| The study area as water conservation forest has the most abundant vegetation and complete biological communities, which is located in the depths of the Qilian Mountain. Subalpine meadow accounted for 7.45% of the total area of the study area, the ecological environment is very fragile, overgrazing, rodent activity is frequent, resulting soil respiration is sensitive to the change of environmental factors, Therefore, it is very necessary to study the process and mechanism of soil respiration and its influencing factors in subalpine meadow.In this study, soil respiration was measured under subalpine meadow using the automated soil CO2 flux system (LI-8100A). First of all, we studied the variations of soil respiration rate and its influencing factors. Secondly, we observed the dynamic changes of the different components of soil respiration rate and its impact factors in vegetation exuberant growth period. The last we measured the dynamic changes of respiration rate after rainfall and snow. The main results and conclusions from this study included:1. Respiration rate has obvious diurnal and monthly dynamic patterns. The diurnal variation of respiration rate showed a single peak curve, whose peak is in the 14:00-16:00. The average of soil respiration and ecosystem respiration rate is 5.06 μmol·m-2·s-1 and 7.73μmol·m-2·s-1 in growing season, the average of soil respiration and ecosystem respiration rate is 1.22μmol·m-2·s-1 and 1.38μmol·m-2·s-1 in non-growing season respectively. Respiration rate had obvious seasonal variation, increasing from May, and reaching the maximum in July, and then decreasing until in January, it is more consistent with the trend of temperature changes. Respiration rate fluctuates obviously in the growing season, and in the non-growing season variation range is small. The maximum and minimum of soil respiration rate is 6.25μmol·m-2-·s-1 and 0.19μmol·m-2·s-1,the maximum and minimum of ecosystem respiration rate is 13.56μmol·m-2·s-1 and 0.11μmol·m-2·-s-1. Soil respiration of non-growing season accounted for 25.04% of the total respiration, ecosystem respiration of non-growing season accounted for 19.83% of the total respiration.There was significant positive correlation between soil respiration rate and soil temperature, the relationship could be expresses as the exponential function, and the correlation of non-growing season is greater than growing season. The range of Q10 values are 2.72-6.05,1.49-2.46 in the non-growing season and growing season respectively. Respiration rate had a significantly negative correlation with surface relative humidity, had a positive correlation with wind speed. Further analysis indicated the significantly positive linear correlation between respiration rate and solar radiation in growing season, but the negative linear correlation between respiration rate and solar radiation in the non-growing season. Principal component analysis showed that the soil temperature and moisture in 0-60cm soil are the first-line impact factors for respiration rate; the environmental factors in surface soil are the second main impact factor; solar radiation is the third main factor.2. The change trend of ecosystem respiration, soil respiration, autotrophic and heterotrophic respiration rate showed a single peak curve. The size of respiration rate is:ecosystem respiration (10.45μmol·m-2·s-1)> soil respiration (8.51μmol·m-2·s-1)> heterotrophic respiration (7.13μmol·m-2·s-1)> autotrophic respiration (1.39 μmol·m-2·s-1). Canopy respiration rate is greater than autotrophic respiration rate, is 2.5 times of the root respiration rate. Daytime respiration rate is higher than night respiration rate, the size of night respiration rate is ecosystem respiration> soil respiration> heterotrophic respiration. The sensitivity of respiration rate to soil temperature was heterotrophic respiration rate> soil respiration rate> ecosystem respiration rate. There had a significant positive linear correlation between aboveground biomass and respiration rate; there are quadratic regression relationship between underground biomass and respiration rate. Cutting length is longer, the smaller the soil respiration rate.3. After the rainfall, the soil respiration rate and ecosystem respiration rate of rainfall treatment group has obviously decreased, and increased rapidly in two hours after a rainfall, rather than respiration rate of the control treatment group varies with soil surface temperature and soil temperature. Soil respiration rate was decreased 66.87% after a rainfall; ecosystem respiration rate was decreased 9.88%. Respiration rate of rainfall treatment group increased significantly higher than control treatment group, stimulating effect of rainfall on soil respiration can be reflected in the next day, and the inhibitory effect is reflected in the rain after a few hours. Under the same rainfall intensity condition, with the increase of rainfall time, inhibition of respiration rate is high. Inhibition of rainfall intensity on respiration rate increases with total of rainfall, but when the rainfall increases to a certain extent inhibitory strength decreases, the greater inhibition on respiration rate when rainfall in 8-30 mm, when rainfall more than 30 mm inhibition on respiration rate began to decrease. There has no significant difference effect of different rainfall intensities on respiration rate.4. Ecosystem and soil respiration rate in no snow covered were greater than there are covered with snow, soil temperature and surface temperature also showed no snow cover higher than snow cover, soil relative humidity are on the contrary. Although the snow covered treatment of ecosystem respiration rate is small, but the increase rate is significantly greater than the no snow cover treatment. Dynamic changes of ecosystem and soil respiration rate in freezing and thawing period is greater than melting state of soil. The correlation between respiration rate and soil temperature are snow covered more than no snow, the temperature sensitivity of Q10 values showed snow covered significantly litter than no snow cover. In the no snow covered respiration rate varies with the temperature, respiration rate in the snow covered did not show a decreasing trend when the temperature began to decrease, but increased with the surface relative humidity when the melting snow. In the non-growing season, effect of cutting age on respiration rate was contrast with the growing season, cutting time is longer, the greater the respiration rate. |
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