共查询到3条相似文献,搜索用时 2 毫秒
1.
D.F. Karnosky B. Mankovska K. Percy R.E. Dickson G.K. Podila J. Sober A. Noormets G. Hendrey M.D. Coleman M. Kubiske K.S. Pregitzer J.G. Isebrands 《Water, air, and soil pollution》1999,116(1-2):311-322
Over the years, a series of trembling aspen (Populus tremuloides Michx.) clones differing in O3 sensitivity have been identified from OTC studies. Three clones (216 and 271[(O3 tolerant] and 259 [O3 sensitive]) have been characterized for O3 sensitivity by growth and biomass responses, foliar symptoms, gas exchange, chlorophyll content, epicuticular wax characteristics, and antioxidant production. In this study we compared the responses of these same clones exposed to O3 under field conditions along a natural O3 gradient and in a Free-Air CO2 and O3 Enrichment (FACE) facility. In addition, we examined how elevated CO2 affected O3 symptom development. Visible O3 symptoms were consistently seen (5 out of 6 years) at two of the three sites along the O3 gradient and where daily one-hour maximum concentrations were in the range of 96 to 125 ppb. Clonal differences in O3 sensitivity were consistent with our OTC rankings. Elevated CO2 (200 ppm over ambient and applied during daylight hours during the growing season) reduced visible foliar symptoms for all three clones from 31 to 96% as determined by symptom development in elevated O3 versus elevated O3 + CO2 treatments. Degradation of the epicuticular wax surface of all three clones was found at the two elevated O3 gradient sites. This degradation was quantified by a coefficient of occlusion which was a measure of stomatal occlusion by epicuticular waxes. Statistically significant increases in stomatal occlusion compared to controls were found for all three clones and for all treatments including elevated CO2, elevated O3, and elevated CO2 + O3. Our results provide additional evidence that current ambient O3 levels in the Great Lakes region are causing adverse effects on trembling aspen. Whether or not elevated CO2 in the future will alleviate some of these adverse effects, as occurred with visible symptoms but not with epicuticular wax degradation, is unknown. 相似文献
2.
Contributions of nitrification and denitrification to N2O emissions from soils at different water-filled pore space 总被引:1,自引:0,他引:1
A combination of stable isotope and acetylene (0.01% v/v) inhibition techniques were used for the first time to determine N2O production during denitrification, autotrophic nitrification and heterotrophic nitrification in a fertilised (200 kg N ha–1) silt loam soil at contrasting (20–70%) water-filled pore space (WFPS). 15N-N2O emissions from 14NH415NO3 replicates were attributed to denitrification and 15N-N2O from 15NH415NO3 minus that from 14NH415NO3 replicates was attributed to nitrification and heterotrophic nitrification in the presence of acetylene, as there was no dissimilatory nitrate reduction to ammonium or immobilisation and remineralisation of 15N-NO3–. All of the N2O emitted at 70% WFPS (31.6 mg N2O-N m–2 over 24 days; 1.12 g N2O-N g dry soil–1; 0.16% of N applied) was produced during denitrification, but at 35–60% WFPS nitrification was the main process producing N2O, accounting for 81% of 15N-N2O emitted at 60% WFPS, and 7.9 g 15N-N2O m–2 (0.28 ng 15N-N2O g dry soil–1) was estimated to be emitted over 7 days during heterotrophic nitrification in the 50% WFPS treatment and accounted for 20% of 15N-N2O from this treatment. Denitrification was the predominant N2O-producing process at 20% WFPS (2.6 g 15N-N2O m–2 over 7 days; 0.09 ng 15N-N2O g dry soil–1; 85% of 15N-N2O from this treatment) and may have been due to the occurrence of aerobic denitrification at this WFPS. Our results demonstrate the usefulness of a combined stable isotope and acetylene approach to quantify N2O emissions from different processes and to show that several processes may contribute to N2O emission from agricultural soils depending on soil WFPS. 相似文献
3.
Seiji Shimoda Shohei Murayama Wenhong Mo Takehisa Oikawa 《Agricultural and Forest Meteorology》2009,149(3-4):603-613
Measurements of δ13C in atmospheric CO2 and plant samples were made in 2003, along with CO2 flux measurements, at a grassland site in Tsukuba in central Japan. The objective of the study was to obtain estimates of relative seasonal contributions of C3 and C4 plants to the net CO2 flux over a C3/C4 grassland area influenced by the Asian monsoon. C4 contribution to the ecosystem respiration (f4R) increased from June to September, and then became constant at 63–67% through October and November. The seasonal variation in f4R reflected the biomass composition of C3 and C4 plants at the measurement site. The seasonal C4 contribution to photosynthesis (f4P) was significantly different from its contribution to f4R in May (8%) while it showed similar values to f4R after June. The seasonal variations in f4R and f4P reflect the biomass composition ratio. Such seasonal transition from C3 to C4 of relative contribution to the carbon flux is similar to that observed in humid prairie ecosystems, while it is different from that in dry prairie ecosystems where the contribution of C3 plants is lower and the seasonal maximum of the C4-plant contribution occurs earlier compared to the humid prairie ecosystems. 相似文献