Burkhard Büdel

Progress in Botany

In the past 55 years, enormous scientific progress was made in many fields of plant physiology and plant biochemistry. Throughout these years, our knowledge on the photosynthetic light processes, the chemical composition and H.K. Lichtenthaler (*) Botanical Institute 2 (Molecular Biology and Biochemistry of Plants), Karlsruhe Institute of Technology (KIT), University Division, Kaiserstr. 12, 76131 Karlsruhe, Germany e-mail: hartmut.lichtenthaler@kit.edu

The ascomycota tree of life: A phylum-wide phylogeny clarifies the origin and evolution of fundamental reproductive and ecological traits

We present a 6-gene, 420-species maximum-likelihood phylogeny of Ascomycota, the largest phylum of Fungi. This analysis is the most taxonomically complete to date with species sampled from all 15 currently circumscribed classes. A number of superclass-level nodes that have previously evaded resolution and were unnamed in classifications of the Fungi are resolved for the first time. Based on the 6-gene phylogeny we conducted a phylogenetic informativeness analysis of all 6 genes and a series of ancestral character state reconstructions that focused on morphology of sporocarps, ascus dehiscence, and evolution of nutritional modes and ecologies. A gene-by-gene assessment of phylogenetic informativeness yielded higher levels of informativeness for protein genes (RPB1, RPB2, and TEF1) as compared with the ribosomal genes, which have been the standard bearer in fungal systematics. Our reconstruction of sporocarp characters is consistent with 2 origins for multicellular sexual reproductive structures in Ascomycota, once in the common ancestor of Pezizomycotina and once in the common ancestor of Neolectomycetes. This first report of dual origins of ascomycete sporocarps highlights the complicated nature of assessing homology of morphological traits across Fungi. Furthermore, ancestral reconstruction supports an open sporocarp with an exposed hymenium (apothecium) as the primitive morphology for Pezizomycotina with multiple derivations of the partially (perithecia) or completely enclosed (cleistothecia) sporocarps. Ascus dehiscence is most informative at the class level within Pezizomycotina with most superclass nodes reconstructed equivocally. Character-state reconstructions support a terrestrial, saprobic ecology as ancestral. In contrast to previous studies, these analyses support multiple origins of lichenization events with the loss of lichenization as less frequent and limited to terminal, closely related species.

Taxonomic composition and photosynthetic characteristics of the 'biological soil crusts' covering sand dunes in the western Negev Desert

We report laboratory studies that aim to characterize the microphyte community composition and metabolic features of crusts covering dunes in the Negev. The crusts are formed by at least one moss, four blue-green (Cyanobacteria) and two green (Chlorophyta) algal species with Microcoleus sociatus being dominant. The sheaths of the latter procaryotic alga, together with a contribution by moss rhizoides and protonemata, are responsible for stability of the topsoil crusts. Following moistening of the dry crust, CO 2 release took place, even in the light, until positive net photosynthesis was achieved (...)

Biological Soil Crusts: Characteristics and Distribution

Biological soil crusts result from an intimate association between soil particles and cyanobacteria, algae, microfungi, lichens, and bryophytes (in different proportions) which live within, or immediately on top of, the uppermost millimeters of soil. Soil particles are aggregated through the presence and activity of these biota, and the resultant living crust covers the surface of the ground as a coherent layer (Fig. 1.1). This definition does not include communities where soil particles are not aggregated by these organisms (e.g., cyanobacterial/algal horizons in littoral sand and mudflats), where organisms are not in close contact with the soil surface (e.g., thick moss-lichen mats growing on top of decaying organic material, as in boreal regions), nor where the majority of the biomass is above the soil surface (e.g., large club-moss mats found in North American grasslands or dense stands of fruticose lichens, such as Niebla and Teloschistes species from the coastal fog deserts of California and of Namibia, respectively). However, the boundaries between the latter communities and biological soil crusts are fluid. In a similar fashion, there is no strict dividing line between the cyanobacterial, green algal, and fungal species that occur in soil-crust communities, yet are also found in a multitude of additional habitats (e.g., intertidal mats, tree trunks and leaves, rock faces).

Ultraviolet-absorbing scytonemin and mycosporine-like amino acid derivatives in exposed, rock-inhabiting cyanobacterial lichens

Abstract The occurrence of ultraviolet (UV)-absorbing substances like scytonemin and mycosporine-glycine is reported for the first time from cyanobacterial lichens of the genera Collema, Gonohymenia and Peltula, all coming from high-light-intensity habitats. Except for Collema with the filamentous Nostoc, all other cyanobionts belong to the unicellular genera Chroococcidiopsis, Cyanosarcina, Gloeocapsa or Myxosarcina. From transmission electron microscope studies it is evident that the pigmentation (scytonemin) is located extracellularly in the sheath of the outer thallus parts. Fluorescence microscopy and microprobe measurements clearly show UV radiation into the lichen thallus and hence the relevance of UV sunscreens for the protection of the organism.

Temperate rainforest lichens in New Zealand : high thallus water content can severely limit photosynthetic CO2 exchange

CO2 exchange rate in relation to thallus water content (WC, % of dry weight) was determined for 22 species of lichens, mainly members of the genera Pseudocyphellaria and Sticta, from a temperate rainforest, Urewere National Park, New Zealand. All data were obtained in the field, either using a standard technique in which the lichens were initially wetted (soaked or sprayed, then shaken) and allowed to slowly dry, or from periodic measurements on samples that were continuously exposed in their natural habitat. A wide range of WC was found, with species varying from 357 to 3360% for maximal WC in the field, and from 86 to 1300% for optimal WC for photosynthesis. Maximal WC for lichens, wetted by the standard technique, were almost always much less than the field maxima, due to the presence of water on the thalli. The relationships between CO2 exchange rate and WC could be divided into four response types based on the presence, and degree, of depression of photosynthesis at high WC. Type A lichens showed no depression, and Type B only a little at maximal WC. Type C had a very large depression and, at the highest WC, CO2 release could occur even in the light. Photosynthetic depression commenced soon after optimal WC was reached. Type D lichens showed a similar depression but the response curve had an inflection so that net photosynthesis was low but almost constant, and never negative, at higher WC. There was little apparent relationship between lichen genus or photobiont type and the response type. It was shown that high WC does limit photosynthetic CO2 uptake under natural conditions. Lichens, taken directly from the field and allowed to dry under controlled conditions, had net photosynthesis rates that were initially strongly inhibited but rose to an optimum, before declining at low WC. The limiting effects of high WC were clearly shown when, under similar light conditions, severe photosynthetic depression followed a brief, midday, rain storm. Over the whole measuring period the lichens were rarely at their optimal WC for photosynthesis, being mostly too wet or, occasionally, too dry. Photosynthetic performance by the lichens exposed in the field was similar to that expected from the relationship between the photosynthetic rate and WC established by the standard procedure.

Evidence for the functioning of photosynthetic CO2-concentrating mechanisms in lichens containing green algal and cyanobacterial photobionts

The photosynthetic properties of a range of lichens containing both green algal (11 species) and cyanobacterial (6 species) photobionts were examined with the aim of determining if there was clear evidence for the operation of a CO2-concentrating mechanism (CCM) within the photobionts. Using a CO2-gas-exchange system, which allowed resolution of fast transients, evidence was obtained for the existence of an inorganic carbon pool which accumulated in the light and was released in the dark. The pool was large (500–1000 nmol · mg Chl) in cyanobacterial lichens and about tenfold smaller in green algal lichens. In Hypogymnia physodes (L.) Nyl., which contains the green alga Trebouxia jamesii, a small inorganic carbon pool was rapidly formed in the light. Carbon dioxide was released from this pool into the gas phase upon darkening within about 20 s when photosynthesis was inhibited by the carbon-reduction-cycle inhibitor glycolaldehyde. In the absence of this inhibitor, release appeared to be obscured by carboxylation of ribulose bisphosphate. The kinetics of CO2 uptake and release were monophasic. The operation of an active CCM could be distinguished from passive accumulation and release accompanying the reversible light-dependent alkalization of the stroma by the presence of saturation characteristics with respect to external CO2. In Peltigera canina (L.) Willd., which contains the cyanobacterium Nostoc sp., a larger CO2 pool was taken up over a longer period in the light and the release of this pool in the dark was slow, lasting 3–5 min. This pool also accumulated in the presence of glycolaldehyde, and under these conditions the CO2 release was biphasic. In both species, photosynthesis at low CO2 was inhibited by the carbonic-anhydrase inhibitor ethoxyzolamide (EZ). Inhibition could be reversed fully or to a considerable extent by high CO2. In Peltigera, EZ decreased both the accumulation of the CO2 pool by the CCM and the rate of photosynthesis. Free-living cultures of Nostoc sp. showed a similar effect of EZ on photosynthesis, although it was more dramatic than that seen with the lichen thalli. In contrast, in Hypogymnia, EZ actually increased the size of the CO2 pool, although it inhibited photosynthesis. This effect was also seen when glycolaldehyde was present together with EZ. Surprisingly, EZ did not alter the kinetics of either CO2 uptake or release. Taken together, the evidence indicates the operation in cyanobacterial lichens of a CCM which is capable of considerable elevation of internal CO2 and is similar to that reported for free-living cyanobacteria. The CCM of green algal lichens accumulates much less CO2 and is probably less effective than that which operates in cyanobacterial lichens.

Ecology and diversity of rock-inhabiting cyanobacteria in tropical regions

The diversity and abundance of terrestrial, lithophytic cyanobacteria in tropical biomes and the variety of rock habitats which they occupy are discussed. The following results are presented in detail. Exposed rock surfaces on different continents and under different climatic conditions are occupied by a cosmopolitan, well-adapted, low-diversity microbial community dominated by cyanobacteria and cyanobacterial lichens. For inselbergs (isolated rock outcrops) in dry savanna, the ratio of rock covered by lichens to that covered by free cyanobacteria is approximately 5:3. In humid savannas this ratio is approximately 1:26, and in rainforests there are hardly any lichens on rocks. The primary production of epilithic communities, expressed as CO2 fixed calculated from chlorophyll a, can reach an annual 27 g m−2. When calculated for a hypothetical inselberg, production values for very dry thorn bush savanna, dry savanna and humid savanna are 1:3.2:4.2 on the basis of the entire inselberg, and 1:3.2:1.4 when cal...

Net Photosynthesis Activation of a Desiccated Cyano-bacterium Without Liquid Water in High air Humidity Alone. Experiments with Microcoleus sociatus Isolated from a Desert Soil Crust

This study shows that water vapour activation of net photosynthesis can not be attributed to green algae and to green algal lichens alone. This capacity might be also imortant for productivity of desert soil crusts which are formed by cyanobacteria

Biological Soil Crusts: An Organizing Principle in Drylands

This volume summarizes our current understanding of biological soil crusts (biocrusts), which are omnipresent in dryland regions. Since they cover the soil surface, they influence, or even control, all surface exchange processes. Being one of the oldest terrestrial communities, biocrusts comprise a high diversity of cyanobacteria, algae, lichens and bryophytes together with uncounted bacteria, and fungi. The authors show that biocrusts are an integral part of dryland ecosystems, stabilizing soils, influencing plant germination and growth, and playing a key role in carbon, nitrogen and water cycling. Initial attempts have been made to use biocrusts as models in ecological theory. On the other hand, biocrusts are endangered by local disruptions and global change, highlighting the need for enhanced recovery methods. This book offers a comprehensive overview of the fascinating field of biocrust research, making it indispensable not only for scientists in this area, but also for land managers, policy makers, and anyone interested in the environment