Norway Spruce Fine Roots and Fungal Hyphae Grow Deeper in Forest Soils After Extended Drought

Global warming will most likely lead to increased drought stress in forest trees. We wanted to describe the adaptive responsesof fineroots and fungal hyphae, at different soil depths, in a Norway spruce stand to long-term drought stress induced by precipitation exclusion over two growing seasons. We used soil cores, minirhizotrons and nylon meshes to estimate growth, biomass and distribution of fineroots and fungal hyphaeat different soil depths. In control plots fineroots proliferated in upper soil layers, whereas in drought plots there was no fineroot growth in upper soil layers and roots mostly occupied deeper soil layers. Fungal hyphaefollowed the same pattern as fineroots, with the highest biomass in deeper soil layers in drought plots. We conclude that both fineroots and fungal hyphaerespond to long-term drought stress by growing into deeper soil layers.