Response Of Urban Forest Soil Respiration To Short-term Nitrogen Addition

Nitrogen deposition changes the progress of the soil carbon cycle,which in turn destroys the stability of the forest ecosystem.With the increasing of atmospheric nitrogen deposition,the response of soil respiration components to nitrogen deposition is studied,and its influence mechanism is discussed,which is of great significance for understanding the carbon dynamics of forest eco-systems[1].In this study,the suburbs(Dashushan),Exurbs(Zipengshan)in Hefei City,Anhui Province,and the Rural(Wanfoshan Mountain)in Lu'an City,Anhui Province were used as research objects.From August 2018 to December 2018,simulated nitrogen deposition experiments were carried out in the experimental sites.We set three treatment levels which are called control plot(0 Kg N·m-2·yr-1),low nitrogen plot(50 Kg N·m-2·yr-1),and high nitrogen plot(100 Kg N·m-2·yr-1),to study the effects of nitrogen addition on soil respiration and it's components of artificial paralyzed forest and natural paralyzed forest;The effects of nitrogen deposition on daily and seasonal changes of soil respiration;The basic physical and chemical properties of soil,etc.The effects of soil temperature and soil moisture on soil respiration under nitrogen deposition conditions,these are the following results:(1)The difference of soil total respiration rate under different concentrations of nitrogen was not significant(p>0.05).Low nitrogen will increase the soil respira tion rate by 5%-20%,but the effect is non-linear,the degree of impact depends on the level of nitrogen application,the location of nitrogen application,the time period of nitrogen application and its interaction,and not significant Impact(p>0.05).At the same time,low nitrogen also inhibited soil respiration rate,but did not significantly affect(p>0.05).High nitrogen increased soil respiration rate by 7%-25%,and also inhibited soil respiration rate,but did not significantly affect(p>0.05),and the regularity was consistent with low nitrogen.Low-nitrogen treatment of root-cutting treatment promoted soil respiration rate,but the effect was not signifi cant.Root-cutting treatment under high nitrogen treatment inhibited soil respiration rate,but the effect was not significant,and the range was about 5%.The soil respiration rate of all kinds of roots under nitrogen addition does not change with fertilization concentration,seasonal variation,and the interaction between the two.(2)The average respiration component of CK soil was Ra 65%,Rh 35%;LN was Ra 68%,Rh 32%;HN was Ra 63%,Rh 37%.Low nitrogen promoted soil a utotrophic respiration and inhibited heterotrophic respiration;high nitrogen inhibited autotrophic respiration and promoted heterotrophic respiration.The two fertilization treatments had no significant effect on the respiration rate of urban forest soil respiration components(p>0.05).Soil respiration and its components are expressed in urban suburbs>rural areas>urban suburbs,indicating that the response of urban forest soil respiration rate to nitrogen addition is not affected by its distance from the city center.(3)Different concentrations of nitrogen added treatment had an effect on the seasonal variation of soil respiration rate in the Maize forest.The overall performance was that low nitrogen promoted the seasonal variation of soil respiration rate,while high nitrogen inhibited the seasonal variation of soil respiration rate,but h ad no significant effect(p>0.05)..The effects of different nitrogen addition sites,fertilization cycles and their interactions on the seasonal variation of soil respiration rate were significant(p<0.05).(4)Nitrogen addition changed the basic physical and chemical properties of the soil and its correlation,but did not significantly affect(p>0.05).Soil pH,SOC,TN,C/N,available phosphorus,NH4+-N,and NO3--N were changed under nitrogen addition,but the effect was not significantly different(p>0.05).The soil respirat ion rate under different concentrations of nitrogen added treatment did not cause 1 arge fluctuations due to its change,and showed no significant effect(p>0.05).There was no significant difference in soil respiration(p>0.05)between soil physical and chemical factors and their correlations under nitrogen supplementation,but sig nificant correlations with fertilization sites,seasonal changes and their interactions(p<0.05).(5)Soil temperature control soil respiration rate variation under different conce ntrations of nitrogen was treated as:LN>CK>HN.The relationship between soil moisture and soil respiration was obvious,with a good linear relationship(p<0.05)and R2 value between 0.63-0.90.However,there was no difference in soil respiration rate between treatments(p>0.05).The effect of soil moisture content on soil respiration rate under nitrogen addition was LN>CK>HN.The relationship between soil moisture and soil respiration was obvious,showing a good exponential relation ship(p<0.05),and the R2 value was between 0.55-0.99.There was no difference in soil respiration rate between the treatments(p>0.05).There was no difference in soil respiration temperature sensitivity coefficient(Q10)under CK,LN and HN treatment(p>0.05).(6)It can be seen from the results of this study that the response of urban forest soil respiration and its components to nitrogen addition is different,and the sample plots selected by the experiment are not comprehensive enough.The follow-up research should pay attention to this in order to better explain the mechanism and study the urban forest.Carbon dynamics provide detailed support.