The general aim of this work was to compare the leaf-level responses of different protective components to water deficit and high temperatures in Quercus cerris L. and Quercus robur L. Several biochemical components of the osmotic adjustment and antioxidant system were investigated together with changes in hormones. Q. cerris and Q. robur seedlings responded to water deficit and high temperatures by: (1) activating a different pattern of osmoregulation and antioxidant mechanisms depending on the species and on the nature of the stress; (2) upregulating the synthesis of a newly-explored osmoprotectant, dimethylsulphoniopropionate (DMSP); (3) trading-off between metabolites; and (4) modulating hormone levels. Under water deficit, Q. cerris had a higher antioxidant capacity compared to Q. robur, which showed a lower investment in the antioxidant system. In both species, exposure to high temperatures induced a strong osmoregulation capacity that appeared largely conferred by DMSP in Q. cerris and by glycine betaine in Q. robur. Collectively, the more stress-responsive compounds in each species were those present at a significant basal level in non-stress conditions. Our results were discussed in terms of pre-adaptation and stress-induced metabolic patterns as related to species-specific stress tolerance features.

This study tried to evaluate the influence of high temperatures (HT) on carbon assimilation of two oak species (Quercus cerris and Quercus robur). The screening of their populations, which are assumed to have a different resistance and acclimatization potential to adverse environmental conditions, can provide essential information for its implementation in reforestation strategies. By employing principal component analysis, the aim was to determine the most variable physiological characteristics of plants exposed to extremely HT during vegetation periods. After 2 d of HT treatment, a significant decline of photosynthetic and transpiration rates, and stomatal conductance were observed in plants of all investigated populations. The decrease of photosynthetic parameters after 2 d of HT treatment was regulated by the stomatal closure which caused the limitation of CO2 assimilation. Contrary, a chronic HT stress led to an increase in gs and inhibition of photosynthesis at the level of carboxylation.

Извод: Две half-sib линије храста цера (Quercus cerris L.) (C1 и C2) су у полу-контролисаним условима биле изложене различитим третманима: оптималној влажности земљишта-контрола (К), суши праћеној опоравком након поновног успостављања оптималне влажности земљишта (T1) и третману константне суше (T2). Испитиване су промене физиолошких параметара везаних за процес фотосинтезе у корелацији са примењеним третманима. Третман T2 је утицао на значајну редукцију интензитета фотосинтезе, стоматалне проводљивости и тренутне ефикасности коришћења воде, као и на сигнификантно повећање интерцелуларне концентрације CO 2 код обе half-sib линије. У односу на контролу, третман T2 није довео до значајног варирања максималне фотохемијске ефикасности код испитиваних half-sib линија. На третману T1, друга half-sib линијa (C2) показала је бољу способност опоравка интензитета фотосинтезе и стоматалне проводљивсти након поновног заливања, док је на истоименом третману пре опоравка ефикасније користила воду у поређењу са првом half-sib линијом (C1). Резултати истраживања указују на специфичне адаптивне предиспозиције испитивних half-sib линија у односу на сушни стрес и опоравак.

No abstract

The paper presents the impact of periodic soil drought on physiological parameters important for bioproductivity of mountain beech populations. The investigated forest population was located near Fruška gora mountain peak, where water runs off quickly, and consequently lack of soil humidity develops very often. Decreasing trends of photosynthesis, transpiration, water use efficiency and stomatal conductance (gs) during the growing season were evident, in correlation with a shortage of precipitation. Diurnally, photosynthesis of beech leaves showed rhythmical changes. It was the most intensive in the morning, then decreased between noon and 1 pm, and increased again during early afternoon. High leaf temperature and water deficit in the deeper soil layers caused a decreasing trend in photosynthesis and daily rhythmic changes of the transpiration rate and water use efficiency. Although surface soil water capacity did not show a significant decreasing trend from July to September, a lack of precipitation was observed, which probably caused a lack of moisture in deeper soil layers, resulting in a decline in photosynthesis and transpiration. Physiological status, linked to primary photosynthetic productivity of forests, could be a significant indicator of environmental conditions and trends in climate changes.