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1.
We tested the hypothesis that elevated CO 2 would stimulate proportionally higher photosynthesis in the lower crown of Populus trees due to less N retranslocation, compared to tree crowns in ambient CO 2. Such a response could increase belowground C allocation, particularly in trees with an indeterminate growth pattern such
as Populus tremuloides. Rooted cuttings of P. tremuloides were grown in ambient and twice ambient (elevated) CO 2 and in low and high soil N availability (89 ± 7 and 333 ± 16 ng N g −1 day −1 net mineralization, respectively) for 95 days using open-top chambers and open-bottom root boxes. Elevated CO 2 resulted in significantly higher maximum leaf photosynthesis ( A
max) at both soil N levels. A
max was higher at high N than at low N soil in elevated, but not ambient CO 2. Photosynthetic N use efficiency was higher at elevated than ambient CO 2 in both soil types. Elevated CO 2 resulted in proportionally higher whole leaf A in the lower three-quarters to one-half of the crown for both soil types. At elevated CO 2 and high N availability, lower crown leaves had significantly lower ratios of carboxylation capacity to electron transport
capacity ( V
cmax/ J
max) than at ambient CO 2 and/or low N availability. From the top to the bottom of the tree crowns, V
cmax/ J
max increased in ambient CO 2, but it decreased in elevated CO 2 indicating a greater relative investment of N into light harvesting for the lower crown. Only the mid-crown leaves at both
N levels exhibited photosynthetic down regulation to elevated CO 2. Stem biomass segments (consisting of three nodes and internodes) were compared to the total A
leaf for each segment. This analysis indicated that increased A
leaf at elevated CO 2 did not result in a proportional increase in local stem segment mass, suggesting that C allocation to sinks other than the
local stem segment increased disproportionally. Since C allocated to roots in young Populus trees is primarily assimilated by leaves in the lower crown, the results of this study suggest a mechanism by which C allocation
to roots in young trees may increase in elevated CO 2.
Received: 12 August 1996 / Accepted: 12 November 1996 相似文献
2.
Soil moisture content and leaf area index (LAI) are properties that will be particularly important in mediating whole system
responses to the combined effects of elevated atmospheric [CO 2], warming and altered precipitation. Warming and drying will likely reduce soil moisture, and this effect may be exacerbated
when these factors are combined. However, elevated [CO 2] may increase soil moisture contents and when combined with warming and drying may partially compensate for their effects.
The response of LAI to elevated [CO 2] and warming will be closely tied to soil moisture status and may mitigate or exacerbate the effects of global change on
soil moisture. Using open-top chambers (4-m diameter), the interactive effects of elevated [CO 2], warming, and differential irrigation on soil moisture availability were examined in the OCCAM (Old-Field Community Climate
and Atmospheric Manipulation) experiment at Oak Ridge National Laboratory in eastern Tennessee. Warming consistently reduced
soil moisture contents and this effect was exacerbated by reduced irrigation. However, elevated [CO 2] mitigated the effects of warming and drying on soil moisture. LAI was determined using an AccuPAR ceptometer and both the
leaf area duration (LAD) and canopy size were increased by irrigation and elevated [CO 2]. Changes in LAI were closely linked to soil moisture status. The climate of the southeastern United States is predicted
to be warmer and drier in the future, and this research suggests that although elevated [CO 2] will ameliorate the effects of warming and drying, losses of soil moisture will cause declines in the LAI of old field ecosystems
in the future. 相似文献
3.
Though field data for naturally senesced leaf litter are rare, it is commonly assumed that rising atmospheric CO 2 concentrations will reduce leaf litter quality and decomposition rates in terrestrial ecosystems and that this will lead
to decreased rates of nutrient cycling and increased carbon sequestration in native ecosystems. We generally found that the
quality of␣naturally senesced leaf litter (i.e. concentrations of C, N and lignin; C:N, lignin:N) of a variety of native plant
species produced in alpine, temperate and tropical communities maintained at elevated CO 2 (600–680 μl l −1) was not significantly different from that produced in similar communities maintained at current ambient CO 2 concentrations (340–355 μl l −1). When this litter was allowed to decompose in situ in a humid tropical forest in Panama ( Cecropia peltata, Elettaria cardamomum, and Ficus benjamina, 130 days exposure) and in a lowland temperate calcareous grassland in Switzerland ( Carex flacca and a graminoid species mixture; 261 days exposure), decomposition rates of litter produced under ambient and elevated CO 2 did not differ significantly. The one exception to this pattern occurred in the high alpine sedge, Carex curvula, growing in the Swiss Alps. Decomposition of litter produced in situ under elevated CO 2 was significantly slower than that of litter produced under ambient CO 2 (14% vs. 21% of the initial litter mass had decomposed over a 61-day exposure period, respectively). Overall, our results
indicate that relatively little or no change in leaf litter quality can be expected in plant communities growing under soil
fertilities common in many native ecosystems as atmospheric CO 2 concentrations continue to rise. Even in situations where small reductions in litter quality do occur, these may not necessarily
lead to significantly slower rates of decomposition. Hence in many native species in situ litter decomposition rates, and the time course of decomposition, may remain relatively unaffected by rising CO 2.
Received: 12 September 1996 / Accepted: 30 November 1996 相似文献
5.
Water relations dynamics during simulated sunflecks at high (36°C) and medium (27°C) temperatures and high and low vapour
pressure deficits beween leaf and air (VPD) were studied on shade-grown Piper auritum H.B. & K. plants, a pioneer tree, common in gaps and clearings of tropical rain forests. The leaves of P. auritum wilt rapidly when exposed to high light. Exposure to high VPD and high light caused substantial and rapid dehydration of
leaves. Dehydration could be prevented under high humidity irrespective of temperature. Water stored in leaf cells served
as initial source for transpiration upon high light exposure. This effect increased with increasing VPD and temperature. The
pronounced decrease in leaf water content over time in high light caused a rapid decrease in leaf water potential (Ψ l) and a concomitant increase in water potential gradient (ΔΨ/Δ x) between trunk and leaf, yet the high leaf elasticity (small bulk elastic modulus, ε) allowed turgor maintenance under most
conditions. Under high VPD and high temperature, stomata remained open and ΔΨ/Δ x frequently exceeded 0.95 MPa · m −1, the cavitation-inducing threshold (ΔΨ/Δ x
cav) causing high rates of acoustic emissions from stems and leaf petioles and leading to concomitant losses in hydraulic conductance
per leaf area ( k
l). At medium temperature (high VPD), stomatal closure contained xylem embolism by keeping ΔΨ/Δ x at or below this threshold. We argue that wilting substantially contributes to creating a sufficient driving force for water
uptake from the soil, and reducing the VPD (through a decrease in radiation load and thus leaf temperature) to avoid excessive
dehydration.
Received: 3 March 1996 / Accepted: 10 November 1996 相似文献
6.
Carbon isotope ratios (δ 13C) were studied in evergreen and deciduous forest ecosystems in semi-arid Utah ( Pinus contorta, Populus tremuloides, Acer negundo and Acer grandidentatum). Measurements were taken in four to five stands of each forest ecosystem differing in overstory leaf area index (LAI) during
two consecutive growing seasons. The δ 13C leaf (and carbon isotope discrimination) of understory vegetation in the evergreen stands (LAI 1.5–2.2) did not differ among canopies
with increasing LAI, whereas understory in the deciduous stands (LAI 1.5–4.5) exhibited strongly decreasing δ 13C leaf values (increasing carbon isotope discrimination) with increasing LAI. The δ 13C values of needles and leaves at the top of the canopy were relatively constant over the entire LAI range, indicating no
change in intrinsic water-use efficiency with overstory LAI. In all canopies, δ 13C leaf decreased with decreasing height above the forest floor, primarily due to physiological changes affecting c
i/ c
a (> 60%) and to a minor extent due to δ 13C of canopy air (< 40%). This intra-canopy depletion of δ 13C leaf was lowest in the open stand (1‰) and greatest in the denser stands (4.5‰). Although overstory δ 13C leaf did not change with canopy LAI, δ 13C of soil organic carbon increased with increasing LAI in Pinus contorta and Populus tremuloides ecosystems. In addition, δ 13C of decomposing organic carbon became increasingly enriched over time (by 1.7–2.9‰) for all deciduous and evergreen dry temperate
forests. The δ 13C canopy of CO 2 in canopy air varied temporally and spatially in all forest stands. Vertical canopy gradients of δ 13C canopy, and [CO 2] canopy were larger in the deciduous Populus tremuloides than in the evergreen Pinu contorta stands of similar LAI. In a very wet and cool year, ecosystem discrimination (Δ e) was similar for both deciduous Populus tremulodies (18.0 ± 0.7‰) and evergreen Pinus contorta (18.3 ± 0.9‰) stands. Gradients of δ 13C canopy and [CO 2] canopy were larger in denser Acer spp. stands than those in the open stand. However, 13C enrichment above and photosynthetic draw-down of [CO 2] canopy below tropospheric baseline values were larger in the open than in the dense stands, due to the presence of a vigorous understory
vegetation. Seasonal patterns of the relationship δ 13C canopy versus 1/[CO 2] canopy were strongly influenced by precipitation and air temperature during the growing season. Estimates of Δ e for Acer spp. did not show a significant effect of stand structure, and averaged 16.8 ± 0.5‰ in 1933 and 17.4 ± 0.7‰ in 1994. However,
Δ e varied seasonally with small fluctuations for the open stand (2‰), but more pronounced changes for the dense stand (5‰).
Received: 15 April 1996 / Accepted: 19 October 1996 相似文献
7.
Increased atmospheric CO 2 often but not always leads to large decreases in leaf conductance. Decreased leaf conductance has important implications for a number of components of CO 2 responses, from the plant to the global scale. All of the factors that are sensitive to a change in soil moisture, either amount or timing, may be affected by increased CO 2. The list of potentially sensitive processes includes soil evaporation, run-off, decomposition, and physiological adjustments of plants, as well as factors such as canopy development and the composition of the plant and microbial communities. Experimental evidence concerning ecosystem-scale consequences of the effects of CO 2 on water use is only beginning to accumulate, but the initial indication is that, in water-limited areas, the effects of CO 2-induced changes in leaf conductance are comparable in importance to those of CO, 2-induced changes in photosynthesis. Above the leaf scale, a number of processes interact to modulate the response of canopy or regional evapotran-spiration to increased CO 2. While some components of these processes tend to amplify the sensitivity of evapo-transpiration to altered leaf conductance, the most likely overall pattern is one in which the responses of canopy and regional evapotranspiration are substantially smaller than the responses of canopy conductance. The effects of increased CO 2 on canopy evapotranspiration are likely to be smallest in aerodynamically smooth canopies with high leaf conductances. Under these circumstances, which are largely restricted to agriculture, decreases in evapotranspiration may be only one-fourth as large as decreases in canopy conductance. Decreased canopy conductances over large regions may lead to altered climate, including increased temperature and decreased precipitation. The simulation experiments to date predict small effects globally, but these could be important regionally, especially in combination with radiative (greenhouse) effects of increased CO 2. 相似文献
8.
This investigation examined the influence of soil moisture and associated parameters on the cold hardiness of the Colorado
potato beetle ( Leptinotarsa decemlineata Say), a temperate-zone species that overwinters in terrestrial burrows. The body mass and water content of adult beetles
kept in sand at 4 °C varied over a 16-week period of diapause according to the substratum's moisture content. Changes in body
water content, in turn, influenced the crystallization temperature (range −3.3 to −18.4 °C; n = 417), indicating that environmental moisture indirectly determined supercooling capacity, a measure of physiological cold
hardiness. Beetles held in dry sand readily tolerated a 24-h exposure to temperatures ranging from 0° to −5 °C, but those
chilled in sand containing as little as 1.7% water (dry mass) had elevated mortality. Thus, burrowing in dry soils not only
promotes supercooling via its effect on water balance, but may also inhibit inoculative freezing. Mortality of beetles exposed
to −5 °C for 24 h was lower in substrates composed of sand, clay and/or peat (36–52%) than in pure silica sand (78%) having
an identical water content (17.0% dry mass). In addition to moisture, the texture, structure, water potential, and other physico-chemical
attributes of soil may strongly influence the cold hardiness and overwintering survival of burrowing insects.
Accepted: 10 September 1996 相似文献
9.
We examined the effects of atmospheric vapor pressure deficit (VPD) and soil moisture stress (SMS) on leaf‐ and stand‐level CO 2 exchange in model 3‐year‐old coppiced cottonwood ( Populus deltoides Bartr.) plantations using the large‐scale, controlled environments of the Biosphere 2 Laboratory. A short‐term experiment was imposed on top of continuing, long‐term CO 2 treatments (43 and 120 Pa), at the end of the growing season. For the experiment, the plantations were exposed for 6–14 days to low and high VPD (0.6 and 2.5 kPa) at low and high volumetric soil moisture contents (25–39%). When system gross CO 2 assimilation was corrected for leaf area, system net CO 2 exchange (SNCE), integrated daily SNCE, and system respiration increased in response to elevated CO 2. The increases were mainly as a result of the larger leaf area developed during growth at high CO 2, before the short‐term experiment; the observed decline in responses to SMS and high VPD treatments was partly because of leaf area reduction. Elevated CO 2 ameliorated the gas exchange consequences of water stress at the stand level, in all treatments. The initial slope of light response curves of stand photosynthesis (efficiency of light use by the stand) increased in response to elevated CO 2 under all treatments. Leaf‐level net CO 2 assimilation rate and apparent quantum efficiency were consistently higher, and stomatal conductance and transpiration were significantly lower, under high CO 2 in all soil moisture and VPD combinations (except for conductance and transpiration in high soil moisture, low VPD). Comparisons of leaf‐ and stand‐level gross CO 2 exchange indicated that the limitation of assimilation because of canopy light environment (in well‐irrigated stands; ratio of leaf : stand=3.2–3.5) switched to a predominantly individual leaf limitation (because of stomatal closure) in response to water stress (leaf : stand=0.8–1.3). These observations enabled a good prediction of whole stand assimilation from leaf‐level data under water‐stressed conditions; the predictive ability was less under well‐watered conditions. The data also demonstrated the need for a better understanding of the relationship between leaf water potential, leaf abscission, and stand LAI. 相似文献
10.
Although there is a great deal of information concerning responses to increases in atmospheric CO 2 at the tissue and plant levels, there are substantially fewer studies that have investigated ecosystem-level responses in
the context of integrated carbon, water, and nutrient cycles. Because our understanding of ecosystem responses to elevated
CO 2 is incomplete, modeling is a tool that can be used to investigate the role of plant and soil interactions in the response
of terrestrial ecosystems to elevated CO 2. In this study, we analyze the responses of net primary production (NPP) to doubled CO 2 from 355 to 710 ppmv among three biogeochemistry models in the Vegetation/Ecosystem Modeling and Analysis Project (VEMAP):
BIOME-BGC (BioGeochemical Cycles), Century, and the Terrestrial Ecosystem Model (TEM). For the conterminous United States,
doubled atmospheric CO 2 causes NPP to increase by 5% in Century, 8% in TEM, and 11% in BIOME-BGC. Multiple regression analyses between the NPP response
to doubled CO 2 and the mean annual temperature and annual precipitation of biomes or grid cells indicate that there are negative relationships
between precipitation and the response of NPP to doubled CO 2 for all three models. In contrast, there are different relationships between temperature and the response of NPP to doubled
CO 2 for the three models: there is a negative relationship in the responses of BIOME-BGC, no relationship in the responses of
Century, and a positive relationship in the responses of TEM. In BIOME-BGC, the NPP response to doubled CO 2 is controlled by the change in transpiration associated with reduced leaf conductance to water vapor. This change affects
soil water, then leaf area development and, finally, NPP. In Century, the response of NPP to doubled CO 2 is controlled by changes in decomposition rates associated with increased soil moisture that results from reduced evapotranspiration.
This change affects nitrogen availability for plants, which influences NPP. In TEM, the NPP response to doubled CO 2 is controlled by increased carboxylation which is modified by canopy conductance and the degree to which nitrogen constraints
cause down-regulation of photosynthesis. The implementation of these different mechanisms has consequences for the spatial
pattern of NPP responses, and represents, in part, conceptual uncertainty about controls over NPP responses. Progress in reducing
these uncertainties requires research focused at the ecosystem level to understand how interactions between the carbon, nitrogen,
and water cycles influence the response of NPP to elevated atmospheric CO 2.
Received: 13 December 1996 / Accepted: 20 November 1997 相似文献
11.
It is not clear whether the consistent positive effect of elevated CO 2 on soil respiration (soil carbon flux, SCF) results from increased plant and microbial activity due to (i) greater C availability through CO 2‐induced increases in C inputs or (ii) enhanced soil moisture via CO 2‐induced declines in stomatal conductance and plant water use. Global changes such as biodiversity loss or nitrogen (N) deposition may also affect these drivers, interacting with CO 2 to affect SCF. To determine the effects of these factors on SCF and elucidate the mechanism(s) behind the effect of elevated CO 2 on SCF, we measured SCF and soil moisture throughout a growing season in the Biodiversity, CO 2, and N (BioCON) experiment. Increasing diversity and N caused small declines in soil moisture. Diversity had inconsistent small effects on SCF through its effects on abiotic conditions, while N had a small positive effect that was unrelated to soil moisture. Elevated CO 2 had large consistent effects, increasing soil moisture by 26% and SCF by 45%. However, CO 2‐induced changes in soil moisture were weak drivers of SCF: CO 2 effects on SCF and soil moisture were uncorrelated, CO 2 effect size did not change with soil moisture, within‐day CO 2 effects via soil moisture were neutral or weakly negative, and the estimated effect of increased C availability was 14 times larger than that of increased soil moisture. Combined with previous BioCON results indicating elevated CO 2 increases C availability to plants and microbes, our results suggest that increased SCF is driven by CO 2‐induced increases in substrate availability. Our results provide further support for increased rates of belowground C cycling at elevated CO 2 and evidence that, unlike the response of productivity to elevated CO 2 in BioCON, the response of SCF is not strongly N limited. Thus, N limited grasslands are unlikely to act as a N sink under elevated CO 2. 相似文献
12.
Abstract Increasing atmospheric CO 2 concentration decreases stomatal conductance in many species, but the savings of water from reduced transpiration may permit the forest to retain greater leaf area index ( L). Therefore, the net effect on water use in forest ecosystems under a higher CO 2 atmosphere is difficult to predict. The free air CO 2 enrichment (FACE) facility ( n = 3) in a 14‐m tall (in 1996) Pinus taeda L. stand was designed to reduce uncertainties in predicting such responses. Continuous measurements of precipitation, throughfall precipitation, sap flux, and soil moisture were made over 3.5 years under ambient (CO 2a) and elevated (CO 2e) ambient + 200 µmol mol ?1). Annual stand transpiration under ambient CO 2 conditions accounted for 84–96% of latent heat flux measured with the eddy‐covariance technique above the canopy. Under CO 2e, P. taeda transpired less per unit of leaf area only when soil drought was severe. Liquidambar styraciflua, the other major species in the forest, used progressively less water, settling at 25% reduction in sap flux density after 3.5 years under CO 2e. Because P. taeda dominated the stand, and severe drought periods were of relatively short duration, the direct impact of CO 2e on water savings in the stand was undetectable. Moreover, the forest used progressively more water under CO 2e, probably because soil moisture availability progressively increased, probably owing to a reduction in soil evaporation caused by more litter buildup in the CO 2e plots. The results suggest that, in this forest, the effect of CO 2e on transpiration was greater indirectly through enhanced litter production than directly through reduced stomatal conductance. In forests composed of species more similar to L. styraciflua, water savings from stomatal closure may dominate the response to CO 2e. 相似文献
13.
Leaf chemistry alterations due to increasing atmospheric CO 2 will reflect plant physiological changes and impact ecosystem function. Longleaf pine was grown for 20 months at two levels
of atmospheric CO 2 (720 and 365 μmol mol –1), two levels of soil N (4 g m –2 year –1 and 40 g m –2 year –1), and two soil moisture levels (– 0.5 and – 1.5 MPa) in open top chambers. After 20 months of exposure, needles were collected
and ergastic substances including starch grains and polyphenols were assessed using light microscopy, and calcium oxalate
crystals were assessed using light microscopy, scanning electron microscopy, and transmission electron microscopy. Polyphenol
content was also determined using the Folin-Denis assay and condensed tannins were estimated by precipitation with protein.
Evaluation of phenolic content histochemically was compared to results obtained using the Folin-Denis assay. Total leaf polyphenol
and condensed tannin content were increased by main effects of elevated CO 2, low soil N and well-watered conditions. Elevated CO 2 and low soil N decreased crystal deposition within needle phloem. Elevated CO 2 had no effect on the percentage of cells within the mesophyll, endodermis, or transfusion tissue which contained visible
starch inclusions. With respect to starch accumulation in response to N stress, mesophyll > endodermis > transfusion tissue.
The opposite was true in the case of starch accumulation in response to main effects of water stress: mesophyll < endodermis
< transfusion tissue. These results indicate that N and water conditions significantly affect deposition of leaf ergastic
substances in longleaf pine, and that normal variability in leaf tissue quality resulting from gradients in soil resources
will be magnified under conditions of elevated CO 2.
Received: 5 November 1996 / Accepted: 7 March 1997 相似文献
14.
Fluxes of CO 2 and N 2O were measured from both natural and experimentally augmented snowpacks during the winters of 1993 and 1994 on Niwot Ridge
in the Colorado Front Range. Consistent snow cover insulated the soil surface from extreme air temperatures and allowed heterotrophic
activity to continue through much of the winter. In contrast, soil remained frozen at sites with inconsistent snow cover and
production did not begin until snowmelt. Fluxes were measured when soil temperatures under the snow ranged from –5°C to 0°C,
but there was no significant relationship between flux for either gas and temperature within this range. While early developing
snowpacks resulted in warmer minimum soil temperatures allowing production to continue for most of the winter, the highest
CO 2 fluxes were recorded at sites which experienced a hard freeze before a consistent snowpack developed. Consequently, the seasonal
flux of CO 2
–C from snow covered soils was related both to the severity of freeze and the duration of snow cover. Over-winter CO 2
–C loss ranged from 0.3 g C m −2 season −1 at sites characterized by inconsistent snow cover to 25.7 g C m −2 season −1 at sites that experienced a hard freeze followed by an extended period of snow cover. In contrast to the pattern observed
with C loss, a hard freeze early in the winter did not result in greater N 2O –N loss. Both mean daily N 2O fluxes and the total over-winter N 2O –N loss were related to the length of time soils were covered by a consistent snowpack. Over-winter N 2O –N loss ranged from less 0.23 mg N m −2 from the latest developing, short duration snowpacks to 16.90 mg N m −2 from sites with early snow cover. These data suggest that over-winter heterotrophic activity in snow-covered soil has the
potential to mineralize from less than 1% to greater than 25% of the carbon fixed in ANPP, while over-winter N 2O fluxes range from less than half to an order of magnitude higher than growing season fluxes. The variability in these fluxes
suggests that small changes in climate which affect the timing of seasonal snow cover may have a large effect on C and N cycling
in these environments.
Received: 5 April 1996 / Accepted: 25 November 1996 相似文献
15.
Soybean ( Glycine max L. Merrill cv `Bragg') plants were grown in pots at six elevated atmospheric CO 2 concentrations and two watering regimes in open top field chambers to characterize leaf xylem potential, stomatal resistance and conductance, transpiration, and carbohydrate contents of the leaves in response to CO 2 enrichment and water stress conditions. Groups of plants at each CO 2 concentration were subjected to water stress by withholding irrigation for 4 days during the pod-filling stage. Under well watered conditions, the stomatal conductance of the plants decreased with increasing CO2 concentration. Therefore, although leaf area per plant was greater in the high CO2 treatments, the rate of water loss per plant decreased with CO2 enrichment. After 4 days without irrigation, plants in lower CO2 treatments showed greater leaf tissue damage, lower leaf water potential, and higher stomatal resistance than high CO2 plants. Stomatal closure occurred at lower leaf water potentials for the low CO2 grown plants than the high CO2 grown plants. Significantly greater starch concentrations were found in leaves of high CO2 plants, and the reductions in leaf starch and increases in soluble sugars due to water stress were greater for low CO2 plants. The results showed that even though greater growth was observed at high atmospheric CO2 concentrations, lower rates of water use delayed and, thereby, prevented the onset of severe water stress under conditions of low moisture availability. 相似文献
16.
In general, C 3 plant species are more responsive to atmospheric carbon dioxide (CO 2) enrichment than C 4-plants. Increased relative growth rate at elevated CO 2 primarily relates to increased Net Assimilation Rate (NAR), and enhancement of net photosynthesis and reduced photorespiration. Transpiration and stomatal conductance decrease with elevated CO 2, water use efficiency and shoot water potential increase, particularly in plants grown at high soil salinity. Leaf area per plant and leaf area per leaf may increase in an early growth stage with increased CO 2, after a period of time Leaf Area Ratio (LAR) and Specific Leaf Area (SLA) generally decrease. Starch may accumulate with time in leaves grown at elevated CO 2. Plants grown under salt stress with increased (dark) respiration as a sink for photosynthates, may not show such acclimation to increased atmospheric CO 2 levels. Plant growth may be stimulated by atmospheric carbon dioxide enrichment and reduced by enhanced UV-B radiation but the limited data available on the effect of combined elevated CO 2 and ultraviolet B (280–320 nm) (UV-B) radiation allow no general conclusion. CO 2-induced increase of growth rate can be markedly modified at elevated UV-B radiation. Plant responses to elevated atmospheric CO 2 and other environmental factors such as soil salinity and UV-B tend to be species-specific, because plant species differ in sensitivity to salinity and UV-B radiation, as well as to other environmental stress factors (drought, nutrient deficiency). Therefore, the effects of joint elevated atmospheric CO 2 and increased soil salinity or elevated CO 2 and enhanced UV-B to plants are physiologically complex. 相似文献
17.
This work examined the effects of elevated CO 2 and temperature and water regimes, alone and in interaction, on the leaf characteristics [leaf area ( LA), specific leaf weight ( SLW), leaf nitrogen content ( NL) based on LA], photosynthesis (light‐saturated net carbon fixation rate, Psat) and carbon storage in aboveground biomass of leaves ( Cl) and stem ( Cs) for a perennial reed canary grass ( Phalaris arundinacea L., Finnish local cultivar). For this purpose, plants were grown under different water regimes (ranging from high to low soil moisture) in climate‐controlled growth chambers under the elevated CO 2 and/or temperature (following a factorial design) over a whole growing season (May–September in 2009). The results showed that the elevated temperature increased the leaf growth, photosynthesis and carbon storage of aboveground biomass the most in the early growing periods, compared with ambient temperature. However, the plant growth declined rapidly thereafter with a lower carbon storage at the end of growing season. This was related to the accelerated phenology regulation and consequent earlier growth senescence. Consequently, the elevation of CO 2 increased the Psat, LA and SLW during the growing season, with a significant concurrent increase in the carbon storage in aboveground biomass. Low soil moisture decreased the Psat, leaf stomatal conductance, LA and carbon storage in above ground biomass compared with high and normal soil moisture. This water stress effect was the largest under the elevated temperature. The elevated CO 2 partially mitigated the adverse effects of high temperature and low soil moisture. However, the combination of elevated temperature and CO 2 did not significantly increase the carbon storage in aboveground biomass of the plants. 相似文献
18.
Atmospheric CO 2 enrichment may stimulate plant growth directly through (1) enhanced photosynthesis or indirectly, through (2) reduced plant water consumption and hence slower soil moisture depletion, or the combination of both. Herein we describe gas exchange, plant biomass and species responses of five native or semi-native temperate and Mediterranean grasslands and three semi-arid systems to CO 2 enrichment, with an emphasis on water relations. Increasing CO 2 led to decreased leaf conductance for water vapor, improved plant water status, altered seasonal evapotranspiration dynamics, and in most cases, periodic increases in soil water content. The extent, timing and duration of these responses varied among ecosystems, species and years. Across the grasslands of the Kansas tallgrass prairie, Colorado shortgrass steppe and Swiss calcareous grassland, increases in aboveground biomass from CO 2 enrichment were relatively greater in dry years. In contrast, CO 2-induced aboveground biomass increases in the Texas C 3/C 4 grassland and the New Zealand pasture seemed little or only marginally influenced by yearly variation in soil water, while plant growth in the Mojave Desert was stimulated by CO 2 in a relatively wet year. Mediterranean grasslands sometimes failed to respond to CO 2-related increased late-season water, whereas semiarid Negev grassland assemblages profited. Vegetative and reproductive responses to CO 2 were highly varied among species and ecosystems, and did not generally follow any predictable pattern in regard to functional groups. Results suggest that the indirect effects of CO 2 on plant and soil water relations may contribute substantially to experimentally induced CO 2-effects, and also reflect local humidity conditions. For landscape scale predictions, this analysis calls for a clear distinction between biomass responses due to direct CO 2 effects on photosynthesis and those indirect CO 2 effects via soil moisture as documented here. 相似文献
19.
Elevated atmospheric CO 2 is known to affect plant–insect herbivore interactions. Elevated CO 2 causes leaf nitrogen to decrease, the ostensible cause of herbivore compensatory feeding. CO 2 may also affect herbivore consumption by altering chemical defenses via changes in plant hormones. We considered the effects of elevated CO 2, in conjunction with soil fertility and damage (simulated herbivory), on glucosinolate concentrations of mustard ( Brassica nigra) and collard ( B. oleracea var. acephala) and the effects of leaf nitrogen and glucosinolate groups on specialist Pieris rapae consumption. Elevated CO 2 affected B. oleracea but not B. nigra glucosinolates; responses to soil fertility and damage were also species‐specific. Soil fertility and damage also affected B. oleracea glucosinolates differently under elevated CO 2. Glucosinolates did not affect P. rapae consumption at either CO 2 concentration in B. nigra, but had CO 2‐specific effects on consumption in B. oleracea. At ambient CO 2, leaf nitrogen had strong effects on glucosinolate concentrations and P. rapae consumption but only gluconasturtiin was a feeding stimulant. At elevated CO 2, direct effects of leaf nitrogen were weaker, but glucosinolates had stronger effects on consumption. Gluconasturtiin and aliphatic glucosinolates were feeding stimulants and indole glucosinolates were feeding deterrents. These results do not support the compensatory feeding hypothesis as the sole driver of changes in P. rapae consumption under elevated CO 2. Support for hormone‐mediated CO 2 response (HMCR) was mixed; it explained few treatment effects on constitutive or induced glucosinolates, but did explain patterns in SEMs. Further, the novel feeding deterrent effect of indole glucosinolates under elevated CO 2 in B. oleracae underscores the importance of defensive chemistry in CO 2 response. We speculate that P. rapae indole glucosinolate detoxification mechanisms may have been overwhelmed under elevated CO 2 forcing slowed consumption. Specialists may have to contend with hosts with poorer nutritional quality and more effective chemical defenses under elevated CO 2. 相似文献
20.
Sensory organs that detect CO 2 are common in herbivorous moths and butterflies, but their function has been unclear until now. As the CO 2 gradients in the vicinity of a host plant depend on its physiological condition, CO 2 could provide a sensory cue for the suitability of the plant as a larval food source. This study investigated whether changing
the atmospheric CO 2 concentration affected oviposition by Cactoblastis cactorum on its host, the cactus Opuntia stricta. On host plants exposed to rapid fluctuations in CO 2 concentration, the frequency of oviposition was reduced by a factor of 3.2 compared to the control. As the fluctuations mask
the much smaller CO 2 signals generated by the plants, this suggests that those signals constitute an important component of the host identification
process. On host plants exposed to a constant background of doubled CO 2, oviposition was also reduced, by a factor of 1.8. An increased background reduces host signal detectability, partially as
a consequence of a general principle of sensory physiology (Weber-Fechner's law), and partially due to other factors specific
to CO 2-receptor neurons.
Received: 4 October 1996 / Accepted: 16 January 1997 相似文献
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