Chloroplast movement rapidly ameliorates the effects of suboptimal light intensity by accumulating along the periclinal cell walls, as well as the effects of excess light by shifting to the anticlinal cell walls. These acclimation responses are triggered by phototropins located at the plasma membrane and chloroplast envelope. Here, we used a recently developed non-invasive system sensitive to very small changes in red light leaf transmittance to perform long-term continuous measurements of dark–light transitions. As a model system, we used variegated Pelargonium zonale leaves containing green sectors (GS) with fully developed chloroplasts and achlorophyllous, white sectors (WS) with undifferentiated plastids, and higher phototropin expression levels. We observed biphasic changes in the red-light transmittance and oscillations triggered by medium intensities of white light, described by a transient peak preceded by a constant decrease in transmittance level. A slight change in red-light transmittance was recorded even in WS. Furthermore, the chloroplast position at lower light intensities affected the rapid light curves, while high light intensity decreased saturated electron transport, maximum quantum efficiency of photosystem II, and increased non-photochemical quenching of chlorophyll fluorescence and epidermal flavonoids. Our results extend the knowledge of light-dependent chloroplast movements and thus contribute to a better understanding of their role in regulating photosynthesis under fluctuating light conditions.

In a high, middle-aged stand of European hornbeam, on a site of mesophilous pedunculate oak, European hornbeam and narrow-leaved ash in the unflooded part of Ravni Srem (Carpino betuli-Quercetum roboris (Anić, 1959) Rauš 1971. subass. Fraxinetosum angustifoliae Tomić, 2007), the following tree species from the natural forest community were present: narrow-leaved ash, field maple and field elm. Pedunculate oak, a primary edificator of the community and economically the most important species was absent. The stand is 55 years old and originates from a failed regeneration of pedunculate oak. Thus, the silvicultural prescription is restoration. The number of trees in the unthinned part of the stand (EP 1) was 1217 trees per hectare and in the thinned part (EP 2) 530 trees per hectare. In the thinned part of the stand, 43.5% of the total number of trees and 40% of the total number of trees of European hornbeam were counted, compared to the unthinned part of the stand. The quadratic mean diameter (dg) and dominant trees diameter (Dg20) in the unthinned part of the stand were 17.4 and 23.6 cm and in the thinned part of the stand 19.0 and 27.6 cm. The Lorey's mean height and the dominant heights were between 22.2 and 23.9 m on EP 1 and 20.5 to 22.2 on EP 2. The amount of European hornbeam seed on the soil surface in different stands is similar. In the unthinned part of the stand, the mean number of European hornbeam seeds was 1195 pcs m-2 (100%) and in the thinned part 1177 pcs m-2 (98.5%). The mean number of healthy seeds on the soil surface in the thinned and unthinned stands was 1117-1142 pcs m-2. The seeds from previous years participate with 12.2-15.0% (136-171 pcs m-2) and the seeds from the 2018 mast year 85.0-87.8% (971-981 pcs m-2), with 95% of the seeds being healthy (971-981 pcs m-2). Due to the effect of thinnings, the stands that were dominated by European hornbeam become more mixed, which is a new element that defines the process of the restoration in the future. Seedbank in the middle-aged stand designated for restoration under different managing strategies is made up of 85-88% of healthy seeds from 2018, with 12-15% from previous years.

Istraživanja su obavljena u kulturi smreke (Picea abies /L./ Karst.), koja je osnovana sa 5.000 sadnica po hektaru na staništu planinske šume bukve na nadmorskoj visini 870 m. Na osnovi usporedbe elemenata rasta istraživane kulture s elementima rasta u drugim mladim do srednjedobnim kulturama smreke, istraživana kultura je u kategoriji visokoproizvodnih kultura u Srbiji i šire u Europi. Na trajnoj pokusnoj plohi, u dobro sklopljenom dijelu istraživane smrekove kulture u starosti 32 godine, izmjereno je 3.911 stabala po hektaru, s volumenom od 384,17 m3·ha-1, a ukupno evidentiran prirast drvne zalihe sastojine do 40. godine iznosio je 561,85 m3·ha-1, a do 50. godine 819,1 m3·ha-1. Na osnovi dvije prorjede, u 32. i 40. godini i naknadno posječenih tanjih stabala u razdoblju od 33. do 40. god., na pokusnoj plohi ukupno je posječeno 2.844 stabla po hektaru (72,7%) volumena 279,4 m3·ha-1 (tablica 1). Numerički pokazatelji strukture stabala na pokusnoj plohi u 32., 40. i 50. godini prikazani su u tablici 2, a debljinska struktura na grafikonima 2, 3 i 4. Za definiranje utjecaja prorjeda na prirast stabala uspoređen je tečajni debljinski (idt) i visinski (iht) prirast u razdoblju od 25. do 32. godine i 33.-40. godine kod detaljno analiziranih dominantnih stabala (D100 i D400), a na sastojinskoj razini uspoređen je tečajni debljinski (idt) i visinski (iht) prirast u razdoblju od 33. do 40. godine i 41.do 50. godine kod dominantnih stabala (D100 i D400). Testiranje razlika između tečajnih prirasta u različitim razdobljima obavljeno je uz pomoć t-testa. Na razini sastojine uspoređen je i tečajni prirast promjera, temeljnice i volumena svih stabala i stabala budućnosti (311 kom.∙ha-1) u razdoblju od 33.-40. godine i u razdoblju od 41.-50. godine. Neparametrijski Kolmogorov-Smirnov test korišten je za međusobnu usporedbu struktura stupnja vitkosti (odnos h/d1,3). Istraživanja su omogućila da se definira utjecaj prorjeda na prirast i stupanj vitkosti različitih kategorija stabla i sastojine u dva starosna razdoblja sastojine, 33.-40. i 41.-50. godine. Prva prorjeda u 32. godini, pri visini dominantnih stabala 15 m, imala je karakter selektivne prorjede, bila je niska (qd<0,85) i jaka (jačina prorjede je 36% volumena). Prorjeda je obavljena u starosti sastojine koja značajnije ne odstupa od razdoblja kada se izvode prve „komercijalne“ prorjede u Europi. Međutim, tokovi tečajnog debljinskog prirasta detaljno analiziranih dominantnih stabala (D100 i D400) pokazali su da je prekasno izvršiti prorjedu u 32. godini, a model rasta (prirasta) visina је pokazao kulminaciju u 25. godini (kada su dominantna stabla postigla visinu 11 m), pa bi se 25. godina mogla označiti i kao godina u kojoj je najkasnije trebalo izvršiti prvu komercijalnu prorjedu (grafikon 7). Zatečeni velik broj stabala, s velikom drvnom zalihom po hektaru, u 32. godini i jaka prorjeda uvjetovali su visoki iznos prorjednog etata, od 115,13 m3∙ha-1, što je u kategoriji najviših iznosa volumena koji se okvirno preporučuju u literaturi za sličnu starost smrekovih kultura. U razdoblju od 33.-40 godine debljinski prirast je iznosio kod preostalih stabala 0,31 cm∙god-1, a kod stabala budućnosti 0,54 cm∙god.-1 (tablica 7). Dominantna stabla, posebno 400 najdebljih stabala po hektaru, nalazila su se u fazi velikog visinskog prirasta u vrijeme i poslije prorjede u 32. godini (tablica 5 i 6), što je za posljedicu imalo povećanje stupnja vitkosti stabala, odnosno povećanje nestabilnosti sastojine (grafikon 8). Druga prorjeda u 40. godini, pri visini dominantnih stabala preko 20 m, imala je karakter selektivne prorjede, bila je niska (qd<0,85) i jaka (jačina prorjede je 34% volumena). Jaka prorjeda u 40. godini, s prorjednim etatom 142,28 m3∙ha-1, uvjetovala je veći debljinski prirast, odnosno bolju reakciju debljinskog prirasta na preostalim stablima, u odnosu na prorjedu u 32. godini. Stabla budućnosti imali su za 29%, a dominantna stabala (D100 i D400) za 36-42%, veći debljinski prirast u starosnom razdoblju od 41.-50. godine, u odnosu na starosno razdoblje 33.-40. godine, što je uz opadajući trend visinskog prirasta uvjetovalo i manji stupanj vitkosti, odnosno veću stabilnost stabala i sastojine (grafikon 8). Na osnovi navedenog, proizlazi da su provedene jake prorjede doprinijele uspostavljanju povoljnih odnosa u debljinskom i visinskom rastu stabala u istraživanoj kulturi i time poboljšale njihovu stabilnost.

U radu su prikazane značajke rasta jednogodišnjih biljaka sladuna u uvjetima potpunog svjetla u poljskom pokusu 2016. godine. U odnosu na višegodišnji prosjek (1981.–2010. godine) srednja temperatura zraka u vegetacijskom razdoblju 2016. godine bila je veća za 1.3°C, a količina oborina za 30.1 mm. Broj ožiljaka terminalnih pupova na jednogodišnjim biljkama sladuna (Slika 1), definira broj faza rasta u visinu na temelju kojega su izdvojeni tipovi rasta biljaka: biljke s jednofaznim, dvofaznim i trofaznim rastom. U analiziranom uzorku, 39,8% biljaka pripada jednofaznom tipu rasta, 58,2% dvofaznom, a svega 2,0% trofaznom tipu rasta (Slika 2). S obzirom na mali broj biljaka s trofaznim rastom u visinu, sve biljke su podijeljene u dvije skupine: biljke sa jednofaznim i biljke sa višestrukim rastom u visinu (Tablica 2). Postoje statistički značajne razlike u varijancama uzoraka kod svih značajki rasta između biljaka s jednofaznim i višestrukim rastom na razini p < 0,05, a na razini p < 0,01 između srednjih vrijednosti svih analiziranih elemenata rasta između biljaka s jednofaznim i višestrukim rastom. Primjetno je da raspodjela svih elemenata rasta varira između dvije definirane skupine biljaka. S obzirom na visinu primarnog rasta (H1), biljke s jednofaznim rastom su po apsolutnoj varijabilnosti nešto manje varijabilne, a po relativnoj duplo manje varijabilne od biljaka s višestrukim rastom, s blago pozitivnom asimetrijom. Što se tiče ukupne visine, biljke sa višestrukim rastom su znatno varijabilnije kako glede apsolutne varijabilnosti, tako i relativne varijabilnosti i s više izraženom desnom asimetrijom u odnosu na biljke s jednofaznim rastom. Kod biljaka s višestrukim rastom, apsolutna varijabilnost broja listova je dvostruko veća, a ukupne površine listova trostruko veća s izraženom desnom asimetrijom u usporedbi s biljkama s jednofaznim rastom. Postoje značajne razlike između raspodjela biljaka s jednofaznim i višestrukim rastom u visinu. Biljke s jednofaznim rastom imaju manju ukupnu visinu, manji promjer korjenovog vrata, manji broj i ukupnu površinu listova, ali se odlikuju većom srednjom visinom primarnog rasta u odnosu na biljke sa višestrukim rastom, što ukazuje na različite značajke rasta u početnoj fazi i tijekom vegetacijskog razdoblja između ovih tipova biljaka.

The paper analyzes the application of silvicultural measures in young stands in the area of National Park 'Fruška gora', which occurred after the clear-cutting and rep- resent the final stage in the process of regressive succession of zonal communities in the southern peripheral area of the Pannonia (Quercetum cerridis virgilianae B. & Jovanović Vukićević 1977). After clear-cutting the largest share in stands has a lime, coppice origin. Colonization and undisturbed development of invasive neophytes, tree of Heaven (Ailanthus altissima Swingle /Mill./), is a factor of their further degradation. Tree of heaven suppresses a lime from the stand structure, usually the only remaining species from natural communities that has a biological potential to sustain the further development of degraded stands. The aforementioned processes are most intense so far undermines diversity of natural forest communities. The study was conducted in the peripheral area of NP 'Fruška gora' (MU 'Gvozden-jak-lice', division 54, section g) in a stand with different participation of tree of heaven in the structure. In two permanent sample plots were measured the diameter at breast height of all trees and the height of a number of trees for the construction of height curves and calculation of wood volume of represented tree species. On the experimental plot 1 (OP-1), in the upper part of stand (170 m a.s.l.), at the age of 17 years there were seven tree species with a total of 6518 trees ha-1, with basal area of 26.24 m2ha-1 and wood volume of 219.13 m3ha-1. The most represented tree species is white lime, with 65.0% in the number of trees and 83.5% by volume, other types of natural communities are represented with 32.7% in the number of trees and 9.7% by volume, and the tree of heaven is represented with 2.3% in the number of trees and 6.8% by volume. On the experimental plot 2 (OP-2), in the lower part of stand (130 m a.s.l.), at the age of 20 years there were eight tree species with a total of 4045 trees ha-1, with basal area of 34.68 m2ha-1 and wood volume of 338.55 m3ha- 1. The most represented tree species is white lime, with 45.5% in the number of trees and 13.2% by volume, other types of natural communities are represented with 16.5% in the number of trees and 1.2% by volume. Tree of heaven is represented with 35.9% in the number of trees and 80.5% by volume and black locust with 1.9% by trees and 4.9% by wood volume. Mean and dominant diameters and heights of tree of heaven indicate dominance in growth compared to the mean and dominant diameter and height of the lime. To limit the spread of tree of heaven in the stands and, generally, in colonized edges of the NP 'Fruška gora', where the trees of tree of heaven are in the stage of fruiting, as a selection criterion for their removal is proposed the sexual dimorphism. Recorded ratio of male (without seed) and female (with seed) trees of tree of heaven, and negligible presence of mixed flowers on the male trees, provides an opportunity for the implementation of sexual dimorphism as a selection criteria in thinning to stop the spread of tree of heaven by generative way. The crown canopy of lime, and in this context, the crown canopy of grown male tress of tree of heaven, in parts of stands where it dominate, is a factor of self-thinning of tree of heaven in a lower layer of colonized stands.

The paper presents the growth characteristics of one-year-old seedlings of three autochthonous oak species (Fagaceae family): Turkey oak (Quercus cerris L.), Hungarian oak (Quercus frainetto Ten.) and downy oak (Quercus pubescens Willd.) in suboptimal growing conditions. The analyzed oak species are widely distributed in Serbia. One of the most important benefits of oak species is wood production (Hungarian and Turkey oak), and they have a promising role for the use in the future regarding the climate change as all species can be encountered on dry sites. Acorns were collected in the autumn of 2017 in natural stands and a sample of 400 acorns per each oak species was immediately sown in a nursery seedbed in the form of a random block system with four replicates. At the end of 2018, the available sample of seedlings was analyzed morphometrically. The seedlings were classified according to the number of shoot growth flushes into one-flush-growth and multi-flush growth seedlings. Turkey Oak had the highest number of seedlings which also recorded higher values in total height, root collar diameter and number of leaves. These results were obtained on alkaline soil with the presence of weeds and rodents and the absence of irrigating. The presence of multi-flush growth was recorded in all three oak species. Differences between analyzed three oak species exist in these suboptimal conditions. However, in full light conditions, a similar growth pattern was recorded, indicating to the similar adaptability of the species.