| Forest soil organic carbon storage is huge,about 70%of the soil carbon of terrestrial ecosystem is stored in forest soil.Thus,even small changes in the forest soil carbon pool can significantly affect global climate.The size of soil organic carbon pool is closely related to its stability,and the source and composition of organic carbon are the primary factors affecting the stability of soil organic carbon.Continues to increase in recent years,nitrogen(N)subsidence become forest soil carbon important factor in the process of "carbon sink ",at the same time the subtropical forest are often restricted by phosphorus(P).At present,in the subtropical phosphorus restricted areas,the synergistic effect of N and P on the organic carbon content and composition of forest soil from different sources has not been widely concerned.This study choose Chinese fir as the object,which is widely planted in the south of our country,established to simulate N and P addition,specific to CK(control),+N(50 kg N·hm-2·a-1)、+P(50 kg P·hm-2·a-1)、and+N+P(50 kg N·hm-2·a-1+50 kg P·hm-2·a-1),to deal with seven years to collect soil samples,combined with the soil organic carbon density biomarkers and grouping method.Analysis of soil organic carbon content,the delta 13C,amino sugars that on behalf of the microbial source and fatty acid content that is the characterization of plant and microorganism source and composition of soil,to clarify the effect of nitrogen and phosphorus additionon Chinese fir forest soil organic carbon source and composition characteristics,aiming to fully understand the impact of global change on forest ecosystem carbon cycle and provide data support.Specific research results are as follows:(1)The addition of N and P significantly affected the OC content of the light faction,but had no significant effect on the OC content of the bulk soil and the heavy faction.Specifically,N addition significantly increased the OC content of the light faction,while P addition significantly reduced the OC content.At the same time,P addition reduced the proportion of light OC in soil OC,and increased the proportion of heavy faction OC.(2)N addition significantly reduced the 13C value of the bulk soil,but had no significant effect on the density factions.P addition significantly increased the value of 13C in the light faction,but had no significant effect on the bulk soil and heavy faction.The 13C value of the light faction increased by 1.1%and 0.8%respectively under+P and+N+P treatment.The abundance of the heavy faction organic carbon 13C was between-29.7‰ and-29.4‰,with an average value of-29.5‰,and was not affected by the addition of N and P.(3)Soil amino sugars can be used to characterize the organic carbon content and composition of soil from microbial sources.The addition of N and P significantly increased the total amino sugar and glucosamine content(GluN)representing the fungal source in the bulk soil,while the effect on the content of galactosamine and MurA representing the bacterial source was not significant.Specifically,the+N,+P and+N+P treatments significantly increased the total amino sugars in the bulk soil by 25.2%,21.7%and 36.5%,respectively.At the same time,the addition of P significantly increased the ratio of amino sugar carbon and glucosamine carbon in bulk soil to OC.In different soil factions,N and P added increased the content of MurA in the light faction,and P added significantly increased the content of galactosamine in the light faction.In different density factions,N and P added significantly affected the content of total sugar and glucosamine,but not of galactosamine and MurA.At the same time,P addition significantly reduced the light component GluN/MurA,indicating that P addition changed the relative contributions of fungal and bacteria-derived carbon in the light faction carbon group.(4)Soil fatty acids are biomarkers for the characterization of microbial and plant-derived organic carbon.The soil fatty acids showed a single peak distribution pattern and the main peak was C16.Among the different components,the light faction showed an obvious bimodal distribution pattern,with the main peak of C18 and the secondary peak of C16,among which the value of C18:1 was the highest.The main peak of the recombination was C16,but the content of C22 in the long chain was also abundant.The addition of P significantly increased the fatty acid content of the bulk soil and the light faction,but the interaction between N addition and NP had no significant effect.C16:1/C16:0 can be used to characterize the relative contribution of microbe-derived fatty acids in soil.N addition increases the ratio of bulk soil,light faction and recombinant C16:1/C16:0,while P addition increases the ratio of bulk soil to recombinant C16:1/C16:0.The average length of carbon chain(ACL),carbon advantage index(CPI)/short chain fatty acids and long chained fatty acids(LC/SC)can be used to characterize the characterization of soil organic matter degradation degree,among them,the ACL value will increase with the increase of the degree of degradation,while the CPI value decreased with increasing the degradation degree,at the same time in the process of decomposition,the short chain is broken down by priority,will be relatively long chain enrichment.It was found that P addition increased the values of ACL and LC/SC of bulk soil and recombination,while N addition increased the CPI of the light faction.In summary,the OC content and 13C values of the light faction were sensitive to the response of N and P addition.The decrease of the proportion of organic carbon in the light faction and the increase of the 13C values after the addition of P represented the increase of the stability of soil organic carbon.The light faction and the recombinant amino sugar monosaccharide had different responses to the addition of N and P,but the addition of N and P increased the OC content of the soil derived from microorganisms as the whole,and the increase effect was more obvious after the addition of P.N addition increased the input of fresh organic matter into soil fatty acids,while P addition was beneficial to the relatively stable accumulation of OC derived from fatty acids in soil. |
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