Is glomalin an appropriate indicator of forest soil reactive nitrogen status

In this paper we address total glomalin-related soil protein (T-GRSP) as a possible indicator of differences in forest soils related to reactive nitrogen and forest composition. We focused especially on the relationship between T-GRSP (g kg(-1)), soil organic carbon (SOC), and reactive nitrogen (N-r) availability among different categories of temperate forests and different horizons. Our study included 105 sampling sites divided into 5 categories, which vary in elevation and tree species composition (coniferous, deciduous, mixed). We detected significantly higher T-GRSP and SOC in the F+H horizon under conifers. We assume that this observation might be attributed to suppression of decomposition of T-GRSP and SOC by nature of coniferous litter. We found a significantly higher content of T-GRSP in the F+H horizon for all studied forest categories. However, the contribution of T-GRSP to SOC is significantly higher in the Ahorizon, which might be caused by stabilization of glomalin by mineral fraction, including clay minerals or by the belowground origin of glomalin. We found the increase of SOC with increasing N-r in the Ahorizon for most categories of forest. T-GRSP follows this trend in the case of deciduous forests (decid), mixed forest (mixed), and mountain forests (mount). On the other hand, we detected a decrease of T-GRSP with increasing N-r in the F+H horizon of coniferous forests (conif). The T-GRSP/SOC decreases with the increase of N-r in the Ahorizon of conif, mixed and mount, which points to the higher sensitivity of forest with prevalence of coniferous trees. Our observations have confirmed an ecosystem-specific relationship between T-GRSP, SOC and N-r. We concluded that T-GRSP in combination with T-GRSP/SOC has the potential to reveal qualitative changes in soil organic matter (SOM) connected with increasing N-r.