Chemical interactions

Prof. Dr. Sybille B. Unsicker, Kiel, Germany
Prof. Dr. Wolfgang W. Weisser, Freising, Germany

SP02 will investigate if plant diversity stabilizes plant VOC emission as an important ecosystem function, both over time, and in the resistance and recovery phase during and after an extreme climatic event as defined in the Coordination Proposal. We hypothesize that individual plants respond to biotic stress, i.e. herbivory, and abiotic stress, i.e. higher temperature and drought, by adjusting plant volatile emission and that this response is affected by plant species richness. We will investigate the stabilizing effects of plant species richness with respect to abrupt changes (extreme events) in abiotic conditions, with and without biotic stress (herbivory), and with respect to temporal stability (seasonal patterns). We will analyse the stability of VOC emissions in several ways. First, we will assess stability of VOC emission over repeated measurements, focussing on the number of compounds emitted, the identity of compounds emitted (beta-diversity), and their total concentrations. We will test if volatile emission of high-diversity plant mixtures is more stable than volatile emission of low-diversity mixtures. Second, we will analyse VOC emission when a drought stress and insect herbivory are applied alone and in combination. We will test the hypothesis that plants in high-diversity (species-rich) communities show higher resistance, and more complete recovery, in their volatile bouquets than plants in low-diversity communities. The stability of VOC emission after stress will be assessed at both the level of an individual target plant, as well as the level of plant community emission.

SP02 has three specific objectives that will be addressed in three work packages (WPs):
O1: To assess how plant diversity stabilizes temporal VOC emission in the field
One-time volatile collections from grassland communities in the Main Experiment during the first funding period showed that the number and concentration of VOCs emitted by a plant community increased along the gradient in plant species richness. In the new phase of the RU, we will test how plant diversity affects the stability of VOC emission over time. We will measure VOC emission over one year across the gradient of plant diversity in the Main Experiment, in the same 24 plots, which were selected for the ResCUE Experiment. These repeated measurements allow us to examine how plant diversity, along with biotic and climatic influences, affects the stability of plant community VOC emission. O1 is addressed in WP1 (Main Experiment).
O2: To assess plant diversity-mediated resistance and recovery in VOC emission under climate extremes
In close collaboration with the other SPs, we will test how plant diversity stabilizes VOC emission both at the individual plant and at the plant community level, under the condition of a simple drought (HerbiCoMic Greenhouse Experiment), and a severe drought coupled with a heatwave (iDiv Ecotron ResCUE Experiment). We will compare VOC emission during (resistance) and after (recovery) a drought is applied to plant communities. We will also study de novo synthesis of VOC compounds after stress using the isotope tracers. O2 is addressed in WP2 (ResCUE Experiment) and WP3 (HerbiCoMic Greenhouse and HerbiCoMic Field Experiment).
O3: To assess stabilizing effects of plant diversity on VOC emission and plant defence after combined abiotic and biotic stress events.
We will test the hypothesis that plant diversity stabilizes VOC emission and plant defence under combined abiotic and biotic stress, by adding a herbivory treatment to Plantago lanceolata phytometers in the hot drought ResCUE Experiment (WP2), by studying the consequences of below- and aboveground herbivory and drought stress in the HerbiCoMic Greenhouse experiment (WP3), and by assessing the consequences of drought on colonization of herbivores and subsequent VOC emission in the HerbiCoMic Field Experiment (WP3). All experiments will be carried out together with a number of other SPs of the RU.