Source: PENNSYLVANIA STATE UNIVERSITY submitted to NRP
MAGNANESE TOXICITY AND OXIDATIVE STRESS IN TREES OF THE EASTERN FOREST
Sponsoring Institution
National Institute of Food and Agriculture
Project Status
COMPLETE
Funding Source
NRI COMPETITIVE GRANT
Reporting Frequency
Annual
Accession No.
0192331
Grant No.
2002-35100-12055
Cumulative Award Amt.
(N/A)
Proposal No.
2002-00748
Multistate No.
(N/A)
Project Start Date
Jun 15, 2002
Project End Date
Jun 14, 2004
Grant Year
2002
Program Code
[22.1]- (N/A)
Recipient Organization
PENNSYLVANIA STATE UNIVERSITY
208 MUELLER LABORATORY
UNIVERSITY PARK,PA 16802
Performing Department
HORTICULTURE
Non Technical Summary
The eastern deciduous forest of North America is a principal terrestrial ecosystem of primary importance for the economy and ecology of the nation. However, the future vitality of the forest is uncertain because of the unknown effects of social policies affecting land use, atmospheric chemistry and soil nutrient cycling. This project focuses on manganese (Mn) biogeochemistry as a critical yet poorly understood determinant of forest health that is being influenced by human activities. There is evidence that Mn toxicity is an important factor associated with forest decline in this region, which is worsening with time. We have recently discovered that Mn toxicity in plants is a photo-oxidative stress, which means that it should have significant interactions with other environmental factors such as light intensity, ultraviolet radiation, temperature, and atmospheric ozone. In this proposal we present preliminary evidence that Mn toxicity causes photo-oxidative stress in deciduous trees of the eastern forest, and that tree species differ in response to Mn toxicity. The goal of this project is to gain a better understanding of how forest trees respond to Mn toxicity, focusing especially on genes, enzymes, and processes involved in oxidative stress. This research would explore a novel dimension of plant responses to the environment with important consequences for ecosystem responses to global change, and with relevance to our management of the forest and social policies regarding atmospheric quality.
Animal Health Component
20%
Research Effort Categories
Basic
80%
Applied
20%
Developmental
(N/A)
Classification

Knowledge Area (KA)Subject of Investigation (SOI)Field of Science (FOS)Percent
1020620102010%
1230620102010%
2010620102010%
2030620102060%
2060620102010%
Knowledge Area
206 - Basic Plant Biology; 102 - Soil, Plant, Water, Nutrient Relationships; 203 - Plant Biological Efficiency and Abiotic Stresses Affecting Plants; 201 - Plant Genome, Genetics, and Genetic Mechanisms; 123 - Management and Sustainability of Forest Resources;

Subject Of Investigation
0620 - Broadleaf forests of the North;

Field Of Science
1020 - Physiology;
Goals / Objectives
OVERALL GOAL: The eastern deciduous forest of North America is a principal terrestrial ecosystem that could play an important role in global climate change by acting as a sink for atmospheric CO2. However, the future growth and vitality of the forest is uncertain because of the unknown effects of social policies affecting land use, atmospheric chemistry and soil nutrient cycling. This project focuses on manganese (Mn) biogeochemistry as a critical yet poorly understood determinant of forest health that is being influenced by human activities. There is evidence that Mn toxicity is an important factor associated with forest decline in this region, which is worsening with time. We have recently discovered that Mn toxicity in bean plants is a photo-oxidative stress, which means that it should have significant interactions with other environmental factors such as light intensity, ultraviolet radiation, temperature, and atmospheric ozone. In this proposal we present preliminary evidence that Mn toxicity also causes photo-oxidative stress in deciduous trees of the eastern forest, and that tree species differ in response to Mn toxicity. Our overall goal is to understand the response of forest species to Mn toxicity, in order to predict the behavior of forest species in contrasting climate and policy scenarios. SPECIFIC OBJECTIVES: 1. Characterize the effects of Mn availability on gene expression in key deciduous tree species of the eastern forest. Test the hypothesis that Mn toxicity and Mn tolerance are related to the expression of genes for antioxidant defenses, focusing specifically on Superoxide dismutases, Ascorbate peroxidases, Guaiacol peroxidase, Dehydroascorbate reductase, Glutathione reductase, and Catalase. 2. Characterize the interaction of Mn toxicity and light intensity in leaves of key deciduous tree species of the eastern forest. Test the hypothesis that Mn toxicity causes photo-oxidative stress in susceptible species.
Project Methods
We will employ controlled environments (greenhouse and growth chambers) as well as observation of intact systems at field sites throughout Pennsylvania. We will focus on two oak species, northern red oak (Quercus rubra) and scarlet oak (Quercus coccinea), and two maple species, sugar maple (Acer saccharum) and red maple (Acer rubrum) representing a relatively tolerant and resistant species within each genus. We hypothesize that heightened Mn levels in oaks and maples will induce the expression of the class of genes that respond to abiotic stresses including the genes for antioxidant defense proteins. We will examine the expression of several genes which we hypothesize to be involved in deciduous tree response to Mn induced photo-oxidative stress. They include Mn, Fe, and Cu/Zn Superoxide dismutase, chloroplastic and cytosolic Ascorbate peroxidases, Guaiacol peroxidase, Dehydroascorbate reductase, Glutathione reductase, and Catalase. We will isolate total RNA from the leaves of young trees grown under controlled greenhouse conditions with supplemental lighting at various levels of Mn, as described in Activity 2 below. The northern technique will be used as an initial screen to examine the differential expression of the 12 selected genes. If the northern blot experiments indicate that gene expression is being regulated by Mn, we will quantify transcript levels by Quantitative Real Time PCR. For the RT-PCR assays we will develop PCR primers to highly conserved regions of the target genes. If the Quantitative RT-PCR assays verify that the expression of the Superoxide dismutase, Ascorbate peroxidase, and Glutathione reductase genes are regulated by Mn levels in samples from greenhouse grown plants, we will then test the assay on leaves sampled from trees of each of the four species at field research sites in PA where Mn toxicity symptoms have been observed, as well as at control sites without Mn stress. These studies will utilize greenhouses and growth chambers that permit control of light, temperature, and humidity regimes. Nutrient regimes will be provided through standard solution culture and solid-phase-buffered sand culture techniques. Two-year old plants of the 4 species will be grown in solution culture and sand culture in greenhouse and growth chamber conditions. MnSO4 will be added to the nutrient solution at varying concentrations. Plants will be exposed to contrasting light regimes. At several times following addition of Mn, data will be collected for diurnal leaf gas exchange (CO2 assimilation and water vapor flux), leaf photosynthetic oxygen evolution, chlorophyll fluorescence, leaf chemistry (i.e. content of chlorophyll, Mn, nutrients, antioxidant systems), leaf expansion, leaf production, leaf longevity, and plant growth. Both mature (fully expanded) and expanding leaves will be assayed. We hypothesize that 1) high light intensity is synergistic with Mn toxicity, 2) Mn-sensitive species are more susceptible to photo-oxidation under Mn stress, and 3) species differences in Mn sensitivity may be due to differences in antioxidant capabilities.

Progress 06/15/02 to 06/14/04

Outputs
We observed substantial differences among tree species in Mn sensitivity. In field and greenhouse environments, deciduous species accumulated more foliar Mn and experienced more photosynthetic damage in response to Mn accumulation than evergreens. Sugar maple was the most sensitive species to excess Mn based on growth and photosynthesis. Photosynthetic sensitivity to Mn toxicity was correlated with foliar Mn concentrations, indicating that species differences in Mn tolerance are not caused by physical or chemical Mn compartmentation. In controlled environments, high light potentiated Mn toxicity in sugar maple and red maple. All sugar maple leaves were sensitive to Mn toxicity except shaded young leaves. For red maple, only mature leaves exposed to high light were prone to Mn toxicity. Antioxidant enzyme and phiPSII /phiCO2 data suggested that photo-oxidative stress did not explain the observed photosynthetic responses to treatment variables. Antioxidant enzyme activity in sugar maple was highest in seedlings growing on nutrient-poor soils and was inversely correlated with photosynthesis, Ca, P, and Mg concentrations. In overstory sugar maple stands on the Allegheny Plateau, trees on poor soils had significantly lower foliar Ca and Mg concentrations and significantly higher foliar Mn concentrations. In the latter half of the summer leaf gas exchange and chlorophyll content were higher in trees on better soils while antioxidant enzyme activity became significantly greater in trees in poor soils. Leaf nutrient status was correlated with both photosynthetic function and antioxidant enzyme activity. Mycorrhizal symbiosis is an important mediator of tree responses to Mn toxicity. Red maple maintained higher levels of root mycorrhization and CER than sugar maple on unlimed soil. Photosynthesis of red maple was not responsive to lime treatments and was not correlated with mycorrhization or foliar nutrient status. In contrast, carbon dioxide exchange rate (CER) and electron transport rate (ETR) of sugar maple seedlings increased significantly in response to lime treatments and were significantly correlated with foliar nutrient concentrations. CO2 exchange rates and ETR in sugar maple were positively correlated with mycorrhization. Based on fungicide treatments it was determined that about half of the lime-induced increase in photosynthesis of sugar maple seedlings was dependent upon mycorrhization. These results suggest that 1) Mn toxicity is an important factor in forest health, 2) Mn toxicity is associated with oxidative stress and is potentiated by high light intensity, 3) acidic, nutrient-depleted soils limit photosynthetic function of sugar maple seedlings directly and through interference of root-mycorrhiza associations, and 4) differential tolerance of red maple and sugar maple to Mn toxicity may contribute to sugar maple decline and the expansion of red maple in the eastern forest of North America.

Impacts
The eastern deciduous forest of North America is a principal terrestrial ecosystem that could play an important role in global climate change by acting as a sink for atmospheric CO2. However, the future growth and vitality of the forest is uncertain because of the unknown effects of social policies affecting land use, atmospheric chemistry and soil nutrient cycling. This project focused on manganese (Mn) biogeochemistry as a critical yet poorly understood determinant of forest health that is being influenced by human activities. We obtained evidence that Mn toxicity is an important factor associated with forest decline in this region, and that tree species differ in their sensitivity to Mn toxicity, which may be related to ongoing changes in the species composition of the forest. We found that sugar maple is particularly sensitive to Mn toxicity. We obtained evidence that Mn toxicity is associated with photo-oxidative stress, which means that it has significant interactions with light intensity, and may have important interactions with other environmental factors, notably atmospheric ozone. This information will be useful in understanding how the health of the eastern forest is being affected by air quality and by climate change factors, helps account for forest decline and sugar maple decline, and suggests practical management options for sugar maple stands and other managed forests, such as the utility of liming.

Publications

  • St.Clair, SB, JP Lynch 2004. Element accumulation patterns of deciduous and evergreen tree seedlings on acid soils and its implications for sensitivity to manganese toxicity. Tree Physiology, in press.
  • St.Clair, SB, JP Lynch. 2005. Base cation stimulation of mycorrhization and photosynthesis of sugar maple on acid soils are coupled by foliar nutrient dynamics. New Phytologist, in press.
  • St.Clair, SB, JP Lynch 2004 Photosynthetic and antioxidant enzyme responses of sugar maple and red maple seedlings to excess manganese in contrasting light environments' Functional Plant Biology, in press.
  • St.Clair, SB, JP Lynch 2005. Differences in photosynthesis, growth and antioxidant enzyme activity of sugar maple and red maple seedlings in response to contrasting nutrition and light environment. Submitted.
  • St.Clair, SB, JE Carlson, JP Lynch 2005. Evidence for oxidative stress in sugar maple stands growing on acidic, nutrient imbalanced forest soils. Submitted.
  • Samuel St.Clair, Ph.D. Ecological and Molecular Plant Physiology, 2004. Responses of sugar maple (Acer saccharum Marsh.) to edaphic stresses in the eastern forests of North America.


Progress 01/01/03 to 12/31/03

Outputs
In 2003 we continued our work investigating the influence of foliar nutrient imbalances in tree species with a specific emphasis on manganese (Mn) toxicity. We conducted three experiments that examined the physiological effects and biochemical responses of selected tree species to nutrient imbalances. Under greenhouse condition we grew seedlings of nine trees species prevalent in Pennsylvania forests. They included six deciduous tree species: sugar maple, red maple, red oak, white oak, black cherry, white ash; and three evergreen tree species: eastern hemlock, white pine and white spruce. Seedlings were grown in a sand culture system and exposed to adequate or excessive levels of manganese. We then monitored photosynthetic responses. We found that deciduous tree species were significantly more sensitive to Mn toxicity than evergreen species. Among deciduous trees sugar maple was the most sensitive. Tolerant species effectively prevented the excess accumulation of Mn in their needles or leaves. To determine if these trends occur in natural forest environments we collected leaf foliage from these nine species growing on acidic nutrient imbalance soils around the state of Pennsylvania. As in the greenhouse study we found that the tolerant species had substantially lower levels of Mn accumulation relative to the sensitive species. In a second study we compared the physiological and biochemical responses of sugar maple and red maple to soils contrasting in pH and nutrient status. Soil cores from upper and lower slope positions, which contrast in pH and nutrient availability were collected from the Allegheny National Forest. Cores were brought back and sugar and red maple seed was germinated on the soil cores. Treatment conditions included nutrient variation inherent in the soils, additions of manganese and magnesium through a fertigation system, and two light regimes (ambient light and shade treatment which was 20% of ambient). We then assessed photosynthesis, chlorophyll content, growth and the regulation of two antioxidant enzymes. We found that growth and photosynthetic responses of sugar maple were more sensitive to nutrient imbalances than red maple. Sugar maples appear to suffer from oxidative stress in low pH, nutrient imbalanced soils based on antioxidant enzyme data. These responses occurred in both low and high light environments. Trends observed in previous experiments under greenhouse conditions were verified in the field during the Summer of 2003. We examined the physiological and biochemical responses of overstory sugar maple trees to variation in foliar nutrient status on acidic soils on the Allegheny National Forest and state forest land. Decreases in photosynthesis and foliar chlorophyll content during the latter half of the summer were correlated with calcium and phosphorus deficiency and manganese and aluminum toxicity. These foliar nutrient imbalances were strongly correlated with an upregulation of antixodiant enzymes suggesting that oxidative stress is the cellular mechanisms that underlies the observed relationship between foliar nutrient imbalances and decreases in physiological function.

Impacts
The eastern deciduous forest of North America is a principal terrestrial ecosystem that could play an important role in global climate change by acting as a sink for atmospheric CO2. However, the future growth and vitality of the forest is uncertain because of the unknown effects of social policies affecting land use, atmospheric chemistry and soil nutrient cycling. This project focuses on manganese (Mn) biogeochemistry as a critical yet poorly understood determinant of forest health that is being influenced by human activities. There is evidence that Mn toxicity is an important factor associated with forest decline in this region, which is worsening with time. We have recently discovered that Mn toxicity in bean plants is a photo-oxidative stress, which means that it should have significant interactions with other environmental factors such as light intensity, ultraviolet radiation, temperature, and atmospheric ozone. Our preliminary evidence that Mn toxicity may also cause photo-oxidative stress in deciduous trees of the eastern forest, and that tree species differ in response to Mn toxicity, has important implications for our ability to understand the response of forest species to Mn toxicity, in order to predict the behavior of forest species in contrasting climate and policy scenarios.

Publications

  • No publications reported this period


Progress 01/01/02 to 12/31/02

Outputs
The health of many sugar maple stands in the eastern forest of North America has declined over the past several decades. Foliar manganese (Mn) hyperaccumulation in trees growing on the acidic soils prevalent in this biome may contribute to decline symptoms, through unknown mechanisms. We hypothesized that foliar Mn hyperaccumulation decreases photosynthesis in susceptible tree species through photo-oxidative stress, particularly at high light intensities. To test this hypothesis, we assessed photosynthetic and photochemical responses (C02 exchange rate, quantum efficiency of C02 fixation, quantum efficiency of photosystem II, electron transport rate and stomatal conductance) of 2nd year sugar maple (Acer saccharum) and red maple (Acer rubrum) seedlings to variable Mn and light levels in greenhouse conditions. Decreases in both the light and dark reactions of photosynthesis were observed in seedlings supplied with excess Mn. Rubisco appeared to be a primary target of Mn toxicity as indicated by decreases in the carboxylation efficiency (initial slope of the A/Ci curve) of leaves exposed to excess Mn. The most important finding in this study was that Mn's toxic affects on photochemistry were exacerbated by high light intensities.

Impacts
The eastern deciduous forest of North America is a principal terrestrial ecosystem that could play an important role in global climate change by acting as a sink for atmospheric CO2. However, the future growth and vitality of the forest is uncertain because of the unknown effects of social policies affecting land use, atmospheric chemistry and soil nutrient cycling. This project focuses on manganese (Mn) biogeochemistry as a critical yet poorly understood determinant of forest health that is being influenced by human activities. There is evidence that Mn toxicity is an important factor associated with forest decline in this region, which is worsening with time. We have recently discovered that Mn toxicity in bean plants is a photo-oxidative stress, which means that it should have significant interactions with other environmental factors such as light intensity, ultraviolet radiation, temperature, and atmospheric ozone. Our preliminary evidence that Mn toxicity may also cause photo-oxidative stress in deciduous trees of the eastern forest, and that tree species differ in response to Mn toxicity, has important implications for our ability to understand the response of forest species to Mn toxicity, in order to predict the behavior of forest species in contrasting climate and policy scenarios.

Publications

  • No publications reported this period