Effects of an Early Successional Biological Soil Crust from a Temperate Coastal Sand Dune (NE Germany) on Soil Elemental Stoichiometry and Phosphatase Activity

Responses of Soil C, N, P and Enzyme Activities to Biological Soil Crusts in China: A Meta-Analysis

Biological soil crusts (BSCs) are often referred to as the "living skin" of arid regions worldwide. Yet, the combined impact of BSCs on soil carbon (C), nitrogen (N), phosphorus (P), and enzyme activities remains not fully understood. This study identified, screened and reviewed 71 out of 2856 literature sources to assess the responses of soil C, N, P and enzyme activity to BSCs through a meta-analysis. The results indicated that BSC presence significantly increased soil C, N, P and soil enzyme activity, and this increasing effect was significantly influenced by the types of BSCs. Results from the overall effect showed that soil organic carbon (SOC), total nitrogen (TN), available nitrogen (AN), total phosphorus (TP), and available phosphorus (AP) increased by 107.88%, 84.52%, 45.43%, 27.46%, and 54.71%, respectively, and four soil enzyme activities (Alkaline Phosphatase, Cellulase, Sucrase, and Urease) increased by 93.65-229.27%. The highest increases in SOC, TN and AN content occurred in the soil covered with lichen crusts and moss crusts, and significant increases in Alkaline Phosphatase and Cellulase were observed in the soil covered with moss crusts and mixed crusts, suggesting that moss crusts can synergistically enhance soil C and N pool and enzyme activity. Additionally, variations in soil C, N, P content, and enzyme activity were observed under different environmental settings, with more pronounced improvements seen in coarse and medium-textured soils compared to fine-textured soils, particularly at a depth of 5 cm from the soil surface. BSCs in desert ecosystems showed more significant increases in SOC, TN, AN, and Alkaline Phosphatase compared to forest and grassland ecosystems. Specifically, BSCs at low altitude (≤500 m) with an annual average rainfall of 0-400 mm and an annual average temperature ≤ 10 °C were the most conducive to improving soil C, N, and P levels. Our results highlight the role of BSCs and their type in increasing soil C, N, P and enzyme activities, with these effects significantly impacted by soil texture, ecosystem type, and climatic conditions. The implications of these findings are crucial for soil enhancement, ecosystem revitalization, windbreak, and sand stabilization efforts in the drylands of China.

Successional Development of the Phototrophic Community in Biological Soil Crusts on Coastal and Inland Dunes

(1) Biological soil crusts (biocrusts) are microecosystems consisting of prokaryotic and eukaryotic microorganisms growing on the topsoil. This study aims to characterize changes in the community structure of biocrust phototrophic organisms along a dune chronosequence in the Baltic Sea compared to an inland dune in northern Germany. (2) A vegetation survey followed by species determination and sediment analyses were conducted. (3) The results highlight a varying phototrophic community composition within the biocrusts regarding the different successional stages of the dunes. At both study sites, a shift from algae-dominated to lichen- and moss-dominated biocrusts in later successional dune types was observed. The algae community of both study sites shared 50% of the identified species while the moss and lichen community shared less than 15%. This indicates a more generalized occurrence of the algal taxa along both chronosequences. The mosses and lichens showed a habitat-specific species community. Moreover, an increase in the organic matter and moisture content with advanced biocrust development was detected. The enrichment of carbon, nitrogen, and phosphorus in the different biocrust types showed a similar relationship. (4) This relation can be explained by biomass growth and potential nutrient mobilization by the microorganisms. Hence, the observed biocrust development potentially enhanced soil formation and contributed to nutrient accumulation.

Driving Factors of Microbial Community Abundance and Structure in Typical Forest Soils of Sanjiang Plain, Northeast China

Until recently, a comprehensive evaluation of the environmental drivers on the abundance and structure of the microbial community in typical forest soils has not been thoroughly conducted. In this study, the typical forest soils (Mongolian oak (Quercus mongolica) soil, MOS; white birch (Betula platyphylla) soil, WBS; and white poplar (Populus davidiana) soil, WPS) in the Sanjiang Plain were selected to ascertain the differences and the major environmental factors driving soil microbial community abundance and structure. Results indicated that differences existed in the abundance and structure of the bacterial, archaeal, and fungal community. Co-occurrence network analysis showed that the bacterial and fungal networks were more complex than those of archaeal networks. Unclassified Acidobacteria and unclassified Pyrinomonadaceae were the keystone taxa in the bacterial networks, while Pleotrichocladium and Leotia were the keystone taxa in the fungal networks. Among all environmental factors, pH, SOM, and total N exhibited dominant roles in affecting the abundance of bacteria, archaea, and fungi. The redundancy analysis (RDA) showed that pH was the vital environmental factor responsible for driving the structure of the bacterial, archaeal, and fungal community.

Exogenous Microorganisms Promote Moss Biocrust Growth by Regulating the Microbial Metabolic Pathway in Artificial Laboratory Cultivation

Moss-dominated biocrusts (moss crusts) are a feasible approach for the ecological restoration of drylands, but difficulty obtaining inoculum severely limits the progress of large-scale field applications. Exogenous microorganisms could improve moss growth and be conducive to moss inoculum propagation. In this study, we investigated the growth-promoting effects and potential mechanisms of exogenous microorganism additives on moss crusts. We used an incubator study to examine the effects of inoculation by heterotrophic microorganisms (Streptomyces pactum, Bacillus megaterium) and autotrophic microorganisms (Chlorella vulgaris, Microcoleus vaginatus) combined with Artemisia sphaerocephala gum on the growth of Bryum argenteum, the dominant moss crusts species in sandy deserts. Amplicon sequencing (16S and 18S rRNA) and PICRUSt2 were used to illustrate the microbial community structure and potential function in the optimal treatment at different developmental stages. Our results showed that exogenous microorganisms significantly promoted moss growth and increased aboveground biomass. After 30 days of cultivation, the Streptomyces pactum (1 g kg-1 substrate) + Chlorella vulgaris (3.33 L m-2) treatment presented optimal moss coverage, height, and density of 97.14%, 28.31 mm, and 2.28 g cm-2, respectively. The best-performing treatment had a higher relative abundance of Streptophyta-involved in moss growth-than the control. The control had significantly higher soil organic carbon than the best-performing treatment on day 30. Exogenous microorganisms improved eukaryotic community diversity and richness and may enhance soil microbial functional and metabolic diversity, such as growth and reproduction, carbon fixation, and cellulose and lignin decomposition, based on functional predictions. In summary, we identified the growth-promoting mechanisms of exogenous additives, providing a valuable reference for optimizing propagation technology for moss inoculum.

Soil nitrogen and climate drive the positive effect of biological soil crusts on soil organic carbon sequestration in drylands: A Meta-analysis

Biological soil crusts (BSCs), known as ecological engineers, play an important role in soil organic carbon (SOC) sequestration in dryland ecosystems. Although numerous individual studies had been conducted, the global patterns of the changes in SOC concentration following BSCs establishment remain unclear. In this study, we performed a comprehensive meta-analysis of 184 independent observations at 47 sites to quantify the responses of SOC and other soil variables to BSCs establishment and identify the underlying mechanisms. Our results showed that BSCs generally increased SOC by 70.9% compared to the controls (uncrusted soil), and the positive effects of BSCs on SOC in deserts (120.3%) were stronger than those in grasslands (32.7%). Mosses and lichens had a stronger positive effect on SOC than algae crusts (67.5%, 82.8%, and 58.2% respectively). Mixed crusts accumulated more SOC (181.6%) than single (moss, lichen and algae) crusts. The presence of BSCs considerably increased total nitrogen (TN) (+80.7%), total phosphorus (TP) (+20.3%), available N (+62.7%), and available P (+14.3%). Significant relationships were observed among the effect size of SOC and climate and soil N and P in both desert and grassland. The random forest analysis showed that TN could be considered as a determinant of the concentration of SOC, followed by climate (P < 0.01). Our study shows that the capacity of the BSCs to fix and store C could be regulated by soil N and P dynamics, indicating a major finding opening new ways to promote soil recovery and formation. Our findings highlight the remarkable contribution of mixed crusts to soil C pools; this contribution needs to be incorporated into regional and global models to predict the effects of human disturbance on drylands worldwide and for assessing the soil C budget.

Mechanism Underlying Flow Velocity and Its Corresponding Influence on the Growth of Euglena gracilis, a Dominant Bloom Species in Reservoirs

The effects of hydrodynamics on algae growth have received considerable attention, and flow velocity is one of the most frequently discussed factors. For Euglena gracilis, which aggregates resources and is highly resistant to environmental changes, the mechanism underlying the impact of flow velocity on its growth is poorly understood. Experiments were conducted to examine the response of algae growth to different velocities, and several enzymes were tested to determine their physiological mechanisms. Significant differences in the growth of E. gracilis were found at different flow velocities, and this phenomenon is unique compared to the growth of other algal species. With increasing flow velocity and time, the growth of E. gracilis is gradually inhibited. In particular, we found that the pioneer enzyme is peroxidase (POD) and that the main antioxidant enzyme is catalase (CAT) when E. gracilis experiences flow velocity stress. Hysteresis between total phosphorus (TP) consumption and alkaline phosphatase (AKP) synthesis was observed. Under experimental control conditions, the results indicate that flow velocities above 0.1 m/s may inhibit growth and that E. gracilis prefers a relatively slow or even static flow velocity, and this finding could be beneficial for the control of E. gracilis blooms.

Prokaryotic community shifts during soil formation on sands in the tundra zone

A chronosequence approach, i.e., a comparison of spatially distinct plots with different stages of succession, is commonly used for studying microbial community dynamics during paedogenesis. The successional traits of prokaryotic communities following sand fixation processes have previously been characterized for arid and semi-arid regions, but they have not been considered for the tundra zone, where the environmental conditions are unfavourable for the establishment of complicated biocoenoses. In this research, we characterized the prokaryotic diversity and abundance of microbial genes found in a typical tundra and wooded tundra along a gradient of increasing vegetation—unfixed aeolian sand, semi-fixed surfaces with mosses and lichens, and mature soil under fully developed plant cover. Microbial communities from typical tundra and wooded tundra plots at three stages of sand fixation were compared using quantitative polymerase chain reaction (qPCR) and high-throughput sequencing of 16S rRNA gene libraries. The abundances of ribosomal genes increased gradually in both chronosequences, and a similar trend was observed for the functional genes related to the nitrogen cycle (nifH, bacterial amoA, nirK and nirS). The relative abundance of Planctomycetes increased, while those of Thaumarchaeota, Cyanobacteria and Chloroflexi decreased from unfixed sands to mature soils. According to β-diversity analysis, prokaryotic communities of unfixed sands were more heterogeneous compared to those of mature soils. Despite the differences in the plant cover of the two mature soils, the structural compositions of the prokaryotic communities were shaped in the same way. Thus, sand fixation in the tundra zone increases archaeal, bacterial and fungal abundances, shifts and unifies prokaryotic communities structure.