Eutrophication of deciduous forests in the Bohemian Karst (Czech Republic):: the role of nitrogen and phosphorus

In this study, we examined certain plant species for their high need of nitrogen (N > 6, Ellenberg's scale) and identified both conditions of soil nutrients, contents of N and P in leaves and light availability in permanent plots of deciduous forests in the Bohemian Karst (Central Bohemia) between 1997 and 1999. For comparison, a similar habitat was studied in SW-Slovenia. According to our results, factors limiting a development of the ground-layer vegetation of deciduous forests were soil moisture, soil NO3- content and light. The nitrophilic plant cover of the study area required for its development a readily available supply of nitrogen (mainly NO3-). In our opinion, an increase in the quantity of soil-available nitrogen may have been caused by an enhanced deposition of nitrogen. On the other hand, an analysis of leaf N and P indicated that the most of deciduous forests in the Bohemian Karst are still limited less by P than N. Therefore, a successful establishment of nitrophilic species seemed to be dependent on both an adequate supply of N and P in these soils. We observed that soil-extractable P contents were lower in plots covered with less than 1% of nitrophilic plants than in all other plots. Diversity of nitrophilic species, i.e., the number of species per plot, was significantly increased in the presence of soil-ex tractable P. A positive effect of P on both nitrogen mineralisation and nutrition of nitrophilic plants has been reported earlier in the literature. Thus, a successful utilisation of increased N in soils of these ecosystems could occur only in the presence of a sufficiently high P content. (C) 2002 Elsevier Science B.V. All rights reserved.