| The Wenchuan Earthquake and its secondary disaster led to a wholesale destruction of vegetation and soil,which resulted in serious soil erosion and damaged ecosystem and intensified the difficulty of the ecological rehabilitation and hazard control.Soil respiration is an important biological indicator for soil quality and fertility.To some extent,Soil respiration reflects the transformation and supply capacity of soil nutrient and the sensitivity and response patterns of ecosystem to stress.To understand the relationship between environmental factors and soil respiration of destroyed restoration ecosystems under the earthquakes and secondary disasters,two ecological restoration areas of Sichuan Province(arid-valley climate(Dayu)and subtropical humid climate areas(Hanwang))were chose as study areas,and each area has three sample plots(the restored destroyed areas,natural recovery areas and the undestroyed areas).We measured variation of soil respiration,investigated the vegetation and got soil samples.By determining the soil physiochemical,enzymes,microorganism and plant biomass,we analyzed seasonal variation and correlation of soil respiration rate and environment factors about three recovery modes in two climatic regions.We wanted to state the present situation of ecological recovery and predict the future development trend in disaster areas.The main results and conclusions were as follows:(1)Diurnal and seasonal dynamics of soil respiration under different recovery modes of typical disaster areas in preliminary stageSoil respiration of six sample sites had a significant diurnal variation,the peak of soil respiration usually appeared at 13:00,but there was a fluctuation between 11:00 and 15:00 in winter and spring.In two climatic areas,the diurnal dynamics of soil respiration showed the tendency of undestroyed areas>restored destroyed areas>natural recovery areas.But the diurnal amplitude dynamics of soil respiration showed the tendency of restored destroyed areas>undestroyed areas>natural recovery areas.The soil respiration rate was remarkably high in summer and autumn and lower in winter.The soil respiration rate of different seasons had a significant difference and was in order of undestroyed areas>restored destroyed areas>natural recovery areas.However,there were no significant difference between the restored destroyed areas and natural recovery areas.Compared with undestroyed areas,the soil respiration of restored destroyed areas and natural recovery areas in arid-valley climate reduced 41%and 50%respectively,but subtropical climate areas only reduced 21%and 23%.(2)Diurnal dynamics of soil temperature and moisture,and the impact on soil respiration under different recovery modes of typical disaster areas in preliminary stage.Diurnal dynamics of 5cm soil temperature and soil respiration had coherent fluctuations.By the fitting equations,we discovered that 5cm soil temperature and soil respiration had a superior fitting correlation in subtropical humid climate areas,but arid-valley climate areas had some variation.For specific performances,Soil respiration had a significant positive correlation to soil temperature at autumn under different recovery modes in arid-valley climate,but there was no significant correlation in summer.In terms of different sample plots,there was a significant correlation between soil respiration and 5cm soil temperature of three plots in two climatic areas,and fitting coefficients was in order of undestroyed areas>restored destroyed areas>natural recovery areas.(3)Seasonal dynamics of soil temperature,soil moisture and Q10,and the impact on soil respiration under different recovery modes of typical disaster areas in preliminary stage.In this study,there was no significant correlation among 5cm soil respiration,soil temperature and soil moisture.When we used the two-factor model of soil temperature and moisture(R=aebTWc)to explain soil respiration of three recovery areas,the values were of great worth.The main results of two-factor model were as follow:Except for the temperature and water factors,soil respiration of undestroyed areas in subtropical humid climate were affected by other environmental factors;Soil respiration of undestroyed areas in arid-valley climate and restored destroyed areas in subtropical humid climate were affected by the factor between 5cm soil temperature or moisture;and other sample plots were affected by 5cm soil temperature and moisture.In this study,the Q10 values in arid-valley climate of undestroyed areas,restored destroyed areas and natural recovery areas were 2.34,1.95 and 2.78 respectively;The Q10 values in subtropical humid climate areas were 1.99,1.20 and 2.90,respectively.Different climate areas about sensitive to changes in 5cm soil temperature are characterized by natural recovery areas,followed by the restored destroyed areas,natural recovery areas to minimum.(4)Seasonal dynamics of soil physical and chemical properties,and the impact on soil respiration of typical disaster areas in preliminary stageThe soil physicochemical properties(except for soil total phosphorus and bulk density)of different recovery areas showed the significant seasonal variation.In terms of different sample plots,Except for total phosphorus(TP),bulk density(BD)and electrical conductivity(EC),the soil physical and chemical properties of two climate areas showed the trend of undestroyed areas>restored destroyed areas>natural recovery areas.Compared with soil physical and chemical properties in 2012,the research showed that restored destroyed areas and natural recovery areas of soil physical and chemical properties had enhanced remarkably,especially for restored destroyed areas.The correlation analysis between soil respiration and physicochemical properties of different climate samples illustrated that soil respiration showed an extremely significant positive correlation with soil organic carbon(SOC),total nitrogen(TN),available nitrogen(AN)and soil porosity(SP),but an extremely significant negative correlation with bulk density(BD).In terms of different seasons,Soil respiration of all seasons had a significant correlation with total nitrogen(TN),available nitrogen(AN),but had no significant correlation with total phosphorus(TP)and electrical conductivity(EC).Soil respiration had a significant correlation with pH only in summer.It was considered that soil respiration was mainly affected by soil organic carbon(SOC),total nitrogen(TN),available nitrogen(AN)in different sample sites of two climate areas.(5)Seasonal dynamics of plant biomass,and the impact on soil respiration of typical disaster areas in preliminary stageThe plant underground biomass and total biomass(except for natural recovery areas in subtropical humid climate)of different recovery areas showed significant seasonal variation.The plant biomass of three recovery areas showed the trend of undestroyed areas>restored destroyed areas>natural recovery areas.And there was a significant difference between undestroyed areas and natural recovery areas.The correlation analysis between soil respiration and plant biomass from three different samples showed that soil respiration had an extremely significant positive correlation with plant underground biomass and total biomass.Except for plant belowground biomass in autumn and plant total biomass in summer,the plant biomass of other seasons all had significant positive correlations with soil respiration.Soil respiration of three recovery areas in arid-valley climate was mainly affected by plant belowground biomass and total biomass,but soil respiration of three recovery areas in subtropical humid climate was affected only by plant belowground biomass.(6)Seasonal dynamics of soil biological properties,and the impact on soil respiration of typical disaster areas in preliminary stageSoil microbial population and biomass,including bacteria,actinomycetes,microbial biomass carbon and nitrogen showed a seasonal dynamics tendency of high value in summer and low value in winter,while fungi showed a seasonal dynamics tendency of high value in winter and low value in summer.Soil microbial population were characterized as bacteria>actinomycetes>fungi.Both soil microbial population and microbial biomass of undestroyed areas in different climate areas had differences with restored destroyed areas and natural recovery areas,and the restored destroyed areas had a higher recovery rate.The microbial population and microbial biomass of different recovery areas had a significant positive correlation with Bacteria,actinomycetes,microbial biomass carbon and nitrogen in typical disaster areas except the number of fungi in arid-valley climate(P<0.05).For different seasons,soil respiration had a significant positive correlation with microbial population and microbial biomass in summer and the growing seasons in 2016 except the bacteria,which had no significant correlation with soil respiration in different seasons.The results indicated that soil respiration of three recovery areas in arid-valley climate was mainly influenced by bacteria and actinomycetes.While the soil respiration of three recovery areas in subtropical humid climate was affected by microbial nitrogen and bacteria.(7)Seasonal dynamics of soil enzymes properties,and the impact on soil respiration of typical disaster areas in preliminary stageFive kinds of soil enzyme activities in two climates had different seasonal dynamics.Generally,enzyme activities showed the highest value in summer and autumn and lowest in winter and spring.Sucrase,alkaline phosphatase and urease in undestroyed areas had a significant difference to them in restored destroyed areas and natural recovery areas.But cellulose and catalase had no significant difference in different recovery areas.The correlation analysis between soil respiration and soil enzyme activities from three different samples showed that soil respiration had a significant positive correlation with urease and sucrase,but had no significant correlation with cellulose,catalase and alkaline phosphatase.In terms of different seasons,except for soil respiration had no significant correlation with urease and sucrase in autumn and summer,soil respiration had a significant positive correlation with urease and sucrase in any seasons.And soil respiration also had a significant positive correlation with Cellulose and alkaline phosphatase at autumn.We concluded that soil respiration of three recovery areas in arid-valley climate was mainly affected by alkaline phosphatase,urease and sucrose,but soil respiration of three recovery areas in subtropical humid climate was affected only by alkaline phosphatase.(8)Principal component analysis of the soil respiration main impact of typical disaster areas in preliminary stageThe primary factors that affect the soil respiration of two climate areas were different.Based on principal component analysis of soil respiration,total nitrogen was the first principal component(PC1)of three recovery areas in arid-valley climate.However,soil temperature and alkaline phosphatase were the first principal component(PC1)of three recovery areas in subtropical humid climate.The comprehensive analysis indicate that thehe ecosystem of typical disaster in preliminary stage were mainly affected by soil organic carbon,total nitrogen,available nitrogen,plant underground biomass and total biomass,bacteria,microbial biomass carbon and nitrogen,urease and sucrase.And 5cm soil temperature,electrical conductivity and cellulase were the second principal component(PC2)of soil respiration.The third and fourth principal component(PC3 and PC4)were pH and total phosphorus respectively.By fitting the average soil respiration of research area and soil respiration of six sample plots with the main components,we found that soil respiration of all typical disaster areas had a significant positive correlation with factors of the first principal component(PC1),but soil respiration had no significant correlation with PC2,PC3 and PC4. |
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