Research interests

Plants are sessile organisms continuously experiencing both abiotic and biotic stresses. Since plants cannot simply escape these potentially harmful situations, they have evolved a wide variety of defence mechanisms. These include external mechanical characteristics that discourage herbivory (e.g. spines and thorns) or diminish the destructive effects of harsh abiotic conditions (e.g. thick, waxy leaves that decrease water losses). In addition, plants produce different chemical substances, generally known as secondary metabolites, which may deter herbivores (e.g. alkaloids and phenolics) or serve as protection against damaging abiotic factors like high UV-light (e.g. flavonoids).

My research interests are plant ecophysiology, plant chemistry and plant-herbivore interactions. Phenolics are low-molecular weight, carbon-based secondary compounds that are commonly found in plants. I am interested in how the concentration of plant phenolics are affected by changes in the abiotic environment (e.g. climate change scenarios like higher temperatures, higher light intensities, increased drought or changed snow conditions) and, subsequently, how this will influence plant susceptibility to herbivory. I am also interested in the genetics behind the complex biochemical pathways producing the phenolic compounds.

Currently, most of my research is conducted within a plant-herbivore-predator study system where I try to understand the interactions between willows (Salix spp.), an herbivorous leaf beetle (Phratora vulgatissima) and a predatory bug (Orthotylus marginalis). Willow species are rich in phenolic compounds and they can be divided into two groups depending on which phenolics they produce: some willow species (e.g. Salix viminalis) demonstrate high concentrations of condensed tannins while others (e.g. Salix dasyclados) exhibit high concentrations of salicylates. The presence or absence of salicylates seems to determine willow susceptibility to herbivory by P. vulgatissima.  At the moment, I am focusing my research on the following questions:

(1) Do increased temperatures influence the trophic interactions within my plant-herbivore-predator study system?

(2) Do different willow species vary in their physiological responses (e.g. growth traits, photosynthesis, carbon/nitrogen and phenolics) to increased temperatures and drought stress?

(3) How does the phenolic profile of Salix cinerea vary throughout the growing season and within the landscape (e.g. open vs. forested habitats), and can the population dynamics of zoophytophagous bugs (mirids) feeding on this willow species be explained by host plant quality (carbon/nitrogen and phenolics)?

(4) How is willow plant chemistry and insect herbivore performance affected by hybridization? In my study system, hybridization between the parental species Salix viminalis (susceptible to herbivory) and Salix dasyclados (resistant to herbivory) and subsequent crosses of two F1 hybrids generated a F2 generation that provides an opportunity to screen for plants with a great variance of chemical traits and correlate them to the performance of the herbivorous insect.

Publications

Torp M, Witzell J, Baxter R & Olofsson J (2010) The effect of snow on plant chemistry and invertebrate herbivory: experimental manipulations along a natural snow gradient. Ecosystems 13: 741-751.

Torp M, Olofsson J, Witzell J & Baxter R (2010) Snow-induced changes in dwarf birch chemistry increase moth larval growth rate and level of herbivory. Polar Biology 33: 693-702.

Torp M (2010) The effect of snow on plants and their interactions with herbivores. Doctoral Thesis. Umeå University, Sweden. ISBN 978-91-7264-923-1.

Srivastava V, Schinkel H, Witzell J, Hertzberg M, Torp M, Srivastava MK, Karpinska B, Melzer M, Wingsle G (2007) Downregulation of high-isoelectric-point extracellular superoxide dismutase mediates alterations in the metabolism of reactive oxygen species and developmental disturbances in hybrid aspen. The Plant Journal 49:135-148.

Witzell J, Karlsson M, Rodriguez-Buey M, Torp M, Wingsle G (2005) Transgenic hybrid aspen with altered defensive chemistry – a model system to study the chemical basis of resistance. In: Rust Diseases of Willow and Poplar. MH Pei and AR McCracken (eds.), CABI Publishing. ISBN 0-85199-999-9.