| Subalpine fir forest (Abies faxoniana) in western China plays important part in subalpine forest located in high elevation and low latitude area. What’s more, subalpine fir forests have principle ecological functions such as water conservation, species conservation and other important ecological functions. Its diverse vegetation and soil association provide a natural laboratory for forest soil science studies. The understory environment of subalpine fir forests, which is low temperature, high humidity, seasonal freezing and thawing, is very different from coniferous forest in the the same latitudes due to its natural climatic conditions (equivalent to cold temperate climate) and the properties of construction species of dark coniferous forest. Therefore, the soil formation and development has its particularity under subalpine fir forest. For a time, soil scientist debated the soil type under coniferous forest at low latitude and high altitude, or at high latitude and low altitude. With the improvement of research methods and the change of research focus, soil basic research, such as soil forming process and the basic characteristics, has been neglected. This phenomenon is not conducive to the rapid development of forest soil science, nor effective in guiding forest management. Thus, in this case, it takes subalpine fir forest soil as the research object using located research methods. And, it has the important theory and the practice significance that focus on the diagnostic soil characteristics, soil water and heat dynamics, the mobile of soil elements in soil solution and solid phase, soil redox system process and other soil formation and development characteristics. The results indicate that,(1) The soil in located research position is A-E-B-C soils the means this soil has obvious organic layer, leached layer, deposition layer and the matrix layer. Notably, the wet color of the surface leaching layer A2is ash (Gleyl5/N), while dry color is powder (2.5Y7/1). The color in two status have reached the bleaching material color standard (chroma<2, wet brightness>3and dry brightness>6, or wet brightness>4and dry brightness>5). That is to say, the horizon can be set as bleached layer that we often say. In comparison, the wet color of deposited layer B2is red (10R4/8), while dry color is yellow brown10YR (-)5/6(-7.5YR5/). Soil quality water content, field capacity, maximum moisture, porosity all decrease with soil depth increases, and the soil bulk density, gravel content increase with soil depth increases. Soil aerates and soil loss has its special variation, which is soil aeration and the degree of loss in the bleached layer was significantly lower than that of other soil. Soil minerals in located research position are primary minerals e.g. quartz, feldspar minerals, failed to detect any number of clay minerals. Soil chemical process mainly started from surface soil (A1), because organic matter content, humus content, mineral element content in the horizon is always higher than other soil horizon in soil pedon. In the vertical profile, fulvic acids, with strong acid and activity, accounted for absolute advantage in humus compsiton. Silicon content is very low in the surface layer, but showed enrichment tendency in bleached layer (A2). Eluviation and deposition of soil profile substance analysis results showed that the silicon in the surface content is lower, but silicon showed enrichment trend in the bleaching layer. Although the soil in localization points has ashing deposition layer formed by humus complexometric leaching, chroma, lightness, saturation, and the content of activity Fe-Al do not satisfy the ashing deposition layer standard of real podzols on in Soil Taxonomy. Therefore, we classified such soil initially as bleached gray soil belonged to the Alfisols.(2) The interaction among soil temperature, moisture and energy cause the seasonal variation of soil water status. In the dry season (November and February), soil moisture of bleaching layer and deposited layer is very close during the November, and it showed soil water content of B2layer was lower than that of A2layer in February. In the rainy season, the soil water content of the B2layer significantly increased steadily due to soil solid water of A2layer of frozen melts and move down to B2layer, meanwhile soil quality water content of A2layer reduced and fluctuation. To the total soil quality water content, soil quality water content of A2layer were higher than those in B2layer of soil in each season. The highest soil quality water content of two soil horizon (i.e. A2and B2) occurs in the rainy season (August), minimum value appeared in the dry season (November and February). To soil temperature, A2horizon was demonstrated diurnal variation law that is first decreased then increased and decreased before soil water temperature reduce to freezing point, diurnal variation of soil temperature in deposition layer has smaller amplitude. In one year, soil temperature changes experienced two stages, one is the deposition layer is higher than that of bleached layers (B2>A2,22nd September-in the year April6th), lasting about7months. The second stage is bleached layer is higher than that of the deposition layer (B2<A2), this phase lasted for about5months. Soil water energy gradient leading by soil temperature leading causes soil water movement, which in June to September, soil water from the leached layer to layer deposition mobile, but the soil water has upward moveing trend after October. The freezing point calculated by soil soluble salt content and soil freezing and thawing results show that even if the soil temperature dropped to zero, the soil is not into the frozen, liquid soil water is forming crystal nucleus stage. Only the soil temperature temperature drops to freezing point and continuous cold, soil will be frozen. In located research soil, A2and B2common in freezing period time is50D (4.16-6.7)(including freezing and thawing process), common in the normal state of191D (6.13-12.24). The rest time in one year is A2or B2in the freezing period or normal state. The soil located normal state about half of year, only1/7.3time in soil freezing penetration status.(3) The existence form and content of iron, aluminium, manganese in maximum leached layer (bleached layer) and maximum deposition layer of bleached podzolic soil has obvious seasonal dry-rewet variation. During the rainy season (August and May), ferrous ions were significantly higher than ferric ion in soluble iron, and during the dry season (November and February), ferric ion content was significantly increased. But the seasonal monsoon and dry season changes did not affect the distribution of soluble iron and carbonate bound iron content between bleaching horizon and deposited horizon, i.e. soluble iron and carbonate bound iron content of the bleached layer was significantly lower than that of the deposited layer. This phenomenon is more intense in the rainy season; By contrast, humic qualitative state and iron with manganese state did not vary from season to season, but the content of deposition horizon is higher than that of leaching horizon. The distribution and mobile of typomophic element of soil (i.e. different forms of iron, aluminum, manganese) results indicates that there are two major chemical processes occurred in soil. One is the rinsing process, which iron, manganese was reduced and then leaching to the different soil layers; And the other is organic chelating leaching, which iron, aluminum leached wiht acid humus (mainly to fulvic acid) and other polyphenols. Although there are free aluminum in bleached layer also, free iron is more easily leaching wih humus acid chelate, and oxidized fixed in deposition layer. Free aluminum in soil more occurred in the exchange interaction. Therefore, soil chelate leaching is mainly dominanted by iron.(4) Litter leaf, about89.45%of total litter amount, is main litter in subalpine fir forest. The period of litter main return is concentrated in the9-11month, in the leaf litter and total litter amount60.32%,48.52%, respectively. Litter extract contains a variety of low molecular weight organic acid. Carboxylic acid such as formic acid was higher, and leading the type and content of low molecular weight organic acids in soil solution. In the same season, soil redox potentials in the A2layer were lower than those of B2layer. The formic acid and other low molecular weight organic acids, as well as having valence state of iron played a major role in soil redox system. Thus, in soil forming process of bleached podzolic, the mobile of low molecular weight organic acids and iron is the major redox reaction system and process, and strongly influences morphology and chemical characteristics formation of the leaching layer and depositing layer. The results of comparison different pH values of Eh indicated that Eh and pH values are suggested to be the most suitable method that coordinates representation. Microcosm control experiments show the linear regression relationship between soil redox potential and pH value, which can only be used as a reference value and has important significance when the field monitoring difficult or indoor assay is not reaction field real field case. The distribution of iron in different soil layer is closely related with soil redox potential changes. Soil of leaching layer is mostly in the restoring state in the dry and rainy seasons, due to high water content and anaerobic decomposition of organic matter. The oxidation reduction potential is relative low. Higher valence Fe is less; the vast majority is low redox state which has high solubility. Thus, Fe is easy to dissolve in organic acids produced by anaerobic decomposition of microorganism in surface soil, and move to subsoil in different forms. Different forms of low iron is oxidized into solid oxide or hydroxide (such as Fe2O3or Fe (OH)3) and then deposited in B2. The reason is that B2soil layer is in contact with the atmosphere than the opportunity for the soil of A2layer is less, the redox potential is high than A2, low valence iron is oxidized easily.These subsidence form a red or brown deposition layer including iron, aluminium, manganese common deposition. At the same time, aluminum silicate mineral was decomposed by organic acids, and then SiO2was ledved that forming a pale leached layer that SiO2relative enrichment. Notably, the color of bleached layer show a small amount of grey because soil of A2layer was mostly in the reduction state, a portion of the high iron is reduced to low iron Fe+compound, Fe2+usually pale green the leaching.(5) soil ammonium nitrogen, available potassium content of maximum leached layer (A2) and maximum deposition layer (B2) layer in the rainy season (August and May) was significant higher than that in the dry season (November and February), nitrate nitrogen is vice versa. During the rainy season, ammonia nitrogen, phosphorus, potassium in performance for the A2layer was significantly higher than that in B2layer, but in the dry season, their content of B2layer and A2layer was close, or the content of B2was significantly higher than that of A2layer. The content of soil organic carbon content in leached layer is greater than that in the deposition layer in each season. Soil total nitrogen, total phosphorus content in B2layer is higher than that of A2layer. Potassium, sodium and other mineral total amount change with the seasonal variation. During the rainy season, the leached layer above the deposition layer, while in dry season, deposited layer higher than the leached layer. Calcium, magnesium, copper, zinc, nickel and other mineral elements content did not change significantly in leaching and deposition horizon. In the process of soil organic matter moves down from the organic layer, bleached layers appeared transient accumulation due to anaerobic microbial activity and slower mineralization. Comprehensive analysis, bleached podzolic soil did not appear on serious impoverishment caused by ashing or rinsing. Ammonia nitrogen, nitrate nitrogen, available phosphorus available nutrients only changed with the seasonal variation of soil moisture. The results of soil nutrients in soil solution concentration have the same regular with above-metioned. |
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