Growth and photosynthesis in Norway spruce infected by the rust ´Chrysomyxa rhododendri´

In the Alps, at altitudes between about 1400 and 1900 m a.s.l., Norway spruce was infected by the rust Chrysomyxa rhododendri very heavily during the last decade. This fungus only attacks the new flush of the trees and may lead to loss of all current-year needles. On the other hand, forestry assesses this rust as rather harmless and it is assumed that infected trees sustain some growth reduction only. However, a thorough study on growth and productivity in rust-infected spruces is still missing. Therefore, we will estimate how much the productivity of Norway spruce is affected by an attack of Ch. rhododendri. Furthermore, the photosynthetic responses in infected new flushes and in non-infected needles should be investigated. In particular the question should be answered to which extent a stimulation of photosynthetic activity of non-infected needles may compensate for some losses of infected ones. We will conduct the project with two approaches: (i) with adult trees at their natural stand and naturally infected to different degrees with Ch. rhododendri measuring photosynthesis and radial growth using dendroecological methods (ii) with artificially inoculated potted seedlings measuring photosynthesis and biomass increment of all parts. This project should provide information about the consequences of a rust infection on the productivity of Norway spruce and should be a valuable contribution in estimating the economic importance of such epidemics to the most important forest tree of the Alps.