Differential responses of stomatal kinetics and steady-state conductance to abscisic acid in a fern: comparison with a gymnosperm and an angiosperm.

Origins of abscisic acid (ABA)-mediated metabolic control of stomatal conductance have been suggested to be recent, based on a gradualistic model of stomatal evolution. In ferns, steady-state stomatal conductance (gs ) was unresponsive to ABA in some studies, supporting this model. Stomatal kinetic responses to ABA have not been considered. We used dynamic gas exchange methods to characterise half times of stomatal opening and closing in response to step changes in light, across a range of ABA exposures in three diverse taxa. All taxa had asymmetric kinetics, with closure slower than opening in fern and cedar, but faster than opening in soybean. Closing was fastest in soybean but opening was slowest. Stomatal kinetics, particularly for closure, responded to ABA in all three taxa. Steady-state gs did not respond significantly to ABA in fern or cedar but responded strongly in soybean. Stomatal kinetics were responsive to ABA in fern. This finding supports a contrasting, single origin model, with ABA-mediated regulation of stomata arising early, in conjunction with stomata themselves. Stomatal kinetics are underutilised. Differential responses of opening and closing rates to environmental and hormonal stimuli may provide insights into phylogeny and stomatal regulatory strategies with potential application to selection for crop improvement.

Global topics and novel approaches in the study of air pollution, climate change and forest ecosystems.

Research directions from the 27th conference for Specialists in Air Pollution and Climate Change Effects on Forest Ecosystems (2015) reflect knowledge advancements about (i) Mechanistic bases of tree responses to multiple climate and pollution stressors, in particular the interaction of ozone (O3) with nitrogen (N) deposition and drought; (ii) Linking genetic control with physiological whole-tree activity; (iii) Epigenetic responses to climate change and air pollution; (iv) Embedding individual tree performance into the multi-factorial stand-level interaction network; (v) Interactions of biogenic and anthropogenic volatile compounds (molecular, functional and ecological bases); (vi) Estimating the potential for carbon/pollution mitigation and cost effectiveness of urban and peri-urban forests; (vii) Selection of trees adapted to the urban environment; (viii) Trophic, competitive and host/parasite relationships under changing pollution and climate; (ix) Atmosphere-biosphere-pedosphere interactions as affected by anthropospheric changes; (x) Statistical analyses for epidemiological investigations; (xi) Use of monitoring for the validation of models; (xii) Holistic view for linking the climate, carbon, N and O3 modelling; (xiii) Inclusion of multiple environmental stresses (biotic and abiotic) in critical load determinations; (xiv) Ecological impacts of N deposition in the under-investigated areas; (xv) Empirical models for mechanistic effects at the local scale; (xvi) Broad-scale N and sulphur deposition input and their effects on forest ecosystem services; (xvii) Measurements of dry deposition of N; (xviii) Assessment of evapotranspiration; (xix) Remote sensing assessment of hydrological parameters; and (xx) Forest management for maximizing water provision and overall forest ecosystem services. Ground-level O3 is still the phytotoxic air pollutant of major concern to forest health. Specific issues about O3 are: (xxi) Developing dose-response relationships and stomatal O3 flux parameterizations for risk assessment, especially, in under-investigated regions; (xxii) Defining biologically based O3 standards for protection thresholds and critical levels; (xxiii) Use of free-air exposure facilities; (xxiv) Assessing O3 impacts on forest ecosystem services.

Developing monitoring techniques for the invasive goldspotted oak borer (Coleoptera: Buprestidae) in California.

The goldspotted oak borer, Agrilus auroguttatus Schaeffer (Coleoptera: Buprestidae), is an invasive species that has colonized oak woodlands in southern California. To better define its seasonal flight activity, assist with forest and integrated pest management activities, and define the current distribution in California, an effective monitoring technique for A. auroguttatus is necessary. We assessed the efficacy of two colors of flight-intercept prism traps, the placement of these traps at three heights, and several commercially available lures [Manuka oil, Phoebe oil, and a green leaf volatile, (3Z)-hexenol] for monitoring the flight of adult A. auroguttatus. Landing rates and the densities of D-shaped emergence holes of A. auroguttatus adults were assessed on the lower stems of coast live oak, Quercus agrifolia Née, of varying size and crown health classes. Purple flight-intercept prism traps placed at heights of 3 m and 4.5 m caught significantly more female A. auroguttatus than green prism traps. In one experiment, males also responded at a significantly higher level to purple than to green prism traps placed at 3 m height. The addition of commercially available lures significantly enhanced male, but not female, A. auroguttatus trap catch when compared with unbaited control traps. There were no differences among male flight responses to the three lures. A. auroguttatus landing rates and emergence hole densities were significantly greater on the largest-diameter trees (>76.2 cm diameter at breast height) and on trees with severe crown thinning or complete crown collapse. The annual increment in emergence hole densities was also significantly greater on trees with severe crown thinning or complete crown collapse. In three trapping studies over multiple years in southern California, the adult flight period began as early as mid-May, peaked in mid-June to early July, and ended in early- to mid-September. To demonstrate the efficacy of the detection method for A. auroguttatus (unbaited purple traps at 3 m height), a delimitation survey conducted from 2009 to 2012 confirmed that the species was only present in San Diego Co., but that the distribution was expanding northward.

Use of introgression lines to determine the ecophysiological basis for changes in water use efficiency and yield in California processing tomatoes.

Field and greenhouse studies examined the effects of growth habit and chloroplast presence in leaf veins for their role in increasing agronomic water use efficiency and yields of California modern processing tomato (Solanum lycopersicum L.) cultivars. Five introgression lines (ILs), made with Solanum pennellii Cor. in the genetic background of cultivar M82, differ in genes that map to a region on Chromosome 5, including the SP5G gene (determinate vs. semideterminate (Det vs. SemiDet)) and the obv gene (presence (obscure) vs. absence (clear) of leaf vein chloroplasts (Obs vs. Clr)). The five ILs and M82 represented three of the four gene combinations (Det-Clr was unavailable). Det-Obs ILs had less leaf, stem and total aboveground biomass with earlier fruit set and ripening than SemiDet-Clr ILs. By harvest, total fruit biomass was not different among ILs. Photosynthetic rates and stomatal conductance were 4-7% and 13-26% higher, respectively, in Det-Obs ILs than SemiDet-Clr ILs. SemiDet-Obs ILs were intermediate for growth and gas exchange variables. The Det-Obs ILs had lower leaf N concentration and similar chlorophyll content per leaf area (but slightly higher per leaf mass) than SemiDet-Clr ILs. The Obs trait was associated with gains in leaf gas exchange-related traits. This study suggests that a more compact growth habit, less leaf biomass and higher C assimilation capacity per leaf area were relevant traits for the increased yields in cultivars with determinate growth. Developing new introgression libraries would contribute to understanding the multiple trait effects of desirable phenotypes.

Ozone exposure and stomatal sluggishness in different plant physiognomic classes.

Gas exchange responses to static and variable light were tested in three species: snap bean (Phaseolus vulgaris, two cultivars), California black oak (Quercus kelloggii), and blue oak (Q. douglasii). The effects of 1-month (snap beans) and 2-month (oaks) O(3) (ozone) exposure (70ppb over 8h per day in open-top chambers) were investigated. A delay in stomatal responses (i.e., 'sluggish' responses) to variable light was found to be both an effect of O(3) exposure and a reason for increased O(3) sensitivity in snap bean cultivars, as it implied higher O(3) uptake during times of disequilibrium. Sluggishness increased the time to open (thus limiting CO(2) uptake) and close stomata (thus increasing transpirational water loss) after abrupt changes in light level. Similar responses were shown by snap beans and oaks, suggesting that O(3)-induced stomatal sluggishness is a common trait among different plant physiognomic classes.

Impacts of air pollution and climate change on forest ecosystems--emerging research needs.

Outcomes from the 22nd meeting for Specialists in Air Pollution Effects on Forest Ecosystems "Forests under Anthropogenic Pressure--Effects of Air Pollution, Climate Change and Urban Development", September 10-16, 2006, Riverside, CA, are summarized. Tropospheric or ground-level ozone (O3) is still the phytotoxic air pollutant of major interest. Challenging issues are how to make O3 standards or critical levels more biologically based and at the same time practical for wide use; quantification of plant detoxification processes in flux modeling; inclusion of multiple environmental stresses in critical load determinations; new concept development for nitrogen saturation; interactions between air pollution, climate, and forest pests; effects of forest fire on air quality; the capacity of forests to sequester carbon under changing climatic conditions and coexposure to elevated levels of air pollutants; enhanced linkage between molecular biology, biochemistry, physiology, and morphological traits.

Defense and avoidance of ozone under global change.

The level II approach of the critical loads concept adopted by the UNECE aims at a flux based evaluation and takes into account environmental factors governing stomatal conductance. These factors will probably be affected by global change. The flux concept predicts that a decrease in stomatal conductance would protect trees from air pollution effects by decreasing uptake. However, experimental evidence is inconclusive. Numerous results suggest that pollutants and factors subject to global change (drought, CO(2)) may interact and even exacerbate effects, probably because antioxidative defense systems are involved in both, defense against pollutant effects and protection from natural stress. An effective pollutant dose, which is weighted by physiological defense capacity, would better predict such effects. In this review paper we argue that the flux-based approach is imperfect, because global change effects may also modify the physiological susceptibility to ozone. Instead, a flux concept weighted by defense capacity should be tested.

Does living in elevated CO2 ameliorate tree response to ozone? A review on stomatal responses.

Short-term elevated O3 reduces photosynthesis, which reduces stomatal conductance (g(s)) in response to increased substomatal CO2 concentration (Ci). Further exposure causes stomata to become sluggish in response to environmental stimuli. Exposure to elevated CO2 stimulates rapid stomata closure in response to increased Ci. This reduction in g(s) may not be sustained over time as photosynthesis down-regulates and with it, g(s). The relationship between g(s) and photosynthesis may not be constant because stomata respond more slowly to environmental changes than photosynthesis, and because elevated CO2 may alter guard cell sensitivity to other signals. Also, reduced stomatal density (and g(s)) in response to long-term CO2 enrichment suggests sustained reduction in g(s). Elevated CO2 is believed to ameliorate the deleterious O3 effects by reducing g(s) and thus the potential O3 flux into leaves. Confirmation that g(s) acclimation to CO2 enrichment does not lessen over time is critical for developing meaningful O3 flux scenarios.

Photochemical smog effects in mixed conifer forests along a natural gradient of ozone and nitrogen deposition in the San Bernardino Mountains.

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.

Summer-time distribution of air pollutants in Sequoia National Park, California.

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 (SO4(2-)); 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 microg/m3), NH3 (seasonal means 1.6-4.5 microg/m3), NO3 (1.1-2.0 microg/m3) and NH4+ (1.0-1.9 microg/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.