Gross nitrogen mineralisation and fungi-to-bacteria ratios are negatively correlated in boreal forests

In terrestrial ecosystems, gross nitrogen mineralisation is positively correlated to microbial biomass but negatively to soil organic matter C-to-N ratios; the influence of the microbial community structure is less well known. Here, we relate rates of gross N mineralisation to fungi-to-bacteria ratios in three natural forest types of contrasting N availability and in a long-term N- loading experiment in a boreal forest. We report, for the first time, a strong negative correlation between gross N mineralisation and the fungi-to-bacteria ratio ( R-adj(2)= 0.91, P= 0.0005, N= 7). There was also a negative correlation between gross N mineralisation and the C-to-N ratio ( R-adj(2)= 0.89, P= 0.001, N= 7), but a weaker positive correlation between gross N mineralisation and soil pH ( R-adj(2)= 0.64, P= 0.019, N= 7). Our analysis suggests that soil fungi-to-bacteria and C-to-N ratios are interrelated and that they exert strong influences on soil N cycling in boreal forests.