Effects Of Nutrients And Carbon Additions On The Decomposition Of Cunninghamia Lanceolata And Albizia Julibrissin Litter

Litter decomposition is an important progress for the global carbon cycle and the forest nutrient return.The mechanism remains unclear how nutrient and carbon addition affect the decomposing rate and nutrient immobilization-release.In this study,two species(Cunninghamia lanceolata(CLL)and Albizia julibrissin(AJL))litters and five treatments(CK,N addition alone [N],N+C additions [N+C],N+P nutrient additions [N+P],N+P+C additions [N+P+C])were selected.We conducted the laboratory microcosm experiment which was incubated for 720 days.Effect of nutrient and carbon addition on litter decomposition was measured by 99.99%15N isotope tracer technique.The quality retention,nutrient concentration,15 N immobilization and enzyme activity were measured according to four stages for 90 days 180 days,360 days and 720 days,which were used to reveal the effect of nutrient and carbon addition on the process of litter decomposition.The major results of this study were as follows:1.The mass remaining percentage of each residue of CLL and AJL was decline trend during the whole decomposition stage,but the mass remaining percentage of each residue was inconsistent with different decomposition stages.The decomposition percentage of AJL was faster than CLL,and the initial concentration of litter organic carbon(OC)of CLL was slightly higher than AJL.The concentration of litter organic carbon of CLL and AJL was decline during the decomposition stage,and there was not significant difference(p<0.05)among five treatments during the same stage.CLL and AJL showed carbon net release,but the carbon release rate of CLL was faster than AJL.2.The nutrient concentration dynamic was affected by both litter types and treatment during the decomposition progress.Comparing with the initial nitrogen concentration,nitrogen concentration of AJL was decline.However,nitrogen concentration of the other treatments of CLL increased Except for CK treatment declining by 720 days decomposition stage,which was related with quality characteristic of CLL and AJL(for example C/N ratio).By the 720 days,phosphorus concentration of CLL and AJP change regulation were not consistent.Phosphorus concentration of three treatments(N+C additions,N+P nutrient additions,and N+P+C additions)of CLL and the treatment N+P nutrient additions of AJL were higher than the original concentration.Phosphorus concentration of two treatments(CK and N addition alone)of CLL and other treatments of AJL were significant lower than the original Phosphorus concentration.3.Dynamic changes of C/N,C/P and N/P were controlled by litter types and treatments during decomposition progress.Comparing with the initial original C/N ratio,by the 720 days,C/N ratio of N+C additions treatment for AJL increased trend,but C/Nratio of the other four treatments was decline.C/N ratio of the five treatments for CLL was decline.Except for C/P ratio of the N addition alone treatment increasing,the other four treatments were decline.N/P ratio of CK and the N addition alone treatments for AJL increased trend,but N/P ratio of the other treatments was decline trend.Change extent of N/P ratio of the five treatments for CLL was little.The effect of litter types and treatment on C/N,C/P and N/P was significant.4.15 N abundance of CK treatment for CLL and AJL was lower than other treatments,but it increased slowly by 720 days.15 N abundance of CK treatment for CLL was net immobilization Pre decomposition.15 N abundance of CK and N+C additions treatments increased 0.34‰ and 0.85‰ respectively,but 15 N abundance of the other treatments was net immobilization medium-term decomposition.15 N abundance of CK treatment immobilized 0.41‰ for later stage.However,15 N abundance of the other treatments was decline.15 N abundance of CK treatment for AJL always increased.15 N abundance of N addition alone and N+C+P additions treatments showed the model of increasing-reducing-reducing,but 15 N abundance of N+C additions and N+P additions treatments showed the model of increasing-increasing-reducing.5.The effect of different treatments on enzyme activities was different,and they was promotion or inhibition or on difference,and they was related with material.By the 720 days,for CLL,N+C+P additions treatment significantly promoted the activity of AP and NAG.N+P additions treatment significantly promoted the activity of CB.However,N addition alone treatment inhibited ?G and NAG activity.All treatment made no difference on LAP.For AJL,N addition alone and N+C+P additions treatments significantly AP activity,and different treatments made no difference.Different treatments significantly inhibited ?G ? CB activity,but made no difference on LAP and NAG activity.Above all,litter decomposition was related with chemical property.The effect of different treatments on litter decomposition was different,and they was promotion or inhibition or on difference.The chemical stoichiometry of litter explained much change of decomposition rate,nutrient dynamics and enzyme activities.Those results showed that exogenous nutrient and carbon supplies could affect litter decomposition.However,litter decomposition depended on endogenous stoichiometry rate.Litter with higher C/N and C/P ratios tended to immobilize more exogenous N.