Effect of Acorn Size on Morphological Development of One-year-old Seedlings of Pedunculate Oak (Quercus robur L.) in Differing Light Conditions

Kakvoća sadnica povezana je s kvalitetom sjemena od kojega se proizvode, a u vrsta krupnoga sjemena, poput hrasta lužnjaka, kvaliteta sadnice nakon prve vegetacijske sezone povezana je s krupnoćom žira, odnosno količinom hranjiva pohranjenom u žiru. Stoga je cilj ovoga istraživanja ispitati utjecaj krupnoće žira na morfološki razvoj lužnjakovih sadnica tijekom prve godine života u uvjetima različite dostupnosti svjetla. Ukupno je u Bosnaplast kontejnere napunjene tresetom posijan 891 okularno zdravi žir hrasta lužnjaka porijeklom iz priznate sjemenske sastojine. Dio kontejnera postavljen je pod zasjenu od trske, kojim je ograničena dostupnost užitnog svjetla na oko 10 %. Na poduzorku od 25 biljaka obavljene su detaljne izmjere lisne površine, te je analizom suhe tvari ustanovljena biomasa glavnih dijelova biljaka. Na kraju vegetacije svim su biljkama izmjerene visine i promjer vrata korijena. Uloga krupnoće žira puno je izraženija kod sadnica uzgojenih u uvjetima punoga užitnog svjetla. S povećanjem krupnoće žira povećavala se prosječna visina i promjer vrata korijena, prosječna lisna površina sadnice i ukupna masa suhe tvari sadnice. Jedino ispitivano svojstvo koje se smanjivalo s povećanjem krupnoće žira je specifična lisna površina, što ukazuje na deblje plojke listova kod sadnica iz krupnijega žira. Kod lužnjakovih sadnica uzgojenih u zasjeni, utvrđeno je da je za mnoga od istraženih morfoloških svojstava važniji utjecaj dostupnoga svjetla, nego krupnoće žira. No, i u uvjetima zasjene sadnice hrasta lužnjaka uzgojene iz krupnijega žira, imale su veće prosječne visine i promjere vrata korijena od sadnica iz sitnoga žira. Rezultati istraživanja ukazuju da postoje mogućnosti za poboljšanje kvalitete u proizvodnji sadnica hrasta lužnjaka s obzirom na veličinu žira. Međutim, daljna detaljna istraživanja potrebna su kako bi se došlo do konačnih zaključaka i preporuka za praktičnu primjenu.Increase of the share of high-quality seedlings in the total production on the one hand enhances the production efficiency of the nursery production, and on the other hand improves the probability for successful planting in the field. The quality of the seedlings after the first growing season is related to the quality of the seeds used. In the tree species with large seeds, like pedunculate oak (QuercusroburL.), quality is related to the size of the seed, i.e. the amount of stored nutrients. Therefore, the aim of this contribution is to evaluate the effect of acorn size on the morphological development of pedunculate oak seedlings during the first growing season under contrasting light regimes. In total, 891 visually healthy acorns collected in the certified seed stand were planted in the “Bosnaplast” containers filled with peat (Figure 1). Part of the containers were kept in the shade of about 10 % of full light during the whole experiment. Before sowing, diameter, weight and length was measured on subsample of 200 acorns. Regression analysis showed that the acorn mass as the most important predictor of the nutrient content much more depends on the acorn diameter, than on the acorn length (Figure 2). Therefore, three acorn size classes were formed according to distribution of the acorn diameters: small acorns (. 16 mm of diameter), medium-sized acorns (16,1 mm to 17,9 mm of diameter) and large acorns (. 18 mm of diameter). During the sowing, acorns were measured for diameter and grouped into three classes of acorn size. Position of each acorn was recorded within the container and each container was labeled to facilitate the connection between the measurements of the acorn size and the subsequent measurements of the emerged seedlings. Subsample of 25 seedlings was removed from the experiment with fully developed leaves for detailed measurements of leaf area, and allocation patterns of dry biomass into three plant compartments: leaf, root, and stem. After the first growing season, height and root collar diameter were measured on all emerged seedlings. Effect of acorn size and light regime on morphological features of one-year old seedlings of pedunculate oak were examined with the analysis of variance. Following morphological features of seedlings were tested: height (Figure 3A and Table 1) and root collar diameter (Figure 3B and Table 1) of the seedlings, leaf area (Figure 4A and Table 2) and specific leaf area (Figure 4B and Table 2) of the seedlings, dry weight (Figure 5A and Table 3) and ratio of aboveground:underground dry weight of the seedlings (Figure 5B and Table 3). In seedlings grown in full sunlight increase in the acorn size resulted in the increase in average height and root collar diameters of the seedlings, average leaf area of the seedlings, and seedlings total dry weight. Specific leaf area was, on the other hand, smaller in seedlings from larger acorns. For the seedlings in the shade, light was the decisive factor influencing their morphological development, but still the seedlings from larger acorns were higher and had larger root collar diameters compared to the seedlings from smaller acorns. According to the results obtained in this research, it is safe to say that there is enough space for the improvements in the nursery production of pedunculate oak seedlings by taking into account the size of the acorns. However, further detailed research efforts are needed to deduce final conclusions and recommendations for the practical nursery production