Effects Of Nitrogen Addition And Temperature Changes On Soil Carbon And Nitrogen Mineralization And Enzyme Activity

The acceleration of nitrogen deposition and global warming have had a significant impact on the functionality of terrestrial ecosystems.Indoor soil simulation experiments under simulated nitrogen addition and temperature change are of great significance for predicting the impact mechanism of future global climate change on soil carbon nitrogen cycle system.This study focuses on the surface soil of slope cultivation in the Wangmaogou watershed.Indoor cultivation experiments were conducted to investigate the effects of nitrogen addition(0mg·kg-1,10mg·kg1,20mg·kg-1,50mg·kg-1)and temperature changes(5℃,15℃,25℃,35℃)on soil carbon and nitrogen mineralization characteristics,temperature sensitivity(Q10),enzyme activity,temperature sensitivity,and enzyme stoichiometry,It reveals the influence mechanism of nitrogen addition and temperature change on soil carbon and nitrogen mineralization,provides data basis for carbon nitrogen cycle in the Loess Plateau,and provides data support for carbon peaking and carbon neutrality goals.The main conclusions are as follows:1.The mineralization rate(R)of soil organic carbon first increases and then decreases with the prolongation of cultivation,and R reaches its maximum value on the 3rd day of cultivation.The nitrogen addition treatment and temperature increase increased the maximum mineralization rate by 0.41-4.51 times and 0.64-3.60 times,respectively.The addition of nitrogen significantly increased the cumulative mineralization(Cm)and potential mineralization(C0)of soil,with Cm and C0 increasing by 0.29-1.28 times and 0.25-1.32 times compared to the unadded treatment.The mineralization of soil organic carbon accelerated and the carbon sequestration capacity decreased.The increase in culture temperature resulted in a significant increase in R,Cm,and C0,with Cm and C0 increasing 0.31-2.73 times and 0.21-2.64 times respectively.The increase in nitrogen addition,the addition of low nitrogen(N1)and medium nitrogen(N2)enhances temperature sensitivity,while high nitrogen(N3)has an inhibitory effect,with the best effect at the N2 level.2.Soil ammonium nitrogen,ammonification rate,nitrification rate,net nitrogen mineralization rate,and net ammonification amount first increase and then decrease with the extension of cultivation time.Soil nitrate nitrogen,inorganic nitrogen,net nitrification amount,and net nitrogen mineralization amount show an increasing trend with the extension of cultivation time.The net nitrification and net nitrogen mineralization of soil increased by 0.18-0.98 times and 0.70-0.91 times,respectively,after nitrogen addition treatment.The increase in temperature promotes nitrogen mineralization,and the net nitrogen mineralization rate and amount are optimal at 35℃;The potential nitrogen mineralization in soil is manifested as T3>T4>T2>T1.Under increasing temperature,the net nitrification and net nitrogen mineralization increased by 0.71-1.17 times and 0.69-1.18 times,respectively.The rate constant k varies with the amount of nitrogen added,depending on the culture temperature.The temperature sensitivity of soil net nitrogen mineralization Q10 is influenced by temperature,as follows:Q10(25℃/15℃)>Q10(15℃/5℃)>Q10(35℃/25℃);The addition of nitrogen enhances the temperature sensitivity of net nitrogen mineralization,manifested as N2>N3>N1>N0.3.The activities of CBH,BG,NAG,and ALP enzymes were 4.98-11.26,12.18-44.06,5.8532.10,and 117.02-602.96 nmol·g-1·h-1,respectively.The promoting effect of nitrogen addition on enzyme activity varies depending on the type of enzyme,with the expression of N2>N3>N1>N0 for C-acquiring enzymes,and N3>N2>N1>N0 for N and P-acquiring enzymes.The temperature sensitivity of CBH,BG,NAG,and ALP were 1.09-1.19,1.03-1.44,1.08-2.97,and 1.08-1.78,respectively.The addition of nitrogen significantly reduces the temperature sensitivity of CBH and ALP,promotes ln(NAG)/ln(ALP),ln(CBH+BG)/ln(ALP).The increase in temperature significantly reduces the temperature sensitivity of CBH,NAG,and ALP;Inhibiting ln(CBH+BG)/ln(NAG)and In(CBH+BG)/ln(ALP),but promoting In(NAG)/ln(ALP).Under the influence of nitrogen addition and temperature increase,CBH,BG,NAG,and ALP are all positively correlated with the mineralization rate of organic carbon,and also significantly positively correlated with ammonium nitrogen,nitrate nitrogen,and inorganic nitrogen.