Study On Enzyme Kinetic Parameters And Temperature Sensitivity Of Soil Organic Carbon Mineralization In Peatland

As a carbon rich wetland,peatlands play an important role in the global carbon cycle and global climate change.Microbial extracellular enzyme catalysis is the rate-limiting step in soil organic matter decomposition and regulates the decomposition process of soil organic matter.Soil enzyme kinetic parameters,including the maximum activity(V_max),the Michaelis constant（K_m）and catalytic efficiency(K_cat),can not only completely describe the enzyme-catalyzed reaction process,but also reflect the tightness of enzyme-substrate binding and the mechanism of soil organic matter decomposition.Therefore,this study revealed the variation patterns of soil enzyme activities,enzyme kinetic parameters and its temperature sesitivities(Q₁₀)in different microtopography parts（hummocks and hollows）in a Sphagnum-dominated peatland of Great Xingan Mountains.This study also explored the variation characteristics of soil organic carbon decomposition rate(C_min)and its temperature sensitivities(Q_10（Cmin）)of different depths in different microtopography parts and expounded their enzymatic kinetic mechanism combined with soil p H,water content（SWC）,soil organic carbon（SOC）,total nitrogen（TN）,total phosphorus（TP）and the enzyme kinetic parameters of soilβ-1,4-glucosidase（βG）,β-1,4-N-acetyl-glucosaminidase（NAG）,and acid phosphatase（AP）.The main conclusions were following:（1）There was a significant spatial heterogeneity in the enzyme activities between the surface and subsurface of hummocks and hollows.Soil BG and NAG activities in hummocks and soil BG and AP activities in hollows showed the pattern of surface>subsurface.Soil enzyme activities were higher in hollows than the hummocks.Soil NAG enzyme activity was significantly and negatively correlated with SWC and TN,but was positively correlated with soil p H and SOC in hummocks.Soil BG enzyme activity was significantly and positively correlated with SWC,SOC,and phenolics,while NAG activity was significantly and negatively correlated with the above elements in hollows（P<0.05）.（2）There was a significant spatial heterogeneity in soil enzyme kinetic parameters between the surface and subsurface of hummocks and hollows.The BG-V_max and NAG-V_maxin hummocks and hollows showed patterns of surface>subsurface at different incubation temperatures.The BG-K_m and AP-K_m in hummocks showed the pattern of surface>subsurface,while there were no consitent patterns for the K_cat of soil encyme activities between surface and subsurface in hummocks and hollows.With the increase of incubation temperature,the V_max of all three soil enzymes and the K_m of BG and AP gradually increased,while NAG-K_m gradually decreased.The results of correlation analysis showed that SWC,SOC,phenolics,TN and p H were the main factors affecting soil NAG and AP enzyme kinetic parameters on the hummocks.SWC,SOC,phenolics,and TN were the main factors affecting soil BG and NAG enzyme kinetic parameters on the hollows.（3）In general,the Q_10（Vmax）of the three soil enzymes in hummocks and the Q_10（Vmax）of BG and NAG enzymes in hollows showed variation patterns of surface>subsurface,while the Q_10（Vmax）of AP enzyme in hollows showed a pattern of surface<subsurface.The Q_10（Km）of all three enzymes showed patterns of surface>subsurface both in hummock and hollows.Except for the Q_10（Kcat）of AP,the Q_10（Kcat）of BG and NAG showed patterns of sub-surface>surface both in hummocks and hollows.Soil TN and SWC were the main factors influencing the Q₁₀ of soil enzyme kinetic parameters in hummock,while phenolic,TN,and SOC were the main factors influencing the Q₁₀ of soil enzyme kinetic parameters in hollows.（4）The C_min and Q_10（Cmin）were significantly different between the surface and subsurface layer in hummocks and hollows.The C_minincreased with the increase of incubation temperature both in hummock and hollows（P<0.0001）.The C_minshowed a pattern of surface>subsurface in hummocks,but did not have a uniform variation pattern in hollows.The Q_10（Cmin）in hummocks and the Q_10（Cmin）in the temperature range of 15-25℃in hummocks showed a pattern of subsurface>surface.During the incubation period,the Q_10（Cmin）showed a pattern of 5-15°C>15-25°C in hummocks,but showed a pattern of 5-15°C<15-25°C in hollows.（5）The C_minwas significantly and positively correlated with SOC,phenolics,NAG-V_max,NAG-K_cat,AP-V_maxand AP-K_m,but significantly and negatively correlated with SWC and TN in hummocks.The C_minwas significantly and positively correlated with soil p H,SWC,SOC,phenolics,TN,BG-V_max and BG-K_cat,but significantly and negatively correlated with NAG-V_max and NAG-K_cat in hollows（P<0.05）.The Q_10（Cmin）was only significantly and positively correlated with and BG-Q_10（Vmax）in hummocks.Soil AP-V_max was the main factor influencing C_minand Q_10（Cmin）in hummocks,and was BG-V_max,NAG-K_cat,BG-K_m and phenolics in hollows.The Q_10（Cmin）was significantly and positively correlated with phenolics,SWC,SOC,TN,and AP-Q_10（Km）,but significantly and negatively correlated with BG-Q_10（Kcat）,NAG-Q10_Kcatand AP-Q10（Kcat）in hollows（P<0.05）.In conclusion,there were variations in the spatial pattern and influencing factors in soil enzyme activities,kinetic parameters,mineralization rate and their temperature sensitivity at different depths in hummocks and hollows of the Sphagnum-dominated peatlands.The results provide a scientific basis for exploring the mechanism of soil organic carbon decomposition in peatlands,and provide an important parameter for evaluating the role of peatlands in global carbon cycle models.</sub>