Effects of drying and wetting cycles on the transformations of extraneous inorganic N to soil microbial residues.

The incorporation of extraneous nitrogen (N) into amino sugars (AS) could reflect the contribution of microbial residues to soil N transformation. Investigating the impact of drying-wetting (DW) on dynamics of newly-produced AS is critical because this represents microbial-driven N retention/losses in soil. A 36-day incubation of soil samples was conducted under different drying intensities, using N-labelled-(NH)SO as an N source together with/without glucose addition. There were multiple DW periods and they ranged from a constant moisture content treatment, to a one day drying (low-drying-intensity, LD), a two day drying (medium-drying-intensity, MD), or a three day drying event (severe-drying-intensity, SD). The immobilization of added-N was restricted in DW when available carbon was not added, thus glucose addition increased the effect of DW on the incorporation of added-N into AS. The response of total N-AS to DW varied depending on drying intensities. The MD was beneficial to the incorporation of added-N into total N-AS, while total N-AS contents were low in SD treatment. The effect of DW on contribution of bacterial and fungal residues to N transformation was also related to drying intensities. Our study indicated that DW altered microbial transformation of added-N, and the effect was drying intensity-specific, and available carbon-dependent.