Effects Of Maize Straw Addition On Organic Carbon Mineralization In Black Soil

Over the past few decades,soil organic carbon content of the black soil in northeast of China decreases seriously.Inadequate input of organic material is considered as one of the main driving factors.However,straw return does not always improve soil organic carbon content efficiently.The reason might be that the addition of exogenous organic materials to soil change（either enhance or inhibit）soil organic carbon mineralization,i.e.,priming effect.While the priming effect is found to be always influenced by soil moisture,temperature and also soil fertility.In order to clarify the fate of straw carbon,we studied the change in soil organic carbon mineralization and straw decomposition with the addition of maize straw into black soils,and quantified the priming effect of soil organic carbon mineralization and the distribution of straw carbon in soil organic matter fractions,with the addition of ¹³C-labelled straw in response to soil fertility,temperature and soil water.Result showed that soil fertility significantly affected the priming effect,with higher intensity of priming effect in the subsoil（15-30 cm）with low fertility than that in the surface soil（0-15 cm）with high fertility,and the lowest intensity of priming effect in the mixed layer soil（0-30 cm）.While for the primed CO₂,the addition of straw had higher influence on soil organic carbon mineralization for surface soil compared with subsurface and mixed soils,which was mainly resulted from the promotion of the turnover of mineral-associated organic carbon with straw addition.Therefore,in the presence of exogenous carbon,carbon sequestration ability is higher for soils with low fertility than that with high fertility.Soil moisture and temperature also had significant influences on the priming effect of soil organic carbon mineralization.We found that the intensity of priming effect under lower soil moisture content（45%WHC）was higher than that under higher soil moisture content（65%WHC）.In addition,the intensity of priming effect at lower temperature（12°C）was higher than that at higher temperature（22°C）.While soil temperature and moisture had a significant interaction on the decomposition of maize straw.The highest decomposition rate was found when the temperature and moisture were 22°C and 65%WHC,respectively.Our findings provide certain guidance on straw return in practice in northeast China.