Changes in southern Piedmont grassland community structure and nutritive quality with future climate scenarios of elevated tropospheric ozone and altered rainfall patterns

Forage species common to the southern USA Piedmont region, Lolium arundinacea, Paspalum dilatatum, Cynodon dactylon and Trifolium repens, were established in a model pasture system to test the future climate change scenario of increasing ozone exposure in combination with varying rainfall amounts on community structure and nutritive quality. Forages were exposed to two levels of ozone [ambient (non-filtered; NF) and twice ambient (2×) concentrations] with three levels of precipitation (average or ±20% of average) in modified open-top chambers (OTCs) from June to September 2009. Dry matter (DM) yield did not differ over the growing season between forage types, except in primary growth grasses where DM yield was higher in 2× than NF treatment. Primary growth clover decreased in nutritive quality in 2× ozone because of increased concentrations of neutral detergent fibre (NDF), acid detergent fibre (ADF) and acid detergent lignin (ADL). Re-growth clover exhibited the largest decrease in nutritive quality, whereas grasses were not adversely affected in 2× ozone. Re-growth grasses responded positively to 2× ozone exposure, as indicated in increased relative food value (RFV) and percentage crude protein (CP) than NF-exposed re-growth grasses. Effects of precipitation were not significant over the growing season for primary or re-growth forage, except in primary growth grasses where DM yield was higher in chambers with above average (+20%) precipitation. Total canopy cover was significantly higher over the growing season in chambers receiving above average precipitation, but no significant effects were observed with ozone. Results indicate shifts in plant community structure and functioning related to mammalian herbivore herbivory in future climate change scenarios.

Disruption of the 'disease triangle' by chemical and physical environmental change

The physical and chemical environment of the Earth has changed rapidly over the last 100 years and is predicted to continue to change into the foreseeable future. One of the main concerns with potential alterations in climate is the propensity for increases in the magnitude and frequency of extremes to occur. Even though precipitation is predicted to increase in some locations, in others precipitation is expected to decrease and evapotranspiration increase with air temperature, resulting in exacerbated drought in the future. Chemical [ozone (O3 ) and other air contaminants] and subsequent physical alterations in the environment will have a profound effect on the 'disease triangle' (a favourable environment, a susceptible host and a virulent pathogen) and should be included in any analysis of biological response to climate change. The chemical and physical environment affects plant health and alters plant susceptibility to insect and pathogen attack through increased frequency, duration and severity of drought and reduction in host vigour. The potential effects of climate change and O3 on tree diseases with emphasis on the western United States are discussed. We describe a generalised modelling approach to incorporate the complexities of the 'disease triangle' into dynamic vegetation models.

Response of total tannins and phenolics in loblolly pine foliage exposed to ozone and acid rain

Tannin and total phenolic levels in the foliage of loblolly pine (Pinus taeda L.) were examined in order to evaluate the effect of atmospheric pollution on secondary plant metabolism. The trees were exposed to four ozone concentrations and three levels of simulated acid rain. Tannin concentration (quantity per gram) and content (quantity per fascicle) were increased in foliage exposed to high concentrations of ozone in both ozone-sensitive and ozone-tolerant families. No effect of acid rain on tannins was observed. Neither total phenolic concentration nor content was significantly affected by any treatment, indicating that the ozone-related increase in foliar tannins was due to changes in allocation within the phenolic group rather than to increases in total phenolics. The change in allocation of resources in the production of secondary metabolites may have implications in herbivore defense, as well as for the overall energy balance of the plant.

Temporal patterns of foliar ozone symptoms on tall milkweed (Asclepias exaltata L.) in Great Smoky Mountains National Park

Incidence and severity of ozone-induced foliar symptoms on tall milkweed (Asclepias exaltata L.) along selected trails in Great Smoky Mountains National Park (GRSM) were determined by two surveys/season conducted from 1992 through 1996. Overall incidence was 73%, and was 84%, 44%, 90%, 58%, and 82% for 1992-1996, respectively for the same clusters. Average incidence was 61% and 84% for the 1st and 2nd surveys, respectively. Seasonal comparisons showed two distinct injury groupings regarding incidence and severity of injury: 1992, 1994 and 1996 (high injury); 1993 and 1995 (low injury). No discernible patterns were observed between symptomatic and asymptomatic plants regarding height, herbivory or flowering. Regression analyses indicated no differentiation in foliar symptoms regarding topographic position, aspect, slope or elevation over the 5-year study period. Our findings indicate other micro-site or genetic factors may control ozone sensitivity of tall milkweed in GRSM.

Stomatal behavior of ozone-sensitive and -insensitive coneflowers (Rudbeckia laciniata var. digitata) in Great Smoky Mountains National Park

* Morphological and physiological attributes were assessed to elucidate the underlying mechanisms of ozone (O(3)) sensitivity in a highly sensitive species, cutleaf coneflower (Rudbeckia laciniata var. digitata). * Foliage at the same height in the canopy on paired O(3)-sensitive and -insensitive cutleaf coneflowers was assessed for level of foliar symptoms, stomatal density, stomatal responsiveness to dynamic changes in light and leaf-to-air vapor pressure deficit (VPD), steady-state responses to light and CO(2), intrinsic transpirational efficiency, and plant water balance. * There were no morphological differences between the sensitivity types that might have contributed to greater O(3) uptake in sensitive individuals. Stomata of sensitive plants were less responsive than those of insensitive plants to experimentally increased and decreased light intensities, and to increased VPD. O(3)-insensitive plants had greater intrinsic transpirational efficiencies, greater maximum assimilation rates under saturating CO(2) and light, and greater carboxylation rates. * Different physiological attributes vary independently within an individual plant, which collectively confer sensitivity or insensitivity to O(3) injury.

Yield and nutritive quality of sericea lespedeza (Lespedeza cuneata) and little bluestem (Schizachyrium scoparium) exposed to ground-level ozone

Sericea lespedeza (Lespedeza cuneata cv. Interstate 76) and little bluestem (Schizachyrium scoparium cv. Aldous) were raised from seed in a glasshouse, transplanted into 5.7-l pots and placed into open-top chambers (OTC) on 6 June 1999. Following a 7-day adjustment period, each of six OTCs (duplicate OTCs per treatment) was ventilated with either air that had been carbon-filtered (CF) to remove ambient ozone (O3); non-filtered (NF), representative of ambient air; or enriched to twice-ambient O3 concentration (2X). Primary-growth forage was harvested on days 7, 32, 46, 59 and 72 following the start of fumigation, and regrowth forage from the first primary-growth harvest was harvested on days 36, 54 and 72 following the start of fumigation. Dry matter (DM) yield of either forage species did not differ among treatments except in the final regrowth period when yield of sericea lespedeza was greater for the NF than 2X O3 treatment. In vitro DM digestibility (IVDMD) and concentrations of crude protein (CP), soluble phenolics (SP) and condensed tannins (CT) in primary-growth sericea lespedeza did not differ between treatments, but NF primary-growth forage had higher concentration of protein-precipitating tannins (PPT) than did 2X primary-growth forage. Concentrations of neutral detergent fiber (NDF), acid detergent fiber (ADF) and acid detergent lignin (ADL) were higher in NF and 2X than in CF primary-growth sericea lespedeza. Similarly, concentrations of NDF and ADL were higher, and IVDMD was lower for NF and 2X than for CF regrowth sericea lespedeza. Concentrations of ADF and ADL were lower, whereas IVDMD, in vitro NDF digestibility (IVNDFD) and concentrations of CP and SP were greater, in CF than in NF and 2X primary-growth little bluestem. Percentages IVDMD and IVNDFD and concentrations of CP and SP in NF primary-growth little bluestem were greater than those in forage exposed to 2X O3 treatment. No significant differences were observed among treatments in percentages IVDMD and IVNDFD, or concentrations of cell wall constituents or SP in little bluestem regrowth. Nutritive quality of little bluestem was decreased by < 2%, and that of sericea lespedeza by approximately 7% as a result of increased concentrations of cell wall constituents and decreased in vitro digestibility of NF and 2X compared with CF forages. Results indicate that existing and projected O3 levels can drive alterations in forage quality of select warm-season forages sufficient to have nutritional and economic implications for their utilization by ruminant herbivores.

Interpreting spatial variation in ozone symptoms shown by cutleaf cone flower, Rudbeckia laciniata L

Visible injury caused by ozone is recorded every year in native plant species growing in Great Smoky Mountains National Park (USA). One of the most sensitive species, cutleaf coneflower (Rudbeckia laciniata L.), shows great variation in symptoms between and within populations but the causes of this variation and its ecological significance are currently unknown. This paper presents data relating to genetic variation, ozone concentrations, stomatal conductance and light (PAR) within populations. The data show that populations differ in genetic diversity, one consisting of only three genets while another was very diverse. In the former population, symptoms varied greatly within a single genet, pointing to a large micro-environmental influence. Measurements of ozone, stomatal conductance and PAR within plant canopies suggest that variation in symptom expression is unlikely to be due to differences in ozone flux and more likely to be due to variation in light. The variation in visible symptoms raises the question of what bioindicators actually indicate, and it suggests that symptoms should be interpreted with great caution until the underlying causes of that variation are fully understood.

Ozone injury on cutleaf coneflower (Rudbeckia laciniata) and crown-beard (Verbesina occidentalis) in Great Smoky Mountains National Park

Incidence and severity of visible foliar ozone injury on cutleaf coneflower (Rudbeckia laciniata L.) and crown-beard (Verbesina occidentalis Walt.) were determined along selected trails at three locations in Great Smoky Mountains National Park during the summers of 2000 and 2001: Clingmans Dome, Cherokee Orchard Road and Purchase Knob. Cutleaf coneflower exhibited a greater amount of foliar injury than crown-beard each year of the 2-year study. Incidence and severity of injury was significantly greater for cutleaf coneflower growing near the edge of the Clingmans Dome trail than in the interior of the stand. Injury was greater at Clingmans Dome than Purchase Knob (70% vs. 40% ozone-injured plants, respectively), coincident with greater ozone exposures. In contrast to Clingmans Dome, there were no differences in injury between plants growing near- and off-trail at Purchase Knob. Differences in sensitivity to ozone were not observed for crown-beard growing near the edge compared with the interior of the stand adjacent to the Cherokee Orchard Road Loop. Ozone injury was greatest on the lower leaves for both species sampled with over 95% of the injured leaves occurring on the lower 50% of the plant. This is the first report of foliar ozone injury on these plant species in situ, in the Park, illustrating the great variability in symptom expression with time, and within and between populations.

Differential response of buddleia (Buddleia davidii Franch.) to ozone

Five cultivars of buddleia, Buddleia davidii Franch., were exposed to sub-ambient, ambient, and twice-ambient levels of ozone in open-top chambers for 8 weeks (June-August) during 1995: Plants were evaluated for foliar injury, growth index, and inflorescence characteristics during and following exposure. Destructive harvests were conducted at the end of the exposure period to determine dry weights of both above- and below-ground plant components. All cultivars had symptoms of visible injury in the twice-ambient treatment at both three and eight weeks after exposures began. No visible symptoms were observed at ambient ozone concentrations. At three weeks of exposure, 'Pink Delight' had the highest percentage of the leaves injured (PLI), 46.2%, followed by 'Opera' with a PLI of 23.3%. The other three cultivars had similar PLIs of less than 15%. After eight weeks of exposure, visible injury was equally severe on all cultivars with a mean PLI of 50.2% and mean Horsfall-Barratt rating of 5.4, indicating 12 to 25% of the leaf area was injured. No ozone x cultivar interaction was found for any growth variable measured. Across cultivars, growth index was reduced by 6%, total dry weight by 35%, and the number of developing floral buds and inflorescences by 29% for plants in twice-ambient ozone concentrations compared to ambient ozone concentrations. Percent biomass allocated to inflorescences was significantly greater for plants exposed to sub-ambient levels compared to those exposed to ozone at either ambient or twice-ambient concentrations. Results indicate that ozone levels similar to those in large urban areas in the southeastern United States have the potential to reduce growth and flowering of this important landscape plant.

Use of Plastic Shelters for Low-Cost Establishment of Street Trees

One-year-old seedlings of 11 commonly used urban shade tree species were protected with plastic shelters to determine effects on survival and growth. Additional seedlings were planted in the cities of Auburn and Opelika, Alabama, to determine seedling performance in actual urban settings and to estimate incidence of vandalism in five urban settings. Shelters increased survival in four species and height growth in seven. Diameter growth responses were mixed. During the first 13 months after planting, only 3% of the seedlings in the cities were damaged by people. However, 20% of the shelters were vandalized at least once. Vandalism rates for shelters were greatest (37-44%) in neighborhoods of privately and publicly owned homes; intermediate (20%) in recreational parks, and lowest (4-6%) in undeveloped or industrial park areas. Installation of each tree with its shelter cost $2.78 (excluding labor) and required 20-25 minutes of labor. Tree shelters show promise as a low-cost alternative to more expensive planting methods, especially in undeveloped portions of cities. South. J. Appl. For. 20(2):85-89.

Predisposition of trees by air pollutants to low temperatures and moisture stress

Air pollution can have direct effects on trees. It can cause visible injury to foliage and a disruption of physiological processes, such as photosynthesis and carbon allocation, leading to losses in growth and productivity. This review suggests that of equal or greater importance is the potential of air pollutants to indirectly affect tree growth and vitality by predisposing them to injury from other abiotic and biotic stresses. Predisposition by air pollutants can be the result of a disruption in biochemical processes, such as enzyme activity or production, or physiological factors (e.g. stomatal closure, carbon allocation). Air pollutants such as SO(2), O(3) and acidic mists have been implicated as predisposing agents to two of the most important of these stresses: low temperature and soil moisture. Probable mechanisms, as well as implications of predicted changes in global climate will be discussed.

Effects of soil-applied lead on seedling growth and ectomycorrhizal colonization of loblolly pine

Six-month-old loblolly pine (Pinus taeda) were grown for 15 weeks in two native soils amended with 0, 30, 60, 120, 240 or 480 mg kg(-1) Pb as PbCl2. Ectomycorrhizae were quantified, by morphotype, as the total number of tips per centimeter, and as the number of tips for each morphotype and for Cenococcum geophilum. Total numbers of non-ectomycorrhizal short roots and necrotic tips were recorded. Total height and biomass exhibited a non-linear response to soil-applied lead. Growth generally was greatest in the controls and higher treatments, and least in the intermediate treatments. In both soils, Pb concentrations in roots increased linearly with increasing levels of soil-applied Pb. Neither foliage nor stems exhibited significant increases in Pb concentrations with increasing levels of Pb. Significant linear decreases in total numbers of ectomycorrhizal tips and significant linear increases in non-ectomycorrhizal short roots and necrotic tips occurred with increasing levels of Pb in the soil. The majority of individual morphotypes decreased with increasing Pb. However, the number of ectomycorrhizal tips formed by C. geophilium increased with increasing soil Pb levels after 15 weeks of treatment. These results indicate that short-term loblolly pine seedling growth is not inhibited by increasing Pb levels. Ectomycorrhizal formation decreased, and alterations in species composition occurred as a result of increasing concentrations of soil-applied Pb. These effects on ectomycorrhizae may cause long-term changes in nutrient and water balances, which could reduce tree vigor.

Two methods to determine plant responses to pollutant mixtures

Two methods are described which enable better interpretation of the effects of pollutant mixtures on plants. The first method is a statistical procedure in which treatment components are partitioned into single degrees of freedom comparisons. With this technique, joint action of pollutants can be calculated. Trends in response, such as linear or quadratic, can be observed for quantitative data. Also, the nature of interactions in experiments of a factorial design can be determined. The second procedure described is growth analysis. Growth analysis provides a method for determination of the effects of pollutants on physiological processes, such as relative rates of growth, carbon allocation and leaf expansion. Advantages, disadvantages and applications of both methods are discussed.

Growth and physiological responses of yellow-poplar seedlings exposed to ozone and simulated acidic rain

Nine-week-old, yellow-poplar (Liriodendron tulipifera L.) seedlings were exposed to ozone (O(3)) 4 h day(-1), 5 days week(-1), in combination with simulated rain (pH 3.0, 4.3, or 5.6, 1 h day(-1), 2 days week(-1), at 0.75 cm h(-1)) for 6 weeks, under controlled laboratory conditions. There was no main treatment effect of O(3) (<0.02, 0.05, 0.10, or 0.15 microlitre(-1)) on height growth or total plant biomass. However, specific leaf area increased linearly (P=0.05) with exposure of plants to increasing O(3) concentrations. Exposure of seedlings to 0.10 microl litre(-1) O(3) reduced the leaf area ratio and the stomatal conductance (S(c)), but increased the mean unit leaf rate compared to control plants. This O(3) concentration also caused S(c) to decrease more rapidly, relative to non-fumigated plants, in response to increasing vapor pressure deficit. The only main treatment effect caused by simulated rain was a linear decrease in S(c) with increasing acidity. For combined pollutant effects, O(3) applied at 0.05 or 0.10 microl litre(-1) resulted in significant (P=0.05) linear decreases in dry weights and relative growth rates (RGR) of stems and leaves, and in cumulative leaf area (LAI), as the solution pH decreased. Root to shoot ratio (RSR) decreased linearly, whereas stem RGR and LAI increased linearly in response to decreasing pH for seedlings exposed to 0.15 microl litre(-1) O(3). Seedlings treated with a pH 5.6 solution exhibited a linear decrease (P=0.05) in leaf dry weight and RGR and a linear increase (P=0.05) in RSR as O(3) concentrations increased.

Field responses of redheaded pine sawfly males to a synthetic pheromone and virgin females in Florida

Field tests using the sawfly pheromone [3,7-dimethylpentadecan-2-ol acetate with (-)-erythro configuration (2S,3S)] were conducted near Gainesville, Florida, during 1978-1981 to determine the attraction ofNeodiprion lecontei males to baited traps with respect to time of year and time of day. Greatest numbers of males were caught during May, July, and September in traps placed within a pine stand from July 1978 to July 1979. Males were only caught between 1400 and 2000 hr on 10 dates in June and 10 dates in September-October 1980, and 10 dates in June 1981, with greatest catches from 1600-1800 hr. Catches in a synthetic-baited trap and in virgin female-baited traps were similar with respect to time of day.