The Biochemical Characteristic Of Soil And Its Response To Human Disturbance In Typical Forestland Of Qinling Mountain

Long term management of pure plantation may cause a series of ecological problems, such as fertility degradation, decrease of land productivity, deterioration of forest resistance to natural disasters. This may not only affect production and service function of forest, but also seriously threaten the sustainable development of forest ecosystem. This study took four kinds of typical forestlands with different tree species (Larix kaempferi,Pinus tabulaeformis,Catalpa fargesii,Q. aliena var. acuteserrata) in Angou watershed , upper reaches of Heihe river, middle of Qinling Mountain as subjects, carried out experiments about human disturbance including extra C and N application, litter exchange and soil exchange, analyzed the biochemical characteristic of soil and its response to human disturbance in different forestlands. The interspecific relationship between tree species was investigated in order to offer theoretical direction for pure plantation management and forest renewal in that area. The main results includes :(1) Comparation of biochemical characteristic of soil in different forestlandsThe amount of organic C and total N in Catalpa fargesii and Q.aliena var.acuteserrata lands was higher than in Larix kaempferi and Pinus tabulaeformis lands, but soil bulk density was lower. Soil enzyme activity of four kinds of forestlands decreased with soil depth. The soil enzyme activity in 0-10 layer was 1.18-2.83 times and 1.37-6.55 times higher than 10-20 layer and 20-30 layer, respectively. The soil enzyme activity in Catalpa fargesiiland was increasing. The soil microbial biomass C(MB-C) and soil microbial biomass N(MB-N) decreased with soil depth. Catalpa fargesii and Q.aliena var.acuteserrata lands had higher MB-C but lower MB-N than Larix kaempferi and Pinus tabulaeformis lands. The litter decomposition rates in four kinds of forest lands follow this sequence: Catalpa fargesii>Q.aliena var.acuteserrata>Larix kaempferi>Pinus tabulaeformis.(2) Disturbance of extra C and N applicationExtra C increased soil enzyme activity and MB-C in 0-10 layer in four kinds of lands, but decreased the soil catalase activity in 20-30 layer by 26.9% in Catalpa fargesiiland. Extra N had inhibitory effect on soil enzyme and decreased MB-C in Larix kaempferi land. Application of C and N jointly increased urase and sucrase activity in 0-10 layer in four kinds of lands, and increased MB-C in Pinus tabulaeformis land. It was not suitable to applied N in Larix kaempferi land. The response to C and N joint disturbance was different for different lands. Under extra C and N disturbance, the litter weight loss rate increased as decomposition continued. Time for 50% and 95% decomposition decreased both.(3)Llitter exchange: exchange the litter of conifer(Pinus tabulaeformis,Larix kaempferi) and broadleaf tree(Catalpa fargesii,Q.aliena var.acuteserrata)After putting litter of Catalpa fargesii and Q.aliena var.acuteserrata into Larix kaempferi land, soil enzyme activity and MB-C decreased. Enzyme activity under other exchange treatments all increased. After litter exchange, decomposition rate all increased except putting litter of Larix kaempferi and Pinus tabulaeformis into Catalpa fargesii land. Time for 50% and 95% decomposition shortened by 2-19 months and 3-7 years respectively. Mixed plantation of Larix kaempferi and Catalpa fargesii was not feasible.(4) Soil exchange: exchange the humus layer soil of conifer(Pinus tabulaeformis,Larix kaempferi) and broadleaf tree(Catalpa fargesii,Q.aliena var.acuteserrata) lands after mixed the soil with different ratiosThe measured value of soil enzyme activity in 0-10 layer was 1.03-2.01 times higher than predicted value. Analysis of variance showed that the difference between predicted value and measured value of soil enzyme activity was significant, which implied soil exchange had a considerable effect on soil enzyme activity. The mixing of soil in Larix kaempferi land with soil in Catalpa fargesii and Q.aliena var.acuteserrata land with ratio of 1/3 or 1/1 had an inhibitory effect on MB-C to a certain extent. Soil exchange improved litter decomposition. Time for 50% and 95% decomposition shortened by 6-24 months and 2-8 years respectively. Combined with results of litter exchange, this study showed that Larix kaempferi was not suitable to be planted with Catalpa fargesii。Mixing plantation of Catalpa fargesii and Pinus tabulaeformis,Pinus tabulaeformis and Q.aliena var.acuteserrata, Larix kaempferi and Q.aliena var.acuteserrata is feasible to a certain extent, but mixing ratio needs to be more studies.