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Dugotrajne će suše u budućnosti dodatno opteretiti šumske ekosustave smanjujući njihovu produktivnost i sveukupnu bioraznolikost što bi moglo rezultirati izmjenom omjera vrsta u mješovitim šumskim sastojinama diljem Europe. Hrast kitnjak bi u odnosu na običnu bukvu mogao postati daleko konkurentniji, zbog dubljeg zakorijenjivanja, kseromorfnije strukture lišća i brzog oporavka asimilacije CO2 nakon popuštanja suše. Pod utjecajem klimatskih promjena u posljednjih 20-ak godina na području Europe dolazi do ometanja uredne ishrane šumskoga drveća s fosforom (P) na što ukazuje opadanje koncentracije P u lišću. Iako istraživanje fiziološke uloge P u metabolizmu šumskoga drveća trenutno predstavlja „state of the art“ problematiku, u literaturi je slabo zastupljena njegova uloga u sušnom stresu šumskoga drveća. Genetska raznolikost i unutarvrsne adaptivne varijacije u odgovoru na sušu kod obje vrste na području jugoistočne Europe do sada nisu bile istraživane. Optimalna ishranjenost šumskoga drveća s P mogla bi podići njihovu toleranciju prema suši jer P regulira fotosintezu i glikolizu te na taj način kontrolira asimilaciju CO2 i kasniju upotrebu ugljikohidrata za produkciju biomase. Optimalna ishranjenost s P pozitivno utječe i na sposobnost zaštite i popravka oštećenog fotosintetskog aparata uslijed pojave oksidacijskog stresa izazvanoga sušnim stresom. Obična bukva i hrast kitnjak diljem Europe tvore mješovite šumske zajednice koje pridolaze na cijelom spektru šumskih tala koja se odlikuju različitom vlažnošću i koncentracijama lakopristupačnog P u tlu. Ciljevi ovoga projekta (kojega financira Hrvatska zaklada za znanost) su utvrditi: (i) utjecaj povišene koncentracije P u tlu na toleranciju obične bukve i hrasta kitnjaka prema sušnom stresu, (ii) postojanje lokalne adaptiranosti provenijencija obične bukve i hrasta kitnjaka na sušni stres, kao i genotipskih razlika u toleranciji na sušu pod utjecajem povišene koncentracije P u tlu i (iii) postojanje tzv. memorijskih efekata kod obične bukve i hrasta kitnjaka nakon pretrpljenog sušnog stresa te utjecaj povišene koncentracije P u tlu na takve efekte.

This research was conducted on four-year-old saplings of common beech and sessile oak originating from two mature mixed beech-oak stands from the Republic of Croatia (RH), which are characterized by similar orographic and edaphic (chemical composition and mechanical soil structure) conditions. In addition, both stands belong to the same phytosociological association, Epimedio-Carpinetum betuli (Horvat 1938) Borhidi 1963. However, during the development of the studied saplings in the period from 2016 to 2020, stands from north-western part of the RH near Karlovac (KA) were more frequently exposed to drought periods than stands from eastern part of RH near Slavonski Brod (SB). Therefore, the aim of this study was to examine the impact of drought on the functional adaptation of growth and dry mass production of common beech and sessile oak saplings. Differences between stands (KA vs. SB) and species (beech vs. oak) were examined using two-factorial ANOVA with respect to a growth and dry mass production parameters, including their allometric relationships. According to the obtained results, the saplings from the KA stand had a thicker and lower stem, rooted deeper, and had a higher dry mass of coarse and fine roots compared to the saplings from the SB stand. This indicates that the saplings from the KA stand could be functionally more adapted to the drought habitat than the saplings from the SB stand due to more frequent exposure to drought periods. Such a result could be the consequences of different phenotypic modifications (drought reactions) and/or actual genetic differences between the studied stands, which could not be more accurately distinguished on this occasion. Furthermore, sessile oak saplings rooted deeper and had a higher dry mass of coarse roots than the common beech saplings that rooted shallower and had a higher dry mass of fine roots. This result corresponds to the previous knowledge on pattern of functional adaptation of sessile oak and common beech to moisture and/or dryness of the habitat, which differs in that sessile oak is oriented to absorb water from deeper soil layers by taproot, while common beech is oriented to absorb precipitation water from shallower layers of soil by fine roots.

This research was conducted on five-year-old saplings of common beech (Fagus sylvatica L.) and sessile oak (Quercus petraea /Matt./ Liebl.) originating from two mature mixed beech-oak stands from the Republic of Croatia. One stand is from the area of Slavonski Brod and one from the area of Karlovac. These two provenances are characterized by similar orographic and edaphic (chemical composition and mechanical soil structure) conditions, but differ in climate, especially in precipitation. In Slavonski Brod provenance average total annual precipitation is 770 mm (dry provenance) and in Karlovac provenance 1112 mm (wet provenance). During 2021, after the establishment of field trial, the saplings grew into two types of substrates. One type of substrate was a treatment with an increased phosphorus concentration (+P) and another type of substrate was a treatment with a lower phosphorus concentration (-P). The aim of this study was to examine the influence of different phosphorus concentrations in the substrate on leaves functional traits (phosphorus concentration in leaves, leaf dry matter content (LDMC), leaf mass per area (LMA), etc.) in beech and oak saplings originating from dry and wet provenance. The results showed that in the +P treatment there was a significant increase in the concentration of phosphorus in the leaves of both species originated from both provenances. However, LDMC and LMA in the +P treatment were significantly higher than the -P treatment in common beech, while LDMC and LMA in sessile oak were the same in both treatments. Saplings originating from dry provenance had a significantly higher LDMC and LMA than saplings from wet provenance. Research has shown that different phosphorus concentrations have different effects on the functional traits leaves depending on the species and provenance.

This research was conducted on a four-year-old common beech and sessile oak saplings originating from two mature mixed common beech and sessile oak stands (provenance) from the Republic of Croatia (HR). Provenances differ in annual amount of precipitation, which in provenance Slavonski Brod (SB) from the eastern part of the HR is about 770 mm (dry provenance), and in Karlovac (KA) from the north-western part of the HR is about 1112 mm (wet provenance). During year 2021, after the establishment of the experimental trail, the transplanted saplings grew into two soil types, one was characterized by high (0.30 g P2O5/l soil) and the other by low (0.16 g P2O5/l soil) phosphorus (P) concentration. The aim of this study was to examine the effect of higher soil P concentration on the average onset of spring bud burst and autumn leaf senescence in beech and oak saplings. The results showed that the onset of bud burst and leaf senescence in beech compared to oak saplings occurred significantly earlier, in six and ten days, respectively. Differences in the onset of bud burst and leaf senescence between oak provenances were not significant, whereas these differences between beech provenances were significant. Therefore, the onset of bud burst and leaf senescence in beech of dry SB provenance compared to wet KA provenance occurred earlier in five and three days, respectively. The higher soil P concentration significantly affected only the onset of leaf senescence in beech saplings. This means that the onset of leaf senescence in beech saplings under the higher compared to lower soil P concentration occurred three days earlier in the dry SB provenance and four days earlier in the wet KA provenance.

This research was conducted on a five-year-old common beech and sessile oak saplings originating from two mature mixed common beech and sessile oak stands (provenance) from the Republic of Croatia (HR). Provenances differ in annual amount of precipitation, which in provenance Slavonski Brod (SB) from the eastern part of the HR is about 770 mm (dry provenance), and in Karlovac (KA) from the north-western part of the HR is about 1112 mm (wet provenance). During year 2021, after the establishment of the experimental trail, the transplanted saplings grew into two soil types, one was characterized by high (0.30 g P2O5/L soil = +P tretment) and the other by low (0.16 g P2O5/l soil = -P treatment) phosphorus (P) concentration. In September 2021, the saplings of both species in the +P treatment had a higher concentration of P in the leaves than the sampligs from the -P treatment. The aim of this study was to examine the effect of different soil P concentration and/or phosphorus nutrition on the leaf dry matter content (LDMC = dry leaf mass/fresh leaf mass) and leaf mass per area (LMA = dry leaf mass/leaf area) of common beech and sessile oak saplings originated from dry and wet provenances. Results of factorial ANOVA with main effects of treatment (+P vs -P), provenences (dry BS vs. wet KA) and species (common beech vs. sessile oak) indicate that LDMC and LMA in +P treatment were significantly higher than in -P treatment, dry SB and wet KA provenance had similar LDMC and LMA, whilest the common beech had significantly lower LDMC and LMA than the sessile oak. Significant interaction between main effects ”treatment x species” indicate thad LDMC and SLA of sessile oak were similar in both +P and -P treatments, whilest LDMC and SLA of common beech in -P treatment were significantly lower than in +P treatment.