During drought, a major abiotic stressor for European forests, excessive reactive oxygen species (ROS) are produced, causing oxidative damage that affects structural and metabolic tree functions. This research examines the effects of drought, phosphorus (P) fertilization, and provenance on photosynthetic pigments, malondialdehyde (MDA) concentrations, and antioxidant enzyme activities in common beech (Fagus sylvatica L.) and sessile oak (Quercus petraea (Matt.) Liebl.) saplings from two provenances. In a common garden experiment, four treatments were applied: regular watering with (+PW) and without P fertilization (−PW), and drought with (+PD) and without (−PD) P fertilization. Results showed that drought increased both MDA concentrations and antioxidant enzyme activity, particularly superoxide dismutase (SOD), catalase (CAT), peroxidase (POD), and ascorbate peroxidase (APX), which are responsible for ROS scavenging. Additionally, chlorophyll a + b concentrations were lower in drought-exposed plants. Phosphorus fertilization minimally affected MDA levels but enhanced antioxidant responses, particularly APX and CAT activities in oak during drought. Provenance differences were notable, with oak and beech from the drier provenance showing better adaptation, reflected in lower MDA levels and higher enzyme activities. This study underscores the importance of antioxidant defenses in coping with drought stress, with phosphorus fertilization and provenance shaping the species’ adaptive capacity.

Increasingly frequent and severe droughts pose significant threats to forest ecosystems, particularly affecting photosynthesis, a crucial physiological process for plant growth and biomass production. This study investigates the impact of phosphorus fertilization on the photosynthesis of common beech (Fagus sylvatica L.) and sessile oak (Quercus petraea (Matt.) Liebl.). In a common garden experiment, saplings originating from two provenances (wetter KA and drier SB provenances) were exposed to regular watering and drought in interaction with moderate and high phosphorus concentrations in the growing substrate. Results indicated that drought significantly reduced pre-dawn leaf water potential (Ψ_PD), net photosynthesis (A_net), stomatal conductance (g_s) and photosynthetic performance index (PI_abs) in both species. Phosphorus fertilization had a negative impact on A_net and PI_abs, thus exacerbating the negative impact of drought on photosynthetic efficiency, potentially due to excessive phosphorus absorption by saplings. Provenance differences were notable, with the KA provenance showing better drought resilience. This research highlights the complexity of nutrient–drought interactions and underscores the need for cautious application of fertilization strategies in reforestation efforts under changing climatic conditions.

The negative impact of drought on plant growth may be modified by the different availability of mineral nutrients and by their adaptation to different local habitat conditions. In this study, we examine the impact of drought, fertilization with phosphorus and provenance, as well as their interactions, on the growth and allometric growth relationships between the belowground and aboveground organs of common beech (Fagus sylvatica L.) and sessile oak (Quercus petraea (Matt.) Liebl.). The research was conducted on saplings originating from two mature mixed stands (dry and wet provenances) dominated by these species. In the common garden experiment, saplings were exposed to regular watering and drought in interaction with moderate and high phosphorus concentrations in the growing substrate (achieved by phosphorus fertilization). The obtained results indicate the negative impact of drought and phosphorus fertilization on the growth of both species. In common beech, a negative impact of phosphorus fertilization on the adaptive capacity to drought was demonstrated by unfavorable ratios between fine root mass and the mass of other organs. The sessile oak provenances under the impact of drought showed a different root collar diameter/stem height increment ratio, which indicates their different phenotypic plasticity as a consequence of adaptation to different frequencies of dry periods in their natural habitats.

Važno je znati kako će klimatske promjene utjecati na pojedine šumske vrste, a pritom je jednako važno istraživati i mjeriti značajke biljaka koje je relativno lako kvantificirati, a koje su snažno povezane s cjelokupnim funkcioniranjem biljke. Iz toga je razloga provedeno istraživanje funkcionalnih značajki lišća na petogodišnjim sadnicama obične bukve (Fagus sylvatica L.) i hrasta kitnjaka (Quercus petraea /Matt./ Liebl.) porijeklom iz dviju provenijencija čija se staništa odlikuju sličnim orografskim i edafskim, a različitim klimatskim značajkama, što je posebno izraženo u količini oborine. Prema tomu, jedna je provenijencija s područja Slavonskoga Broda koja raste na staništu s manjom količinom oborine (suha provenijencija), a druga s područja Karlovca koja uspijeva na staništu s većom količinom oborine (vlažna provenijencija). Na lišću biljaka iz tih provenijencija mjerena je površina lišća (LA), gustoća puči (SD), lisna masa izražena po površini (LMA) i sadržaj suhe tvari u lišću (LDMC). Provedeno istraživanje funkcionalnih značajki lišća potvrdilo je da je hrast kitnjak u odnosu na običnu bukvu bolje prilagođen na sušne stanišne uvjete pa se može pretpostaviti da će pod utjecajem globalnih klimatskih promjena biti kompetitivniji u odnosu na običnu bukvu. Međutim, obična je bukva pokazala veću fenotipsku plastičnost koja joj može omogućiti bolju prilagodbu na buduće suše stanišne uvjete. Nadalje, utvrđeni obrazac diferencijacije sušnije i vlažnije provenijencije, uzimajući u obzir obje vrste, pokazuje njihovu ekotipsku diferencijaciju. Pri razmatranju utjecaja klimatskih promjena na prirodne populacije tih dviju vrsta treba uzeti u obzir njihovu fenotipsku plastičnost, ali i uočenu funkcionalnu ekotipsku diferencijaciju.

The negative impact of drought on plant growth may be modified by different availability of mineral nutrients and by their adaptation to different local habitat conditions. In this study, we examine the impact of drought, fertilization with phosphorus and provenance, as well as their interactions, on the growth and allometric growth relationships between belowground and aboveground organs of common beech (Fagus sylvatica) and sessile oak (Quercus petraea). The research was conducted on saplings originating from two mature mixed stands (dry and wet provenances) dominated by these species. In the common garden experiment, saplings were exposed to regular watering and drought in interaction with moderate and high phosphorus concentrations in the growing substrate (achieved by phosphorus fertilization). Obtained results indicate negative impact of drought and phosphorus fertilization on the growth of both species. In common beech, phosphorus fertilization had a negative impact on its adaptive capacity to drought, because of the unfavourable ratios between fine root mass and mass of other organs. The sessile oak provenances under the impact of drought showed a different root collar diameter/stem height increment ratio, which indicates its different phenotypic plasticity as a consequence of adaptation to different frequencies of dry periods in their natural habitats.