Badr Alaoui-Sossé

Effects of copper on growth and on photosynthesis of mature and expanding leaves in cucumber plants

Abstract The aim of this study was to study the relationship between growth inhibition in Cu-treated Cucumis sativus L. seedlings and photosynthesis. Twenty-two days after sowing, copper was added to the nutrient solution for 5 days, leading to final Cu supplementary concentration in sand of, respectively 0 (control) and 10 μg g −1 (Cu stress). The responses of cucumber leaves to copper addition depend on their growth stage. Young expanding leaves showed a reduction in leaf area, while mature leaves exhibited a significant decline in photosynthesis. Sucrose and starch content rose in both types of leaves. For mature leaf, net CO 2 assimilation declined at a nearly constant intercellular CO 2 mole fraction, indicating that stomatal closure did not account for the inhibition of photosynthesis. Maximal photochemical yield of PSII in dark-acclimated leaves was unaffected, indicating that the dark phase of photosynthesis rather than the light phase was affected. Relative growth rate and leaf area ratio of stressed plants were significantly below that of control plants while no significant decrease of net assimilation rate was observed for Cu-stressed plants. Thus despite a reduction in mature leaf photosynthesis, growth reduction is more likely due to a reduction in whole plant leaf area. This decline in photosynthesis is probably a consequence of an altered source–sink relationship, rather than due to a toxic effect of copper on photosynthesis.

Sewage sludge application in a plantation: Effects on trace metal transfer in soil–plant–snail continuum

We studied the potential bioaccumulation of Cu, Zn, Pb and Cd by the snail Cantareus aspersus and evaluated the risk of leaching after application of sewage sludge to forest plantation ecosystems. Sewage sludge was applied to the soil surface at two loading rates (0, and 6 tons ha(-1) in dry matter) without incorporation into the soil so as to identify the sources of trace metal contamination in soil and plants and to evaluate effects on snail growth. The results indicated a snail mortality rate of less than 1% during the experiment, while their dry weight decreased significantly (<0.001) in all treatment modalities. Thus, snails showed no acute toxicity symptoms after soil amendment with sewage sludge over the exposure period considered. Additions of sewage sludge led to higher levels of trace metals in forest litter compared to control subplots, but similar trace metal concentrations were observed in sampling plants. Bioaccumulation study demonstrated that Zn had not accumulated in snails compared to Cu which accumulated only after 28 days of exposure to amended subplots. However, Pb and Cd contents in snails increased significantly after 14 and 28 days of exposure in both the control and amended subplots. At the last sampling date, in comparison to controls the Cd increase was higher in snails exposed to amended subplots. Thus, sludge spread therefore appears to be responsible for the observed bioaccumulation for Cu and Cd after 28days of exposure. Concerning Pb accumulation, the results from litter-soil-plant compartments suggest that soil is this metals best transfer source.

Factors driving epilithic algal colonization in show caves and new insights into combating biofilm development with UV-C treatments.

The proliferation of epilithic algae that form biofilms in subterranean environments, such as show caves, is a major problem for conservators. In an effort to reduce the use of chemical cleansers when addressing this problem, we proposed investigating the effects of UV-C on combating algal biofilm expansion in a cave located in northeastern France (Moidons Cave). First, the biofilms and cavity were studied in terms of their algal growth-influencing factors to understand the dynamics of colonization in these very harsh environments. Next, colorimetric measurements were used both to diagnose the initial colonization state and monitor the UV-C-treated biofilms for several months after irradiation. The results indicated that passive dispersal vectors of the viable spores and cells were the primary factors involved in the caves algae repartition. The illumination time during visits appeared to be responsible for greater colonization in some parts of the cave. We also showed that colorimetric measurements could be used for the detection of both thin and thick biofilms, regardless of the type of colonized surface. Finally, our results showed that UV-C treatment led to bleaching of the treated biofilm due to chlorophyll degradation even one year after UV-C treatment. However, a re-colonization phenomenon was colorimetrically and visually detected 16months later, suggesting that the colonization dynamics had not been fully halted.

Heritage materials and biofouling mitigation through UV-C irradiation in show caves: state-of-the-art practices and future challenges

Biofouling, i.e., colonization of a given substrate by living organisms, has frequently been reported for heritage materials and particularly on stone surfaces such as building facades, historical monuments, and artworks. This also concerns subterranean environments such as show caves, in which the installation of artificial light for tourism has led to the proliferation of phototrophic microorganisms. In Europe nowadays, the use of chemicals in these very sensitive environments is scrutinized and regulated by the European Union. New and environmentally friendly processes must be developed as alternative methods for cave conservation. For several years, the UV irradiation currently used in medical facilities and for the treatment of drinking water has been studied as a new innovative method for the conservation of heritage materials. This paper first presents a review of the biofouling phenomena on stone materials such as building facades and historical monuments. The biological disturbances induced by tourist activity in show caves are then examined, with special attention given to the methods and means to combat them. Thirdly, a general overview is given of the effects of UV-C on living organisms, and especially on photosynthetic microorganisms, through different contexts and studies. Finally, the authors’ own experiments and findings are presented concerning the study and use of UV-C irradiation to combat algal proliferation in show caves. Both laboratory and in situ results are summarized and synthesized from their previously published works. The application of UV in caves is discussed and further experiments are proposed to enhance research in this domain.

Microbial composition and ecological features of phototrophic biofilms proliferating in the Moidons Caves (France): investigation at the single-cell level

The authors investigated the microbial composition of phototrophic biofilms proliferating in a show cave using flow cytometry for the first time in such a context. Results are based on several biofilms sampled in the Moidons Caves (France) and concern both heterotrophic prokaryotes and autotrophic microorganisms. Heterotrophic microorganisms with low nucleic acid content were dominant in biofilms, as can be expected from the oligotrophic conditions prevailing within the cave. Analysis of the biofilm autotrophic components revealed the presence of several taxa, particularly the unicellular green algae Chlorella minutissima, specifically well adapted to this cave. Relationships between flow cytometry results and environmental variables determined in the cave were established and discussed so as to better understand biofilm proliferation processes in caves.

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.

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 sewage sludge amendment on snail growth and trace metal transfer in the soil-plant-snail food chain

Cu, Zn, Pb, and Cd concentrations in a soil plant (Lactuca sativa) continuum were measured after sewage sludge amendment. The effects of sewage sludge on growth and trace metal bioaccumulation in snails (Cantareus aspersus) were investigated in a laboratory experiment specifically designed to identify contamination sources (e.g., soil and leaves). Application of sewage sludge increased trace metal concentrations in topsoil. However, except Zn, metal concentrations in lettuce leaves did not reflect those in soil. Lettuce leaves were the main source of Zn, Cu, and Cd in exposed snails. Bioaccumulation of Pb suggested its immediate transfer to snails via the soil. No apparent toxic effects of trace metal accumulation were observed in snails. Moreover, snail growth was significantly stimulated at high rates of sludge application. This hormesis effect may be due to the enhanced nutritional content of lettuce leaves exposed to sewage sludge.

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.

Influence of different sludge compositions on understorey vegetation in an amended Pinus pinatser forest plantation

The present study reports on the influence of sludge application on understory abundance and species richness in an eight year-old maritime pine forest. Four types of sludge (liquid, dewatered, limed and composted sludge) were applied at a rate equivalent to 3 tons dry weight per ha-1 per year-1. Understorey vegetation was monitored before treatment and for three successive years following initial sludge application. Species richness, the biodiversity index and naturally occurring plant community cover in maritime pine forests were measured. Results showed a significant increase in species richness two years following initial sludge application. In fact, compared to the unamended plot, eighteen additional species (Aira caryophyllea, Cerastium glomeratum, Conyza canadensis, Danthonia decumbens, Geranium robertianum, Gnaphalium sylvaticum, Hypericum humifusum, Hypericum perforatum ssp. perforatum, Jasione montana, Lonicera periclymenum ssp. periclymenum, Ornithopus compressus, Phytolacca americana, Rhamnus frangula, Teesdalia nudicaulis, Veronica arvensis, Vicia sativa angustifolia and Vulpia myuros) appeared after sludge application. Most of these species were observed with the solid limed or composted sludge treatments. The new species then declined the following year, highlighting the temporary effect of sludge treatment on species diversity. However, the cover by these eighteen new species was low and did not exceed 1%, except for Hypericum perforatum and Jasione montana for the limed sludge treatment and Vulpia myuros for the liquid sludge treatment. Additionally, sludge significantly reduces bare soil percentage, which ranged from 5 to 18% compared to the control (38%). According to sludge type, treatment also led to a significant change in species dominance of the understorey plant communities. Indeed, the cover of Molinia caerulea decreased in spite of an increase in Agrostis capillaris and/or Holcus lanatus following application of solid limed, liquid or composted sludge.