Soil Physicochemical Property Dynamics Following Different Restoration Pattern In Subtropical Forests

Soil nutrient content and availability are fundamental to terrestrial biodiversity and ecosystem functionality.Measures of soil nutrient concentrations are important indicators of terrestrial productivity.Equally important are their stoichiometric balances in relation to carbon(C)concentration,since strict proportions of C,nitrogen(N),and Phosphorus(P)are key regulatory mechanisms for optimal plant growth and ecosystem functioning.Intensive plantation and undisturbed secondary forests are the two main restoration models of subtropical forests.However,the intensive plantation can reduce species diversity and weakens ecosystem services.Therefore,the comparative study on the ecosystem functions of intensive plantation and secondary forests is an important way to understand the causes of loss of biodiversity and ecosystem service functions of plantation.In this study,we investigated soil physicochemical properties in three soil layers and driving factors of different restoration mode after clear cutting by using two chronosequence and regarding secondary forests older than 100 years as a reference.The results will provide a theoretical basis for the restoration of subtropical forests and plantation management.The main conclusions are as follows:(1)Forest type and stand age exert no significant effects on soil carbon and nitrogen contents and stock.Linear regression analysis showed that the soil carbon and nitrogen stock and contents were unchanged with the restoration time in both two forest type.During the development of Cunninghamia lanceolata plantation,the available P content decreased with stand age at soil depth of 0-10 cm,while the available potassium content increased with stand age.In addition,during the development of secondary forest,the ammonium content increased with stand age at soil depth of 0-10 cm.(2)We also found that the forest type and stand age exert significant effects on soil P stock and content.The contents and stock of soil total P and total calcium(Ca)in Cunninghamia lanceolata plantation decreased rapidly from young forest to mature forest,and reached the lowest level in mature forest.However,in secondary forest,the soil P stock and content remained unchanged with restoration,while the stock and content of calcium at 0-10 cm soil layer increased significantly.The interaction of soil layer and stand age had significant effects on soil C: P and N: P ratios.Soil C: P and N: P in Cunninghamia lanceolata plantation reached their peak values at mature stage.P is a key factor limiting the growth of Cunninghamia lanceolate plantation in the rapid growth stage.Phosphorus fertilizer during the rapid growth period of Cunninghamia lanceolate may be important to sustain the growth of Cunninghamia lanceolate and to improve nutrient cycling between plant and soil.(3)The stand basal area of Cunninghamia lanceolate increased rapidly with stand age and was larger than that of natural secondary forest at all stages.The soil C and N content and soil available potassium content in three soil layers increased with the development of biomass under Cunninghamia lanceolate plantation.The results showed that the richness of shrub layer was the key factor that affecting soil physical and chemical properties in Cunninghamia lanceolate plantation.The coverage of shrub layer and diversity in secondary forest were significantly higher than those in Cunninghamia lanceolate plantation in the early stage of stand development,but they tended to be the same with stand age.In the process of plantation management,the reduction of planting density,the preservation of shrub layer,and an appropriate extension of rotation could be beneficial to the improvement and restoration of soil fertility conditions of Cunninghamia lanceolate plantation.(4)The soil carbon and nitrogen contents and stock under Cunninghamia lanceolate plantation were lower than those under secondary forest at 5 and 8 years.In secondary forests,shrub layer richness,herb layer richness and litter cover all significantly affected the soil physical and chemical properties.These results indicated that Cunninghamia lanceolate plantation may be more conducive to the rapid recovery of aboveground biomass in the short-term restoration of artificial tending.However,secondary forests may be conducive to the restoration of biodiversity and can form forest communities with complex structures more quickly.