U ovom radu prikazani su rezultati izmjere parametara koji opisuju fotosintetsku aktivnost bukovih klijanaca pod utjecajem suboptimalne ishranjenosti s mineralnim hranivima. Cilj rada bio je približiti ovu problematiku šumarskoj praksi kroz raspravu dobivenih rezultata u kontekstu dosadašnjih spoznaja o utjecaju mineralne ishrane na fotosintetski proces šumskoga drveća. U rano proljeće 2019. godine bukovi klijanci porijeklom iz jedne prirodne mješovite sastojine hrasta kitnjaka i obične bukve presađeni su u sterilni supstrat (agroperlit). Nakon presadnje redovito su zalijevani (tretirani) kompletnom hranivom otopinom (KO tretman), odnosno hranivim otopinama u kojima su izostavljeni dušik (–N tretman), fosfor (–P tretman), magnezij (–Mg tretman) ili željezo (–Fe tretman). Na šest klijanaca unutar svakog od pet prethodno opisanih tretmana tijekom vegetacijskog razdoblja 2019. godine redovito su mjereni sljedeći parametri: stopa fotosinteze (A), provodljivost puči (gs), intercelularna koncentracija CO2 (ci), indeks relativnog sadržaja klorofila u lišću (CCI) te indeks fotosintetske učinkovitosti (PIABS). Svi parametri bili su lošiji kod klijanaca iz –N, –P i –Mg tretmana u odnosu na klijance iz KO tretmana. Takav rezultat vjerojatno proizlazi iz fizioloških funkcija N, P i Mg koji sudjeluju u građi proteina i enzima, prometu i skladištenju energije te građi klorofila, što je sve skupa neophodno za uredno funkcioniranje cjelokupnog fotosintetskog procesa. Unatoč važnoj ulozi Fe u gotovo svim životnim procesima biljaka pa tako i fotosintezi svi mjereni parametri kod klijanaca iz –Fe i KO tretmana bili su podjednaki. Međutim, za razliku od N, P i Mg koji pripadaju skupini makrohraniva, Fe pripada skupini mikrohraniva, čije su koncentracije u biljnom tkivu relativno niske. Prema tome, moguće je pretpostaviti da su istraživani klijanci iz tla prirodne sastojine i/ili iz rezervi u sjemenu tijekom početne faze svoga razvoja uspjeli usvojiti i/ili mobilizirati dovoljnu količinu Fe koja im je bila dostatna za normalno funkcioniranje tijekom cijelog vegetacijskog razdoblja, bez obzira na kasniju primjenu tretmana. S obzirom na ovakav rezultat, inicijalno praćenje parametara fotosintetske aktivnosti bit će nastavljeno tijekom sljedećih nekoliko vegetacijskih razdoblja. U tom periodu planira se započeti s praćenjem dinamike vegetativnoga rasta, fenologije listanja i razvoja vizualnih simptoma pri suboptimalnoj ishranjenosti obične bukve s mineralnim hranivima s ciljem dodatnog približavanja ove problematike šumarskoj praksi. This paper presents the results of measuring parameters that describe the photosynthetic activity of beech seedlings under suboptimal mineral nutrition. The aim of paper was to present the issue of mineral nutrition of forest trees to forestry practice through the discussion of the obtained results in the context of previous knowledge about the impact of mineral nutrition on the photosynthetic process of forest trees. In the early spring of 2019, beech seedlings originating from a natural mixed stand of sessile oak and common beech were transplanted into a sterile substrate (agroperlite). After transplanting, the seedlings were regularly watered (treated) with a complete nutrient solution (KO treatment), and nutrient solutions in which nitrogen (–N treatment), phosphorus (–P treatment), magnesium (–Mg treatment) or iron (–Fe treatment) were omitted. The following parameters were regularly measured on six seedlings within each of the five previously described treatments during the 2019 growing season: rate of photosynthesis (A), stomatal coonductance (gs), intercellular concentration of CO2 (ci), relative chlorophyll content index (CCI) and the photosynthetic performance index (PIABS). All parameters were worse in seedlings from –N, –P and –Mg treatment compared to seedlings from KO treatment. Such a result is probably due to the physiological functions of N, P and Mg that participate in the structure of proteins and enzymes, energy turnover and storage, and the structure of chlorophyll, which together are necessary for the proper functioning of the overall photosynthetic process. Despite the important role of Fe in all life processes of plant, including photosynthesis, all measured parameters in seedlings from –Fe and KO treatments were very similar. However, unlike N, P and Mg which belong to the group of macronutrients, Fe belongs to the group of micronutrients whose concentrations in plant tissue are relatively low. Therefore, it is possible to assume that the investigated seedlings from natural stand soil and/or from seed reserves during the initial phase of their development could absorb and/or retraslocate enough Fe for normal functioning throughout the growing season, regardless of subsequent treatment. Given such a results, initial monitoring of photosynthetic activity parameters will be continued over the next few growing seasons. In this period, it is planned to start monitoring the vegetative growth dynamics, leaf phenology and the development of visual symptoms under suboptimal mineral nutrition of beech seedlins in order to further approximate this issue to forestry practice.