Seasonal patterns of carbohydrate concentration in coarse and fine roots, stem or bole, and foliage of ponderosa pine (Pinus ponderosa Laws) were described across five treeage classes from seedlings to mature trees at an atmospherically clean site. Relative to all other tree-age classes, seedlings exhibited greater tissue carbohydrate concentration in stems and foliage, and greater shifts in the time at which maximum and minimum carbohydrate concentration occurred. To determine the effect of environmental stressors on tissue carbohydrate concentration, two tree-age classes (40-year-old and mature) were compared at three sites along a well-established, long-term O3 and N deposition gradient in the San Bernardino Mountains, California. Maximum carbohydrate concentration of 1-year-old needles declined with increasing pollution exposure in both tree-age classes. Maximum fine root monosaccharide concentration was depressed for both 40-year-old and mature trees at the most polluted site. Maximum coarse and fine root starch concentrations were significantly depressed at the most polluted site in mature trees. Maximum bole carbohydrate concentration of 40-year-old trees was greater for the two most polluted sites relative to the cleanest site: the bole appeared to be a storage organ at sites where high O3 and high N deposition decreased root biomass.
Concentrations of air pollutants were monitored during the May–November 1999 period on a network of forested sites in Sequoia National Park, California. Measurements were conducted with: (1) active monitors for nitric oxide (NO), nitrogen dioxide (NO2) and ozone (O3); (2) honeycomb denuder/filter pack systems for nitric acid vapor (HNO3), nitrous acid vapor (HNO2), ammonia (NH3), sulfur dioxide (SO2), particulate nitrate (NO3–), ammonium (NH4+, and sulfate (SO42–); and (3) passive samplers for O3, HNO3 and NO2. Elevated concentrations of O3 (seasonal means 41–71 ppb), HNO3 (seasonal means 0.4–2.9 µg/m3), NH3 (seasonal means 1.6–4.5 µg/m3), NO3 (1.1–2.0 µg/m3) and NH4+ (1.0–1.9 µg/m3) were determined. Concentrations of other pollutants were low. With increasing elevation and distance from the pollution source area of O3, NH3 and HNO3 concentrations decreased. Ammonia and NH4+ were dominant N pollutants indicating strong influence of agricultural emissions on forests and other ecosystems of the Sequoia National Park. Published by Elsevier Science Ltd.
• The effect of O3 exposure or uptake on carbon acquisition (net assimilation (A) or gross photosynthesis (Pg)), with and without drought stress, is reported here in 40-yr-old-ponderosa pine (Pinus ponderosa) trees. • Maximum daily gas exchange was measured monthly for 12 trees at four sites differing in pollutant exposure over two growing seasons with above- and below-average annual precipitation. Gas exchange measures were estimated between sampling periods using a generalized additive regression model. • Both A and Pg generally declined with cumulative O3 exposure or uptake at all sites. As a response variable, Pg was slightly more sensitive than A to cumulative O3 exposure. As a metric, O3 uptake vs exposure permitted slightly better statistical resolution of seasonal response between sites. • The effect of late summer drought stress was statistically significant only at the moderate pollution site, and combined synergistically with O3 exposure or uptake to reduce Pg. The general additive model allows the user to define a deleterious level of cumulative O3 exposure or uptake, and to quantitatively assess biological response.
Toxic effects of photochemical smog on ponderosa and Jeffrey pines in the San Bernardino Mountains were discovered in the 1950s. It was revealed that ozone is the main cause of foliar injury manifested as chlorotic mottle and premature needle senescence. Various morphological, physiological and biochemical alterations in the affected plants have been reported over a period of about 40 years of multidisciplinary research. Recently, the focus of research has shifted from studying the effects of ozone to multiple pollutant effects. Recent studies have indicated that the combination of ozone and nitrogen may alter biomass allocation in pines towards that of deciduous trees, accelerate litter accumulation, and increase carbon sequestration rates in heavily polluted forests. Further study of the effects of multiple pollutants, and their long-term consequences on the mixed conifer ecosystem, cannot be adequately done using the original San Bernardino Mountains Air Pollution Gradient network. To correct deficiencies in the design, the new site network is being configured for long-term studies on multiple air pollutant concentrations and deposition, physiological and biochemical changes in trees, growth and composition of over-story species, biogeochemical cycling including carbon cycling and sequestration, water quality, and biodiversity of forest ecosystems. Eleven sites have been re-established. A comparison of 1974 stand composition with data from 2000 stand composition indicate that significant changes in species composition have occurred at some sites with less change at other sites. Moist, high-pollution sites have experienced the greatest amount of forest change, while dryer low-pollution sites have experienced the least amount of stand change. In general, ponderosa pine had the lowest basal area increases and the highest mortality across the San Bernardino Mountains. Published by Elsevier Science Ltd.
Crown morphology and leaf tissue chemical and biochemical attributes associated with ozone (O3) injury were assessed in the lower, mid- and upper canopy of Jeffrey pine (Pinus jeffreyi Grev. & Balf.) growing in mesic and xeric microsites in Sequoia National Park, California. Microsites were designated mesic or xeric based on topography and bole growth in response to years of above-average precipitation. In mesic microsites, canopy response to O3 was characterized by thinner branches, earlier needle fall, less chlorotic leaf mottling, and lower foliar antioxidant capacity, especially of the aqueous fraction. In xeric microsites, canopy response to O3 was characterized by higher chlorotic leaf mottling, shorter needles, lower needle chlorophyll concentration, and greater foliar antioxidant capacity. Increased leaf chlorotic mottle in xeric microsites was related to drought stress and increased concurrent internal production of highly reactive oxygen species, and not necessarily to stomatal O3 uptake.Within-canopy position also influenced the expression of O3 injury in Jeffrey pine.
Ponderosa pine (Pinus ponderosa Dougl. exLaws.) is widely distributed in the western USA.We report the lack of stomatal closure at night in early summer for ponderosa pine at two of three sites investigated. Trees at a third site with lower nitrogen dioxide and nitric acid exposure, but greater drought stress, had slightly open stomata at night in early summer but closed stomata at night for the rest of the summer. The three sites had similar background ozone exposure during the summer of measurement (2001). Nighttime stomatal conductance (gs) ranged from one tenth to one fifth that of maximum daytime values. In general, pole-sized trees (< 40 years old) had greater nighttime gs than mature trees (> 250 years old). In late summer, nighttime gs was low (< 3.0 mmol H2O m–2 s–1) for both tree size classes at all sites. Measurable nighttime gs has also been reported in other conifers, but the values we observed were higher. In June, nighttime ozone (O3) uptake accounted for 9, 5 and 3% of the total daily O3 uptake of pole-sized trees from west to east across the San Bernardino Mountains. In late summer, O3 uptake at night was < 2% of diel uptake at all sites. Nocturnal O3 uptake may contribute to greater oxidant injury development, especially in pole-sized trees in early summer.
Decreased root biomass in forest trees in response to anthropogenic pollutants is believed to be one of the first steps in forest health degradation. Although decreased root biomass has been observed in controlled experiments, ozone effects on mature tree roots in natural stands has not previously been documented. Here we report standing root biomass of ponderosa pine at three sites in the San Bernardino Mountains distributed along a known, long-term pollution gradient of ozone and nitrogen deposition. Trees at each site were assessed for foliar ozone injury and below-ground attributes, in addition to other environmental factors known to influence root growth. During the period of peak root growth in the spring, root biomass at the least polluted site was 6-14 times greater than that observed at the most polluted site. Known differences in climatic and edaphic factors among the sites potentially contributing to the observed response were discounted as primary contributors to the response since in most cases the site differences would have driven the patterns of root growth in the opposite direction to that observed. Differences in biotic competitive interactions, also known to affect root growth, did not explain the observed pattern for the same reason. The data suggests that elevated ozone, high nitrogen deposition, and possibly other contributing factors such as soil acidification are primarily responsible for lowering root biomass in ponderosa pine stands in the San Bernardino Mountains. Published by Elsevier Science Ltd.
In a nitrogen (N) saturated forest downwind from Los Angeles, California, the cumulative response to long-term background-N and N-amendment on black oak (Quercus kelloggii) was described in a below-average and average precipitation year. Monthly measurements of leaf and branch growth, gas exchange, and canopy health attributes were conducted. The effects of both pollutant exposure and drought stress were complex due to whole tree and leaf level responses, and shade versus full sun leaf responses. N-amended trees had lower late summer carbon (C) gain and greater foliar chlorosis in the drought year. Leaf water use efficiency was lower in N-amended trees in midsummer of the average precipitation year, and there was evidence of poor stomatal control in full sun. In shade, N-amendment enhanced stomatal control. Small differences in instantaneous C uptake in full sun, lower foliar respiration, and greater C gain in low light contributed to the greater aboveground growth observed.
Seeds from two full-sib families of ponderosa pine (Pinus ponderosa) with known differences in growth rates were germinated and grown in an ambient (350 µl l-1) or elevated (700 µl I-1) CO2 concentration. Gas exchange at both ambient and elevated CO2 concentrations was measured 1,6,39, and 112 days after the seed coat was shed. Initial stimulation of CO2 exchange rate (CER) by elevated CO2 was large (> 100%). On Day 1, CER of seedlings grown in elevated CO2 and measured at ambient CO2 was significantly lower than the CER of seedlings grown and measured at ambient CO2, indicating physiological adjustment of the seedlings exposed to elevated CO2. Physiological acclimation to elevated CO2 was complete by Day 39 when there was no significant difference in CER between seedlings grown and measured at ambient CO2 and seedlings grown and measured at elevated CO2. After 4 months, the light response of seedlings in the two treatments was determined at both ambient and elevated CO2. Light compensation point, CER at light saturation, and apparent quantum efficiency of seedlings grown and measured at ambient CO2 were not significantly different from those of seedlings grown and measured at elevated CO2. With a short-term increase in CO2, CER at light saturation (5.16 ± 0.52 versus 3.13 ± 0.30 µmol CO2 m-2 s-1) and apparent quantum efficiency (0.082 ± 0.011 versus 0.045 ± 0.003 µmol CO2 µmol-1 quanta) were significantly increased. Leaf C/N ratio was significantly increased in the elevated CO2 treatment. There were few significant differences between families for any response to elevated CO2. Under the experimental conditions, high growth rate was not correlated with a greater response to elevated CO2.