Modeling of Stomatal Conductance for Estimating Ozone Uptake of Fagus crenata Under Experimentally Enhanced Free-air Ozone Exposure

We examined a performance of the multiplicative stomatal conductance model to estimate the stomatal ozone uptake for Fagus crenata. Parameterization of the model was carried out by in-situ measurements in a free-air ozone exposure experiment. The model performed fairly well under ambient conditions, with low ozone concentration. However, the model overestimated stomatal conductance under enhanced ozone condition due to ozone-induced stomatal closure. A revised model that included a parameter representing ozone-induced stomatal closure showed better estimation of ozone uptake. Neglecting ozone-induced stomatal closure induced a 20?% overestimation of the stomatal uptake of ozone. The ozone-induced stomatal closure was closely related to stomatal ozone uptake rather than accumulated concentrations of ozone exceeding 40?nmol mol^?1. Our results suggest that ozone-induced stomatal closure should be implemented to stomatal conductance model for estimating ozone uptake for F. crenata. The implementation will contribute to adequate risk assessments of ozone impacts on F. crenata forests in Japan.     

Stomatal behaviour in an oak canopy

Measurements of stomatal conductance in an oak canopy (Quercus robur) in The Netherlands are described. Diurnal changes in conductance were found to be dependent on solar radiation and vapour pressure deficit. A model describing these relationships was derived from the observed data. Model performance was rather poor, possibly as a result of the neglect of leaf water potential influences on stomatal conductance. A simple approximation for this influence is suggested and discussed.     

Modelling and Mapping Ozone Deposition in Europe

A new dry deposition module has been developed for European-scale mapping and modelling of ozone deposition fluxes (Emberson et al., 2000a,b). The module is being implemented in the photochemical long-range transport model of EMEP that is currently used to estimate exceedance of the existing critical levels for ozone within the UN ECE LRTAP programme. The deposition model evaluates the atmospheric, boundary layer and surface resistances to ozone transfer with the calculation of the dry deposition velocity performed according to a standard resistance formulation. The approach differs from other existing methods through the use of a detailed stomatal uptake model that describes stomatal conductance as a function of plant species, phenology and four environmental variables (air temperature, solar radiation, water vapour pressure deficit and soil moisture deficit). Comparison of preliminary model outputs for selected land-cover types indicate that the model is capable of predicting the seasonal and diurnal range in deposition velocities that have been reported previously in the literature. The application of this deposition scheme enables calculations of ambient ozone concentrations to be made using a biologically based method that can distinguish stomatal and non-stomatal components of total ozone deposition. The ability to estimate stomatal ozone fluxes (according to vegetation type, phenology and spatial location) that are consistent with evaluations of atmospheric ozone concentrations will be helpful in future assessments of ozone impacts to vegetation.     

Effect of carbon dioxide on sorghum yield,root growth,and water use

The concentration of atmospheric carbon dioxide (CO₂) is rising. The effect of higher than ambient levels of CO₂ on plants grown in the sub-humid central Great Plains of the U.S.A. has not been investigated. Therefore, an experiment was conducted at Manhattan, Kansas, to study the effect of elevated levels of CO₂ on grain sorghum [Sorghum bicolor (L.) Moench]. During the summer of 1984, the sorghum was grown in rhizotrons in which root and shoot growth could be monitored throughout the growth cycle. The tops of the plants were enclosed in plastic chambers, which contained one of four concentrations of CO₂ : 330 (ambient), 485, 660, and 795 μl 1⁻¹.Enriched CO₂ delayed the boot, half bloom, and soft dough stages. Sorghum grown at elevated concentrations of CO₂ yielded more roots and shoots than plants grown with 330 μl 1⁻¹. At all soil-profile depths, root numbers and weights were higher at elevated CO₂ than at ambient CO₂. However, water use per unit dry matter of leaf, stem, root, and grain was decreased 13, 30, 31, and 29%, respectively, in plants grown at 795 μl 1⁻¹ CO₂ compared to plants at 330 μl 1⁻¹ CO₂. Although elevated CO₂ levels increased the stomatal resistance and leaf temperature, an increase in leaf area indices resulted in a lower canopy resistance.     

Quantifying effects of atmospheric CO2 enrichment on stomatal conductance and evapotranspiration of water hyacinth via infrared thermometry

Measurements of stomatal conductance and evaporative water loss from two tanks of water hyacinths growing at Phoenix, AZ, one under ambient conditions and one considerably enriched in atmospheric CO₂, are reported. Stomatal conductances of plants in the CO₂-enriched treatment were reduced to values half as great as those of plants in the ambient treatment at a mean mid-day CO₂ concentration of 550 ppm, which resulted in a 22% decrease in total evaporative water loss; while in going from an ambient CO₂ concentration of 310 ppm to a doubled concentration of 620 ppm there was a 27% decrease in evaporative water loss. Both of these physiological responses were well characterized by the Idso—Jackson plant water stress index. Additionally, it was found that the stomatal response to increasing atmospheric CO₂ was identical to that induced by removing water from the plant roots, and that the reduction in evaporative water loss with increasing atmospheric CO₂ was an inverse linear function of the plant water stress index — both of which phenomena had previously been theorized but never before experimentally verified.     

Physiological Effects of Exposure to Arsenic,Mercury, Antimony and Selenium in the Aquatic Moss Fontinalis antipyretica Hedw.

This study assessed the effect of ambient air pollution on leaf characteristics of white willow, northern red oak, and Scots pine. Willow, oak, and pine saplings were planted at sixteen locations in Belgium, where nitrogen dioxide (NO₂), ozone (O₃), sulfur dioxide (SO₂), and particulate matter (PM₁₀) concentrations were continuously measured. The trees were exposed to ambient air during 6 months (April–September 2010), and, thereafter, specific leaf area (SLA), stomatal resistance (R _s), leaf fluctuating asymmetry (FA), drop contact angle (CA), relative chlorophyll content, and chlorophyll fluorescence (F _v/F _m) were measured. Leaf characteristics of willow, oak, and pine were differently related to the ambient air pollution, indicating a species-dependent response. Willow and pine had a higher SLA at measuring stations with higher NO₂ and lower O₃ concentrations. Willow had a higher R _s and pine had a higher F _v/F _m at measuring stations with a higher NO₂ and lower O₃ concentrations, while oak had a higher F _v/F _m and a lower FA at measuring stations with a higher NO₂ and lower O₃ concentrations. FA and R _s of willow, oak, and pine, SLA of oak, and CA of willow were rather an indicator for local adaptation to the micro-environment than an indicator for the ambient air pollution.     

Changes in soil microbial biomass carbon and enzyme activities under elevated CO2 affect fine root decomposition processes in a Mongolian oak ecosystem

The relationships between soil microbial properties and fine root decomposition processes under elevated CO₂ are poorly understood. To address this question, we determined soil microbial biomass carbon (SMB-C) and nitrogen (SMB-N), enzymes related to soil carbon (C) and nitrogen (N) cycling, the abundance of cultivable N-fixing bacteria and cellulolytic fungi, fine root organic matter, lignin and holocellulose decomposition, and N mineralization from 2006 to 2007 in a Mongolian oak (Quercus mongolica Fischer ex Ledebour) ecosystem in northeastern China. The experiment consisted of three treatments: elevated CO₂ chambers, ambient CO₂ chambers, and chamberless plots. Fine roots had significantly greater organic matter decomposition rates under elevated CO₂. This corresponded with significantly greater SMB-C. Changes in the activities of protease and phenol oxidase under elevated CO₂ could not explain the changes in fine root N release and lignin decomposition rates, respectively, while holocellulose decomposition rate had the same response to experimental treatments as did cellulase activity. Changes in cultivable N-fixing bacterial and cellulolytic fungal abundances in response to experimental treatments were identical to those of N mineralization and lignin decomposition rates, respectively, suggesting that the two indices were closely related to fine root N mineralization and lignin decomposition. Our results showed that the increased fine root organic matter, lignin and holocellulose decomposition, and N mineralization rates under elevated CO₂ could be explained by shifts in SMB-C and the abundance of cellulolytic fungi and N-fixing bacteria. Enzyme activities are not reliable for the assessment of fine root decomposition and more attention should be given to the measurement of specific bacterial and fungal communities.     

Methane production in a flooded soil in response to elevated atmospheric carbon dioxide concentrations

 CH₄ production in a flooded soil as affected by elevated atmospheric CO₂ was quantified in a laboratory incubation study. CH₄ production in the flooded soil increased by 19.6%, 28.2%, and 33.4% after a 2-week incubation and by 38.2%, 62.4%, and 43.0% after a 3-week incubation under atmospheres of 498, 820, and 1050 μl l^–1 CO₂, respectively, over that in soil under the ambient CO₂ concentration. CH₄ production in slurry under 690, 920, and 1150 μl l^–1 CO₂ increased by 2.7%, 5.5%, and 5.0%, respectively, after a 3-day incubation, and by 6.7%, 12.8%, and 5.4%, respectively, after a 6-day incubation over that in slurry under the ambient CO₂ concentration. The increase in CH₄ production in the soil slurry under elevated CO₂ concentrations in a N₂ atmosphere was more pronounced than that under elevated CO₂ concentrations in air. These data suggested that elevated atmospheric CO₂ concentrations could promote methanogenic activity in flooded soil. Received: 2 March 1998     

Modelling ozone deposition fluxes: The relative roles of deposition and detoxification processes

A new Model of Ozone Deposition and Detoxification (MODD) is presented. This model describes stomatal ozone uptake and deposition on external plant surfaces and soil; it accounts for diurnal variability of detoxification processes and reactive ozone uptake on cuticular waxes and soil surface. The mechanistic modelling of plant defense reactions is based on the Plöchl et al. (2000) detoxification model in which the dynamics of apoplast chemistry are considered. To estimate ozone deposition fluxes on cuticular waxes and soil surface, we use a revised version of the Morrison and Nazaroff (2002) model developed to account for ozone uptake on material surfaces. This model which has been fully integrated with a soil-plant-atmosphere continuum model ensures a complete coupling between stomatal conductance and O₃ exchanges between leaves and the atmosphere. The observed diurnal variations in stomatal conductance which largely control the influx of O₃ into the leaf are well reproduced. Model simulations point out that the pool of ascorbate located in the mesophyll cell wall plays a significant role in the detoxification of O₃. Besides stomatal conductance, it is the key process involved in the control of ozone flux to the cell wall. A decrease in the pool of ascorbate lengthens the chemical lifetime of O₃ in the cell wall then the virtual apoplastic resistance is found to increase with decreasing ascorbate. Although the atmospheric ozone concentration increases as the weather becomes hot and dry, the virtual apoplastic resistance follows the same trend, indicating a decrease of the ascorbate pool in the mesophyll cell wall. Results also indicate that for the pre-senescence period 57% of the ozone is deposited onto the cuticular surfaces, 4% on soil and only 37% is absorbed by stomata. The comparison of modelled and measured data reported in this study indicates that the model is capable of predicting the major features of the patterns of total ozone flux.     

Elevated CO<Subscript>2</Subscript> concentration affected pine and oak litter chemistry and the respiration and microbial biomass of soils amended with these litters

Elevated atmospheric CO₂ concentration ([CO₂]) may change litter chemistry which affects litter decomposability. This study investigated respiration and microbial biomass of soils amended with litter of Pinus densiflora (a coniferous species; pine) and Quercus variabilis (a deciduous species; oak) that were grown under different atmospheric [CO₂] and thus had different chemistry. Elevated [CO₂] increased lignin/N through increased lignin concentration and decreased N concentration. The CO₂ emission from the soils amended with litter produced under the same [CO₂] regime was greater for oak than pine litter, confirming that broadleaf litter with lower lignin decomposes faster than needle leaf litter. Within each species, however, soils amended with high lignin/N litter grown under elevated [CO₂] emitted more CO₂ than those with low lignin/N litter grown under ambient [CO₂]. Such contrasting effects of lignin/N on inter- and intra-species variations in litter decomposition should be ascribed to the effects of other litter chemistry variables including nonstructural carbohydrate, calcium and manganese as well as inhibitory effect of N on lignin decomposition. The microbial biomass was also higher in the soils amended with high lignin/N litter than those with low lignin/N litter probably due to low substrate use efficiency of lignin by microbes. Our study suggests that elevated [CO₂] increases lignin/N for both species, but increased lignin/N does not always reduce soil respiration and microbial biomass. Further study investigating a variety of tree species is required for more comprehensive understanding of inter- and intra-species variations of litter decomposition under elevated [CO₂].     

Considering sink strength to model crop production under elevated atmospheric CO2

Climatic changes and elevated atmospheric CO₂ concentrations will affect crop growth and production in the near future. Rising CO₂ concentration is a novel environmental aspect that should be considered when projections for future agricultural productivity are made. In addition to a reducing effect on stomatal conductance and crop transpiration, elevated CO₂ concentration can stimulate crop production. The magnitude of this stimulatory effect (‘CO₂ fertilization’) is subject of discussion. In this study, different calculation procedures of the generic crop model AquaCrop based on a foregoing theoretical framework and a meta-analysis of field responses, respectively, were evaluated against experimental data of free air CO₂ enrichment (FACE) environments. A flexible response of the water productivity parameter of the model to CO₂ concentration was introduced as the best option to consider crop sink strength and responsiveness to CO₂. By varying the response factor, differences in crop sink capacity and trends in breeding and management, which alter crop responsiveness, can be addressed. Projections of maize (Zea mays L.) and potato (Solanum tuberosum L.) production reflecting the differences in responsiveness were simulated for future time horizons when elevated CO₂ concentrations and climatic changes are expected. Variation in future yield potential associated with sink strength could be as high as 27% of the total production. Thus, taking into account crop sink strength and variation in responsiveness is equally relevant to considering climatic changes and elevated CO₂ concentration when assessing future crop production. Indicative values representing the crop responsiveness to elevated CO₂ concentration were proposed for all crops currently available in the database of AquaCrop as a first step in reducing part of the uncertainty involved in modeling future agricultural production.     

The effect of increased atmospheric carbon dioxide concentration on emissions of nitrous oxide, carbon dioxide and methane from a wheat field in a semi-arid environment in northern China

There are no reports on the effects of elevated carbon dioxide [CO₂] on the fluxes of N₂O, CO₂ and CH₄ from semi-arid wheat cropping systems. These three soil gas fluxes were measured using closed chambers under ambient (420 ± 18 μmol mol⁻¹) and elevated (565 ± 37 μmol mol⁻¹) at the Free-Air Carbon dioxide Enrichment experimental facility in northern China. Measurements were made over five weeks on a wheat crop (Triticum aestivum L. cv. Zhongmai 175). Elevated [CO₂] increased N₂O and CO₂ emission from soil by 60% and 15%, respectively, but had no significant effect on CH₄ flux. There was no significant interaction between [CO₂] and N application rate on these gas fluxes, probably because soil N was not limiting. At least 22% increase in C storage is required to offset the observed increase in greenhouse gas emissions under elevated [CO₂].     

Can a mixed stand of N2-fixing and non-fixing plants restrict N2O emissions with increasing CO2 concentration?

Initial effects of elevated atmospheric CO₂ concentration on N₂O fluxes and biomass production of timothy/red clover were studied in the laboratory. The experimental design consisted of two levels of atmospheric CO₂ (ca. 360 and 720 μmol CO₂ mol⁻¹) and two N fertilisation levels (5 and 10 g N m⁻²). There was a total of 36 mesocosms comprising sandy loam soil, which were equally distributed in four thermo-controlled greenhouses. In two of the greenhouses, the CO₂ concentration was kept at ambient concentration and in the other two at doubled concentration. Forage was harvested and the plants fertilised three times during the basic experiment, followed by harvest, a fertilisation with the double amount of nitrogen and rise of water level. Under elevated CO₂, harvestable and total aboveground dry biomass production of a mixed Trifolium/Phleum stand was increased at both N treatments compared to ambient CO₂. The N₂O flux rates under ambient CO₂ were significantly higher at both N treatments during the early growth of mixed Phleum/Trifolium mesocosms compared to the N₂O flux rate under elevated CO₂. However, when the conditions were favourable for denitrification at the end of the experiment, i.e. N availability and soil moisture were high enough, the elevated CO₂ concentration enhanced the N₂O efflux.     

Growth and Leaf Gas Exchange in Three Birch Species Exposed to Elevated Ozone and CO2 in Summer

We examined the effects of ozone and elevated CO₂ concentration in summer on the growth and photosynthetic traits of three representative birch species in Japan (mountain birch, Monarch birch, and white birch). Seedlings of the three birch species were grown in 16 open-top chambers and were exposed to two levels of ozone (6 and 60?nmol?mol^?1 for 7?h per day) in combination with two levels of CO₂ (370?C380 and 600???mol?mol^?1 for daytime) from July to October. No adverse effects of ozone were found in the Monarch birch or the white birch, but elevated ozone in summer reduced branch biomass and net photosynthesis, and accelerated leaf abscission, in the mountain birch. Elevated CO₂ promoted root development and thereby reduced the ratio of shoot dry mass (stem + branch) to root dry mass (S/R ratio) in the mountain birch and white birch. In contrast, there was no difference in dry mass between ambient and elevated CO₂ for the Monarch birch, due to downregulation of photosynthesis. Studies of the combined effect of CO₂ and ozone revealed that elevated CO₂ did not ameliorate the effect of ozone on mountain birch in late summer. In considering the ameliorating effect of CO₂ on ozone damage, it is necessary to take account of the species and the season.     

Root biomass dynamics in a semi-natural grassland exposed to elevated atmospheric CO2 for five years

The effects of elevated atmospheric CO₂ on root dynamics were studied in a semi-natural grassland in central Sweden during five consecutive summer seasons. Open-top chambers were used for ambient and elevated (+350 μmol mol^?1) concentrations of CO₂, and chamberless rings were used for control. Root dynamics were observed in situ with minirhizotrons during the five summers and root biomass production was measured with root in growth cores during the last two years, from which total root biomass was estimated for each of the five years. The elevated CO₂ treatment showed both a greater increase in root numbers during the early summer and a greater decline in root numbers during autumn and winter than the ambient CO₂ treatment. Mean root production under elevated CO₂ was 50% greater than ambient CO₂ during the five years, and the difference increased from +25% in the first year to +80% in the last two years. Conversely, during the same period, the elevated to ambient CO₂ difference in shoot biomass decreased from +50% to +5%. This resulted in a dramatic change in root to shoot ratios in elevated CO₂ compared with the ambient treatment, which increased from ?15% in 1996 to +70% in 2000. Similar differences were seen between elevated CO₂ and the chamberless grown control plants, where root to shoot ratios increased steadily from ?47% in 1996 to +27% in 2000. Less dynamically, the root to shoot ratios of ambient CO₂ grown plants compared with the chamberless control plants were consistently ?29%±6% during the experimental period. In conclusion, during the 5 years this grassland was studied, there was a clear shift in plant biomass partitioning from above to below ground for plants exposed to elevated CO₂.     

Critical levels of O3 for wood production of European beech (Fagus sylvatica L.)

During recent decades, ozone (O₃) has gained much attention as a possible contributor to forest decline. Attempts have been made to set critical levels for O₃ in order to protect vegetation. Damage to vegetation seems to depend on the pattern of exposure. Episodic peaks followed by periods with low concentrations are more phytotoxic than exposures with generally elevated concentrations but without peaks. The present experiment aims to examine whether O₃ affects the wood production of beech seedlings. The seedlings were exposed to three different air pollution regimes: charcoal-filtered ambient air (CF), non-filtered ambient air (NF), and NF+30nl^1?l^?1 O₃ 8 hours day¹ during summer periods (NFO). Basal stem diameter was measured regularly during three growing seasons. The relative diameter increase was significantly reduced with increased O₃ concentration. AOT40 is calculated for all treatments and evaluated in relation to the relative diameter growth.     

Influence of Soil Type on the Effects of Elevated Atmospheric CO2 and N Deposition on the Water Balance and Growth of a Young Spruce and Beech Forest

Sixteen open-top chambers, each equipped with two non-weighablegravity-drained lysimeter compartments, were used to investigate the impacts of elevated atmospheric carbon dioxide (CO₂) concentration and nitrogen (N) deposition on the water relations and growth of young model forest ecosystems on two different types of soils. The same vegetation of a mixed spruce and beech overstorey and various herbs in the understorey was planted in all treatments on both soils. The soils were repacked on top of a drainage layer. Four combinations of treatments were applied in four replicates each: ambient (370 cm³ m^-3) CO₂ + low (7 kg N ha^-1 a^-1) N deposition, ambient CO₂ + high(70 kg N ha^-1 a^-1) N deposition, elevated (590 cm³ m^-3) CO₂ + low N deposition, and elevated CO₂ + high N deposition. After canopy closure, treatment effects on evapotranspiration and growth during the third year of study were very different for the two soils.On the acidic sandy loam, elevated CO₂ enhanced growth(leaf biomass +21%, roots +27%) at reduced evapotranspiration (–9%). High N deposition increased aboveground growth even more strongly (+50%), but also increased evapotranspiration (+16%). Together, elevated CO₂ and high N had a more than additive fertilizer effect on growth, while their effects on evapotranspirationcompensated. On the calcareous loamy sand, elevated CO₂not only tended to enhance growth (leaf biomass +17%, roots +20%), but also increased evapotranspiration (+5%).On this soil, aboveground growth was stimulated by N only incombination with elevated CO₂, but less than on the acidic soil, while evapotranspiration (–6.5%) and root growth into the subsoil (–54%) were decreased by increased N deposition at both CO₂ concentrations, in contrast to the N treatments on the acidic sandy loam. The influence of the soil on the observed ecosystem responses canbe interpreted in terms of the concept of optimal resource allocation.     

Physiological responses of Quercus ilex Leaves to Water Stress and Acute Ozone Exposure Under Controlled Conditions

The combined effect of water stress and ozone (O₃) on stomatal O₃ flux, damage to photosynthesis, and detoxification by biogenic volatile organic compounds (BVOC) in Quercus ilex leaves was studied. A 4-weeks O₃ exposure (250 ppb, 4 h per day) caused a reduction of photosynthesis and stomatal conductance, which was fully recovered 1 week after the end of the treatment, in well-watered and water-stressed plants. Measurements of stomatal O₃ flux revealed a low stomatal flux of the pollutant, which became minimal after stomatal closure caused by water stress. An induction of volatile monoterpenes, important compounds in the O₃ scavenging system in Q. ilex, and a burst of lipoxygenase compounds (LOX), which are released as gaseous by-products of membrane peroxidation, was observed after 2–3 weeks of O₃ fumigation. However, these compounds were also released in control leaves that were exposed to ozone only briefly, to determine stomatal O₃ flux. The low stomatal flux that occurred in water stress conditions helped avoiding permanent damage to Q. ilex leaves, although during the O₃ treatment photosynthesis was severely limited by stomatal closure. In well-watered plants, O₃ fumigation caused a noticeable increase of nocturnal stomatal conductance. If confirmed on adult plants under field conditions, this effect can imply larger flux of O₃ at night and possible detrimental effects of O₃ on leaf functions in plants exposed to high nocturnal O₃ levels.     

Effects of Tropospheric O3 on Trembling Aspen and Interaction with Co2: Results from an O3-Gradient and a Face Experiment

Over the years, a series of trembling aspen (Populus tremuloides Michx.) clones differing in O₃ sensitivity have been identified from OTC studies. Three clones (216 and 271[(O₃ tolerant] and 259 [O₃ sensitive]) have been characterized for O₃ sensitivity by growth and biomass responses, foliar symptoms, gas exchange, chlorophyll content, epicuticular wax characteristics, and antioxidant production. In this study we compared the responses of these same clones exposed to O₃ under field conditions along a natural O₃ gradient and in a Free-Air CO₂ and O₃ Enrichment (FACE) facility. In addition, we examined how elevated CO₂ affected O₃ symptom development. Visible O₃ symptoms were consistently seen (5 out of 6 years) at two of the three sites along the O₃ gradient and where daily one-hour maximum concentrations were in the range of 96 to 125 ppb. Clonal differences in O₃ sensitivity were consistent with our OTC rankings. Elevated CO₂ (200 ppm over ambient and applied during daylight hours during the growing season) reduced visible foliar symptoms for all three clones from 31 to 96% as determined by symptom development in elevated O₃ versus elevated O₃ + CO₂ treatments. Degradation of the epicuticular wax surface of all three clones was found at the two elevated O₃ gradient sites. This degradation was quantified by a coefficient of occlusion which was a measure of stomatal occlusion by epicuticular waxes. Statistically significant increases in stomatal occlusion compared to controls were found for all three clones and for all treatments including elevated CO₂, elevated O₃, and elevated CO₂ + O₃. Our results provide additional evidence that current ambient O₃ levels in the Great Lakes region are causing adverse effects on trembling aspen. Whether or not elevated CO₂ in the future will alleviate some of these adverse effects, as occurred with visible symptoms but not with epicuticular wax degradation, is unknown.     

混种少花龙葵嫁接后代对镉胁迫枇杷幼苗光合生理的影响

采用盆栽试验,将4种少花龙葵嫁接后代分别和枇杷(大五星枇杷和川早枇杷)幼苗混种于镉含量为10 mg/kg的污染土壤中,研究了混种对两种植物光合生理的影响。结果表明:混种后,枇杷幼苗相应的叶绿素a含量、叶绿素b含量、叶绿素总量、净光合速率、蒸腾速率、胞间CO2浓度、气孔导度及可溶性糖含量均高于单种,叶表面蒸汽压亏缺降低;少花龙葵嫁接后代相应的SPAD值和净光合速率、蒸腾速率、胞间CO2浓度、气孔导度均高于单种,其可溶性糖含量较单种有所降低,混种大五星枇杷的少花龙葵嫁接后代的叶表面蒸汽压亏缺高于其单种,但混种少花龙葵嫁接后代的川早枇杷叶表面蒸汽压亏缺低于其单种。因此,少花龙葵嫁接后代混种枇杷可提高两种植物的光合作用,进而可促进两种植物的生长。