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Analysis of relationship between soil respiration and environmental factors has become essential for understanding changes in ecosystem carbon cycles under global warming. However, rough predictions have been made that soil respiration will increase with increasing temperature, but long-term data to support this theory were scarce. We measured soil respiration and environmental factors continuously using an automatic open-closed chamber system in a Korean cool-temperate forest from 2004 to 2016 to ascertain the reliability of this prediction and to more accurately predict changes in carbon cycle. Average air and soil temperatures were 11.0°C and 10.2°C. The increase in temperature was greater in winter (the inactive period for soil respiration) than in summer (the active period). Additionally, precipitation decreased sharply because of patter changes in 2012, and through 2016, it was approximately 69% of the previous period. Effect of precipitation on soil respiration was expected to be larger than temperature because the change in precipitation appeared in summer. Soil respiration exhibited a significant decline in 2012 because of precipitation. From 2004 to 2011, it averaged 344.4 mgCO2 m−2 h−1 and from 2012 to 2016 the average was 205.3 mgCO2 m−2 h−1. This phenomenon hasn’t been detected in short-term studies, suggesting that the prediction of previous studies is inaccurate. Additionally, to predict future ecosystem carbon cycle changes in a cool-temperate monsoon climate, changes in precipitation pattern should be regarded as equally important to temperature, and the prediction cannot be based solely on temperature. Therefore, long-term and continuous measurements are needed with consideration of the effects of both precipitation and temperature. Abbreviations: Rs: soil respiration; Ts: soil temperature; Ta: air temperature; AOCC: automatic open/closed chamber

Background For understanding and evaluating a more realistic and accurate assessment of ecosystem carbon balance related with environmental change or difference, it is necessary to analyze the various interrelationships between soil respiration and environmental factors. However, the soil temperature is mainly used for gap filling and estimation of soil respiration (Rs) under environmental change. Under the fact that changes in precipitation patterns due to climate change are expected, the effects of soil moisture content (SMC) on soil respiration have not been well studied relative to soil temperature. In this study, we attempt to analyze relationship between precipitation and soil respiration in temperate deciduous broad-leaved forest for 2 years in Gwangneung. Results The average soil temperature (Ts) measured at a depth of 5 cm during the full study period was 12.0 °C. The minimum value for monthly Ts was − 0.4 °C in February 2015 and 2.0 °C in January 2016. The maximum monthly Ts was 23.6 °C in August in both years. In 2015, annual precipitation was 823.4 mm and it was 1003.8 mm in 2016. The amount of precipitation increased by 21.9% in 2016 compared to 2015, but in 2015, it rained for 8 days more than in 2016. In 2015, the pattern of low precipitation was continuously shown, and there was a long dry period as well as a period of concentrated precipitation in 2016. 473.7 mm of precipitation, which accounted for about 51.8% of the precipitation during study period, was concentrated during summer (June to August) in 2016. The maximum values of daily Rs in both years were observed on the day when precipitation of 20 mm or more. From this, the maximum Rs value in 2015 was 784.3 mg CO2 m−2 h−1 in July when 26.8 mm of daily precipitation was measured. The maximum was 913.6 mg CO2 m−2 h−1 in August in 2016, when 23.8 mm of daily precipitation was measured. Rs on a rainy day was 1.5~1.6 times higher than it without precipitation. Consequently, the annual Rs in 2016 was about 12% higher than it was in 2015. It was shown a result of a 14% increase in summer precipitation from 2015. Conclusions In this study, it was concluded that the precipitation pattern has a great effect on soil respiration. We confirmed that short-term but intense precipitation suppressed soil respiration due to a rapid increase in soil moisture, while sustained and adequate precipitation activated Rs. In especially, it is very important role on Rs in potential activating period such as summer high temperature season. Therefore, the accuracy of the calculated values by functional equation can be improved by considering the precipitation in addition to the soil temperature applied as the main factor for long-term prediction of soil respiration. In addition to this, we believe that the accuracy can be further improved by introducing an estimation equation based on seasonal temperature and soil moisture.

For various reasons such as agricultural and economical purposes, land-use changes are rapidly increasing not only in Korea but also in the world, leading to shifts in the characteristics of local carbon cycle. Therefore, in order to understand the large-scale ecosystem carbon cycle, it is necessary first to understand vegetation on this local scale. As a result, it is essential to comprehend change of the carbon balance attributed by the land-use changes. In this study, we attempt to understand accumulated soil carbon (ASC) and soil respiration (Rs) related to carbon cycle in two ecosystems, artificially turned forest into pastureland from forest and a native deciduous temperate forest, resulted from different land-use in the same area. Rs were shown typical seasonal changes in the alpine pastureland (AP) and temperate deciduous forest (TDF). The annual average Rs was 160.5 mg CO2 m− 2 h− 1 in the AP, but it was 405.1 mg CO2 m− 2 h− 1 in the TDF, indicating that the Rs in the AP was lower about 54% than that in the TDF. Also, ASC in the AP was 124.49 Mg C ha− 1 from litter layer to 30-cm soil depth. The ASC was about 88.9 Mg C ha− 1, and it was 71.5% of that of the AP. The temperature factors in the AP was high about 4 °C on average compared to the TDF. In AP, it was observed high amount of sunlight entering near the soil surface which is related to high soil temperature is due to low canopy structure. This tendency is due to the smaller emission of organic carbon that is accumulated in the soil, which means a higher ASC in the AP compared to the TDF. The artificial transformation of natural ecosystems into different ecosystems is proceeding widely in the world as well as Korea. The change in land-use type is caused to make the different characteristics of carbon cycle and storage in same region. For evaluating and predicting the carbon cycle in the vegetation modified by the human activity, it is necessary to understand the carbon cycle and storage characteristics of natural ecosystems and converted ecosystems. In this study, we studied the characteristics of ecosystem carbon cycle using different forms in the same region. The land-use changes from a TDF to AP leads to changes in dominant vegetation. Removal of canopy increased light and temperature conditions and slightly decreased SMC during the growing season. Also, land-use change led to an increase of ASC and decrease of Rs in AP. In terms of ecosystem carbon sequestration, AP showed a greater amount of carbon stored in the soil due to sustained supply of above-ground liters and lower degradation rate (soil respiration) than TDF in the high mountains. This shows that TDF and AP do not have much difference in terms of storage and circulation of carbon because the amount of carbon in the forest biomass is stored in the soil in the AP.

Because of climate change, interest in the development of carbon pools has increased. In agricultural ecosystems, which can be more intensively managed than forests, measures to control carbon dioxide (CO2) emission and absorption levels can be applied relatively easily. However, crop residues may be released into the atmosphere by decomposition or combustion. If we can develop scientific management techniques that enable these residues to be stocked on farmland, then it would be possible to convert farmlands from carbon emission sources to carbon pools. We analyzed and investigated soil respiration (Rs) rate characteristics according to input of carbonized residue of red peppers (Capsicum annuum L.), a widely grown crop in Korea, as a technique for increasing farmland carbon stock. Rs rate in the carbonized biomass (CB) section was 226.7 mg CO2 m− 2 h− l, which was 18.1% lower than the 276.9 mg CO2 m− 2 h− l from the red pepper residue biomass (RB) section. The Rs rate of the control was 184.1 mg CO2 m− 2 h− l. In the following year, Rs in the CB section was 204.0 mg CO2 m− 2 h− l, which was 38.2% lower than the 330.1 mg CO2 m− 2 h− l from the RB section; the control emitted 198.6 mg CO2 m− 2 h− l. Correlation between Rs and soil temperature ((Ts) at a depth of 5 cm) was R 2 = 0.51 in the RB section, which was higher than the other experimental sections. A comparison of annual decomposition rates between RB and CB showed a large difference, 41.4 and 9.7%, respectively. The results showed that carbonization of red pepper residues reduced the rates of decomposition and Rs. The present study confirmed that the Rs rate can be reduced by carbonization of residue biomass and putting it in the soil and that the Rs rate and Ts (5 cm) were positively correlated. Based on the results, it was determined that approximately 1.2 t C ha− 1 were sequestered in the soil in the first year and 3.0 t C ha− 1 were stored the following year. Therefore, approximately 1.5 t C ha− 1 year− 1 are expected to be stocked in the soil, making it possible to develop farmlands into carbon pools.

Some researchers have attempted to evaluate the ecological function of various additional services, away from the main point of view on the timber production of Korean forests. However, basic data, evaluation models, or studies on the absorption of air pollutants related to major plant communities in Korea are very rare. Therefore, we evaluated the functional value of the forest ecosystem in Gongju-city. Plantation manual for air purification, supplied from the Ministry of Environment in Japan, was referred to process and method for assessment of air pollutant absorption. Gross primary production was calculated about average 18.2 t/ha/year. It was a relatively low value in forests mixed with deciduous broad and evergreen coniferous compared to pure coniferous forest. Net primary production was the highest value in deciduous coniferous and was the lowest value in mixed forest with deciduous broad and evergreen broad. And the mean sequestration amount of each air pollutant per unit area per year assessed from gross primary production and concentration of gas was the highest with 75.81 kg/ha/year in O3 and was 16.87 and 6.04 kg/ha/year in NO2 and SO2, respectively. In addition, total amounts of CO2 absorption and O2 production were 716,045 t CO2/year and 520,760 t O2/year in all forest vegetation in Gongju-city. In this study, we evaluated the absorption ability of air pollutant in 2014 on forest in Gongju-city area. Gongju-city has the broad mountain area about 70.3%, and area of deciduous broad leaves forest was established the broadest with 47.4% of genus Quercus. Pg was calculated about average 18.2 t/ha/year. The mean sequestration amount of each air pollutant per unit area per year assessed from Pg and C gas was the highest with 75.81 kg/ha/year in O3 and were 16.87 and 6.04 kg/ha/year in NO2 and SO2, respectively. Absorption rates of O3, NO2, and SO2 were the highest in evergreen coniferous forest about 14.87 kgO3/ha/year, 3.30 kgNO2/ha/year, 1.18 kgSO2/ha/year, and the lowest were 5.95 kgO3/ha/year, 1.32 kgNO2/ha/year, and 0.47 kgSO2/ha/year in deciduous broad forest. In conclusion, it was evaluated that Japanese model is suitable for estimating air pollutants in Japan to Korean vegetation. However, in Korea, there is a very limited basic data needed to assess the ability of forests to absorption of air pollutants. In this study, the accuracy of a calculated value is not high because the basic data of trees with similar life form are used in evaluation.

Large-scale land-use change is being caused by various socioeconomic problems. Land-use change is necessarily accompanied by changes in the regional carbon balance in terrestrial ecosystems and affects climate change. Therefore, it is crucial to understand the correlation between environmental factors altered by land-use change and the carbon balance. To address this issue, we studied the characteristics of soil carbon flux and soil moisture content related to rainfall events in mountain pastures converted from deciduous forest in Korea. The average soil moisture contents (SMC) during the study period were 23.1% in the soil respiration (SR) plot and 25.2% in the heterotrophic respiration (HR) plot. The average SMC was increased to 2.1 and 1.1% in the SR and HR plots after rainfall events, respectively. In addition, saturated water content was 29.36% in this grassland. The soil water content was saturated under the consistent rainfall of more than 5 mm h−1 rather than short-term heavy rainfall event. The average SR was increased to 28.4% after a rainfall event, but the average HR was decreased to 70.1%. The correlation between soil carbon flux rates and rainfall was lower than other environmental factors. The correlation between SMC and soil carbon flux rates was low. However, HR exhibited a tendency to be decreased when SMC was 24.5%. In addition, the correlation between soil temperature and respiration rate was significant. In a mountain pasture ecosystem, rainfall induced the important change of soil moisture content related to respiration in soil. SR and HR were very sensitive to change of SMC in soil surface layer about 0–10-cm depth. SR was increased by elevation of SMC due to a rainfall event, and the result was assumed from maintaining moderate soil moisture content for respiration in microorganism and plant root. However, HR was decreased in long-time saturated condition of soil moisture content. Root has obviously contributed to high respiration in heavy rainfall, but it was affected to quick depression in respiration under low rainfall. The difference of SMC due to rainfall event was causative of a highly fluctuated soil respiration rate in the same soil temperature condition. Therefore, rainfall factor or SMC are to be considered in predicting the soil carbon flux of grassland ecosystems for future climate change.