Branching and competitive hierarchies in populations of Galium aparine

The role of branching on the development of size hierarchies was studied on experimental populations of the annual herb Galium aparine L. (Rubiaceae). All branches of plants growing at high and low density were severed as plants developed, and the growth of individual plants, the development of growth and size inequalities, and the mean change in the size ranking of plants over time were compared with those of populations of naturally branched plants. Size allometries were analysed for all treatments. The effect of the branch-severing treatment on growth and size inequalities was not significant for crowded populations. The position of individual plants in the ranking of weights in crowded conditions was less variable for populations of unbranched plants than for those of branched plants. Size and growth inequalities among branched plants were not significantly affected by population density. The hypothesis that branching increases the development of competitive hierarchies in G. aparine populations is not supported by the results. The role of height growth limitation in crowded conditions as a constraint to competitive hierarchy development is discussed. Key words: allometry, branching pattern, competitive hierarchy, Galium aparine, intraspecific competition.

Growth responses of Urtica dioica to nutrient supply

This study examines the effects of nutrient supply (three N–P–K treatments: 75, 225, and 375 kg∙ha−1; 12.5% N, 8.5% P, 16% K) on growth, allometry, and architecture of Urtica dioica L., an expansive clonal plant found throughout Central Europe. Biomass allocation was significantly affected by nutrient supply: higher nutrient doses resulted in less biomass allocation to belowground organs, whereas the period of intensive production of aboveground biomass was prolonged. Shoot height increases with nutrient supply. The height ratios were constant over time. Within each treatment and each harvest, inflorescence biomass was positively correlated with shoot height. Branching of the main shoots (number of lateral branches) was positively correlated with plant height and changed with time. The number of new rhizomes was affected by both treatment and harvest, especially in older plants. The results suggest that high nutrient supply increased the allocation of biomass both to reproductive organs and to vegetative organs. Key words: allometry, biomass allocation, clonal plant, nutrients, plant architecture, Urtica dioica.