Different responses of soil nitrogen to combined addition of labile carbon sources with fresh versus decomposed litter

Abstract

Background It is well known that litter releases dissolved organic carbon (DOC), which would impact the role of litter in soil nitrogen (N) transformation. Thus, this study aimed to explore the effect of litters decomposed at different levels on soil N dynamics in the presence of labile carbon. Methods An incubation experiment was carried out with fresh litter (SF), partially decomposed litter (SP) or the combined addition of glucose and alanine in soils for 210 days. The influence of litter addition on soil was investigated by changes of soil soluble organic N, NH4+-N, NO3--N and microbial biomass N (MBN). Results There was higher soil NH4+-N and NO3--N in SF, nonetheless lower in SP than control. Litter addition decreased soil dissolved organic N (DON), but increased DOC compared to control. These results suggested that the effects of litter on soil N might change with the varying status of decomposed litter. Alanine addition increased each soil N form, which was more of DON and less of MBN in SP than SF. After adding amino acids, the priming amount of DON was computed positive at 0.5 day with the highest soil MBN, simultaneously. Moreover, the net N transformation rate preceded the gross rate. Glucose addition also improved soil NH4+-N and DON more in SP than SF, while lessened MBN in SF than SP. These results indicated that the differential effect of labile C sources, alanine and glucose, on soil N might be related to the chemistry of the differently decomposed litter. As a labile C source, glucose had a lesser effect on soil N than alanine. Conclusions Our findings highlighted the coexistence of litters at varied decomposition status and C sources released from litters, which are contributed to the N dynamics in soil and are critical for the ecological functioning of the degraded litter.