The Exchange Of Nitrogen Dioxide And Ozone Between Vegetation And The Atmosphere

Author : Wenwen Wang
Publisher :
ISBN 13 : 9781267642264
Total Pages : 192 pages
Book Rating : 4.6/5 (422 download)

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Download or read book Nitrogen Biogeochemistry of Plants and Soils in a Semi-arid Urban Ecosystem written by Wenwen Wang and published by . This book was released on 2012 with total page 192 pages. Available in PDF, EPUB and Kindle. Book excerpt: Nitrogen (N) biogeochemical cycles of plants and soils in urban ecosystems are greatly altered by intensive anthropogenic impacts, yet poorly studied. In order to improve our understanding of altered plant-environment interactions and the consequences to N biogeochemistry in urban ecosystems, it is important to (1) test new methodologies (such as plant isotopic tracers) for studying plant gas exchange; (2) link plant gas exchange with plant-soil N cycling; (3) understand the effects of management regimes on plant and soil N dynamics; and (4) construct N budgets for common types of urban land cover, in order to evaluate their efficiencies of N retention and potential N pollution. To evaluate the application of plant isotopic composition of carbon (C), nitrogen (N), and oxygen (O) as "bio-indicators" of carbon dioxide (CO2) and air pollutants derived from fossil-fuel combustion, I analyzed a large dataset of foliar isotopic composition of stable C ([delta]13 C), N ([delta]15 N), oxygen ([delta]18 O), and radiocarbon ([delta]14 C) of unmanaged C3 and C4 grasses sampled from the urban areas of the Los Angeles Basin. I found distinct spatial patterns of plant isotopic tracers along urban-rural gradients in relation to the spatial distributions of air pollutants and other urban variables, and demonstrated that plant isotopic tracers could be used as proxies of air pollutants, such as [delta]14 C and [delta]13 C for CO2, ozone (O3), and carbon monoxide (CO), [delta]15 N for nitrogen dioxide (NO2), and [delta]188 O for O3. However, the unexplained variation in plant [delta]15 N suggested an important role of soil [delta]15 N and N properties. Therefore, I conducted a follow-up study to evaluate the potential of plant [delta]15 N as an integrative tracer of NO2 and soil N cycling. I found that plant [delta]15 N enrichment factor (EF), or the deviation of plant [delta]15 N from soil [delta]15 N, was correlated to both atmospheric NO2 and soil N cycling rates. Meanwhile, plant [delta]13 C was correlated with both CO2 related air pollutants (CO, NO2, and O3) and soil moisture, and therefore may be a potential indicator for plant gas exchange and water deficiency. To fully explore plant-soil N cycling under direct human impacts, I also studied the effects of human management on the plant and soil N dynamics in urban lawns. I compared the soil inorganic N (IN) availability, gaseous N fluxes, plant productivity, and plant N% in a typical (Typical) and an environmentally retrofitted lawn (Retrofitted) in southern California. The results suggested that with reduced fertilization and irrigation, the "Retrofitted" lawn had higher soil IN availability, stronger biological control on soil IN, and higher overall plant productivity than the "Typical" lawn. I also constructed short-term and annual N budgets for three lawns in order to evaluate their efficiencies of N retention in plant and soil vs. potential N losses relative to N inputs. I found that the choice of a warm-season C4 turf species for semi-arid urban ecosystems could maintain high productivity and N retention in plants and soils at lower N and water inputs. Gaseous and leaching IN losses were relatively small in all lawns, though there were relatively high uncertainties in the magnitudes of denitrification. My work has provided needed empirical data about the fate and transformations of N in unmanaged and managed urban plants and soils.