Plant water use efficiency (WUE) links physiological processes to ecosystem-scale carbon and water cycles, making it a crucial parameter for climate change adaptation modelling. Climate and stratospheric ozone dynamics expose plants to varying intensity of ultraviolet-B radiation (UV-B), which affects stomatal function and transpiration. This meta-analysis evaluates UV-B effects on WUE using gas exchange and isotopic proxies. While UV-B radiation reduces stomatal conductance and transpiration, it also suppresses photosynthesis, particularly under non-saturating light. As a result, WUE remains unchanged or declines in UV-B exposed plants, depending on the measurement method. Instantaneous gas exchange-based WUE proxies indicate a decrease, whereas isotope-based proxies, integrating long-term fluxes, show no significant UV-B effect. The suppression of photosynthesis due to UV-B occurs only when UV-B lamps are used to increase the UV-B dose; when UV-B is excluded under field conditions there is no significant effect on WUE. Only some field studies report improved WUE under ambient UV-B, suggesting potential adaptive benefits. Overall, the findings challenge the assumption that UV-B-induced decreases in transpiration enhance WUE. Instead, they highlight a complex interplay between UV radiation, photosynthesis, and stomatal regulation, emphasizing the need to reconsider UV-B's role in plant water relations under future climate conditions.

• Klíčová slova
• photosynthesis, stable carbon isotopes, stomata, ultraviolet radiation,
• MeSH
• fotosyntéza účinky záření   MeSH
• klimatické změny MeSH
• průduchy rostlin účinky záření   fyziologie   MeSH
• rostliny * účinky záření   metabolismus   MeSH
• transpirace rostlin * účinky záření   fyziologie   MeSH
• ultrafialové záření * MeSH
• voda * metabolismus   MeSH
• Publikační typ
• časopisecké články MeSH
• metaanalýza MeSH
• Názvy látek
• voda * MeSH

UV-B and UV-A radiation are natural components of solar radiation that can cause plant stress, as well as induce a range of acclimatory responses mediated by photoreceptors. UV-mediated accumulation of flavonoids and glucosinolates is well documented, but much less is known about UV effects on carotenoid content. Carotenoids are involved in a range of plant physiological processes, including photoprotection of the photosynthetic machinery. UV-induced changes in carotenoid profile were quantified in plants (Arabidopsis thaliana) exposed for up to ten days to supplemental UV radiation under growth chamber conditions. UV induces specific changes in carotenoid profile, including increases in antheraxanthin, neoxanthin, violaxanthin and lutein contents in leaves. The extent of induction was dependent on exposure duration. No individual UV-B (UVR8) or UV-A (Cryptochrome or Phototropin) photoreceptor was found to mediate this induction. Remarkably, UV-induced accumulation of violaxanthin could not be linked to protection of the photosynthetic machinery from UV damage, questioning the functional relevance of this UV response. Here, it is argued that plants exploit UV radiation as a proxy for other stressors. Thus, it is speculated that the function of UV-induced alterations in carotenoid profile is not UV protection, but rather protection against other environmental stressors such as high intensity visible light that will normally accompany UV radiation.

• Klíčová slova
• UV-B, arabidopsis, carotenoid, photoreceptor, photosynthesis, xanthophyll,
• MeSH
• Arabidopsis * metabolismus   MeSH
• chromozomální proteiny, nehistonové metabolismus   MeSH
• fotosyntéza MeSH
• karotenoidy metabolismus   MeSH
• proteiny huseníčku * metabolismus   MeSH
• ultrafialové záření škodlivé účinky   MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH
• Názvy látek
• chromozomální proteiny, nehistonové MeSH
• karotenoidy MeSH
• proteiny huseníčku * MeSH
• Uvr8 protein, Arabidopsis MeSH Prohlížeč
• violaxanthin MeSH Prohlížeč

An increase in extreme weather and changes in other conditions associated with ongoing climate change are exposing ecosystems to a very wide range of environmental drivers that interact in ways which are not sufficiently understood. Such uncertainties in how ecosystems respond to multifactorial change make it difficult to predict the impacts of environmental change on ecosystems and their functions. Since water deficit (WD) and ultraviolet radiation (UV) trigger similar protective mechanisms in plants, we tested the hypothesis that UV modulates grassland acclimation to WD, mainly through changes in the root/shoot (R/S) ratio, and thus enhances the ability of grassland to acquire water from the soil and hence maintain its productivity. We also tested the potential of spectral reflectance and thermal imaging for monitoring the impacts of WD and UV on grassland production parameters. The experimental plots were manipulated by lamellar shelters allowing precipitation to pass through or to be excluded. The lamellas were either transmitting or blocking the UV. The results show that WD resulted in a significant decrease in aboveground biomass (AB). In contrast, belowground biomass (BB), R/S ratio, and total biomass (TB) increased significantly in response to WD, especially in UV exclusion treatment. UV exposure had a significant effect on AB and BB, but only in the last year of the experiment. The differences in the effect of WD between years show that the effect of precipitation removal is largely influenced by the potential evapotranspiration (PET) in a given year and hence mainly by air temperatures, while the resulting effect on production parameters is best correlated with the water balance given by the difference between precipitation and PET. Canopy temperature and selected spectral reflectance indices showed a significant response to WD and also significant relationships with morphological (AB, R/S) and biochemical (C/N ratio) parameters. In particular, the vegetation indices NDVI and RDVI provided the best correlations of biomass changes caused by WD and thus the highest potential to remotely sense drought effects on terrestrial vegetation.

• Klíčová slova
• UV radiation, drought, grassland, infrared thermography, nitrogen, precipitation, spectral reflectance,
• Publikační typ
• časopisecké články MeSH