| By using forest ecosystems to increase carbon storage in terrestrial ecosystems,it has become one of the main measures to regulate and control atmospheric CO2concentration and slow down global warming at present and in the future.Chinese fir(Cunninghamia lanceolata)is one of the most widely distributed plantations in the subtropical region of China.With the transformation of Chinese forestry strategy,plantation has gradually changed from wood production to ecological public welfare.How to evaluate the carbon sequestration potential of plantation is the focus of current academic attention.At present,the proportion of Chinese fir plantation is mainly medium and young forest,and the productivity is relatively low.In the practice of forestry production,Directional Cultivation of large diameter timber is an effective measure to increase forest volume and improve the quality of plantation.However,there are few reports on its ecological benefits.In this study,four plots(20m×20m)of Chinese fir plantations with 40 years of age(over mature forest)were selected as the research object.Soil samples were collected from December 2018 to December 2019 in winter(2018.11),spring(2019.03),summer(2019.06)and autumn(2019.09).The soil characteristics and microbial community composition were analyzed,and the differences were measured at the end of each month from 9:00 to 11:00 a.m The purpose of this study was to investigate the soil carbon flux and its relationship with litter decomposition,microbial community composition and soil physical and chemical properties,and to reveal the carbon sequestration characteristics of Chinese fir plantations,and to predict the carbon sequestration potential of Chinese fir plantations for sustainable management and scientific evaluation Force provides reference.The main results are as follows:(1)The total soil respiration rate,autotrophic respiration rate and heterotrophic respiration rate showed a single peak trend in seasonal variation,and the average proportions of autotrophic and heterotrophic respiration rates to total soil respiration rates were 13.38%and 86.62%,respectively.The annual carbon flux of soil respiration in Chinese fir plantation was 1.35-4.10?mol·CO2·m-2·s-1The annual carbon flux of heterotrophic respiration was about 0.55t·C·hm?2·a?1,and that of autotrophic respiration was about0.08t·C·hm?2·a?1.In addition,litter coverage reduced CO2emissions by 6.35%in the whole year.Combined with the annual carbon sequestration of tree layer(2.26±0.82t·C·hm?2·a?1),the net productivity is about-8.08tt·C·hm?2·a?1.The carbon sequestration capacity of tree layer of Chinese fir plantation is lower than that of soil respiration carbon emission.(2)The contents of soil organic carbon(C),total nitrogen(N)and total phosphorus(P)were 20.13-28.87g/kg,1.25-1.77g/kg and 0.34-1.09g/kg in the whole year,and there were significant differences in seasonal variation(P<0.05).C?N content was in autumn,winter>spring and summer,and P content was in summer,winter>autumn and spring.The C/N,C/P and N/P values were 15.31-18.85,11.55-28.46 and 0.74-2.36,respectively.The C/P and N/P values showed significant differences in seasonal variation(P<0.05).Correlation analysis showed that soil autotrophic respiration rate was negatively correlated with soil moisture content and p H,heterotrophic respiration rate and P content(P<0.05).(3)Soil microorganisms and their activity characteristics showed that the activities of soil enzymes(sucrase,urease and catalase),total PLFAs amount of soil microorganisms and PLFAs amount and fungi/bacteria(F/B)of different species(except gram negative bacteria and arbuscular mycorrhizal fungi)were significantly different in seasonal variation(P<0.05).Correlation analysis showed that soil heterotrophic respiration rate was significantly negatively correlated with invertase activity,autotrophic respiration rate and catalase activity(P<0.01);soil heterotrophic respiration rate was significantly negatively correlated with gram positive bacteria PLFAs,actinomycetes PLFAs,eukaryotes PLFAs,Simpson index(D)(P<0.05),and positively correlated with evenness index(EH)(P<0.05)?(4)The average value of litter decomposition coefficient of Chinese fir plantation is0.048±0.005,50%decomposition time is 1.068±0.050 a,95%decomposition time is2.085±0.115a;after one year decomposition,the dry weight residual rate of litter is54.77%±2.37%,and the C/N,C/P,N/P values change from 2.96 to 13.55,from 2.84 to17.85,and from 1.10 to 1.60,respectively There was significant difference(P<0.05).The annual return of litter in year C was 1.91t·C·hm?2·a?1.In conclusion,the carbon sequestration capacity of tree layer in the oriented cultivation of Chinese fir over mature forest was less than that of soil respiration carbon emission.Therefore,in the management of directed cultivation of Cunninghamia lanceolata plantation,measures such as strengthening the management of understory vegetation or interplanting cash crops can improve the carbon fixation capacity of the plantation ecosystem. |
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