Study On Soil Respiration And Soil Carbon Cycle Of Different Terrestrial Ecosystem

The experiment was conducted in the typical terrestrial ecosystem in arid region Sangong River drainage area in Xinjiang (and the selected grassland ecosystem is at Bayinbuluke Grassland) with Fukang Desert. Ecology Experimental Station of Xinjiang Ecological Geography Academic Institution of Chinese Academy of Sciences as the main backing, typical terrestrial ecosystem in arid region as the subject investigated. CO₂ source/sink relation of typical terrestrial ecosystem in arid region is studied systematically based on field-study data in the field, and carbon concerning Sangong River drainage area and Bayinbuluke subalpine meadow ecosystem is estimated. The main conclusions are as follows:Oasis field ecosystem: There are certain differences among the fixation quantity of CO₂ of different types of field ecosystems. All field ecosystems are carbon source, i. e. net discharge of CO₂ during the 11 hours at night. However, there is one hour acting as carbon source for wheat-soil ecosystem and cotton-soil ecosystem in the daytime. Study shows that maize-soil ecosystem has biggest capability of CO₂ net fixation with fixation quantity of 38.47g/m² per hour. And wheat-soil ecosystem and cotton-soil ecosystem stand second on the list. From the point of view of annual carbon fixation quantity oasis maize-soil ecosystem is highest up to 141.66t CO₂/hm². a; the following one is wheat-soil ecosystem with 122.60 t CO₂ /hm². a; and cotton-soil ecosystem is lowest with 50.39 t CO₂/hm². a.Desert forestland ecosystem: All forestland ecosystems are carbon source, i.e. net discharge of CO₂ during the 11 hours at night. However, there is 7 hours acting as carbon source for Picea schrenkiana forestland ecosystem. Study shows that Picea schrenkiana forestland ecosystem has the weakest capability of CO₂ net fixation with net discharge of 4.22g/m² within 24 hours. And Haloxylon ammodendron forestland ecosystem is of the strongest capability with CO₂ net fixation of 18.34g/m² within 24 hours. The CO² fixation capability of Tamarix ramosissima forestland ecosystem is slightly weaker than that of Haloxylon ammodendron forestland ecosystem. From the point of view of annual carbon fixation quantity of each observed plot, Haloxylon ammodendron forestland ecosystem is highest up to 9.29t CO₂/hm². a; the following one is Tamarix ramosissima forestland ecosystem with 2.68 t CO₂/hm². a; And Picea schrenkiana forestland ecosystem is a weak carbon source as a whole with annual discharge quantity of 8.20 t CO₂/hm². a which is at variance with traditional opinion and further study is needed.Subapline meadow ecosystem: Under the condition of animal raising shut with fencing, the daily net fixation of CO₂ of grassland ecosystem is 12.76gCO₂/m².d, it is a carbon sink during the day except at 18:00 and 21:00 during which it is a weak source and of the rest time of the day it is an obvious strong carbon sink before 16:00 with CO₂ net fixation of 12.02g CO₂/m² which occupies 94.20% of daily total CO₂ net fixation. Under the natural pasturing condition, the daily net fixation of CO₂ of grassland ecosystem is 11.52gCO₂/m².d, it is a carbon sink during the day except at 9:00, 13:00, 14:00 and 21:00 during which it is a weak source and from 15:00 to 19:00 it is an obvious strong carbon sink with·CO₂ net fixation of 9.46gCO₂/m² which occupies 82.00% of daily total CO₂ net fixation. The lnain reason why a weak source appears at 13:00 and 14:00 is that photosynthesis rate of vegetation declines a little at noon, i.e. the so-called noon break. The period from May to September every year is growing period of forage grass, for which the annual CO₂ fixation of Bayinbuluke Subapline meadow ecosystem is up to 7.14 t CO₂/hm².a according to the preliminary estimate.Estimation of carbon in Sangong River drainage area: Total reserves of carbon in Sangong River drainage area, Xinjiang is estimated to be about 11.18Pg, of which organic carbon is about 5.43Pg which occupying 48.54%, and inorganic carbon is about 5.75Pg which occupying 51.46% by taking soil ecosystem as basic unit, making use of GIS software, MapInfo software for statistics of corresponding soil ecosystem area in the way of field investigation and sampling analysis.Comparing soil ecosystems with each other and the result shows that forest soil and meadow soil have bigger organic carbon flux and organic carbon capacity, but their inorganic carbon flux and inorganic carbon capacity are lower than other soil ecosystems obviously. Desert soil ecosystem has lowest organic flux and capacity, but higher inorganic carbon reserves.Because of influence from. human factor on agricultural soil ecosystem, its inorganic carbon flux is lower than that of desert soil ecosystem markedly. But its organic carbon reserve is higher than that of desert soil ecosystem obviously owing to organic fertilizer application and some agriculture measures artificially. Different agricultural method of land usage and different agronomic crop decide that corresponding agriculture measures adopted are also not same absolutely, thus result in differences concerning the distribution of carbon in soil.Estimation of carbon in subalpine meadow ecosystem: Aboveground biolnass on-the-spot survey is obtained in the way of actual quadrat harvesting and moisture converting. And combining with researching data from predecessors, the total carbon of aboveground vegetation in Bayinbuluke subalpine meadow ecosystem is estimated and the result shows that it is about 71.98 thousand t. Of which the aboveground part is about 31.99 thousand t occupying around 44.44%, and underground root system is about 39.99 thousand t occupying around 55.56%.On the basis of actual measured bulk density of soil, organic carbon content of soil and investigated soil depth etc., area of corresponding grassland type is obtained in the way of using GIS MapInfo software to interpret remote sensing images, the organic carbon of soil in in Bayinbuluke subalpine meadow ecosystem is estimated by using corresponding formula. The results show that average carbon flux of soil in Bayinbuluke subalpine meadow ecosystem is 16.801Ckg/m², and the total organic carbon reserves of soil is about 30192.24 thousand t.Effect of soil condition on decomposition rate of litter fall: Decomposition rate of organic matter on loamy soil is higher than that of clayey soil and sandy soil; decomposition rate of organic matter gains the highest under condition of medium moisture of soil; it is higher with deep bury than with shallow bury; it gains the highest under condition of medium saline concetnration. Different types of little falls also have different decomposition rates under same conditions because of different content of lignin mainly. Only one factor is studied in this paper under the condition that other factors are fixed. The interaction among the factors should be studies further Total NPP of terrestrial vegetation: The remote sensing model used in this paper is a parameter-based model. The parameters of the model can be inverted from the remote sensing data. Comparing with those models that compute the NPP by the correlation between NDVI and NPP, the remote sensing model based on the light energy utilization principle has three obvious advantages. On the basis of RS and GIS, the net primary production of terrestrial vegetation of China in every of ten days using the NOAA AVHRR data with five channels and 8km x 8km resolution is calculated...