Rhizobium deserti sp. Nov Isolated from Biological Soil Crusts Collected at Mu Us Sandy Land, China.

A novel gram-negative, aerobic, non-spore-forming, rod-shaped, and non-nitrogen-fixing bacterium, named SPY-1T, was isolated from biological soil crusts collected at Mu Us Sandy Land, China. Based on 16S rRNA sequence similarity, strain SPY-1T was most closely related to Neorhizobium alkalisoli CCTCC AB 2014138T (98.7%), Neorhizobium huautlense CGMCC 1.2538T (98.6%), Neorhizobium galegae DSM 11542T (98.4%), Rhizobium wenxiniae 166T (97.9%), and Rhizobium smilacinae CCTCC AB 2013016T (97.5%). Phylogenetic analysis based on 16S rRNA sequencing and multilocus sequence analysis of partial sequences of atpD-glnII-glnA-recA-ropD-thrC housekeeping genes both indicated that strain SPY-1T was a member of the genus Rhizobium. The draft genome of strain SPY-1T was 4.75 Mb in size, and the G + C content was 60.0%. The average nucleotide identity (ANI) values to N. alkalisoli CCTCC AB 2014138T and R. smilacinae CCTCC AB 2013016T were both 84.0%. The digital DNA-DNA hybridization (dDDH) values to N. alkalisoli CCTCC AB 2014138T and R. smilacinae CCTCC AB 2013016T were 20.9% and 20.2%, respectively. The major cellular fatty acids were summed feature 8 (C18:1ω7c and/or C18:1ω6c) and C16:0. Based on the data from chemotaxonomic, phylogenetic, and phenotypic evidence, strain SPY-1T represents a novel species in the genus Rhizobium, for which the name Rhizobium deserti sp. nov. is proposed. The type strain is SPY-1T (= ACCC 61627T = JCM 33732T).

Sphingomonas deserti sp. nov., isolated from Mu Us Sandy Land soil.

A Gram-stain-negative, rod-shaped bacterium, designated as strain GL-C-18T, was isolated from soil sample collected at Mu Us Sandy Land, China, and its taxonomic position was investigated using a polyphasic approach. Growth was observed in the presence of 0-1 % (w/v) NaCl (optimum, 0 %), pH 6.0-9.0 (optimum, pH 7.0-8.0) and 20-37 °C. On the basis of 16S rRNA gene sequence similarity, strain GL-C-18T belonged to the family Sphingomonadaceae and was most closely related to Sphingosinicella vermicomposti YC7378T (95.7 %), Sphingomonas oligophenolica S213T (95.0 %) and Sphingobium boeckii 301T (94.8 %). The draft genome of strain GL-C-18T was 6.09 Mb, and the G+C content was 66.0 %. The average nucleotide identity value to Sphingosinicella vermicomposti YC7378T was 83.7 %. The predominant respiratory quinone was Q-10. The major fatty acids were C18 : 1ω7c, summed feature 3 (C16 : 1ω7c and/or C16 : 1ω6c), C16:0 and C14 : 0 2OH. The main polar lipids were sphingoglycolipid, diphosphatidylglycerol, phosphatidylglycerol, phosphatidylethanolamine and phosphatidylcholine. On the basis of chemotaxonomic, phylogenetic and phenotypic evidence, strain GL-C-18T represents a novel species of the genus Sphingomonas, for which the name Sphingomonasdeserti sp. nov. is proposed. The type strain is GL-C-18T (=ACCC 60076T=KCTC 62411T).

Rainfall partitioning characteristics and simulation of typical shelter forest in Chinese Mu Us Sandy Land.

Numerous shelter forests have been established to combat desertification in the Mu Us Sandy Land, China. Shelter forests modify the characteristics of the underlying surface and affect the regional water cycle by altering rainfall partitioning. Understanding the rainfall partitioning process and its controlling factors for indigenous and exotic species is crucial for vegetation restoration and sustainable soil water management. This study developed an event-based rainfall partitioning process for three typical shelter forests. Indigenous vegetation, Amygdalus pedunculata Pall. (A. pedunculata), and two exotic species, Amorpha fruticosa L. (A. fruticose) and Pinus sylvestris var. mongholica Litv. (P. sylvestris), were observed during the rainy seasons (July and August) of 2021 and 2022. The results showed that throughfall, stemflow, and interception loss constituted 71.01 %, 8.23 %, and 20.76 % of rainfall, respectively, for A. pedunculata. The corresponding values were 74.65 %, 8.47 %, and 16.88 % for A. fruticose and 73.27 %, 1.44 %, and 25.29 % for P. sylvestris. Compared with the introduced P. sylvestris, the shrub canopy showed a greater funneling ratio and was conducive to recharging soil water by precipitation. The amount and intensity of rainfall were significantly correlated with the rainfall partitioning characteristics, whereas the correlation between rainfall duration and partitioning was insignificant. Based on the results of the revised Gash model, the stemflow was primarily influenced by the percentage of rainfall diverted to the stemflow. The interception loss for P. sylvestris was primarily influenced by the canopy storage capacity. However, the canopy storage capacity and the ratio of mean evaporation rate to mean rainfall intensity had significant effects on the interception loss in A. pedunculata and A. fruticose. It is necessary to comprehensively consider the vegetation type (tree/shrub and indigenous/exotic species) and the corresponding rainfall partitioning characteristics of shelter forests for the scientific construction and management of shelter forests in the Mu Us Sandy Land.

No increase of soil wind erosion with the establishment of center pivot irrigation system in Mu-Us sandy land.

Center Pivot Irrigation system (CPIs) is widely used in newly exploited arable land in sandy lands. These sandy lands are currently stable because of climate change and ecological restoration efforts since the beginning of the 21st century in northern China. The exploitation of these fixed sandy lands to arable land with CPIs may affect the soil wind erosion, yet it remains unknown. The temporal changes of CPIs and its effect on wind erosion module were analyzed and modeled from 2000 to 2020 in Mu-Us sandy land using satellite images and Revised Wind Erosion Equation (RWEQ). The establishment of CPIs started from 2010, boomed in 2015 and peaked in 2020. They were mainly transformed from woodland, grassland, and barren land near rivers in east and southeast, and from cropland in inter-dunes in west and southwest of Mu-Us sandy land. The temporal and spatial pattern of CPIs well aligns with the land consolidation and requisition-compensation balance policies. In most of the Mu-Us sandy land, the annual erosion module is <25 t ha-1 a-1. Despite great variation, the annual, Winter and Spring erosion module of the Mu-Us sandy land or in Otog Qian and Yuyang, the CPIs concentrated counties, all decreased during 2000-2019. Although, wind erosion module in CPIs was lower than the surrounding area, it increased in 2019 given the same climate conditions as in 2010. Our results suggest 1) the establishment of CPIs in Mu-Us sandy land greatly depends on the local policy and natural endowment, and 2) although the set-up of CPIs showed no impact on the wind erosion with CPIs accounting for <1 % of Mu-Us sandy land, post-harvest of CPIs should be carefully concerned to prevent soil wind erosion.

Change pattern and stability of oasisization land in Mu Us Sandy Land.

Understanding land structure change and stability in the process of oasisization is particularly important for the desertification control in sandy land. Based on land use data of eight periods from 1980 to 2020, we extracted the spatial distribution information of oasis land in Mu Us Sandy Land, and analyzed the spatio-temporal variations of land transformation patterns and stability of oasis land with overlay analysis and grid analysis. The results showed that desertification in the Mu Us Sandy Land had reversed, with a significant process of oasis. The area of forest and grassland increased from 10.2% in 1980 to 73.7% in 2020, while the area of oasisization land increased from 32500 km2 in 1980 to 33900 km2 in 2020. The area of extremely severe, severe, and moderate desertification significantly decreased, while the area of non-desertification and mild desertification obviously increased. The four patterns of oasisization land transformation, including stability, fluctuation, expansion, and retreat, which accounted for 78.7%, 12.2%, 6.2%, and 2.9% of the oasisization land area in 2020, respectively. The oasisization land with low change intensity (the cumulative change intensity less than 0.12) in the Mu Us Sandy Land accounted for 82.7% of the total oasisization area, and the oasisization land in the sandy land was generally stable. Zoning management strategies should be applied according to the stability of sand belt and transformation pattern of oasisization land to achieve the goal of efficient system management and improvement, including eliminating sand hazards at desertification expansion areas with strong wind and sand activities, consolidating sand resources at oasisization areas where ecologically fragile desertification was frequent, and sustainably managing and utilizing sand resources at stable expansion of oases in forest- and grass-rich oasisization areas.

Effects of γ-polyglutamic acid supplementation on alfalfa growth and rhizosphere soil microorganisms in sandy soil.

This study aimed at exploring the effects of γ-polyglutamic acid on the growth of desert alfalfa and the soil microorganisms in the rhizosphere. The study examined the effects of varying concentrations of γ-polyglutamic acid (0%-CK, 2%-G1, 4%-G2, 6%-G3) on sandy soil, the research investigated its impact on the growth characteristics of alfalfa, nutrient content in the rhizosphere soil, and the composition of bacterial communities. The results indicated that there were no significant differences in soil organic matter, total nitrogen, total phosphorus, total potassium, and available phosphorus content among the G1, G2, and G3 treatments. Compared to CK, the soil nutrient content in the G2 treatment increased by 14.81-186.67%, showing the highest enhancement. In terms of alfalfa growth, the G2 treatment demonstrated the best performance, significantly increasing plant height, chlorophyll content, above-ground biomass, and underground biomass by 54.91-154.84%. Compared to the CK treatment, the number of OTUs (operational taxonomic units) in the G1, G2, and G3 treatments increased by 14.54%, 8.27%, and 6.84%, respectively. The application of γ-polyglutamic acid altered the composition and structure of the bacterial community, with Actinobacteriota, Proteobacteria, Chloroflexi, Acidobacteriota, and Gemmatimonadota accounting for 84.14-87.89% of the total bacterial community. The G2 treatment significantly enhanced the diversity and evenness of soil bacteria in the rhizosphere. Redundancy analysis revealed that organic matter, total nitrogen, total potassium, moisture content, and pH were the primary factors influencing the structure of bacterial phyla. At the genus level, moisture content emerged as the most influential factor on the bacterial community. Notably, moisture content exhibited a strong positive correlation with Acidobacteriota, which in turn was positively associated with indicators of alfalfa growth. In summary, the application of γ-polyglutamic acid at a 4% ratio has the potential for improving sandy soil quality, promoting plant growth, and regulating the rhizosphere microbial community.

Effects of soft rock on soil properties and bacterial community in Mu Us Sandy Land, China.

Soft rock is a new material that could be used for the improvement of Mu Us Sandy Land, China. It can be utilized for wind prevention and sand fixation, both of which are of great importance to ecological restoration aims and cultivated land replenishment in desert areas. Four treatments with different compound ratios of soft rock and sand-0:1 (CK), 1:5 (P1), 1:2 (P2), and 1:1 (P3)-were studied. Fluorescence quantitative PCR (qPCR) and high-throughput sequencing were used to analyze the structure and diversity of the bacterial community in the compound soil and its relationship with physical and chemical parameters in the soil. The results showed that in comparison to CK treatment, soil organic carbon (SOC), total nitrogen (TN), and NH4 +-N increased significantly in the P1 treatment; available phosphorus (AP), available potassium (AK), and NO3 --N increased significantly in the P3 treatment. The bacterial gene copy number with P3 treatment was highest, showing a significant increase of 182.05% compared with the CK treatment. The three bacterial groups with the highest relative abundance at the phylum level were Actinobacteria, Proteobacteria, and Chloroflexi, accounting for more than 70% of the total population. The bacterial α diversity showed the same trend, the diversity and abundance indices of the P1 and P3 treatments were the highest, and the ß diversity showed that the community structure of the two groups in these treatments were similar. norank_f__Roseiflexaceae and Gaiella (belonging to Actinobacteria) significantly differed with differing compound ratios in each treatment. NO3 --N, NH4 +-N and SOC were the main factors affecting bacterial community structure, and had a significant positive correlation with Gaiella abundance. These species are known to play an important role in stabilizing the soil structure of sandy land. Overall, 1:5 and 1:1 compound soil mixtures were beneficial towards the microbial community of sandy land, which plays an important role in biological sand fixation. This study provides an important theoretical basis for the supplementation of arable land area and the improvement of sandy land productivity, and has a good promotion prospect.

[Spatial distribution and the influencing factors of organic carbon of biological crusts on regional scale in Mu Us sandy land, China]. / æ¯›ä¹Œç´ æ²™åœ°åŒºåŸŸå°ºåº¦ç”Ÿç‰©ç»“çš®æœ‰æœºç¢³.

As an important soil cover in deserts, biological crusts play a central role in ecosystem function such as nutrient cycling, nitrogen fixation, and carbon sequestration. Many biological crust organisms could fix CO2 through photosynthesis to improve soil organic carbon content. There is a knowledge gap in the origin of soil organic carbon (SOC) from biological crusts on a regional level, which restricts the prediction of soil carbon pool. Based on 45 plots in the Mu Us sandy land (42200 km2), we measured the SOC content and soil organic carbon density (SOCD) of two types of typical biological crusts (moss crusts, algal crusts) and their underlying soils, and analyzed together with the climate data, soil and vegetation factors to investigate the spatial distribution characteristics and controlling factors of organic carbon of biological crusts at the regional scale. The results showed that: 1) biological crusts significantly increased SOC and SOCD compared with bare ground. Moss crusts and the underlying SOC (4.93 g·kg-1) and SOCD (0.41 kg·m-2) were higher than those of algal crusts (1.89 g·kg-1, 0.18 kg·m-2). 2) On the regional scale, the SOC and SOCD of biological crusts had clear spatial distribution characteristics, demonstrating a banded distribution and block mosaic from northeast to central and west to southeast. 3) The SOC and SOCD of biological crusts and their underlying soils were mainly affected by climate, soil and vegetation conditions, while the main controlling factors depended on the types of biological crusts. The SOC and SOCD of moss crust were controlled by annual maximum temperature and potential evapotranspiration, whereas those of algal crusts were controlled by water vapor pressure.

[Changes of soil water budget in the area covered by biological soil crusts in Mu Us sandy land, China]. / æ¯›ä¹Œç´ æ²™åœ°ç”Ÿç‰©ç»“çš®è¦†ç›–åŒºåœŸå£¤æ°´åˆ†æ”¶æ”¯å˜åŒ–ç‰¹å¾.

Exploring and quantifying the impacts of biological soil crusts on soil hydrological processes and soil water budget in semi-arid ecosystems can provide a theoretical basis for vegetation restoration and reconstruction in deserts. Based on continuous observation of soil water content in different types of areas covered by biological soil crusts (e.g., algae, moss) and bare sand in the Mu Us sandy land during the growing season (May to October) from 2018 to 2020, we examined the effects of biological soil crusts on soil water budget at a depth of 0-40 cm. Results showed that algae and moss crusts significantly reduced soil water supplement below 40 cm by rainfall and increased soil water evaporation loss, compared with that under bare sand. In the relatively wet year (2018), the amount of soil water expenditure (seepage+evaporation) covered by bare sand and the various types of biological soil crusts was less than that of rainfall, resulting in net soil water income. In the relative dry years (2019 and 2020), the amount of soil water expenditure covered by dominant algae and moss crusts was higher than that of rainfall, causing net soil water deficit, but opposite for bare sand. Biological soil crusts led to the imbalance of soil water budget of 0-40 cm depth and even soil water deficit in relatively dry years, which may lead to the succession of plant communities to be dominated by shallow-rooted plants in this area.

Correlation assessment of NDVI and land use dynamics with water resources for the southern margin of Mu Us Sandy Land, China.

To prevent desertification, countries worldwide have made diversified efforts, and vegetation restoration has been demonstrated to be an effective approach. However, in regard to sandy land with limited water resources, measures such as revegetation may lead to an increased drought risk. Despite confirmed sand utilization achievements, many controversies remain regarding the advantages of desert greening, especially considering water scarcity. Therefore, the long-run and causal relationships between sandy land, water consumption, and vegetation coverage are necessarily explored. Choosing the southern margin of the Mu Us Sandy Land as the study area, this study explored the interactions between sandy land, water consumption, and normalized difference vegetation index (NDVI) of 2000-2018 with the vector autoregression (VAR) model approach. In the study area, various revegetation projects have been implemented, resulting in a notable reduction in the sandy land area. In addition, the NDVI increased from 0.196 in 2000 to 0.371 in 2018, an increase of 89.3%. The results indicated that there exist long-term stable equilibrium and causal relationships existed between water consumption and sandy land and NDVI. NDVI enhancement is relatively the direct factor that causes the increase of water consumption. It could be inferred that the implemented revegetation measures may rely on a large water consumption amount, which may further aggravate water shortages and ecological damage issues. More scientific and stronger effective water resource management measures should be locally implemented to achieve a balance between water resources and revegetation.

Response of the characteristics of organic carbon mineralization of soft rock and soil composed of sand to soil depth.

The addition of soft rock to aeolian sandy soil can improve the level of fertility and ability of the soil to sequester carbon, which is of substantial significance to improve the ecological environment of the Mu Us sandy land and supplement newly added cultivated land. S oft rock and sand were combined using the ratio (v/v) of 0:1 (CK), 1:5 (S1), 1:2 (S2), and 1:1 (S3). The process of mineralization of organic carbon at different depths (0-10 cm, 10-20 cm, and 20-30 cm) in the combined soil was studied by 58 days of incubation indoors at a constant temperature. The content of soil nutrient s increased significantly under the S2 and S3 treatments and was higher in the 0-10 cm soil depth. The mineralization of rate of soil organic carbon (SOC) of different combination ratios can be divided into three time periods: the stress mineralization stage (1-7 d), the rapid mineralization stage (7-9 d) and the slow mineralization stage (9-58 d). At the end of incubation, the rates of mineralization of SOC and accumulated mineralization amount (Ct) were relatively large in the 0-10 cm soil depth, followed by the 10-20 cm and 20-30 cm soil layers , indicating that the stability of SOC in the surface layer was poor, which is not conducive to the storage of carbon. The content of potentially mineralizable organic carbon (C0) in the soil was consistent with the trend of change of Ct. Compared with the CK treatment, the cumulative organic carbon mineralization rate (Cr) of the S2 and S3 treatment s decreased by 7.77% and 6.05%, respectively; and the C0/SOC decreased by 22.84% and 15.55%, respectively. Moreover, the Cr and C0/SOC values in the 10-20 cm soil depth were small, which indirectly promoted the storage of organic carbon. With the process of SOC mineralization, the contents of soil microbial biomass carbon (SMBC) and dissolved organic carbon (DOC) tended to decrease compared with the initial contents, with larger amplitudes in the 20-30 cm and 10-20 cm soil depth s, respectively. SOC, total nitrogen, available potassium, SMBC and DOC were all closely related to the process of mineralization of organic carbon. Therefore, the accumulation of soil carbon could be enhanced when the proportion of soft rock and sand composite soil was between 1:2 and 1:1, and the 10-20 cm soil depth was relatively stable. These results provide a theoretical basis for the improvement of desertified land.

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The study aimed to reveal the cumulative effects and stability characteristics of soil organic carbon (SOC) during forest development at the Mu Us sandy land, China. Using space for time substitution, surface soil samples were collected from semi-fixed sandy lands and restored arbor and shrub lands with the ages of 22, 32 and 53 years in the Yulin sand control region in Northern Shaanxi Province. The content of total organic carbon (TOC), oxidizable labile organic carbon, and resistant carbon and the characteristics of mineralized carbon emission and decomposition ratio were analyzed. The results showed that the increment of TOC for 22 to 53 years shrub and arbor lands from resistant carbon were 3.5-6.2 g·kg-1 and 3.2-7.7 g·kg-1, and from oxidized labile carbon were 2.8-3.4 g·kg-1 and 1.3-2.8 g·kg-1, respectively, compared with semi-fixed sand land. The ratio of soil oxidizable labile carbon in shrub land and arbor land were stable and maintained at 37.0% and 26.8%, respectively. However, the ratio decreased to 25.7% and 17.4% after incubated at a constant temperature for 60 days. The mineralization rate of shrub and arbor lands with 22-53 years was not significant at the ending of soil incubation. Carbon losses from oxidized liable carbon were 76.9%-98.7%, and only 1.3%-23.5% from resistant carbon in all sand-fixing forest plots. Compared with the maximum carbon emission rate, the soil cumulative carbon release exhibited a higher correlation with soil enzyme activities of ß-glucosidase and dehydrogenase, but the enzyme activities did not change from 32-53 years. In conclusion, SOC pool showed stable characteristics of lower emission and higher sequestration with the increases of sand-fixing forest stand age. The carbon fixation effect of arbor sand-fixing forest was better than that of shrub sand-fixing forest.