Components Of Biological Soil Crusts Research Articles

First draft of an annotated genome for a lichenised strain of the green alga Diplosphaera chodatii (Prasiolales, Trebouxiophyceae)

ABSTRACT Although genome sequences of lichenized fungi are increasingly becoming available, genome sequences of microalgae involved in the lichen symbiosis are still scarce. For lichenized eukaryotic algae, genome sequencing has focused mostly on Trebouxia and Asterochloris, with little genomic data available for Stichococcus-like algae, such as Diplosphaera. The genus Diplosphaera is a common component of biological soil crusts, and often occurs associated with lichens of the family Verrucariaceae. It is characterized by cylindrical to spherical cells containing a plate-like chloroplast, and more specifically by a vegetative cell division that leads to the formation of typical two- to four-celled clusters. Here, we present a draft genome sequence for the algal partner of an Australian lichen specimen of Endocarpon pusillum. The genome was sequenced with Pac Bio long read and Illumina short read technologies, and transcriptome data were generated to inform the structural annotations. This algal strain is here identified as Diplosphaera chodatii based on nuSSU and ITS data. Compared with closely related lichenized and non-lichenized algae, the genome of D. chodatii stands out for its large size (85.6 Mb) and gene content (21,261 protein-encoding regions), as well as its high rate of duplicated genes (60% of the BUSCO genes are duplicated). These results suggest that whole genome duplication or large-scale segmental duplications may have occurred in the evolutionary history of this algal species. HIGHLIGHTS Little genome data are available for lichenized algae. We generated the first genome for a lichenized Diplosphaera chodatii. Results suggest a possible whole genome duplication in this species.

Immobilization of metal(loid)s from acid mine drainage by biological soil crusts through biomineralization.

Acid mine drainage is harmful to the environment. Bioremediation based on biological soil crusts (BSCs) can be used as a new method to alleviate metal pollution in acid mine drainage. In this study, we found that BSCs can survive in a strongly acidic environment (pH = 3.28) and have a high metal(loid)s accumulation ability. The algae of genera Fragilaria, Klebsormidium, Cymbella, Melosira, Microcystacea, and Planctonema a're the main components of BSCs. These organisms in the BSCs regulated fatty acids and produced acid-resistant enzymes. The bioconcentration factors for As, Cd, Pb, Zn, and Cu were as high as 16,000, 200, 50, 26, and 400, respectively. The concentration of As and Cd in acid mine drainage decreased from 7.1μg and 350μg/L to 1.9μg and 110μg/L, respectively. Intotal, 56% of As, 73% of Cd, 88% of Pb, 85% of Zn, and 92% of Cu were present in BSCs as residual or mineral-bound forms. The XRD results (e.g., quarartz and phyllosilicates), SEM results (e.g., phylosilicates and diatom shells) and correlation results show that these metal(loid)s are immobilized by Cymbella (diatoms) during the deposition of silica in the acidic environment. Furthermore, adsorption and co-precipitation are other ways that metal(loid)s could have been bound. These findings provide new insights into the removal of metals (loid) in acidic water.

Review of the Cyanobacterial Genus Phormidesmis (Leptolyngbyaceae) with the Description of Apatinema gen. nov.

Cyanobacteria are crucial components of biological soil crusts of polar landscapes and carry out many functions in subaerial environments. Simple untapered filamentous cyanobacteria are typically in the terrestrial biotopes. They appear to be a group with an abundance of cryptic taxa. We isolated 23 strains of cyanobacteria from the different habitats of the Arctic and temperate zone, from 10 locations in order to characterize their morphological and genotypic diversity. Phylogenetic analyses were conducted on the 16S and 16S–23S ITS rRNA gene regions using Bayesian inference and maximum likelihood. A morphological comparison of the isolated strains with similar known species, as well as its phylogenetic analyses, revealed that they belong to three species of the genus Phormidesmis (P. nigrescens, P. pristley, and P. communis)—and to the previously unknown genus of Leptolyngbyaceae. Using an integrative approach, we provide here a description of a new taxon Apatinema gen. nov.

Eco-physiological functions of soil microbial biofilms: A review

Soil microbial biofilms (SMBs) are a biological community of soil bacteria and their accumulative extracellular polymeric substances (EPS), which are the initial status and the most important components of biological soil crusts. SMBs, as the most common mode of soil bacterium survival, not only greatly contribute to the survival of free-living cells, but also stick to soil particles and roots, performing a variety of important ecological functions. Based on the structure and composition analysis of SMBs, we gave a summary of eco-physiological functions of SMBs involving soil quality and plant health. SMBs have higher metabolic activity than free-living cells. It promotes EPS secretion and organic turnover, which is important for soil fertility, pollutant decomposition, and aggregate formation. SMBs help improve plant nutrient utilization and stress resistance through the synergy of microorganisms, promotion of plant growth, promoting substance secretion and immobilization of EPS. In the future, it will be critical to uncover the micro-mechanisms underlying SMBs' eco-physiological functions and to screen functional soil bacterium strains.

Diversity and spatial distribution of soil diatoms along a natural altitudinal gradient in the High Atlas (Morocco)

Microscopic algae especially diatoms (Class Bacillariophyceae) are an important component of biological soil crusts (or biocrust) communities in arid and semi-arid environments. In Morocco, a largely arid and semi-arid African Mediterranean country, the soil diatom diversity and ecology remain unexplored, unlike aquatic diatoms. This study aims to understand the spatial distribution of soil diatoms and to investigate the effects of soil properties and land use on their diversity and taxonomic composition in the region of Marrakesh (Morocco). Five sampling sites with different land use and vegetation cover were selected along a natural altitudinal gradient in the Ourika watershed (from the humid mountain highlands of Oukaimeden at 2634 m (High Atlas) to the arid Haouz plain at 765 m). Biological soil crusts were taken and soil physicochemical characteristics (soil moisture and texture, pH, electrical conductivity, total organic carbon, ammoniacal nitrogen, available phosphorus) were measured at five locations and two seasons (February and May). The spatial distribution of soil diatom communities and associated influencing factors were investigated via statistical analysis using Canonical Correspondence Analysis (CCA). A total of 27 diatom taxa belonging to 16 genera were recorded. The results showed that the distribution of soil diatoms was mainly influenced by altitude, bioclimate, substratum type, land use and vegetation cover. These environmental factors induce spatial variability in the soil physicochemical properties. Diatom composition and species richness were correlated with soil moisture, pH, texture, conductivity, nutrient and organic matter content. Diatoms showed higher species richness in siliceous soils of high altitudinal humid grassland dominated by acidophilous and neutral taxa with a preference for low conductivity. In contrast diatom communities of forests and sedimentary lowland arid steppe were relatively species poor, dominated by typically alkaliphilous and halophilous soil species. This exploratory survey provides a first account of the diatom assemblages of biological soil crusts over an altitudinal range in Morocco, necessary for understanding their structure and ecological function, including improving soil condition and sustainable fertility management.

Dehydration rates impact physiological, biochemical and molecular responses in desert moss Bryum argenteum

Dehydration rates significantly impact the amount of damage and rate of recovery of desiccation-tolerant mosses and thus play a role in the ability of these plants to occupy desert ecosystems. The desiccation-tolerant moss Bryum argenteum Hedw. is a component of biological soil crusts in northwestern China and has been extensively studied, but the effects of dehydration rates on its physiological and molecular responses to desiccation and rehydration are still unclear. We evaluated the physiological, biochemical, and molecular responses of B. argenteum during and upon recovery from rapid dehydration, ambient air dehydration, and slow dehydration rates. Our results demonstrated that (1) photosynthesis decreased significantly in response to all dehydration rates and recovered to the control level following rehydration; however, recovery from slow dehydration was more rapid. Ultrastructural investigations revealed that chloroplasts did not degrade and remained intact during desiccation regardless of the dehydration rates. (2) The activities of antioxidant enzymes increased under all drying regimes. Superoxide dismutase (SOD) and catalase (CAT) were the main scavenging enzymes that responded during the dehydration and rehydration processes. The transcripts encoding these enzymes also increased in abundance during desiccation and rehydration. (3) The extent of the increase of the abundance of stress-related transcripts was correlated with the dehydration rates, and all the transcripts displayed decreased abundance throughout rehydration. The majority of the transcripts showed similar accumulation patterns under the rapid and air dehydration treatments; however, slow dehydration resulted in a greater increase in transcript abundance. Our work provides insights into how desiccation and rehydration play roles in the ability of B. argentum to endure harsh environments.

When Is A Lineage A Species? A Case Study In Myxacorys gen. nov. (Synechococcales: Cyanobacteria) With The Description of Two New Species From The Americas.

Soil cyanobacteria are crucial components of biological soil crusts and carry out many functions in dryland ecosystems. Despite this importance, their taxonomy and population genetics remain poorly known. We isolated 42 strains of simple filamentous cyanobacteria previously identified as Pseudophormidium hollerbachianum from 26 desert locations in the North and South America and characterized these strains using a total evidence approach, that is, using both morphological and molecular data to arrive at taxonomic decisions. Based on a phylogenetic analysis of 16S rRNA gene sequences, we propose and characterize Myxacorys gen. nov. with two new species Myxacorys chilensis, the generitype, and M.californica. We also found distinct 16S-23S ITS sequence variability within species in our dataset. Especially interesting was the presence of two distinct lineages of M.californica obtained from locations in close spatial proximity (within a few meters to kilometers from each other) suggesting niche differentiation. The detection of such unrecognized lineage-level variability in soil cyanobacteria has important implications for biocrust restoration practices and conservation efforts.

Is the length of the drying period critical for photosynthesis reactivation in lichen and moss components of biological soil crusts?

Lichens and mosses represent the macroscopic components of biological soil crusts (biocrusts). Their ability to exploit short periods of water availability and reversibly deactivate metabolism is crucial for their growth and survival. In this work we investigated photosynthesis reactivation, respectively after long (65–66 days) and short (15 days) dry periods, in lichen and moss species widespread in two Mediterranean environments (Portugal and Italy). Chlorophyll a fluorescence emission of the samples was investigated and the parameter Fv/Fm, an indicator of vitality of photosynthetic organisms, was used as a proxy for photosynthesis reactivation. The fruticose lichens Cladonia convoluta and C. rangiformis, and the moss Pleurochaete squarrosa, typical of Mediterranean environments, showed a significantly slower reactivation of photosynthetic activity when subjected to a longer period of drought. Conversely, the alien invasive moss Campylopus introflexus was not affected by prolonged dry conditions. The study showed that drought duration influences the reactivation of photosynthetic activity in terricolous lichens and mosses forming biocrusts in re-hydration cycles. These results indicate the likelihood of a reduction in biocrust productivity as a consequence of climate change in Mediterranean drylands.

The Influence of Edaphic and Orographic Factors on Algal Diversity in Biological Soil Crusts on Bare Spots in the Polar and Subpolar Urals

The influence of edaphic and orographic factors on the formation of algal diversity in biological soil crusts was studied in mountain tundras of the Polar and Subpolar Urals. Bare spots developed in the soils on different parent materials and overgrown to different extents were investigated. Overall, 221 algal species from six divisions were identified. Among them, eighty-eight taxa were new for the region studied. The Stigonema minutum, S. ocellatum, Nostoc commune, Gloeocapsopsis magma, Scytonema hofmannii, Leptolyngbya foveolarum, Pseudococcomyxa simplex, Sporotetras polydermatica species and species of the Cylindrocystis, Elliptochloris, Fischerella, Leptosira, Leptolyngbya, Myrmecia, Mesotaenium, Phormidium, Schizothrix genera were permanent components of biological soil crusts. The basis of the algal cenoses in soil crusts was composed of cosmopolitan cyanoprokaryotes, multicellular green algae with thickened covers and abundant mucus. The share of nitrogen fixers was high. The physicochemical properties of primary soils forming under the crusts of spots are described. The more important factors affecting the species composition of algae in the crusts are the elevation gradient, temperature, soil moisture, and the contents of Ca, Mg, mobile phosphorus, and total nitrogen.

Resolving neutral and deterministic contributions to genomic structure in Syntrichia ruralis (Bryophyta, Pottiaceae) informs propagule sourcing for dryland restoration

Syntrichia ruralis is a cosmopolitan moss that occupies steep environmental gradients. In arid to semi-arid regions of the world it is a key component of biological soil crusts, which are fundamental to healthy dryland ecosystem processes. As such, S. ruralis has attracted the attention of conservationists seeking to restore degraded biological soil crust communities and their associated vascular flora. Here, we generate genomic data for S. ruralis populations that span climatic gradients across the Colorado Plateau of the southwestern USA to investigate the contributions of neutral and deterministic processes to the partitioning of genomic structure. Although S. ruralis appears to be highly dispersible, geographic proximity significantly predicts genomic similarity. In addition, even when taking into account apparently high migration rates among populations and spatial autocorrelation of allele frequencies, some genomic variation is explained by environmental gradients correlated with elevation and latitude. Consequently, efforts to restore dryland ecosystems by establishing S. ruralis as a foundation should include strategies to ensure that propagule sources of this moss are environmentally stratified and targeted to the current/future climates of restoration sites.

Two new species of Endocarpon (Verrucariaceae, Ascomycota) from China

Endocarpon species are key components of biological soil crusts. Phenotypic and systematic molecular analyses were carried out to identify samples of Endocarpon collected from the southeast edge of the Tengger Desert in China. These morphological and molecular analyses revealed two previously undescribed species that form highly supported independent monophyletic clades within Endocarpon. The new taxa were named Endocarpon deserticola sp. nov. and E. unifoliatum sp. nov. Furthermore, our results indicated that the newly developed protein coding markers adenylate kinase (ADK) and ubiquitin-conjugating enzyme h (UCEH) are useful for assessing species boundaries in phylogenic analyses.

Habitat-specific composition of morphotypes with low genetic diversity in the green algal genus Klebsormidium (Streptophyta) isolated from biological soil crusts in Central European grasslands and forests

ABSTRACT Terrestrial filamentous green algae of the widely distributed, cosmopolitan genus Klebsormidium (Klebsormidiophyceae, Streptophyta) are typical components of biological soil crusts (BSCs). These communities occur in all climatic zones and on all continents, where soil moisture is limited or where there has been disturbance. BSCs form water-stable aggregates that have important ecological roles in primary production, nitrogen fixation, nutrient cycling, water retention and stabilization of soils. Although available data on Klebsormidium are limited, its functional importance in BSCs is regarded as high. Therefore, in the present study Klebsormidium strains were isolated from BSCs sampled from various grassland and forest plots of different land use intensities in Central Europe, as provided by the Biodiversity Exploratories, and its intraspecific genetic diversity was evaluated. Previous phylogenetic analyses revealed a relationship between sequence similarity and habitat preference with a higher genetic diversity than expected from a morphological classification. We isolated and sequenced 75 Klebsormidium strains. The molecular phylogeny based on the ITS regions showed that all strains belong to either the previously described clade B/C or clade E. This classification was supported by morphological characteristics: strains assigned to clade B/C were identified as Klebsormidium cf. flaccidum or Klebsormidium cf. dissectum, and strains from clade E as K. nitens or Klebsormidium cf. subtile. Within one clade the strains showed low sequence divergences. These minor differences were independent of the sampling region and land use intensity. Interestingly, most of the strains assigned to clade E were isolated from forest sites, whereas strains from clade B/C occurred equally in grassland and forest sites. Therefore, it is reasonable to assume that habitat with its microenvironmental conditions, and not biogeography, controls genetic diversity in Klebsormidium.

Dehydration, temperature, and light tolerance in members of the aeroterrestrial green algal genus interfilum (streptophyta) from biogeographically different temperate soils.

Unicellular green algae of the genus Interfilum (Klebsormidiales, Streptophyta) are typical components of biological soil crusts. Four different aeroterrestrial Interfilum strains that have previously been molecular-taxonomically characterized and isolated from temperate soils in Belgium, Czech Republic, New Zealand, and Ukraine were investigated. Photosynthetic performance was evaluated under different controlled abiotic conditions, including dehydration, as well as under a light and temperature gradient. For standardized desiccation experiments, a new methodological approach with silica gel filled polystyrol boxes and effective quantum yield measurements from the outside were successfully applied. All Interfilum isolates showed a decrease and inhibition of the effective quantum yield under this treatment, however with different kinetics. While the single cell strains exhibited relatively fast inhibition, the cell packet forming isolates dried slower. Most strains fully recovered effective quantum yield after rehydration. All Interfilum isolates exhibited optimum photosynthesis at low photon fluence rates, but with no indication of photoinhibition under high light conditions suggesting flexible acclimation mechanisms of the photosynthetic machinery. Photosynthesis under lower temperatures was generally more active than respiration, while the opposite was true for higher temperatures. The presented data provide an explanation for the regular occurrence of Interfilum species in soil habitats where environmental factors can be particularly harsh.

Green algae in alpine biological soil crust communities: acclimation strategies against ultraviolet radiation and dehydration.

Green algae are major components of biological soil crusts in alpine habitats. Together with cyanobacteria, fungi and lichens, green algae form a pioneer community important for the organisms that will succeed them. In their high altitudinal habitat these algae are exposed to harsh and strongly fluctuating environmental conditions, mainly intense irradiation, including ultraviolet radiation, and lack of water leading to desiccation. Therefore, green algae surviving in these environments must have evolved with either avoidance or protective strategies, as well as repair mechanisms for damage. In this review we have highlighted these mechanisms, which include photoprotection, photochemical quenching, and high osmotic values to avoid water loss, and in some groups flexibility of secondary cell walls to maintain turgor pressure even in water-limited situations. These highly specialized green algae will serve as good model organisms to study desiccation tolerance or photoprotective mechanisms, due to their natural capacity to withstand unfavorable conditions. We point out the urgent need for modern phylogenetic approaches in characterizing these organisms, and molecular methods for analyzing the metabolic changes involved in their adaptive strategies.

Size Effects on Water Characteristic of Moss Crust in the Gurbantunggut Desert, Northwestern China

In arid land, water is a limiting factor, the distribution and species of vegetation are greatly affected by water supply. Moss crust is the main components of biological soil crusts (BSCs), it plays an important role in water retention than crusted lichen and algae and generally, moss crust remain distributed in patches. This paper focuses on further explaining the reason that moss crust distribute in the form of different sizes patches from the point of water using. In this study, sizes of moss crust was calculated by Photoshop CS 5.0, dew deposition and water evaporation were measured by micro-lysimeters, soil water content was analyzed by drying oven. The results showed size effect of moss crust on water evaporation which was not consistent, smaller patch evaporated slowly but later, they evaporated fast and large patch evaporated slowly; the medium-size patch showed the greatest deposition ability, and the smallest exhibited the least; there was heterogeneity of soil water content of moss crusts patches, the waterisland of moss crust was a little smaller than patch size; usually, water content of moss crusts patch decreased from center to edge. In whole, medium size patches showed high water using efficiency, it was one of the reasons why there were few large moss crusts patches in the Gurbantunggut Desert. We inferred preliminarily it was a tactic to raise water using efficiency for moss crusts to distribute in patches.

叶片毛尖对齿肋赤藓结皮凝结水形成及蒸发的影响

凝结水(隐匿降水)和降水是荒漠地区两种不同形式的水分来源,对荒漠生态系统极为重要。叶片毛尖(leaf hair points, LHPs)是很多荒漠藓类的重要外部形态结构特征,但它在藓类植物利用凝结水和降水中的作用尚不清楚。齿肋赤藓(<em>Syntrichia caninervis</em>)是古尔班通古特沙漠藓类结皮的优势种,其叶片顶端具有较长的白色毛尖。采用自制微渗计(<em>h</em>=3.5 cm, <em>d</em>=5.7 cm)研究了正常有毛尖和人工去除毛尖的齿肋赤藓结皮的凝结水特征及其在3种模拟降水梯度(1,3,6 mm)下的短期蒸发特征,结果表明:(1) 在凝结阶段,有毛尖结皮每时段的凝结水量均大于无毛尖结皮,但日出后有毛尖结皮凝结水下降速度稍快;有毛尖结皮的日凝结水量均大于无毛尖结皮,且前者的总凝结水量比后者多10.26%,即毛尖能增加10.26%的凝结水量。(2) 3种模拟降水梯度下,有毛尖结皮在各时段的累积蒸发率始终小于无毛尖结皮,以蒸发前期阶段最为明显,表明毛尖能显著减少和延缓结皮内的水分蒸发、延长植株水合时间,而且降水量越大减缓效果越明显。毛尖对这2种不同形式水分利用的差异是因为利用方式不同:对凝结水的利用主要归因于毛尖增大了结皮表面粗糙度,而减少对降水的蒸发主要是毛尖能反射阳光、形成内部毛细管及减小植株间隙的缘故。因此,毛尖的存在有利于齿肋赤藓结皮对凝结水和降水的利用,增强了藓类结皮对干旱环境的适应能力。;In arid areas where rainfall is rare and solar radiation is strong, reducing water loss and efficient water use are extremely important for plant survival. Desiccation-tolerant mosses are the dominant components of biological soil crusts (BSCs) in desert ecosystems. These mosses play important roles in soil surface stability, fertility, and ecological restoration. Crust-forming mosses have presumably developed special morphological and anatomical features to cope with harsh desert conditions, but the nature of these remains largely unknown. Some special morphological features (such as convex or concave leaves, papilla, and thick marginal cell walls) have been observed; providing evidence of long-term adaptation to the desert environment. Leaf hair points (LHPs) are important morphological structures in many desiccation-tolerant mosses. These are elongations of leaf midribs; they are generally white, with many small spiny teeth on their surfaces. A few preliminary studies have indicated that LHPs in several kinds of cushion mosses can reflect sunshine, absorb moisture from the air, and reduce water loss. Precipitation is the main water source in desert areas. The rainfall in the center of the Gurbantunggut Desert is only 70 to 150 mm per annum, and most rainfall events (89.8% in 1998-2007 data) are less than 5 mm. Even so, these events still enable desert mosses to reach and to maintain hydration for a time. In addition, dew and fog (occult precipitation) provide small amounts of water; not enough to hydrate mosses, but with a greater frequency than rainfall. Occult precipitation is thus another important water source for desert biology, and has a crucial role in these ecosystems. Research into the role of the LHPs of drought-resistant mosses is timely. We collected a dominant desert moss, <em>Syntrichia caninervis</em>, from the Gurbantunggut Desert of Xinjiang, China, to investigate the effect of LHPs on water use. The LHPs of <em>S. caninervis</em> are often broken in nature. Our method involved comparison of moss patches with LHPs and moss patches with LHPs manually removed. Characteristics of dew deposition and short-term rainfall evaporation (1 mm, 3 mm, 6 mm) of <em>S. caninervis</em> crusts with and without LHPs were studied using purpose-built micro-lysimeters (PVC, <em>h</em>=3.5 cm, <em>d</em>=5.7 cm). Results indicated that (1) Dew amounts on crusts with LHPs were greater than on crusts without LHPs. After sunrise, the dew on crusts with LHPs dried slightly faster. Daily dew amounts on crusts with LHPs were greater than on crusts without LHPs. The total dew amount for seven days on crusts with LHPs was 10.26% greater than on crusts without LHPs. Thus LHPs can improve dew amounts on <em>S. caninervis</em> crusts by 10.26%. (2) Rainfall evaporation rates from crusts with LHPs were lower than from crusts without LHPs at every time of evaporation; this was most obvious during the early period. LHPs can significantly delay and reduce water evaporation, thus extending the hydration time of <em>S. caninervis</em> crusts. These differences in water utilization are a result of two aspects. More efficient dew use is attributable to LHPs increasing the surface roughness of the crusts. By reflecting light, forming internal capillaries, and reducing gaps between individuals, LHPs are able to reduce rainfall evaporation. In conclusion, the existence of LHPs is favorable for the utilization of dew and rainfall by <em>S. caninervis</em> crusts, and increases the ability of these moss crusts to adapt to arid conditions.

Genome of the Cyanobacterium Microcoleus vaginatusFGP-2, a Photosynthetic Ecosystem Engineer of Arid Land Soil Biocrusts Worldwide

The filamentous cyanobacterium Microcoleus vaginatusis found in arid land soils worldwide. The genome of M. vaginatus strain FGP-2 allows exploration of genes involved in photosynthesis, desiccation tolerance, alkane production, and other features contributing to this organism's ability to function as a major component of biological soil crusts in arid lands.

ECOPHYSIOLOGICAL PERFORMANCE OF THE AEROTERRESTRIAL GREEN ALGA KLEBSORMIDIUM CRENULATUM (CHAROPHYCEAE, STREPTOPHYTA) ISOLATED FROM AN ALPINE SOIL CRUST WITH AN EMPHASIS ON DESICCATION STRESS1

Aeroterrestrial filamentous green algae of the genus Klebsormidium (Klebsormidiales, Streptophyta) are typical components of biological soil crusts, which occur worldwide in arid and semiarid habitats including alpine regions. In the present study, Klebsormidium crenulatum (Kütz.) Lokhorst was isolated from an alpine soil crust above the timberline of the Austrian Alps. Growth responses, photosynthetic performance, and desiccation tolerance were measured under controlled laboratory conditions. K. crenulatum exhibited optimal growth and the highest photosynthetic efficiency under relatively low photon fluence densities (30 and 21.9 μmol photons · m−2 · s−1, respectively), indicating low‐light requirements. It grew in a narrow range of salinities between 1.2 and 15 practical salinity units (psu), pointing to a pronounced stenohaline response pattern. Increasing temperatures from 5°C to 40°C led to different effects on photosynthetic oxygen evolution and respiratory oxygen consumption in K. crenulatum. While at low temperatures (5°C–10°C) photosynthesis was relatively high, respiration was not detectable or was at a very low level. Conversely, at the highest temperature of 40°C, photosynthesis was inhibited, and respiration unaffected, indicating strong differences in temperature sensitivity between both physiological processes. K. crenulatum was capable of photosynthesizing efficiently for up to 2.5 h under desiccation, followed by a decrease to 15% of the initial value after 3 h. Complete recovery took place within 2 h after rehydration. All ecophysiological data explain the widespread abundance of K. crenulatum in soil crusts of the alpine regions of the European Alps.

The effects of drying following heat shock exposure of the desert moss Syntrichia caninervis

Desert mosses are components of biological soil crusts (BSCs) and their ecological functions make assessment and protection of these mosses a high-ranking management priority in desert regions. Drying is thought to be useful for desert mosses surviving heat shock. In this study, we investigated the role of drying by monitoring the responses of physiological characters and asexual reproduction in the typical desert moss Syntrichia caninervis. Heat significantly decreased chlorophyll content and weakened rapid recovery of photochemical activity, and increased carotenoid content and membrane permeability. Lethal temperatures significantly destroyed shoot regeneration potential. In comparison with heat alone, drying significantly increased protonema emergence time and depressed protonema emergence area. Drying combined with heat accelerated water loss, followed by a decrease of photosynthetic activity. Drying had different influences on membrane permeability at different temperatures. When moss leaves were subjected to a combined stress of drying and heat shock, photosynthesis was maintained mainly due to the effects of drying on physiological activity although the cellular morphological integrity was affected. Drying caused opposing effects on moss physiological and reproductive characteristics. On the one hand, drying caused a positive synergistic effect with heat shock when the temperature was below 40 degrees C. On the other hand, drying showed antagonism with heat shock when the moss was subjected to temperatures higher than 40 degrees C. These findings may help in understanding the survival mechanism of dessert mosses under heat shock stress which will be helpful for the artificial reconstruction of BSCs.

A Technology for Rapid Reconstruction of Moss-Dominated Soil Crusts

Reconstruction of moss-dominated soil crusts is crucial for ecological restoration. A desert moss Tortula desertorum (Broth.), the main component of biological soil crusts in the Gurbantunggut desert, was used to build a procedure for construction of moss-dominated crust. Micropropagation of desert mosses is a core technology to build biological soil crusts. Although the micropropagation of mosses has been extensively studied, little is known about that of desert mosses. Effects of media, explants, and culture temperature on regeneration potential of T. desertorum were investigated respectively in this study. The factors such as relative humidity, light intensity, and photoperiod, which might take an important role in the regeneration and development of the desert moss T. desertorum, were optimized through an orthogonal test design. The life cycle of the desert moss T. desertorum in cultivation was also investigated according to several factors affecting asexual reproduction. The results showed the explants cultivated with in situ soil had produced more protonema and shoots than those cultivated with other media. Detached leaves as explants yielded more biomass per gametophyte. It was found that a slightly higher temperature facilitated shoot growth. It should be pointed out that the favorable period for T. desertorum asexual reproduction occurred mainly in early summer, which contributes to the efficient protection of biological soil crusts. Based on the life cycle of T. desertorum in cultivation, a procedure for artificial reconstruction of moss-dominated soil crusts was established and assessed. A large number of protonema were induced to grow by breeding detached green leaves in agar-solid Knop medium after 1 month as day/night temperature and humidity were set at 20/10°C and 60–85%, respectively. Moss-dominated crusts formed through transplanting protonema into sand supplemented with liquid Knop medium under day/night temperatures of 25/15°C after another month.