The relationship between N mineralization or microbial biomass N with micromorphological properties in beech forest soils with different texture and pH

To test relationships between net N-mineralization, organic matter and soil organisms, we combined micromorphology with laboratory incubation experiments over a soil gradient. Microbial biomass N generally increased with pH, and from sandy to loamy soil, but net N-mineralization showed the opposite, and was highest in acid, sandy soil. Twenty-two micromorphological characteristics were analyzed with principal component analysis. PC1 had high eigenvalue (0.70), and clearly separated fungi from earthworms, microarthropods and bacteria. PC2 was less important (0.15). Organic layer and sand content clearly correlated with the fungi-end of PC1, but pH and C-content of the Ah with the opposite. Microbial N also correlated with the earthworm-bacteria end, but net N-mineralization did not. Efficiency of N-mineralization per unit microbe even correlated with the fungi end of PC1, in both organic layer and mineral topsoil. The results support the hypothesis that high (or low) litter turnover and biological activity can be counteracted by high (or low) microbial N-demand.