Root growth dynamics of three beech (Fagus sylvatica L.) provenances

European beech (Fagus sylvatica L.) is commercially and ecologically important tree species in Central European forests but its intra-specific variability in drought and temperature tolerance might endanger its future distribution in Europe. Beech phenological and growth traits have been studied in large-scale international beech provenance trials, yet the growth and turnover of its fine roots (FR) has not been included among the observations. FR growth dynamics and FR architectural traits of three beech provenances in the international beech provenance trial Straza/Kamenski hrib, established in Slovenia in 1998, and from a natural beech regeneration site growing at its border, were studied from 2007 to 2010. We studied FR biomass using soil cores (SC), root production using ingrowth soil cores (IC), and root longevity using minirhizotrons (MR). Significant differences in FR biomass (live and dead) between the provenance P37 and other provenances were discovered in SC, FR biomass of P37 being significantly higher than FR biomass of latter, which could be connected with overall excellent growth performance of P37 due to favourable environmental conditions at trial. Values of specific root length (SRL) in IC varied significantly among P37 and P54. The turnover rates in IC were at the end of the experiment close to MR results. Median MR-based longevities of FR varied between 625 and 934 days. Survival curve of the slowest growing provenance (considering its aboveground characteristics) was significantly different from the other two, median longevities of the latter being higher. Death of FR, older than two years, occurred most likely in the winter. Our results suggest that there are significant differences in FR longevity among provenances, which might contribute to their adaptation to future environmental conditions. Furthermore, the calculated annual C investment into FR growth per ha differs up to twofold between provenances, contributing to different C dynamics of their future stands.