USDA Forest Service
 

Pacific Southwest Research Station

 

Pacific Southwest Research Station
800 Buchanan Street
West Annex Building
Albany, CA 94710-0011

(510) 559-6300

United States Department of Agriculture Forest Service. USDA logo which links to the department's national site. Forest Service logo which links to the agency's national site.

Programs and Projects

(RWU-4451)

Air Pollution and Global Change Impacts on Western Forest Ecosystems

Pamela E. Padgett
Plant Biologist
E-mail: ppadgett@fs.fed.us
Phone: (951) 680-1585

Pacific Southwest Research Station
Forest Fire Laboratory
4955 Canyon Crest Drive
Riverside, CA 92507

Ph: (951) 680-1500
Fx: (951) 680-1501

Education
BS Agronomy Virginia Polytechnic Institite & SU 1987
Ph.D. Botany University of Californa Riverside 1993
Research Interests/Duties

My research uses experimental studies to understand the interactions between the living (biotic) and nonliving (abiotic) world. Most of the studies are conducted in controlled environments such as greenhouses, growth chambers, or research plots in the field. This enables us to control the environment while measuring changes in plant characteristics. The scientific approach is to simplify very complicated environmental conditions into things we can control and measure. We can then evaluate how changing environmental characteristics are reflected in plant growth and function. Establishing testable hypotheses is key to this type of research.

Assimilation and metabolism of plant nutrients
  • Padgett PE, Leonard RT, 1994. The effect of the physical and chemical environment on nitrate uptake in Zea mays cell suspension cultures. Journal of Experimental Botany 45:1387-1396
  • Padgett PE, Leonard RT, 1996. The interaction between cellular amino acid concentration and the regulation of nitrate transport in Zea mays cell suspension cultures. Journal of Experimental Botany 47:871-883
  • Padgett PE, Allen EB, 1999. Differential responses to nitrogen fertilization in native shrubs and exotic annuals common to the Mediterranean coastal sage scrub of California. Plant Ecology 144: 93-101
Photo of growth responses of Bromus rubens to increasing soil nitrogen
Growth responses of Bromus rubens to increasing soil nitrogen.

The ability of plants to convert inorganic molecules such as nitrate, phosphate, sulfate and carbon dioxide into organic molecules such as sugars, amino acids, proteins and ATP is the foundation of all food webs. Without plants' ability to convert solar energy into chemical energy (photosynthesis), life, as we know it could not exist. It is photosynthesis that drives the biochemical machinery enabling simple molecules absorbed from the earth and air to be chemically reduced to form the large complicated molecules that make life possible.

Monitoring and measuring dry deposition of nitrogen containing air pollutants
  • Padgett PE, Allen EB, Bytnerowicz A, Minnich RA, 1999. Changes in levels of soil inorganic nitrogen as a result of atmospheric nitrogenous pollutants in southern California. Atmospheric Environment 33:769-781
  • Bytnerowicz, A., Padgett P.E. 2000. Dry deposition of nitrogenous air pollutants to plant and soils - implications for N inputs to California forests and other ecosystems. In: Proceedings of the North American IUFRO meeting May 29 - May 31, 2000 Houghton, Michigan.
  • Padgett PE, Bytnerowicz A. 2001. Deposition and adsorption of the air pollutant HNO3 vapor to soil surfaces. Atmospheric Environment 35:2405-2415
Photo of passive samplers for monitoring ozone and HNO<sub>3</sub> in the Eastern Sierra.
Passive samplers for monitoring ozone and HNO3 in the Eastern Sierra

Deposition of nitrogen-containing air pollutants is analogous to agricultural nitrogen fertilization. Where rain is plentiful, deposition occurs as wet fall (occasionally still referred to as acid rain). Nitrogen deposition also occurs in snowfall and fog events. In arid or semi arid zones, deposition most commonly occurs as dry deposition. Dry deposition can be either the accumulation of gaseous molecules on a surface or accumulation of particulates. Small daily incremental accumulation of dry-deposited nitrogen can lead to substantially changes in ecosystem fertility. Yet, the ability to measure and quantify dry deposition is poorly developed.

Direct interactions between plants and air pollutions
  • Bytnerowicz A, Percy KE, Riechers G, Padgett P, Krywult M. 1998. Nitric acid vapor effects on forest trees - Deposition and cuticular changes. Chemosphere. 36:697-702
  • Tausz, A. Padgett, P.E., Monschein, S., Bytnerowicz, A. 2002. The effects of nitric acid on antioxidants and protective pigments in Pinus ponderosa needles. Phyton 42: 209-214.
  • Padgett PE, Bytnerowicz A, Dawson PJ, Riechers GH, Fitz, DR. 2004. Design, evaluation and application of a continuously stirred tank reactor system for use in nitric acid air pollution studies. Water, Air and Soil Pollution 151:35-51.
Photo of trichomes on white sage before HNO3 deposition
Trichomes on white sage before HNO3 deposition
Photo of trichomes on white sage after HNO3 deposition

Trichomes on white sage after HNO3 deposition

Dry deposition not only results in increased soil fertility, but direct deposition of nitric acid, a common secondary pollutant associated with ozone, can be directly absorbed by leaves and seems to attack components of the leaves protective cuticle layer. Nitric acid is unique among the urban air pollutants in that it tends to stick and accumulate on surfaces it comes in contact with. But there are many questions about how the chemical interactions between a gaseous nitric acid and solid or aqueous substrates.

Plant community changes as a result of air pollution stress
  • Padgett PE, Allen EB, 1999. Differential responses to nitrogen fertilization in native shrubs and exotic annuals common to the Mediterranean coastal sage scrub of California. Plant Ecology 144: 93-101
  • Padgett PE, Kee SN, Allen EB. 2000. The effects of irrigation on revegetation of semiarid coastal sage scrub in southern California. Environmental Management 26:427-435.
  • Padgett PE, Vasaquez L, Allen, EB. 2000. Seed viability and germination behavior of the desert shrub Encelia farinosa. Torrey and A. Gray (compositae) Madroño 46:126-133.
Native shrubs growing along a road cut.  Invasive annual occupying the original grade above
Native shrubs along a road cut. Invasive annual grasses on the original topography

Ultimately, our concern with nitrogen deposition centers around the influence nitrogen fertility has on plant community structure. Ecological and agricultural science has known for many years that changes in nutrient availability results in changes in plant growth and function. Many wild plant species are well adapted to low nitrogen soils, which gives them a competitive advantage over less adapted species, particularly weedy species. When the native fertility changes, so does the plant community. The biological mechanisms that drive those changes are not well understood, however.

Restoration and remediation of disturbed habitats
  • Padgett PE, Kee SN, Allen EB. 2000. The effects of irrigation on revegetation of semiarid coastal sage scrub in southern California. Environmental Management 26:427-435.
  • Padgett PE, Vasaquez L, Allen, EB. 2000. Seed viability and germination behavior of the desert shrub Encelia farinosa. Torrey and A. Gray (compositae) Madroño 46:126-133
  • Cione, NK, Padgett, PE, Allen, EB. 2002 Restoration of a native shrubland impacted by exotic grasses, frequent fire and nitrogen deposition in southern California. Restoration Ecology. 10:376-384
Intact native coastal sage scrub
Intact coastal sage scrub

The final stage in understanding the mechanisms and processes that drive ecological responses to air pollution is to apply that information to repairing the damage. Restoration of nitrogen impacted ecosystems is in its infancy, but because air pollution damage tends to be combined with other disturbance events such as fire, road building and urbanization, there are opportunities to couple restoration with other remediation efforts.

For more information on air pollution and atmospheric deposition please visit these links:

The National Atmospheric Deposition Program (NADP)

EPA's CASTNET dry deposition network

California Air Resources Board

The Air Pollution Workshop


Last Modified: Mar 28, 2013 02:54:59 PM