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The Acidification Of Atmospheric N Deposition And Its Mechanism To Forest Red Soil Under Different Vegetation Stands In Subtropical Area In Southern China

Posted on:2008-07-15Degree:DoctorType:Dissertation
Country:ChinaCandidate:B H SunFull Text:PDF
GTID:1103360215494664Subject:Soil science
Abstract/Summary:PDF Full Text Request
Human activities have increased the inputs of oxidized and reduced nitrogen compounds to forest ecosystems. The excessive amounts of nitrogen will result in soil acidification and nutrient imbalance in plants. China has become the third largest acid region in the world. The most highly polluted areas are currently found in central and southwestern China, such as Guizhou, Sichuan, Hunan, Jiangxi, Guangdong Province etc. It needs urgently to understand the flux of atmospheric nitrogen and their consequence to soil qualities. A field observation on atmospheric nitrogen deposition was conducted at the Forest Micro-Meteorological Experiment Sub-Station, Red Soil Ecological Experiment Station, Chinese Academy of Sciences in Yingtan, Jiangxi Province, China, for 12 months from Feb. 2003 to Jan. 2004, meanwhile an eight-month leaching experiment using soil columns (10cm as diameter, 60cm tall) was carried out to investigate the responses of soils under different vegetation stands to the nitrogen inputs. It was expected to explore the mechanism of the effect of atmospheric nitrogen deposition to forest red soil qualities. The results were summarized as below.1. The obvious variation of the monthly average concentration and monthly deposition amounts of NH4+-N, NO3--N and inorganic N were observed. The monthly average concentration and monthly deposition amounts of NH4+-N, NO3--N and inorganic N were greater in winter– spring than in summer-autumn. The annual average concentrations of NH4+-N, NO3--N and inorganic N were 0.63, 0.43 and 1.06 mg.L-1 respectively. The deposition amounts of NH4+-N, NO3--N and total inorganic nitrogen were 7.15, 4.85 and 12.00 kg hm-2.a-1 respectively. The deposition of NH4+-N accounted for 60% of total nitrogen deposition.2. The leaching of NO3-, acid ions and base cations increased with increasing the rates of simulated N supply under three vegetations of grassland, broadleaf forest and coniferous forest. The leaching losses of Ca2+, Mg2+ and acid ions (H+ and Al3+) increased with increasing the rates of simulated N supply, but no effects on the leaching of K+ and Na+ were found. The nitrogen deposition resulted in a significant decrease in the amount of sulfate leached from soil. The mineralization of soil organic N increased with increasing the rates of simulated N deposition. The responses of the mineralization of soil organic N to increased N deposition were significantly different under different vegetation stands. The maximal mineralization of organic N in red soil was under the grassland, the next was under the broadleaf forest, and the minimal was under the coniferous forest. The nitrogen deposition caused the acidification of red soils, especially at the top of red soil. High N inputs caused the decreases of pH(H2O) of top red soil by 0.42 under the grassland, by 0.39 under the broadleaf forest, and by 0.36 under the coniferous forest. The acidification of N deposition rates to different vegetation stands performed as grassland > broadleaf forest > coniferous forest.3. Significant differences of the leaching of NO3-, Al3+, H+ and base cations were observed in dependence on the ratios of NH4+-N to NO3--N in nitrogen deposition and stands (grassland, broadleaf forest and coniferous forest). The leaching losses of Ca2+, Mg2+, soil organic N and acid ions (H+ and Al3+ ) were greater at higher ratio of NH4+-N to NO3--N than at lower ratio of NH4+-N to NO3--N , but no effects on the leaching of K+ and Na+. The responses of the mineralization of organic N to two different ratios of NH4+-N to NO3--N were significantly different under different vegetation stands, performing as grassland > broadleaf forest > coniferous forest. The differences of the mineralization of organic N between two ratios of NH4+-N to NO3--N in red soil under 3 vegetation stands of the grassland, the broadleaf forest and the coniferous forest were 118.2 mg, 49.7 mg and 26.0 mg respectively. The soil pH was low when the ratio of NH4+-N to NO3--N was high. The maximal difference of pH between two ratios of NH4+-N to NO3--N at the top of red soil was under the grassland by 0.16, the next was under the broadleaf forest by 0.15, and the minimal was under the coniferous forest by 0.13. It could be concluded that the acidification of red soil caused by NH4+-N could be much stronger than that by NO3--N.In summary, atmospheric nitrogen deposition in forest ecosystem could be moderate in the study site. Integrated monitoring of spatio-temporal variability of atmospheric nitrogen deposition in various forest ecosystems is highly needed to estimate the effects of nitrogen deposition in a forest ecosystem. Effect of atmospheric nitrogen deposition on acidification of forest red soil depended on level of atmospheric nitrogen deposition, ratio of NH4+-N to NO3--N in nitrogen deposition, soil profile, and forest stands. So far, the potential role of atmospherically derived reactive nitrogen in acidification has received little attention in China. Therefore, nitrogen deposition should be taken into account when soil acidification and critical loads of atmospheric deposition on soils in this region are estimated.
Keywords/Search Tags:Forest field, red soil, atmospheric N deposition, base cation, nutrients leaching, soil acidification, soil quality
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