Effect Of Root Litter Addition On Nitrogen Mineralization Rate Under Laboratory Low-Temperature Conditions In Soil From A Japanese Northern Hardwood Forest

Soil freeze-thaw can alter the soil nitrogen (N) mineralization rate by increasing root litter. However, the mechanism remains unclear. We compared the effect of adding root litter from two plant species on soilNH4+production rate and soilNO3-production rate under low-temperature conditions in laboratory incubation. Root litter of oak (Quercus crispula) or dwarf bamboo, Sasa (Sasa nipponica) was added to soil and incubated under nonfrost and soil freeze-thaw treatments. We monitored temporal change of net/grossNH4+production rate andNO3-production rate throughout the soil frost period and the following melting period. We measured dissolved organic N (DON) in root litter leachate under the two temperature treatments. The soil N mineralization with Sasa root litter was higher than that with oak root litter in the two temperature treatments. The DON in root litter leachate of Sasa was larger than that of oak. The effect of root litter addition on netNH4+production rate was larger than that on netNO3-production rate. The higher netNH4+production rate of soil with Sasa was considered to be caused by higher DON in leachate from root litter of Sasa. The higher inducement of N mineralization of Sasa root litter than oak root litter was related to quantity of organic N in the root litter leachate.