| The important method for studying the formation process of soil organic matter and nutrients is detritus input removal treatment.The most previous detritus-removal studies only focused on net changes in soil carbon(C),and rarely reported related factors such as soil ecological stoichiometry and physical properties,which limits the interpretation of soil C change.The detritus-removal experiment was conducted in a temperate deciduous broad-leaved forest in 2007 at the Maoershan Ecological Station in Northeast China,including two treatments:no litter(NL),no root(NR).The concentrations of soil carbon(C),nitrogen(N),phosphorus(P),soil water content,bulk density,dissolved organic carbon(DOC),dissolved organic nitrogen(DON),available phosphorous(A-P),microbial biomass carbon(MBC),microbial biomass nitrogen(MBN),microbial biomass phosphorus(MBP)were measured in 2016 and 2017.(1)The concentration of C at the surface soil(0?10 cm)was reduced by 15.6%and 10.7%for the NL and NR treatments,respectively.while the weighted-mean C concentration at the 0?30 cm depth of soil was reduced by 7.9%and 4.6%,respectively.The standardized major axis regressions showed that the regression slopes between the C,N and P at each layer of the 0-30 cm depth of soil differed significantly between the treatments and the control;and the intercepts of the regressions between soil C concentration and bulk density or soil water content also varied significantly among the treatments.The results suggested that the detritus-removal experiment caused a coordinated variation in the stoichiometry of soil C,N and P and soil physical properties.(2)Carbon mineralization rate per soil carbon(Rc)decreased with time.But the rate of reduction is different.At the early stage of mineralization,NL,NR and CK showed significant differences with Rc.In the first day mineralization,NL was 15.9%lower than CK,NR decreased by 18.8%;But in the later stage of mineralization,NL almost coincides with CK,which is significantly different from NR,and NR keeps a stable difference compared with CK(the average value is 20.1 ±0.9%).For 67 days in the lab cultivation,NL mineralized organic carbon 2.4%(1.96±0.10 mg CO2-C g drying soil-1),NR mineralized soil organic carbon 2%(1.96±0.10 mg CO2-C g drying soil-1),CK mineralized soil organic carbon 2.5%(2.67±10.16 mg CO2-C g drying soil-1),the cumulative percentage of NL mineralization is 4.1%lower than CK,while NR is 19.9%lower than CK.(3)By measuring soil microbial biomass carbon(MBC)and soil soluble organic carbon(DOC),it was found that MBC and DOC of NR decreased by 10.6%and 12.5%compared with CK,Through the analysis of fraction of microbial respiration rate per unit biomass carbon(qCO2),total substrate carbon in microbe(qMBC)and carbon and nitrogen ratio of microbial biomass can be found that the qCO2 of NL and NR is lower,but the qMBC of NL is higher than CK,the qMBC of NL is higher than CK,while MBC:MBN and MBC:MBP of NL are significantly higher than CK,and NR MBC:MBP is significantly higher.Collectively,during the decadal scale,the NL treatment had a larger effect than the NR treatment,NR reduced the mineralization rate by decreasing microbial biomass and stabilizing organic carbon,this difference does not change over time;NL can reduce the reduction rate of mineralization rate after depletion of active organic carbon in the later stage of culture.Therefore,the effect of NR on mineralization is greater.Although the removal of roots may have a greater impact on the soil carbon cycle on a longer time scale,it is not possible to show a significant reduction in the carbon content of the soil;however,due to the decrease of carbon input and the increase of carbon output,NL decreases carbon content faster.The study suggests that litter and root removal can affect soil carbon pool.They affect soil carbon content and carbon cycle through soil ecological stoichiometry,soil physical and chemical properties and microbial metabolic regulation. |
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