土壤學(xué)基本知識-土壤有機質(zhì)性質(zhì)及其分解-資料下載頁
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【正文】 ffect. Nitrification rates are high when vegetation is disturbed because of high soil moisture, amp。 soil temp., rapid ammonification, low vegetation uptake, low microbial immobilization (in temperate forests). In the SE pine forest ecosystems, strong microbial immobilization hold up ~80% N. Nitrification generate acidity, and loss of NO3 usually acpanied by increases of cations removed from soil particle surface by H+. Conditions stimulate nitrification also increases NO emission. Nitrogen biogeochemical Cycle: Some points on N mineralization/nitrification/denitrification: High atmospheric NO ? plants amp。 soil may take up NO, but in most cases, atmospheric NO is below the pensation point:10 ppbvN lose through NO is limited. Denitrification = dissimilatory reduction as N is not incorporated into microbial tissue as NO3 is reduced. Denitrification is widespread in terrestrial ecosystems, even in welldrained soils: in soil aggregates amp。 anoxic microsites. Increase NO3 in high OM content soil stimulates denitrification, while increase anic carbon in mineral soil stimulates denitrification. Soil pH, soil moisture, soil temperature affect nitrification and denitrification, as well as the amount of NO, N2O and N2 emission ? may be highly spatially heterogeneous. Fire … Nitrogen biogeochemical Cycle: Animal… Conceptual illustration of Nitrogen Biogeochemical Cycle in ecosystems anything wrong? N fixation Dry/wet deposition Nitrous Oxides amp。 N2 uptake leaching Retrans location Biogeochemical Cycle of Sulfur Sulfur cycle is similar to nitrogen in many ways, but: 1. S cycles mainly among plants, litter and soil microbes 2. S is usually unlimited element, retranslocation and immorbilazation are less important to its biogeochemical cycle. 3. Rock weathering is one important source. 4. S can be strongly fixed in soil by Fe and Al. 5. S gaseous exchange with atmosphere is small. 6. Sulfate is an important source of acid rainhuman made Comparison of N and S cycles Phosphorus Biogeochemical Cycle Internal cycle of P is similar to N cycle w/ major transfer among plant uptake, litter fall, retranslocation and deposition major active pools: vegetation and soil OM P mineralization is hard to measure ? quick plexation input from wet/dry deposition is very small, new input is from soil mineral weathering, and decreases as soil profile develops soil Fe and Al oxides has very high potential to fix P in unavai lable forms ? very little leaching ? low in aquatic systems. Potassium Biogeochemical Cycle unlike C, N, S amp。 P, metallike cation K cycles in ecosystem in a unique way: it is not bound into anic pounds but moves in the plant in ionic form ? very easy to be leached ? K enriched in stem flow and throughfall ?important in K cycle. only loosely held in the litter and is leached quickly. in soil, K is held by soil surface negative charges, not involved in reactions leading to unavailable forms. major new inputs are from precipitation and rock weathering. tight cycling within ecosystems, but excess K can lead to leaching to groundwater Calcium amp。 Magnesium Biogeochemical Cycles anic cycling, weathering and cation exchange are important processes in Ca and Mg biogeochemical cycles. both are important constituent elements in anic pounds. exchangeable cations of Ca amp。 Mg are the major available pool in ecosystems. stem flow and throughfall are less important input source. litter and deposition are important in Ca amp。 Mg cycles. immobilization is unimportant for both Ca amp。 Mg. they both can leached to ground water. Mg concentration in biological materials is much less than Ca, mostly in leaves (chlorophyll).
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