Factors Of Soil Nitrogen Transformation And Greenhouse Gas Emissions Under Different Landuse In Hilly-gullied Loess Area

Nowadays Climate change became a widely accepted society problem around the world. It is generally accepted that the concentration of greenhouse gases, of which a large proportion came from soil, highly related to carbon and nitrogen cycling processes in the terrestrial ecosystem. Factors affected emissions of greenhouse gases from soil mainly contain soil texture, irrigation, water conditions, fertilization, crop growth, temperature and so on. With some main factors, It has great significance to discuss how flux exchange of greenhouse gases helps to understand the mechanism of the greenhouse gases emission and estimate its fluxes accurately. This experiment cultured undisturbed soil samples collected from different land use type (orchard, forestland, and grassland) in the Hill-Gully area of the Loess Plateau, aiming to find out characteristics of NOx and CO₂ release from soil and changing patterns of nitrogen forms in the soil under different moisture content and temperatures. The objective of this study is to reveal characteristics of the mechanism of various factors which impacted greenhouse gas fluxes from soils, and provide the theoretical basis for estimating and forecasting the potential of regional greenhouse gas emission, and referencing optimal adjustment of land use structure in the region. The rusults showed:(1) N₂O flux in Soil sample was significantly correlated with temperature (r = 0.1599, P <0.05), and increasing with the rise of temperature, reached maximum at 35℃. N₂O flux and soil moisture content was significantly correlated (r = 0. 2499, P <0. 0001), N₂O flux in the soil sample was positively correlated with soil moisture content under lower water content, N₂O flux reached maximum close to field capacity, N₂O flux dramatically decline more than field capacity. The influence of N₂O flux with soil moisture and temperature can be fitted equation F=a+b×T+c×T²+d×T³+ e×T⁴+f×W. In the culture conditions, the order of the N₂O total release in soil: orchard soil>forest land>grassland soil. The total N₂O amount of the release in Orchard soil is more than 30% of that in forest soil and more than 14% of that in grassland soil .(2) Interaction with the temperature and water , NO flux maximum of orchard soil and grass soil appeared 25℃,FCW, NO flux maximum of the forest soil appeared at 35℃, FCW. NO flux of the soil significantly associated with the temperature and moisture content (P<0.0001). The impact of temperature and moisture content can be described : F=a+b×T+c×T2+d×W+e×W2+f×W3. In the culture conditions, the order of total NO release in soil: grassland soil>forest soil>orchard soil.(3) In the training process, NO₂ flux and soil moisture content was significantly negatively correlated (r =-0.1813, P = 0.0048<0.0001), NO₂ flux and soil temperature had no significant correlation. The total NO release of three different use patterns vary greatly, From largest to smallest as follows: grassland soil, orchard soil, the forest land.(4) Ammonia volatilization and absorption has reached a peak at 25℃. Different moisture content had different effects on ammonia volatilization in soil: moisture change had largely effect on the orchard soil and forest soil, but Small influence on the grass soil. NH3 flux and soil temperature was significantly negatively correlated (r=-0.3286, P<0.0001), NH3 flux and soil moisture content had no significant correlation. The order of the total release of NH3: forest land>grassland soil>orchard soil.(5) The change of soil respiration rate is mainly caused by temperature changes.The moisture content has little effect on soil respiration rate, but has obvious effect on the Q10 value. The order of the orchard soil respiration rate: orchard soil<grassland soil<forest soil, the organic carbon plays a important role on differences, followed by organic nitrogen. The microbial biomass carbon indirectly effect CO₂ release in soil respiration through the relationship with organic carbon.(6) In a variety of water conditions, ammonium concentrations of grassland soil are significantly higher than forest soil and orchard soil; nitrate concentrations of orchard soil are significantly higher than grassland soil; and in addition to WW, the nitrate content of orchard soil was significantly higher than forest soil; nitrite concentration of forest soil in various water conditions were significantly higher than the grassland soil and orchard soil (P<0.05, n = 4). The variation of nitrogen content changeed with water in three soil samples vary from each other.