| Atmospheric CO2concentration increase caused by global climate change has aroused the universal concern, terrestrial ecosystems and the atmosphere CO2exchange flux absorbed more and more attention.The terrestrial ecosystem plays an important role in global carbon cycle and the carbon stored in soil and plant efflux into atmosphere through respiration in the form of CO2. The influence of land use change on CO2efflux had been thought as a main caused of increased atmospheric CO2concentrations. Studying on contribution of different land use type to the carbon cycle of terrestrial ecosystems is an important part of global climate change.The Loess Tableland is located at the south edge of the Loess Plateau, where is a semi-arid partial sub-humid area, with the uneven distribution of the annual and inter-annual rainfall. In recent years, the agricultural industrial restructuring has caused a variety of land use type and complexity of ecosystem water&carbon process. In this study, improved multi-channel automatic flux chamber system was used to measure surface CO2fluxes and soil respiration of four different land use(maize, wheat, alfalfa and bare land) in the Loess Tableland. Results are as follows:1. Within the observation period (June3-September29,2011), the average carbon flux of maize field, alfalfa field and bare land were-0.14g·m-2·d-1、1.01g·m-2·d-1'0.96g·m-2·-d-1respectively; the average carbon flux was1.92g·m-2·d-1during wheat harvest period (June3-June25), at the same time the average carbon flux of maize field, alfalfa field and bare land were-1.13g·m-2·d-1,2.58g·m-2·d-1and0.95g·m-2·d-1respectively. The different photosynthesis characteristics and management of maize and alfalfa caused the differences in carbon flux of the two plants, and overall, alfalfa presents the release of carbon because the fixed carbon were less than the released in the biomass formation process.2. Within the observation period of soil respiration (July9-September29), the average soil respiration rate in maize field, wheat stub field and bareland were2.40g·m-2·d-1,2.01g·m-2·d-1and0.95g·m-2·d-1respectively; the average soil respiration rate of alfalfa field and bare land between October6and December31were1.48g·m-2·d-1and0.22g·m-2·d-1respectively. Tillage had a significant impact on soil respiration. 3. The carbon exchange flux of four landuse had an obvious seasonal variation. June, July and August covered the main part of total carbon flux during measurement period, carbon flux during June to August in maize, alfalfa, bare land and wheat stub field accounted for77.95%、96.03%'80.33%respectively.4. CO2flux of maize, wheat and alfalfa showed significant diurnal variation with the trend of temperature and photosynthetically active radiation(PAR), at the same time, soil respiration with temperature changes of the four land use was also very sigmificant. Photosynthetically active radiation(PAR), is an important factor affecting the three crops of diurnal carbon exchange flux, as a result of photosynthesis, PAR and CO2flux have a significant negative correlation.There was significant correlation between monthly soil respiratory carbon release and monthly average temperature.5. Q10value was used to present the corresponding multiples increased when soil temperature increasd by10℃. Temperature sensitivity of soil respiration in alfalfa field was29.2%-36.5%bigger than that of the bare land, while temperature sensitivity of soil respiration in wheat stub field was34.5%-36.9%smaller than that of the bare land, temperature sensitivity in maize field showed little difference.6. Soil temperature and moisture both had a pronounced effect on CO2flux and soil respiration, and it was more significant when the two factors had cross impact. Sensitivity of soil respiration to precipitation in different land use were different. |
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