Effects of substrate on ecophysiology of young silver fir and Norway spruce growing on shallow calcareous soils

Regeneration of mixed mountain forests after disturbances frequently fails due to causes like seed limitation, unfavorable microclimate, competition and ungulate browsing. Due to water and nutrient limitations, shallow soils on dolomite and limestone bedrock constitute a challenge for artificial regeneration. A thorough understanding of the interaction between substrate and tree ecophysiology and the suitability of various tree species for such unfavorable sites is of ultimate importance for post-disturbance regeneration management of protective forests, which have faced dramatically accelerated disturbance regimes during recent decades. Hence, this study compares the effect of soil substrate on the performance of young silver fir ( Abies alba Mill.) and Norway spruce ( Picea abies Karst.) by analyzing the interaction between tree ecophysiology and soil conditions at two windthrow sites on dolomite and limestone. On both sites, silver fir and Norway spruce suffered from foliar nutrient deficiencies. For both species, soil nutrient content as well as photosynthetic and growth rates were higher on limestone than on dolomite. Silver fir showed lower photosynthetic rates on both dolomite and limestone. While fir stayed smaller than spruce on limestone, it showed slightly better recent shoot growth on dolomite. Mycorrhization was higher on limestone. There was a tendency of higher fine root mass density and higher ectomycorrhizal root colonization of silver fir in the mineral soil developed from dolomite, compared to Norway spruce. These results reflect the central role of substrate and nutrition for tree growth and development and indicate better ecophysiological performance for both species on limestone than on dolomite. Our findings suggest better adaption of silver fir to unfavorable soil conditions due to different root characteristics. • Mn, P, S and K deficiencies on dolomite more severe than on limestone substrate. • Higher photosynthesis and tree growth on limestone substrate. • Ecophysiological performance of spruce > fir on limestone, fir ≥spruce on dolomite. • Rooting of spruce restricted to forest floor, on dolomite fir utilizes mineral soil.