Cilj ovoga rada bio je usporediti dvije mješovite sastojine (provenijencije) obične bukve i hrasta kitnjaka, iz istočne (provenijencija Slavonski Brod - SB) i sjeverozapadne (provenijencija Karlovac - KA) Hrvatske, s obzirom na klimatske i edafske prilike te raspraviti njihov utjecaj na rast i produkciju suhe tvari prirodnog pomlatka hrasta kitnjaka i obične bukve u kontekstu njegove funkcionalne prilagodbe na prethodno spomenute stanišne prilike. Glavna razlika između provenijencija s obzirom na klimatske prilike ogleda se u prosječno većoj količini oborina na području provenijencije KA. Unatoč tomu, zbog nepovoljnog rasporeda oborina za vrijeme rasta i razvoja istraživanog pomlatka u razdoblju 2016. – 2020. godine područje provenijencije KA odlikovalo se učestalijom pojavom sušnih perioda nego područje provenijencije SB. S obzirom na edafske prilike (fizikalne i kemijske značajke tla) provenijencije se nisu značajnije razlikovale. Međutim, tlo provenijencije KA odlikovalo se nešto lakšom strukturom (manje gline i više skeleta) u odnosu na tlo provenijencije SB. Razlike između provenijencija i vrsta s obzirom na cijeli niz mjerenih parametara koji opisuju rast i produkciju suhe tvari istraživanog pomlatka uključujući i njihove alometrijske odnose ispitan je pomoću dvofaktorske ANOVA-e. Dobiveni rezultati ukazuju da je pomladak iz provenijencije KA ulagao više suhe tvari u rast i razvoj korijenja s posebnim naglaskom na sitno korijenje i pri tom se dublje zakorjenjivao te razvijao deblju i nižu stabljiku nego pomladak iz provenijencije SB. To ukazuje da je pomladak iz provenjencije KA funkcionalno prilagođeniji sušem staništu. Takav rezultat mogao bi biti posljedica različito ispoljene fenotipske modifikacije (reakcije na sušu) i/ili stvarnih genetskih razlika između provenijencija, što ovom prilikom nije bilo moguće točnije razlučiti. Dobivene razlike u rastu i produkciji suhe tvari između kitnjakova i bukova pomlatka odgovaraju već otprije poznatom načinu njihove funkcionalne prilagodbe na vlažnost, odnosno suhoću staništa. To znači da se kitnjakov pomladak dublje zakorjenjivao i pri tom je više suhe tvari ulagao u rast krupnog korijenja u odnosu na bukov pomladak koji se pliće zakorjenjivao i pri tom više suhe tvari ulagao u rast sitnog korijenja.

Research highlights: The susceptibility of oaks to late spring and early autumn frosts is directly related to their leaf phenology. Drought may alter the leaf phenology and therefore frost tolerance of oaks. However, the effects of drought on oak leaf phenology and frost resistance have not been thoroughly studied. Background and objectives: One of the consequences of climate change is an increase in the frequency of dry episodes during the vegetation period. Pedunculate oak (Quercus robur L.) is an economically and ecologically important forest tree species that prefers humid habitats. Therefore, knowledge of the impact of drought on this species is of great importance for the adaptation of forestry strategies and practices to altered environmental conditions. The aim of this study was to determine the impact of drought on leaf phenology and spring frost susceptibility in nine provenances. Materials and methods: One-year-old saplings originating from nine European provenances were used in the trial. The saplings were exposed to experimental drought and then re-watered in two subsequent years. Spring and autumn leaf phenology were scored. The trial was impacted by a late spring frost in the third year, and the resulting leaf frost injury was scored. The effects of drought treatment on the phenology and frost susceptibility of plants from the provenances were analysed. Results: Leaf phenology of plants from most of the studied provenances was significantly influenced by the drought treatment (p < 0.001). Drought induced a carry-over effect on flushing phenology, which was observed as delayed bud burst (from 0.6 to 2.4 days) in the second year and as advanced bud burst (from 0.1 to 6.3 days) in the third year. Therefore, opposite shifts in flushing phenology may be induced as a result of differences in the time span when plants sense water deficits. In contrast to flushing, autumn leaf phenology was unambiguously delayed following the drought treatments for all studied provenances (from 2.1 to 25.8 days). Differences in late frost susceptibility were predominantly caused by among-provenance differences in flushing phenology. However, the drought treatment significantly increased frost susceptibility in the plants (the rate of frost-injured plants per provenance increased from 3% to 78%). This higher susceptibility to spring frost was most likely caused by the advanced flushing phenology that resulted from the drought treatment in the previous year.

Abstract. Provenance trials, where populations of different geographical origin are tested in a common environment (common garden test), are a tool suited to allow the study of intraspecific adaptive genetic variation. Research of pedunculate oak (Quercus robur L.) adaptive genetic variability through analyses of populations in common garden tests has a long tradition. However, pedunculated oak populations originating south-eastern from the Alps have been scarcely studied in this way. This study addresses the adaptive genetic variability and differentiation of pedunculate oak populations originating from Austria and Croatia in a provenance/progeny field trial. Studied plants were six years old and were growing at the trial for three years. After two years of unusually low precipitations height and survival were analysed. The total mean height of all plants in the trial was 137.8 cm and ranged from 123.0 cm to 151.8 cm. The overall mean survival rate was rather high (0.85). Mean population survival ranged from 0.64 to 0.94. Individual narrow-sense heritabilities (hi2), family mean heritabilities (hf2), the coefficients of additive genetic variation (CVA) and quantitative genetic differentiation coefficients (QST) were calculated. A multivariate regression tree (MRT) analysis was used to determine the pattern of genetic differentiation of the populations. Individual heritabilities for height ranged between 0.00 and 0.39. Family mean heritabilities for height were rather low in most populations as well (<0.5). Family mean heritabilities for survival were higher than for height (ranging between 0.00 and 0.77). Calculated QST coefficients (0.25 for height and 0.14 for survival) indicated between-population genetic differentiation. The populations were separated into two clusters by MRT analysis regarding a climatic variable, namely Hargreaves' reference evapotranspiration. Populations originating from comparatively more humid habitats were grouped in the first cluster. The first cluster had a lower mean height and survival compared to the second one. The differences between these clusters were highly statistically significant. The observed quantitative genetic differentiation might have been driven by natural selection caused by differences in the relative moisture of the habitats 2

background and Purpose: Natural stands of pedunculate oak in Croatia have been delineated in seed areas, zones and regions. The current bylaw recommends that the transfer of reproductive material remains limited within zones, but that it is permitted within areas. Clonal seed orchards (CSOs) of pedunculate oak were established to increase genetic quality of seed and to acquire a more regular seed yield than in natural stands. In total 150 plus trees were selected within three seed regions. The selection included a number of favourable traits of tree size and stem quality. Three CSOs were planted with grafted plus-trees. We aimed to establish whether these orchards encompass enough genetic diversity to potentially produce genetically improved and sufficiently diverse reproductive material. We also wanted to assess neutral genetic differentiation between these orchards and compare it with the genetic diversity obtained from chloroplast DNA markers, depicting conserved lineages from recolonization routes. We wanted to investigate spatial genetic structure in the area of our research and provide additional information on the transfer of forest reproductive material. Materials and Methods: Leaves were collected from all clones in the CSOs. Total genomic DNA was extracted and clones were analysed with eight nuclear and ten chloroplast microsatellite markers. Spatial autocorrelation analysis was performed with nuclear microsatellite data and original plus trees' coordinates, for each CSO separately, to determine whether shared favourable traits among the selected plus trees in smaller distances are the results of relatedness, which the sampling strategy tried to avoid. results: We found 28 chloroplast haplotypes belonging to four maternal lineages, and significant differentiation between CSOs, indicating origin from different refuges. Nuclear microsatellites' diversity in the CSOs is quite high and comparable to diversity found within a recent study of Croatian natural populations. Nuclear microsatellites did not show genetic differentiation between CSOs, i.e. between the seed regions and seed zones they represent. No genetic differentiation was found with nuclear microsatellites among haplotypic lineages. We found no genetic structure within the analysed regions. Conclusions: Lack of differentiation between CSOs found with nuclear microsatellites confirms the permission for transfer of reproductive material between zones within the seed area 1-Lowland Forests. If original differentiation between chloroplast haplotypic lineages was present after recolonization, it was erased by subsequent gene flow. Lack of genetic structure, with nuclear microsatellites within regions indicates successful sampling strategy.

The few studies dealing with leaf phenological responses to elevated nutrients in forest trees have given ambiguous results, i.e., while some reported delayed leaf-out and autumn leaf senescence, others reported advanced leaf phenology caused by increased nutrition. This study aimed to determine the effects of experimentally increased phosphorus (+P treatment) on the leaf phenologies of two juvenile provenances of common beech and sessile oak. Other objectives were to determine whether there were interspecific differences as well as intraspecific variations. Saplings were excavated in two mixed beech–oak stands and transplanted into four wooden boxes filled with a commercial soil substrate. Phosphorus fertilizer was added to two of the boxes, while the remaining boxes served as controls. Both species responded to +P treatment with advanced autumn leaf senescence in the first year of the experiment. Leaf senescence in common beech began significantly earlier, while in both species, the process was accelerated compared to that in the control. In the second year, the leaf senescence response to +P treatment was even more pronounced in both species. The +P effect on leafing phenology was absent in both common beech provenances and in an oak provenance. However, the other oak provenance showed advanced leafing, indicating the existence of intraspecific differences.