Ecophysiological Response of Sun-Exposed Common Beech (Fagus Sylvatica L.) Seedlings under Different Fertilization Levels

Sušenje obične jele (Abies alba Mill.) većih razmjera, prisutno u Hrvatskoj u zadnjih dvadesetak godina, dovelo je do netipičnih stanišnih uvjeta za rast podmlatka obične bukve (Fagus sylvatica L.) na područjima bu kovo-jelovih šuma. Ovakav razvoj događaja u kontradikciji je s prihvaćenom šumarskom praksom i poznatim ekološkim zahtjevima bukve (skiofilnost, osje tljivost na sušu). Da bismo odredili osnovne parametre ekofiziološkog odziva klijanaca bukve na uvjete punog osvjetljenja, postavljen je rasadnički pokus s tri razine gnojidbe (2, 4 i 6 g Osmocote Exact kompleksnog mineralnog gnojiva po litri uzgojnog supstrata), s ciljem oponašanja različitih uvjeta plodnosti tla (niska, optimalna i visoka dostupnost hraniva). Za svako tretiranje utvrđena je ukupna biomasa klijanaca (lišće, stabljika, korijen) a biljni materijal analiziran je na sadržaj biogenih elemenata (du šika, fosfora, kalija, kalcija i magnezija). Izmjerena je visina i promjer korije novog vrata biljaka, a morfologija korijena analizirana je pomoću WinRhizo softverskog paketa. Za mjerenja fotosintetskog kapaciteta, krivulje svjetlo snog zasićenja (0, 50, 250, 600 i 1200 µmol/m2s) i A-Ci krivulje (0, 100, 400, 700 i 1000 µmol CO2/l) dobivene su pomoću Li-Cor LI-6400 u kontroliranom okruženju. Visina, promjer i biomasa sadnica povećavala se s dozom gnojiva. Kon centracije N, P i K rasle su s dozom gnojiva, dok su koncentracije Ca i Mg po kazivale negativni učinak prekomjerne gnojidbe pri najvišoj dozi gnojiva. Duljina korijena, površina korijena i broj vrhova bili su najveći u srednjem tretiranju, a korijen se najslabije razvijao pri najvećoj dozi gnojidbe. U svim tretiranjima asimilacijska sposobnost bila je povezana s masom lišća (r2=0,59), koncentracijom N u lišću (r2=0,44) i korijenu (r2=0,58) kao i koncentracijom P u lišću (r2=0,45).The large-scale dieback of Silver fir (Abies alba Mill.), pre sent in Croatia in the past two decades, has led to atypical growth conditions for young Common beech (Fagus sylvatica L.) trees on beech-fir sites. This is in contradiction with recent forestry practice and ecological requirements of beech (skiophytic, drought sensitive). The aim of this study was to improve the fundamental understanding of the influence of light and nutrient availability in early stages of the development of beech seedlings. To determine the ecophysiological response of beech see dlings to full sunlight conditions, a nursery experiment was established with three fertilization treatments (2, 4 and 6g of Osmocote Exact per 1 liter of sub strate) to simulate various soil fertility conditions (low, optimal and high avai lability of nutrients). For every treatment, total biomass of seedlings (foliage, stem, roots) and the elemental concentrations of nitrogen, phosphorous, potassium, calcium and magnesium in the plant material determined by chemical analysis. Height and root-collar diameter have been measured and roots morphologi cally analyzed (WinRhizo software package). Light saturation curves (0, 50, 250, 600 in 1200 µmol/m2s) and A-Ci curves (0, 100, 400, 700 in 1000 µmol CO2/l) have been measured (Li-Cor LI-6400) in a controlled environment. Height, diameter and biomass of seedlings increased with fertilizer dose. Concentrations of N, P and K were growing with fertilizer dose, while Ca and Mg concentrations showed negative effects of overfertilization at the highest fertilizer dose. Root length, surface area and number of root tips were highest in the intermediate treatment while roots were least developed at the highest fertilizer dose. In all cases assimilation rates of seedlings corresponded well with leaf mass (r2 = 0,59), leaf (r2 = 0,44) and root total nitrogen (r2 = 0,58) and total leaf phosphorus (r2 = 0,45). Regardless of the conditions of full sunlight and an irregular water supply to seedlings while growing in the nursery, they showed a standard ecophysio logical response to fertilization treatments, indicating that despite the chan ged site conditions in beech and fir stands, the seedlings may keep the capacity to adapt to the environment. The most successful development of see dlings can be expected on nutrient-rich sites