TY  - THES
AB  - As one of the most important biotic interactions between plants, competition is considered to be a major force of influence for plant morphology, distribution and abundance up to the structuring of entire biocoenosises.
In unproductive ecosystems, where plant growth is limited by edaphic resources, belowground competition is one of the most decisive processes. Due to laborious methods, though, competition experiments examining root properties in detail are still scarce.
Different parameters influencing the zone of influence or the resource-uptake of plants can be determining for belowground competitive ability, while the impact on competitive effect (the ability to affect neighbours) can be independent of the impact on competitive response (the ability to tolerate neighbours).
Early successional stages in sand ecosystems are commonly resource-poor in terms of water and nutrient availability and are therefore utilised in this study to examine the impact of morphological and functional root parameters in belowground competition in general as well as in competition for nitrate in special.
This thesis thus contributes to investigations to identify the most relevant morphological and functional root parameters concerning belowground competition in general and on competition for nitrate in particular.
In a controlled field experiment in a sand-pit allowing the unhampered development of roots, five species from early successional stages of sand ecosystems (Festuca psammophila, Corynephorus canescens, Conyza canadensis, Hieracium pilosella and Hypochoeris radicata) were used to examine the importance of root distribution for the competitive ability (chapter 3). Special emphasis was put on the effect that neighbouring plants have on the root distribution of target plants. As far as the competitive effect is concerned, the results from a small-scale fractional harvest of the rooted soil space by application of a modified monolith-method highlighted the importance of a vast zone of influence with predominance in the uppermost soil layers. Interestingly, the competitive response was by contrast rather connected to the root system's capability for a plastic reaction involving both root segregation and aggregation. While root segregation and its biological reason in diminishing competition are well known, the aggregation of roots towards a neighbouring plant is a phenomenon that has yet been unknown and can be connected to self-/nonself recognition and the biological sense to maintain already occupied soil.
In a second sand-pit experiment with the above mentioned species, short-term competition for nitrate was assessed by means of a 15N-nitrate application between competing roots (chapter 4). By inclusion of detailed root sizes, evidence for the so far unproven size symmetry of competition for nitrate was provided, meaning that the nitrate uptake by roots is not impeded overproportionally by bigger neighbouring plants. Nonetheless, root system size was again the decisive feature for the competitive effect, while for the competitive response both size and the already mentioned plastic reactions were most important.
Moreover, the role of nitrate transporters for the competitive ability in nitrogen-poor sand was examined in a pot-experiment (chapter 5). Their importance, especially in competition, was unclear as not the relatively fast transport over the plasmalemma but the comparably slow movement of nitrate through the substrate is considered to be the rate-limiting step. Plants of the species Arabidopsis thaliana with a T-DNA-insertion in a nitrate-transporter-gene showed weaker competitive response ability to H. pilosella than the wild type, highlighting the important role of nitrate transporters in nitrate uptake especially in competition. Another important, though contrasting result, was the observation of an (over-)compensation of the defect for the competitive effect which hints at a complex regulation and stresses the role of plastic reactions.
Concerning the importance of functional and morphological root parameters for belowground competitive ability, this study on the whole presents a novel and detailed picture that especially gains significance from the differentiation of competitive effect and response: for the competitive effect, especially the size of the belowground zone of influence is important, while the competitive response appears to depend on multiple components like the capability for plastic reactions, the localization and size of the zone of influence and the uptake capacity for resources.
DA  - 2005
KW  - Sandboden , Pflanzen , Konkurrenz (Biologie) , Wurzel , Nährstoffaufnahme , Unterirdische Wurzeln , Stickstoffisotop , Pflanzenökologie , Corynephorus canescens , Competition , Plants , Ecology , Isotope , Belowground
LA  - ger
PY  - 2005
TI  - Pflanzliche Interaktionen in ressourcenarmen Sandökosystemen : die Bedeutung funktioneller und morphologischer Wurzelparameter für die unterirdische Konkurrenzfähigkeit
UR  - https://nbn-resolving.org/urn:nbn:de:hbz:361-7270
Y2  - 2024-11-21T23:06:21
ER  -