Airborne Nitrogen and Ozone: A large-Scale Threat to Semi-Natural Ecosystems
During the last century, concentrations of tropospheric ozone (O3) and reactive nitrogen compounds (Nr) have risen substantially on a global scale as a result of increasing anthropogenic emissions from industry, agriculture and other sources. Today, both ozone concentrations and N inputs exceeding thresholds for ecological effects are widespread and threaten the structure and function of sensitive natural and semi-natural plant communities even in remote regions. Even further increases are projected by regional and global air pollution models in several hot-spot regions. Both N input and ozone have been found separately to affect plant communities. Elevated ozone causes visible injury on leaves in sensitive species and impairs photosynthesis and transpiration, reduces leaf life span, and affects reproduction, biomass allocation and growth. In grassland communities, experimental exposure to elevated ozone consistently causes shifts in species dominance, with the effect developing more slowly in less productive, old systems, than in productive newly sown systems. There is also evidence that ozone causes slow shifts in the genetic structure of specific plant populations. As an essential nutrient, excess N causes a displacement of species characteristic of nutrient-poor conditions by a few fast growing and highly competitive species, and affects productivity and changes the quality of the forage. Where both pollutants occur together, their effects may interact, but little is known about the resulting change in ecological risks for grassland ecosystems covering large areas in many regions of the world and providing important goods and services to society. This review summarizes some of the trends observed in the exposure to these pollutants, their potential effects on semi-natural grassland ecosystems such as changes in species, productivity, water budgets and carbon storage, and it highlights the need for ecological criteria as targets for air pollution abatement strategies with the goal to preserve biodiversity, and to maintain the functioning of grasslands on larger scales. Finally, pollutant risks may be altered by future changes in climate and atmospheric CO2 through direct effects on vegetation or indirectly through altered nutrient cycling, or through effects on the flux of ozone from the atmosphere to the site of action. This may lead to either higher or lower risks depending on region, system characteristics, and on additional human interference.
nitrogen ozone air pollution semi-natural vegetation grasslands critical levels/loads
J. FUHRER
Air Pollution/Climate Research Group, Agroscope Research Station ART, Reckenholzstrasse 191, CH-8046 Zurich, Switzerland
国际会议
2007环境科学与技术国际会议(The 2007 International Symposium on Environmental Science and Technology)
北京
英文
2007-11-13（万方平台首次上网日期，不代表论文的发表时间）