Comparing indicators of N status of 50 beech stands (Fagus sylvatica L.) in northeastern France

Abstract We compared different potential indicators of nitrogen (N) availability across 50 beech forests growing on a wide range of soils in northeastern France. Among the 50 sites measured, high elevation acidic soils had the highest potential net N mineralization in the A horizon (PNM 0–5 cm ), while low elevation neutral and calcareous soils had the lowest (PNM 0–5 cm ). We found that (PNM 0–5 cm ) was negatively correlated with soil pH ( R 2  = 0.47***) and positively correlated with microbial C/N ( R 2  = 0.34***). However, when high elevation sites were excluded from analyses, the relationship between PNM 0–5 cm and soil pH as well as microbial C/N became weaker ( R 2  = 0.23*** for both variables). We found no relationship between PNM 0–5 cm and organic N concentration, soil C/N, or vegetation-based indices for N availability (Ellenberg N and Ecoplant C/N). Bivariate linear regression analyses showed that 69% of the variability in percent nitrification (%Nitrif) was explained by both soil pH (0–5 cm) and soil C/N. Percent nitrification was strongly correlated with vegetation-based indices for N availability. The Ellenberg N and R (pH index) values together explained 74% of the variation in %Nitrif. No relationship was found between %Nitrif and soil δ 15 N (natural abundance in 15 N). Of the 76 plant species evaluated, the probability of presence of 61 plant species was significantly correlated with %Nitrif while the probability of presence of 27 plant species only was correlated with PNM 0–5 cm . From these results, we believe that the use of plant community composition or the combination of soil pH and C/N are robust indicators of N availability.