Interspecific and intraspecific competition of A. trifida and A. artemisiifolia

In addition to Ambrosia artemisiifolia (common ragweed), Ambrosia trifida L. (giant ragweed) is also locally present and naturalized in Serbia. Taking into account its vegetative and generative potential, its further expansion and, consequently, greater damage to agriculture can be expected. The aim of this study was to determine the impact of A. artemisiifolia on the vegetation yield of A. trifida in the conditions of their coexistence. The experiment was set according to the Replacement Design model, where intra and interspecific competition was monitored. The experiment was set up in six treatments (a completely random block system in four repetitions) with different plant proportions of A. artemisiifolia / A. trifida (%) per m2: 100:0, 80:20, 40:60, 60:40, 20:80 and 0:100 in two series: small (total of 10 plants m-2) and large density (total of 100 plants m-2). During the season, the dry biomass of the plants of A. trifida and A. artemisiifolia was measured in three assessments, but in this paper the results will only be shown for A. trifida. To investigate the analyzed parameters, a three-factor analysis of variance (ANOVA) was used and the data were processed in the statistical package SPSS. In low density treatment, the average values of the dry weight of A. trifida ranged from 5.36-8.99 g plant-1 (July), from 7.4-13.01 g plant-1 (August) and from 9.08-16.13 g plant-1 (September), while in high density treatment the values ranged from 6.35-8.38 g plant-1 (July), 8.66-11.71 g plant-1 (August) and 9.53-13.54 g plant-1. The obtained results show that A. trifida expresses interspecific competition in lower population densities, while with the increase in the number of individuals per unit area, intraspecific competition is more pronounced.