Effects Of Nitrogen And Phosphorus Addition On Soil Respiration And Physicochemical Properties In Chinese Fir

With the development of the industrial revolution,the burning of a large amount of fossil fuels,the increase in the application of agricultural fertilizers and the vigorous development of animal husbandry,the content of reactive nitrogen species(NOx,NO,N2 O,NH3)in the atmosphere has become higher and higher.After the reactive nitrogen species enters the atmosphere,it returns to the ground again through a series of chemical reactions through nitrogen deposition.The nitrogen content of the nitrogen deposition into the terrestrial ecosystem far exceeds the demand of the terrestrial ecosystem,resulting in a series of negative effects.At present,my country has become the third largest nitrogen deposition area in the world,and this trend will continue to intensify in the coming decades.Because the contentof available phosphorousin the soil is low and easily fixed,a large amount of phosphorus cannot be effectively used by plants,resulting in low phosphorus stress.Studies have shown that under the environment of nitrogen deposition,the plants are more severely under low phosphorus stress.However,there are few studies on low phosphorus stress under nitrogen deposition in my country.Chinesefir(Cunninghamia lanceolata)is one of the unique high-quality fast-growing timber species in southern China.It is distributed in large quantities in Zhejiang,and Zhejiang is a major forestry province in China.Therefore,the experimental research on nitrogen deposition and phosphorus addition in fir forest in Zhejiang can make up for China.The deficiencies in the study of nitrogen deposition and low phosphorus stress on forest ecosystems can lay the foundation for further research on nitrogen deposition and low phosphorus stress in China and even the subtropical regions.In this experiment,10 years old Chinese fir was used as the research object,and a total of 9 treatment levels were set: CK,LN(N30: 30 kg · ha-1 · a-1),HN(N60: 60 kg · ha-1a-1),LP(P20: 20 mgkg-1),HP(P40: 40 mgkg-1),LNLP(N30 + P20),LNHP(N30 + P40),HNLP(N60 + P20),HNHP(N60 + P40),to study the effect of phosphorus addition on nitrogen respiration and soil physicochemical properties under nitrogen deposition.The results of the study are as follows:(1)There are obvious seasonal changes in the soil respiration of Chinesefir.Nitrogen deposition,phosphorus addition,and their combined treatment have not changed the seasonal trends of the soil respiration of Chinese fir.Soil temperature and humidity are decisive factors affecting soil respiration(P<0.05).The interaction between soil temperature and soil moisture better describes changes in soil respiration.The addition of nitrogen and phosphorus changed the temperature sensitivity of soil respiration,and its Q10 value was expressed asLNLP(3.626)> HNHP(3.422)> HNLP(3.393)> LNHP(3.355)> LP(3.542)> HP(3.501)> CK(3.18)= HN(3.18)> LN(3.087).(2)Nitrogen deposition significantly promoted the soil respiration of Chinese fir(P<0.05),each treatment reached the highest value in summer,CKwas 4.04 ± 0.6583?mol·m2·s-1,LNwas 6.66 ± 0.2733?mol·m2·s-1,HN was 7.2 ± 0.213?mol·m2·s-1;reached the lowest value in winter,CK was 0.31 ± 0.0153?mol·m2·s-1,LN was 0.66 ± 0.053?mol·m2·s-1,HN was 0.52 ± 0.0153?mol·m2·s-1.Nitrogen deposition increased AN,MBC,and reduced MBN,and soil respiration was significantly positively correlated with MBC(P<0.01),and significant positivecorrelation with MBN(P<0.05),significant negative correlation with AN(P<0.05).(3)Phosphorus additionsignificantly promoted the soil respiration of Chinese fir(P <0.05),each treatment reached the highest value in summer,CKwas 4.04 ± 0.6583?mol·m2·s-1,LPwas 7.5 ± 0.153?mol·m2·s-1,HP was 7.16 ± 0.2913?mol·m2·s-1 reaches the lowest value in winter,CK was 0.31 ± 0.0153?mol·m2·s-1,LP was 0.53 ± 0.0153?mol·m2·s-1,HP was 0.53 ± 0.013?mol·m2·s-1.Phosphorus addition increased AP,AN,SOC and MBC,and reduced MBN,and the ratio of soil respiration.There was a very significant positive correlation with AP,SOC and MBC,MBNand MBC/MBN.(P<0.01).(4)The combined treatment of nitrogen and phosphorus significantly promoted the soil respiration of Chinese fir(P <0.05),each treatment reached the highest value in summer,LNLP was 9.15 ± 0.6123?mol·m2·s-1,LNHP was 6.27 ± 0.214 3?mol·m2·s-1,HNLP was 8.58 ± 0.83?mol·m2·s-1,HNHP was 5.63 ± 0.0413?mol·m2·s-1,reaching the lowest value in winter,LNLP was 0.6 ± 0.013?mol·m2·s-1,LNHP was 0.46 ± 0.0423?mol·m2·s-1,HNLP was 0.61 ± 0.0553?mol·m2·s-1,HNHP was 0.48 ± 0.013?mol·m2·s-1.Adding phosphorus under LNincreased AP,AN,SOC,MBNand MBC,and soil respiration was extremely significantly positively correlated with AP,SOC,MBC and MBN(P <0.01);Adding phosphorus under HNincreased AP,MBC and MBN,and soil respiration was significantly positively correlated with AP and MBC(P<0.01).In summary,nitrogen deposition and phosphorus addition treatment promoted the respiration of Chinese fir soil and changed its soil physical and chemical properties.The change of soil respiration is the result of soil physical and chemical properties and the interaction of various environmental factors.