Ecological Stoichiometry Of Carbon,nitrogen And Phosphorus In Litter-soil-soil Microbial Biomass Of Cunninghamia Lanceolata Plantations Across An Elevation Gradient

Cunninghamia lanceolata is a fast-growing coniferous tree species unique to southern China,and it plays an important role in China's forest resources.However,with the rapid development of Cunninghamia lanceolata plantations,the decline in the quality of artificial forest sites has affected the long-term maintenance of forestland productivity.Therefore,an investigation of carbon(C),nitrogen(N),phosphorus(P),and their stoichiometric characteristics of litter,soil,soil microbial biomass in mature Cunninghamia lanceolata plantations along an elevation gradient(750,850,1000,1150 m a.s.l.)was conducted in Tianma National Nature Reserve,Anhui Province,in order to provide scientific basis for sustainable management of Cunninghamia lanceolata plantations.The results obtained are as follows.(1)The contents of C,N and P in leaf litter are higher than those in branch litter at different altitude gradient.There is a significant differences between leaf and branch litters along an altitude gradient(p<0.05).In the process of elevation rise,the C content of leaf litter presents a trend of gradual decline with the elevation increasing,while the C content of branch litter presents a trend of first rise,then decline and then rise.However,there is no significant difference in the C content of leaf and branch litters(p>0.05).With the elevation rising,the contents of N and P in branch litter decrease first,and then increase,while the contents of N and P in leaf litter gradually decrease.There are significant differences in the contents of N and P in leaf and branch litters at different elevations(p<0.05).Compared with other parts of China,the content of litter C and N is higher,and the conversion rate of P content is lower at the study site.(2)The ratios of C/N,C/P,and N/P in leaf litter were all higher than those in branch litter at different altitude.There were significant differences for C/N and C/P between leaf and branch litters in the four elevation gradients(p<0.05),while there was significant difference between them at the elevation of 750 m in N/P,and no significant difference between the other three elevations(p>0.05).With the increase of altitude,the C/N,C/P and N/P of leaf and branch litters showed different change trends.The C/N of leaf litter first decreases and then increases,and the C/P first increases and then decreases,and the N/P gradually increases.C/N of branch litter showed a trend of gradual increase,and C/P showed a trend of first increase and then decrease,and N/P showed a trend of first increase and then decrease and then increase.Under different altitudes,there was no significant difference in N/P of leaf and branch litters(p>0.05),while there were significant differences in C/N and C/P(p<0.05).The analysis showed that the litter C/N and C/P in the area were higher,which had nitrogen-limitation effects on microorganisms,which was not conducive to the decomposition of litter,but was conducive to the storage of nutrients by litter.(3)With the increase of elevation,the contents of SOC,TN and TP in different soil layers show different change rules.SOC and TN decrease first and then increase with the increase of altitude,while soilTP increases first and then decreases.The lowest value of SOC and TN and the highest value of soil TP all appeared in the altitude of 850 m,and the altitude has a significant impact on SOC,TN and TP(p<0.05).In addition,the contents of SOC,TN and TP all decrease with the increase of soil depth in the process of elevation increase,but the changes of SOC and TN were larger,while the changes of soil TP was relatively small.Soil layer had significant influence on SOC and TN(p<0.05),but no significant influence on soil TP(p>0.05).However,the interaction between soil layer and altitude has no significant effect on soil C,N and P(p>0.05).The C,N and P accumulations in the study area were abundant,the C and N contents were relatively stable,and the TP content was affected by the soil parent material.The unique ecological environment is conducive to the maintenance of the soil fertility of Cunninghamia lanceolate plantation.(4)Soil C/N first increases and then decreases with the increase of altitude,and the maximum value appears at the altitude of 850 m.The change range is not obvious at the other three elevations,and the influence of altitude on soil C/N is not significant(p>0.05).Soil C/P and N/P tend to decrease first and then increase with the increase of altitude.Similarly,the lowest value also appears at the altitude of 850 m,and altitude has a significant impact on C/P and N/P(p<0.05).In addition,the vertical distribution of soil C/N,C/P and N/P at different depth is obviously different with the elevation rise:soil C/N decreases with the increase of soil depth at 750 m elevation,increases with the increase of soil depth at 850 m elevation,and first increases and then decreases with the increase of soil depth at 1000 m and 1150 m elevations,but the change range is not obvious.Soil C/P and N/P shows a trend of decreasing with the increase of soil depth,and soil layer has a significant impact on soil C/N,C/P and N/P ratios(p<0.05).The interaction effect between soil layer and elevation has no significant effect on C/P and N/P taios(p>0.05),but significant effect on C/N ratio(p<0.05).Those results might indicate that the soil P content in the study area was rich,higher than the national average,but on the other hand,the forest land might be restricted by N to some extent.(5)Soil MBC and MBN show the same change trend with the increase of altitude,and both decrease first and then increase.The maximum value appears at 750 m,and the minimum value is at 850 m.In addition,With the elevation increase,both soil MBC and MBN decrease with the increase of soil depth,which is also similar to the change of soil carbon and nitrogen.With the increase of elevation,MBC/MBN of different soil depth presents different change trends,and MBC/MBN ratio presents an increasing trend with the increase of soil layer.(6)There is a significant correlation between C content in leaf litter and soil C/P and N/P,while there is no significant correlation between C,N and P content in branch litter and ecological stoichiometry and between C,N and P content of soil and ecological stoichiometry.There is no significant correlation between nutrient content of litters and MBC and MBN,but MBC/MBN ratio shows a significant positive correlation with litter N and P,and a significant negative correlation with litters C/N and C/P ratios.There is no significant correlation between branch litter and MBC,MBN,MBC/MBN.MBC is positively correlated with soil C,N,C/P and N/P,and negatively correlated with soil P and C/N.MBN is positively correlated with soil C,N,C/P and N/P,and negatively correlated with soil P and C/N.MBC/MBN ratio is not correlated with soil carbon,nitrogen,phosphorus or ecological stoichiometry.