| In recent years, terrestrial carbon cycle received people attention with the global warming. As an important component of terrestrial ecosystems, Arid agroecosystem have a major impact of the global carbon cycle changes becase of its fragile ecological environment and less soil organic matter content, and carbon cycle is more complicated due to intensive human disturbance. There is significant to study the carbon cycle of semi-arid agroecological system for understanding terrestrial ecosystem carbon cycle and exploring the "missing carbon sink".This experiment was carried out in Northwest China Gansu Dunhuang Nanhu Township vineyards from 2013 to 2014. By using the eddy covariance technique and the gas chamber method, we analysed the diurnal and seasonal variation of grape farmland ecosystem soil CO2 flux in the different time scales. We also compared the relationship between soil CO2 flux and net ecosystem carbon flux, and estimated ecosystem carbon balance of the grape farmland. The results showed that:(1) By using the root elimination method, this study analyzed diurnal variations in soil respiration in root area and no root area of grapevines, and found that the diurnal variations of the two areas showed unsymmetrical single peak curve, the maximum values appeared between 12:00 and 18:00 and the minimum about 8:00. Soil respirations were also significantly different under different weather conditions. During two typical growing seasons of 2013 and 2014(from July to October), soil respiration ranged between 1.56 and 6.3 μmol·m-2·s-1, and the maximum value appeared in July in both two years. The proportion of autotrophic respiration in total respiration gradually decreased during the typical growing season, which varied between 21% and 42%. The soil respiration accumulation during two typical growing seasons ranged from 843.18 g ·m-2 and 892.15g· m-2 respectively.(2)At different time scales, the environmental factors which affecting soil respiration have a Difference. Soil temperature of 0-5cm and photosynthetically active radiation affect the daily variation regularity of soil respiration. Both of them had a hysteresis with soil respiration, and lag time diminished over time. Along with the vegetation growth, the soil water content of 0-5cm was the main factor affecting soil respiration seasonal variation in arid regions. The relationship between soil moisture and soil respiration could be well fitted with a polynomial model, which can explain 71% of the variation in soil respiration. when soil moisture about 19%, soil respiration reached maximum, when greater than or less than 19%, the soil respiration had a downward trend. In addition, soil physical and chemical properties, such as soil organic matter, total nitrogen and soil p H significantly affected soil respiration rate.(3)Two growing seasons(from July to October) of plant photosynthesis and the net ecosystem carbon fluxes day cumulant change presence consistency. With plant growth, decline of vegetation photosynthesis was greater than soil respiration rate. The cumulative amount of net ecosystem carbon flux, ecosystem respiration and gross primary productivity in main grape growing season in 2014 were:-1945.09 g C·m-2, 1994.0g C·m-2, 3940.09 g C·m-2 respectively. The changes in soil respiration and net ecosystem carbon flux had some relevance. The proportion of net ecosystem carbon flux by the total primary production was about 51% and grape farm in the growing season showed strong carbon sink. |
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