Different contributions of bacterial and fungal communities to nitrogen mineralization in Moso bamboo-invaded subtropical forests

Purpose Although both bacterial and fungal communities play a substantial role in the transformation of soil nitrogen (N), it is unclear how each community contributes to soil net N mineralization during plant invasion. The current study examined the contributions of bacterial and fungal communities to soil N mineralization in soils from Moso bamboo (a natively invasive forest), mixed bamboo-broadleaf (a moderately invaded forest), and broadleaf (an uninvaded forest) forests using the bactericides and fungicides. Methods The incubation experiment comprised three different invasion stages of bamboo and three treatments including no biocide (control), bactericide (streptomycin), and fungicide (cycloheximide). The contributions of bacterial and fungal communities to soil net ammonification and nitrification were determined by measuring soil N mineralization rate, microbial gene abundance, community composition, and by constructing structural equation model (SEM). Results Compared with the broadleaf forest, the bamboo forest had 72.6% higher net ammonification in net mineralization. The net nitrification rate in the broadleaf forest was 118.2% higher than in the bamboo forest. Bactericide application reduced net ammonification rates significantly, but fungicide application raised net nitrification rates in all three forest types. In contrast to the control, bactericide decreased the alpha diversity indices of bacterial and fungal communities and altered the fungal composition. According to the SEM results, forest type had positive effects on fungal composition after adding bactericide, which reduced soil ammonification rate. In contrast, the addition of fungicide increased the bacterial abundance but decreased the fungal abundance, and changed the fungal composition. The SEM results suggested that forest type had positive effects on bacterial abundance after adding fungicide, thus increasing the soil net ammonification rate. Conclusions These results provide relevant experimental evidence for the role of bacterial and fungal communities in the net ammonification and nitrification of soil, indicating that the bacterial community played a leading role in soil net ammonification during the bamboo invasion.