Troposphere ozone contamination produces unexpected changes in adaptive traits of Spergula arvensis in herbaceous communities

Background/Question/Methods

Environmental change caused by human activities imposes new challenges to organisms that may be directly or indirectly affected. Organisms may respond by changes in demographic processes and adaptive traits in specific populations. Theoretically, in fertile environments biotic stress factors lead to communities dominated by competitor species that have physiological and morphological traits enabling them to capture resources and grow fast in crowded habitats. In contrast, under abiotic stressful ecological conditions communities are dominated by stress tolerant species, which grow slowly and with adaptations to reduce the negative impact of the stress. Under this theory, long-term exposure to ozone oxidative stressful environment would change species hierarchies within the community, increasing the abundance of stress tolerant genotypes. In this study we evaluated adaptive trait changes in Spergula arvensis, a dominant species of a temperate climate herbaceous community of fertile soils, after five years of exposing the community to recurrent episodes of high levels of ozone contamination. Abundance of Spergula arvensis in the community was monitored, and tolerance to ozone, growth, shoot/root ratio, reproductive effort, competitive ability and aggressiveness, seed dormancy and ageing, and response to herbivore attack of populations subjected to ozone selection pressure were compared to that of the original population growing them in a common garden.

Results/Conclusions

Individuals of communities exposed to ozone expressed change in all of the studied traits, clearly showing that microevolution was driven by ozone stressful environment. Tolerance to ozone, seed aging rate, competitive ability and aggressiveness were reduced, whereas growth, reproductive effort, shoot/root ratio and defense against herbivores were increased.  Spergula arvensis remained in the community by evolving in the opposite direction expected for stress tolerant species syndromes (increased ability to tolerate stress and low growth rate) towards many of the adaptive trait characteristics expected for ruderal species (high competitive ability, abundant seed production and rapid growth).