Responses Of Greenhouse Gas Fluxes To The Extraneous Nitrogen And Phosphorus In Subtropical Moso Bamboo(Phyllostachys Edulis) Forest

As the main body of terrestrial ecosystem,forest soil is one of the sources and sinks of important greenhouse gases such as CO₂,CH₄and N₂O,and plays an important role in mitigating global climate change.China is one of the three global nitrogen deposition concentration areas,the average atmospheric nitrogen deposition is 21.1 kg·N·hm^-2·a^-1,local areas up to 63.5 kg·N·hm^-2·a^-1.With the continuous increase of nitrogen deposition,the soil phosphorus restriction in forest land of subtropical region will be gradually strengthened,N and P are important factors affecting forest soil greenhouse gas.To explore the effect of soil greenhouse gases and the influence of the enzyme activity by N,P and NP addition in moso bamboo forest.To research object,this study we set up four treatments:control(CK),phosphorus(P,120 kg·P·hm^-2·a^-1)addition,nitrogen(N,120 kg·N·hm^-2·a^-1)addition,nitrogen and phosphorus(NP,120 kg·N·hm^-2·a^-1+120 kg·P·hm^-2·a^-1)addition,respectively,in subtropical moso bamboo forest.The research results can provide data support and scientific basis for revealing the effect of global change on soil greenhouse gas in moso bamboo forest.The results are as follows:(1)N addition and P addition significantly affected the content of ammonium nitrogen,available phosphorus and p H value of soil(P<0.05),but had no significant effect on the content of nitrate nitrogen(P>0.05).The average annual soil p H value under CK,P,N and NP treatments was 4.89,5.04,4.84 and 4.98,respectively.The soil p H value under P and NP treatment significantly increased,while that under N treatment significantly decreased(P<0.05).The average annual contents of ammonium nitrogen in soil under CK,P,N and NP treatments were 5.43,6.08,6.06 and 6.15 mg·kg^-1,respectively.Compared with the CK,the contents of ammonium nitrogen in soil under P,N and NP treatment increased by 11.83%,11.54%and 13.18%,respectively.The annual values of soil available P under CK,P,N and NP treatments were 4.75,10.24,5.46 and 12.19 mg·kg^-1,respectively.P and NP treatments significantly increased the soil available P content(P<0.05),while N treatments had no significant effect on the soil available P content P,N and NP treatments had no significant effect on soil nitrate nitrogen content and water soluble organic carbon content.(2)The annual mean of soil urease activity under CK,P,N and NP treatments were 15.39,16.79,16.40 and 16.10?g^-1·g^-1·h^-1,respectively,P treatment significantly promoted urease activities(P<0.05),while N and NP treatments had no significant effect on urease activities(P>0.05).The average annual soil invertase activities under CK,P,N and NP treatments were 2.91,3.17,3.54 and 3.62 mg·g^-1·h^-1,respectively,and N and NP treatments significantly increased invertase activities(P<0.05).The annual mean values of soil acid phosphatase under CK,P,N and NP treatments were 45.98,48.66,47.81 and47.14?g·g^-1·h^-1,respectively,with no significant difference between treatments(P>0.05).The average annual catalase activities in the soil under CK,P,N and NP treatments was 0.25,0.29,0.29 and 0.29m L·g^-1·h^-1,respectively,and P,N and NP treatments significantly increased the catalase activities in the soil(P<0.05).(3)The soil CO₂and N₂O fluxes in moso bamboo forest showed significant seasonal changes(P<0.05),the maximum values in summer,and the minimum values in summer,however,the CH₄fluxes did not show significant seasonal changes.Soil in moso bamboo forest is the source of CO₂and N₂O,but the sink of CH₄.Compared with the CK,the fluxes of soil CO₂and CH₄increased by 23.89%and120.10%(P<0.05),respectively,with no significant effect on the N₂O emission flux(P>0.05)under the P addition.N addition had no significant effect on CO₂flux(P>0.05),however,inhibited soil CH₄flux(53.12%),and promoted soil N₂O flux(35.26%).NP addition had no significant effects on soil CO₂,CH₄and N₂O(P>0.05).Soil N₂O fluxes were positively correlated with underground soil temperature of 5cm(P<0.05)and soil moisture,the soil CO₂emission fluxes were significantly positively correlated with underground soil temperature of 5cm(P<0.05).There was no significant correlation between soil CH₄absorption flux and soil temperature and water content(P>0.05).(4)Under different treatments,the GWP was dominated by CO₂emissions(97.4-98.92%).The GWP under CK,P,N and NP addition were 20577.59,25420.59,20119.32 and 20722.85kg·CO₂·hm^-2·a^-1,respectively.The soil greenhouse gas GWP significantly increased by P addition,but there was no significant difference between N addition and NP addition.The results showed that:the effects of N and P deposition on greenhouse gases can be alleviated to a certain extent by N,P addition simultaneously,which can provide a basis for discussing the regulation measures of soil greenhouse gas emission against the background of continuous increase of nitrogen and phosphorus deposition.