| Northern peatlands may have positive and negative feedback on permafrost degradation caused by climate warming,yet how it responds to that caused by logging disturbances remains unclear.The fluxes of CO2 and CH4 emissions,net primary productivity(NPP)and annual net carbon sequestration(ANCS)from Larix gmelinii-marsh forested wetlands under different cutting treatments(Control-D,light selective cutting(15%)-Z15,strength cutting(45%)-Z45 and clear cutting-J)(the harvesting test has been done for 10 years)were measured synchronously by using the static chamber gas chromatography method and the relative growth equation,as well as related environmental factors(such as temperature,water level,freezing depth and soil carbon and nitrogen content,etc.)at temperate island-like permafrost habitats in Xiaoxin'anling of China,so as to reveal the medium-term effects of harvesting disturbance on carbon source/sink of temperate forested wetlands at island-like permafrost sites according to net carbon budget of ecosystem.(1)Selective cutting(Z15 and Z45)increased the mean annual fluxes of CH4 emissions(0.07?1.53 mg·m-2·h-1)by 5.7-6.4 times(P>0.05),but the clear cutting made it significantly increased by 20.9 times(P<0.05);There were three types of seasonal dynamic trends(control CH4 was constant trend,selective cutting(Z15 and Z45)were unimodal trends,-J was bimodal trend);There are four types of seasonal distribution patterns(The control was a constant type of spring?summer?autumn?winter,selective cutting(Z15 and Z45)and J were in an approximate unimodal trends of summer>autumn>spring?winter,summer>autumn?spring?winter and summer>autumn?spring?winter).(2)Selective cutting(Z15 and Z45)reduced the mean annual fluxes of CO2 emissions(84.94?106.35 mg·m-2·h-1)by 20.1%,14.5%,20.1%(P<0.05);Seasonal dynamic trends were bimodal(peaks at the end of August and the end of October);There were two types of seasonal distribution patterns(the control and Z15 were summer>autumn>spring?winter,and the cut Z15 and J were summer>autumn?spring?winter).(3)The soil CH4 flux was controlled by temperature,water level,freezing depth and soil C/N.Harvesting disturbance changed the environment factors of CH4 emission converted from temperature and 0?10 cm soil layer temperature to air temperature,0-40 cm soil layer temperature,water level,freezing depth and soil C/N.ratio.The soil CO2 flux was controlled by air temperature,soil temperature,water level,freezing depth,soil organic carbon content and soil C/N.After harvesting disturbance tne main control factors of CO2 emissions were not changed,but the correlation of individual soil layers changed.(4)J and strength cutting were significantly reduced the net primary productivity(7.18 t.hm-2.a-1)and annual net carbon sequestration of vegetation(4.46 tC.hm-.a-1)by 28.7%-45.1%and 28.7%-59.9%(P<0.05),but light selective cutting has no significant impact on it(-1.8%and-2.7%,P>0.05),so its carbon sequestration capacity generally shows a decreasing trend with increasing harvesting intensity.(5)Larix gmelinii-marsh of the temperate Xiaoxin anling was carbon sinks(0.50?1.3 tC·hm-2·a-1).After cutting 10 disturbances,the light selective cutting increased the sink(2.31 tC.hm-2.a-1)by 18.5%(P>0.05),and strength cutting((1.00 tC.hm'2.a-1)reduced the strength of the sink by 48.7%compared with the control(P>0.05),but clear cutting had been converted it into carbon source(-0.34 tC.hm-2.a-1,P<0.05).Therefore,the Larix gmelinii-swamp in Xiaoxin'anling island-like frozen soil area after harvest disturbance 10 years,the function of light selective cutting(15%)carbon sink has been restored(slightly higher than the control is about 1/5),the function of strength cutting(45%)carbon sink has been initially restored(equivalent to control 1/2),and the function of clear cutting carbon sink has not been restored(still maintained the carbon source). |
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