| Soil organic carbon(SOC)plays an important role in the carbon cycle of karst ecosystem,is an important medium for carbon transfer,and is also one of the important indicators of soil quality.Vegetation restoration is an important measure to control karst rocky desertification,promote carbon sequestration and storage in recent years.Geological background plays an important role in regulating the size,dynamic change and stability of soil organic carbon pools.However,there is a lack of research on different vegetation restoration patterns and different vegetation types.Simultaneous studies on soil microorganisms,enzyme activities,soil respiration and other biological processes associated with soil organic carbon are relatively weak.Based on this,the size,stability,dynamic change and modulate mechanism of soil carbon pools of different vegetation types(natural secondary forest,Eucalyptus maideni F.Muell.and Pinus yunnanensis Franch.plantations)under different geological background(karst and non-karst areas)in karst fault basin area were studied.The contents of soil organic carbon(SOC),easily oxidized organic carbon(EOC),microbial biomass carbon(MBC),dissolved organic carbon(DOC),water soluble organic carbon(WSOC),hot water extractable organic carbon(WHEOC)and non-labile carbon(NLC)of the different vegetation types in karst and non-karst areas were quantitatively calculated the reserve variation characteristics and stability;the effects of soil microorganisms and enzyme activities on soil organic carbon fractions in karst and non-karst areas.Soil respiration rates and carbon emission fluxes in karst and non-karst areas were measured simultaneously.Carbonate erosion rates were calculated by dissolution rate of the limestone tablets,and then carbon sinks were estimated.Through this study,the difference of soil organic carbon storage between karst and non-karst areas and its intrinsic mechanism were explained,and the important role of vegetation restoration in soil carbon sequestration in karst ecosystem was highlighted,which provided scientific basis for dealing with global climate change,reducing sources and increasing sinks in southwest karst area.The main results and conclusions are as follows:(1)The SOC,EOC,MBC,DOC,WSOC,WHEOC and NLC contents and reserves of the three vegetation types in karst and non-karst areas all showed a decreasing trend with the increase of soil depth.Under the same vegetation restoration pattern,soil organic carbon storage in karst area is significantly higher than that in non-karst area,natural secondary forest are superior to Eucalyptus and Pinus yunnanensis plantations in carbon sequestration.Soil organic carbon reserves of natural secondary forest,Eucalyptus maideni and Pinus yunnanensis in karst of 0-30 cm depth were 74.08 t/ha,50.52 t/ha and 42.79 t/ha,respectively.Soil organic carbon reserves of natural secondary forest,Eucalyptus maideni and Pinus yunnanensis in 0-30 cm depth of non-karst area were 32.43 t/ha,27.49 t/ha and 25.52 t/ha,respectively.The average soil organic carbon storage of 0-30 cm depth in karst area was 1.93 times of the non-karst area.Under the same vegetation type,soil carbon efficiency(EOC/SOC,MBC/SOC,DOC/SOC,WSOC/SOC and WHEOC/SOC)and organic carbon lability in karst area were lower than those in non-karst area,which indicated that soil organic carbon activity was higher,strong mineralization and decomposition ability,poor stability.(2)Geological background leads to significant differences in adaptation strategies of soil microbial communities between karst and non-karst areas,soil microbial biomass and enzyme activities were higher in karst area than in non-karst area.Soil microbial biomass and soil enzyme activities of the three vegetation types in karst area were as follows:natural secondary forest>Eucalyptus maideni>Pinus yunnanensis,while soil microbial biomass in non-karst area were as follows:natural secondary forest>Pinus yunnanensis>Eucalyptus maideni.Soil microbial biomass and enzyme activities in karst and non-karst areas have obvious "surface aggregation effect" under the same vegetation types.GP:GN of the three vegetation types in karst area was significantly higher than that in non-karst area(P<0.05),indicating that the geological background led to the accumulation of "Oligotrophic Bacteria" in the karst area.The higher F:B can accelerate the mineralization and decomposition of soil organic carbon substrates of Pinus yunnanensis.In karst area,except GP:GN,other microbial community indicators were significantly positively correlated with carbon fractions(P<0.05).The total fatty acids,bacteria,Gram-positive bacteria,Gram-negative bacteria,fungi,actinomycetes and arbuscular mycorrhizal fungi in non-karst area were only positively correlated with the labile organic carbon fractions(P<0.05).Soil invertase,cellulase,acid phosphatase and catalase in karst area were significantly positively correlated with soil carbon fractions(P<0.05);soil enzyme activities were only positively correlated with MBC,DOC,WSOC and WHEOC in non-karst area(P<0.05).(3)Soil respiration rate of the three vegetation types in non-karst area was significantly higher than that of the same vegetation type in karst area,indicating that the role of soil respiration in regulating global carbon balance should not be neglected in karst areas.The diurnal and seasonal variations of soil respiration rate of the three vegetation types in karst and non-karst areas showed a "single peak"dynamic tendency.Soil respiration rate of different vegetation types showed natural secondary forest>Eucalyptus maideni>Pinus yunnanensis in karst and non-karst areas.Soil respiration rate in karst area was positively correlated with EOC,DOC,WSOC,WHEOC and NLC(P<0.01),while in non-karst area,soil respiration rate was positively correlated with SOC,MBC,DOC and WHEOC(P<0.01).(4)Dissolution rates of the three different vegetation types in karst area showing natural secondary forest>Pinus yunnanensis>Eucalyptus maideni,indicating that the effect of karst carbon sink of natural secondary forest was significantly higher than that of Pinus Junnanensis and Eucalyptus maideni,vegetation restoration in karst area is beneficial to limestone dissolution and absorption CO2 concentration in lower soil layer.The dissolution rates of the three vegetation types in different years were higher in rainy season than in dry season.The dissolution rates in rainy season contributed greatly to the annual dissolution rates,and the simultaneous precipitation and heat was beneficial to karstification.There was a significant positive correlation between soil respiration rate and dissolution rate(R2=0.775,P<0.01),indicating that CO2 generated by soil respiration promoted karstification,and soil CO2 actively participated in the reaction process of karstification.Soil carbon fractions is positively correlated with karstification.(5)Soil respiration,as the main form of C output have significant effect on soil carbon fractions in karst and non-karst areas.The total fatty acid,bacterial and sucrase have greatest influence on soil carbon fractions in karst area,although the effect of dissolution rate on soil carbon fractions is small,but it can not be ignored;the number of microorganisms in non-karst area is small,so the "Eutrophic bacteria" and cellulase are the main factors affecting soil carbon fractions.In conclusion,the special environment in karst area is more conducive to the accumulation of soil organic carbon than that in non-karst area.The stability of soil organic carbon in non-karst area is poor,promoting the transformation of soil labile organic carbon pool into more stable organic carbon maybe the main form of soil carbon sequestration in non-karst area in the future.The key biological processes of soil organic carbon under the same vegetation restoration pattern are regulated by geological.Under the background of global change,soil carbon cycle in karst area is different from that in non-karst area,and karst area plays an important role in carbon sequestration. |
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