Responses Of Litter Decomposition And Nutrient Release Of Picea Purpurea And Abies Faxoniana To Increasing Temperature

Global changes,mainly climate warming,have a profound impact on the structure and function of forest ecosystems.Decomposition of forest litter is an important part of the nutrition cycle of terrestrial ecosystems,which is extremely vulnerable to global warming.Therefore,the presented thesis studied the effect of natural simulated warming induced by altitude gradients on the decomposition and nutrient releases of subalpine forest litter within the western Sichuan Province.In October of 2017,the fresh above-ground litters of Picea purpurea and Abies faxoniana were collected from the primary fir-spruce forests at 3000 m in Wanglang National Nature Reserve randomly.Leaves,Twigs,fruits,and mixed leaves(1:1)were dried,put into decomposition bags(1 mm pore size-"soil animal + microorganism",LDB;0.02 mm pore size-"microorganism",SDB),and placed in the forest at 3000m(CK,control group),2800 m(EW-?,warming 0.49 ?),2600 m(EW-?,warming 1.77 ?),respectively.The litters were taken back at the start and end of growing season in the following years(May and October of 2018 and 2019).The results were as follows:(1)Warming had significant effect on the leaves of A.faxoniana(p<0.05)and the other litters(p<0.01).There were significant differences in litter RQs among different species under warming conditions.Warming(0.49 ? and 1.77 ?)increased the RQs of P.purpurea twigs,A.faxoniana leaves and mixed leaves in all decomposition bags,and P.purpurea fruits in SDBs,and inhibited their decomposition;warming reduced the RQs of P.purpurea fruit in all decomposition bags,the leaves of A.faxoniana in LDBs,the twigs and fruits of A.faxoniana.There was no obvious changes of the mass residual rate of other litters under different altitudes.After 23 months,the mass loss of leaves,twigs and fruits of P.purpurea were36.92%-45.36%,24.03%-34.02% and 15.24%-19.63%;and those of A.faxoniana were29.69%-35.71%,17.54%-33.08% and 20.19%-25.73%,and that of the mixed leaves was34.71%-43.94%,respectively.(2)Warming affected the change of litter ash content significantly(p<0.01).After 23 months,there were significant differences in ash content under different altitudes(p<0.05):Warming of 0.49 ? significantly increased the ash content of the twigs and fruits of P.purpurea in SDBs,and A.faxoniana fruits in LDBs(p<0.05),and those decreased significantly at 1.77 ?(p<0.05).Warming of 1.77 ? significantly increased the ash content of P.purpurea and A.faxoniana twigs in LDBs(p<0.05);and decreased significantly at0.49 ?(p<0.05);the ash content increased under other altitudes.(3)Warming had minor effect on the carbon contents of the twigs of P.purpurea and A.faxoniana(p>0.05),and a significant effects on the other litters.After 23 months,warming(0.49 ? and 1.77 ?)significantly reduced the carbon content of twigs of A.faxoniana in LDBs about 14.28%(p=0.012)and 12.54%(p=0.022),and the fruits of A.faxoniana in SDBs increased by 17.70%(p=0.003)and 21.42%(p=0.001);significantly increased the nitrogen content of twigs in SDBs of P.purpurea by 17.27%(p=0.024)and 36.27%(p=0.001),increased the nitrogen content of mixed leaves in LDBs by 10.29%(p=0.016)and 17.18%(p=0.002);significantly reduced the phosphorus content of the twigs in LDBs of A.faxoniana(p<0.001);increased the potassium content of twigs in LDBs of P.purpurea;significantly increased the carbon to nitrogen ratio of leaves in SDBs of P.purpurea by 23.51%(p=0.013)and 6.92%(p=0.029),significantly reduced the twigs in LDBs of A.faxoniana by 10.44%(p=0.012)and 32.66%(p<0.001).(4)Warming significantly affected the nitrogen,phosphorus and potassium residual rates of A.faxoniana and the potassium residual rate of P.purpurea(p<0.01).After 23 months,there was no significant difference in the carbon residual rate of P.purpurea under different altitudes,the control group had the smallest residual rate and fastest carbon release rate.The leaves in LDBs of A.faxoniana showed net carbon release at 0.49 ?.The nitrogen residual rates fluctuated in different decomposition periods,and enriched at 23 months;The phosphorus residual rate released at studied periods.The potassium residual rate declined in studied periods.(5)Correlation analysis showed that nitrogen and potassium content,potassium residual rate were significantly negatively correlated(p<0.01).The potassium content of P.purpurea and A.faxoniana were significantly positively correlated with phosphorus residue rate and weight(p<0.01).There were significantly positively correlated between the carbon residual rate and the potassium residual rate(p<0.01),and the phosphorus residual rate and the potassium residual rate were the same(p<0.01).The potassium residual rate of P.purpurea and A.faxoniana were significantly positively correlated with weight(p<0.01),and the carbon to nitrogen ratio and weight were the same(p<0.01).