| Great Xing’an region is main permafrost distribution zone in northeast of China, which locates in the most northern frontier of China and is only boreal coniferous forest region. Perennial frozen earth can prevent surface water permeate to underground to makes active soil saturated in long term and is advantageous to the formation of wetlands, hence perennial frozen regions also are the main distribution zones of global wetlands. Northern high altitude region distributes more than 50 percent of global wetlands, the interaction of wetlands and frozen soil leads their special symbiosis model and because it locates the southern boundary of eurasia perennial tundra, perennial frozen soil which its annual average soil temperature is relativity high and soil layer weak and is sensitive to the global warming. The degradation of permafrost have great effect on wetland which distribute under frozen soil, including the variation of permafrost active depth, hydrology, soil temperature, the availability of soil nutrient, vegetation composition and productivity, microbial components and activity changes of wetlands etc, which are main control factors of soil respiration. Hence, the degradation of permafrost and a series of variation of environments and biological factors its causes,which strongly affect on a large area of swamp wetland that distribute on it, and play a great role on current soil respiration and its future tends of the wetland, obviously, it is significant in the research of global carbon balance to launch project on the system of forestry-wetland of soil respiration.This study selected ecological system of forestry-wetland in the largest cold temperate zone permafrost region in northeast. And chose the typical and representative tussock swamp, the main forest swamp (Alnus sibirica swamp, Betula platyphylla swamp, Larix swamp), island forest swamp (Betula platyphylla and Larix gmelinii swamp) and Larix gmelinii forest as research projects, it is aimed at via studying seasonal dynamics and the size of flux of soil respiration rate of different types of ecological systems in growing season, analysising seasonal distribution rules of forest-swamp ecological system in permafrost zone, to reveal the difference of soil respiration rate in different types of swamp wetlands and explore the main factors which control the difference of soil respiration and discuss the potential impact in soil respiration because of the variation tendency of the environmental factors of swamp wetland and biological factors caused by permafrost degradation. Meanwhile using trenches partition method to research the soil respiration among various components between the island forest of Betula platyphylla and Larix gmelinii in growing season. This study indicated:(1)Apparently, soil respiration rate of forest wetland ecological system has remarkably seasonal variation rules, most peak value occurred in late June and mid-July, rarely in late July; and the emission rule of soil respiration rate of forest wetland is similar to Larix forest, the peak value of 2011 appeared in mid-July,2012 brought forward to the end of June.As the permafrost degradation degree increasing, the time of the peak value of the soil respiration rate emission appears in different types of forest-wetland ecological system during growing season, emission peak value does not appear in midsummer but late spring and early summer.The depth of permafrost active layer and seasonal thawing of frozen soil play a great role on soil respiration rate, with permafrost degrading, the depth of swamp soil active layer and soil temperature and vegetation components could change, in turn affect the emission of soil respiration in the swamp, led the peak value appear in advance, increased duration, meanwhile, the gross of respiration rate increases during growing season.(2) It all expresses in the source of carbon dioxide emission in cold temperate frozen soil during growing season in different years, apparently carbon dioxide emission of 2011 higher than 2012 at the same sample plot.The gross of soil respiration rate during growing season in 2011 shows:marsh swamps(TC-2) (15.80 t/hm2)>marsh swamps (TC-1) (14.10t/hm2)>Larix frosts (11.79t/hm2)> Betula platyphylla island forested swamps(11.21 t/hm2)>Betula platyphylla swamps (9.31t/hm2)> Larix island forested swamps(9.17 t/hm2)>Alnus sibirica swamps(8.35t/hm2)>Zarix swamps (7.34t/hm2).(3)2012(5-10months):marsh swamps(TC-2) (24.11t/hm2)>marsh swamps (TC-1) (7.83 t/hm2)>Zarix swamps (7.36 t/hm2)> Larix island forested swamps(7.07 t/hm2)>Betula platyphylla swamps(7.02t/hm2)> Betula platyphylla island forested swamps(6.86 t/hm2)>Larix frosts (6.62t/hm2)>Alnus sibirica swamps (6.23t/hm2). Because of micro terrain difference, soil vegetation and hydrological environment restricts the differentiation of respiration rate of swamp wetland ecological system.Under the condition of the same climate, hydrological condition and soil temperature caused by hydrologcial environment could be the important factors affects the respiration rate in different types wetland ecological system.(4) The emission of respiration rate of island forest swamp soil has apparently seasonal rule in different components, the soil respiration of Betula platyphylla island frost during growing season in 2011,2012 respectively 368.60,204.14 mg·m-2·h-1. The soil respiration rate showed Betula platyphylla island forest higher than Larix in 2011. To the contrary in 2012. The difference of soil respiration affected by temperature and water level in the same plot but different years. But it primarily affected by hydrops and ground flora led by micro terrain in different plots.(5) The rule of soil heterotrophic respiration seasonal variation is in correspondence with respiration in Betula platyphylla island forest during growing season in 2011,2012, respectively 300.57,171.55mg·m-2·h-1. Hence, it can gain root autotrophic respiration rate, respectively 68.03,32.59mg·m-2·h-1. The seasonal rule of soil heterotrophic respiration is similar to respiration of Larix swamp forest during growing season in 2011,2012, respectively 215.70,159.94mg·m-2·h-1. It concluded that root autotrophic respiration average rate during growing season respectively 96.76,50.48 mg·m-2·h-1. There is a significant correlation between soil respiration and temperature in island swamp, but non-distinctive with soil humidity.(6) Comparative analysed different permafrost areas in Great and Small Xing’an range, there is a difference in soil respiration rate rule in different permafrost swamps during growing season, with the different permafrost degradation degree, the timing of growing seasonal soil respiration peak appears increased gradually and soil respiration rate too. Also, there is a difference in soil respiration rate in different swamp types in frozen regions which affected not only by temperature, vegetational formation, micro terrain, but also annual precipitation. In general, the contribution rates of forest swamp soil respiration of seasonal hydrops Small Xing’an range higher than cold temperate permafrost zone.(7) With the permafrost zone degradation degree exacerbated, the vegetation type would change from based-(trees, shrubs, sphagnum) to based-(carex, sedge family vegetation), this change of vegetation type would improve the quality of substrate and the potential of soil respiration rate, in turn accelerate swamp soil respiration rate emission. With the intensification of global warming, this permafrost area would further degrade which affects soil active layer depth, soil temperature, water level and vegetation formation, and then influence the swamp growing seasonal soil respiration rate. |
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