Characteristics of spatial and temporal variability in the distribution of biological soil crusts on the Loess Plateau, China.

Biological soil crust (biocrust) is widely distributed on the Loess Plateau and plays multiple roles in regulating ecosystem stability and multifunctionality. Few reports are available on the distribution characteristics of biocrust in this region, which limits the assessment of its ecological functions. Based on 388 sampling points in different precipitation zones on the Loess Plateau from 2009 to 2020, we analyzed the coverage, composition, and influencing factors of biocrust across different durations since land abandonment, precipitation levels, topography (slope aspect and position), and utilization of abandoned slopelands (shrubland, forest, and grassland). On this base, with the assistance of machine learning and spatial modeling methods, we generated a distribution map of biocrust and its composition at a resolution of 250 m × 250 m, and analyzed the spatial distribution of biocrust on the Loess Plateau. The results showed that the average biocrust coverage in the woodlands and grasslands was 47.3%, of which cyanobacterial crust accounted for 25.5%, moss crust 19.7%, and lichen crust 2.1%. There were significant temporal and spatial variations. Temporally, the coverage of biocrust in specific regions fluctuated with the extension of the abandoned durations and coverage of cyanobacterial crust, while moss crust showed a reverse pattern. In addition, the coverage of biocrust in the wet season was slightly higher than that in the dry season within a year. Spatially, the coverage of biocrusts on the sandy lands area on the Loess Plateau was higher and dominated by cyanobacterial crusts, while the coverage was lower in the hilly and gully area. Precipitation and utilization of abandoned land were the major factors driving biocrust coverage and composition, while slope direction and position did not show obvious effect. In addition, soil organic carbon content, pH, and texture were related to the distribution of biocrust. This study uncovered the spatial and temporal variability of biocrust distribution, which might provide important data support for the research and management of biocrust in the Loess Plateau region.

[Reduction of flow velocity by biological soil crust of revegetated grassland in the hilly Loess Plateau, China]. / 黄土丘陵区草本植物覆盖下生物结皮对坡面径流流速的削减作用.

Biological soil crusts (biocrusts) are the common cover in arid and semiarid areas. Together with plants, biocrusts affect runoff and flow velocity. However, few studies have focused on the effects of the co-covering of plant and biocrust (plant+biocrust) on the flow velocity, with a knowledge gap in the study of driving factors for slope erosion in arid and semiarid areas. In this study, simulated rainfall experiments were used to investigate the effects of biocrust and three types of biocrusts (more cyanobacteria less moss, more moss less cyanobacteria, and moss) on the flow velocity of revegetated grassland in the hilly Loess Plateau. The results showed that plant and plant+biocrust significantly reduced flow velocity, with that of plants and plant+biocrust being 70.7% and 83.1% lower than bare soil. The reduction benefits of plant and biocrust on flow velocity were 70.7% and 12.4%, respectively, when they were co-covered. Biocrust composition under plant cover affected flow velocity. The reduction benefits of more cyanobacteria less moss, more moss less cyanobacteria, and moss crust on flow velocity were 11.5%, 12.4%, and 19.4%, respectively. There was a significant negative correlation between flow velocity and moss coverage and a significant positive correlation between flow velocity and cyanobacteria coverage. The relationship between moss cove-rage (x) and flow velocity (y) was y=-2.081x+0.03 (R2=0.469). The moss coverage was a key factor affecting the flow velocity of co-covering of plant and biocrust slope with similar plant coverage (40%±10%). In conclusion, biocrusts under plant cover significantly slowed flow velocity, and the effect magnitude was related to its composition, implying that the role of biocrusts should be considered in understanding the mechanism underlying slope erosion in revegetated grassland.

[Effects of biological soil crusts on the initial abstraction ratio of SCS-CN model in the Loess Plateau]. / 黄土高原生物结皮对SCS-CN模型初损率的影响.

Hydrological model is an effective tool for hydrological research. The initial abstraction ratio (λ) is a key parameter of SCS-CN model, a commonly used runoff model of great significance to simulate the hydrological process at the watershed scale. In order to examine the effects of biological soil crusts (biocrusts) on λ and improve the accuracy of the model used in the restored grasslands where biocrusts widely presented in the Loess Plateau region, we firstly determined the relationship between the amount of the potential maximum infiltration (S) and the amount of the actual infiltration (F), and then investigated the effects of biocrust coverage on λ by using the simulated rainfall experiment in the Yingwoshanjian watershed in Dingbian County, Shaanxi Province. The revised model was verified by the runoff results of the simulated rainfall experiments in the Zhifanggou watershed in Ansai County, Shaanxi Province. The results showed that the relationship between S and F on biocrust slope was described as S/F=2.5×60/T (where T was the rainfall duration). There was a negative correlation between λ and biocrust coverage (CBSC) described as λ=0.0791×e(-0.015×CBSC), R2=0.60. Compared with that using the standard value of λ, the efficiency coefficient of the model was increased by 338.7% and the qualified rate was increased by 16.1% after revising λ according to the biocrust coverage. The results provided a scientific basis for the calibration of λ on biocrust slopes in the Loess Plateau region, and were of great significance to accurately assess the hydrological effects of the implementation of the "Grain for Green" Program on the Loess Plateau.

Effects of the distribution of biological soil crust on the hydrodynamic characteristics of surface runoff.

The distribution pattern of biological soil crusts (biocrusts) is one of the main factors affecting runoff and sediment yield. The relationship between runoff and sediment yield and biocrusts' distribution pattern is not clear, which hinders understanding the mechanism underlying the effects of biocrusts on runoff and sediment from slopes. To fill the knowledge gap, we investigated the relationship between the landscape indices of three biocrusts' distribution patterns, i.e. zonation, chessboard and random, and the hydraulic parameters, using of simulated rainfall experiments and landscape ecology methods. The results showed that biocrust significantly affected the erosion force of slopes and that its distribution pattern could affect slope erosion dynamics. Compared to bare soil, the presence of biocrusts significantly reduced the runoff velocity (54.6%) and Froude number (67.0%), increased the runoff depth (86.2%) and Darcy-Weisbach resistance coefficient (10.68 times), but did not affect the Reynolds number and runoff power. Expect for the runoff depth, there were significant differences in the hydraulic parameters of the three biocrusts' distribution patterns, with the random pattern having the strongest impacts on the dynamics of slope erosion. Based on factor analysis and cluster analysis, five indices of percentage of patch to landscape area, patch density, landscape shape index, patch cohesion and splitting could be used as the indicators for the distribution characteristics of biocrust patches. The patch cohesion and splitting of biocrust patches were the main distribution pattern indices of the hydrodynamics of surface runoff. As the patches patch cohesion decreased, the splitting increased, which caused the surface runoff velocity increase, the resistance decrease, and the slope erosion became more severe.

[Responses of runoff and soil loss from biological soil crustal slope to rainfall intensity under simulated rainfall]. / 模拟降雨条件下生物结皮坡面产流产沙对雨强的响应.

Biological soil crust (biocrust) is a common surface cover on the rehabilitated slope land in Hill Loess Plateau. We investigated the responses of runoff and soil loss from biological soil crustal slope to rainfall intensity by using simulated rainfall trial. The results showed that the runoff and soil loss from biocrust slopes increased sharply at the beginning stage of rainfall and then became stable during 10 to 18 min. Compared to bare soil slope, the initial runoff generation time of biological soil crustal slope was significantly increased. The presence of biocrust could significantly decrease runoff and sediment by 21%-78% and 77%-95%, respectively. Rainfall intensities affected soil erosion of biocrust slopes mainly via affecting runoff. The transition from insignificant to significant correlation between runoff and soil loss from biological soil crustal slopes and rainfall intensities was observed with the increases of rainfall intensities. Once the rainfall intensity was higher than 1.5 mm·min-1, there was a significant decrease in the function of biocrust to decrease runoff and soil loss with the increases of rainfall intensities. Our results laid the foundation for the model simulation of runoff and soil loss from biocrust slopes under rainfall conditions.

[Effects of trampling disturbance on soil organic carbon fractions and mineralization potential of biological soil crusts in the Loess Plateau Region, China]. / 黄土丘陵区踩踏干扰对生物土壤结皮有机碳组分及碳矿化潜力的影响.

The experiment was conducted in the plots that had been enclosed for nearly 20 years in the hilly Loess Plateau region. The effects of trampling disturbance on the biological soil crust (biocrust) coverage, soil organic carbon (SOC), soil easily oxidizable carbon (SEOC), SOC mineralization amount and mineralization rate were investigated. The biocrust SOC mineralization potential after disturbance in different soil layers were simulated by a first-order kinetic equation. The results showed that the coverage of cyanobacteria biocrust and moss biocrust significantly decreased with the increases of disturbance intensity. Compared to no disturbance, the cyanobacteria coverage declined by 264%-339% and moss coverage declined by 46%-127%. Compared to no disturbance, SOC content in biocrust layer significantly decreased by 211%-300%. No significant difference was found among the five disturbance intensities. Disturbance increased SEOC content in biocrust layer, and the variation amounted to 1.5-3.4 g·kg-1, with 30%, 40% and 50% distur-bance differed significantly to no disturbance. Disturbance significantly increased biocrust SOC mineralization cumulative amount. However, SOC mineralization rate did not show any significant change. The SOC mineralization cumulative amount under 40% disturbance intensity increased by 77% compared to that under no disturbance. Disturbance significantly increased SOC mineralization potential in biocrust layer, but with no influence in 0-2 cm and 2-5 cm soil layers. The 40% disturbance intensity significantly increased SOC mineralization potential by 4.7 g·kg-1. The results of principal component analysis showed that SOC, SEOC, SMC and mineralization rate explained 76.7% of the variation of SOC mineralization potential in biocrust layer. Disturbance might be a main factor driving the increases of biocrust SOC mineralization potential in this area.

[Impact of short-term grazing disturbance on nitrogen accumulation of biological soil crusts in the hilly Loess Plateau region, China]. / çŸ­æœŸæ”¾ç‰§å¹²æ‰°å¯¹é»„åœŸä¸˜é™µåŒºç”Ÿç‰©ç»“çš®åœŸå£¤æ°®ç´ ç´¯ç§¯çš„å½±å“.

The variations of total nitrogen, available nitrogen and microbial biomass nitrogen caused by simulated grazing disturbance were investigated in the sixth and twelfth months by using field survey combined with laboratory analysis in order to reveal the sensitivity of nitrogen content in biocrustal soils to disturbance in the hilly Loess Plateau region. The results showed that nitrogen contents in biocrustal soil were sensitive to disturbance. Total nitrogen and available nitrogen in the biocrustal layers were decreased by 0.17-0.39 g·kg-1 and 1.78-5.65 mg·kg-1 during the first half-year compared to the undisturbed treatment, and they were found respectively decreased by 0.13-0.40 g·kg-1 and 11.45-32.68 mg·kg-1 one year later since disturbance. The content of microbial biomass nitrogen in the biocrustal layer was reduced by 69.99-330.97 mg·kg-1, whereas the content was increased by 25.51-352.17 mg·kg-1 in soil of 0-2 cm layer. The induction of nitrogen accumulation depended on the intensity of disturbance. Slight variation was observed in the nitrogen accumulation in biocrustal layer under 20% and 30% disturbance, while significant reduction was found in the 40% and 50% disturbance. Significant reduction was detected only in nitrogen accumulation in the biocrustal layers, whereas no significant influence was found in the top 5 cm soil layer.

A capillary electrophoresis method to explore the self-assembly of a novel polypeptide ligand with quantum dots.

Polyhistidine peptides are effective ligands to coat quantum dots (QDs). It is known that both the number of histidine (His) residues repeats and their structural arrangements in a peptide ligand play important roles in the assembly of the peptide onto CdSe/ZnS QDs. However, due to steric hindrance, a peptide sequence with more than six His residue tandem repeats would hardly coordinate well with Zn(2+) in the QD shell to further enhance the binding affinity. To solve this problem, a His-containing peptide ligand, ATTO 590-E2 G (NH)6 (ATTO-NH), was specifically designed and synthesized for assembly with QDs. With sequential injection of QDs and ATTO-NH into the capillary electrophoresis with fluorescence detection, strong Förster resonance energy transfer phenomenon between the QDs and the ATTO 590 dye was observed, indicating efficient self-assembly of the novel peptide onto the QDs to form ATTO-NH capped QDs inside the capillary. The binding stability of the ligand onto the QD was then systematically investigated by titrating with imidazole, His, and a his-tag containing competitive peptide. It is believed that this new in-capillary assay significantly reduced the sample consumption and the analysis time. By functionalizing QDs with certain metal cation-specific group fused peptide ligand, the QD-based probes could be even extended to the online detection of metal cations for monitoring environment in the future.

Developing a fluorescence-coupled capillary electrophoresis based method to probe interactions between QDs and colorectal cancer targeting peptides.

As is well known, quantum dots (QDs) have become valuable probes for cancer imaging. In particular, QD-labeled targeting peptides are capable of identifying cancer or tumors cells. A new colorectal cancer targeting peptide, cyclo(1, 9)-CTPSPFSHC, has strong targeting ability and also shows great potential in the identification and treatment of colon cancer. Herein, we synthesized a dual functional polypeptide, cyclo(1, 9)-CTPSPFSHCD2 G2 DP9 G3 H6 (H6 -TCP), to investigate its interaction with QDs inside the capillary. Fluorescence-coupled CE was adopted and applied to characterize the self-assembly of H6 -TCP onto QDs. It was indicated that the formation of the assembly was affected by H6 -TCP/QD molar ratio and sampling time. This novel in-capillary assay greatly reduced the sample consumption and the detection time, which was beneficial for the environment. It is expected that this kind of detection method could find more applications to provide more useful information for cancer diagnosis and detection of harm and hazardous substances/organisms in the environment in the future.

[Effects of biological soil crust on soil erodibility in Hilly Loess Plateau region of Northwest China].

Based on the analysis of the effects of biological soil crust (biocrust) in re-vegetated grasslands on soil physical and chemical properties, and by using EPIC estimation model in combining with simulated rainfall trials, this paper studied the effects of biocrust with different biomass and different soil texture on the soil erodibility (K value) in Hilly Loess Plateau Region of Northwest China in different seasons. The results showed biocrust could significantly decrease soil erodibility, with the K value of biocrust soil decreased by about 17%, compared with subsoil. The soil erodibility decreased with the increasing biomass of biocrust. The K value of moss crust soil decreased by 21%, compared with cyanobacteria crust soil. The erodibiliy of biocrust soil differed with different seasons, being significantly higher in rainy season than before or after the rainy season due to the differences in the biological activity of the biocrust organisms. The erodibilty of biocrust soil with different texture also varied significantly, with the K value in the order of sandy loam soil > silt soil > sandy soil. The measurement under simulated rainfall showed that the development of biocrust could decrease the erodibility of biocrust soil by about 90%, compared with that of the subsoil (5-10 cm).