Rhododendrons in numerous gardens in Central Europe are frequently endangered by adverse summer drought periods associated with the climate change. Therefore, in this work drought-resistance strategies in recent genotypes of these highly aesthetic shrubs were investigated. Dehydrated Rhododendron groenlandicum ‘Helma’, R. obtusum ‘Michiko’ and R. hybridum ‘Polarnacht’ showed high initial stomatal conductances (gS), after few days steeply falling to the stable minimum at ca. 20, 85 and 70% leaf relative water content (RWC), respectively. Except of ‘Polarnacht’, they had relatively large specific leaf area and ‘Michiko’ also free proline accumulation. On the other hand, R. repens ‘Scarlet Wonder’ and R. hybridum ‘Red Jack’ started with half gS values, continuously declining 1.5–2 fold longer compared to the first group of genotypes (RWC of ca. 60 and 75%, respectively). Both produced relatively thick leaves but did not show any osmotic adjustment. Among observed drought-resistance strategies, lower and longer period active transpiration with stomata sensitive to the water loss, as found in R. repens ‘Scarlet Wonder’ and R. × hybridum ‘Red Jack’, were accepted as the most effective for drought-affected rhododendron plantations.
Barberries as undemanding shrubs with high aesthetic value are often planted in city parks and street greeneries. However, severe urban environment combined with climate change puts pressure on these plants in terms of their ability to cope with drought. In order to avoid plantation fall-offs, a common garden experiment was carried out on the drought tolerance of two Asian barberry species, namely Hooker's barberry (Berberis hookeri Lem.) and warty barberry (Berberis verruculosa Hemsl. and Wils.). Higher leaf relative water content, postponed but more sensitive stomatal closure (decrease in stomatal conductivity for water) as well as osmotic adjustment (free proline accumulation) and antioxidant defence onset (total antioxidant activity of the hydrophilic phase), and faster photosynthetic pigment decomposition in Hooker's barberry transplants compared to warty barberry, point to better water management and advanced protection of leaf structures in this species under limited soil moisture. Moreover, warty barberry plants with half total leaf area suffered from drought earlier, because of enhanced soil water loss through evaporation. Thus, Hooker's barberry can be taken as more drought tolerant than its counterpart, therefore making it more suitable for plantings in areas that are prone to this environmental constraint.
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