Root morphology, mycorrhizal roots and extramatrical mycelium growth in silver birch (Betula pendula Roth) genotypes exposed to experimental warming and soil moisture manipulations

Abstract

In the future, boreal forests will be growing in a warmer climate with more fluctuating soil moisture conditions. However, the knowledge about the effects of simultaneous warming and drought on boreal trees, and especially on their belowground compartments, is still scarce. We studied the responses of four silver birch genotypes to experimental warming at normal and low watering levels after two growing seasons. Variables analysed include mycorrhizal short root growth, fungal biomass (ergosterol) in roots and extramatrical mycelium, and root morphology (root tissue density, root length density, specific root length, specific root surface area). In addition, root and shoot mass fractions were determined. Gt26 had more root mass and also more 2–5 mm diameter roots, but less short roots and ergosterol in its roots than the other genotypes. There were no treatment effects on extramatrical mycelium and mycorrhizal infection levels, but root ergosterol concentrations increased in gt12 due to warming. Drought increased root mass at the expense of shoot growth in gt12, but warming did not cause allometric growth changes in any of the genotypes. Our results show some genotype-dependent responses to warming and drought but also significant within population differences in belowground allocation patterns among the silver birch genotypes.