Changes Of Soil Characteristics During Typical Vegetation Restoration In Karst Mountain Area

The karst mountain areas are characterized of vulnerable envrioments which lie at the intersection where atmosphere,water shpere,creature sphere and human activities converge at.The soil here has special features such as shallow soil thickness,discontinuity of soil distrubution,lack of C horizon,lack of sTableility,in a state of negative growth in amount and in a state of non-renewable nature compared with the low rate of soil process.Irrational land-use patterns superimposed on the fragile karst ecosystem, causing serious decline in soil quality and land productivity.Karst habitat specificity determines the appropriate plant that can living in calcium,drought resistance, barren nature,and the only species that can adapt to the special surroundings can have a good growth there.Researches about soil quality change during vegetation restoration periods in karst regions are helpful for better understanding the ecological restoration process,as well as providing references for taking appropriate measures.This study inlvolved cypress plant (Sabina chinensis) community succession in mountain areas as the background,analysing the soil physical and chemical properties and microbiological characteristics during the vegetation recovery process.14 soil profiles of differecnt vegetation in the similar slope position were selected.And five vegetations include farmland,1-year dropped farmland-bush-grass land,15-year scattered woodland and 25-year woodland.From cultivated land to forests,the clay content shifts from draining to accumulation eventually until the time of sTableility.Soil bulk density has linear increase trend but reduces finally.Soil bulk density of dropped farmland and bush-grass land are higher than control group,increasing by 6.6% and 11.57%.Scattered woodland and woodland are respectively lower by 5.0% and 10.0% than vultivated land.The change trend of total porosity and bulk density are just reverse. Small size water-sTablele aggregats are oriented in soil of farmland and dropped farmland and giant size water-sTablele aggregates are oriented in soil of scattered woodland and woodland.Amount of>0.25mm water-sTablele aggregate in scattered woodland soil is highest,increasing by 5.1%-12.5% in comparison with cultivated land. Amount of>5mm water-sTablele aggregate was found accumulated higher in cultivated land and dropped land.The results also showed that percentage of aggregate destruction gradually decreased.That in the last four stages decreasing by 64.7%-34.0% compared with the farm land,showing significantly negative correlation with soil organic matter and correlation with clay amount.Therefore,the accumulation of soil organic matter is vital for the soil recovery in karst areas,since the increase of it can promote the abilitis of sTableility and erosion resistance along with the number of growing years after dropping.Soil water eco-effect could be construed as water-keeping property and water-providing property.Soil water-keeping property of woodland and dropped-land are much higher than the other vegetations.Soil water-providing property of cultivated land is best in all the vegetations.These two kinds of soil abilities are not consistance all the time but they are all correlated with soil clay content,porosity and sTableility of aggregate.The composition of ground-surface plant has an important influence on soil nutrient and soil carbone reserves. Soil organic matter has close correlation with acidity as well as amount of effective nitrogen. From cultivated farmland to woodland,the accumulation of organic matter is obvious which shows that soil in the last four stage are respectively much higher by 5.9%,45.6%,93.8% and 86.8% than famland.The reason of soil organic matter amount of farmland is at a low level can be summarized as follow:origion of organic fertilizer,loss from soil erosion,decomposition action of microoganism.The agriculture activity also break the soil structure,increasing the organic matter decomposition rate with a content of 20.5g/kg.And the conditions start to shift along with the litterfall accumulation.The amount in woodland is something less than scattered land due to small quantity of suface plants,less too lacking litterfall under cypress special specie.All these lead low rate of organic matter cycle.In accordance with plant restoration series,number of microoganisms,indeed,on the decend,tends to the peak at the stage of farmland due to the input mode of organicmatter and the convertion and use of litterfall.Among the microorganisms,the number of bacteria is highest(66.7%-93.3%),then followed by the actinobacteriia,fungi is the lowest.Actinobacteria plays a significant role in the decomposition of cypress litterfall.Among the last four stages,soil breathe intensity is respectively higher by 34.3%,139.4%,34.0%,19.1% than farmland soil.So it decreases after a increase and tends to the peak at the stage of bush-grass land.The correlation between microorganisms content and soil respiration is not significant(>0.05),but soil respiration has a significant correlation with the proportion of bacteria,which illustrating the bacteria is the most obvious contributor.Considering the aspects mentioned above,the change of soil characteristcs during cypress plant restoration is complicated and it is a result of composition of vegetation as well as litterfall character and chmical,physical and microbial eco-characteristics. The physiological feature of cypress litterfall in cellulose and lignin fertility result in higher soil quality comprehensive index in bush-grass land compared respectively with the other vegetation soil types according its variation trend.