Optimizing the algae-bacteria biofilm reactor for imidacloprid wastewater treatment: An evaluation of hydraulic retention times for enhanced efficiency and energy savings.

Recent observations have highlighted the rapidly growing prevalence of emerging contaminants such as Imidacloprid (IMI) within our environment. These insecticidal pollutants, coexisting with more traditional contaminants, have become predominant in aquatic systems, posing risks to both human and ecological well-being. Among the various wastewater treatment approaches tested, biofilm reactors are currently gaining prominence. In this study, we employed an Algae-Bacteria Biofilm Reactor (ABBR) to concurrently address both conventional and emergent contaminants, specifically IMI, over an extended timeframe. Following a 60-day assessment, the ABBR consistently demonstrated removal efficiencies exceeding 85% for total dissolved nitrogen, ammonia nitrogen, and total dissolved phosphorus, and also achieved removal efficacy for the soluble chemical oxygen demand (sCOD). Despite the removal efficiency of IMI (with initial concentration is 1.0 mg/L) in ABBR showed a gradual decline over the extended period, it remained consistently effective over 50% due to the microalgae-mediated free radical reactions, indicating the ABBR's sustained efficiency in long-duration operations. Additionally, applying some non-conventional modifications, like aeration removal and reducing light exposure, demonstrated minimal impact on the reactor's pollutant removal efficiencies, achieving comparable results to the control group (which utilized aeration with a 14:10 light/dark ratio), 0.92 kW h/L/d of electricity can be saved economically, which accentuated the potential for energy conservation. An in-depth analysis of the treated effluents from the ABBRs, using ultra-performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) technique, uncovered four potential transformation pathways for IMI. Overall, our findings suggest that these optimized processes did not influence the transformation products of IMI, thereby reaffirming the viability of our proposed optimization.

Performance of a biocrust cyanobacteria-indigenous bacteria (BCIB) co-culture system for nutrient capture and transfer in municipal wastewater.

This study aimed to explore the potential for transferring nutrients from municipal wastewater through the cultivation of biocrust cyanobacteria, since little is known regarding the growth and bioremediation performance of biocrust cyanobacteria in actual wastewater, especially their interaction with indigenous bacteria. Therefore, in this study, the biocrust cyanobacterium, Scytonema hyalinum was cultivated in municipal wastewater under different light intensities, to establish a biocrust cyanobacteria-indigenous bacteria (BCIB) co-culture system, in order to investigate its nutrient removal efficiency. Our results revealed that the cyanobacteria-bacteria consortium could remove up to 91.37 % and 98.86 % of dissolved nitrogen and phosphorus from the wastewater, respectively. The highest biomass accumulation (max. 6.31 mg chlorophyll-a L-1) and exopolysaccharide secretion (max. 21.90 mg L-1) were achieved under respective optimized light intensity (60 and 80 µmol m-2 s-1). High light intensity was found to increase exopolysaccharide secretion, but negatively impacted cyanobacterial growth and nutrient removal. Overall, in the established cultivation system, cyanobacteria accounted for 26-47 % of the total bacterial abundance, while proteobacteria consisted up to 50 % of the mixture. The composition and ratio of cyanobacteria to indigenous bacteria were shown to be altered by adjusting the light intensity of the system. Altogether, our results clearly illustrate the potential of the biocrust cyanobacterium S. hyalinum in establishing a BCIB cultivation system under different light intensity for wastewater treatment and other end-applications (e.g., biomass accumulation and exopolysaccharide secretion). This study presents an innovative strategy for transferring nutrients from wastewater to drylands through cyanobacterial cultivation and subsequent biocrust induction.

The living forms of Microcoleus vaginatus and their contributions to the aggregate structure of biocrusts.

Microcoleus vaginatus has been regarded as the important contributor for biocrust formation and ecological services. However, little is known about its living forms in biocrusts, and whether the living form is related to biocrust structure. Therefore, in this study, natural biocrusts collected from the Gurbantunggut Desert were divided into different aggregate/grain fractions, aiming at investigating the living forms of M. vaginatus in biocrusts at fine scale, and exploring its roles in aggregate structure and ecological functions of biocrusts. The results showed that two distinct living forms of M. vaginatus had been identified from the biocrusts. The non-bundling M. vaginatus was mainly distributed in the fractions of > 0.5 mm, forming aggregate structure by cementing sand particles firmly; while the bundling M. vaginatus, distributed mainly among the free sand particles with diameter < 0.5 mm, and easily migrated up to biocrust surface after hydration. Furthermore, the aggregate structure formed by non-bundling M. vaginatus supported a higher biomass, nutrient contents, and enzyme activities. Altogether, our results suggest that the strong migrating ability of bundling M. vaginatus contributes to the environmental adaptation and light resource acquirement, while non-bundling M. vaginatus acts as the constructor of the aggregate structure in biocrusts.

Physical Disturbance Reduces Cyanobacterial Relative Abundance and Substrate Metabolism Potential of Biological Soil Crusts on a Gold Mine Tailing of Central China.

As the critical ecological engineers, biological soil crusts (biocrusts) are considered to play essential roles in improving substrate conditions during ecological rehabilitation processes. Physical disturbance, however, often leads to the degradation of biocrusts, and it remains unclear how the physical disturbance affects biocrust microorganisms and their related metabolism. In this study, the photosynthetic biomass (indicated by chlorophyll a), nutrients, enzyme activities, and bacterial communities of biocrusts were investigated in a gold mine tailing of Central China to evaluate the impact of physical disturbance on biocrusts during the rehabilitation process of gold mine tailings. The results show that physical disturbance significantly reduced the photosynthetic biomass, nutrient contents (organic carbon, ammonium nitrogen, nitrate nitrogen, and total phosphorus), and enzyme activities (ß-glucosidase, sucrase, nitrogenase, neutral phosphatase, and urease) of biocrusts in the mine tailings. Furthermore, 16S rDNA sequencing showed that physical disturbance strongly changed the composition, structure, and interactions of the bacterial community, leading to a shift from a cyanobacteria dominated community to a heterotrophic bacteria (proteobacteria, actinobacteria, and acidobacteria) dominated community and a more complex bacterial network (higher complexity, nodes, and edges). Altogether, our results show that the biocrusts dominated by cyanobacteria could also develop in the tailings of humid region, and the dominants (e.g., Microcoleus) were the same as those from dryland biocrusts; nevertheless, physical disturbance significantly reduced cyanobacterial relative abundance in biocrusts. Based on our findings, we propose the future work on cyanobacterial inoculation (e.g., Microcoleus), which is expected to promote substrate metabolism and accumulation, ultimately accelerating the development of biocrusts and the subsequent ecological restoration of tailings.

Cyanobacterial persistence and influence on microbial community dynamics over 15 years in induced biocrusts.

Biocrusts provide numerous ecological functions in drylands. Recovering biocrusts via cyanobacterial inoculation recently gathered interest for ecological restoration, yet it still lacks long-term experiments to unravel biocrust community dynamics. To examine how cyanobacterial inoculants influenced local microbial community and biocrust development, we observed a 2 km2 (Qubqi Desert, China) inoculation experiment after 10 and 15 years, following biocrust formation. Our results revealed that biocrust development was in line with ecological regime shift, providing evidence for biocrust community succession, from cyanobacteria- to moss-dominated types. Associated with biocrust development, microbial communities differed significantly with less specialists compared to shifting sands. Cyanobacterial community analysis showed that Microcoleus vaginatus and Scytonema javanicum are an ideal inoculating model, as they were still dominating the community after 15 years since inoculation, while other nitrogen-fixing cyanobacteria occurred profusely with biocrust development. Biocrust community composition combined with thickness, Chl-a and exopolysaccharide measurements revealed the large variation of cyanobacterial ecological functions along biocrust development, suggesting a main function shift: from carbon fixation associated with exopolysaccharide secretion in bare sandy soils to nitrogen fixation in developed biocrusts. This large-scale field study verifies that cyanobacterial inoculation accelerates biocrust development and forwards succession, shaping the biocrust community composition over a long time.

Cyanobacterial community composition and their functional shifts associated with biocrust succession in the Gurbantunggut Desert.

Cyanobacteria, as key biocrust components, provide a variety of ecosystem functions in drylands. In this study, to identify whether a cyanobacterial community shift is involved in biocrust succession and whether this is linked to altered ecological functions, we investigated cyanobacterial composition, total carbon and nitrogen contents of biocrusts in the Gurbantunggut Desert. Our findings showed that the biocrust cyanobacteria in the Gurbantunggut desert were mostly filamentous, coexisting with abundant unicellular colonial Chroococcidiopsis. Heterocystous Nostoc, Scytonema and Tolypothrix always represented the majority of biocrust nitrogen-fixing organisms, comprising an average of 92% of the nifH gene reads. Community analysis showed a clear shift in prokaryotic community composition associated with biocrust succession from cyanobacteria- to lichen- and moss-dominated biocrusts, and filamentous non-nitrogen-fixing cyanobacteria-dominated communities were gradually replaced by nitrogen-fixing and unicellular colonial communities. Along the succession, there were concomitant reductions in cyanobacterial relative abundance, whereas Chl-a, total carbon and nitrogen contents increased. Concurrently, distinct carbon and nitrogen stores shifts occurred, implying that the main ecological contribution of cyanobacteria in biocrusts changes from carbon- to nitrogen-fixation along with the succession. Our results suggest that any activity that reverses biocrust succession will influence cyanobacterial community composition and eventually lead to large reductions in soil carbon and nitrogen stores.

Metagenomic Insight Into Patterns and Mechanism of Nitrogen Cycle During Biocrust Succession.

The successional ecology of nitrogen cycling in biocrusts and the linkages to ecosystem processes remains unclear. To explore this, four successional stages of natural biocrust with five batches of repeated sampling and three developmental stages of simulated biocrust were studied using relative and absolute quantified multi-omics methods. A consistent pattern across all biocrust was found where ammonium assimilation, mineralization, dissimilatory nitrite to ammonium (DNiRA), and assimilatory nitrate to ammonium were abundant, while denitrification medium, N-fixation, and ammonia oxidation were low. Mathematic analysis showed that the nitrogen cycle in natural biocrust was driven by dissolved organic N and NO3 -. pH and SO4 2- were the strongest variables affecting denitrification, while C:(N:P) was the strongest variable affecting N-fixation, DNiRA, nitrite oxidation, and dissimilatory nitrate to nitrite. Furthermore, N-fixation and DNiRA were closely related to elemental stoichiometry and redox balance, while assimilatory nitrite to ammonium (ANiRA) and mineralization were related to hydrological cycles. Together with the absolute quantification and network models, our results suggest that responsive ANiRA and mineralization decreased during biocrust succession; whereas central respiratory DNiRA, the final step of denitrification, and the complexity and interaction of the whole nitrogen cycle network increased. Therefore, our study stresses the changing environmental functions in the biocrust N-cycle, which are succession-dependent.

Effects of vegetation on bacterial communities, carbon and nitrogen in dryland soil surfaces: implications for shrub encroachment in the southwest Kalahari.

Shrub encroachment is occurring in many of the world's drylands, but its impacts on ecosystem structure and function are still poorly understood. In particular, it remains unclear how shrub encroachment affects dryland soil surfaces, including biological soil crust (biocrust) communities. In this study, soil surfaces (0-1 cm depth) were sampled from areas of Grewia flava shrubs and Eragrostis lehmanniana and Schmidtia kalahariensis grasses in the southwest Kalahari during two different seasons (March and November). Our hypothesis is that the presence of different vegetation cover types (shrubs versus grasses) alters the microbial composition of soil surfaces owing to their contrasting microenvironments. The results showed that more significant differences in microclimate (light, soil surface temperatures) and soil surface microbial communities were observed between shrubs and grasses than between sampling seasons. Based on high-throughput 16S rRNA gene sequencing, our findings showed that approximately one third (33.5%) of the operational taxonomic units (OTUs) occurred exclusively in soil surfaces beneath shrubs. Soil surfaces with biocrusts in grass areas were dominated by the cyanobacteria Microcoleus steenstrupii, whereas the soil surfaces beneath shrubs were dominated by the proteobacteria Microvirga flocculans. Soil surfaces beneath shrubs are associated with reduced cyanobacterial abundance but have higher total carbon and total nitrogen contents compared to biocrusts in grass areas. These findings infer changes in the relative contributions from different sources of carbon and nitrogen (e.g. cyanobacterial and non-cyanobacterial fixation, plant litter, animal activity). The distinctive microbial composition and higher carbon and nitrogen contents in soil surfaces beneath shrubs may provide a positive feedback mechanism promoting shrub encroachment, which helps to explain why the phenomenon is commonly observed to be irreversible.

Temperature modulating sand-consolidating cyanobacterial biomass, nutrients removal and bacterial community dynamics in municipal wastewater.

Cultivating sand-consolidating cyanobacteria using wastewater has unique advantages on both nutrients recycling and ecological restoration by transferring excessive nutrients from wastewaters to desert areas. Although previous study showed that sand-consolidating cyanobacterium well adapted to synthetic domestic wastewater, no study has been carried out on actual wastewater. This study aims to investigate the sand-consolidating cyanobacterial biomass production and nutrients removal by cultivating Scytonema hyalinum in the municipal wastewater under different temperatures. The results showed that biomass accumulation increased with temperature from 20 â„ƒ to 30 â„ƒ, while severely depressed at 35 â„ƒ. More than 81.63% sCOD, 90.64% TDN and 97.08% TDP were removed by day 30 under each temperature except for 35℃. The inoculation of S. hyalinum strongly regulated the native wastewater bacterial community. These results indicated that sand-consolidating cyanobacterium S. hyalinum well adapted to municipal wastewater and temperature had remarkable effects on cyanobacterial biomass accumulation, nutrients removal and wastewater native bacterial community dynamics.

Small-Scale Spatial Heterogeneity of Photosynthetic Fluorescence Associated with Biological Soil Crust Succession in the Tengger Desert, China.

In dryland regions, biological soil crusts (BSCs) have numerous important ecosystem functions. Crust species and functions are, however, highly spatially heterogeneous and remain poorly understood at a range of scales. In this study, chlorophyll fluorescence imaging was used to quantify millimeter-scale patterns in the distribution and activity of photosynthetic organisms in BSCs of different successional stages (including cyanobacterial, lichen, moss three main successional stages and three intermixed transitional stages) from the Tengger Desert, China. Chlorophyll fluorescence images derived from the Imaging PAM (Pulse Amplitude Modulation) showed that with the succession from cyanobacterial to lichen and to moss crusts, crust photosynthetic efficiency (including the maximum and effective photosynthetic efficiency, respectively) and fluorescence coverage increased significantly (P < 0.05), and that increasing photosynthetically active radiation (PAR) reduced the effective photosynthetic efficiency (Yield). The distribution of photosynthetic organisms in crusts determined Fv/Fm (ratio of variable fluorescence to maximum fluorescence) frequency pattern, although the photosynthetic heterogeneity (SHI index) was not significantly different (P > 0.05) between cyanobacterial and moss crusts, and showed a unimodal pattern of Fv/Fm values. In contrast, photosynthetic heterogeneity was significantly higher in lichen, cyanobacteria-moss and lichen-moss crusts (P < 0.05), with a bimodal pattern of Fv/Fm values. Point pattern analysis showed that the distribution pattern of chlorophyll fluorescence varied at different spatial scales and also among the different crust types. These new results provide a detailed (millimeter-scale) insight into crust photosynthetic mechanisms and spatial distribution patterns associated with their community types. Collectively, this information provides an improved theoretical basis for crust maintenance and management in dryland regions.

Nutrient transferring from wastewater to desert through artificial cultivation of desert cyanobacteria.

Realizing the reasonable allocation of resources is possible to solve the dual problems of resources and environment. Therefore, in this study desert cyanobacterium Scytonema javanicum was cultivated in artificial synthetic wastewater to explore the feasibility of nutrient transferring from wastewater to desert. After inoculation, S. javanicum grew well in the wastewater; nitrogen and phosphorus were gradually removed from the wastewater. In general, cyanobacterial biomass, exopolysaccharide content, COD, nitrogen and phosphorus contents were all significantly affected by the cultivation time, wastewater dilution treatment and their interaction (P<0.001). Comprehensively considering the producing period, biomass accumulation and nutrient removal efficiency, cultivation time of cyanobacterium S. javanicum in the synthetic wastewater should be controlled around 20days, with wastewater dilution ratio at 1:1. Conclusively, desert cyanobacterium S. javanicum is a promising species for nutrient transferring from wastewater to desert, and its maximum biomass yield could reach 3.91mgChl-aL-1 in the synthetic wastewater.

A new biofilm based microalgal cultivation approach on shifting sand surface for desert cyanobacterium Microcoleus vaginatus.

Biofilm based microalgal cultivation has recently received great attention because of its low water requirement and harvesting cost. However, the contradiction between microalgal attachment and harvesting still hinders the development of this technology. Therefore, in this study the most readily available and inexpensive shifting sand was used as attached substrate for microalgal (Microcoleus vaginatus) biofilm cultivation under different water conditions. After the inoculation, a stable and easily peeled microalgal biofilm formed through filamentous binding and exopolysaccharide cementing. In general, microalgal biomass, photosynthetic activity and exopolysaccharide accumulation were all significantly affected by the cultivation time, water content and their interaction (P<0.001). According to the maximal photosynthetic activity and microalgal productivity, cultivation time of microalgal biofilm on sand surface should be controlled around 15-25days, with water content at 10%. Based on the biofilm cultivation system, microalgal biomass yield reached up to 11gm-2 eventually on the sand surface.

Photosynthetic recovery and acclimation to excess light intensity in the rehydrated lichen soil crusts.

As an important successional stage and main type of biological soil crusts (BSCs) in Shapotou region of China (southeastern edge of Tengger Desert), lichen soil crusts (LSCs) often suffer from many stresses, such as desiccation and excess light intensity. In this study, the chlorophyll fluorescence and CO2 exchange in the rehydrated LSCs were detected under a series of photosynthetically active radiation (PAR) gradients to study the photosynthetic acclimation of LSCs. The results showed that although desiccation leaded to the loss of photosynthetic activity in LSCs, the fluorescence parameters including Fo, Fv and Fv/Fm of LSCs could be well recovered after rehydration. After the recovery of photosynthetic activity, the effective photosynthetic efficiency ΦPSII detected by Imaging PAM had declined to nearly 0 within both the lichen thallus upper and lower layers when the PAR increased to 200 µE m-2 s-1, however the net photosynthesis detected by the CO2 gas analyzer in the LSCs still appeared when the PAR increased to 1000 µE m-2 s-1. Our results indicate that LSCs acclimating to high PAR, on the one hand is ascribed to the special structure in crust lichens, making the incident light into the lichen thallus be weakened; on the other hand the massive accumulation of photosynthetic pigments in LSCs also provides a protective barrier for the photosynthetic organisms against radiation damage. Furthermore, the excessive light energy absorbed by crust lichens is also possibly dissipated by the increasing non-photochemical quenching, therefore to some extent providing some protection for LSCs.

Analysis of environmental factors determining development and succession in biological soil crusts.

Biological soil crusts play important ecological functions in arid and semi-arid regions, while different crust successional patterns appeared in different regions. Therefore in this study, the environmental conditions between Shapotou (with cyanobacterial, lichen and moss crusts) and Dalate Banner (with only cyanobacterial and moss crusts) regions of China were compared to investigate why lichen crusts only appeared in Shapotou; at the same time, artificial moss inoculation was conducted to find out the environmental factors promoting crust succession to moss stage. The results showed lichen crusts always developed from cyanobacterial crusts, which provide not only the stable soil surface, but also the biomass basis for lichen formation; furthermore, addition of crust physicochemical characteristics (primarily silt content) play a facilitating effect on lichen emergence (R(2)=0.53). The inoculation experiment demonstrated early crust soil surface and enough water holding content (>4%) provided the essential guarantee for moss germination. Our results show that there is heterogeneity in crust succession in different regions, which may be mainly affected by the ambient soil microenvironments. It is concluded that a positive feedback mechanism is expected between crust succession and ambient soil microenvironments; while a negative feedback mechanism forms between crust succession and free living cyanobacteria and algae.

Effects of light and temperature on open cultivation of desert cyanobacterium Microcoleus vaginatus.

Microalgae cultivation has recently been recognized as an important issue to deal with the increasingly prominent resource and environmental problems. In this study, desert cyanobacterium Microcoleus vaginatus was open cultivated in 4 different cultivation conditions in Qubqi Desert, and it was found Chlorella sp., Scenedesmus sp. and Navicula sp. were the main contaminating microalgal species during the cultivation. High light intensity alone was responsible for the green algae contamination, but the accompanied high temperature was beneficial to cyanobacterial growth, and the maximum biomass productivity acquired was 41.3mgL(-1)d(-1). Low temperature was more suitable for contaminating diatoms' growth, although all the microalgae (including the target and contaminating) are still demand for a degree of light intensity, at least average daily light intensity >5µEm(-2)s(-1). As a whole, cultivation time, conditions and their interaction had a significant impact on microalgal photosynthetic activity (Fv/Fm), biomass and exopolysaccharides content (P<0.001).

[Development and succession of artificial biological soil crusts and water holding characteristics of topsoil].

In order to understand the improving effects of cyanobacterial inoculation on water retention of topsoil in desert regions, this work focused on the development and succession of biological soil crusts and water holding characteristics of topsoil after cyanobacterial inoculation in Qubqi Desert. The results showed that after the artificial inoculation of desert cyanobacteria, algal crusts were quickly formed, and in some microenvironments direct succession of the algal crusts to moss crusts occurred after 2-3 years. With the development and succession of biological soil crusts, the topsoil biomass, polysaccharides content, crust thickness and porosity increased, while the soil bulk density decreased. At the same time, with crust development and succession, the topsoil texture became finer and the percents of fine soil particles including silt and clay contents increased, while the percents of coarse soil particles (sand content) decreased proportionately. In addition, it was found that with crust development and succession, the water holding capacity and water content of topsoil showed an increasing trend, namely: moss crust > algal crusts > shifting sand. The water content (or water holding capacity) in algal and moss crusts were 1.1-1.3 and 1.8-2.2 times of those in shifting sand, respectively. Correlation analysis showed that the water holding capacity and water content of topsoil were positively correlated with the crust biomass, polysaccharides content, thickness, bulk density, silt and clay content; while negatively correlated with the porosity and sand content. Furthermore, stepwise regression analysis showed that the main factor affecting water content was the clay content, while that affecting water holding capacity was the porosity.

[Development and succession of biological soil crusts and the changes of microbial biomasses].

Biological soil crusts (BSCs) play important ecological roles in vegetation and ecological restoration in desert regions, and different crust developmental and successional stages have different ecological functions. In this experiment, the BSCs in Shapotou region (at southeast edge of Tengger Desert) were investigated to study crust development and succession through field investigation, microscopic observation combined with quantitative analysis of microbial biomasses. The results showed that BSCs in this region generally developed and succeeded from algal crusts, lichen crusts to moss crusts. With the development and succession of BSCs, crust photosynthetic biomass gradually increased, while microalgal biomass showed a first increasing and then decreasing trend. Among the crust algae (cyanobacteia), Microcoleus vaginatus, as the first dominant species, occupied the most algal biomass and reached a maximum of 0.33 mm3 x g(-1) crusts in algal crusts; while Scytonema javanicum and Nostoc sp. have their maximal biomasses in the later lichen crusts. In addition, it was found that the heterotrophic microbial biomass began to increase in algal crusts, and then decreased in lichen crusts; followed by another increase and the increase achieved the maximum at last in moss crusts. Through the correlation analysis, it was found that bacterial biomass significantly positively correlated with crust organic carbon and Na+ content, while fungal biomass positively correlated with K+ and Na+ content (P < 0.05). In conclusion, this study investigated the developmental and successional patterns of BSCs in Shapotou region, and discussed the effects of crust development and succession on several microbial biomasses from the point of view of environmental adaptation and functional requirement, which may be helpful for us to understand crust development and succession, and provide theoretical and practical significances for crust maintenance and management in ecological restoration of desertification regions.

Desiccation provides photosynthetic protection for crust cyanobacteria Microcoleus vaginatus from high temperature.

As the dominant cyanobacterial species in biological soil crusts (BSCs), Microcoleus vaginatus often suffer from many stress conditions, such as desiccation and high temperature. In this study, the activities of light-harvesting complexes (LHCs) and reaction centers of photosystem II (PS II) in crust cyanobacteria M. vaginatus were monitored under high temperature and desiccation conditions using chlorophyll fluorescence technology. The results showed that all the fluorescence signals were significantly inhibited by high temperature or desiccation treatments. Under high temperature conditions, it was further demonstrated that PS II reaction centers were first destructed within the first hour, then the LHCs gradually dissociated and free phycocyanin formed within 1-5 h, and the activities of all the light harvesting and reaction center pigment proteins were fully suppressed after 24 h of high temperature treatment. Furthermore, the high temperature treated M. vaginatus lost its ability to recover photosynthetic activity. On the contrary, although desiccation also led to the loss of photosynthetic activity in M. vaginatus, after rehydration in the light the fluorescence parameters including Fo, Fv and Fv/Fm could be well recovered within 12 h. It was concluded that desiccation could provide crust cyanobacteria M. vaginatus some protection from other stresses, such as high temperature demonstrated in this experiment. The combine of temperature change and precipitation pattern in the field provide a guarantee for the alternate metabolism and inactivity in crust cyanobacteria. That may be a very important strategy for the survival of crust cyanobacteria in high temperature regions.

Longitudinal photosynthetic gradient in crust lichens' thalli.

In order to evaluate the self-shading protection for inner photobionts, the photosynthetic activities of three crust lichens were detected using Microscope-Imaging-PAM. The false color images showed that longitudinal photosynthetic gradient was found in both the green algal lichen Placidium sp. and the cyanolichen Peltula sp. In longitudinal direction, all the four chlorophyll fluorescence parameters Fv/Fm, Yield, qP, and rETR gradually decreased with depth in the thalli of both of these two lichens. In Placidium sp., qN values decreased with depth, whereas an opposite trend was found in Peltula sp. However, no such photosynthetic heterogeneity was found in the thalli of Collema sp. in longitudinal direction. Microscope observation showed that photobiont cells are compactly arranged in Placidium sp. and Peltula sp. while loosely distributed in Collema sp. It was considered that the longitudinal photosynthetic heterogeneity was ascribed to the result of gradual decrease of incidence caused by the compact arrangement of photobiont cells in the thalli. The results indicate a good protection from the self-shading for the inner photobionts against high radiation in crust lichens.

Artificially accelerating the reversal of desertification: cyanobacterial inoculation facilitates the succession of vegetation communities.

Desertification has been recognized as a global environmental problem, and one region experiencing ongoing desertification is the eastern edge of Qubqi Desert (Inner Mongolia). To investigate the facilitating effects of cyanobacterial inoculation technology on the desertification control along this steppe-desert transition region, artificial cyanobacterial crusts were constructed with two filamentous cyanobacteria 3 and 8 years ago combined with Salix planting. The results showed that no crusts formed after 3 years of fixation only with Salix planting, whereas after cyanobacterial inoculation, the crusts formed quickly and gradually succeed to moss crusts. During that course, topsoil environments were gradually improved, providing the necessary material basis for the regeneration of vascular plants. In this investigation, total 27 species of vascular plants had regenerated in the experimental region, mainly belonging to Asteraceae, Poaceae, Chenopodiaceae and Leguminosae. Using space time substitution, the dominant species along with the application of cyanobacterial inoculation technology succeeded from Agriophyllum squarrosum ultimately to Leymus chinensis. In addition, it was found that the shady side of the dunes is more conducive to crust development and succession of vegetation communities. Conclusively, our results indicate artificial cyanobacterial inoculation technology is an effective and desirable path for desertification control.