Adaptive genetic variability of selected pedunculate oak (Quercus Robur L.) european provenances exposed to drought stress

Poznavanje genetske varijabilnosti vrsta visoke ekonomske i ekološke vrijednosti kao što je hrast lužnjak (Quercus robur L.) te njihovih svojstava u promjenjivim uvjetima okoliša osobito je važno u kontekstu aktualnih klimatskih promjena. Prostorna varijabilnost pojave klimatskih ekstrema, poput dugoročnog izostanka oborina, predstavlja potencijalni rizik za hrast lužnjak obzirom na njegovu široku rasprostranjenost i preferiranog vlažnog staništa. Istraživanje je provedeno na potomstvu iz devet različitih europskih provenijencija uzduž gradijenta zemljopisne širine (sjever-jug). Test provenijencija formiran je sa jednogodišnjim sadnicama. Sadnice su izložene eksperimentalnoj suši tijekom četiri uzastopne godine. Evidentirane su proljetna i jesenska fenologija, visinski rast, provodljivost puči te stopa asimilacije. Putem odgovora provenijencija na sušni stres, ciljevi istraživanja fokusirani su na utvrđivanje razine adaptivne genetske diferencijacije među provenijencijama, razine adaptivne genetske varijabilnosti unutar odabranih provenijencija te utvrđivanje obrasca njihove adaptivne genetske diferencijacije. Rezultati su pokazali memorijski efekt sušnog stresa na lisnu fenologiju kod većine promatranih provenijencija, u vidu naknadnog pomaka datuma prolistavanja i odbacivanja lišća. Uz istaknuti pomak prema kasnijem završetku vegetacije kod svih provenijencija, svojstvo prolistavanja bilježi promjenjive reakcije na sušni stres. Na osnovi fenoloških i morfoloških svojstava utvrđena je genetska diferencijacija među i unutar istraživanih provenijencija. Detektiran je klinalni obrazac genetske diferencijacije provenijencija obzirom na svojstvo prolistavanja, a analize svojstava visinskog rasta i završetka vegetacije ukazuju na ekotipski obrazac diferencijacije. Brzi oporavak jedinki nakon rehidracije potvrđuje toleranciju vrste na kratkoročnu izloženost sušnim uvjetima.Understanding the genetic variability of species with high economic and ecological value such as pedunculate oak (Quercus robur L.) and their properties in changing environmental conditions is particularly important in the context of current climate change. Suggested spatial variability of climate change impacts in Europe implies that widespread species like pedunculate oak may face different levels of climatic risks in different parts of their ranges. 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 one of the species that prefers moist 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 research was conducted on offspring from nine different European provenances along the latitude (north-south) gradient. The provenance test was initialized with one-year-old seedlings. The saplings were exposed to experimental drought and then re-watered in four consecutive years. Spring and autumn leaf phenology, height growth, stomatal conductance and assimilation rate were scored. Through the responses of provenances to drought stress, the research objectives are focused on determining the level of adaptive genetic differentiation among provenances, the level of adaptive genetic variability within selected provenances and determining the pattern of their adaptive genetic differentiation. The results showed a carry-over effect of drought stress with opposite shifts in flushing phenology. Autumn leaf phenology was unambiguously delayed following the drought treatments for all studied provenances in every year during the trial. With respect on the phenological and morphological traits, genetic differentiation between and within the studied provenances was detected. A clinal pattern of genetic differentiation of provenances was detected with respect to the flushing phenology, but analyzes of the growth and autumn leaf phenology indicate on an ecotypic pattern of differentiation. Rapid recovery of individuals after re-wtering confirms the species' tolerance to short-term exposure to drought conditions