| Due to the long-term interference of human activities and the vulnerability determined by the climate and soil characteristics of the red soil region,the red soil region in the south of China has become one of the regions with the most serious erosion and degradation.Vegetation restoration is an effective way to improve and restore soil degraded ecosystem.Soil aggregate,as an important index of erosion resistance,is an important storage place of organic carbon.On the other hand,organic carbon is an important cementitious material for the formation of soil aggregates.They affect each other and are indispensable conditions for each other.Therefore,the study of soil aggregate and their organic carbon can provide an effective reference for the ecological benefit evaluation and soil quality improvement of different vegetation restoration measures.In this paper,different vegetation restoration models（Pinus massoniana pure forest,Pinus elliottii pure forest,Schima superba pure forest,Pinus massoniana plus Schima superba forest,Pinus elliottii plus Schima superba forest,mixed forest of Pinus elliottii plus Schima superba forest and natural restoration control area）were analyzed in the degraded red soil area of Taihe County.The soil layers of 0-10cm,10-20cm and 20-40cm were divided to study the distribution characteristics and stability of aggregates and the active carbon components of aggregates The purpose of this study is to provide a theoretical basis for the optimization of vegetation restoration model in degraded red soil area.The results show that:1)In different soil layers,the content of>0.25mm large aggregates was the main content of soil water-stable aggregates in different vegetation restoration modes.With the decrease of particle size,the content of>0.25mm large aggregates was gradually reduced.As the soil depth increases,the aggregate content of>0.25mm particle size generally decreased.Compared with mechanical aggregates,the content of>0.053mm particle size aggregates in water-stable aggregates was generally reduced,whereas the content of small particle size aggregates<0.053mm increased.According to the content of water stable aggregates(WR>0.25mm)in>0.25mm particle size of each vegetation recovery model,it can be known that the content of>0.25mm particle size aggregates in Schima superba pure forest was significantly higher than that in other vegetation restoration modes（P<0.05）,and the natural recovery control area was minimal,indicating that the soil aggregate structure was significantly improved by vegetation restoration treatment.2)The average weight diameter（MWD）and>0.25mm water stable aggregates（WSA）were significantly different in the soil layers of 0-10cm and 10-20cm,and the MWD and WAS values of 0-10 cm soil layers are the largest in general,It shows that 0-10cm soil layer is more stable;The damage rate（PAD）value of certain size aggregates in soil 10-20cm and20-40cm is quite different,with the increase of soil depth,the total pad value of different vegetation restoration is gradually increasing,among which the value of pure forest of Schima superba is the smallest,the value of natural recovery control area is the largest,while the value of MWD and WSA of pure forest of Schima superba is the largest,and the value of natural recovery control area is the smallest,in other words,the vegetation restoration model increased the stability of soil aggregates,and the most obvious performance was at 0-10cm.3)Different vegetation restoration has apparent accumulation effect on the accumulation of active carbon components,and the carbon content is mainly concentrated in 0-10cm soil layer,and significant higher than that in 10-20mm and 20-40cm soil layer;with the decrease of particle size,the total organic carbon and easily oxidized organic carbon content of different vegetation restoration modes generally show a"U"shape change trend,The organic carbon content of granule was decreasing.Moreover,>0.25mm particle size large aggregate has a strong holding capacity for the particle organic carbon content Compared with the natural recovery control area,soil quality improved significantly,the soil carbon content of the vegetation restoration control area is significantly increased,it shows that soil quality has been improved significantly.4)According to the correlation analysis,there are differences in the correlation between the carbon component of soil aggregates and the stability index of aggregates.Total organic carbon（TOC）and easily oxidized organic carbon（EOC）was more significantly correlated with MWD,and particulate organic carbon（POC）was more significantly correlated with PAD,while the correlation between POC and PAD is more significant.As the soil depth increases,the correlation between soil aggregate TOC and soil aggregate stability indexes MWD、WSA and PAD gradually decreased.The soil aggregate POC and EOC showed a trend of decreasing first and then increasing.The correlation between the soil aggregate POC and the stability index was the most significant in the 20-40cm soil layer,which was mainly reflected in the>0.25mm particle size large aggregates.The correlation between>0.053mm particle size aggregate EOC and the stability index was the most significant in the 0-10cm soil layer.5)The carbon components of aggregates with different particle sizes were positively correlated with total nitrogen（P<0.01）,and positively correlated with p H（P<0.05）.There are different correlations between the carbon components of aggregates and the physical and chemical properties of soil,among which the aggregates TOC、POC and EOC were significantly positively correlated with total nitrogen（P<0.01）,indicating that the soil nitrogen mainly existed in organic carbon in the form of organic nitrogen and had the same trend of decrease and increase.>2mm particle size aggregate TOC had a significantly positive correlation with porosity（P<0.05）,the remaining particle size had a significantly negative correlation with bulk density（P<0.05）,and the TOC had a significantly positive correlation with p H（P<0.05）.The correlation between POC,EOC,p H and bulk density porosity of aggregates with particle size of 2-0.053mm was more significant（P<0.05）.Through the study of soil aggregate structure,stability and organic carbon content,it can be seen that different vegetation restoration has different effects on the improvement of soil quality.Among them,pure forest of Schima superba has more significant effects on soil improvement than other vegetation restoration modes,and soil p H and nutrient total nitrogen have more obvious effects on the carbon composition of soil aggregate,this provides a theoretical basis for quality improvement and ecological construction in degraded red soil areas. |
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