The use of photosystem II (PSII) inhibitors allows simulating cascade of defense and damage responses, including the oxidative stress. In our study, PSII inhibiting herbicide metribuzin was applied to the leaf of the model plant species Chenopodium album. The temporally and spatially resolved cascade of defense responses was studied noninvasively at the leaf level by combining three imaging approaches: Raman spectroscopy as a principal method, corroborated by chlorophyll a fluorescence (ChlF) and infrared thermal imaging. ChlF imaging show time-dependent transport in acropetal direction through veins and increase of area affected by metribuzin and demonstrated the ability to distinguish between fast processes at the level of electron transport (1 − V_j) from slow processes at the level of non-photochemical energy dissipation (NPQ) or maximum efficiency of PSII photochemistry (Fv/Fm). The high-resolution resonance Raman images show zones of local increase of carotenoid signal 72 h after the herbicide application, surrounding the damaged tissue, which points to the activation of defense mechanisms. The shift in the carotenoid band indicates structural changes in carotenoids. Finally, the increase of leaf temperature in the region surrounding the spot of herbicide application and expanding in the direction to the leaf tip proves the metribuzin effect on slow stomata closure.

Plants produce specific terpenes, secondary metabolites conferring tolerance to biotic and abiotic stresses. Our study aims to investigate the effects of altitude, light intensity and season on contents of mono- and sesquiterpenes in needles of coniferous Norway spruce (Picea abies). Needles of current shoots representing upper and lower canopy were collected from adult trees growing along an altitudinal gradient (400–1100 m a.s.l.) in summer and autumn. After the extraction in cold heptane, the content of extractable terpenes was determined by gas chromatography coupled with mass spectrometry. Our results show that the total content of terpenes decreases with increasing altitude regardless of canopy position and season. Needles of the upper canopy have a higher total content of terpenes than lower canopy needles, but this difference decreases with increasing altitude in summer. Total content of extractable terpenes increases in autumn when compared to summer particularly in upper canopy needles of trees from high altitudes. Limonene, camphene, α-pinene and myrcene are the most abundant monoterpenes in spruce needles forming up to 85% of total monoterpenes, while germacrene D-4-ol is the most abundant sesquiterpene. Altitude, canopy position and season have a significant interactive effect on most monoterpenes, but not on sesquiterpenes. Terpenoid biosynthesis is thus tightly linked to growth conditions and likely plays a crucial role in the constitution of stress tolerance in evergreen conifers.

We investigated how reduced summer precipitation modifies photosynthetic responses of two model tree species—coniferous Norway spruce and broadleaved sessile oak—to changes in atmospheric CO₂ concentration. Saplings were grown under mountainous conditions for two growing seasons at ambient (400 μmol CO₂ mol^–1) and elevated (700 μmol CO₂ mol^–1) CO₂ concentration. Half were not exposed to precipitation during the summer (June–August). After two seasons of cultivation under modified conditions, basic photosynthetic characteristics including light-saturated rate of CO₂ assimilation (A_max), stomatal conductance (G_Smax), and water use efficiency (WUE) were measured under their growth CO₂ concentrations together with in vivo carboxylation rate (V_C) and electron transport rate (J) derived from CO₂-response curves at saturating light. An increase in A_max under elevated CO₂ was observed in oak saplings, whereas it remained unchanged or slightly declined in Norway spruce, indicating a down-regulation of photosynthesis. Such acclimation was associated with an acclimation of both J and V_C. Both species had increased WUE under elevated CO₂ although, in well-watered oaks, WUE remained unchanged. Significant interactive effects of tree species, CO₂ concentration, and water availability on gas-exchange parameters (A_max, G_Smax, WUE) were observed, while there was no effect on biochemical (V_C, J) and chlorophyll fluorescence parameters. The assimilation capacity (A_sat; CO₂ assimilation rate at saturating light intensity and CO₂ concentration) was substantially reduced in spruce under the combined conditions of water deficiency and elevated CO₂, but not in oak. In addition, the stimulatory effect of elevated CO₂ on A_max persisted in oak, but completely diminished in water-limited spruce saplings. Our results suggest a strong species-specific response of trees to reduced summer precipitation under future conditions of elevated CO₂ and a limited compensatory effect of elevated CO₂ on CO₂ uptake under water-limited conditions in coniferous spruce.

To ensure the selection of wheat genotypes that are resilient to future climatic conditions, with drought already being the most significant and acute problem in many areas, twenty winter wheat cultivars were tested for drought stress tolerance from the beginning of stem elongation (DC 30; Zadoks decimal codes) for 49 days (until the stage of grain development, DC 73–75) within an automatic phenotyping platform. The control plants were regularly irrigated to 70% of soil water capacity (SWC), while the drought-stressed plants were subjected to controlled drying until the permanent wilting point (15% of SWC) was reached. Then, the drought-stressed plants were rewatered again to 70% of the maximum SWC. After they recovered, the plants were again exposed to ambient weather conditions. The final yield formation parameters were assessed at the fully ripe stage. Our results showed that the genotypes originating in Western Europe manifested the highest response to the experimentally set drought in the grain number per spike measurement, while the genotypes originating in the warmer regions of southeastern Europe manifested the highest response to the experimental drought mainly in thousand grain weight measurement. Similar response patterns were evident for late- and early-maturing genotypes. The results indicate the potential of selecting genotypes with increased drought resistance even within the existing set of cultivars.