| The experiment was conducted in the typical terrestrial ecosystem in arid region ----Sangong River drainage area in Xinjiang (and the selected grassland ecosystem is atBayinbuluke Grassland) with Fukang Desert Ecology Experimental Station of XinjiangEcological Geography Academic Institution of Chinese Academy of Sciences as the mainbacking, typical terrestrial ecosystem in arid region as the subject investigated. CO2source/sink relation of typical terrestrial ecosystem in arid region is studied systematicallybased on field-study data in the field, and carbon concerning Sangong River drainage area andBayinbuluke subalpine meadow ecosystem is estimated. The main conclusions are as follows:1. Oasis field ecosystem There are certain differences among the fixation quantity of CO2 of different types offield ecosystems. All field ecosystems are carbon source, i.e. net discharge of CO2 during the11 hours at night. However, there is one hour acting as carbon source for wheat-soilecosystem and cotton-soil ecosystem in the daytime. Study shows that maize-soil ecosystemhas biggest capability of CO2 net fixation with fixation quantity of 38.47g/m2 per hour. Andwheat-soil ecosystem and cotton-soil ecosystem stand second on the list. From the point ofview of annual carbon fixation quantity oasis maize-soil ecosystem is highest up to 141.66 tCO2 /hm2.a; the following one is wheat-soil ecosystem with 122.60 t CO2 /hm2.a; andcotton-soil ecosystem is lowest with 50.39 t CO2 /hm2.a.2. Desert forestland ecosystem All forestland ecosystems are carbon source, i.e. net discharge of CO2 during the 11hours at night. However, there is 7 hours acting as carbon source for Picea schrenkianaforestland ecosystem. Study shows that Picea schrenkiana forestland ecosystem has theweakest capability of CO2 net fixation with net discharge of 4.22g/m2 within 24 hours. AndHaloxylon ammodendron forestland ecosystem is of the strongest capability with CO2 netfixation of 18.34g/m2 within 24 hours. The CO2 fixation capability of Tamarix ramosissimaforestland ecosystem is slightly weaker than that of Haloxylon ammodendron forestlandecosystem. From the point of view of annual carbon fixation quantity of each observed plot,Haloxylon ammodendron forestland ecosystem is highest up to 9.29 t CO2 /hm2.a; thefollowing one is Tamarix ramosissima forestland ecosystem with 2.68 t CO2 /hm2.a; AndPicea schrenkiana forestland ecosystem is a weak carbon source as a whole with annualdischarge quantity of 8.20 t CO2 /hm2.a which is at variance with traditional opinion andfurther study is needed.3. Subapline meadow ecosystem Under the condition of animal raising shut with fencing, the daily net fixation of CO2 ofgrassland ecosystem is 12.76gCO2 /m2.d, it is a carbon sink during the day except at 18:00and 21:00 during which it is a weak source and of the rest time of the day it is an obviousstrong carbon sink before 16:00 with CO2 net fixation of 12.02g CO2/m2 which occupies94.20% of daily total CO2 net fixation. Under the natural pasturing condition, the daily netfixation of CO2 of grassland ecosystem is 11.52gCO2 /m2.d, it is a carbon sink during the dayexcept at 9:00, 13:00, 14:00 and 21:00 during which it is a weak source and from 15:00 to19:00 it is an obvious strong carbon sink with CO2 net fixation of 9.46gCO2/m2 whichoccupies 82.00% of daily total CO2 net fixation. The main reason why a weak source appearsat 13:00 and 14:00 is that photosynthesis rate of vegetation declines a little at noon, i.e. theso-called noon break. The period from May to September every year is growing period offorage grass, for which the annual CO2 fixation of Bayinbuluke Subapline meadow ecosystemis up to 7.14 t CO2 /hm2.a according to the preliminary estimate.4. Estimation of carbon4.1 Estimation of carbon in Sangong River drainage area Total reserves of carbon in Sangong River drainage area, Xinjiang is estimated to beabout 11.18Pg, of which organic carbon is about 5.43Pg whic...
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