AbstractsBiology & Animal Science

Interactions between plants generally are of great importance for successional processes and plant community structure and thus, research on the underlying mechanisms is essential for a attaining a comprehensive understanding in the field of vegetation ecology. In this regard, the relevance of belowground interactions has long been neglected, although they represent the dominant interaction type in several biomes of global importance, such as grassland ecosystems. In particular, the impact of the mutualistic relationship between plants and arbuscular mycorrhizal fungi (AMF) has been ignored for a long time. Although it has been revealed that AMF are involved in the nutrition of the majority of grassland plants and may have considerable influence on belowground plant-plant interactions between them, there is still only poor knowledge on the underlying mechanisms. Intensive research is particularly required on the relevance of mycotrophy (i.e., the species-specific dependency of a plant on AMF for nutrient acquisition) for the competitive ability of a plant, as well as on the mediation of plant-plant interactions via common mycelial networks (CMNs; mycorrhizal mycelia that interlink different plant individuals). The present study addresses these questions and presents the results of four controlled pot experiments in this connection. The experiments were performed on five grassland plant species of Central Europe. In a first experiment (Ch. 2), competition between the grassland forbs Hieracium pilosella and Plantago lanceolata was investigated to test the suitability of foraging via AMF compared to foraging via roots with respect to the competitive ability. The results revealed that, although a highly mycotrophic life-style (with predominantly AMF-mediated foraging) may be a very successful trait on the individual scale, it may be a disadvantageous trait for the competitive ability as compared to a more root-mediated nutrition. Further, it is concluded that for making predictions on the outcome of a competitive interaction, both, the mycotrophy level as well as root properties of the involved plants need to be considered. The second experiment (Ch. 3) compared differences between growth dynamics and nutrient depletion capacities of mycorrhizal hyphae and roots between the coarse-rooted forbs P. lanceolata, H. pilosella and Hypochaeris radicata, and the fine-rooted grasses Corynephorus canescens and Festuca psammophila. The results demonstrated completely contrasting foraging strategies (i.e., AMF-mediated vs. root-mediated nutrient acquisition) in potentially competing plant species. It further revealed that in highly mycotrophic plants, initiation of an adequate phosphorus (P) uptake is strictly dependent on presence of AMF. Nevertheless, the results led to the conclusion that AMF-mediated foraging may provide some (competitive) advantages over root-mediated foraging in terms of rapid exploitation of P from of bare soil patches, due to comparatively high growth rates of hyphal absorptive surface area. CMN-effects…