Influence of seedling roots, environmental factors and soil characteristics on soil CO2 efflux rates in a 2-year-old loblolly pine (Pinus taeda L.) plantation in the Virginia Piedmont

To understand the role of managed forests in carbon sequestration an understanding of factors controlling soil CO2 efflux will be necessary. This study examined the influence of seedling roots, environmental factors, nutrient availability, and soil characteristics on soil CO2 efflux patterns in a 2-year-old pine plantation in the Virginia Piedmont. Efflux rates were measured both near the base of seedlings and midway between rows in plots that had received fertilization and mulch treatments in a factorial combination. Soil CO2 efflux rates were consistently higher near the base of seedlings, fertilization increased seedling growth with no significant effect on rates. and mulching increased winter efflux rates. In a regression analysis of seasonal soil CO2 efflux, soil temperature explained 42.2% of the variance followed by the interaction of soil temperature and moisture and of soil temperature and plot position, which together explained an additional 9.8% of the observed variance in seasonal rates. During March 2000 measurements, the spatial pattern of soil CO2 efflux between plots was most influenced by differences in soil nitrogen and pine root biomass. Furthermore, spatial differences observed in mean annual efflux rates were found to be highly influenced by the amount of soil coarse fragments in the upper soil profile.     

Urban polluted forest soils induce elevated root peroxidase activity in Scots pine (Pinus sylvestris L.) seedlings.

Plant biomass. mycorrhizal status and root peroxidase activity were measured in ectomycorrhizal Scots pine (Pinus sylvestris L.) seedlings grown in urban polluted and native, non-polluted forest soils with added ammonium or potassium sulphates simulating N and S deposition of urban areas. Peroxidase activity in the fine roots of seedlings planted in polluted forest soils was higher than in those planted in non-polluted soils and correlated positively with the activities measured in an earlier study in the roots of mature Scots pines growing at the sites from where the soils were collected. Growth of seedlings and mycorrhizal status were not affected by the origin of soil. Exposing the seedlings to winter acclimation conditions for 6 weeks elevated peroxidase activity in the roots. The addition of ammonium or potassium sulphate to non-polluted soils did not induce elevated root peroxidase activity, although at the levels of 0.5 and 1.0 g of ammonium sulphate a slight increasing trend was observed. We suggest, that indirect biotic factors, i.e. changes in the community structure of soil fungi, early stages of recognition, and defence reactions of pine roots against saprophytic and pathogenic fungi may be participating in the elicitation of peroxidase (POD) activity, although the possible role of heavy metals cannot be excluded.     

Response of mycorrhizal Norway spruce seedlings to various nitrogen loads and sources

Norway spruce seedlings were grown under greenhouse conditions in Rootrainers with a vermiculite-peat moss mixture under various N-regimes for 6 months. Either ammonium or nitrate was applied in loads of 100 or 800 kg N ha(-1) year(-1) to seedlings which were either non-mycorrhizal or inoculated with the mycorrhizal fungi Hebeloma crustuliniforme or Laccaria bicolor. The use of increasing N loads enhanced shoot and total biomass, whereas root/shoot ratio, number of short roots and mycorrhization decreased. A significant enhancement of the concentration and content was obvious for the element N, whereas a significant decrease was obvious for P and Zn concentrations. The use of ammonium, as opposed to nitrate, significantly enhanced the biomass and the numbers of short roots, and reduced the root/shoot ratios, but did not influence the mycorrhization. It further significantly enhanced the N concentrations in roots and shoots. Fungal inoculation with H. crustuliniforme or L. bicolor compared to non-inoculated controls significantly enhanced shoot and total biomass, but reduced root/shoot ratios. The mycorrhization further significantly enhanced N and P concentrations and contents, but reduced Mn. Overall, the mycorrhization improved the P nutrition of the seedlings independently on the applied N loads or N sources. Dose response curves using ammonium nitrate as N source with a maximum load of 1600 kg N ha(-1) year(-1) applied on seedlings associated with H. crustuliniforme revealed that the maximum growth was reached at a load of 800 kg N ha(-1) year(-1) with a simultaneous decrease of the mycorrhization. In both shoots and roots, N concentrations increased constantly with increasing N loads, while P, Ca, and Zn concentrations decreased constantly.     

Foliar injury, leaf gas exchange and biomass responses of black cherry (Prunus serotina Ehrh.) half-sibling families to ozone exposure

Open pollinated families of black cherry seedlings were studied to determine genotypic differences in foliar ozone injury and leaf gas exchange in 1994 and growth response following three growing seasons. An O(3)-sensitive half-sibling family (R-12) and an O(3)-tolerant half-sibling family (MO-7) planted in natural soil were studied along with generic nursery stock (NS) seedlings. Ozone exposure treatments were provided through open top chambers and consisted of 50, 75, and 97% of ambient ozone, and open plots from May 9 to August 26, 1994. Ambient ozone concentrations reached an hourly peak of 88 ppb with 7-hour averages ranging from 39 to 46 ppb. Seedlings in the 50 and 75% of ambient chambers were never exposed to greater than 80 ppb O(3). Visible foliar ozone injury (stipple) was significantly higher for R-12 seedlings than MO-7 seedlings and increased with increasing ozone exposures. For the chamber treatments averaged over all families, there was no significant difference in stomatal conductance and net photosynthetic rates, but there was a significant decrease in root biomass, and a significant decrease in root/shoot ratio between the 50 and 97% of ambient chambers. Stomatal conductance and net photosynthetic rates were significantly different between families with R-12 seedlings generally greater than MO-7 seedlings. The R-12 seedlings had a 7.5 mmol m(-2) increase in ozone uptake compared to MO-7, and at the same cumulative O(3) exposure R-12 exhibited 40.9% stippled leaf area, whereas MO-7 had 9.2% stippled leaf area. Significant differences were observed in stem volume growth and total final biomass between the open-top chambers and open plots. Although R-12 had the most severe foliar ozone injury, this family had significantly greater stem volume growth and total final biomass than MO-7 and NS seedlings. Root:shoot ratio was not significantly different between MO-7 and R-12 seedlings.     

Ectomycorrhizal colonization of loblolly pine seedlings during three growing seasons in response to ozone, acidic precipitation, and soil Mg status

A three-year study was initiated in 1987 to evaluate the impact of O3, acidic precipitation, and soil Mg on ectomycorrhizal colonization of loblolly pine (Pinus taeda L.) seedlings. Thirty-six open-top chambers equipped with a rainfall exclusion/addition system were utilized to administer three levels of O3 (subambient, ambient, or twice ambient) and two precipitation acidity levels (pH 3.8 or 5.2) to seedlings growing in 24-liter plastic pots containing soil having either 35 or 15 mg kg(-1) of exchangeable Mg. Seedlings exposed to the twice ambient O3 treatment exhibited smaller percentages of total ectomycorrhizal short roots at the end of each year of the study, but trends were statistically significant in 1989 only. Changes in number of specific ectomycorrhizal morphotypes in response to O3 were not consistent from year to year. Acidic precipitation treatments had no effect on number or percent of mycorrhizal short roots, and responses of two morphotypes to soil Mg treatments were probably due to differences in the soil environment rather than a result of changes in aboveground processes. Temporal shifts in morphotype frequencies were observed for seedlings in all treatments and indicate that mycorrhizal succession occurred during the study period.     

Interactive effects of CO2 and O3 on a ponderosa pine plant/litter/soil mesocosm.

To study individual and combined impacts of two important atmospheric trace gases, CO2 and O3, on C and N cycling in forest ecosystems; a multi-year experiment using a small-scale ponderosa pine (Pinus ponderosa Laws.) seedling/soil/litter system was initiated in April 1998. The experiment was conducted in outdoor, sun-lit chambers where aboveground and belowground ecological processes could be studied in detail. This paper describes the approach and methodology used, and presents preliminary data for the first two growing seasons. CO2 treatments were ambient and elevated (ambient + 280 ppm). O3 treatments were elevated (hourly averages to 159 ppb, cumulative exposure > 60 ppb O3, SUM 06 approximately 10.37 ppm h), and a low control level (nearly all hourly averages <40 ppb. SUM 06 approximately 0.07 ppm h). Significant (P < 0.05) individual and interactive effects occurred with elevated CO2 and elevated O3. Elevated CO2 increased needle-level net photosynthetic rates over both seasons. Following the first season, the highest photosynthetic rates were for trees which had previously received elevated O3 in addition to elevated CO2. Elevated CO2 increased seedling stem diameters, with the greatest increase at low O3. Elevated CO2 decreased current year needle % N in the summer. For 1-year-old needles measured in the fall there was a decrease in % N with elevated CO2 at low O3, but an increase in % N with elevated CO2 at elevated O3. Nitrogen fixation (measured by acetylene reduction) was low in ponderosa pine litter and there were no significant CO2 or O3 effects. Neither elevated CO2 nor elevated O3 affected standing root biomass or root length density. Elevated O3 decreased the % N in coarse-fine (1-2 mm diameter) but not in fine (< 1 mm diameter) roots. Both elevated CO2 and elevated O3 tended to increase the number of fungal colony forming units (CFUs) in the AC soil horizon, and elevated O3 tended to decrease bacterial CFUs in the C soil horizon. Thus, after two growing seasons we showed interactive effects of O3 and CO2 in combination, in addition to responses to CO2 or O3 alone for a ponderosa pine plant/litter/soil system.     

The effects of elevated CO2 on clonal growth and nutrient content of submerge plant Vallisneria spinulosa

An approximately four months long glasshouse experiment was conducted to examine the effects of elevated carbon dioxide (CO(2)) concentration (1,000 +/- 50 micromol mol(-1)) in the atmosphere on biomass accumulation and allocation pattern, clonal growth and nitrogen (N), phosphorus (P) accumulation by the submerged plant Vallisneria spinulosa Yan. Elevated CO(2) significantly increased V. spinulosa total fresh biomass ( approximately 130%) after 120 days, due to more biomass accumulation in all morphological organs than in those at ambient CO(2) (390 +/- 20 micromol mol(-1)). About 75% of the additional total biomass at elevated CO(2) was accounted for by leaf and rhizome (above ground) biomass and only 25% of it belonged to root and turion (below ground). However, the turions biomass exhibited a greater increase rate than that of organ above ground, which caused reduction in the above/below ground biomass ratio. The clonal growth of V. spinulosa responded positively to elevated CO(2). The number of primary ramets increased up to 1.4-folds at elevated CO(2) and induced a dense growth pattern. For nutrients absorption, concentration of N in leaf and in turion was significantly (p 相似文献   

The effect of ozone on below-ground carbon allocation in wheat

Short-term (14)CO(2) pulse and chase experiments were conducted in order to investigate the effect of ozone on below-ground carbon allocation in spring wheat seedlings (Triticum aestivum L. 'ANZA'). Wheat seedlings were grown in a sand-hydroponic system and exposed to either high ozone (38-40 ppm-h) or low ozone (23-31 ppm-h) for 21 days in a series of replicated experiments. Following the ozone exposures, the plants were pulsed with (14)CO(2) and allocation of (14)C-labeled photosynthate was measured in the plant and growth media. Soluble root exudates were measured, without disturbing the plant roots, 24 h after the (14)CO(2) pulse. Shoot biomass was reduced by 17% for the high ozone and 9% for the low ozone exposures, relative to control treatments. Root biomass was reduced by 9% for the high ozone exposures, but was not significantly different than the controls for the low ozone. The amount of (14)C activity in the shoot and root tissue 24 h after the (14)CO(2) pulse, normalized to tissue weight, total (14)CO(2) uptake, or the total (14)C retention in each plant, was not affected by either high or low ozone exposures. The amount of (14)C activity measured in the growth media solution surrounding the roots increased 9% for the high ozone exposures, and after normalizing to root size or root (14)C activity, the growth media solution (14)C activity increased 29 and 40%, respectively. Total respiration of (14)CO(2) from the ozone-treated plants decreased, but the decrease was not statistically significant. Our results suggest that soluble root exudation of (14)C activity to the surrounding rhizosphere increases in response to ozone. Increased root exudation to the rhizosphere in response to ozone is contrary to reports of decreased carbon allocation below ground and suggests that rhizosphere microbial activity may be initially stimulated by plant exposure to ozone.     

Active carbon-pools in rhizosphere of wheat (Triticum aestivum L.) grown under elevated atmospheric carbon dioxide concentration in a Typic Haplustept in sub-tropical India

Study on active and labile carbon-pools can serve as a clue for soil organic carbon dynamics on exposure to elevated level of CO2. Therefore, an experimental study was conducted in a Typic Haplustept in sub-tropical semi-arid India with wheat grown in open top chambers at ambient (370 micromol mol-1) and elevated (600 micromol mol-1) concentrations of atmospheric CO2. Elevated atmospheric CO2 caused increase in yield and carbon uptake by all plant parts, and their preferential partitioning to root. Increases in fresh root weight, volume and length have also been observed. Relative contribution of medium-sized root to total root length increased at the expense of very fine roots at elevated CO2 level. All active carbon-fractions gained due to elevated atmospheric CO2 concentration, and the order followed their relative labilities. All the C-pools have recorded a significant increase over initial status, and are expected to impart short-to-medium-term effect on soil carbon sequestration.     

Uptake of selected PAHs from contaminated soils by rice seedlings (Oryza sativa) and influence of rhizosphere on PAH distribution

The uptake of selected polycyclic aromatic hydrocarbons (PAHs) by rice (Oryza sativa) seedlings from spiked aged soils was investigated. When applied to soils aged for 4 months, naphthalene, phenanthrene, and pyrene exhibited volatilization loss of 98, 95, and 30%, respectively, with the remaining fraction being fixed by soil organic matter and/or degraded by soil microbes. In general, concentrations of the three PAHs in rice roots were greater than those in the shoots. The concentrations of root associated PHN and PYR increased proportionally with both soil solution and rhizosphere concentrations. PAH concentrations in shoots were largely independent of those in soil solution, rice roots, or rhizosphere soil. The relative contributions of plant uptake and plant-promoted rhizosphere microbial biodegradation to the total mass balance were 0.24 and 14%, respectively, based on PYR concentrations in rhizosphere and non-rhizosphere soils, the biomass of rice roots, and the dry soil weight.     

Interaction between cadmium and atrazine during uptake by rice seedlings (Oryza sativa L.)

The uptake of atrazine by rice seedlings (Oryza sativa L.) through plant roots from nutrient solution was investigated in the presence and absence of Cd2+ over an exposure period of four weeks. It was found that both atrazine and Cd2+ were toxic to rice seedlings. Both shoot and root biomasses decreased when the seedlings were exposed to increasing atrazine or Cd2+ concentrations in nutrient solutions. In the absence of Cd2+, a linear relationship was observed between atrazine concentrations in roots/shoots and in external solution, and more atrazine is concentrated in roots than in shoots. When atrazine and Cd2+ concentrations in solution were maintained at mole ratio of 1:1, the accumulation of atrazine by seedlings was less and the seedling biomass was greater than found with other ratios, such as 1:2 or 2:1. Therefore, the formation of the complex between atrazine and Cd2+ reduced the individual toxicities. Analyses of data with the quasi-equilibrium partition model indicated that the atrazine concentrations in rice seedlings and external water were close to equilibrium. In the presence of Cd2+, however, the measured bioconcentration factor (BCF) of atrazine with roots and shoots were considerably greater. The latter findings resulted presumably from the atrazine-Cd2+ complex formation that led to a large apparent BCF.     

Adsorption and absorption of polycyclic aromatic hydrocarbons to rice roots

Rice roots and surrounding air, soil and water samples were collected for polycyclic aromatic hydrocarbon (PAH) analysis. The rice roots were separated into lateral roots and nodal roots, and the PAH concentration in the former was found to be higher than that in the latter. In addition, root physiological characteristics including root biotic mass, root lipid content and specific surface area are also discussed. When normalizing the total, adsorption and absorption PAH fractions on a dry root weight basis to root biomass, root lipid, and surface area bases respectively, the differences between PAHs in the two types of roots diminished by 2 to 3 times on average. Results from sequential extraction indicated that PAHs were more easily absorbed by interior rice roots than adsorbed on the surface. In addition, more than 60% of total PAHs accumulated in root tissue for both lateral and nodal roots. However, the results were highly related to the solvent used, extraction time and methodology. Correlation analysis between bioconcentration factors (root over environment) and K(OA), K(OW) showed water to be more significant for PAH adsorption in rice roots than other environmental media.     

Effect of bound residues of metsulfuron-methyl in soil on rice growth

A pot experiment was conducted to appraise the hazards of bound residues of metsulfuron-methyl in soil at six levels (0, 0.050, 0.089, 0.158, 0.281, and 0.500 mg kg(-1)) to the growth of four rice varieties (Xiushui 63, Eryou 810, Liangyoupeijiu, and Zhenong 952). The morphological characteristics of rice roots like root number, total length, surface area of rice roots, and rice biomass were determined. The results showed that the bound residues of metsulfuron-methyl in soil impacted the growth of rice. Root number, total length of roots, surface area of roots, and biomass were restrained by bound residues of metsulfuron-methyl in soil. The inhibition rate of root growth increased from 69.46-81.32% to 85.18-95.97% with the increasing of levels of bound residues of metsulfuron-methyl from 0.05 mg kg(-1) to 0.50 mg kg(-1). The number of rice roots could be taken as a sensitive index to screen the rice varieties endurable to bound residues of metsulfuron-methyl in soil and to predict the potential hazards of bound residues of metsulfuron-methyl in soil to rice. The level of bound residues of metsulfuron-methyl in soil causing the root numbers decreased by 50% (IC50) followed the order of Xiushui 63 < Eryou 810 < Liangyoupeijiu < Zhenong 952.     

Effects of host plant exposure to cadmium on mycorrhizal infection and soluble carbohydrate levels of Pinus sylvestris seedlings

In a Cd-contaminated environment, not only mature trees but also their seeds and young seedlings can be exposed to Cd. Cadmium taken up by young seedlings may influence mycorrhizal infection, which might in turn influence resistance to Cd toxicity. In order to eliminate soil-mediated responses of mycorrhizal infection to Cd, Pinus sylvestris seedlings were exposed to Cd prior to fungal inoculation and replanted to clean substrates with fungal inoculum. Cadmium pretreatment reduced the proportion of living mycorrhizal short roots of seedlings inoculated with Paxillus involutus. However, no such effect was observed for seedlings inoculated with Suillus bovinus and Rhizopogon subcaerulescens. Therefore, infection by P. involutus appeared to be affected by Cd taken up by seedlings. Overall stem length and biomass of the seedlings were reduced by Cd pretreatment. Infection by S. bovinus and R. subcaerulescens increased stem length and biomass of the seedlings. Root soluble carbohydrate concentrations were lower in mycorrhizal seedlings than non-mycorrhizal seedlings.     

Arbuscular mycorrhizae enhance metal lead uptake and growth of host plants under a sand culture experiment

A sand culture experiment was conducted to investigate whether mycorrhizal colonization and mycorrhizal fungal vesicular numbers were influenced by metal lead, and whether mycorrhizae enhance host plants tolerance to metal lead. Metal lead was applied as Pb(NO3)2 in solution at three levels (0, 300 and 600 mg kg(-1) sand). Five mycorrhizal host plant species, Kummerowia striata (Thunb.) Schindl, Ixeris denticulate L., Lolium perenne L., Trifolium repens L. and Echinochloa crusgalli var. mitis were used to examine Pb-mycorrhizal interactions. The arbuscular mycorrhizal inoculum consisted of mixed spores of mycorrhizal fungal species directly isolated from orchard soil. Compared to the untreated control, both Pb concentrations reduced mycorrhizal colonization by 3.8-70.4%. Numbers of AM fungal vesicles increased by 13.2-51.5% in 300 mg Pb kg(-1) sand but decreased by 9.4-50.9% in 600 mg Pb kg(-1) sand. Mycorrhizae significantly enhanced Pb accumulation both in shoot by 10.2-85.5% and in root by 9.3-118.4%. Mycorrhizae also enhanced shoot biomass and shoot P concentration under both Pb concentrations. Root/shoot ratios of Pb concentration were higher in highly mycorrhizal plant species (K.striata, I. denticulate, and E. crusgalli var. mitis) than that in poorly mycorrhizal ones (L. perenne and T. repens,). Mycorrhizal inoculation increased the root/shoot ratio of Pb concentration of highly mycorrhizal plant species by 7.6-57.2% but did not affect the poorly mycorrhizal ones. In the treatments with 300 Pb mg kg(-1) sand, plant species with higher vesicular numbers tended to show higher root/shoot ratios of the Pb concentration. We suggest that under an elevated Pb condition, mycorrhizae could promote plant growth by increasing P uptake and mitigate Pb toxicity by sequestrating more Pb in roots.     

Productivity responses of Acer rubrum and Taxodium distichum seedlings to elevated CO2 and flooding

Elevated levels of atmospheric CO2 are expected to increase photosynthetic rates of C3 tree species, but it is uncertain whether this will result in an increase in wetland seedling productivity. Separate short-term experiments (12 and 17 weeks) were performed on two wetland tree species, Taxodium distichum and Acer rubrum, to determine if elevated CO2 would influence the biomass responses of seedlings to flooding. T. distichum were grown in replicate glasshouses (n = 2) at CO2 concentrations of 350 or 700 ppm. and A. rubrum were grown in growth chambers at CO2 concentrations of 422 or 722 ppm. Both species were grown from seed. The elevated CO2 treatment was crossed with two water table treatments, flooded and non-flooded. Elevated CO2 increased leaf-level photosynthesis, whole-plant photosynthesis, and trunk diameter of T. distichum in both flooding treatments, but did not increase biomass of T. distichum or A. rubrum. Flooding severely reduced biomass, height, and leaf area of both T. distichum and A. rubrum. Our results suggest that the absence of a CO2-induced increase in growth may have been due to an O2 limitation on root production even though there was a relatively deep (approximately 10 cm) aerobic soil surface in the non-flooded treatment.     

Antioxidant responses to simulated acid rain and heavy metal deposition in birch seedlings

This study measured the responses of different anti-oxidants in 2-year-old birch (Betula pendula Roth) seedlings subjected to simulated acid rain (pH 4.0) and heavy metals (Cu/Ni), applied alone or in combination for 2 months. The applied concentrations of pollutants did not significantly affect seedling biomass or total glutathione levels. Acid rain alone increased superoxide dismutase (SOD) activity both in leaves and roots, while heavy metals alone inhibited SOD activity in roots. Both acid rain and heavy metals applied singly increased ascorbate peroxidase (APX) and guaiacol peroxidase (GPX) activities in leaves but decreased activities in roots. In contrast, acid rain and heavy metal treatments increased glutathione reductase (GR) activity in roots but not in leaves. Spraying birch seedlings with a mixture of acid rain and heavy metals increased SOD, APX and GPX activities in leaves and GR activity in roots. However, the effects of mixed pollutants on enzyme activities usually were less than the summed effects of individual pollutants. Enzyme responses also depended on where pollutants were applied: spraying pollutants onto the shoots initiated higher responses in SOD, APX and GPX than did application to the soil surface, while the opposite was true for GR.     

Differences in responses of summer and winter spinach to elevated UV-B at varying soil NPK levels

Seasonal variations in response of spinach to elevated ultraviolet-B (UV-B) during summer and winter were assessed with respect to growth, biomass, yield, NPK uptake and NPK use efficiencies at varying NPK levels. The nutrient amendments were recommended NPK (RNPK) and 1.5 times recommended NPK (1.5 RNPK). Season significantly affected the measured parameters except the number of leaves. Under ambient UV-B, the growth performance of summer spinach was better in both the NPK levels, higher being at 1.5 RNPK leading to higher nutrient uptake. However, more reduction in biomass under elevated UV-B in 1.5 RNPK was recorded during summer, while during winter in RNPK. Reduction in biomass under elevated UV-B was accompanied by the modification in its partitioning with more biomass allocation to root during summer compared to winter at both the NPK levels. NPK uptake was higher in summer, while NPK use efficiencies were higher during winter. At higher than recommended NPK level, better NPK use efficiencies were displayed during both the seasons. Increased NPK supply during winter enabled spinach to capitalize light more efficiently and hence increased biomass accumulation. Strategies for surviving elevated UV-B in winter differ from those that provided protection from the same stress when it occurs in summer.     

Rape (Brassica chinensis L.) seed germination, seedling growth, and physiology in soil polluted with di-n-butyl phthalate and bis(2-ethylhexyl) phthalate

Phthalic acid esters (PAEs) pollution in agricultural soils caused by widely employed plastic products is becoming more and more widespread in China. PAEs polluted soil can lead to phytotoxicity in higher plants and potential health risks to human being. We evaluated the individual toxicity of di-n-butyl phthalate (DnBP) and bis(2-ethylhexyl) phthalate (DEHP), two representative PAEs, to sown rape (Brassica chinensis L.) seeds within 72 h (as germination stage) and seedlings after germination for 14 days by monitoring responses and trends of different biological parameters. No significant effects of six concentrations of PAE ranging from 0 (not treated/NT) to 500 mg?kg^?1 on germination rate in soil were observed. However, root length, shoot length, and biomass (fresh weight) were inhibited by both pollutants (except root length and biomass under DEHP). Stimulatory effects of both target pollutants on malondialdehyde (MDA) content, superoxide dismutase (SODase) activity, ascorbate peroxidase (APXase) content, and polyphenoloxidase (PPOase) activity in shoots and roots (SODase activity in shoots excluded) were in the same trend with the promotion of proline (Pro) but differed with acetylcholinesterase activity (except in shoots under DnBP) for analyzed samples treated for 72 h and 14 days. Responses of representative storage compounds free amino acids (FAA) and total soluble sugar (TSS) under both PAEs were raised. Sensitivity of APXase and Pro in roots demonstrates their possibility in estimation of PAE phytotoxicity and the higher toxicity of DnBP, which has also been approved by the morphological photos of seedlings at day 14. Higher sensitivity of the roots was also observed. The recommended soil allowable concentration is 5 mg DnBP?kg^?1 soil for the development of rape. We still need to know the phytotoxicity of DEHP at whole seedling stage for both the growing and development; on the other hand, soil criteria for PAE compounds are urgently required in China.     

Effects of sulfur dioxide on growth, photosynthesis and enzyme activities of Chinese Guger-Tree seedlings

The Chinese Guger-Tree (Schima superba Gard et Champ var. superba) is an important harwood species in Taiwan where the ambient SO(2) concentration in some areas is high. Seedlings were raised in field chambers with and without SO(2) to determine whether this species is affected by this pollutant. After 4 weeks of exposure to 325 ppb of SO(2), the photosynthetic rate of seedlings decreased immediately. During the fumigation period, stem height growth was not inhibited, however, the stem diameter growth was reduced significantly. The dry weight of leaves was unchanged, while stem, root and total seedling weight were lower than those of control plants. Sulfhydryl groups in leaves increased by 75%, whereas they did not change in roots following SO(2) uptake. Superoxide dismutase in leaves did not change, however, peroxidase activity increased significantly. Results suggest that ambient SO(2) in some areas in Taiwan may affect the physiology and growth of the Chinese Guger-Tree.