The Impact Of Land Use On Soil Respiration And Soil Organic Carbon Mineralization In Tablelands Of The Loess Plateau

Land use is one of the key factors to influence soil carbon sequestration and greenhouse gas emissions,and accurately evaluate land use changes,that is very important for terrestrial ecosystem carbon cycle and global climate change. In this paper,arable land,natural grassland,shrub forest,shrub and arbor mixed forest,arbor forest and orchard were selected for the study,select one or two sunny weather days in each middle month from April in 2015 to March in 2016,using static chamber to collect soil respiration gas,with determining the main environmental factors that affecting the soil respiration rate simultaneously,such as the soil temperature,soil moisture,air temperature and humidity,and analying soil respiration rate variation characteristics monthly and the response rules of environmental factors on soil respiration rate,and establishing the relation model between soil respiration and its influencing factors.At the same time,using indoor closed-culture method to do dynamic monitoring for soil organic carbon mineralization, analysing the effects of soil organic carbon mineralization characteristics and various soil carbon components on soil organic carbon mineralization,provided relevant data and theory for soil carbon sequestration.The results of the study are as follows:(1) Month change rules of different land use type on soil respiration rate are almost same, all present unimodal curve.The maximum respiration rate value of Forest land and natural grassland all occurred in August, and cultivated land in July, orchard in June. The minimum soil respiration rate value of all land use types was in December. The highest average of soil respiration rate is natural grassland, followed by arbor forest land, shrub land, shrubbery, mixed forest land, cultivated land, and orchard lowest.(2)The soil respiration of six kinds of land use type are positively related tosoil temperature, atmospheric temperatureand atmospheric humidity, while negatively related to soil water content. The soil respiration rate of various land use types are under influence by soil temperature and moisture content, when soil temperature is low, the soil respiration rate is also low, with the increase of soil temperature, soil respiration rate increases, when the temperature of the soil is around 20℃ and soil water content is also moderate, the soil respiration rate is higher, then with the increase of soil temperature and soil water content, soil respiration rate begin to reduce.(3)Single factor model of exponential model can simulate the the relationship well between soil respiration and soil temperature of 5-20 cm in the study area, the soil temperature of 5-20 cm can explain 64% ~ 89% of the variation of soil respiration rate. The two-factor model decision coefficient of soil respiration and temperature water content is larger than that of single factor model. And the power function model can well fitting the relationship between soil respiration of cultivated land, natural grassland and soil temperature moisture content,while the exponential model can well fitting the relationship between soil respiration of mixed forest land, shrub land, shrubbery arbor forest, orchard and soil temperature, moisture content.(4)Soil organic carbon mineralization rate trend of Loess platform tableland different land use type is developing the rapid growth in the early and slow growth in the late; organic carbon mineralization cumulant of grassland soil in 0-5 cm is 1.26 ~ 1.34 times of woodland, 1.82 times of cultivated land, soil layer in 5-20 cm showed a trend of decrease compare with soil in 0-5 cm, cultivated land up to 48%; Different land use soil mineralization carbon potential Cp value between 0.81 ~ 2.70 mg?kg-1 have significant difference(P < 0.05), and soil organic carbon decomposition rate constant k of the difference between different land usewas not significant.(5)The difference of various soil carbon components between different land use was significant, but the soil total organic carbon(TOC) distribution pattern was consistent with that of active carbon component,grassland is significantly higher than forest land,while the forest land is significantly higher than cultivated land(P<0.05). Soil mineralization carbon potential Cp value are positively related to soluble organic carbon and organic carbon light group(P<0.01), are also positively related to soil total organic carbon, total nitrogen, coarse particle easy oxidation of organic carbon, fine particulate organic carbon, organic carbon(P<0.05)。Regression analysis suggesting that light fraction of soil organic carbon content and dissolved organic carbon content both explain the 82.4% variation of soil organic carbon mineralization.Therefore,the loess tableland area soil mineralization carbon potential is affected by light group of organic carbon and dissolved organic carbon in the soil.