GENOME SIZE IS ASSOCIATED WITH DIFFERENTIAL SURVIVAL OF PLANT SPECIES
T Vidic1, J Greilhuber2 and B Vilhar1
1 University of Ljubljana, Biotechnical Faculty, Department of Biology, Ljubljana, Slovenia
2 University of Vienna, Institute of Botany, Vienna, Austria
We investigated whether genome size is associated with differential survival of plant species in a comparative study of five grassland communities occurring on a gradient of environmental conditions caused by pollution from a former lead smelter at Zerjav, Slovenia. The concentration of Pb in the soil on the five plots ranged from 0.01% on an unpolluted reference plot to 3% on the most polluted plot close to the smelter stack. The number of vascular plant species per plot correlated negatively with the level of metal contamination and ranged from 106 to 20. We measured genome sizes (2C-values) of 70 herbaceous dicotyledon perennial species occurring on the plots, using Feulgen image densitometry(1). In addition, we counted the number of chromosomes and estimated the mean metaphase chromosome sizes (chromosomal DNA content). We detected a negative correlation between the concentration of contaminating metals in the soil and the proportion of species with both large genomes (C-values) and large chromosomes in plant communities. In contrast, we detected no significant correlation between soil pollution and chromosome numbers, although the most polluted site had fewer plants with high chromosome number. These results represent the first direct evidence, based on a field study, that a large genome is a selective disadvantage for plants in extreme environmental conditions.
1. Vilhar B et al. (2001). Annals of Botany 87: 719-728.