Mineral nutrients are often regarded as important factors limiting the fitness of plant species through their seed production. However, numerous studies investigating the effects of soil nutrient enrichment in seed production have contradictory results and usually are short-term. In the present study, we aimed to investigate the response of the reproductive traits (number of generative shoots, NGS) of alpine plants to long-term (26 years) nutrient addition and to assess the applicability of the Liebig’s law to a natural plant community. We added individual soil resources (N, P, Ca, water) and their combination (NP) in alpine lichen heath (ALH) to remove potential limitation of generative shoots production. The studied nutrients did not limit the NGS of ALH plants in general: the sum of generative shoots of all species from each treatment has been not increased during the experiment. In contrast, addition of P and irrigation decreased it. The species diversity of generative shoots decreased after long-term N, P, and NP additions. Calcium did not decrease NGS in any studied species, but several species increased their NGS after liming. The response of individual species was individual. The NGS of Trifolium polyphyllum (a non-nitrogen-fixing legume) increased in the N treatment, in contrast to the typical response of legumes to nitrogen fertilizers. The response of about half of the ALH species confirm Liebig’s law (a positive response to only one of the separately applied nutrients), while the remaining species did not show a positive response to the addition of individual nutrients. Only Carex umbrosa responded positively to both nitrogen and phosphorus applications.
Sofronov et al. (Sun,) studied this question.