Morphological and root system characteristics of smallleaved lime Tilia cordata Mill. seedlings as indicators of planting stock quality

Small−leaved lime Tilia cordata Mill. is primarily found in Poland as an admixture species, fulfilling important ecological, biocenotic, and cultural functions. Consequently, there is a continuous demand for high−quality planting stock of this species. The aim of the study was to compare morphological traits, root system characteristics, and nursery quality indices of three small−leaved lime stock types produced under standard nursery conditions, with particular emphasis on root system parameters as indicators of planting stock quality. Three stock types were analysed: one−year−old seedlings (1+0), two−year−old non−transplanted seedlings (2+0), and two−year−old seedlings transplanted after the first growing season (1+1). For each seedling, shoot height, root system length, and root collar diameter were measured. In addition, a detailed morphometric analysis of the root system was conducted, including total root length, root surface area, mean root diameter, and root volume. The dry mass of roots and shoots was determined, and functional indices (root tissue density, specific root area, and specific root length) as well as seedling quality indices (sturdiness quotient – SQ, shoot−to−root ratio – S/R, and Dickson Quality Index – DQI) were calculated. The results showed significant differences among the analysed stock types in terms of morphological traits and seedling quality indices. The most favourable nursery quality indicators were found in transplanted seedlings (1+1), which were characterised by the longest root systems (27.8 cm), the largest root collar diameter (8.0 mm), and the highest values of the Dickson Quality Index (1.01) and root tissue density (950.74). The greatest height was recorded in the 2+0 variant (61.6 cm); however, these seedlings exhibited considerable slenderness and an unfavourable shoot−to−root ratio (S/R=2.16). The obtained results indicate that transplanted seedlings may have greater planting suitability under the analysed nursery conditions, mainly due to more favourable biometric proportions and better−developed root systems. At the same time, the findings demonstrate that the assessment of small−leaved lime planting stock should not be based solely on height criteria, but should also include root system parameters and functional root traits as complementary indicators of nursery stock quality.