Nathalie Beaucourt

Physiological changes and UV protection in the aquatic liverwort Jungermannia exsertifolia subsp. cordifolia along an altitudinal gradient of UV-B radiation

Here we report the effects of a natural altitudinal gradient of UV-B radiation, from 1140 to 1816 m altitude, on the physiology of the aquatic liverwort Jungermannia exsertifolia Steph. subsp. cordifolia (Dumort.) Váña collected in mountain streams. Photosynthetic pigments, net photosynthesis and dark respiration rates, chlorophyll fluorescence, protein concentration, sclerophylly, and UV-absorbing compounds [both global UV absorbance of methanol-extractable UV-absorbing compounds (MEUVAC) and concentrations of five individual compounds] were measured. Two new caffeic acid derivatives were discovered: 5″-(7″,8″-dihydroxycoumaroyl)-2-caffeoylmalic acid and 5″-(7″,8″-dihydroxy-7-O-β-glucosyl-coumaroyl)-2-caffeoylmalic acid, whereas three additional compounds were already known in other species: p-coumaroylmalic acid, phaselic acid (both compounds in their cis- and trans- forms) and feruloylmalic acid. Most physiological variables changed considerably along the altitudinal gradient, but only six showed significant linear relationships with altitude: MEUVAC levels, the concentrations of the two new secondary compounds, the maximal apparent electron transport rate through PSII (ETRmax) and the maximal non-photochemical quenching (NPQmax) increased with altitude, whereas photoinhibition percentage decreased. A principal components analysis (PCA) was conducted to rank the values of the physiological and ecological variables obtained along the altitudinal transect, showing that those variables correlated with altitude were responsible for the ordination of the sampling points. The liverwort was not adversely affected by the changing conditions along the altitudinal gradient and, in particular, by the increasing UV-B irradiance, probably because the characteristics shown by high-altitude populations may confer tolerance to high UV-B levels. The response to UV-B of the two new compounds suggests that they could be used as indicators of the spatial changes in UV-B radiation.

Influence of Temperature on the Effects of Artificially Enhanced UV-B Radiation on Aquatic Bryophytes Under Laboratory Conditions

We examined, under laboratory conditions, the influence of temperature (2 °C vs. 10 °C) on the physiological responses of two aquatic bryophytes from a mountain stream to artificially enhanced UV-B radiation for 82 d. These organisms may be exposed naturally to relatively low temperatures and high levels of UV-B radiation, and this combination is believed to increase the adverse effects of UV-B radiation. In the moss Fontinalis antipyretica, UV-B-treated samples showed severe physiological damages, including significant decreases in chlorophyll (Chl) and carotenoid (Car) contents, Chl a/b and Chl/phaeopigment ratios, Chl a fluorescence parameters Fv/Fm and ΦPS2, electron transport rate (ETRmax), and growth. In the liverwort Jungermannia cordifolia, UV-B radiation hardly caused any physiological change except for growth reduction. Thus, this liverwort seemed to be more tolerant to UV-B radiation than the moss under the specific experimental conditions used, maybe partly due to the accumulation of UV-B absorbing compounds. The influence of temperature on the effects of UV-B radiation depended on the species: the higher the UV-B tolerance, the lower the influence of temperature. Also, different physiological variables showed varied responses to this influence. Particularly, the lower temperature used in our study enhanced the adverse effects of UV-B radiation on important physiological variables such as Fv/Fm, growth, and Chl/phaeopigment ratios in the UV-B-sensitive F. antipyretica, but not in the more UV-B-tolerant J. cordifolia. Thus, the adverse effects of cold and UV-B radiation were apparently additive in the moss, but this additiveness was lacking in the liverwort. The Principal Components Analyses (PCA) conducted for both species with the physiological data obtained after 36 and 82 d of culture confirmed the above results. Under natural conditions, the relatively high water temperatures in summer might facilitate the acclimation of aquatic bryophytes from mountain streams to high levels of UV-B radiation. This may be relevant to predict the consequences of concomitant global warming and increasing UV-B radiation.

Effects of cadmium and enhanced UV radiation on the physiology and the concentration of UV-absorbing compounds of the aquatic liverwort Jungermannia exsertifolia subsp. cordifolia

The aquatic liverwort Jungermannia exsertifolia subsp. cordifolia was cultivated for 15 d under controlled conditions to study the single and combined effects of cadmium and enhanced ultraviolet (UV) radiation. Both cadmium and UV radiation caused chlorophyll degradation and a decrease in the maximum quantum yield of photosystem II (PSII), together with an increase in the mechanisms of non-photochemical dissipation of energy (increase in the xanthophyll index). Cadmium was more stressing than UV radiation, since the metal also influenced photosynthesis globally and caused a decrease in net photosynthetic rates, in the effective quantum yield of photosynthetic energy conversion of PSII, and in the maximal apparent electron transport rate through PSII. Ultraviolet radiation increased the level of trans-p-coumaroylmalic acid and cadmium increased trans-phaselic and feruloylmalic acids. The increase in these compounds was probably related to both a more efficient absorption of harmful UV radiation and an enhanced protection against oxidative stress. DNA damage was specifically caused by UV-B radiation, but was intensified under the presence of cadmium, probably because the metal impairs the DNA enzymatic repair mechanisms. Ultraviolet radiation and cadmium seemed to operate additively on some physiological processes, while other responses were probably due to either factor alone.

Assessing the UV-B Tolerance of Sun and Shade Samples of Two Aquatic Bryophytes Using Short-term Tests

Abstract Sun and shade samples of two aquatic bryophytes, the moss Fontinalis antipyretica and the liverwort Jungermannia exsertifolia subsp. cordifolia, were collected from a mountain stream and cultivated in the laboratory under two artificially imposed radiation regimes: control (only photosynthetically active radiation, PAR) and UV-B (PAR + UV-B). Samples were cultured at 2°C for 78 hr under continuous radiation to determine whether the physiological responses of the two bryophytes to UV-B radiation depended on their previous field acclimation to sun or shade conditions. We also aimed to study whether the short-term effects of UV-B were similar to those caused by longer exposure. Fontinalis antipyretica was more sensitive to UV-B treatment than Jungermannia exsertifolia subsp. cordifolia, showing significant decreases in several physiological variables indicative of vitality: PN rates, OD430/OD410, OD665/OD665a and especially Fv/ Fm. This higher sensitivity occurred in both sun and shade samples of the moss. These results reproduce the differences between both species that were found in previous more prolonged (36– 82 days) experiments. These types of short-term tests may therefore be used instead of long-duration tests to evaluate the UV-B tolerance of bryophytes. Shade samples were more sensitive to UV-B treatment than sun samples, but only in the more UV-B-sensitive species (Fontinalis antipyretica). Fv/Fm was the physiological variable that better discriminated both types of samples in the moss, since it decreased 42% in the shade samples and only 27% in the sun samples at the end of the culture period. In Jungermannia exsertifolia subsp. cordifolia, controls and UV-B-treated samples were not significantly different in either the sun or the shade samples. Principal Components Analyses (PCA) for each species, ranking the physiological results along the culture period for each radiation regime and field exposure strongly supported these conclusions and also showed that the loading factors of PCAs may be helpful for establishing the combination of key variables responsible for the differences between controls and UV-B-treated samples, or between UV-B-treated sun and shade samples.

Element Concentrations and Enrichment Ratios in the Aquatic Moss Rhynchostegium riparioides along the River Iregua (La Rioja, Northern Spain)

Abstract The concentrations of seven elements (N, P, K, Ca, Mg, Fe, and Na), five of which are macroelements, were measured in 3-cm apices of 17 populations of the euryecious aquatic moss Rhynchostegium riparioides (Hedw.) Card. located along the course of the Iregua River (La Rioja, northern Spain). A principal components analysis (PCA) revealed two key factors ordinating the sampling sites on the basis of their physicochemical data 1) substrate lithology, since the rivers upper course is predominantly siliceous whereas the middle and lower courses are influenced by CaCO3 and 2) human impact, especially observed in the irrigation channels of the lower course. The element concentrations in the tissues of R. riparioides, generally comparable to those cited for other aquatic bryophytes, were strongly and significantly correlated with the respective element concentrations in the surrounding water. Therefore, the PCA ordinating the moss populations on the basis of their element concentrations was highly coincident with the physicochemical PCA: the headwater populations had the lowest element concentrations, the middle course populations were notably Ca-enriched, and the lower course populations showed the highest concentrations of N, P, K and Na. The significant correlations between the element concentrations differentiated two groups of elements: mainly intracellular ones (N, P, and K), and mainly exchangeable ones (Ca and Mg). This dichotomy was also noticed in other respects 1) the relationship between the water and the tissue element concentrations was linear for N, P, and K, but similar to a Michaelis-Menten saturation-type curve in the case of Ca and Mg; 2) the quotients between the concentration of a given element in moss and in water (enrichment ratios, ER) were much higher for N, P, and K than for Ca and Mg; 3) only the tissue concentrations of Ca and Mg were correlated–negatively–with their respective ERs. Na showed somewhat peculiar characteristics, probably reflecting weak uptake efficiency and metabolic irrelevancy. ERs were strongly dependent on the respective element concentrations in water through hyperbolic relationships, suggesting that the uptake efficiency may be higher when elements are more diluted in water and decreases as the moss becomes saturated. This plasticity, to be expected in such an euryecious species as R. riparioides, would permit the acclimation of the different populations to changing water chemical conditions in order to avoid nutrient deficiencies.

Short-Term Physiological Responses of the Aquatic Liverwort Jungermannia exsertifolia subsp. cordifolia to KH2PO4 and Anoxia

Abstract The effects of four increasing levels of KH2PO4 on the physiology of the aquatic liverwort Jungermannia exsertifolia subsp. cordifolia were analyzed in the laboratory in the short term (15 d). The accumulation of P and K in the liverwort tissues was influenced (ANOVA) by the level of KH2PO4-enrichment and was significantly higher in the more enriched culture solutions. However, only the concentration of P was influenced by the effect of time (ANOVA), and the gradual P accumulation throughout the culture period contrasted with the fluctuations observed in K accumulation; these were presumably due to the higher liability of K to be leaked from the cells. Our results suggest that the analysis of P in transplants of J. cordifolia may be a useful bioindicator of short term water eutrophication both in the spatial and the temporal scales, although the highest PO43− concentration used in this study (20 mg liter−1) may induce a P saturation in J. cordifolia tissue (0.53% DM). The rates of net photosynthesis showed a significant quadratic regression with the tissue P concentration, which might resemble the action curve of mineral nutrients. Using this regression as an indicator, there was no clear deficiency zone, probably due to the relatively high tissue P concentration initially found in the liverwort. The lack of stimulation of net photosynthesis with increasing tissue P could be due either to a deficiency in other mineral elements such as N, or to an intrinsic inability to use the excess of nutrients. The decline in net photosynthesis when the tissue P concentration exceeded 0.45% DM could be interpreted as a toxicity process. Chlorophyll concentration was not affected by P enrichment, but the decline in the chlorophyll a/b ratio and in the proportions of chlorophylls to phaeopigments, together with the increase in the proportion of carotenoids to chlorophylls, suggested also P toxicity. This phenomenon needs further investigation to be confirmed in other species and conditions, but it may help to explain the disappearance of certain aquatic bryophytes in eutrophicated water courses. The physiological effects of increasing tissue K concentration (decreases in the rate of dark respiration and in the chlorophyll a/b ratio) were slighter than those of P, probably because the accumulation of K was lower than that of P (1.44 and 1.96 times the initial value, respectively). In a different experiment in which J. cordifolia was cultured in P-enriched aerated and non-aerated solutions, anoxia caused a strongly diminished P accumulation in the first three days, probably because the mitochondrial respiration was blocked. Then, a clear net loss of P from the liverwort tissues was observed, maybe caused by membrane damage.