| China subtropical area is an important agricultural and forestry production base in China,which maintains the ecological security of the basin.The zonal forest vegetation evergreen broad-leaved forest has been transformed into secondary forest and plantation because of long-term human production and business activities.In order to reveal the formation and evolution mechanism of forest soil fertility in the area,four forest types composed of different tree species were chosen in the central hilly area of Hunan province,China,comprising of:Cunninghamia lanceolata plantation(CL),Pinus massoniana ?lithocarpus glaber coniferous-broad leaved mixed forest(PM),Choerospondias axillaries deciduous broad-leaved forest(CA),lithocarpus glaber + Cyclobalanopsis glauca evergreen broad-leaf forest(LG).Soil enzyme activity,nutrient contents and the dynamic characteristics of the process with seasons and succession were studed,and the particularity of forest soil enzyme activity were discussed.In order to reveal the mechanism with subtropical secondary forest protection to influence soil enzyme activity and nutrients,and provide scientific basis for the reasonable operation of subtropical natural forest.The results were as follows:The spatial distribution characteristics of soil enzyme activity showed the same law:The 0-15cm soil layer was higher than the 15-30cm soil layer,and the activity of the same enzyme decreased with the increase of soil depth in different forests,but the decreasing range of enzyme activity was different,the decreasing range of sucrase was the largest.Different forest species had different effects on soil enzyme activities.The soil enzyme activity in the study area has obvious seasonal changes.Seasonal variation of soil urease activity was shown in the order as following:autumn>winter>summer>spring in CL,PM forest soils,but those in CA,LG forest performanced in the order:summer>autumn>winter? spring.Sucrase activity was showed:summer>autumn?winter>spring,acid phosphatase activity is:summer>spring ? autumn>winter,catalaseactivity activity was:autumn>spring>summwe>winter in the four kinds of forest soil.Forest type had significantly affect to soil enzyme synthesis index(SEI),LG was the most,CA,PM took second place,CL was the minimum.The seasonal variation of SEI in two soils of the same forest was basically no difference,all this showed:summer was the highest,autumn,winter took second place,spring was the minimum.SEI was the same with vertical distribution of single enzyme activity;SEI had highly significant positive correlation with forest tree species diversity,with the stand density,there was no significant correlation.There was a significant positive correlation between catalase,urease,sucrase,and acid phosphatase activity.The content of organic matter in the studed forest soil area is high,but total P,total K,available P content was very low,hydrolysis N,available K content was low.The content of organic matter in three secondary forest was higher than CL,The average content of total N in the four kinds of forests varied from high to low:CA>LG>PM>CL,but the changing trend of total P average content was:CA was the hghest,LG was the minimum,the average content of total K was:PM,CA were higher than CL,the lowest was in LG.the average content of hydrolysis N was:CA was the highest,PM was the minimum.The three kinds of secondary forest average content of the available P and the available K was significantly higher than CL.The contents of 4 kinds forest soil of hydrolysis N,available P and available K had obvious seasonal changes,and had the same changing trend with two soil layers in the same forest,but different forest of hydrolysis N,available P rhythm had different seasonal rhythm,and the available K content of two soils in different forests had the same changing trend with seasonal variation,showed that the forest of different tree species had certain influence on the soil hydrolysis N and available P with seasonal variation,However,the effect of the available K content was not obvious.The comprehensive index of soil nutrients in central hilly area of hunan province ranged from 2.52 to 3.67,the highest was in CA,as followed by LG,the lowset was in CL.The comprehensive index of forest soil nutrients was significantly correlated with the diversity of forest species,but there was no significant correlation with the stand density.Soil pH value was significantly correlated with sucrase and acid phosphatase,there is no significant correlation with urease and Catalase.It showed that soil sucrase and acid phosphatase activity was significantly affected by the soil acidity and alkalinity.Soil enzyme activity had a very significant positive correlation with soil total N,hydrolyzed N,total P and available P,soil urease and sucrase activities had extremely significant negative correlation with soil total K content,but acid phosphatase and total K content showed a significant positive correlation,indicating that soil enzyme activity had significant effects on soil nutrient contentsoil,enzyme activity could indicate the evolution of soil quality characteristics.The synergistic coupling effect between total N and total P,hydrolysis N,available P contents,total P content and hydrolysis N content were observed in different forest soils.The increases of soil total N content promoted the effectiveness of soil N,and soil P accumulation.The antagonistic effect of soil P and K content was observed.The influence of hydrolysis N content on available P,available K content was consisted with the influence of available P content on available K content,which showed synergistic coupling effect.The soil fertility of secondary forests(LG,AC,PM)were higher than that of cunninghamia lanceolata(CL),and LG,AC is higher than PM,soil enzyme activity was closely related to soil nutrient concentration which could indicate the characteristics of forest soil fertility and its evolution in in the hilly area of central Hunan,China. |
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