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Northwest Agriculture and Forestry University (2019)

Impact and Mechanism of Simulated Grazing Disturbance on Carbon Cycling of Biocrustal Soils in the Loess Plateau Hilly Region,China


Titre : Impact and Mechanism of Simulated Grazing Disturbance on Carbon Cycling of Biocrustal Soils in the Loess Plateau Hilly Region,China

Auteur : 杨雪芹;

Grade : Doctoral Dissertation 2019

Université : Northwest Agriculture and Forestry University

Biological soil crust(biocrusts),as an important part of the ecosystem in arid and semi-arid regions,can fix CO2 in the atmosphere through photosynthesis,and affect soil water and heat environment and soil carbon emissions,and significantly affect soil carbon cycling.Interference is a common natural phenomenon,can significantly affect the coverage,composition and physicochemical properties of biocrusts,which in turn may affect their soil carbon cycle.In this study,taking the mixture of cyanobacteria and moss as research object in the loess hilly region,the located monitoring of field experiment was conducted.Based on the effect of five simulated grazing disturbance intensities(disturbance)on the community composition and coverage characteristics of biocrusts,and taked no disturbance as control,including 10%-15%(1th intensity)、15%-20%(2th intensity)、20%-25%(3th intensity)、25%-30%(4th intensity)and 30%-40%(5th intensity)by in different disturbance intensities.We researched the effects of disturbance on the physical and chemical properties,soil organic carbon(SOC)content and carbon fractions,and carbon cycle in biocrusts.By means of statistical analysis method about principal component analysis,cluster analysis and first-order dynamic equation,our study revealed the effect of disturbance on the characteristics of carbon balance and the mechanism of soil carbon cycling in theory,provided scientific basis for the study of soil carbon pool management and the research of carbon cycle in practice.Main conclusions are as follows:1.Disturbance can reduce the coverage and biomass of biocrusts,and affect their physical and chemical properties,thus lead to the degradation of biocrusts,and the impact degree are related to the disturbance intensity and species recovery rate.After disturbance,the biocrust coverage showed a linear downward trend as the intensities of disturbance increased,mainly including cyanobacteria and moss coverage.Compared with no disturbance,and the cyanobacteria coverage of the 1-5th intensities can significantly reduce 4.8%-10.3%,and moss coverage of the 1-5th intensities can significantly reduce 3.5%-6.9%,the biocrust coverage of the 4-5th intensities can significantly reduce17.1%-18.5%.The disturbance reduced biocrust biomass.Compared with no disturbance,the cyanobacteria biomass of the 1-5th intensities can reduce 8%-38%,and the moss biomass of the 1-5th intensities can reduce 55%-92%.Among them,the reduction range of the 5thh intensities is relative greatest.After the disturbance,the order of biocrust recovery rate was2thh disturbance faster than 4th disturbance,and the disturbance in rainy season was faster than that in dry season,with the order as follows:cyanobacteria biocrust>moss biocrust>lichen biocrust.Disturbance impacted physicochemical properties in biocrust soil,which focused mainly on the biocrust layer and less impact on the soil layers of 0-2 cm and 2-5 cm.Disturbance reduced bulk density and increased biocrust porosity,reached a significant level when being the 5thh intensities compared with no disturbance.The influence of disturbance on the soil temperature and moisture of biocrust is that the biocrust layer is larger than 5 cm.The variation coefficient of soil temperature and water showed that 1-5 disturbance is hgher than no disturbance,especially in the biocrust layer.When being 2-3thh intensities,disturbance significantly decreased carbon and nitrogen ratio compared with no disturbance.2.Disturbance significantly increased soil labile carbon fractions such as soil easily oxidized carbon,soil microbial biomass carbon and soil mineralizable carbon,and reduced the soil organic carbon content of biocrusts.The disturbance mainly affected SOC and carbon fractions of the biocrust layer and had no significant effect on the soil layers of 0-2 cm and 2-5 cm.The disturbance increased the content of soil easily oxidized carbon(SEOC).Compared with no disturbance,the SEOC change of 1-3th intensities have greater similarity,and 4-5th intensities has significant difference.The 5thh intensities notably increased SMBC by 70%compared with no disturbance.The 4thh intensities notably increased soil mineralizable carbon(SMC)by 77%compared with no disturbance.The 1-5thh intensities decreased SOC content by 1.90 to 2.38g·kg-1 compared with no disturbance biocrust.After disturbance,there have a positive correlation between SEOC and SMBC.The SMBC was significantly positive correlated with SMC.There is a significant negative correlation between SOC and SEOC,SOC and SMBC.3.Disturbance significantly reduced the rate of photosynthetic carbon sequestration in biocrusts,and increased the rate of soil carbon emission,and change the daily and seasonal dynamic characteristics in biocrusts photosynthetic carbon sequestration and carbon emissions.With the increase of disturbance intensities,the photosynthetic carbon sequestration rate of biocrusts decreased a linear downward trend(R2=0.832,P<0.05).The photosynthetic carbon sequestration rate under the 5thh intensity reduced by 0.81μmol CO2·m-2·s-1 compared to that of the control(with no disturbance).There had no significant difference between other intensities and no disturbance biocrust

Mots clés : Loess Hilly Region; biological soil crust; simulated grazing disturbance; SOC fractions; SOC cycling;

Présentation (CNKI)

Page publiée le 25 mars 2020