Soil-plant-gall relationships: the elementary irony on plant gall ecophysiology

Abstract

The evolution of the habit of gall induction has been explained by the nutrition, microenvironment, and enemy hypotheses. Soil attributes have direct relationships with these three hypotheses at both cellular and macroecological scales, serving as the primary source of raw materials necessary for the synthesis of metabolites that support their premises. However, the influence of soils has been relegated to the impact of the nutritional status (carbon and nitrogen concentrations) of the host plant on gall richness and abundance. Thus, the objective of this thesis was to present evidence and arguments on the importance of investigating the involvement of multiple soil elements in the dynamics of cell wall composition, antioxidant activity, and regulation of water dynamics during the development of plant-gall interactions. We demonstrated that the accumulation of metals such as aluminum and iron is involved in the formation of the red coloration of galls on Nothofagus obliqua (Nothofagaceae) and in the increase of their photosynthetic capacity, enriching the discussion about the phenomenon of the reddish coloration of these structures in nature. We also demonstrated that the temporal and spatial water dynamics in vereda environments shape nutrient allocation in galls induced on Macairea radula (Melastomataceae), affecting their growth and local abundance. The overview of the different soil-plant-gall relationships investigated in this work highlights the complexity of the nutritional requirements of gall inducers, especially the involvement of antioxidant activity with the distribution of Fe2+ and Fe3+ in the nutritive tissues of the galls investigated here, in N. obliqua (induced by a hymenopteran), M. radula (by a lepidopteran), and two galls (by a nematode and a dipteran) on Miconia corallina (Melastomataceae). These observations support the role of iron as an important nutritional resource and potential ecological protagonist, complementing the premises of the Nutrition Hypothesis for the adaptive value of galls. Thus, this thesis corroborates that soil and plant chemistry interact to determine the outcome of plantherbivore interactions and must be addressed considering not only soil characteristics but also, with equal importance, the physiology of the host plant and the nutritional aspects of the gall inducers. In this sense, the combination of quantitative and qualitative approaches to study the ionome and plant nutrition proved essential to understanding the functions of elements during gall development.