An overview of the direct and indirect effects of acid rain on plants: Relationships among acid rain, soil, microorganisms, and plants

Acid rain (AR) causes numerous environmental problems and complex negative effects on plants globally. Many studies have previously reported on direct effects of AR or its depositional substances on plant injury and performance. However, few studies have addressed the indirect effects of AR on plants as mediated by soil microorganisms and the abiotic environment of the soil rhizosphere. The indirect effects (e.g., AR → soil microorganisms→plants) need greater attention, because acidic deposition not only affects the distribution, composition, abundance, function, and activity of plant-associated microorganisms, but also influences the dynamics of some substances in the soil in a way that may be harmful to plants. Therefore, this review not only focused on the direct effects of AR on plant performance, growth, and biomass allocations from a whole-plant perspective, but also addressed the pathway of AR-soil chemical characteristics-plants, which explains how soil solute leaching and acidification by AR will reduce the availability of essential nutrients and increase the availability of heavy metals for plants, affecting carbon and nitrogen cycles. Mainly, we evaluated the AR-soil microorganisms-plants pathway by: 1) synthesizing the potential roles of soil microbes in alleviating soil acidic stress on plants and the adverse effects of AR on plant-associated soil microorganisms; 2) exploring how plant mycorrhizal types affect the detection of AR effect on plants. The meta-analysis showed that the effects of AR-induced pH on leaf chlorophyll content, plant height, and plant root biomass were dependent on plant mycorrhizal types. Some possible reasons for different synergy between mycorrhizal symbiotic types and plants were discussed. Future research relating to the effects of AR on plants should focus on the combined direct and indirect effects to evaluate how AR affects plant performance comprehensively.

Modification of plasma membrane H+-ATPase in Masson pine (Pinus massoniana Lamb.) seedling roots adapting to acid deposition

To understand the regulation of roots plasma membrane H+-ATPase in Masson pine responding to acid deposition, the changes in biomass, plant morphology, intracellular H+, enzyme activity and H+-ATPase genes expression in Masson pine seedlings exposed to simulated acid rain (SAR, pH 5.6 and 4.6) with and without vanadate were studied. Simulated acid rain exposure for 60 days increased the intracellular H+ in pine roots whether added with 0.1 mM Na3VO4 or not. The growth of seedlings treated with SAR was maintained well, even the primary lateral root length, root dry weight and number of root tips in seedlings exposed to SAR at pH 4.6 were higher than that of the control (pH 6.6). However, the addition of vanadate resulted in severe growth inhibition and obvious decline in morphological parameters. Similarly, ATP hydrolytic activity and H+ transport activity of roots plasma membrane H+-ATPase, both were stimulated by SAR whereas they were inhibited by vanadate, and the highest activity stimulation was observed in pine roots subjected to SAR at pH 4.6. In addition, SAR also induced the expression of the investigated H+-ATPase subunits (atpB, atpE, atpF, atpH and atpI). Therefore, the roots plasma membrane H+-ATPase is instrumental in the growth of Masson pine seedlings adapting to acid rain by a manner of pumping more protons across the membrane through enhancing its activity, and which involves the upregulated gene expression of roots H+-ATPase subunits at transcriptional level.

Exogenous Ca2+ enhances antioxidant defense in rice to simulated acid rain by regulating ascorbate peroxidase and glutathione reductase

Exogenous calcium enhances rice tolerance to acid rain stress by regulating isozymes composition and transcriptional expression of ascorbate peroxidase and glutathione reductase. Calcium (Ca) participates in signal transduction in plants under abiotic stress, and addition of Ca²⁺ is beneficial to alleviate damage of plants caused by acid rain. To clarify the effect of exogenous Ca²⁺ on tolerance of plants to acid rain stress, we investigated regulation of Ca²⁺ (5 mM) on activities, isozymes composition and transcriptional expression of ascorbate peroxidase (APX) and glutathione reductase (GR), redox state, and H₂O₂ concentration and growth in rice leaves and roots under simulated acid rain (SAR) stress. SAR (pH 3.5/2.5) decreased the total activities of APX and GR in rice by decreasing the concentration of APX isoforms (APXII in leaves and APXIII in roots) as well as activation degree of GR isozymes and transcription level of GR1, indicating that SAR (pH 3.5/2.5) destroyed the redox state in rice cells and induced H₂O₂ excessive accumulation, and inhibited growth of rice. Exogenous Ca²⁺ alleviated SAR-induced inhibition on activities of APX and GR by regulating the concentration, activation, and transcription of their isozymes, and then maintained the redox level of cells and protected cells from oxidative damage, being beneficial to the growth of rice. Therefore, the promotion of exogenous Ca²⁺ on activities of APX and GR can be important to enhance rice tolerance to acid rain by maintaining redox state and avoiding oxidative damage.

Calcium regulates antioxidative isozyme activity for enhancing rice adaption to acid rain stress

Acid rain, as a typical abiotic stress, damages plant growth and production. Calcium (Ca) mediates plant growth and links the signal transduction in plants for adapting to abiotic stresses. To understand the effect of Ca²⁺ on plant adaptable response to acid rain, we investigated changes in activities and gene expression of antioxidative enzymes and fatty acid composition of membrane lipid in rice seedlings treated with exogenous Ca²⁺ (5 mM) or/and simulated acid rain (SAR, pH 3.5 / 2.5). Exogenous Ca²⁺ enhanced activities of superoxide dismutase, catalase and peroxidase isozymes in rice leaves under SAR stress by promoting activation of existing isoforms and up-regulation of Cu/Zn-SOD1, Cu/Zn-SOD2, Cu/Zn-SOD3, CAT1, CAT2 and POD1. Compared to SAR treatment alone, exogenous Ca²⁺ alleviated SAR-induced oxidative damage to cell membrane by enhancing antioxidative capacity, as shown by the decrease in concentrations of H₂O₂, O₂^- and malondialdehyde in rice leaves. Meanwhile, Ca²⁺ alleviated SAR-induced decrease in unsaturation of membrane lipid for maintaining membrane fluidity. Finally, exogenous Ca²⁺ alleviated SAR-induced inhibition on relative growth rate of rice. Therefore, Ca²⁺ could play a role in regulating activities of antioxidative enzymes as well as maintaining unsaturation of membrane lipid for enhancing tolerance in rice seedlings to acid rain stress.

The legacy from the 50 years of acid rain research, forming present and future research and monitoring of ecosystem impact : This article belongs to Ambio's 50th Anniversary Collection. Theme: Acidification

Acid rain and acidification research are indeed a multidisciplinary field. This field evolved from the first attempts to mitigate acid freshwater in the 1920s, then linking acid rain to the acidification in late 1950s, to the broad project-concepts on cause and effect from the late 1960s. Three papers from 1974, 1976 and 1988 demonstrate a broad approach and comprise scientific areas from analytical chemistry, biochemistry, limnology, ecology, physiology and genetics. Few, if any, environmental problems have led to a public awareness, political decisions and binding limitations as the story of acid rain. Acid precipitation and acidification problems still exist, but at a lower pressure, and liming has been reduced accordingly. However, the biological responses in the process of recovery are slow and delayed. The need for basic science, multidisciplinary studies, long time series of high-quality data, is a legacy from the acid rain era, and must form the platform for all future environmental projects.

Environmental impacts of nitrogen emissions in China and the role of policies in emission reduction

Atmospheric reactive nitrogen (N_r) has been a cause of serious environmental pollution in China. Historically, China used too little N_r in its agriculture to feed its population. However, with the rapid increase in N fertilizer use for food production and fossil fuel consumption for energy supply over the last four decades, increasing gaseous N_r species (e.g. NH₃ and NO_x) have been emitted to the atmosphere and then deposited as wet and dry deposition, with adverse impacts on air, water and soil quality as well as plant biodiversity and human health. This paper reviews the issues associated with this in a holistic way. The emissions, deposition, impacts, actions and regulations for the mitigation of atmospheric N_r are discussed systematically. Both NH₃ and NO_x make major contributions to environmental pollution but especially to the formation of secondary fine particulate matter (PM_2.5), which impacts human health and light scattering (haze). In addition, atmospheric deposition of NH₃ and NO_x causes adverse impacts on terrestrial and aquatic ecosystems due to acidification and eutrophication. Regulations and practices introduced by China that meet the urgent need to reduce N_r emissions are explained and resulting effects on emissions are discussed. Recommendations for improving future N management for achieving 'win-win' outcomes for Chinese agricultural production and food supply, and human and environmental health, are described. This article is part of a discussion meeting issue 'Air quality, past present and future'.

Melatonin-mediate acid rain stress tolerance mechanism through alteration of transcriptional factors and secondary metabolites gene expression in tomato

Acid rain is a widespread environmental issue intensely affecting normal plant growth of crops. Melatonin is well known pleiotropic molecule which improves abiotic and biotic stress tolerance of plants through physiological and molecular mediation. However, the impact of exogenous melatonin on molecular activities under acid rain conditions in plants has never been studied. The objective of the study is to expose the possible role of exogenous melatonin on physiological and molecular changes against acid rain stress in tomato. Transcriptome profile through RNA-sequence analysis identified 1228, 1120 and 1537 differentially expressed genes (DEGs) in control plant (Ctr) vs simulated acid rain stressed plant (P25) comparison, control plant vs melatonin treatment in simulated acid rain stressed plant (P25M) comparison and P25 vs P25M comparison, respectively. Among them, 152 differentially expressed genes (DEGs) were commonly expressed and the expression of secondary metabolites related gene was noticeably observed in all comparison. Moreover, transcript families such as ERF, WRKY, MYB and bZIP related gene accounted more in all treatment comparison. The RNA-sequence and qPCR results indicated that exogenous melatonin is closely associated with acid rain stress moderator and might be involved in alteration of differentially expressed genes (DEGs), biosynthesis of plant secondary metabolites and transcriptional factor encoding genes expression which might have potential application against environmental hazardous conditions.

Simulated sulfuric and nitric acid rain inhibits leaf breakdown in streams: A microcosm study with artificial reconstituted fresh water

Acid rain containing SO₄^2- and NO₃^- in China has been a public concern for decades. However, a decrease of SO₂ has been recorded since the government enacted a series of policies to control its emission. To comprehensively evaluate the consequence of realistic and future acid deposition scenarios, this study explored the effects of mixed acid rain with different molar ratios of SO₄^2- and NO₃^- (0:1, 1:0, 2:1, 1:1, and 1:2) on stream leaf breakdown through a microcosm experiment. A significant inhibition of leaf breakdown rate was observed when the ratio was 1:2 with reduced microcosm pH, fungal biomass, enzyme activities as well as the frequencies of hub general in the fungal community. In conclusion, the ratio of SO₄^2- and NO₃^- in acid rain was an important factor that could have a profound impact on leaf breakdown, even on ecosystem structure and functioning of streams.

Physiological effects of the combined stresses of freezing-thawing, acid precipitation and deicing salt on alfalfa seedlings

BACKGROUND

Frequent freeze-thaw phenomena, together with widely used deicing salt and intense acid precipitation, often occur in northeastern China, causing damage to various aspects of plants, such as the permeability of biological membranes, osmotic adjustment, and photosystems. Aiming to explore the resistance of alfalfa to freezing-thawing (F), acid precipitation (A) and deicing salt (D), this study used Medicago sativa cv. Dongmu-70 as the experimental material, and the contents of malondialdehyde (MDA), soluble protein, soluble sugars, proline and chlorophyll were evaluated.

RESULTS

As the temperature decreased, the MDA content in the seedlings of the group under combined stress (A-D-F) increased and was significantly higher than that of group F (by 69.48 ~ 136.40%). Compared with those in the control (CK) group, osmotic substances such as soluble sugars and proline in the treatment groups were higher, while the soluble protein content was lower. The chlorophyll contents in the seedlings of the treatment groups were lower than those of the CK group; however, the chlorophyll content displayed a non-significant change during the free-thaw cycle.

CONCLUSION

Injury to the permeability of the biological membranes and photosystems of alfalfa results from stress. Moreover, alfalfa maintains osmotic balance by adaptively increasing the potential of osmotic substances such as soluble sugars and proline. Furthermore, the influence of stress from freezing-thawing and deicing salt is highly substantial, but the combined stresses of acid precipitation with the two factors mentioned above had little effect on the plants.

Physiological responses of Elaeocarpus glabripetalus seedlings exposed to simulated acid rain and cadmium

Combined effects of cadmium (Cd) and acid rain on physiological characteristics in Eleocarpus glabripetalus seedlings were investigated under controlled conditions. The single Cd treatment and the combined Cd and acid rain treatment increased growth at low Cd concentrations, while decreased growth and photosynthesis at high Cd²⁺ concentrations. A low Cd²⁺ concentration (50 mg kg^-1) combined with different acid rain treatments increased the seedling biomass. A high Cd²⁺ concentration (100 mg kg^-1) under different acid rain treatments significantly decreased the biomass, the Fe content, chlorophyll fluorescence and photosynthetic parameters. Relative electric conductivity, malondialdehyde (MDA) content and peroxidase (POD) activity were increased while the reduced glutathione (GSH) content and catalase (CAT) activity were significantly lower at high Cd²⁺ concentration under acid rain. The results indicated that the combination of a high concentration of Cd²⁺ and acid rain aggravated the toxic effect of Cd²⁺ or acid rain alone on the growth and physiological parameters of E. glabripetalus due to serious damage to the chloroplast structure. These results provide novel insights into the combined effects of Cd²⁺and acid rain on woody plants and might also serve as a guide to evaluate forest restoration and biological safety in areas with Cd²⁺and acid rain pollution.

Melatonin, glutathione and thiourea attenuates lead and acid rain-induced deleterious responses by regulating gene expression of antioxidants in Trigonella foenum graecum L

Lead and acid rain are important abiotic stress factors that limit the growth, development, metabolic activity and yield of the crops. Melatonin (MT; an indoleamine molecule), glutathione (GSH; free thiol tripeptide) and thiourea (TU; non physiological thiol based ROS scavenger) have been known to mediate several physiological, biochemical and molecular processes in plants under different kinds of environmental threats. However, the roles of MT, GSH and TU in stress tolerance against combined effect of lead and simulated acid rain (SAR) remains inexpressible. In this study, we investigated the response of Trigonella foenum graecum L. (Fenugreek) to combined application of lead (1200 ppm) and SAR (pH 3.5), and the potential roles of MT (50 μM), GSH (1 mM) and TU (3 mM) in enhancing lead and SAR stress tolerance of Fenugreek. The results showed that co-application of each MT, GSH and TU along with lead and SAR improved the growth and development of seedlings. Moreover, MT, GSH and TU treatments stabilized the cell membrane integrity, reduced ROS accumulation [superoxide radical (O₂-) and hydrogen peroxide (H₂O₂)], malondialdehyde (MDA) content, lipoxygenase (LOX) activity and, enhanced protein accumulation and up-regulated the gene expressions of catalase (CAT) and superoxide dismutase (SOD) significantly. Furthermore, the present work provides strong evidence regarding protective roles of MT, GSH and TU against oxidative stress resulted from lead and SAR stress in Fenugreek. Considering these observations, MT, GSH and TU can be utilized as efficient ROS scavengers, for improving growth and increasing antioxidant capacity in lead and SAR stressed seedlings.

Effect of exogenous abscisic acid on morphology, growth and nutrient uptake of rice (Oryza sativa) roots under simulated acid rain stress

Application of proper ABA can improve acid tolerance of rice roots by balancing endogenous hormones and promoting nutrient uptake. Abscisic acid (ABA) has an important signaling role in enhancing plant tolerance to environmental stress. To alleviate the inhibition on plant growth and productivity caused by acid rain, it is crucial to clarify the regulating mechanism of ABA on adaptation of plants to acid rain. Here, we studied the effects of exogenously applied ABA on nutrients uptake of rice roots under simulated acid rain (SAR) stress from physiological, biochemical and molecular aspects. Compared to the single SAR treatment (pH 4.5 or 3.5), exogenous 10 μM ABA alleviated the SAR-induced inhibition of root growth by balancing endogenous hormones (abscisic acid, indole-3-acetic acid, gibberellic acid and zeatin), promoting nutrient uptake (nitrate, P, K and Mg) in rice roots, and increasing the activity of the plasma membrane H⁺-ATPase by up-regulating expression levels of genes (OSA2, OSA4, OSA9 and OSA10). However, exogenous 100 μM ABA exacerbated the SAR-caused inhibition of root growth by disrupting the balance of endogenous hormones, and inhibiting nutrient uptake (nitrate, P, K, Ca and Mg) through decreasing the activity of the plasma membrane H⁺-ATPase. These results indicate that proper concentration of exogenous ABA could enhance tolerance of rice roots to SAR stress by promoting nutrients uptake and balancing endogenous hormones.

Elevated nitrogen metabolism and nitric oxide production are involved in Arabidopsis resistance to acid rain

Acid rain (AR) can induce great damages to plants and could be classified into different types according to the different SO₄^2-/NO₃^- ratio. However, the mechanism of plants' responding to different types of AR has not been elucidated clearly. Here, we found that nitric-rich simulated AR (N-SiAR) induced less leaves injury as lower necrosis percentage, better physiological parameters and reduced oxidative damage in the leaves of N-SiAR treated Arabidopsis thaliana compared with sulfate and nitrate mixed (SN-SiAR) or sulfuric-rich (S-SiAR) simulated AR treated ones. Of these three types of SiAR, N-SiAR treated Arabidopsis maintained the highest of nitrogen (N) content, nitrate reductase (NR) and nitrite reductase (NiR) activity as well as N metabolism related genes expression level. Nitric oxide (NO) content showed that N-SiAR treated seedlings had a higher NO level compared to SN-SiAR or S-SiAR treated ones. A series of NO production and elimination related reagents and three NO production-related mutants were used to further confirm the role of NO in regulating acid rain resistance in N-SiAR treated Arabidopsis seedlings. Taken together, we concluded that an elevated N metabolism and enhanced NO production are involved in the tolerance to different types of AR in Arabidopsis.

Effects of rare earth and acid rain pollution on plant chloroplast ATP synthase and element contents at different growth stages

Combined rare earth and acid rain pollution has become a new environmental problem, seriously affecting plant survival. The effects of these two kinds of pollutants on plant photosynthesis have been reported, but the micro mechanisms are not very clear. In this research, we studied the effects of lanthanum [La(III), 0.08, 1.20 and 2.40 mM] and acid rain (pH value = 2.5, 3.5 and 4.5) on the ATPase activity and gene transcription level and the functional element contents in rice leaf chloroplasts. The results showed that the combined 0.08 mM La(III) and pH 4.5 acid rain increased the ATPase activity and gene transcription level as well as contents of some functional elements. But other combined treatments of acid rain and La(III) reduced the ATPase activity and gene transcription level as well as functional element contents. The change magnitude of the above indexes at rice booting stage was greater than that in seedling stage or grain filling stage. These results reveal that effects of La(III) and acid rain on ATPase activity and functional element contents in rice leaf chloroplasts are related to the combination of La(III) dose and acid rain intensity and the plant growth stage. In addition, the changes in the ATPase activity were related to ATPase gene transcription level. This study would provide a reference for understanding the microcosmic mechanism of rare earth and acid rain pollution on plant photosynthesis and contribute to evaluate the possible environmental risks associated with combined La(III) and acid rain pollution.

ONE SENTENCE SUMMARY

The effects of La(III) and acid rain on activity and gene transcription level of rice chloroplast ATPase and contents of functional elements were different at different growth stages.

Direct effect of acid rain on leaf chlorophyll content of terrestrial plants in China

Anthropogenic emissions of acid precursors in China have resulted in widespread acid rain since the 1980s. Although efforts have been made to assess the indirect, soil mediated ecological effects of acid rain, a systematic assessment of the direct foliage injury by acid rain across terrestrial plants is lacking. Leaf chlorophyll content is an important indicator of direct foliage damage and strongly related to plant productivity. We synthesized data from published literature on experiments of simulated acid rain, by directly exposing plants to acid solutions with varying pH levels, to assess the direct effect of acid rain on leaf chlorophyll content across 67 terrestrial plants in China. Our results indicate that acid rain substantially reduces leaf chlorophyll content by 6.71% per pH unit across the recorded plant species. The direct reduction of leaf chlorophyll content due to acid rain exposure showed no significant difference across calcicole, ubiquist or calcifuge species, implying that soil acidity preference does not influence the sensitivity to leaf injury by acid rain. On average, the direct effects of acid rain on leaf chlorophyll on trees, shrubs and herbs were comparable. The effects, however varied across functional groups and economic use types. Specifically, leaf chlorophyll content of deciduous species was more sensitive to acid rain in comparison to evergreen species. Moreover, vegetables and fruit trees were more sensitive to acid rain than other economically used plants. Our findings imply a potential production reduction and economic loss due to the direct foliage damage by acid rain.

Analysis of the combined effects of lanthanum and acid rain, and their mechanisms, on nitrate reductase transcription in plants

Rare earth element (REE) pollution and acid rain are major global environmental concerns, and their spatial distributions overlap. Thus, both forms of pollution combine to act on plants. Nitrogen is important for plant growth, and nitrate reductase (NR) is a key plant enzyme that catalyzes nitrogen assimilation. Studying the combined effects of REEs and acid rain on plant nitrogen-based nutrients has important environmental significance. Here, soybean (Glycine max) plants, commonly used for toxicological studies, were exposed to lanthanum (La), a REE, and acid rain to study the NR activities and NR transcriptional levels in the roots. To explain how the pollution affected the NR transcriptional level, we simultaneously observed the contents of intracellular La and nutrient elements, protoplast morphology, membrane lipid peroxidation and intracellular pH. A combined treatment of 0.08mmol/L La and pH 4.5 acid rain increased the NR activity, decreased the NR transcriptional level, increased the intracellular nutrient elements' contents and caused deformations in membrane structures. Other combined treatments significantly decreased the aforementioned parameters and caused serious damage to the membrane structures. The variation in the amplitudes of combined treatments was greater than those of individual treatments. Compared with the control and individual treatments, combined treatments increased membrane permeability, the malondialdehyde content, and intracellular H+ and La contents, and with an increasing La concentration or acid strength, the change in amplitude increased. Thus, the combined effects on NR gene transcription in soybean seedling roots were related to the intracellular nutrient elements' contents, protoplast morphology, membranous lipid peroxidation, intracellular pH and La content.

Effects of simulated acid rain on soil respiration and its components in a subtropical mixed conifer and broadleaf forest in southern China

Soil respiration is a major pathway in the global carbon cycle and its response to environmental changes is an increasing concern. Here we explored how total soil respiration (RT) and its components respond to elevated acid rain in a mixed conifer and broadleaf forest, one of the major forest types in southern China. RT was measured twice a month in the first year under four treatment levels of simulated acid rain (SAR: CK, the local lake water, pH 4.7; T1, water pH 4.0; T2, water pH 3.25; and T3, water pH 2.5), and in the second year, RT, litter-free soil respiration (RS), and litter respiration (RL) were measured simultaneously. The results indicated that the mean rate of RT was 2.84 ± 0.20 μmol CO2 m(-2) s(-1) in the CK plots, and RS and RL contributed 60.7% and 39.3% to RT, respectively. SAR marginally reduced (P = 0.08) RT in the first year, but significantly reduced RT and its two components in the second year (P < 0.05). The negative effects were correlated with the decrease in soil microbial biomass and fine root biomass due to soil acidification under the SAR. The temperature coefficients (Q10) of RT and its two components generally decreased with increasing levels of the SAR, but only the decrease of RT and RL was significant (P < 0.05). In addition, the contribution of RL to RT decreased significantly under the SAR, indicating that RL was more sensitive to the SAR than RS. In the context of elevated acid rain, the decline trend of RT in the forests in southern China appears to be attributable to the decline of soil respiration in the litter layer.

Effects of acidic deposition on in-lake phosphorus availability: a lesson from lakes recovering from acidification

Lake water concentrations of phosphorus (P) recently increased in some mountain areas due to elevated atmospheric input of P rich dust. We show that increasing P concentrations also occur during stable atmospheric P inputs in central European alpine lakes recovering from atmospheric acidification. The elevated P availability in the lakes results from (1) increasing terrestrial export of P accompanying elevated leaching of dissolved organic carbon and decreasing phosphate-adsorption ability of soils due to their increasing pH, and (2) decreasing in-lake P immobilization by aluminum (Al) hydroxide due to decreasing leaching of ionic Al from the recovering soils. The P availability in the recovering lakes is modified by the extent of soil acidification, soil composition, and proportion of till and meadow soils in the catchment. These mechanisms explain several conflicting observations of the acid rain effects on surface water P concentrations.

Effects of simulated acid rain on germination, seedling growth and oxidative metabolism of recalcitrant-seeded Trichilia dregeana grown in its natural seed bank

Increased air pollution in a number of developing African countries, together with the reports of vegetation damage typically associated with acid precipitation in commercial forests in South Africa, has raised concerns over the potential impacts of acid rain on natural vegetation in these countries. Recalcitrant (i.e. desiccation sensitive) seeds of many indigenous African species, e.g. must germinate shortly after shedding and hence, may not be able to avoid exposure to acid rain in polluted areas. This study investigated the effects of simulated acid rain (rainwater with pH adjusted to pH 3.0 and 4.5 with 70:30, H2 SO4 :HNO3 ) on germination, seedling growth and oxidative metabolism in a recalcitrant-seeded African tree species Trichilia dregeana Sond., growing in its natural seed bank. The results suggest that acid rain did not compromise T. dregeana seed germination and seedling establishment significantly, relative to the control (non-acidified rainwater). However, pH 3.0 treated seedlings exhibited signs of stress typically associated with acid rain: leaf tip necrosis, abnormal bilobed leaf tips, leaf necrotic spots and chlorosis, reduced leaf chlorophyll concentration, increased stomatal density and indications of oxidative stress. This may explain why total and root biomass of pH 3.0 treated seedlings were significantly lower than the control. Acid rain also induced changes in the species composition and relative abundance of the different life forms emerging from T. dregeana's natural seed bank and in this way could indirectly impact on T. dregeana seedling establishment success.

Effects and mechanisms of the combined pollution of lanthanum and acid rain on the root phenotype of soybean seedlings

Rare earth pollution and acid rain pollution are both important environmental issues worldwide. In regions which simultaneously occur, the combined pollution of rare earth and acid rain becomes a new environmental issue, and the relevant research is rarely reported. Accordingly, we investigated the combined effects and mechanisms of lanthanum ion (La(3+)) and acid rain on the root phenotype of soybean seedlings. The combined pollution of low-concentration La(3+) and acid rain exerted deleterious effects on the phenotype and growth of roots, which were aggravated by the combined pollution of high-concentration La(3+) and acid rain. The deleterious effects of the combined pollution were stronger than those of single La(3+) or acid rain pollution. These stronger deleterious effects on the root phenotype and growth of roots were due to the increased disturbance of absorption and utilization of mineral nutrients in roots.

[Effects of exogenous nitric oxide on physiological characteristics of longan (Dimocarpus longana) seedlings under acid rain stress]

This paper studied the effects of exogenous nitric oxide donor sodium nitroprusside (SNP) on the chlorophyll content, antioxidant enzyme activities, and osmotic regulation substances of longan (Dimocarpus longana 'Fuyan') seedlings under acid rain (pH 3.0) stress. Under the acid rain stress, the seedling leaf superoxide dismutase (SOD), peroxidase (POD) and catalase (CAT) activities and chlorophyll, soluble protein and soluble sugar contents decreased obviously, while the leaf malondialdedyde content had a remarkable increase, suggesting the toxic effect of the acid rain on the seedlings. Exogenous nitric oxide had dual nature on the physiological characteristics of longan seedlings under acid rain stress. Applying 0.1-0.5 mmol x L(-1) of SNP improved the SOD, POD and CAT activities and the chlorophyll, soluble protein and soluble sugar contents significantly, and decreased the malondialdedyde content. Low concentrations SNP reduced the oxidative damage caused by the acid rain stress, and 0.5 mmol x L(-1) of SNP had the best effect. Under the application of 0.5 mmol x L(-1) of SNP, the total chlorophyll, soluble protein, and soluble sugar contents and the SOD, POD and CAT activities increased by 76.0%, 107.0%, 216.1%, 150. 0%, 350.9% and 97.1%, respectively, and the malondialdedyde content decreased by 46.4%. It was suggested that low concentration (0.1-0.5 mmol x L(-1)) SNP could alleviate the toxic effect of acid rain stress on longan seedlings via activating the leaf antioxidant enzyme activities and reducing oxidative stress, while high concentration SNP (1.0 mmol x L(-1)) lowered the mitigation effect.

[Current status of surface water acidification in Northeast China]

In order to evaluate the status of surface water acidification in Northeast China, chemical composition of 33 small streams was investigated in August, 2011. It was found that only a few waters located in Changbai Mountain had pH of lower than 6.0, and all waters had acid neutralizing capacity (ANC) of higher than 0.2 meq x L(-1). This indicated that surface water acidification was not a regional environmental issue in Northeast China. HCO3- was the major anion, with SO4(2-) concentration mostly below 150 microeq x L(-1) and even much lower NO3- concentration. Low concentration of SO4(2-) and NO3- means no serious acid deposition in this area. However, the distribution of acidic forest soils, with low base cation weathering rate, could only provide limited buffering capacity for surface water to acidification in Northeast China, and the potential risk of water acidification still existed. Currently, acid deposition in Northeast Asia could hardly cause severe acidification of surface water. The neighboring countries should therefore not amplify the environmental impact by transboundary air pollutants from China.

Mannitol can mitigate negative effects of simulated acid mist and fluoranthene in juvenile Japanese red pine (P. densiflora Sieb. et Zucc.)

The negative health effects of simulated acid mists and fluoranthene on juvenile Japanese red pine were investigated, and the methods of protection from these pollutants were examined. The needle gas exchange, chlorophyll fluorescence, chemical contents and visual damage to needles caused by acid mist applied alone or its conjunction with fluoranthene were investigated over 60 d and 20 d, respectively. Acid mist at pH 2 and 3 caused physiological and visual damage, which was enhanced by the addition of fluoranthene to the mist. However, fluoranthene and acid mist at pH 4 and 5 showed only minor effects. These findings indicate that acid mist may be more harmful to pine trees if it occurs in conjunction with polycyclic aromatic hydrocarbons. Moreover, suppression of the singular and additive effects of these compounds was achieved using mannitol, which may be widely applicable to suppression of reactive oxygen species-mediated plant damage.

Photosynthetic and antioxidant responses of Liquidambar formosana and Schima superba seedlings to sulfuric-rich and nitric-rich simulated acid rain

To study whether differential responses occur in photosynthesis and antioxidant system for seedlings of Liquidambar formosana, an acid rain (AR)-sensitive tree species and Schima superba, an AR-tolerant tree species treated with three types of pH 3.0 simulated AR (SiAR) including sulfuric-rich (S-SiAR), nitric-rich (N-SiAR), sulfate and nitrate mixed (SN-SiAR), we investigated the changes of leaf necrosis, chlorophyll content, soluble protein and proline content, photosynthesis and chlorophyll fluorescence characteristics, reactive oxygen species production, membrane lipid peroxidation, small molecular antioxidant content, antioxidant enzyme activities and related protein expressions. Our results showed that SiAR significantly caused leaf necrosis, inhibited photosynthesis, induced superoxide radical and hydrogen peroxide generation, aggravated membrane lipid peroxidation, changed antioxidant enzyme activities, modified related protein expressions such as Cu/Zn superoxide dismutase (SOD), l-ascorbate peroxidase (APX, EC 1. 11. 1. 11), glutathione S transferase (GST, EC 2. 5. 1. 18) and Rubisco large subunit (RuBISCO LSU), altered non-protein thiols (NPT) and glutathione (GSH) content in leaves of L. formosana and S. superba. Taken together, we concluded that the damages caused by SiAR in L. formosana were more severe and suffered from more negative impacts than in S. superba. S-SiAR induced more serious damages for the plants than did SN-SiAR and N-SiAR.

Distribution and turnover of (137)Cs in birch forest ecosystems: influence of precipitation chemistry

The aim of the present work was to study radioactive caesium in soil and plants from birch forests subject to different chemical climate. Four areas and three types of precipitation regimes were considered, representing a natural climatic range found in Norway: (A) acidic precipitation (southernmost part of the country); (B) precipitation rich in "sea salts"/marine cations (coastal areas); and (C) + (D) low concentrations of sea salts (inland areas). The results showed significant regional differences in plant uptake between the investigated areas. For instance the aggregated soil-to-plant transfer coefficients (Tag) were generally up to 7-8 times higher for the area receiving acid rain. Differences in caesium speciation partly explained the regional variability - e.g. the exchangeable fraction ranged from 1 to 40% (with the largest fraction of exchangeable caesium found in southernmost Norway). Transfer coefficients estimated on the basis of exchangeable fractions showed no significant differences between the areas of highest (A) and lowest (C) Tags. However, exchangeable fractions taken into consideration, the uptake of (137)Cs in plants in the acid rain-influenced area is still about twice that in the sea salt influenced area B. A significantly lower concentration of soluble base cations and a higher share of acid components in soils in area A is a likely explanation for this observation.

Modeled dosage-response relationship on the net photosynthetic rate for the sensitivity to acid rain of 21 plant species

This study investigated the sensitivity of plant species to acid rain based on the modeled dosage-response relationship on the net photosynthetic rate (P (N)) of 21 types of plant species, subjected to the exposure of simulated acid rain (SAR) for 5 times during a period of 50 days. Variable responses of P (N) to SAR occurred depending on the type of plant. A majority (13 species) of the dosage-response relationship could be described by an S-shaped curve and be fitted with the Boltzmann model. Model fitting allowed quantitative evaluation of the dosage-response relationship and an accurate estimation of the EC(10), termed as the pH of the acid rain resulting in a P (N) 10 % lower than the reference value. The top 9 species (Camellia sasanqua, Cinnamomum camphora, etc. EC(10) ≤ 3.0) are highly endurable to very acid rain. The rare, relict plant Metasequoia glyptostroboides was the most sensitive species (EC(10) = 5.1) recommended for protection.

Correlation between microstructural characteristics and weight loss of natural stones exposed to simulated acid rain

The correlation between stone microstructural characteristics and material degradation (in terms of weight loss), in given environmental conditions, was investigated. Seven lithotypes, having very different microstructural characteristics, were used. Four acidic aqueous solutions were prepared to simulate acid rain (two adding H(2)SO(4) and two adding HNO(3) to deionized water, in order to reach, for each acid, pH values of 5.0 and 4.0), and deionized water at pH=5.6 was used to simulate clean rain. Stone samples were then immersed in such aqueous solutions, the surface alteration being periodically inspected and the weight loss periodically measured. After 14 days of immersion, a good correlation was found between weight loss and the product of carbonate content and specific surface area in the starting materials. This was explained considering that this product accounts for the weight loss owing to the sample's fraction actually composed of calcite (the most soluble fraction) and the effective surface area exposed to dissolving solution (which depends on stone porosity and pore size distribution). Such correlation between stone microstructure and degradation may be useful for comparing the durability of different lithotypes, in given environmental conditions, and quantitatively predicting the weight loss of a lithotype, compared to another one. Hence, the correlation found in this study may be used to specifically tailor to various stone types, with different microstructural characteristics, some results that have been calculated in literature for specific stone types and then proposed as possibly representative for a broad category of stones with similar characteristics.

Response of soybean seed germination to cadmium and acid rain

Cadmium (Cd) pollution and acid rain are the main environmental issues, and they often occur in the same agricultural region. Nevertheless, up to now, little information on the combined pollution of Cd(2+) and acid rain action on crops were presented. Here, we investigated the combined effect of Cd(2+) and acid rain on the seed germination of soybean. The results indicated that the single treatment with the low level of Cd(2+) (0.18, 1.0, 3.0 mg L(-1)) or acid rain (pH ≥3.0) could not affect the seed germination of soybean, which was resulted in the increased activities of peroxidase and catalase. The single treatment with the high concentration of Cd(2+) (>6 mg L(-1)) or acid rain at pH 2.5 decreased the activities of peroxidase and catalase, damaged the cell membrane and then decreased the seed germination of soybean. Meanwhile, the same toxic effect was observed in the combined treatment with Cd(2+) and acid rain, and the combined treatment had more toxic effect than the single treatment with Cd(2+) or acid rain. Thus, the combined pollution of Cd(2+) and acid rain had more potential threat to the seed germination of soybean than the single pollution of Cd(2+) or acid rain.

Effects of calcium on seed germination, seedling growth and photosynthesis of six forest tree species under simulated acid rain

We selected six tree species, Pinus massoniana Lamb., Cryptomeria fortunei Hooibr. ex Otto et Dietr., Cunninghamia lanceolata (Lamb.) Hook., Liquidambar formosana Hance, Pinus armandii Franch. and Castanopsis chinensis Hance, which are widely distributed as dominant species in the forest of southern China where acid deposition is becoming more and more serious in recent years. We investigated the effects and potential interactions between simulated acid rain (SiAR) and three calcium (Ca) levels on seed germination, radicle length, seedling growth, chlorophyll content, photosynthesis and Ca content in leaves of these six species. We found that the six species showed different responses to SiAR and different Ca levels. Pinus armandii and C. chinensis were very tolerant to SiAR, whereas the others were more sensitive. The results of significant SiAR × Ca interactions on different physiological parameters of the six species demonstrate that additional Ca had a dramatic rescue effect on the seed germination and seedling growth for the sensitive species under SiAR. Altogether, we conclude that the negative effects of SiAR on seed germination, seedling growth and photosynthesis of the four sensitive species could be ameliorated by Ca addition. In contrast, the physiological processes of the two tolerant species were much less affected by both SiAR and Ca treatments. This conclusion implies that the degree of forest decline caused by long-term acid deposition may be attributed not only to the sensitivity of tree species to acid deposition, but also to the Ca level in the soil.

[Combined effects of copper and simulated acid rain on copper accumulation, growth, and antioxidant enzyme activities of Rumex acetosa]

A pot experiment was conducted to study the combined effects of Cu (0-1500 mg x kg(-1)) and simulated acid rain (pH 2.5-5.6) on the copper accumulation, growth, and antioxidant enzyme activities of Rumex acetosa. With the increasing concentration of soil Cu, the Cu accumulation in R. acetosa increased, being higher in root than in stem and leaf. The exposure to low pH acid rain promoted the Cu uptake by R. acetosa. With the increase of soil Cu concentration and/or of acid rain acidity, the biomass of R. acetosa decreased, leaf and root MDA contents increased and had good correlation with soil Cu concentration, and the SOD and POD activities in leaf and root displayed a decreasing trend after an initial increase. This study showed that R. acetosa had a strong adaptive ability to Cu and acid rain stress, exhibiting a high application potential in the remediation of Cu-contaminated soil in acid rain areas.

Guided-inquiry learning in environmental health

The field of environmental health requires the knowledge of many facts and terms, and it also requires mastery of an array of concepts that can be difficult for many students to thoroughly comprehend. Guided-inquiry learning is a process by which students "discover" basic concepts through active investigation. In this article, the authors describe several guided-inquiry learning modules used in their undergraduate environmental health program and their experience in using them. Some modules are used in professional courses while others are used in a general education course. Overall, the authors experienced increased student engagement and interest with guided-inquiry learning. Students are able to comprehend some abstract concepts more quickly and seem to retain the concepts longer.

[Effects of simulated acid rain on oilseed rape (Brassica napus) physiological characteristics at flowering stage and yield]

A pot experiment was conducted to study the effects of different acidity simulated acid rain on the physiological characteristics at flowering stage and yield of oilseed rape (B. napus cv. Qinyou 9). Comparing with the control (pH 6.0), weak acidity (pH = 4.0-5.0) simulated acid rain stimulated the rape growth to some extent, but had less effects on the plant biomass, leaf chlorophyll content, photosynthetic characteristics, and yield. With the further increase of acid rain acidity, the plant biomass, leaf chlorophyll content, photosynthetic rate, antioxidative enzyme activities, and non-enzyme antioxidant contents all decreased gradually, while the leaf malonyldialdehyde (MDA) content and relative conductivity increased significantly. As the results, the pod number per plant, seed number per pod, seed weight, and actual yield decreased. However, different yield components showed different sensitivity to simulated acid rain. With the increasing acidity of simulated acid rain, the pod number per plant and the seed number per pod decreased significantly, while the seed weight was less affected.

[Concentrations and acidity contributions of acetate and formate in precipitation at 14 stations of China]

To investigate the concentrations of organic acids in precipitation in China and their contributions to the total acidity of precipitation, samples were taken at 14 stations of regional representativeness in 2007 and analyzed for acetate and formate using ion chromatography. In this paper, data of acetate and formate in precipitation at 14 stations are presented, wet depositions of these organic acids are calculated, and contributions of them to the total free acidity (TFA) of precipitation are estimated. Based on the measurements, the mean concentrations of formate at different stations were in the range of 0.96-3.43 micromol/L, and those of acetate in the range of 0-5.13 micromol/L, close to the levels at remote sites in other countries and at the lower ends of concentration ranges from previous measurements in China. Comparisons indicate that the concentrations of the organic acids at remote sites are lower than those at sites in the vicinity of urban areas. The annual wet depositions of formate and acetate were estimated to be in the ranges of 0.38-4.18 mmol/(m2 x a) and 0.06-5.87 mmol/(m2 x a), respectively, with larger depositions in southern China and smaller depositions in northern China. The relative contributions of the two organic acids to the TFA of precipitation were estimated to be in the range of 0.02%-51.6%, with an overall average of 2.95%. This suggests that although acid rain in China is mainly caused by emissions of sulfur and nitrogen oxides, organic acids can significantly contribute to the acidification of precipitation in some regions and during some periods, hence need to be included in observational studies of acid rain.

[Complex effects of simulated acid rain and Cu on the physiological characteristics of Paulownia fortunei and its detoxification mechanism]

A pot experiment was conducted to study the effects of simulated acid rain (pH 4.0, 5.0) and Cu (0-200 mg x kg(-1)) on the physiological characteristics of Paulownia fortunei and its detoxification mechanism. With no Cu addition, the leaf chlorophyll, carotenoid, O2 division by, H2O2, and MDA contents of P. fortunei had no significant differences between the two acid rain treatments. However, with the addition of 100 and 200 mg Cu x kg(-1), the chlorophyll and carotenoid contents of treatment pH 4.0 were lower, while the O2 divided by, H2O2 and MDA contents were higher thanthose of treatment pH 5.0. The chlorophyll a/b ratio of treatments Cu was higher than that of the control. The leaf Cu content decreased obviously with the increasing acidity of stimulated acid rain, but the root Cu content was in reverse. With increasing Cu addition, both the activities of superoxide dismutase (SOD), peroxidase (POD), catalase (CAT), and ascorbate peroxidase (APX) and the total contents of phytochelatins (PCs) and glutathione (GSH) in treatment pH 5.0 increased, while the activities of SOD, POD, CAT and APX in treatment pH 4.0 decreased after an initial increase, and the total contents of glutathione (GSH) decreased greatly in treatment 200 mg Cu x kg(-1). All of these demonstrated that the oxidative stress of high Cu concentration to P. fortunei was aggravated by stimulated acid rain.

[Effects of simulated acid rain on respiration rate of cropland system with different soil pH]

To evaluate the effects of acid rain on the respiration rate of cropland system, an outdoor pot experiment was conducted with paddy soils of pH 5.48 (S1), pH 6.70 (S1) and pH 8.18 (S3) during the 2005-2007 wheat-growing seasons. The cropland system was exposed to acid rain by spraying the wheat foliage and irrigating the soil with simulated rainwater of T1 (pH 6.0), T2 (pH 6.0, ionic concentration was twice as rainwater T1), and T3 (pH 4.4, ionic concentration was twice as rainwater T1), respectively. The static opaque chamber-gas chromatograph method was used to measure CO2 fluxes from cropland system. The results showed that acid rain affected the respiration rate of cropland system through crop plant, and the cropland system could adapt to acid rain. Acid rainwater significantly increased the average respiration rate in alkaline soil (S3) cropland system, while it had no significant effects on the average respiration rate in neutral soil (S2) and acidic soil (S1) cropland systems. During 2005-2006, after the alkaline soil cropland system was treated with rainwater T3, the average respiration rate was 23.6% and 27.6% higher than that of alkaline soil cropland system treated with rainwater T1 and T2, respectively. During March to April, the respiration rate was enhanced with the increase of rainwater ionic concentration, while it was dropped with the decrease of rainwater pH value in acidic soil cropland system. It was demonstrated that soil pH and crop plant played important roles on the respiration rate of cropland system.

Effects of simulated deposition of acid mist and iron ore particulate matter on photosynthesis and the generation of oxidative stress in Schinus terebinthifolius Radii and Sophora tomentosa L

Particulate matter is a natural occurrence in the environment, but some industries, such as the iron ore sector, can raise the total amount of particles in the atmosphere. This industry is primarily a source of iron and sulfur dioxide particulates. The effects of the pollutants from the iron ore industries on representatives of restinga vegetation in a Brazilian coastal ecosystem were investigated using physiological and biochemical measures. Two species, Schinus terebinthifolius and Sophora tomentosa, were exposed to simulated deposition of acid mist and iron ore particulate matter in acrylic chambers in a greenhouse. Parameters such as gas exchange, fluorescence emission, chlorophyll content, total iron content, antioxidant enzyme activity and malondialdehyde content were assessed in order to evaluate the responses of the two species. Neither treatment was capable of inducing oxidative stress in S. terebinthifolius. Nevertheless, the deposition of iron ore particulates on this species increased chlorophyll content, the maximum quantum efficiency of photosystem II and the electron transport rate, while iron content was unaltered. On the other hand, S. tomentosa showed a greater sensitivity to the treatments. Plants of S. tomentosa that were exposed to acid mist had a decrease in photosynthesis, while the deposition of iron particulate matter led to an increase in iron content and membrane permeability of the leaves. The activities of antioxidant enzymes, such as catalases and superoxide dismutase, were enhanced by both treatments. The results suggested that the two restinga species use different strategies to overcome the stressful conditions created by the deposition of particulate matter, either solid or wet. It seems that while S. terebinthifolius avoided stress, S. tomentosa used antioxidant enzyme systems to partially neutralize oxidative stress. The findings also point to the potential use of S. tomentosa as a biomarker species under field conditions.

Susceptibility to acidic precipitation contributes to the decline of the terricolous lichens Cetraria aculeata and Cetraria islandica in central Europe

The effective quantum yield of photochemical energy conversion in photosystem II (Phi2) was shown to be reduced in the terricolous lichens Cetraria aculeata and Cetraria islandica by short-term exposure to aqueous SO2 at pH values occurring in the precipitation of areas with high SO2 pollution. Significant reduction of Phi2 was found at pH<or=3.3. At pH 2.8, Phi2 was close to zero and did not recover within 24 h. This suggests that sensitivity to SO2 (primarily associated with epiphytic lichens in the past) has contributed to the decline of both species in central Europe. In C. islandica, but not in C. aculeata, thalli with the natural content of lichen substances were more tolerant to SO2 than thalli where the extracellular lichen substances were extracted before the experiment. This supports published results that the depsidone fumarprotocetraric acid, a major lichen substance of C. islandica, increases the pollution tolerance in lichens.

Acid rain and its ecological consequences

Acidification of rain-water is identified as one of the most serious environmental problems of transboundary nature. Acid rain is mainly a mixture of sulphuric and nitric acids depending upon the relative quantities of oxides of sulphur and nitrogen emissions. Due to the interaction of these acids with other constituents of the atmosphere, protons are released causing increase in the soil acidity Lowering of soil pH mobilizes and leaches away nutrient cations and increases availability of toxic heavy metals. Such changes in the soil chemical characteristics reduce the soil fertility which ultimately causes the negative impact on growth and productivity of forest trees and crop plants. Acidification of water bodies causes large scale negative impact on aquatic organisms including fishes. Acidification has some indirect effects on human health also. Acid rain affects each and every components of ecosystem. Acid rain also damages man-made materials and structures. By reducing the emission of the precursors of acid rain and to some extent by liming, the problem of acidification of terrestrial and aquatic ecosystem has been reduced during last two decades.

Leaf responsiveness of Populus tremula and Salix viminalis to soil contaminated with heavy metals and acidic rainwater

Fast-growing trees such as Salix viminalis L. and Populus tremula L. are well suited to phytoremediate heavy metal contaminated soils. However, information on tree performance, particularly leaf function, under conditions of heavy metal contamination is scarce. We used yearly coppiced saplings of S. viminalis and P. tremula growing in model ecosytems to test four hypotheses: (1) heavy metal contamination impairs photosynthesis by injuring leaf structure; (2) the effects of heavy metal contamination are enhanced by acidified rainwater and low soil pH; (3) heavy metal contamination increases dark respiration and, thus, repair processes; and (4) heavy metal contamination is tolerated and remediated better by S. viminalis than by P. tremula. We investigated heavy metal accumulation, tissue injury and gas exchange in leaves of plants subjected to controlled soil contamination with heavy metal dust. Additional treatments included acidic and calcareous natural forest subsoils in combination with irrigation with rainwater at pH 5.5 or 3.5. In both provenances of P. tremula that were studied, but not in S. viminalis, heavy metal treatment reduced photosynthesis and transpiration by varying amounts, except in the hot and dry summer of 2003, but had no effect on dark respiration. At light saturation, net CO(2) uptake and water-use efficiency were reduced by heavy metal contamination, whereas the CO(2) concentration in the leaf intercellular air space was increased. Rainwater pH and subsoil pH only slightly modified the effects of the heavy metal treatment on P. tremula. Gas exchange responses of P. tremula to heavy metals were attributed to leaf structural and ultrastructural changes resulting from hypersensitive-response-like processes and accelerated mesophyll cell senescence and necroses in the lower epidermis, especially along the transport pathways of heavy metals in the leaf lamina. Overall, the effects of heavy metals on P. tremula corroborated Hypothesis 1, but refuted Hypotheses 2 and 3, and were inconclusive for Hypothesis 4. Both P. tremula and S. viminalis showed appreciable potential for storing heavy metals in aging foliage.

Effect of acid rain on building material of the El Tajín archaeological zone in Veracruz, Mexico

Three limestone slabs (approx. 20 cm2 each) were extracted from the El Tajin archaeological zone in Veracruz, Mexico. X-ray diffraction analysis revealed three components: calcite (81.2%), quartz (17.9%) and feldspar (0.9%). Calcite content by x-ray diffraction analysis was slightly higher than that determined by chemical reaction between the limestone sample and nitric acid. The latter analysis, carried out in triplicate, yielded a calcite content of 77.1%. Mean water absorption, density and porosity of the limestone samples were also determined. Dissolution of limestone samples was investigated using an experimental rainfall simulation chamber, in which the stone samples were irrigated with artificial rain matching the pH and the ionic composition with 40 rainfall samples collected at El Tajin from August 18, 2002, to April 9, 2003. According to calcium and bicarbonate net concentrations found in the effluent of the chamber, a chemical mechanism by which limestone at El Tajin is dissolved by acid rain is proposed. A model used to investigate the air transport pathways corresponding to precipitation events at El Tajin shows that air parcels come mainly from the Gulf of Mexico, although no directional preference is evident for acidic vs. non-acidic events.

Health hazards from volcanic gases: a systematic literature review

Millions of people are potentially exposed to volcanic gases worldwide, and exposures may differ from those in anthropogenic air pollution. A systematic literature review found few primary studies relating to health hazards of volcanic gases. SO2 and acid aerosols from eruptions and degassing events were associated with respiratory morbidity and mortality but not childhood asthma prevalence or lung function decrements. Accumulations of H2S and CO2 from volcanic and geothermal sources have caused fatalities from asphyxiation. Chronic exposure to H2S in geothermal areas was associated with increases in nervous system and respiratory diseases. Some impacts were on a large scale, affecting several countries (e.g., Laki fissure eruption in Iceland in 1783-4). No studies on health effects of volcanic releases of halogen gases or metal vapors were located. More high quality collaborative studies involving volcanologists and epidemiologists are recommended.

A fresh look at the benefits and costs of the US acid rain program

The US Acid Rain Program (Title IV of the 1990 Clean Air Act Amendments) has achieved substantial reductions in emissions of sulfur dioxide (SO2) and nitrogen oxides (NOx) from power plants in the United States. We compare new estimates of the benefits and costs of Title IV to those made in 1990. Important changes in our understanding of and ability to quantify the benefits of Title IV have occurred. Benefits to human health now take a much higher profile because the contribution of SO2 and NOx emissions to the formation of fine particulate (PM2.5) is substantial, and evidence of the harmful human health effects of PM2.5 has emerged in the last 15 years. New estimates of the health benefits of PM2.5 reductions are the largest category of quantified health and environmental benefits and total over 100 billion US dollars annually for 2010 when the program is expected to be fully implemented. Although important uncertainties exist in any specific estimate of the benefits, even if the estimates were calculated using more limiting assumptions and interpretations of the literature they would still substantially exceed the costs. Estimates of annualized costs for 2010 are about 3 billion US dollars, which is less than half of what was estimated in 1990. Research since 1990 also suggests that environmental problems associated with acid deposition and nitrogen deposition are more challenging to resolve than originally thought and will require larger reductions in emissions to reverse. The greater than expected benefits to human health, the greater vulnerability of natural resources and ecosystems, and the lower than expected costs all point to the conclusion that further reductions in SO2 and NOx emissions from power plants beyond those currently required by Title IV are warranted.

[Response of POD and CAT during seeds of rice, wheat and rape germination on acid rain stress]

The effects of simulated acid rain (pH 2.5 - 5.0) on the activities of POD and CAT were investigated during germination of rice (O. sativa), wheat (T. aestivum) and rape (B. chinensis var. oleifera) seeds. Compared with the control (CK), the amplitude of the change in the activity of CAT and POD is that rice (28.8%, 31.7%) < wheat (34.7%, 48.3%) < rape (79.3%, 50.0%), respectively. The pH significantly different (p < 0.05) from CK follows the order: rice (3.5) > wheat (4.0) > rape (5.0). All of these revealed that the ability of resisting acid rain stress is that rice is stronger than wheat and rape is the worst. Under the same condition, the amplitude of the change in the activity of CAT is more sensitivity toward acid rain stress than that of POD. The difference in free radicals removed by these 3 species is one of the reasons why the germinating indexes behaved differently.

[Effects of simulated acid rain and its acidified soil on soluble sugar and nitrogen contents of wheat seedlings]

The study showed that the cation release of simulated rain caused soil acidification and base ions release. With the decrease of simulated acid rain pH from 5.6 to 2.5, the acid rain-leached soil pH decreased from 6.06 to 3.41, and its total amount of exchange base ions decreased from 56.5 to 41.1 mmol x kg(-1). Spraying simulated acid rain on the shoots of wheat seedlings planted on such acidified soils caused a rapid decrease in the soluble sugar and nitrogen contents of wheat seedlings, and reduced some of their physiological activities. The effect of spraying simulated acid rain on the soluble sugar, nitrogen, and chlorophyll contents and photosynthetic rate of wheat stems and leaves was larger than that of acidified soil, while the effect of the latter on the soluble sugar and nitrogen contents and the physiological activity of NR and GOGAT in root system of wheat seedlings was larger than that of the former. The intensive acid rain of pH < or = 3.0 and the corresponding acidified soil had an obvious harm to the growth and physiological activity of wheat seedlings.

Acidic mist reduces foliar membrane-associated calcium and impairs stomatal responsiveness in red spruce

Acidic deposition can leach essential pools of calcium (Ca) directly from plant foliage. Because of the central role of Ca in environmental signal transduction, disruptions of labile foliar Ca pools could impair physiological responses to a variety of environmental stimuli and stressors. We investigated the possibility that acidic mist-induced depletion of membrane-associated Ca (mCa), which is one form of labile Ca, may alter stomatal responsiveness to water stress, a process known to include Ca in signal transduction cascades. Red spruce (Picea rubens Sarg.) seedlings were exposed to either pH 3.0 or pH 5.0 mist treatments for one growing season. Foliar nutrition was assessed following treatments, and declines in stomatal conductance and net photosynthesis were measured on current-year shoots following stem excision. Seedlings exposed to pH 3.0 acidic mist treatments had reduced mCa relative to the pH 5.0 treated seedlings. Seedlings subjected to the pH 3.0 acidic mist treatment exhibited impaired stomatal functions, including a smaller maximum aperture, slower closure and an increased lag time between stomatal closure and photosynthetic decline following experimental water stress. Delayed stomatal closure could undermine desiccation avoidance mechanisms. Previous work has demonstrated that acidic mist treatments deplete mCa in red spruce and impair cold tolerance, with similar effects in other species. The results we present provide further evidence that acidic mist-induced mCa depletion may cause disruption of a broad range of plant stress responses.

[Roles of calcium in stress-tolerance of plants and its ecological significance]

Calcium loss from soil has dramatically increased for decades due to the increase of nitrogen input and/or the extension of acid rain, while calcium input into soil has declined substantially for the replacement of superphosphate by ammonium phosphate in fertilization, which intensified the imbalance of calcium input and output in agro-ecosystems, and needed to be solved in the near future for the sustainability of agriculture in such a country like China where the arable land resource is very limited. In recent years, the intensified soil acidification is mainly attributed to the root proton secretion stimulated by fertilization, and the nitrogen input from precipitation near industrialized regions promotes plant growth but results in other nutrients deficiency, which in turn acidifies soil and causes tree death. One of the most important mechanisms of saline soil bioremediation by sesbania is the activation of soil calcium by sesbania's proton secretion and the increase of soil calcium supply for subsequent crops. The present paper summarized the roles of calcium in plant tolerance to the stresses like acidosis, toxic metals, osmosis, ammonium toxicity, drought, extreme temperature (cold or heat shock), anoxia and pathogen infection, and the measures for maintaining soil calcium fertility. It was suggested that the production of ammonium phosphate should not be a pursued target for China's phosphorus fertilizer industry, and the roles of calcium in plant growth should be taken into account in fertilization experimental designs to make the experiments more accurate.

[Effects of simulated acid rain on physiological and biochemical characters of eggplant, the host plant of Tetranychus cinnabarinus]

In a series of laboratory trials, this paper studied the responses of eggplant (Solanum melongena), the host plant of carmine spider mite Tetranychus cinnabarinus, to different pH values simulated acid rain. The results showed that with the increasing acidity of simulated acid rain, the CAT activity and the contents of P and soluble protein in egg plant leaves increased significantly first, reaching the highest at pH 4.0 or 3.0, and then decreased; while the POD activity and soluble sugar content were in adverse. The reduced sugar content and SOD activity of eggplant leaves increased, but the pH value decreased with increasing acidity of acid rain. Acid rain had no effect on leaf water content. Among the test indices, leaf POD was most insensitive to the acid rain, followed by leaf pH, SOD and CAT, while the others were very sensitive. Weak acid rain (pH > 4.0) promoted the protective ability of eggplant leaf and its growth, and the growth of T. cinnabarinus was also promoted because of the changed contents of soluble sugar, P and soluble protein in eggplant leaves being more favorable to its eating; while strong acid rain (pH < 3.0) inhibited the growth of both host plant and mite.

Quantifying the role of forest soil and bedrock in the acid neutralization of surface water in steep hillslopes

The role of soil and bedrock in acid neutralizing processes has been difficult to quantify because of hydrological and biogeochemical uncertainties. To quantify those roles, hydrochemical observations were conducted at two hydrologically well-defined, steep granitic hillslopes in the Tanakami Mountains of Japan. These paired hillslopes are similar except for their soils; Fudoji is leached of base cations (base saturation <6%), while Rachidani is covered with fresh soil (base saturation >30%), because the erosion rate is 100-1000 times greater. The results showed that (1) soil solution pH at the soil-bedrock interface at Fudoji (4.3) was significantly lower than that of Rachidani (5.5), (2) the hillslope discharge pH in both hillslopes was similar (6.7-6.8), and (3) at Fudoji, 60% of the base cations leaching from the hillslope were derived from bedrock, whereas only 20% were derived from bedrock in Rachidani. Further, previously published results showed that the stream pH could not be predicted from the acid deposition rate and soil base saturation status. These results demonstrate that bedrock plays an especially important role when the overlying soil has been leached of base cations. These results indicate that while the status of soil acidification is a first-order control on vulnerability to surface water acidification, in some cases such as at Fudoji, subsurface interaction with the bedrock determines the sensitivity of surface water to acidic deposition.

[Effects of acid rain on nitrogen content in the water body of Wenzhou Sanyang wetland]

In order to understand the effects of acid rain on the nitrogen (N) content in the water body of Wenzhou Sanyang wetland, this paper measured the concentrations of different N forms in the wetland, of which, NH4+-N was 2.90-10.75 mg x L(-1), average in 5.38 mg x L(-1); NO3(-)-N was 0.16-0.44 mg x L(-1), average in 0.31 mg x L(-1); and total was 34.04-63.20 mg x L(-1), average in 55.75 mg x L(-1). The pH value was 6.1-6.5, average in 6.4. The measurement of the N input from precipitation in the past two years and its proportion to the existed N in the water body of the wetland showed that the input of NH4+-N, NO3(-)-N and total N was 2.48 x 10(4)-2.86 x 10(4) kg, 2.87-4.96 x 10(4) kg and 5.35 x 10(4)-7.82 x 10(4) kg, and its proportion was 56-64%, 11.21-19.38 times and 12%-17%, respectively. The N amount directly to the wetland water body was 0.72 x 10(4)-0.84 x 10(4) kg, 0.83 x 10(4)-1.44 x 10(4) kg and 1.55 x 10(4)-2.27 x 10(4), and its proportion was 16%-19%, 3.24-5.63 times and 3%-5%. The results indicated that acid rain was one of the main sources of pollutant nitrogen which aggravated the water pollution of the Sanyang wetland.