Winter photosynthetic activity of twenty temperate semi-desert sand grassland species

Photoprotection and high-light acclimation in semi-arid grassland lichens – a cooperation between algal and fungal partners

In lichens, each symbiotic partner cooperates for the survival of the symbiotic association. The protection of the susceptible photosynthetic apparatus is essential for both participants. The mycobiont and photobiont contribute to the protection against the damaging effect of excess light by various mechanisms. The present study investigated the effect of seasonality and microhabitat exposure on photoprotection and photoacclimation in the photo- and the mycobiont of six lichen species with different thallus morphology in inland dune system in the Kiskunság region (Hungary) with shaded, more humid and exposed, drier dune sides. High-Performance Liquid Chromatography, spectrophotometry, chlorophyll a fluorescence kinetic technique were used, and micrometeorological data were collected. The four years data series revealed that the north-east-facing side was characterized by higher relative humidity and lower light intensities compared to the south-west-facing drier and more exposed sides. The south-west facing side was exposed to direct illumination 3–4 hours longer in winter and 1–2 hours shorter in summer than the north-east facing side of the dune, influencing the metabolism of sun and shade populations of various species. Because rapid desiccation caused short active periods of lichens during bright and drier seasons and on exposed microhabitats, the rapid, non-regulated non-photochemical quenching mechanisms in the photobiont had a significant role in protecting the photosynthetic system in the hydrated state. In dehydrated conditions, thalli were mainly defended by the solar screening metabolites produced by the mycobiont and curling during desiccation (also caused by the mycobiont). Furthermore, the efficacy of light use (higher chlorophyll and carotenoid concentration) increased because of short hydrated periods. Still, a lower level of received irradiation was appropriate for photosynthesis in dry seasons and on sun exposed habitats. In humid seasons and microhabitats, more extended active periods lead to increased photosynthesis and production of solar radiation protectant fungal metabolites, allowing a lower level of photoprotection in the form of regulated non-photochemical quenching by the photobiont. Interspecific differences were more pronounced than the intraspecific ones among seasons and microhabitat types.

Seasonality affects function and complexity but not diversity of the rhizosphere microbiome in European temperate grassland

Knowledge on how grassland microbiota responds on gene expression level to winter-summer change of seasons is poor. Here, we used a combination of quantitative PCR-based assays and metatranscriptomics to assess the impact of seasonality on the rhizospheric microbiota in temperate European grassland. Bacteria dominated, being at least one order of magnitude more abundant than fungi. Despite a fivefold summer increase in bacterial community size, season had nearly no effect on microbiome diversity. It, however, had a marked impact on taxon-specific gene expression, with 668 genes significantly differing in relative transcript abundance between winter and summer samples. Acidobacteria, Bacteroidetes, Planctomycetes, and Proteobacteria showed a greater relative gene expression activity in winter, while mRNA of Actinobacteria and Fungi was, relative to other taxa, significantly enriched in summer. On functional level, mRNA involved in protein turnover (e.g., transcription and translation) and cell maintenance (e.g., chaperones that protect against cell freezing damage such as GroEL and Hsp20) were highly enriched in winter. By contrast, mRNA involved in central carbon and amino acid metabolisms had a greater abundance in summer. Among carbohydrate-active enzymes, transcripts of GH36 family (hemicellulases) were highly enriched in winter, while those encoding GH3 family (cellulases) showed increased abundance in summer. The seasonal differences in plant polymer breakdown were linked to a significantly greater microbial network complexity in winter than in summer. Conceptually, the winter-summer change in microbiome functioning can be well explained by a shift from stress-tolerator to high-yield life history strategy.

Effects of global change factors on fatty acids and mycosporine-like amino acid production in Chroothece richteriana (Rhodophyta)

Under natural conditions, Chroothece richteriana synthesizes a fairly high proportion of fatty acids. However, nothing is known about how environmental changes affect their production, or about the production of protective compounds, when colonies develop under full sunshine with high levels of UV radiation. In this study, wild colonies of C. richteriana were subjected to increasing temperature, conductivity, ammonium concentrations and photosynthetically active radiation (PAR), and UV radiations to assess the potential changes in lipid composition and mycosporine-like amino acids (MAAs) concentration. The PERMANOVA analysis detected no differences for the whole fatty acid profile among treatments, but the percentages of α-linolenic acid and total polyunsaturated fatty acids increased at the lowest assayed temperature. The percentages of linoleic and α-linolenic acids increased with lowering temperature. γ-linolenic and arachidonic acids decreased with increasing conductivity, and a high arachidonic acid concentration was related with increased conductivity. The samples exposed to UVB radiation showed higher percentages of eicosapentaenoic acid and total monounsaturated fatty acids, at the expense of saturated fatty acids. MAAs accumulation increased but not significantly at the lowest conductivity, and also with the highest PAR and UVR exposure, while ammonium and temperature had no effect. The observed changes are probably related with adaptations of both membrane fluidity to low temperature, and metabolism to protect cells against UV radiation damage. The results suggest the potential to change lipid composition and MAAs concentration in response to environmental stressful conditions due to climate change, and highlight the interest of the species in future research about the biotechnological production of both compound types.

Features of chlorophyll fluorescence transients can be used to investigate low temperature induced effects on photosystem II of algal lichens from polar regions ( Short Communication )

Chlorophyll fluorescence is an effective tool for investigating characteristics of any photosynthesizing organisms and its responses due to different stressors. Here, we have studied a short-term temperature response on three Antarctic green algal lichen species: Umbilicaria antarctica, Xanthoria elegans, and Rhizoplaca melanophtalma. We measured slow chlorophyll fluorescence transients in these Antarctic lichen species during slowely cooling of thallus temperature from 20°C to 5, 0 and -5°C with 20 minute acclimation at each temperature. The measurements were supplemented with saturation pulses for the analysis of chlorophyll fluorescence parameters: maximum yield of PS II photochemistry (FV/FM), effective quantum yield of PS II photochemistry (FPSII) and quenching parameters. In response to decreasing thallus temperature, we observed species-specific changes in chlorophyll fluorescence parameters as well as in the shape of the chlorophyll fluorescence transients. We propose that species-specific changes in the slow phase of chlorophyll fluorescence transients can be potentially used as indicators of freezing stress in photosynthetic apparatus of lichen algal photobionts.