Growth, pigment changes, and photosystem II activity in the aquatic macrophyte Lemna minor exposed to bisphenol A.

As a result of its high production, bisphenol A (BPA) has become ubiquitous in aquatic and terrestrial habitats. In this study, we investigated the toxicity of BPA at 10 mg L-1 on Lemna minor after 7 days of exposure under controlled conditions according to ISO 20079. BPA statistically reduced the total frond number and frond area, while frond number per colony was significantly elevated in BPA-treated group. However, no change was recorded in root number, while root length was significantly reduced by BPA. BPA also decreased the content of Chl a, Chl b, Chl a + b, and carotenoid by 36%, 44%, 38%, and 32%, respectively, versus the control leading to a decrease in the quantum yield of photosystem II. In addition, non-photochemical quenching (NPQ) values were 2.4- and 4.5-fold higher in light than in dark conditions for control and BPA-treated plants, respectively. Thus, there is a significant activation (61.8%; p<0.01) of PSII photoprotection mechanism (NPQ) in BPA-treated plants compared to control but without removing the negative effect of BPA on PSII. The total amount of soluble sugars was reduced by 40% compared to control, and starch accumulation was mainly observed in fronds exposed to BPA. Even if the response patterns of Lemna minor based on fresh and dry weight measurements were less sensitive in our experiment conditions, further studies should be addressed since BPA represents a threat to the dynamic equilibrium governing aquatic ecosystems.

Factors inducing bryophyte growth on prehistoric pigments and effect of UV-C treatment.

In La Glacière cave (France), the touristic activity has been conducted to an environmental parameter change that has led to photosynthetic organism proliferation (microalgae, diatoms, cyanobacteria, bryophytes). The present study is focused on bryophyte development occurring in the show cave that was responsible of limestone biodeterioration. In order to understand the colonization process of limestone, we have maintained limestone blocks under optimal Lampenflora growth conditions. Moreover, some limestone blocks were painted with several pigments that were used in the prehistory (e.g., red ocher, bone char). Microorganisms and bryophyte growth were monitored during 1 year, and then, the block samples were treated using UV-C light (254 nm). Thus, obtained results were compared with in situ treatment in La Glacière cave. Results have showed dense bryophyte propagation on the several blocks. However, the growth rate was correlated with the chemical composition of the pigment. In fact, the presence of some chemical elements such as As, Cr, Ti, and Co contributed to reduce bryophyte growth. Finally, moss treatment using UV-C light has demonstrated high efficiency under in situ condition, while a fast recolonization has been observed for samples maintained in laboratory. This difference was explained by the high bryophyte density under laboratory conditions that make UV-C light penetration difficult.

Influence of hydro- and osmo-priming on sunflower seeds to break dormancy and improve crop performance under water stress.

This study explored the effects of two hydro- and osmo-priming durations (8 and 16 h) on growth and yield components of sunflowers (Helianthus annuus L.) under water stress. The pot experiment, performed under a rain shelter, consisted of 9 treatments replicated five times: unprimed seeds as control (C), hydro-primed seeds (T0), osmo-primed seeds in 10, 20, and 30% PEG-6000 (T1, T2, and T3, respectively). Severe water stress was applied for 12 days to all treatments at the beginning of the flowering stage. Statistical analysis revealed a very highly significant positive effect (p < 0.01) by all treatments on sunflower seed germination compared with the control. Moreover, primed seeds improved significantly for all growth parameters and yield components, but no significant differences were observed according to either priming technique or duration. The highest value of germination capacity, for fresh and dry biomasses, was obtained with PEG-primed seeds at 10% for 16 h. The grain number per anthodium and grain yield per plant from primed seeds were higher than those in the control (1.9- to 2.5-fold and 2.8- to 3.3-fold respectively). Under conditions of water stress, the proline content in primed plants was significantly higher than that in unprimed ones, with the exception of T3 treatment primed for 8 h. Soluble sugars and chlorophyll contents increased significantly with all applied treatments compared with the control. The study showed that the applied priming treatments improved germination characteristics in particular and increased growth and yield components for sunflowers under drought stress conditions.

Assessment of fungi proliferation and diversity in cultural heritage: Reactions to UV-C treatment.

Fungi are present in natural and non-touristic caves due to the presence of organic matter provided mainly by insects or animals such as bats. In show caves, however, tourist infrastructure and the visitors themselves are an important source of organic matter. In addition, photosynthetic biofilms provide a high amount of carbon and nitrogen sources for fungi. This study was conducted to identify the fungal communities present in caves along with the potential use of UV-C treatment against their proliferation. Thus, fungal communities proliferating in biofilms in six French and Swiss show caves were analyzed using high throughput sequencing. The results show 385 species recorded, some of them previously described in cases of fungal outbreak. This preliminary study also aimed to test the use of UV-C light as an environmentally friendly method to treat fungal proliferation. Six fungal strains, from three different sources (Lascaux cave, La Glacière cave, a church in Vicherey, France), were cultivated in an agar dish. Spores, mycelia and the entire colony were irradiated using several UV-C intensities. Results showed that four of the six fungi spores and mycelium died following a low-intensity UV-C treatment (2 kJ m-2, 160 s), though Ochroconis lascauxensis and Penicillium bilaiae spores showed higher resistance. Finally, it was demonstrated that the fungal colony could resist the UV-C light due to a shadow effect. The structure of the fungal colony was affected from the periphery to its inner part. However, after four 30 kJ m-2 treatments (39 min irradiation) all strains there definitively eradicated. Further studies will be necessary to examine the potential of UV-C light under cave conditions as a preventive and curative treatment.

Biofilm biodiversity in French and Swiss show caves using the metabarcoding approach: First data.

In recent decades, show caves have begun to suffer from microorganism proliferation due to artificial lighting installations for touristic activity. In addition to the aesthetic problem, light encourages microorganisms that are responsible for physical and chemical degradation of limestone walls, speleothems and prehistoric paintings of cultural value. Microorganisms have previously been described by microscopy or culture-dependent methods, but data provided by new generation sequencing are rare. The authors identified, for the first time, microorganisms proliferating in one Swiss and in four French show caves using three different primers. The results showed that both photosynthetic and non-photosynthetic bacteria were the dominant taxa present in biofilms. Microalgae were heavily represented by the Trebouxiophyceae, Eustigmatophyceae and Chlorophyceae groups. Twelve diatoms were also recorded, with dominance of Syntrichia sp. (96.1%). Fungi were predominantly represented by Ascomycota, Zygomycota and Basidiomycota, fully half of the sampled biofilms where Fungi were detected. Comparing microbial communities from bleach-treated caves to those in untreated caves showed no significant difference except for a low-level change in the abundance of certain taxa. These findings provided by Illumina sequencing reveal a complex community structure in the 5 caves based on the assembly of bacteria, cyanobacteria, algae, diatoms, fungi and mosses.

Bleaching of biofilm-forming algae induced by UV-C treatment: a preliminary study on chlorophyll degradation and its optimization for an application on cultural heritage.

Green microalgae colonizing stone surfaces represent a major problem for the conservation of heritage monuments, since they lead to biodegradation and aesthetic issues. Previous studies in La Glacière show cave (France) have demonstrated that UV-C may have a strong effect on microalgae, thus leading to chlorophyll bleaching, which was increased when biofilms were maintained under VIS-light condition unlike to those maintained in the dark. To understand the physiological mechanisms underlying this response and in order to optimize in situ treatment, 30 kJ m-2 UV-C exposure times were applied to Chlorophyta Chlorella sp. and chlorophyll degradation kinetics were then monitored. UV-C irradiation was enough to inhibit photosynthesis and to directly kill all algal cells. Results also showed that chlorophyll a was degraded faster than chlorophyll b and that 14 h were necessary for complete degradation of all the present chlorophyll. In addition, our results highlighted the importance of visible light exposition after UV-C treatment which leading to chlorophyll bleaching. Irradiated algae cultivated in the dark were still green 5 days after treatment while cultivated samples in the light lost their green color after 14 h. An efficient UV-C treatment applicable to show caves and other heritage monuments was proposed.

Potential vulnerability of oak forests to climate change-induced flooding: effects of mild oxygen deficiency on Quercus robur and Quercus petraea seedling physiology.

Flooding is characterized by saturation of soil pores with water, leading to hypoxic conditions which affect plant root development and metabolism. We investigated the oxygen deficiency tolerance observed in Quercus robur and Quercus petraea and seek to understand whether it can be explained by enhanced efficiency in oxygen use in the roots, as estimated through radial oxygen loss visualization in relation to growth measurements and root apex respiration. The study showed that root growth, under oxygen deficiency conditions, was significantly reduced only in Q. robur seedlings. Root respiration was maintained in Q. robur, whereas it was decreased in Q. petraea. Both species set up a barrier against radial oxygen loss, though measurement of apex oxygen leakage showed greater oxygen efficiency in Q. robur seedlings. This strategy might allow Q. robur to maintain its respiration and thus to survive longer under oxygen deficiency conditions by facilitating the seedling establishment in transient flooded soils.

UV-C as an efficient means to combat biofilm formation in show caves: evidence from the La Glacière Cave (France) and laboratory experiments.

Ultra-violet C (UV-C) treatment is commonly used in sterilization processes in industry, laboratories, and hospitals, showing its efficacy against microorganisms such as bacteria, algae, or fungi. In this study, we have eradicated for the first time all proliferating biofilms present in a show cave (the La Glacière Cave, Chaux-lès-Passavant, France). Colorimetric measurements of irradiated biofilms were then monitored for 21 months. To understand the importance of exposition of algae to light just after UV radiation, similar tests were carried out in laboratory conditions. Since UV-C can be deleterious for biofilm support, especially parietal painting, we investigated their effects on prehistoric pigment. Results showed complete eradication of cave biofilms with no algae proliferation observed after 21 months. Moreover, quantum yield results showed a decrease directly after UV-C treatment, indicating inhibition of algae photosynthesis. Furthermore, no changes in pigment color nor in chemical and crystalline properties has been demonstrated. The present findings demonstrate that the UV-C method can be considered environmentally friendly and the best alternative to chemicals. This inexpensive and easily implemented method is advantageous for cave owners and managers.

UV-C as a means to combat biofilm proliferation on prehistoric paintings: evidence from laboratory experiments.

A laboratory investigation of UV-C effects was conducted over a 62-h period: a much higher dose than in classic UV-C treatment was applied to five pigments and two painting binders used by prehistoric humans. Colorimetric parameters were compared to a control to see if UV-C can change pigment and binder color. Infrared spectroscopy, scanning electron microscopy, inductively coupled plasma and X-ray crystallography were also carried out to confirm colorimetric measurement. In order to understand how microorganism may physically deteriorate paintings, limestone blocks were painted and monitored until their complete colonization by algae, cyanobacteria, fungi and/or mosses. The results show that UV-C has no effect on mineral compounds. Conversely, it is noteworthy that binder color changed under both UV-C light conditions as well as in visible light. Concerning painted blocks, a fast proliferation has been observed with deterioration of the paintings. These results show the high importance of treating biofilm as soon as possible. Moreover, these findings may be a promising avenue inducing cave managers to use friendly UV-C light to treat contaminated cave paintings and also in the prevention of biodeterioration by lampenflora.

Effects of repeated soil irrigation with liquid biological paper sludge on poplar Populus alba saplings: potential risks and benefits.

The authors explored the risks and benefits of repeated irrigation of Populus alba saplings with aqueous paper sludge (APS). Saplings were cultivated in pots of forest soil (3 L) in a greenhouse for 7 weeks and watered twice a week with differing concentrations of APS (0, 10, 20, 30, 50, 75, and 100 % v/v with deionized water). Plant growth and ecophysiological variables along with zinc and aluminum transfer were monitored. A stimulation of plant growth was observed with sludge treatments of 30 or 50 %, significantly correlated to APS input (r = 0.81). This may be explained by the easily available nitrogen as is shown with the positive correlation of CO2 assimilation and leaf nitrogen (r = 0.70). However, a significant reduction in plant growth was observed when treatments of 75 and 100 % of APS were administered, despite a high nutritional level (nitrogen and phosphorus). The study suggests that APS concentrations from 30 to 50 % may positively affect the growth of poplar saplings; however, the higher concentrations indicated a risk for plant growth and the environment.