Efeitos da herbivoria e condições ambientais sobre a instabilidade no desenvolvimento e resposta vegetativa em Tithonia diversifolia (Asteraceae)

Abstract

Venancio, H. 2017. Effects of herbivory and environmental conditions on developmental instabiblity and vegetative responses of Tithonia diversifolia (Asteraceae). MSc. Thesis. UFU. Uberlandia-MG. 102p. Herbivory, edaphic competition and shading can induce phenotypic variation, decrease performance and increase levels of fluctuating asymmetry (FA, a stress measurer) in invasive plants. The association of these can further increase the FA, also harming severely or disrupting phenotypic variations o f plants. On the other hand, fertilization can increase FA, performance and decrease the negative impacts of herbivory and edaphic competition on weeds. However, there are doubts about the relationship o f FA with some o f these factors. Thus, we used the invasive Tithonia diversifolia (Asteraceae) in greenhouse experiments to verify how herbivory, shading, edaphic competition and fertilization can influence fitness and phenotypic variation o f this species. In the first chapter, we analyzed how herbivory can cause changes in foliar nitrogen (type o f induced defense) and FA o f injured leaves. For this, we used seedlings of this species and separated them in group treatment, where we caused simulated herbivory damage on leaves; and the control group, which did not suffer injuries. The FA o f these leaves was followed from the first to the fourth week o f study, when the nitrogen was also verified. Our results showed that plants o f the treatment group had higher FA on the fourth week when compared to control group; but nitrogen did not differ between treatments. In this way, herbivory can increase FA. In the second chapter, we associate for four weeks, herbivory with shade condition, as well as for edaphic competition and fertilization. We believe that herbivory, shading and competition decrease performance and increase FA. We further hypothesized that fertilization increases fitness and levels o f FA of T. diversifolia, and reduces negative impacts o f herbivory and competition. For the herbivory-shade experiment, the treatment group suffered two simulated herbivory damage on leaves, with individuals distributed between sun and shade. The plants were followed for four weeks. We also checked the leaves that came up after treatments. For herbivory, edaphic competition and fertilization, we removed 50% area from the leaves o f the plants in the first and third week o f study, along with and without fertilization and competition. The results of these experiments revealed that shading causes negative impacts on T. diversifolia, and increases leaf FA. This condition also caused phenotypic variation in shoot structures. Herbivory and edaphic competition did not influence phenotypic variations and FA, but the two factors in the second experiment negatively impacted this species. Fertilization increased plant fitness and FA, and decreased the negative effects o f herbivory and competition. Herbivory associated with shading and edaphic competition did not intensify negative fitness nor influenced phenotypic variation responses. ...