UV-screening and springtime recovery of photosynthetic capacity in leaves of Vaccinium vitis-idaea above and below the snow pack

Abstract

Evergreen plants in boreal biomes undergo seasonal hardening and dehardening adjusting their photosynthetic capacity and photoprotection; acclimating to seasonal changes in temperature and irradiance. Leaf epidermal ultraviolet (UV)-screening by flavonols responds to solar radiation, perceived in part through increased ultraviolet-B (UV-B) radiation, and is a candidate trait to provide cross-photoprotection. At Hyytiälä Forestry Station, central Finland, we examined whether the accumulation of flavonols was higher in leaves of Vaccinium vitis-idaea L. growing above the snowpack compared with those below the snowpack. We found that leaves exposed to colder temperatures and higher solar radiation towards the top of hummocks suffered greater photoinhibition than those at the base of hummocks. Epidermal UV-screening was highest in upper-hummock leaves, particularly during winter when lower leaves were beneath the snowpack. There was also a negative relationship between indices of flavonols and anthocyanins across all leaves suggesting fine-tuning of flavonoid composition for screening vs. antioxidant activity in response to temperature and irradiance. However, the positive correlation between the maximum quantum yield of photosystem II photochemistry (F/F) and flavonol accumulation in upper hummock leaves during dehardening did not confer on them any greater cross-protection than would be expected from the general relationship of F/F with temperature and irradiance (throughout the hummocks). Irrespective of timing of snow-melt, photosynthesis fully recovered in all leaves, suggesting that V. vitis-idaea has the potential to exploit the continuing trend for longer growing seasons in central Finland without incurring significant impairment from reduced duration of snow cover.

Seasonal Patterns in Spectral Irradiance and Leaf UV-A Absorbance Under Forest Canopies

“…Low temperature-enhanced flavonol synthesis is dependent on light (Bhatia et al, 2018), and although this could have relevance especially in high latitudes with extended daylight hours during summer, it seems unlikely to be the only mechanism producing the differences in I flav between adaxial and abaxial leaf sides that we found ( Figure S6). A combination of harsh environmental conditions, including excessive irradiance and low temperatures during early spring, could feasibly explain the trends in I flav , as reported for partially exposed plants compared to those under snowpack in winter (Solanki et al, 2019). This implies that differences in snow cover and winter PAI between the stands in our study might to some extent explain early spring stand-level differences in I flav.…”

Leaf-Level Spectral Fluorescence Measurements: Comparing Methodologies for Broadleaves and Needles

“…We used a PAM-2500 fluorometer (Heinz Walz GmbH, Effeltrich, Germany) and the cut shoots after one hour of dark acclimation (n = 5). F V /F M remained at the level of 0.78 ± 0.023 for lingonberry, 0.79 ± 0.012 for birch, and 0.83 ± 0.012 for pine, which is well within the range of non-stressed summer values for each of the respective species [38,39]. More details can be found in Table 1 Figure S1) in OC.…”

“…Second, because the leaves showed F V /F M levels typical for the species in the absence of stress (see Section 2.1. ), the potential impact of sustained physiological stress can also be ruled out [11,38,39]. We, therefore, suggest that the slightly higher levels of red/far-red ChlF ratio observed in 1N and 3N relative to those observed in birch and lingonberry leaves would respond to differences in [Chl] induced reabsorption coupled with differences in leaf morphology.…”

Pollen‐chemistry variations along elevation gradients and their implications for a proxy for UV‐B radiation in the plant‐fossil record

“…A second explanation is that the population-level random effects structures may be explained by the result of interactions of UV-B radiation with other environmental variables. Both experimental (Coffey, Prinsen, Jansen, & Conway, 2017) and field evidence (Martz et al, 2007;Solanki et al, 2019) indicate that plants can screen UV radiation more effectively under low temperatures, and that the accumulation of UV-B-absorbing compounds in plant-leaf tissue can sometimes be the result of interactive effects with temperature at high elevations and latitudes (Neale et al, 2021). For example, Martz et al (2007) assessed the variations in both the concentration and composition of UV-B-absorbing compounds in Pinus sylvestris needles using UV-exclusion field chambers in Finland, and found UV-A/B exclusion had a significant effect on five out of 46 soluble phenolic compounds within the leaf needles.…”