| Global climate change is changing profoundly the environment where human beings live.Vegetation restoration has become one of the most effective ways to cope with global climate change and to reduce the impact on the environment,because vegetation has mutifunctions,including regulating the climate,conserving water resource,improving soil quality and carbon sequestration vegetation restoration has become one of the effective ways to prevent the environment from deterioration.To scientifically evaluate the effect of vegetation restoration on the environment,we must understand vegetation restoration process and its influence on the soil quality systematically.At present,there is still a lack of systematic research on the impact of natural forest on soil properties in deep soil,especially in soil different aggregate-size fractions during the long-term recovery process.In this dissertation,we selected natural liaodong oak forests with 30,60,90 and 120year ages and grasslands as control plots in the Loess Plateau using space for time method.Then,we studied the changes of communities characteristics?ie.litters and root charactdiameter with different diamaters?with natural restoration process,and the effect of community restorataion on the soil physicochemical properties,soil nutrient content and stoichiometric characteristics,soil microbial community,the weight percentage of soil aggregates,and different active organic carbon contents?high activating carbon,HAC;activating carbon,AC,and inert carbon,IC contents?,and glomalin-related soil protein contents?total glomalin-related soil protein,T-GRSP,and easily-extracted glomalin-related soil protein,E-GRSP?in different size of aggregates in the 0-80 cm soil profile.The results are as follows:?1?With the restoration of the liaodong oaks forest,the community biomass and litter biomass increased significantly.In the surface soil profile?0-20 cm?,the total biomass,total length and total area density of the roots with four diameter classes?<0.5 mm;0.5-1 mm;1-2mm;>2 mm?tended to increase,and the growth rate of root biomass,length and area were0.56 kg·m-3·yr-1,0.17 cm·m-3·yr-1and 0.08 cm2·m-3·yr-1,respectively.In the deep soil profile?60-80 cm?,however,the total biomass,total root length and total root area density had a trend of increase with restoration,and the growth rate were 0.71 kg·m-3·yr-1,0.08 cm·m-3·yr-1and 0.01 cm2·m-3·yr-1,respectively.On the other hand,with the increasing of soil depth,the biomass of all the four diameter roots decreased significantly.The percentage of root biomass with diameter above 2 mm increased fastest with soil depth,while the percentage of root length with diameter was less than 0.5 mm,and the root area with diameter above 2 mm declined rapidest.?2?The content of soil aggregate in soil profile showed different trend with the restoration of the liaodong oaks forest.In the surface soil profile,the weight percentage in soil macroaggregates from 30 to 120 years increased rapidly,with the rising rate of 0.10%yr-1,while the decreasing rate of the microaggregates and silt-clay aggregates were 0.06 yr-1 and0.04%yr-1,respectively.In the deep soil profile,the increase rates of macroaggregates weight percentage was 0.07%yr-1,while the decrease rate of microaggregates and silt-clay aggregates weight percentage were 0.04%yr-1 and 0.03%yr-1,respectively.Moreover,with the increase of soil depth,the content of macroaggregates in the control,30,60,90 and 120years decreased by 26.02%,24.78%,21.54%,36.80%and 19.77%,respecitively,compared with those of the surface soil.?3?The easily-extracted carbon?EC?,easily-extracted nitrogen?EN?and easily-extracted phosphorus?EP?increased significantly,and the increase rates were 0.03 g kg-1 yr-1,0.005 g kg-1 yr-1 and 0.001 g kg-1 yr-1,respecitively,with the restoration of the liaodong oaks forest,indicating that carbon,nitrogen and phosphorus were activated obviously.In the deep soil,the SC,SN and EP changed significantily with the increasing rates of 0.004 g kg-1 yr-1,-0.0003 g kg-1 yr-1 and 0.0003 g kg-1 yr-1,indicating an increasing carbon sequestration capacity and an increasing nitrogen and phosphorus availability.With the increasing of soil depth,the content of SC,EN and EP decreased significantly,and the contents of SC,EN and EP in the surface were 8.38,7.23 and 1.21 times as high as those in the deep soil,indicating a decreasing capacity of soil carbon sequestration and nitrogen and phosphorus availability with soil depth.In addition,the soil C/P ratio decreased significantly with soil depth,and the surface C/P ratio was 6.51 times as higher than in the deep soil.Soil C/N changed significantly with the forest restoration.?4?The microbial biomass carbon?MBC?contents in the control,30,60,90 and 120 year forests were 259.63,561.55,458.48,321.31 and 606.75 mg·kg-1 in the surface soil,and the microbial biomass nitrogen?MBN?contents were 48.81,140.08,77.56,66.88 and 131.12mg·kg-1,respectively.In addition,MBC in deep soil decreased by 45.03%,79.23%,68.70%,59.08%and 58.60%,respectively,compared with those in the surface soil,while MBN in deep soil decreased by 69.19%,94.52%,60.87%,64.05%and 70.31%,respectively.The microbial dominant species in the whole soil profiles were gram-negative bacteria?G-?and gram-positive bacteria?G+?.In the surface soil,the ratios of bacteria to actinomycetes,fungi to actinomycetes and G-to G+microbial biomass were 13.29-9.12,10.55-2.56 and 2.10-1.00from 30 to 90 years,indicating a decreasing trend of those ratios with the forest restoration.In the deep layer,the ratios of those parameters decreased by 13.22-8.17,7.50-2.97 and2.84-1.51,indicating a decreasing ratio the bacteria versus fungi,fungi versus actinomycetes,and G-relative versus G+,the ratios in the surface and deep soil decreased with vegetation succession,?5?The contents of HAC,AC and IC of the macroaggregate in the 60-year forests increased more significantly by 62.32%,77.41%and 132.88%than those in the control in the surface soil,respectively.In the deep soil,the contents of HAC,AC and IC of macroaggregate reached the maximum in 120-year forests,which were 30.93%,31.71%and 85.84%higher than those in the control.With the increase of soil depth,the decline rates of HA,AC and IC in the macroaggregates were 0.016 g·kg-1·cm-1,0.0089 g·kg-1·cm-1 and 0.0793 g·kg-1·cm-1,respectively.IC had the most significant influence on the aggregate stability,and the correlation coefficients between aggregate stability and IC in surface and deep soil were 0.52and 0.42,respectively.?6?With the restoration of the liaodong oaks forest,the growth rates of T-GRSP content in the macroaggregate and microaggregate in the surface soil were 0.004 g·kg-1·yr-1 and 0.006g·kg-1·yr-1,respectively.In the deep soil profile,the growth rates of T-GRSP in the macroaggregate and microaggregate were 0.006 g·kg-1·yr-1 and 0.008 g·kg-1·yr-1,respectively.In addition,T-GRSP had the greatest effect on the stability of the aggregate,and the mean weight diameter and T-GRSP correlation in macroaggregate coefficient was 0.66.With the increase of soil depth,T-GRSP concentration of the macro-and micro-aggregates in the surface soil were 0.20 and 0.46 times higher than those in the deep soil.?7?The stability of soil aggregate was affected by microorganism and plant,etc.The path analysis showed that the stability of the surface soil aggregate was mainly affected by the contents of microbial nitrogen and carbon,and the path coefficients of microbial nitrogen and carbon were 50.91 and 19.21,respectively.In deep soil,the aggregate stability was mainly affected by the biomass of roots with above 2 mm diameter and the soil C content,and the path coefficients were 0.10 and 0.07.?8?Different activated carbon contents in different aggregate-size fractions were affected by different factors.In the surface soil,HAC content in macroaggregate was mainly affected by the microbial nitrogen and carbon content,and the path coefficient was 50.87 and 1.03,respectively.The AC in macroaggregate was mainly affected by the biomass of root system of0.5-1 mm and 1-2 mm diameter,and the indirect path coefficients were 3467.35 and 2580.94respectively.The IC content in macroaggregate was mainly affected by the biomass of root systems of 0.5-1 mm and 1-2 mm diameters,with the path coefficients of 1707.34 and1224.89,respectively.In the deep soil,HAC content in macroaggregates was mainly affected by the biomass of roots with>2 mm and 1-2 mm diameter,and the path coefficients were 1.19and 0.54 respectively.The content in macroaggregates was mainly affected by gram-negative germ and microbial carbon content,with path coefficients of 0.08 and 0.02.The IC content in macroaggregate was mainly affected by>2 mm diameter biomass and soil carbon content,and the indirect path coefficients were 1.57 and 0.9.?9?The factors affecting the content of glomalin in aggregates of different size classes were different.In the surface soil,T-GRSP in the soil macroaggregate was mainly affected by soil carbon and EC,with the indirect path coefficients of 0.01 and 0.0021.E-GRSP in macroaggregate was mainly affected by the biomass of root systems of 1-2 mm and 0.5-1 mm diameters,with the indirect path coefficients of 0.11 and 0.08.In the deep soil,T-GRSP in the soil macroaggregate was mainly influenced by>2 mm diameter root biomass and microbial nitrogen content,and the indirect path coefficients were 0.09 and 0.05.E-GRSP in macroaggregate was mainly affected by soil carbon and EC content,and indirect path coefficients were 0.01 and 0.002.The results suggested that the biomass of plant communities continued to increase with the natural restoration of the liaodong oak forest.The contents of active C,N and P in soil increased generally,the stability of soil aggregates was continuously increasing,and the contents of inert carbon and T-GRSP in macroaggregate,microaggregate and silt-clay aggregate increased.It indicated that vegetation restoration could effectively promote soil nutrients,aggregate formation,and soil organic carbon fixation,especially in the macroaggregate.The results provided basic data for natural forest restoration and theoretical guidance for regional forest management. |
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