Redox Process Of Soil Under Subalpine Abies Faxoniana In Western Sichuan

Redox reaction is one type of vital chemical reaction in soil formation,which has a profound effect on differentiation and morphological characteristics of soil type.The primordial subalpine Abies faxoniana in western Sichuan was regarded as the object of study, while the podzol in popular idea was chosen as located site based on route investigation,where terrain was relatively flat, vegetation composition was relatively homogeneous and soil layers were relatively integrated.Measurement of redox potential of the forest soil,redox potential in soil of layer A2and B2in different seasons in study area,relationship between Eh and pH as well as the influences on soil formation from redox process in study area were studied according to the combination of field survey and laboratory analysis. Results could supply further study on process and characteristics of soil formation in study area and development of basic theory on forest soil science with scientific and experimental data.Main results were as follows.(l)For the most part,soil redox potential(Eh) had been measured in soft hydromorphic soil, while measured in soil suspensions or after the soil had been disposed else at home and abroad.Moreover the instruments used for measuring Eh were mainly acidimeters,but the potentiometers applied for measuring Eh of forest soil in situ were relatively not many.In order to measure Eh of the forest soil in situ,the redox potentiometer was made autonomously and its measured values were compared with the newly-purchased FJA-5redox potentiometer. Results showed that the self-made redox potentiometer had better precision and accuracy,which could objectively reflect the redox situations of forest soil under field condition.The self-made redox potentiometer was suitable for measuring redox potential of forest soil in situ.(2)Soil samples were made into suspensions and certain water-soil ratios and standing time were designed to measure redox potential.For variation trend of Eh values with multiple water-soil ratios and prolonged standing time,measured Eh values were viewed as dependent variable and water-soil ratios and standing time were viewed as independent variables to establish regression model. Result indicated that the Eh values measured in suspensions showed decreased gradually trend with multiple water-soil ratios and prolonged standing time.According to Nernst equation,when water-soil ratios were adding,the original state of soil was changing,the concentrations of redox systems were declining and reducing substances’reduction abilities were improving so that the concentrations of reducing substances were higher than that of oxidating substances.So Eh values also decreased.Tests about significance of difference between Eh values measured under this circumstance and which measured in situ were made.Results manifested that most of highly significant or significant differences existed between them.would had great biggish differences with Eh values measured in situ and could not really reflect the redox situations of forest soil under field condition.Because soil redox potential was significantly related to water levels,moisture content,soil texture and structure,the amount of oxidizable and reducible materials as well as vegetation,it was only possible to detect actual oxidation-reduction conditions in soil when Eh measurement was carried out in situ.(3)Redox potential in study area changed with soil layer and season.In the mass,Eh value in dry season was higher than that in rainy season in the same soil layer,while Eh value in Layer A2was lower than that in Layer B2in the same season.Due to more moisture and organic matter and smaller porosity and venting quality,soil of Layer A2was often reducing,whereas soil of Layer B2was usually oxidating because of less moisture and organic matter and bigger porosity and venting quality.Besides,there was a negative linear correlation relationship between Eh and pH values under waterlogging condition.In other words,Eh values were gradually decreasing while pH values were going up little by little.The absolute value of related coefficient(r=-0.9204)between Eh and pH of soil in Layer B2was higher than that of soil in Layer A2(r=-0.6341),which made clear that there was a more certain negative linear correlation relationship between Eh and pH values in soil of Layer B2.(4)Reducing state in surface soil of study area was in the highest flight so that organic matter was decomposing anaerobically and Fe and Mn had lower valence.Organic acid produced from anaerobic decomposition of organic matter and Fe and Mn with low price jointly created clathrate,which put up seasonal reductive bleaching.So contents of Fe and Mn with low price lessenned.Meanwhile aluminosilicate in mineral was decomposed by organic acid,which produced abundant SiO2.Soil of Layer A2was off-white because of SiO2detained in it.By the way, soil of Layer A2was also light caesious because some Fe with high price were reduced into which with low price,secondly residual Fe with low price through reductive bleaching existed in it.By contrast,oxidating state in bottom soil was in the highest flight.When Fe and Mn with low price in soil of Layer A2moved down to soil of Layer B2,their valences rose and they became reddish-brown,so soil of Layer B2was reddish-brown.In addition,soil of Layer B2had Fe and Mn with high price itself so that reddish-brown colour was more obvious in it.