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1.
In order to predict the potential impacts of global change, it is important to understand the impact of increasing global atmospheric [CO2] on the growth and yield of crop plants. The objectives of this study were to determine the interaction of N fertilization rates and atmospheric [CO2] on radiation interception and radiation-use efficiency of rice (Oryza sativa L. cv. IR72) grown under tropical field conditions. Rice plants were grown inside open top chambers in a lowland rice field at the International Rice Research Institute in the Philippines at ambient (about 350 μmol mol-1) or elevated (about 600 μmol mol-1 during the 1993 wet season and 700 μmol mol-1 during the 1994 dry season) in combination with three levels of applied N (0, 50 or 100 kg N ha-1 in the wet season; 0, 90 or 200 kg N ha-1 in the dry season). Light interception was not directly affected by [CO2], but elevated [CO2] indirectly increased light interception through increasing total absorbed N. Plant N requirement for radiation interception was similar for rice grown under ambient [CO2] or elevated [CO2] treatments. The conversion efficiency of intercepted radiation to dry matter, radiation-use efficiency (RUE), was about 35% greater at elevated [CO2] than at ambient [CO2]. The relationship between leaf N and RUE was curvilinear. At ambient [CO2], RUE was fairly stable across levels of leaf N, but leaf N less than about 2.5% resulted in lower RUE for plants grown with elevated [CO2] than for plant grown at ambient [CO2]. Decreased leaf N with increased [CO2], therefore decreased RUE of rice plants grown at elevated [CO2]. When predicting responses of rice to elevated [CO2], RUE should be adjusted with a decrease in leaf N. This revised version was published online in June 2006 with corrections to the Cover Date.  相似文献   

2.
We grew a C4 grass from the Serengeti ecosystem under ambient (370 ppm) and elevated (700 ppm) CO2, and under clipped and unclipped conditions to test whether regrowth following grazing would be affected by elevated CO2. Above-ground productivity was slightly decreased under elevated CO2, and was similar between clipped and unclipped plants. Regrowth (clipping offtake) following clipping was similar in the two CO2 treatments, and there was no CO2 by clipping interaction on biomass, productivity, or leaf nutrient concentrations. Based on this evidence, we suggest that C4 grasses from the Serengeti will show little direct response to future increases in atmospheric CO2.  相似文献   

3.
M. F. Cotrufo  P. Ineson 《Oecologia》1996,106(4):525-530
The effect of elevated atmospheric CO2 and nutrient supply on elemental composition and decomposition rates of tree leaf litter was studied using litters derived from birch (Betula pendula Roth.) plants grown under two levels of atmospheric CO2 (ambient and ambient +250 ppm) and two nutrient regimes in solar domes. CO2 and nutrient treatments affected the chemical composition of leaves, both independently and interactively. The elevated CO2 and unfertilized soil regime significantly enhanced lignin/N and C/N ratios of birch leaves. Decomposition was studied using field litter-bags, and marked differences were observed in the decomposition rates of litters derived from the two treatments, with the highest weight remaining being associated with litter derived from the enhanced CO2 and unfertilized regime. Highly significant correlations were shown between birch litter decomposition rates and lignin/N and C/N ratios. It can be concluded, from this study, that at levels of atmospheric CO2 predicted for the middle of the next century a deterioration of litter quality will result in decreased decomposition rates, leading to reduction of nutrient mineralization and increased C storage in forest ecosystems. However, such conclusions are difficult to generalize, since tree responses to elevated CO2 depend on soil nutritional status.  相似文献   

4.
Does elevated atmospheric CO2 concentrations affect wood decomposition?   总被引:10,自引:0,他引:10  
This study was conducted to test the hypothesis that wood tissues generated under elevated atmospheric [CO2] have lower quality and subsequent reduced decomposition rates. Chemical composition and subsequent field decomposition rates were studied for beech (Fagus sylvatica L.) twigs grown under ambient and elevated [CO2] in open top chambers. Elevated [CO2] significantly affected the chemical composition of beech twigs, which had 38% lower N and 12% lower lignin concentrations than twigs grown under ambient [CO2]. The strong decrease in N concentration resulted in a significant increase in the C/N and lignin/N ratios of the beech wood grown at elevated [CO2]. However, the elevated [CO2] treatment did not reduce the decomposition rates of twigs, neither were the dynamics of N and lignin in the decomposing beech wood affected by the [CO2] treatment, despite initial changes in N and lignin concentrations between the ambient and elevated [CO2] beech wood. This revised version was published online in June 2006 with corrections to the Cover Date.  相似文献   

5.
Short-term studies of tree growth at elevated CO2 suggest that forest productivity may increase as atmospheric CO2 concentrations rise, although low soil N availability may limit the magnitude of this response. There have been few studies of growth and N2 fixation by symbiotic N2-fixing woody species under elevated CO2 and the N inputs these plants could provide to forest ecosystems in the future. We investigated the effect of twice ambient CO2 on growth, tissue N accretion, and N2 fixation of nodulated Alnus glutinosa (L.) Gaertn. grown under low soil N conditions for 160 d. Root, nodule, stem, and leaf dry weight (DW) and N accretion increased significantly in response to elevated CO2. Whole-plant biomass and N accretion increased 54% and 40%, respectively. Delta-15N analysis of leaf tissue indicated that plants from both treatments derived similar proportions of their total N from symbiotic fixation suggesting that elevated CO2 grown plants fixed approximately 40% more N than did ambient CO2 grown plants. Leaves from both CO2 treatments showed similar relative declines in leaf N content prior to autumnal leaf abscission, but total N in leaf litter increased 24% in elevated compared to ambient CO2 grown plants. These results suggest that with rising atmospheric CO2 N2-fixing woody species will accumulate greater amounts of biomass N through N2 fixation and may enhance soil N levels by increased litter N inputs.  相似文献   

6.
We examined whether the effects of elevated CO2 on growth of 1-year old Populus deltoides saplings was a function of the assimilation responses of particular leaf developmental stages. Saplings were grown for 100 days at ambient (approximately 350 ppm) and elevated (ambient + 200 ppm) CO2 in forced-air greenhouses. Biomass, biomass distribution, growth rates, and leaf initiation and expansion rates were unaffected by elevated CO2. Leaf nitrogen (N), the leaf C:N ratio, and leaf lignin concentrations were also unaffected. Carbon gain was significantly greater in expanding leaves of saplings grown at elevated compared to ambient CO2. The Rubisco content in expanding leaves was not affected by CO2 concentration. Carbon gain and Rubisco content were significantly lower in fully expanded leaves of saplings grown at elevated compared to ambient CO2, indicating CO2-induced down-regulation in fully expanded leaves. Elevated CO2 likely had no overall effect on biomass accumulation due to the more rapid decline in carbon gain as leaves matured in saplings grown at elevated compared to ambient CO2. This decline in carbon gain has been documented in other species and shown to be related to a balance between sink/source balance and acclimation. Our data suggest that variation in growth responses to elevated CO2 can result from differences in leaf assimilation responses in expanding versus expanded leaves as they develop under elevated CO2. Received: 28 September 1998 / Accepted: 23 June 1999  相似文献   

7.
8.
Elevated atmospheric CO2 and feedback between carbon and nitrogen cycles   总被引:13,自引:1,他引:12  
We tested a conceptual model describing the influence of elevated atmospheric CO2 on plant production, soil microorganisms, and the cycling of C and N in the plant-soil system. Our model is based on the observation that in nutrient-poor soils, plants (C3) grown in an elevated CO2 atmosphere often increase production and allocation to belowground structures. We predicted that greater belowground C inputs at elevated CO2 should elicit an increase in soil microbial biomass and increased rates of organic matter turnover and nitrogen availability. We measured photosynthesis, biomass production, and C allocation of Populus grandidentata Michx. grown in nutrient-poor soil for one field season at ambient and twice-ambient (i.e., elevated) atmospheric CO2 concentrations. Plants were grown in a sandy subsurface soil i) at ambient CO2 with no open top chamber, ii) at ambient CO2 in an open top chamber, and iii) at twice-ambient CO2 in an open top chamber. Plants were fertilized with 4.5 g N m−2 over a 47 d period midway through the growing season. Following 152 d of growth, we quantified microbial biomass and the availabilities of C and N in rhizosphere and bulk soil. We tested for a significant CO2 effect on plant growth and soil C and N dynamics by comparing the means of the chambered ambient and chambered elevated CO2 treatments. Rates of photosynthesis in plants grown at elevated CO2 were significantly greater than those measured under ambient conditions. The number of roots, root length, and root length increment were also substantially greater at elevated CO2. Total and belowground biomass were significantly greater at elevated CO2. Under N-limited conditions, plants allocated 50–70% of their biomass to roots. Labile C in the rhizosphere of elevated-grown plants was significantly greater than that measured in the ambient treatments; there were no significant differences between labile C pools in the bulk soil of ambient and elevated-grown plants. Microbial biomass C was significantly greater in the rhizosphere and bulk soil of plants grown at elevated CO2 compared to that in the ambient treatment. Moreover, a short-term laboratory assay of N mineralization indicated that N availability was significantly greater in the bulk soil of the elevated-grown plants. Our results suggest that elevated atmospheric CO2 concentrations can have a positive feedback effect on soil C and N dynamics producing greater N availability. Experiments conducted for longer periods of time will be necessary to test the potential for negative feedback due to altered leaf litter chemistry. ei]{gnH}{fnLambers} ei]{gnA C}{fnBorstlap}  相似文献   

9.
The effects of global change on the emission rates of isoprene from plants are not clear. A factor that can influence the response of isoprene emission to elevated CO2 concentrations is the availability of nutrients. Isoprene emission rate under standard conditions (leaf temperature: 30°C, photosynthetically active radiation (PAR): 1000 μmol photons m?2 s?1), photosynthesis, photosynthetic capacity, and leaf nitrogen (N) content were measured in Quercus robur grown in well‐ventilated greenhouses at ambient and elevated CO2 (ambient plus 300 ppm) and two different soil fertilities. The results show that elevated CO2 enhanced photosynthesis but leaf respiration rates were not affected by either the CO2 or nutrient treatments. Isoprene emission rates and photosynthetic capacity were found to decrease with elevated CO2, but an increase in nutrient availability had the converse effect. Leaf N content was significantly greater with increased nutrient availability, but unaffected by CO2. Isoprene emission rates measured under these conditions were strongly correlated with photosynthetic capacity across the range of different treatments. This suggests that the effects of CO2 and nutrient levels on allocation of carbon to isoprene production and emission under near‐saturating light largely depend on the effects on photosynthetic electron transport capacity.  相似文献   

10.
Decomposition of Quercus myrtifolia leaf litter in a Florida scrub oak community was followed for 3 years in two separate experiments. In the first experiment, we examined the effects CO2 and herbivore damage on litter quality and subsequent decomposition. Undamaged, chewed and mined litter generated under ambient and elevated (ambient+350 ppm V) CO2 was allowed to decompose under ambient conditions for 3 years. Initial litter chemistry indicated that CO2 levels had minor effects on litter quality. Litter damaged by leaf miners had higher initial concentrations of condensed tannins and nitrogen (N) and lower concentrations of hemicellulose and C : N ratios compared with undamaged and chewed litter. Despite variation in litter quality associated with CO2, herbivory, and their interaction, there was no subsequent effect on rates of decomposition under ambient atmospheric conditions. In the second experiment, we examined the effects of source (ambient and elevated) of litter and decomposition site (ambient and elevated) on litter decomposition and N dynamics. Litter was not separated by damage type. The litter from both elevated and ambient CO2 was then decomposed in both elevated and ambient CO2 chambers. Initial litter chemistry indicated that concentrations of carbon (C), hemicellulose, and lignin were higher in litter from elevated than ambient CO2 chambers. Despite differences in C and fiber concentrations, litter from ambient and elevated CO2 decomposed at comparable rates. However, the atmosphere in which the decomposition took place resulted in significant differences in rates of decomposition. Litter decomposing under elevated CO2 decomposed more rapidly than litter under ambient CO2, and exhibited higher rates of mineral N accumulation. The results suggest that the atmospheric conditions during the decomposition process have a greater impact on rates of decomposition and N cycling than do the atmospheric conditions under which the foliage was produced.  相似文献   

11.
Soil N availability may play an important role in regulating the long-term responses of plants to rising atmospheric CO2 partial pressure. To further examine the linkage between above- and belowground C and N cycles at elevated CO2, we grew clonally propagated cuttings of Populus grandidentata in the field at ambient and twice ambient CO2 in open bottom root boxes filled with organic matter poor native soil. Nitrogen was added to all root boxes at a rate equivalent to net N mineralization in local dry oak forests. Nitrogen added during August was enriched with 15N to trace the flux of N within the plant-soil system. Above-and belowground growth, CO2 assimilation, and leaf N content were measured non-destructively over 142 d. After final destructive harvest, roots, stems, and leaves were analyzed for total N and 15N. There was no CO2 treatment effect on leaf area, root length, or net assimilation prior to the completion of N addition. Following the N addition, leaf N content increased in both CO2 treatments, but net assimilation showed a sustained increase only in elevated CO2 grown plants. Root relative extension rate was greater at elevated CO2, both before and after the N addition. Although final root biomass was greater at elevated CO2, there was no CO2 effect on plant N uptake or allocation. While low soil N availability severely inhibited CO2 responses, high CO2 grown plants were more responsive to N. This differential behavior must be considered in light of the temporal and spatial heterogeneity of soil resources, particularly N which often limits plant growth in temperate forests.  相似文献   

12.
Increased biomass production in terrestrial ecosystems with elevated atmospheric CO2 may be constrained by nutrient limitations as a result of increased requirement or reduced availability caused by reduced turnover rates of nutrients. To determine the short-term impact of nitrogen (N) fertilization on plant biomass production under elevated CO2, we compared the response of N-fertilized tallgrass prairie at ambient and twice-ambient CO2 levels over a 2-year period. Native tallgrass prairie plots (4.5 m diameter) were exposed continuously (24 h) to ambient and twice-ambient CO2 from 1 April to 26 October. We compared our results to an unfertilized companion experiment on the same research site. Above- and belowground biomass production and leaf area of fertilized plots were greater with elevated than ambient CO2 in both years. The increase in biomass at high CO2 occurred mainly aboveground in 1991, a dry year, and belowground in 1990, a wet year. Nitrogen concentration was lower in plants exposed to elevated CO2, but total standing crop N was greater at high CO2. Increased root biomass under elevated CO2 apparently increased N uptake. The biomass production response to elevated CO2 was much greater on N-fertilized than unfertilized prairie, particularly in the dry year. We conclude that biomass production response to elevated CO2 was suppressed by N limitation in years with below-normal precipitation. Reduced N concentration in above- and belowground biomass could slow microbial degradation of soil organic matter and surface litter, thereby exacerbating N limitation in the long term.  相似文献   

13.
J. Taylor  A. S. Ball 《Plant and Soil》1994,162(2):315-318
The biodegradability of aerial material from a C4 plant, sorghum grown under ambient (345 µmol mol–1) and elevated (700 µmol mol–1) atmospheric CO2 concentrations were compared by measuring soil respiratory activity. Initial daily respiratory activity (measured over 10 h per day) increased four fold from 110 to 440 cm3 CO2 100g dry weight soil–1 in soils amended with sorghum grown under either elevated or ambient CO2. Although soil respiratory activity decreased over the following 30 days, respiration remained significantly higher (t-test;p>0.05) in soils amended with sorghum grown under elevated CO2 concentrations. Analysis of the plant material revealed no significant differences in C:N ratios between sorghum grown under elevated or ambient CO2. The reason for the differences in soil respiratory activity have yet to be elucidated. However if this trend is repeated in natural ecosystems, this may have important implications for C and N cycling.  相似文献   

14.
Effects of elevated atmospheric carbon dioxide (CO2) levels on the production and spread of ectomycorrhizal fungal mycelium from colonised Scots pine roots were investigated. Pinus sylvestris (L.) Karst. seedlings inoculated with either Hebeloma crustuliniforme (Bull:Fr.) Quél. or Paxillus involutus (Fr.) Fr. were grown at either ambient (350 ppm) or elevated (700 ppm) levels of CO2. Mycelial production was measured after 6 weeks in pots, and mycelial spread from inoculated seedlings was studied after 4 months growth in perlite in shallow boxes containing uncolonised bait seedlings. Plant and fungal biomass were analysed, as well as carbon and nitrogen content of seedling shoots. Mycelial biomass production by H. crustuliniforme was significantly greater under elevated CO2 (up to a 3-fold increase was observed). Significantly lower concentrations and total amounts of N were found in plants exposed to elevated CO2.  相似文献   

15.
The direct and indirect effects of increasing levels of atmospheric carbon dioxide (CO2) on plant nitrogen (N) content were studied in a shortgrass steppe ecosystem in northeastern Colorado, USA. Beginning in 1997 nine experimental plots were established: three open-top chambers with ambient CO2 levels (approximately 365 mol mol–1), three open-top chambers with twice-ambient CO2 levels (approximately 720 mol mol–1), and three unchambered control plots. After 3 years of growing-season CO2 treatment, the aboveground N concentration of plants grown under elevated atmospheric CO2 decreased, and the carbon–nitrogen (C:N) ratio increased. At the same time, increased aboveground biomass production under elevated atmospheric CO2 conditions increased the net transfer of N out of the soil of elevated-CO2 plots. Aboveground biomass production after simulated herbivory was also greater under elevated CO2 compared to ambient CO2. Surprisingly, no significant changes in belowground plant tissue N content were detected in response to elevated CO2. Measurements of individual species at peak standing phytomass showed significant effects of CO2 treatment on aboveground plant tissue N concentration and significant differences between species in N concentration, suggesting that changes in species composition under elevated CO2 will contribute to overall changes in nutrient cycling. Changes in plant N content, driven by changes in aboveground plant N concentration, could have important consequences for biogeochemical cycling rates and the long-term productivity of the shortgrass steppe as atmospheric CO2 concentrations increase.  相似文献   

16.
Wang X W  Ji L Z  Liu Y 《农业工程》2006,26(10):3166-3173
Changes in the concentrations of phytochemical compounds usually occur when plants are grown under elevated atmospheric CO2. CO2-induced changes in foliar chemistry tend to reduce leaf quality and may further affect insect herbivores. Increased atmospheric CO2 also has a potential influence on decomposition because it causes variations in chemical components of plant tissues. To investigate the effects of increased atmospheric CO2 on the nutritional contents of tree tissues and the activities of leaf-chewing forest insects, samples of Populus pseudo-simonii [Kitag.] grown in open-top chambers under ambient and elevated CO2 (650 μmol mol-1) conditions were collected for measuring concentrations of carbon, nitrogen, C : N ratio, soluble sugar and starch in leaves, barks, coarse roots (>2 mm in diameter) and fine roots (<2 mm in diameter). Gypsy moth (Lymantria dispar) larvae were reared on a single branch of experimental trees in a nylon bag with 1 mm 1 mm grid. The response of larval growth was observed in situ. Elevated CO2 resulted in significant reduction in nitrogen concentration and increase in C : N ratio of all poplar tissues. In all tissues, total carbon contents were not affected by CO2 treatments. Soluble sugar and nonstructural carbohydrate (TNC) in the poplar leaves significantly increased with CO2 enrichment, whereas starch concentration increased only on partial sampling dates. Carbohydrate concentration in roots and barks was generally not affected by elevated CO2, whereas soluble sugar contents in fine roots decreased in response to elevated CO2. When second instar gypsy moth larvae consuming poplars grew under elevated CO2 for the first 13 days, their body weight was 30.95% lower than that of larvae grown at ambient CO2, but no significant difference was found when larvae were fed in the same treatment for the next 11 days. Elevated atmospheric CO2 had adverse effects on the nutritional quality of Populus pseudo-simonii [Kitag.] tissues and the resultant variations in foliar chemical components had a significant but negative effect on the growth of early instar gypsy moth larvae.  相似文献   

17.
With the ability to symbiotically fix atmospheric N2, legumes may lack the N-limitations thought to constrain plant response to elevated concentrations of atmospheric CO2. The growth and photosynthetic responses of two perennial grassland species were compared to test the hypotheses that (1) the CO2 response of wild species is limited at low N availability, (2) legumes respond to a greater extent than non-fixing forbs to elevated CO2, and (3) elevated CO2 stimulates symbiotic N2 fixation, resulting in an increased amount of N derived from the atmosphere. This study investigated the effects of atmospheric CO2 concentration (365 and 700 mol mol–1) and N addition on whole plant growth and C and N acquisition in an N2-fixing legume (Lupinus perennis) and a non-fixing forb (Achillea millefolium) in controlled-chamber environments. To evaluate the effects of a wide range of N availability on the CO2 response, we incorporated six levels of soil N addition starting with native field soil inherently low in N (field soil + 0, 4, 8, 12, 16, or 20 g N m–2 yr–1). Whole plant growth, leaf net photosynthetic rates (A), and the proportion of N derived from N2 fixation were determined in plants grown from seed over one growing season. Both species increased growth with CO2enrichment, but this response was mediated by N supply only for the non-fixer, Achillea. Its response depended on mineral N supply as growth enhancements under elevated CO2 increased from 0% in low N soil to +25% at the higher levels of N addition. In contrast, Lupinus plants had 80% greater biomass under elevated CO2 regardless of N treatment. Although partial photosynthetic acclimation to CO2 enrichment occurred, both species maintained comparably higher A in elevated compared to ambient CO2 (+38%). N addition facilitated increased A in Achillea, however, in neither species did additional N availability affect the acclimation response of A to CO2. Elevated CO2 increased plant total N yield by 57% in Lupinus but had no effect on Achillea. The increased N in Lupinus came from symbiotic N2 fixation, which resulted in a 47% greater proportion of N derived from fixation relative to other sources of N. These results suggest that compared to non-fixing forbs, N2-fixers exhibit positive photosynthetic and growth responses to increased atmospheric CO2 that are independent of soil N supply. The enhanced amount of N derived from N2 fixation under elevated CO2 presumably helps meet the increased N demand in N2-fixing species. This response may lead to modified roles of N2-fixers and N2-fixer/non-fixer species interactions in grassland communities, especially those that are inherently N-poor, under projected rising atmospheric CO2.  相似文献   

18.
Lee TD  Reich PB  Tjoelker MG 《Oecologia》2003,137(1):22-31
Legumes, with the ability to fix atmospheric nitrogen (N), may help alleviate the N limitations thought to constrain plant community response to elevated concentrations of atmospheric carbon dioxide (CO2). To address this issue we assessed: (1) the effects of the presence of the perennial grassland N2 fixer, Lupinus perennis, on biomass accumulation and plant N concentrations of nine-species plots of differing plant composition; (2) leaf-level physiology of co-occurring non-fixing species (Achillea millefolium, Agropyron repens, Koeleria cristata) in these assemblages with and without Lupinus; (3) the effects of elevated CO2 on Lupinus growth and symbiotic N2 fixation in both monoculture and the nine-species assemblages; and (4) whether assemblages containing Lupinus exhibit larger physiological and growth responses to elevated CO2 than those without. This study was part of a long-term grassland field experiment (BioCON) that controls atmospheric CO2 at current ambient and elevated (560 µmol mol–1) concentrations using free-air CO2 enrichment. Nine-species plots with Lupinus had 32% higher whole plot plant N concentrations and 26% higher total plant N pools than those without Lupinus, based on both above and belowground measurements. Co-occurring non-fixer leaf N concentrations increased 22% and mass-based net photosynthetic rates increased 41% in plots containing Lupinus compared to those without. With CO2 enrichment, Lupinus monocultures accumulated 32% more biomass and increased the proportion of N derived from fixation from 44% to 57%. In nine-species assemblages, Lupinus N derived from fixation increased similarly from 43% to 54%. Although Lupinus presence enhanced photosynthetic rates and leaf N concentrations of co-occurring non-fixers, and increased overall plant N pools, Lupinus presence did not facilitate stronger photosynthetic responses of non-fixing species or larger growth responses of overall plant communities to elevated CO2. Non-fixer leaf N concentrations declined similarly in response to elevated CO2 with and without Lupinus present and the relationship between net photosynthesis and leaf N was not affected by Lupinus presence. Regardless of the presence or absence of Lupinus, CO2 enrichment resulted in reduced leaf N concentrations and rates of net photosynthesis.  相似文献   

19.
Heteroblastic leaf development in Taraxacum officinale is compared between plants grown under ambient (350 ppm) vs. elevated (700 ppm) CO2 levels. Leaves of elevated CO2 plants exhibited more deeply incised leaf margins and relatively more slender leaf laminae than leaves of ambient CO2 plants. These differences were found to be significant in allometric analyses that controlled for differences in leaf size, as well as analyses that controlled for leaf developmental order. The effects of elevated CO2 on leaf shape were most pronounced when plants were grown individually, but detectable differences were also found in plants grown at high density. Although less dramatic than in Taraxacum, significant effects of elevated CO2 on leaf shape were also found in two other weedy rosette species, Plantago major and Rumex crispus. These observations support the long-standing hypothesis that leaf carbohydrate level plays an important role in regulating heteroblastic leaf development, though elevated C02 may also affect leaf development through direct hormonal interactions or increased leaf water potential. In Taraxacum, pronounced modifications of leaf shape were found at CO2 levels predicted to occur within the next century.  相似文献   

20.
Forest trees are major components of the terrestrial biome and their response to rising atmospheric CO2 plays a prominent role in the global carbon cycle. In this study, loblolly pine seedlings were planted in the field in recently disturbed soil of high fertility, and CO2 partial pressures were maintained at ambient CO2 (Amb) and elevated CO2 (Amb + 30 Pa) for 4 years. The objective of the study was to measure seasonal and long-term responses in growth and photosynthesis of loblolly pine exposed to elevated CO2 under ambient field conditions of precipitation, light, temperature and nutrient availability. Loblolly pine trees grown in elevated CO2 produced 90% more biomass after four growing seasons than did trees grown in ambient CO2. This large increase in final biomass was primarily due to a 217% increase in leaf area in the first growing season which resulted in much higher relative growth rates for trees grown in elevated CO2. Although there was not a sustained effect of elevated CO2 on relative growth rate after the first growing season, absolute production of biomass continued to increase each year in trees grown in elevated CO2 as a consequence of the compound interest effect of increased leaf area on the production of more new leaf area and more biomass. Allometric analyses of biomass allocation patterns demonstrated size-dependent shifts in allocation, but no direct effects of elevated CO2 on partitioning of biomass. Leaf photosynthetic rates were always higher in trees grown in elevated CO2, but these differences were greater in the summer (60–130% increase) than in the winter (14–44% increase), reflecting strong seasonal effects of temperature on photosynthesis. Our results suggest that seasonal variation in the relative photosynthetic response to elevated CO2 will occur in natural ecosystems, but total non-structural carbohydrate (TNC) levels in leaves indicate that this variation may not always be related to sink activity. Despite indications of canopy-level adjustments in carbon assimilation, enhanced levels of leaf photosynthesis coupled with increased total leaf area indicate that net carbon assimilation for the whole tree was greater for trees grown under elevated CO2 compared with ambient CO2. If the large growth enhancement observed in loblolly pine were maintained after canopy closure, then these trees could be a large sink for fossil carbon emitted to the atmosphere and produce a negative feedback on atmospheric CO2.  相似文献   

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