| Spruce trees are very sensitive to drought and the climate change predictions are that drought events will become more common under future climate conditions. The drought of 2018 and the devastation by spruce bark beetle (SBB) in its wake might give a bleak prediction for the future of spruce in Sweden. Hence, we need to understand the relationship between stand conditions and spruce susceptibility to SBB. Recent studies showed that indeed drought makes spruce more vulnerable to SBB but it is not the driest stands that showed the highest damage. Hence, our project sets out to create a better understanding of the relationship between soil moisture conditions and spruce bark beetle susceptibility. One factor that so far has not been included in this research is tree symbiosis with mycorrhiza (EM). Our project aims to investigate the relationship between soil moisture conditions, mycorrhizal colonisation and community composition and spruce resistance against spruce bark beetle attack. We do this by using a soil moisture gradient to establish the effect on EM symbiosis and subsequently build roofs in selected stands to simulate drought and study consequences on EM symbiosis, and tree susceptibility to SBB and recovery of tree vitality after drought. Methods include meta-barcoding of soil and root fungal communities using the ITS region of ribosome encoding genes and the PacBio platform at SciLife Lab, Uppsala. Root samples will be analysed for mycorrhizal colonisation degree and fine root mortality. We use standardized methods to quantify soil characteristics and fertility. For aboveground measurements assessing tree vitality we analyse tree vitality, specifically volumetric soil water content, relative water content of the xylem and secondary phloem, osmotic potential of the phloem, constitutive resin flow on the stem and bark anatomy. SBB attack willingness and success is assessed using attack boxes. These boxes are developed specifically to release limited number spruce bark beetles and allow attack on a restricted surface of the tree. This way attractiveness for the SBB and susceptibility to SBB can be measured non-destructively. By the end of our study, we will be able to show the effects of drought on spruce-EM relationships and how this relationship affects SBB attack success. The project is ideally suited as PhD project, the individual subprojects have scientific importance in their own right and the four subproject together will provide an integrated understanding of the direct and indirect interactions studied. Maartje Klapwijk will be main supervisor, Petra Fransson (SLU), Sigrid Netherer (BOKU, Austria) will be co-supervisors. Martin Schroeder will be part of the advisory committee to provide expertise on SBB and John Marshall (SLU) will if possible join the supervisory team as tree vitality expert. |