Characteristics Of Soil Respiration And Its Response To Impact Factors In Typical Forests At Jinyun Mountain

Forest soil respiration is the main source of atmospheric CO2, researches of which are turning into the study hotpot in recent years in the background of global warming is becoming more and more serious. However, few studies were performed to determine the characteristics of forest soil components and their controlling factors. Therefore, trenching and litter removed method were used to distinguish the proportion of soil respiration of different components under 4 typical forest stands of Chongqing Jinyun Mountain region as evergreen broadleaved forests, broadleaf and needleleaf mixed forests, bamboo forest and evergreen needle leaf forests. Meanwhile, temporal variation characteristics of respiration of different soil components were monitored and analyzed by using carbon flux observation system, and the mechanism of them to the impact index was studied as well. Moreover, contribution ratio of respiration of soil components of 4 typical forest stands to soil total respiration and CO2 emissions were estimated. The results are as follows:(1) The components of soil respiration of 4 typical forest stands in diurnal, monthly and annual variation scales were obviously. The diurnal variations of which showed a single peak curve variation, all the typical forest stands of soil components respiration maximum rate appeared at around 14:00 pm, the minimum rate in around 2:00 am; soil respiration rate of the components (except litter respiration) showed significant single peak curve variation in monthly. The maximum value generally appeared in June or In July; the components of soil respiration of 4 typical forest stands existed interannual variability, on the whole, the annual average value were smallest in 2012 year, but the difference was not significant in three years (p> 0.05).(2) The components of soil respiration of 4 typical forests in addition to the litter respiration were significantly positively correlated (p<0.05) with the temperature (air temperature, soil temperature at 5 cm and 10cm depth in the forests), there are differences in the extent of the relationship between different components of soil respiration and temperature. The exponential model was best applied to describe the relationships between the components of soil respiration of four typical forests and temperature in this study; In addition to the litter respiration, the short-term temperature sensitivity Q10s value of each component of soil respiration presents obvious unimodal curve in the monthly change. In addition, the Q10s value or the Q10y value.There were no significant relationship between the soil moisture and the components of soil respiration of four typical forests, soil depth influenced the relationship between the soil moisture and the components of soil respiration of 4 typical forests. Cubic curve model is best suited for describing the relationship between the respiration of each soil components and soil moisture of the four typical stands in this study. A linear two-factor model of hydrothermal is better than the Single-factor model of temperature or soil moisture in fitting the relations of each component soil respiration, soil temperature and humidity. We found that the influence of soil organic carbon on soil respiration rate were maximum among the selected 12 soil physical and chemical factors by analyzing respectively on the relationship between soil physical, chemical properties and soil respiration in different typical stands and the same typical stands.(3) There is a linear relationship between soil respiration and fine-root biomass of 4 typical forest stands. And the difference of soil respiration could be seen in process with and without litter cover on different scales of time. What’s more, removing litter can affect the relationship between soil respiration and soil temperature as much as moisture in 4 typical forest stands, which leading to the low level of temperature sensibility in different time scale. The difference of vegetation type is the most fundamental and important reason of discrepancy of the respiration and effect factors in soil component in 4 typical forest stands.(4) Simulation of different nitrogen deposition will impact on soil respiration rate of four kinds of typical forests, and each forest has different response to different concentrations of nitrogen deposition. Meanwhile, the relationship between soil respiration and temperature、soil humidity is influenced by applied the nitrogen. Nitrogen deposition also influences the temperature sensibility of soil respiration. Nitrogen concentration has different influences on the temperature sensibility of each kind of typical forest.(5) The monthly CO2 emissions of soil total respiration in four typical stands showed a single curve and the CO2 emissions were maximum in the growing season.4 typical forest stands CO2 emissions throughout the observation period in 4 typical forest stands ordered:Bamboo forest (80.83t/hm2)> evergreen broadleaved forests (71.41t/hm2)> evergreen needle leaf forests (58.84t/hm2)> broadleaf and needleleaf mixed forests (55.94t/hm2). Each soil respiration component contributed to soil total respiration in 4 typical forest stands changed in diurnal, monthly and annual time scales. Contribution of soil respiration component to soil total respiration in each typical stands are changed, it is also true for the same soil respiration component to soil total respiration in different typical stands. In addition to the litter respiration, the monthly CO2 emissions of other components respiration showed a obvious single peak curve and the biggest CO2 emissions also happened in the growing season. The total annual CO2 emissions of the components of soil respiration among each typical stand differed, CO2 emissions of the same component respiration throughout the observation period are also differences due to different forest stands.