Nitrogen mineralization in the oldest climax communities in the eastern Mediterranean region

In this study, we investigated how tree species affect N mineralization in connection to some soil properties and seconder metabolite levels of litter, in the soil of the oldest native forest communities. In the oldest pure communities of Pinus nigra (PN), Fagus orientalis (FO), and Abies bornmuelleriana (AB) in the mountain range of Mount Uludağ, Bursa, Turkey, annual net yield and N mineralization in the 0–5- and 5–20-cm soil layers were determined in a field incubation study over 1 year. Sampling locations were chosen from 1300 to 1600 m a.s.l., and moisture content (%), pH, water-holding capacity (%), organic C, total N, and C/N ratio, and annual net mineral N yield of the soil and hydrolyzed tannic acid and total phenolic compounds in litter were compared for these forest communities. F. orientalis had the highest annual net Nmin yield (43.9 ± 4.8 kg ha^–1 a^–1), P. nigra the lowest (30.5 ± 4.2 kg ha^–1 a^–1). Our findings show that in the oldest forest ecosystems, the seasonal soil moisture content and tree species play an essential role in N cycling and that hydrolyzed tannic acids and total phenolic compounds effectively control N turnover. Tannic acid and total phenolics in the litter were found to inhibit nitrification, but total phenolics were found to stimulate ammonification.