Multivariate patterns of biochemical responses of Pinus ponderosa trees at field plots in the San Bernardino Mountains, southern California

Most environmental stress conditions promote the production of potentially toxic active oxygen species in plant cells. Plants respond with changes in their antioxidant and photoprotective systems. Antioxidants and pigments have been widely used to measure these responses. Because trees are exposed to multiple man-made and natural stresses, their responses are not reflected by changes in single stress markers, but by complex biochemical changes. To evaluate such response patterns, explorative multivariate statistics have been used. In the present study, 12 biochemical variables (chloroplast pigments, state of the xanthophyll cycle, alpha-tocopherol, ascorbate and dehydroascorbate, glutathione and oxidized glutathione) were measured in previous-year needles of field-grown Pinus ponderosa Dougl. ex Laws. The trees were sampled in two consecutive years in the San Bernardino Mountains in southern California, where a pollution gradient is overlaid by gradients in natural stresses (drought, altitude). To explore irradiance effects, needle samples were taken directly in the field (sun exposed) and from detached, dark-adapted branches. A principal component analysis on this data set (n = 80) resulted in four components (Components 1-4) that explained 67% of the variance in the original data. Component 1 was positively loaded by concentrations of alpha-tocopherol, total ascorbate and xanthophyll cycle pools, as well as by the proportion of de-epoxides in the xanthophyll cycle. It was negatively loaded by the proportion of dehydroascorbate in the ascorbate pool. Component 2 was negatively loaded by chlorophyll concentrations, and positively loaded by the ratios of lutein and beta-carotene to chlorophyll and by the de-epoxidation state of the xanthophyll cycle. Component 3 was negatively loaded by GSH concentrations and positively loaded by the proportions of GSSG and tocopherol concentrations. Component 4 was positively loaded by neoxanthin and negatively loaded by beta-carotene. The four components could be assigned to the concerted action of the biochemical protection system: high scores on Component 1 represent highly activated antioxidative defense, changes in pigment composition are represented in Components 2 and 4, and the glutathione system, which is important for antioxidant regeneration, is represented in Component 2. Although Component 1 scores were generally higher (indicating activation of antioxidant defense) in light-adapted needles relative to dark-adapted needles, they were also site dependent with increased scores at sites with less pollution, but higher natural stress impacts. High scores of Components 2 and 3 at the highest elevation site, which was only moderately polluted, indicated an increase in photoprotection by pigments and activation of the glutathione system. Significant differences between light- and dark-adapted needles in Components 2 and 3 were only found at the site with the highest pollution. Use of accumulated variables (components) instead of single biochemical variables enabled recognition of response patterns at particular sites and a better comparison with results of other studies is expected. Typical response patterns could be assigned to particular environmental stress combinations, providing a means of assessing potential biological risks within individual forest stands.     

Design,Evaluation and Application of a Continuously Stirred Tank Reactor System for Use in Nitric Acid Air Pollutant Studies

Nitric acid (HNO₃) vapor is a significant component of air pollution. Dry deposition of HNO₃ is thought to be a major contributor to terrestrial loading of anthropogenically-derived nitrogen (N), but many questions remain regarding the physico-chemical process of deposition and the biological responses to accumulation of dry-deposited HNO₃ on surfaces. To examine these processes experimentally, a continuously stirred tank reactor (CSTR) fumigation system has been constructed. This system enables simultaneous fumigation at several concentrations in working volumes 1.3 m dia by 1.3 m ht, allowing for simultaneous fumigation of many experimental units. Evaluation of the system indicates that it is appropriate for long-term exposures of several months duration and capable of mimicking patterns of diurnal atmospheric HNO₃ concentrations representative of areas with different levels of pollution.     

Chemical Composition of Air, Soil and Vegetation in Forests of the Silesian Beskid Moutains, Poland

For the first time concentrations of trace nitrogenous (N) air pollutants, gaseous nitric acid (HNO₃), nitrous acid (HNO₂), ammonia (NH₃), and fine particulate nitrate (NO₃) and ammonium (NH₄), were measured in the montane forests of southern Poland. Determinations were performed in two forest locations of the Silesian Beskid Mountains in the western range of the Carpathian Mountains, and in an industrial/urban location in Karowice, Poland. The measurements performed in summer 1997 with honeycomb denuder/filter pack systems showed elevated concentrations of the studied pollutants. These findings agree with the low carbon/nitrogen (C/N) ratios and the results of ¹⁵N analyses of soil and moss samples. High concentrations of N air pollutants help to explain previously determined high levels of NO₃ and NH4 deposition to Norway spruce (Picea abies Karst.) canopies in these mountains. Ambient concentrations of sulfur dioxide (SO2) and ozone (O3) were elevated and potentially phytotoxic. Deficiencies of phosphorus (P) and magnesium (Mg) in Norway spruce foliage were found while concentrations of other nutrients were normal.     

Changes in Free-Radical Scavengers Describe the Susceptibility of Pinus Ponderosa to Ozone in Southern Californian Forests

Damage of Pinus ponderosa Dougl. Ex P. and C. Laws, in the San Bernardino Mountains in Southern California is a well-known example for ozone-phytotoxic effects in forests. In October 1997, needles were collected at the severely impacted Dogwood plot, where pines showing severe crown thinning (‘symptomatic’) and asymptomatic ones grow together. Visible chlorosis was not or only mildly developed on the sampled current year's (c) and previous year's (c+l) needles at the time of collection. In sun exposed needles of symptomatic trees, but not in needles which were dark adapted overnight, significantly lower glutathione contents were found compared to asymptomatic trees. In asymptomatic trees sun-exposed and dark adapted needles contained 85 to 90% of the glutathione pool in the reduced state, whereas in sun exposed needles of symptomatic trees a significantly higher proportion of oxidised glutathione was observed (>20%). The redox state of the ascorbate pool remained unaffected, but needles of asymptomatic trees showed a significant decrease of total ascorbate upon darkening. Tocopherol contents were not significantly different between symptomatic and asymptomatic individuals. The results indicate oxidative alterations in needles of symptomatic trees. Since these changes are detectable before severe visual symptoms appear on the needles, they represent initial physiological damage and might be useful for an early risk assessment of ozone phytotoxic potential on pine trees in the field.