased and decreased water availability in two different treatment implementations: (1) from seedlings exposed to 360, 550, and 700 μmol mol–1 CO2 in a glasshouse; and (2) from intact adults exposed to 360 and 550 μmol mol–1 CO2 at the Nevada Desert FACE (Free Air CO2 Enrichment) Facility. FACE and glasshouse well-watered Larrea significantly down-regulated photosynthesis at elevated CO2, reducing maximum photosynthetic rate (Amax), carboxylation efficiency (CE), and Rubisco catalytic sites, whereas droughted Larrea showed a differing response depending on treatment technique. Amax and CE were lower in droughted Larrea compared with well-watered plants, and CO2 had no effect on these reduced photosynthetic parameters. However, Rubisco catalytic sites decreased in droughted Larrea at elevated CO2. Operating Ci increased at elevated CO2 in droughted plants, resulting in greater photosynthetic rates at elevated CO2 as compared with ambient CO2. In well-watered plants, the changes in operating Ci, CE and Amax resulted in similar photosynthetic rates across CO2 treatments. Our results suggest that drought can diminish photosynthetic down-regulation to elevated CO2 in Larrea, resulting in seasonally transient patterns of enhanced carbon gain. These results suggest that water status may ultimately control the photosynthetic response of desert systems to rising CO2. 相似文献
2.
Sean C. Clifford Ian M. Stronach Colin R. Black Paul R. Singleton-Jones Sayed N. Azam-Ali Neil M. J. Crout 《Physiologia plantarum》2000,110(1):78-88
Stands of groundnut (Arachis hypogaea L. cv. Kadiri‐3) were grown in controlled environment glasshouses at mean atmospheric CO2 concentrations of 375 or 700 μmol mol?1 and daily mean air temperatures of 28 or 32°C on irrigated or drying soil profiles. Leaf water (Ψl) and solute potential (Ψs), relative water content (RWC), stomatal conductance (gl) and net photosynthesis (Pn) were measured at midday for the youngest mature leaf throughout the growing season. Elevated CO2 and temperature had no detectable effect on the water relations of irrigated plants, but higher values of RWC, Ψl and Ψs were maintained for longer under elevated CO2 during progressive drought. Turgor potential (Ψp) reached zero when Ψl declined to ?1.6 to ?1.8 MPa in all treatments; turgor was lost sooner when droughted plants were grown under ambient CO2. A 4°C increase in mean air temperature had no effect on Ψs in droughted plants, but elicited a small increase in Ψl; midday gl values were lower under elevated than under ambient CO2, and Ψl and gl declined below ?1.5 MPa and 0.25 cm s?1, respectively, as the soil dried. Despite the low gl values recorded for droughted plants late in the season, Pn was maintained under elevated CO2, but declined to zero 3 weeks before final harvest under ambient CO2. Concurrent reductions in gl and increases in water use efficiency under elevated CO2 prolonged photosynthetic activity during drought and increased pod yields relative to plants grown under ambient CO2. The implications of future increases in atmospheric CO2 for the productivity of indeterminate C3 crops grown in rainfed subsistence agricultural systems in the semi‐arid tropics are discussed. 相似文献
3.
The nature of the interaction between drought and elevated CO2 partial pressure (pCa) is critically important for the effects of global change on crops. Some crop models assume that the relative responses of transpiration and photosynthesis to soil water deficit are unaltered by elevated pCa, while others predict decreased sensitivity to drought at elevated pCa. These assumptions were tested by measuring canopy photosynthesis and transpiration in spring wheat (cv. Minaret) stands grown in boxes with 100 L rooting volume. Plants were grown under controlled environments with constant light (300 µmol m?2 s?1) at ambient (36 Pa) or elevated (68 Pa) pCa and were well watered throughout growth or had a controlled decline in soil water starting at ear emergence. Drought decreased final aboveground biomass (?15%) and grain yield (?19%) while elevated pCa increased biomass (+24%) and grain yield (+29%) and there was no significant interaction. Elevated pCa increased canopy photosynthesis by 15% on average for both water regimes and increased dark respiration per unit ground area in well‐watered plants, but not drought‐grown ones. Canopy transpiration and photosynthesis were decreased in drought‐grown plants relative to well‐watered plants after about 20–25 days from the start of the drought. Elevated pCa decreased transpiration only slightly during drought, but canopy photosynthesis continued to be stimulated so that net growth per unit water transpired increased by 21%. The effect of drought on canopy photosynthesis was not the consequence of a loss of photosynthetic capacity initially, as photosynthesis continued to be stimulated proportionately by a fixed increase in irradiance. Drought began to decrease canopy transpiration below a relative plant‐available soil water content of 0.6 and canopy photosynthesis and growth below 0.4. The shape of these responses were unaffected by pCa, supporting the simple assumption used in some models that they are independent of pCa. 相似文献
4.
Iraya Güerere Wilmer Tezara Cecilia Herrera María Dolores Fernández Ana Herrera 《Physiologia plantarum》1996,98(3):471-476
To investigate the possible induction of Crassulacean acid metabolism (CAM) by drought in Talinum paniculatum ([Jacq.] Gaertn.), a deciduous herb with succulent leaves and lignified stems, nocturnal acid accumulation and CO2-exchange were studied in watered and droughted greenhouse-grown plants. Watered plants had a typical C3 pattern of CO2-exchange. When plants were subjected to drought, nocturnal acid accumulation increased significantly from 0.9 to 13.4 μmol H+ cm?2 after 21 days. Water deficit provoked a rapid reduction of daytime CO2 assimilation of as much as 92% and a slower increase in night-time fixation. A maximum of 24% of the diel carbon gain was contributed by dark fixation in droughted plants. After 34 days of drought, only CO2 compensation and a small accumulation of acid (idling) was detected during the night. Relative recycling of respiratory CO2 was approximately 100% for most of the water deficit treatment, the amount of CO2 recycled showing a high positive correlation with nocturnal acid accumulation. A low rate of nocturnal loss of CO2 in watered plants did not explain the amount recycled nightly in droughted plants, implying that respiration increased with drought. Leaf lamina area was reduced by 49% during drought due to rolling. Leaf biomass remained unchanged during the water-deficit treatment. Neither apparent quantum yield nor light-saturated photosynthetic rate differed significantly between control and 14-day water-stressed plants rewatered for 20 h. Chlorophyll content did not change with drought. These results confirm that CAM is induced by drought in T. paniculatum; the carbon acquired through this pathway only contributes to maintain, but not to increase, leaf biomass; also, CAM is responsible for a high recycling of respiratory CO2 during the night. Recycling through CAM, plus the reduction of exposed leaf area during drought, may help explain the maintenance of chlorophyll, quantum yield and saturated photosynthetic rates in water-stressed plants of T. paniculatum. 相似文献
5.
Soybean leaf growth and gas exchange response to drought under carbon dioxide enrichment 总被引:1,自引:0,他引:1
This study was conducted to determine the response in leaf growth and gas exchange of soybean (Glycine max Merr.) to the combined effects of water deficits and carbon dioxide (CO2) enrichment. Plants grown in pots were allowed to develop initially in a glasshouse under ambient CO2 and well-watered conditions. Four-week old plants were transferred into two different glasshouses with either ambient (360 μmol mol-1) or elevated (700 μmol mol-1) CO2. Following a 2-day acclimation period, the soil of the drought-stressed pots was allowed to dry slowly over a 2-week period. The stressed pots were watered daily so that the soil dried at an equivalent rate under the two CO2 levels. Elevated [CO2] decreased water loss rate and increased leaf area development and photosynthetic rate under both well-watered and drought-stressed conditions. There was, however, no significant effect of [CO2] in the response relative to soil water content of normalized leaf gas exchange and leaf area. The drought response based on soil water content for transpiration, leaf area, and photosynthesis provide an effective method for describing the responses of soybean physiological processes to the available soil water, independent of [CO2]. 相似文献
6.
Soybean nodulation and N2 fixation response to drought under carbon dioxide enrichment 总被引:1,自引:1,他引:0
The combined effects of carbon dioxide (CO2) enrichment and water deficits on nodulation and N2 fixation were analysed in soybean [Glycine max (L.) Merr.]. Two short-term experiments were conducted in greenhouses with plants subjected to soil drying, while exposed to CO2 atmospheres of either 360 or 700 μmol CO2 mol–1. Under drought-stressed conditions, elevated [CO2] resulted in a delay in the decrease in N2 fixation rates associated with drying of the soil used in these experiments. The elevated [CO2] also allowed the plants under drought to sustain significant increases in nodule number and mass relative to those under ambient [CO2]. The total non-structural carbohydrate (TNC) concentration was lower in the shoots of the plants exposed to drought; however, plants under elevated CO2 had much higher TNC levels than those under ambient CO2. For both [CO2] treatments, drought stress induced a substantial accumulation of TNC in the nodules that paralleled N2 fixation decline, which indicates that nodule activity under drought may not be carbon limited. Under drought stress, ureide concentration increased in all plant tissues. However, exposure to elevated [CO2] resulted in substantially less drought-induced ureide accumulation in leaf and petiole tissues. A strong negative correlation was found between ureide accumulation and TNC levels in the leaves. This relationship, together with the large effect of elevated [CO2] on the decrease of ureide accumulation in the leaves, indicated the importance of ureide breakdown in the response of N2 fixation to drought and of feedback inhibition by ureides on nodule activity. It is concluded that an important effect of CO2 enrichment on soybean under drought conditions is an enhancement of photoassimilation, an increased partitioning of carbon to nodules and a decrease of leaf ureide levels, which is associated with sustained nodule growth and N2 rates under soil water deficits. We suggest that future [CO2] increases are likely to benefit soybean production by increasing the drought tolerance of N2 fixation. 相似文献
7.
Elevated CO2 reduces the drought effect on nitrogen metabolism in barley plants during drought and subsequent recovery 总被引:1,自引:0,他引:1
The objective of this study was to determine the response of nitrogen metabolism to drought and recovery upon rewatering in barley (Hordeum vulgare L.) plants under ambient (350 μmol mol−1) and elevated (700 μmol mol−1) CO2 conditions. Barley plants of the cv. Iranis were subjected to drought stress for 9, 13, or 16 days. The effects of drought under each CO2 condition were analysed at the end of each drought period, and recovery was analysed 3 days after rewatering 13-day droughted plants. Soil and plant water status, protein content, maximum (NRmax) and actual (NRact) nitrate reductase, glutamine synthetase (GS), and aminant (NADH-GDH) and deaminant (NAD-GDH) glutamate dehydrogenase activities were analysed. Elevated CO2 concentration led to reduced water consumption, delayed onset of drought stress, and improved plant water status. Moreover, in irrigated plants, elevated CO2 produced marked changes in plant nitrogen metabolism. Nitrate reduction and ammonia assimilation were higher at elevated than at ambient CO2, which in turn yielded higher protein content. Droughted plants showed changes in water status and in foliar nitrogen metabolism. Leaf water potential (Ψw) and nitrogen assimilation rates decreased after the onset of water deprivation. NRact and NRmax activity declined rapidly in response to drought. Similarly, drought decreased GS whereas NAD-GDH rose. Moreover, protein content fell dramatically in parallel with decreased leaf Ψw. In contrast, elevated CO2 reduced the water stress effect on both nitrate reduction and ammonia assimilation coincident with a less-steep decrease in Ψw. On the other hand, Ψw practically reached control levels after 3 days of rewatering. In parallel with the recovery of plant water status, nitrogen metabolism was also restored. Thus, both NRact and NRmax activities were restored to about 75-90% of control levels when water supply was restored; the GS activity reached 80-90% of control values; and GDH activities and protein content were similar to those of control plants. The recovery was always faster and slightly higher in plants grown under elevated CO2 conditions compared to those grown in ambient CO2, but midday Ψw dropped to similar values under both CO2 conditions. The results suggest that elevated CO2 improves nitrogen metabolism in droughted plants by maintaining better water status and enhanced photosynthesis performance, allowing superior nitrate reduction and ammonia assimilation. Ultimately, elevated CO2 mitigates many of the effects of drought on nitrogen metabolism and allows more rapid recovery following water stress. 相似文献
8.
Leaf gas exchange and nitrogen dynamics of N2 -fixing, field-grown Alnus glutinosa under elevated atmospheric CO2 总被引:1,自引:0,他引:1
Few studies have investigated the effects of elevated CO2 on the physiology of symbiotic N2-fixing trees. Tree species grown in low N soils at elevated CO2 generally show a decline in photosynthetic capacity over time relative to ambient CO2 controls. This negative adjustment may be due to a reallocation of leaf N away from the photosynthetic apparatus, allowing for more efficient use of limiting N. We investigated the effect of twice ambient CO2 on net CO2 assimilation (A), photosynthetic capacity, leaf dark respiration, and leaf N content of N2-fixing Alnus glutinosa (black alder) grown in field open top chambers in a low N soil for 160 d. At growth CO2, A was always greater in elevated compared to ambient CO2 plants. Late season A vs. internal leaf p(CO2) response curves indicated no negative adjustment of photosynthesis in elevated CO2 plants. Rather, elevated CO2 plants had 16% greater maximum rate of CO2 fixation by Rubisco. Leaf dark respiration was greater at elevated CO2 on an area basis, but unaffected by CO2 on a mass or N basis. In elevated CO2 plants, leaf N content (μg N cm?2) increased 50% between Julian Date 208 and 264. Leaf N content showed little seasonal change in ambient CO2 plants. A single point acetylene reduction assay of detached, nodulated root segments indicated a 46% increase in specific nitrogenase activity in elevated compared to ambient CO2 plants. Our results suggest that N2-fixing trees will be able to maintain high A with minimal negative adjustment of photosynthetic capacity following prolonged exposure to elevated CO2 on N-poor soils. 相似文献
9.
Effect of elevated CO2 , temperature and limited water supply on antioxidant status during regrowth of nodulated alfalfa 总被引:1,自引:0,他引:1
Gorka Erice Iker Aranjuelo Juan J. Irigoyen Manuel Sánchez-Díaz 《Physiologia plantarum》2007,130(1):33-45
Atmospheric CO2 is a major contributor to the greenhouse effect and is one of the main inducers of climate change. Previous studies with nodulated alfalfa plants have shown that elevated CO2 increased the growth of plants grown under well‐watered or limited water supply conditions. The beneficial effects of atmospheric CO2 enrichment included higher photosynthetic rates, growth and water‐use efficiency and an increase in the root/shoot ratio. However, at the moment, we do not have information on the possible implications of the beneficial effect of elevated CO2 as it may relate to a higher capacity of the violaxanthin–antheraxanthin–zeaxanthin (VAZ) cycle, the dissipation of excess radiation as heat and the effect on photooxidation, and to an improved leaf antioxidant system (Halliwell–Asada cycle). The aim of the present study was to determine the effects of the interaction between CO2 (ambient, around 350 vs 700 μmol mol−1), temperature (ambient vs ambient + 4°C) and water availability (well irrigated vs partially irrigated) on the leaf antioxidant status of nodulated alfalfa during regrowth. Parameters measured in this study included relative growth rate (RGR), H2O2 content, oxidative damage [measured as thiobarbituric acid‐reacting substances (TBARS)], leaf pigment composition (chlorophylls and xanthophylls), ascorbate (ASA) and glutathione pool levels and antioxidant enzymes. Our results revealed that during alfalfa regrowth, the effects of elevated CO2, limited water supply, temperature and their interactions on growth were not related to significant or general changes in leaf antioxidant capacity, H2O2 accumulation or oxidative stress (TBARS concentrations). The beneficial effects of CO2 enrichment in well‐watered and limited water‐subjected plants were not associated with an increase in the capacity of alfalfa leaves to dissipate excess radiation as heat through the VAZ cycle or with an increase in the antioxidant capacity, measured in terms of Halliwell–Asada cycle enzymes and antioxidant compounds. Furthermore, elevated CO2 did not affect RGRs during the last 15 days of regrowth and reduced the activity of several antioxidant enzymes (catalase, superoxide dismutase and glutathione reductase and ASA peroxidase in limited water‐subjected plants), suggesting a lower basal rate of oxygen activation and H2O2 formation, leading to a relaxation of the antioxidant system. 相似文献
10.
Soil moisture profiles can affect species composition and ecosystem processes, but the effects of increased concentrations of atmospheric carbon dioxide ([CO2]) on the vertical distribution of plant water uptake have not been studied. Because plant species composition affects soil moisture profiles, and is likely to shift under elevated [CO2], it is also important to test whether the indirect effects of [CO2] on soil water content may depend on species composition. We examined the effects of elevated [CO2] and species composition on soil moisture profiles in an annual grassland of California. We grew monocultures and a mixture of Avena barbata and Hemizonia congesta– the dominant species of two phenological groups – in microcosms exposed to ambient (~370 μmol mol?1) and elevated (~700 μmol mol?1) [CO2]. Both species increased intrinsic and yield‐based water use efficiency under elevated [CO2], but soil moisture increased only in communities with A. barbata, the dominant early‐season annual grass. In A. barbata monocultures, the [CO2] treatment did not affect the depth distribution of soil water loss. In contrast to communities with A. barbata, monocultures of H. congesta, a late‐season annual forb, did not conserve water under elevated [CO2], reflecting the increased growth of these plants. In late spring, elevated [CO2] also increased the efficiency of deep roots in H. congesta monocultures. Under ambient [CO2], roots below 60 cm accounted for 22% of total root biomass and were associated with 9% of total water loss, whereas in elevated [CO2], 16% of total belowground biomass was associated with 34% of total water loss. Both soil moisture and isotope data showed that H. congesta monocultures grown under elevated [CO2] began extracting water from deep soils 2 weeks earlier than plants in ambient [CO2]. 相似文献
11.
Inter-generational effects on the growth of Poa annua (L.) in ambient and elevated atmospheric CO2 conditions (350 and 550 μl l–1, respectively) were studied in two different experiments. Both experiments showed similar results. In a greenhouse experiment growth, measured as the numbers of tillers produced per week, was compared for plants grown from first and second generation seeds. Second generation seeds were obtained from plants grown for one whole generation in either ambient or elevated atmospheric CO2 (‘ambient’ and ‘elevated’ seeds, respectively). First generation plants and second generation ‘ambient’ plants did not respond to elevated CO2. Second generation ‘elevated’ plants produced significantly more tillers in elevated CO2. In the second experiment model terrestrial ecosystems growing in the Ecotron and which included Poa annua were used. Above-ground biomass after one and two generations of growth were compared. At the end of Generation 1 no difference was found in biomass production while at the end of Generation 2 biomass increased in elevated CO2 by 50%. The implications for climate change research are discussed. 相似文献
12.
Effects of elevated CO2 on leaf gas exchange in beech and oak at two levels of nutrient supply: consequences for sensitivity to drought in beech 总被引:1,自引:1,他引:0
Beech (Fagus sylvatica L.) and pedunculate oak (Quercus robur L.) were grown from seed for two whole seasons at two CO2 concentrations (ambient and ambient + 250 μmol mol?1) with two levels of soil nutrient supply. Measurements of net leaf photosynthetic rate (A) and stomatal conductance (gs) of well-watered plants were taken over both seasons; a drought treatment was applied in the middle of the second growing season to a separate sample of beech drawn from the same population. The net leaf photosynthetic rate of well-watered plants was stimulated in elevated CO2 by an average of 75% in beech and 33% in oak; the effect continued through both growing seasons at both nutrient levels. There were no interactive effects of CO2 concentration and nutrient level on A or gs in beech or oak. Stomatal conductance was reduced in elevated CO2 by an average of 34% in oak, but in beech there were no significant reductions in gs except under cloudy conditions (–22% in elevated CO2). During drought, there was no effect of CO2 concentration on gs in beech grown with high nutrients, but for beech grown with low nutrients, gs was significantly higher in elevated CO2, causing more rapid soil drying. With high nutrient supply, soil drying was more rapid at elevated CO2 due to increased leaf area. It appears that beech may substantially increase whole-plant water consumption in elevated CO2, especially under conditions of high temperature and irradiance when damage due to high evaporative demand is most likely to occur, thereby putting itself at risk during periods of drought. 相似文献
13.
DONALD L. PHILLIPS MARK G. JOHNSON DAVID T. TINGEY CHRISTINA E. CATRICALA† TONI L. HOYMAN† ROBERT S. NOWAK‡ 《Global Change Biology》2006,12(1):61-73
Fine roots (≤1 mm diameter) are critical in plant water and nutrient absorption, and it is important to understand how rising atmospheric CO2 will affect them as part of terrestrial ecosystem responses to global change. This study's objective was to determine the effects of elevated CO2 on production, mortality, and standing crops of fine root length over 2 years in a free‐air CO2 enrichment (FACE) facility in the Mojave Desert of southern Nevada, USA. Three replicate 25 m diameter FACE rings were maintained at ambient (~370 μmol mol?1) and elevated CO2 (~550 μmol mol?1) atmospheric concentrations. Twenty‐eight minirhizotron tubes were placed in each ring to sample three microsite locations: evergreen Larrea shrubs, drought‐deciduous Ambrosia shrubs, and along systematic community transects (primarily in shrub interspaces which account for ~85% of the area). Seasonal dynamics were similar for ambient and elevated CO2: fine root production peaked in April–June, with peak standing crop occurring about 1 month later, and peak mortality occurring during the hot summer months, with higher values for all three measures in a wet year compared with a dry year. Fine root standing crop, production, and mortality were not significantly different between treatments except standing crop along community transects, where fine root length was significantly lower in elevated CO2. Fine root turnover (annual cumulative mortality/mean standing crop) ranged from 2.33 to 3.17 year?1, and was not significantly different among CO2 treatments, except for community transect tubes where it was significantly lower for elevated CO2. There were no differences in fine root responses to CO2 between evergreen (Larrea) and drought‐deciduous (Ambrosia) shrubs. Combined with observations of increased leaf‐level water‐use efficiency and lack of soil moisture differences, these results suggest that under elevated CO2 conditions, reduced root systems (compared with ambient CO2) appear sufficient to provide resources for modest aboveground production increases across the community, but in more fertile shrub microsites, fine root systems of comparable size with those in ambient CO2 were required to support the greater aboveground production increases. For community transects, development of the difference in fine root standing crops occurred primarily through lower stimulation of fine root production in the elevated CO2 treatment during periods of high water availability. 相似文献
14.
Maize and grain sorghum seeds were sown in pots and grown for 39 days in sunlit controlled-environment chambers at 360 (ambient) and 720 (double-ambient, elevated) μmol mol−1 carbon dioxide concentrations [CO2]. Canopy net photosynthesis (PS) and evapotranspiration (TR) was measured throughout and summarized daily from 08:00 to 17:00 h Eastern Standard Time. Irrigation was withheld from matched pairs of treatments starting on 26 days after sowing (DAS). By 35 DAS, cumulative PS of drought-stress maize, compared to well-watered plants, was 41% lower under ambient [CO2] but only 13% lower under elevated [CO2]. In contrast, by 35 DAS, cumulative PS of drought-stress grain sorghum, compared to well-watered plants, was only 9% lower under ambient [CO2] and 7% lower under elevated [CO2]. During the 27-35 DAS drought period, water use efficiency (WUE, mol CO2 Kmol−1 H2O), was 3.99, 3.88, 5.50, and 8.65 for maize and 3.75, 4.43, 5.26, and 9.94 for grain sorghum, for ambient-[CO2] well-watered, ambient-[CO2] stressed, elevated-[CO2] well-watered and elevated-[CO2] stressed plants, respectively. Young plants of maize and sorghum used water more efficiently at elevated [CO2] than at ambient [CO2], especially under drought. Reductions in biomass by drought for young maize and grain sorghum plants were 42 and 36% at ambient [CO2], compared to 18 and 14% at elevated [CO2], respectively. Results of our water stress experiment demonstrated that maintenance of relatively high canopy photosynthetic rates in the face of decreased transpiration rates enhanced WUE in plants grown at elevated [CO2]. This confirms experimental evidence and conceptual models that suggest that an increase of intercellular [CO2] (or a sustained intercellular [CO2]) in the face of decreased stomatal conductance results in relative increases of growth of C4 plants. In short, drought stress in C4 crop plants can be ameliorated at elevated [CO2] as a result of lower stomatal conductance and sustaining intercellular [CO2]. Furthermore, less water might be required for C4 crops in future higher CO2 atmospheres, assuming weather and climate similar to present conditions. 相似文献
15.
Elevated atmospheric CO2 increases fine root production, respiration, rhizosphere respiration and soil CO2 efflux in Scots pine seedlings 总被引:2,自引:0,他引:2
IVAN. A. JANSSENS MEG. CROOKSHANKS† GAIL. TAYLOR† REINHART CEULEMANS 《Global Change Biology》1998,4(8):871-878
In this study, we investigated the impact of elevated atmospheric CO2 (ambient + 350 μmol mol–1) on fine root production and respiration in Scots pine (Pinus sylvestris L.) seedlings. After six months exposure to elevated CO2, root production measured by root in-growth bags, showed significant increases in mean total root length and biomass, which were more than 100% greater compared to the ambient treatment. This increased root length may have lead to a more intensive soil exploration. Chemical analysis of the roots showed that the roots in the elevated treatment accumulated more starch and had a lower C/N-ratio. Specific root respiration rates were significantly higher in the elevated treatment and this was probably attributed to increased nitrogen concentrations in the roots. Rhizospheric respiration and soil CO2 efflux were also enhanced in the elevated treatment. These results clearly indicate that under elevated atmospheric CO2 root production and development in Scots pine seedlings is altered and respiratory carbon losses through the root system are increased. 相似文献
16.
The influence of mycorrhizal symbiosis, atmospheric CO2 concentration and the interaction between both factors on biomass production and partitioning were assessed in nodulated alfalfa (Medicago sativa L.) associated or not with arbuscular mycorrhizal fungi (AMF) and grown in greenhouse at either ambient (392 μmol?mol?1) or elevated (700 μmol?mol?1) CO2 air concentrations. Measurements were performed at three stages of the vegetative period of plants. Shoot and root biomass achieved by plants at the end of their vegetative period were highly correlated to the photosynthetic rates reached at earlier stages, and there was a significant relationship between CO2 exchange rates and total nodule biomass per plant. In non-mycorrhizal alfalfa, the production of leaves, stems and nodules biomass significantly increased when plants had been exposed to elevated CO2 concentration in the atmosphere for 4 weeks. Regardless CO2 concentration at which alfalfa were cultivated, mycorrhizal symbiosis improved photosynthetic rates and growth of alfalfa at early stages of the vegetative period and then photosynthesis decreased, which suggests that AMF shortened the vegetative period of the host plants. At final stages of the vegetative period, AMF enhanced both area and biomass of leaves as well as the leaves to stems ratio when alfalfa plants were cultivated at ambient CO2. The interaction of AMF with elevated CO2 improved root biomass and slightly increased the leaves to stems ratio at the end of the vegetative growth. Therefore, AMF may favor both the forage quality of alfalfa when grown at ambient CO2 and its perennity for next cutting regrowth cycle when grown under elevated CO2. Nevertheless, this hypothesis needs to be checked under natural conditions in field. 相似文献
17.
B. J. Mulholland J. Craigon C. R. Black J. J. Colls J. Atherton† G. Landon 《Global Change Biology》1998,4(2):121-130
Spring wheat cv. Minaret was grown to maturity under three carbon dioxide (CO2) and two ozone (O3) concentrations in open-top chambers (OTC). Green leaf area index (LAI) was increased by elevated CO2 under ambient O3 conditions as a direct result of increases in tillering, rather than individual leaf areas. Yellow LAI was also greater in the 550 and 680 μmol mol–1 CO2 treatments than in the chambered ambient control; individual leaves on the main shoot senesced more rapidly under 550 μmol mol–1 CO2, but senescence was delayed at 680 μmol mol–1 CO2. Fractional light interception (f) during the vegetative period was up to 26% greater under 680 μmol mol–1 CO2 than in the control treatment, but seasonal accumulated intercepted radiation was only increased by 8%. As a result of greater carbon assimilation during canopy development, plants grown under elevated CO2 were taller at anthesis and stem and ear biomass were 27 and 16% greater than in control plants. At maturity, yield was 30% greater in the 680 μmol mol–1 CO2 treatment, due to a combination of increases in the number of ears per m–2, grain number per ear and individual grain weight (IGW). Exposure to a seasonal mean (7 h d–1) of 84 nmol mol–1 O3 under ambient CO2 decreased green LAI and increased yellow LAI, thereby reducing both f and accumulated intercepted radiation by ≈ 16%. Individual leaves senesced completely 7–28 days earlier than in control plants. At anthesis, the plants were shorter than controls and exhibited reductions in stem and ear biomass of 15 and 23%. Grain yield at maturity was decreased by 30% due to a combination of reductions in ear number m–2, the numbers of grains per spikelet and per ear and IGW. The presence of elevated CO2 reduced the rate of O3-induced leaf senescence and resulted in the maintenance of a higher green LAI during vegetative growth under ambient CO2 conditions. Grain yields at maturity were nevertheless lower than those obtained in the corresponding elevated CO2 treatments in the absence of elevated O3. Thus, although the presence of elevated CO2 reduced the damaging impact of ozone on radiation interception and vegetative growth, substantial yield losses were nevertheless induced. These data suggest that spring wheat may be susceptible to O3-induced injury during anthesis irrespective of the atmospheric CO2 concentration. Possible deleterious mechanisms operating through effects on pollen viability, seed set and the duration of grain filling are discussed. 相似文献
18.
Elevated CO2 enhances water relations and productivity and affects gas exchange in C3 and C4 grasses of the Colorado shortgrass steppe. 总被引:2,自引:0,他引:2
Jack A. Morgan Daniel R. Lecain Arvin R. Mosier† Daniel G. Milchunas‡ 《Global Change Biology》2001,7(4):451-466
Six open‐top chambers were installed on the shortgrass steppe in north‐eastern Colorado, USA from late March until mid‐October in 1997 and 1998 to evaluate how this grassland will be affected by rising atmospheric CO2. Three chambers were maintained at current CO2 concentration (ambient treatment), three at twice ambient CO2, or approximately 720 μmol mol?1 (elevated treatment), and three nonchambered plots served as controls. Above‐ground phytomass was measured in summer and autumn during each growing season, soil water was monitored weekly, and leaf photosynthesis, conductance and water potential were measured periodically on important C3 and C4 grasses. Mid‐season and seasonal above‐ground productivity were enhanced from 26 to 47% at elevated CO2, with no differences in the relative responses of C3/C4 grasses or forbs. Annual above‐ground phytomass accrual was greater on plots which were defoliated once in mid‐summer compared to plots which were not defoliated during the growing season, but there was no interactive effect of defoliation and CO2 on growth. Leaf photosynthesis was often greater in Pascopyrum smithii (C3) and Bouteloua gracilis (C4) plants in the elevated chambers, due in large part to higher soil water contents and leaf water potentials. Persistent downward photosynthetic acclimation in P. smithii leaves prevented large photosynthetic enhancement for elevated CO2‐grown plants. Shoot N concentrations tended to be lower in grasses under elevated CO2, but only Stipa comata (C3) plants exhibited significant reductions in N under elevated compared to ambient CO2 chambers. Despite chamber warming of 2.6 °C and apparent drier chamber conditions compared to unchambered controls, above‐ground production in all chambers was always greater than in unchambered plots. Collectively, these results suggest increased productivity of the shortgrass steppe in future warmer, CO2 enriched environments. 相似文献
19.
Pedunculate oak (Quercus robur L.) was germinated and grown under nutrient non-limiting conditions for a total of 10–15 weeks at ambient CO2 concentration and 1100 μmol mol–1 CO2 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 CO2 each enhanced total plant biomass per tree. Whereas additional biomass accumulation of trees grown under elevated CO2 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 CO2 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 CO2, irrespective of mycorrhization. A higher proportion of the exported GSH was transported to the roots than to basipetal stem sections under elevated CO2 as compared to ambient CO2. 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 CO2. Apparently, drought inhibited basipetal transport of reduced sulphur at the level of phloem loading and/or phloem transport. Elevated CO2 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 CO2 as compared to trees exposed to drought and ambient CO2. 相似文献
20.
Field-grown spring wheat (Triticum aestivum L. cv. Dragon) was exposed to ambient and elevated CO2 concentrations (1.5 and 2 times ambient) in open-top chambers. Contents of non-structural carbohydrates were analysed enzymatically in leaves, stems and ears six times during the growing season. The impact of elevated CO2 on wheat carbohydrates was non-significant in most harvests. However, differences in the carbohydrate contents due to elevated CO2 were found in all plant compartments. Before anthesis, at growth stage (GS) 30 (the stem is 1 cm to the shoot apex), the plants grown in elevated CO2 contained significantly more water soluble carbohydrates (WSC), fructans, starch and total non-structural carbohydrates (TNC) in the leaves in comparison with the plants grown in ambient CO2. It is hypothesised that the plants from the treatments with elevated CO2 were sink-limited at GS30. After anthesis, the leaf WSC and TNC contents of the plants from elevated CO2 started to decline earlier than those of the plants from ambient CO2. This may indicate that the leaves of plants grown in the chambers with elevated CO2 senesced earlier. Elevated CO2 accelerated grain development: 2 weeks after anthesis, the plants grown in elevated CO2 contained significantly more starch and significantly less fructans in the ears compared to the plants grown in ambient CO2. Elevated CO2 had no effect on ear starch and TNC contents at the final harvest. Increasing the CO2 concentration from 360 to 520 μmol mol?1 had a larger effect on wheat non-structural carbohydrates than the further increase from 520 to 680 μmol mol?1. The results are discussed in relation to the effects of elevated CO2 on yield and yield components. 相似文献