Effekte der Landnutzung auf die Lebensdauer und anatomische Merkmale des Stängels von ausdauernden zweikeimblättrigen Arten im Grasland
Zusammenfassung der Projektergebnisse
As a consequence of higher land-use intensity plant species diversity of agricultural grasslands has dramatically decreased over the last decades, but so far it is not well understood which population-biological processes are mechanistically linked to this decline in species richness and how the “functioning” of plants is affected by increased land-use intensity. In this project we used growth ring analysis to study the longevity of plant individuals (or ramets) and to measure stem anatomical traits for a large number of perennial forb species in the grasslands of the Biodiversity Exploratories. On each experimental grassland plot (= 150 plots) we sampled all forb species which reached a cover of >1% with five individuals. In addition, we chose four common forb species (Achillea millefolium, Galium mollugo, Plantago lanceolata, Trifolium pratense), which we sampled each with 20 individuals in 60 populations across the Exploratory regions to get more detailed information on the age structure of populations. We found that the longevity of perennial forb species studied in the Exploratories (in total 99 species) is an inherent species characteristic, which is phylogenetically conserved. Apparently, increased land-use intensity selects for “faster” species with a shorter longevity. At the same time, we found consistently across all study species and the four more intensively studied species that the average age of individual species increases at higher land-use intensity, which is in contrast to our initial hypotheses. We suppose that the higher average age at higher land-use intensity is due to reduced establishment of new individuals suggesting that early stages of the plant life cycle are especially vulnerable to increased land-use intensity. Apart from the significant impact of land-use intensity we found that environmental variables related to water availability (i.e. soil moisture, amount of precipitation, soil texture) had significant effects on plant longevity, indicating that populations at sites with lower water availability had a higher mean age. Analyses of stem anatomical traits showed that the expression of several tissue types, especially the cortex, phloem and xylem, is also affected by land-use intensity, i.e. the width of these tissue types is greater at higher land-use intensity. At the same time, species richness of the experimental plots had negative effects on the width of these tissues, indicating that direct effects of land-use intensity as well as indirect effects mediated through changes in species diversity and altered competitive interactions could influence the expression of stem anatomical traits. In summary, the results of this project provide novel insights in population-biological mechanisms underlying changes in land-use intensity across a large number of perennial forb species. We conclude that the study of life-history characteristics and demographic processes requires more attention to better understand the consequences of global change drivers for species diversity.
