Effects Of Nitrogen Fertilization On Soil Respiration On Arid-Highland Of The Loess Plateau

Soil respiration as the most active part of the soil carbon cycle, the amount ofCO₂emissions accounted for21%-25%of the anthropogenic greenhouse gasemissions （Lin2001）. The nitrogen supply is an important factor affecting soilrespiration. Exogenous nitrogen input is not consistent with reported effects on soilrespiration. It has an important significance to understand the mechanism of theinfluence of nitrogen fertilization on soil respiration, and regulation of the rational useof nitrogen fertilizer to promote soil organic carbon accumulation and sustainabledevelopment of agriculture.Based on the the Changwu long-term experiment station （since1984）, selectedfive different nitrogen treatment （N0, N45, N90, N135and N180）, from2009to2011（March17-November10in2009and2010, the total year of2011）, monitoring thesoil respiration rate by different N treatment with the Li-8100soil CO₂fluxobservation system, and determining the soil moisture and temperature （0-10cm） atthe same time, researching:1) seasonal and inter-annual variation of soil respirationunder different nitrogen conditions;2)the effects of moisture, temperature, nitrogenlevels on soil respiration;3) variation of soil respiration and its influencing factors inthe fallowing stage. The main results are as follows:The seasonal variation: the average soil respiration rate showed a significantseasonal variability during the three-year observation period, it is the lowest duringthe seedling stage （October-November）, the highest during the elongating-ripeningstage （Marth-June）, the center during the fallowing stage （July-September）. The soilrespiration rate of seedling stage in2009,2010,2011is1.49,1.15,1.04μmolCO₂·m^-2·s^-1respectively,1.83,1.78,1.81μmolCO₂·m^-2·s^-1in the elongating-ripening stage,1.51,1.68,1.48μmolCO₂·m^-2·s^-1in the fallowing stage. The soilrespiration rate under N0treat during seedling stage is1.06μmolCO₂·m^-2·s^-1,comparing with the N0treat, it increases16%,16%,21%,13%with the treats of N45, N90, N135, N180respectively, comparing with the N0treat(1.42μmolCO₂·m^-2·s^-1),itincreases17%,25%,42%,27%with the treats of N45, N90, N135, N180respectivelyduring the elongating-ripening stage, comparing with the N0treat(1.22μmolCO₂·m^-2·s^-1), it increases24%,35%,31%,38%with the treats of N45, N90,N135, N180respectively during the fallowing stage.The inter-annual variation: N application significantly affects the inter-annualvariability of soil respiration, the accumulation of soil respiration with N applicationwas significantly higher than the control treatment, the inter-annual variability ofaccumulation of soil respiration showed as N135> N180> N90> N45> N0trends withdifferent nitrogen levels during the three-years, the average breathing accumulationwas786,753,725,694,577gCO₂·m^-2followed the N135, N180, N90, N45, N0treatment; accumulation of soil respiration in2011was significantly lower than in2009and2010under the conditions of different nitrogen levels, the differencebetween2009and2010was not statistical significant. In2009,2010,2011, theaccumulation of soil respiration under N135is844,836,677gCO₂·m^-2respectively,800,803,655gCO₂·m^-2under N180,771、767、637gCO₂·m^-2under N90,724、772、585gCO₂·m^-2under N45,604、658、469gCO₂·m^-2under N0.The relationship between respiration and environmental factors: soil temperatureand moisture are two foremost environmental factors affecting soil respiration rate, in2011, it presented as exponential relationship between soil respiration and soiltemperature under different N levels, the model was F=β₀e^β₁T, and soil temperaturecan explain22%-43%of the variability of soil respiration; it showed as a quadraticrelationship between soil respiration and soil moisture, the modelwas F=β₁θ²+β₂θ+β₃, and the soil moisture can explain37%-45%of the variabilityof soil respiration, the bivariate model of soil temperature and moisture can explainmore than80%of the variation of soil respiration, with the modelF=β₀e^β₁Te^{β₂θ+β₃θ2}. In the fallowing stage of2009, the bivariate model of soiltemperature and moisture was significantly better than the single-variable model,when taking the nitrogen fertilization variables into the model, the nitrogen can beused alone to explain8%of the variation of soil respiration. the modelwas F=β₀e^β₁Te^{β₂θ+β₃θ2}e^β₄N...