Preamble

Journal of Arid Land (2025) 17(6): 808–822
doi: 10.1007/s40333-025-0019-5; CSTR: 32276.14.JAL.02500195
Science Press Springer-Verlag

Artificial cyanobacteria crusts can improve soil fertility and plant growth in a semi-arid area, northern China

JING Haimeng¹,², ZHOU Nan¹,², TANTAI Yu¹,², ZHAO Yunge²,³*

¹ College of Natural Resources and Environment, Northwest A&F University, Yangling 712100, China
² State Key Laboratory of Soil and Water Conservation and Desertification Control, Northwest A&F University, Yangling 712100, China
³ College of Soil and Water Conservation Science and Engineering, Northwest A&F University, Yangling 712100, China

Abstract: Artificial cyanobacteria crusts are formed by inoculating soil with cyanobacteria. These crusts help prevent soil erosion and restore soil functionality in degraded croplands. However, how fast the artificial cyanobacteria crusts can be formed is a key issue before their practical application. In addition, the effects of artificial cyanobacteria crusts on soil nutrients and plant growth are not fully explored. This study analyzed the effect of inoculation of cyanobacteria from local biological soil crusts on soil nutrients and Pak-choi (Brassica campestris L. ssp. Chinensis Makino var. communis Tsen et Lee; Chinese cabbage) growth in a cropland, northern China through field experiments by comparing with no fertilizer. The results showed that artificial cyanobacteria crusts were formed on the 18th d after inoculation with a coverage of 56.13%, a thickness of 3.74 mm, and biomass of 22.21 μg chla/cm². Artificial cyanobacteria crusts significantly improved the soil organic matter (SOM), NO₃⁻-N, total nitrogen (TN) contents, and the activities of sucrase, alkaline phosphatase, urease, and catalase enzymes of plants on the 50th d after inoculation. Additionally, artificial cyanobacteria crusts led to an increase in plant biomass, improved root morphology, and raised the phosphorus and potassium contents in the plants. Furthermore, the biomass of plant grown with artificial cyanobacteria crusts was comparable with that of grown with chemical fertilizer. The study suggested that, considering plant biomass and soil nutrients, it is feasible to prevent wind erosion in the cropland of arid and semi-arid areas by inoculating cyanobacteria crusts. This study provides new perspectives for the sustainable development and environmental management of cropland in arid and semi-arid areas.

Keywords: artificial cyanobacteria crusts; wind erosion; soil fertility; plant growth; soil enzyme

Citation: JING Haimeng, ZHOU Nan, TANTAI Yu, ZHAO Yunge. 2025. Artificial cyanobacteria crusts can improve soil fertility and plant growth in a semi-arid area, northern China. Journal of Arid Land, 17(6): 808–822. https://doi.org/10.1007/s40333-025-0019-5; https://cstr.cn/32276.14.JAL.02500195

1 Introduction

Arid and semi-arid areas account for approximately 41.00% of the Earth's land (FAO, 2019). The ecosystem in these areas is fragile, and wind erosion is a major cause of soil degradation. Preventing wind erosion in the soils of dryland is crucial for the maintenance of soil quality and ensuring the sustainable development of the ecosystem. It was reported that approximately 14.00% of the areas in arid and semi-arid areas are cropland (FAO, 2019). Cropland always suffers from strong wind erodibility due to low vegetation cover and frequent surface disturbance caused by tillage practices (Zhao et al., 2005), making it more susceptible to wind erosion than other land use types such as grassland and woodland (Guo et al., 2020; Wu et al., 2020). Liu et al. (2023) assessed the global average annual dust emissions from cropland to be 1.75×10⁹ g/s from 2017 to 2021, which seriously deteriorates air quality and human living environment. Wind erosion reduces the content of fine particles in the surface soil. This phenomenon leads to coarsening of the surface and loss of soil nutrients, resulting in a decrease in land productivity (Du et al., 2019). It was estimated that the global average annual organic carbon loss from wind erosion in cropland was 2.970×10¹² g/a from 2017 to 2021 (Liu et al., 2023). Song et al. (2019) reported that annual losses of SOC, TN, and TP were 0.985×10¹², 0.094×10¹², and 0.089×10¹² g/a, respectively due to wind erosion in spring in northern China. Meanwhile, wind erosion increases the suspended particle content in the air. Therefore, preventing wind erosion of cropland in dry areas is of great significance for improving soil quality, increasing food production and environmental management.

Many studies were conducted on preventing wind erosion in cropland. The existing researches identify three types of strategy for wind erosion: (1) conservation tillage, including straw mulching, stubble retention, minimum tillage, and no tillage (Cong et al., 2016; Li et al., 2020); (2) mulching such as gravel cover and film mulching (Li et al., 2021); and (3) biological measures such as cropland windbreaks or winter planting of oilseed grape, wheat, and camas (Ma et al., 2019; Chang et al., 2021). Nevertheless, despite the effectiveness of these measures in preventing wind erosion in cropland, limitations still exist. For example, stubble and straw mulching affect economic benefits and seed growth. Mulching is a laborious measure, and the mulching materials are easily damaged, potentially causing environmental pollution. Biological measures do not yield immediate results. Hence, it is essential to explore environmentally friendly, cost-effective, and efficient ways to prevent wind erosion in cropland.

Biological soil crusts (BSCs) are complexes formed by the cementation of cyanobacteria, algae, microfungi, lichens, and bryophytes with soil surface particles through pseudoroots, mycelia, and secretions (Weber et al., 2022), and are widely distributed in arid and semi-arid areas. BSCs have ecological functions such as improving soil texture, increasing soil organic matter content (Belnap and Lange, 2003; Gao et al., 2017), and improving soil aggregate stability (Bowker and Belnap, 2008). During the primary developmental stage of BSCs, cyanobacteria crusts can create a strong bond between soil particles through their exudation of exopolysaccharides and network of filaments, increasing the ability of the sand to withstand wind forces (Kheirfam and Asadzadeh, 2020). It was demonstrated that artificial inoculation supplemented with cultivation measures like irrigation can promote the formation and development of cyanobacteria crusts. Artificial cyanobacteria crusts are now a mature biological technique for wind erosion and soil desertification control in drylands. Many studies were conducted to develop the technique of inoculation and cultivation of cyanobacteria crusts (Chamizo et al., 2018; Lu et al., 2022; Rossi et al., 2022) and demonstrated its feasibility in desertification and wind erosion control (Fattahi et al., 2020). For example, Chen et al. (2006) found that artificial cyanobacteria crusts formed after 20 d of inoculation could resist the erosion with a wind speed of 7.9 m/s. Kheirfam and Asadzadeh (2020) observed that artificial cyanobacteria crusts with a thickness of 2.27 mm could reduce the sand flowing by 96.60% under the wind speed of 20.0 m/s for 30 min. In addition, a wind tunnel test from our research team showed that artificial cyanobacteria crusts with a 50.00% coverage can reduce the wind erosion rate by more than 90.00% (Huang et al., 2023). However, the time it takes for artificial cyanobacteria crusts with wind erosion protection to form in the cropland is not clarified.

Cyanobacteria crusts can influence the contents of organic carbon, nitrogen (N), and other nutrients in the soil. They also contribute to plant seed germination and seedling growth (Pushkareva et al., 2015; Sharma et al., 2021). Previous studies showed that cyanobacteria fix N₂ in specialized cells known as heterocysts, enabling them to provide the host with fixed N (Adams and Duggan, 2008), and the mineralization of their biomass after cyanobacterial death is the main mechanism of N transfer from cyanobacteria to plants (Roger, 2004). In addition, cyanobacterial photosynthesis drives CO₂ sequestration, elevating soil organic carbon levels (Pushkareva et al., 2015). Concurrent oxygen release enhances soil aeration, creating favorable conditions for aerobic microbial activity and overall soil health (Obana et al., 2007). Elbert et al. (2009) estimated that the global annual net uptake of carbon by biocrusts reached about 3.600×10¹⁵ g/a, and the estimated rate of nitrogen fixation by biocrusts was about 45.000×10¹² g/a. In addition, recent studies found that soil cyanobacteria might be able to inhibit fungal plant pathogens (Eckstien et al., 2024). It is evident that artificial cyanobacteria crusts also have good application prospects in soil nutrient improvement and crop growth promotion. Despite these advantages, existing studies focus almost exclusively on desert ecosystems. Whether similar success can be achieved in cropland through targeted inoculation remains unknown.

The Loess Plateau of China is one of the most severely wind-eroded areas in the world, with an annual average wind erosion amount of 5×10³–10×10³ t/km² (Tang, 2004). Traditional farming practices in this area require plowing and mounding in the spring, severely damaging the ground surface and resulting in higher wind erosion intensity overall (Mendez and Buschiazzo, 2009). It is necessary to control wind erosion on cropland in this area. Therefore, in this study, the wind-water erosion crisscross area of Loess Plateau was selected as the study area, and we used Pak-choi (Brassica campestris L. ssp. chinensis Makino var. communis Tsen et Lee; Chinese cabbage) as an indicator plant and answered the following three questions by inoculation with cyanobacteria crusts: (1) how fast cyanobacteria crusts can be formed in cropland soils after inoculation? (2) whether artificial cyanobacteria crusts promote plant growth? and (3) can artificial cyanobacteria crusts partially replace chemical fertilizer? This study might provide a basis for a comprehensive assessment of the feasibility of wind erosion prevention in cropland through inoculating cyanobacteria crusts in arid and semi-arid areas. Meanwhile, this study might provide new ideas for the sustainable development and environmental management of cropland in arid and semi-arid areas.

2.1 Study area

The study was carried out in the Liudaogou Watershed in Shenmu City, Shaanxi Province, northern China (38°46′–38°51′N, 110°21′–110°23′E; 1094.0–1273.9 m a.s.l.). The watershed has a semi-arid climate in the middle temperate zone, and the topography is characterized by typical sandy loess hills (Wang and Takahashi, 1999; Dan et al., 2023). The watershed experiences dramatic climate change, with low precipitation and severe sandstorms in winter and spring, and heavy rainfall in summer (Zha and Tang, 2000). The multi-year average precipitation is 409 mm, and the rainfall is mostly concentrated in June–September (Li and Xiao, 2022). The main land use types of the watershed are cropland, agricultural land, fruit intercropping land, shrubland, woodland, and grassland. The main crop types include corn (Zea mays L.), soybean (Glycine max (L.) Merr.), sunflower (Helianthus annuus L.), etc.

2.2 Experimental design

The experiment was conducted from 3 August to 22 September, 2022, in the terraces of Liudaogou Watershed. The daily average temperature was 9.5°C–27.5°C during the test period. The soil type is loessal soil. The field plots were previously cultivated with corn as the preceding crop. Due to experimental time constraints, Pak-choi (B. campestris), a common crop in the Loess Plateau, was selected as the indicator crop for this study due to its broad leaf morphology and rapid responsiveness to soil nutrient alterations during short-term cultivation periods. The Pak-choi variety used in this study was "Jinzaosheng", and its growth period is about 50 d. Excess seedlings were removed when the seedlings grew to 2 cm, ensuring that one seedling was left every 10 cm. In addition to different fertilizers applied to the treatments, other field measures such as weeding and pest control were the same. Weeds were pulled out every 3 d. Pak-choi was harvested on the 50th d after sowing. Rainfall and watering amounts during the plant growth period are shown in Figure 1 [FIGURE:1]. The experiment consisted of three treatments, which were arranged in a random complete block design and replicated four times. The treatments included control treatment with no fertilizer, nitrogen (15.00% N), phosphorus (P; 15.00% P), and potassium (K; 15.00% K) treatment with 700 kg/hm² application rate and artificial cyanobacteria crusts treatment. There was a total of 12 plots with an area of 1 m×1 m.

Fig. 1 Water supply from rainfall and watering during the growth period of Pak-choi

2.3 Cultivation of artificial cyanobacteria crusts

The cyanobacteria crusts used in the experiment were collected from the cropland in the Liudaogou Watershed. Firstly, the samples of cyanobacteria crusts were ground and sieved through a 0.1-mm sieve. We transferred sieved soil samples (10 g) to 150 mL of BG11 culture solution for cyanobacteria and green algae (Rippka et al. 1979) with the chemical composition detailed in Tables S1 and S2. The samples were shaken for 24 h and then placed in an incubator with a temperature of 25.0°C and light intensity of 1000–2000 lm/m² using a 12-h light/darkness regime for cultivation (about 15 d). After observing the growth of cyanobacteria, we transferred the cyanobacteria suspension to a white plastic bucket containing the appropriate amount of BG11 culture solution, and we expanded the culture at room temperature for subsequent experiments.

The cyanobacteria crusts used in this study were identified as a mixed cyanobacteria, and the dominant species were Scytonema sp. and Nosto sp. Chlorophyll concentrations of cyanobacterial suspensions were determined by using the method of Wintermans and De Mots (1965).

After the Pak-choi was sown, we sprayed cyanobacteria suspension uniformly on the soil surface at an inoculum concentration of 6 μg chla/cm². After inoculation, the soil moisture content was measured by moisture meter (HH2, Delta-T Devices, Burwell, UK), and water was added when the soil moisture content was lower than 20.00%, as shown in Figure 1. The cyanobacteria crust biomass was measured every 3 d in the first 18 d after inoculation. The cyanobacteria crust biomass, thickness, and biocrusts coverage were measured on the 18th d of inoculation and at the time of Pak-choi harvest, i.e., the 50th d of inoculation.

2.4 Soil sampling

To clarify the effect of artificial cyanobacteria crusts on the nutrients and enzyme activities of cropland, we collected soil samples of 0–2 cm soil layer on the 30th and 50th d since the Pak-choi was sown from each plot by a five-point sampling method. Soil samples of 0–2, 2–5, and 5–10 cm soil layers of each plot were collected on the 50th d of inoculation. The samples were transported to the laboratory and air-dried for the determination of soil nutrients and enzyme activities.

2.5 Determination of plant growth dynamics and its sampling

To clarify the effect of artificial cyanobacteria crusts on plant growth, when the plant had grown for 20 d, we randomly selected 5 plants with uniform growth from each replicate every 5 d. The plant height, leaf width, and leaf number were measured and recorded. The part above the cotyledons was cut as the aboveground part on the 50th d of plant growth. Then we weighed the aboveground part to obtain the fresh weight of the plant. The aboveground part was pulverized and mixed well for the determination of plant nutrients. Roots below the cotyledons were put into plastic bags, carefully cleaned, and dried to determine the dry weight of the plants.

2.6.1 Cyanobacteria crusts biomass, thickness, and coverage

Cyanobacteria crust biomass was expressed as chlorophyll a content per square centimeter of soil. The collected crust samples were ground and put into 15 mL centrifuge tubes with 8 mL of 95.00% ethanol. The sample was heated in a water bath for 5 min, then cooled, shaken for 20 min, and centrifuged at 4000 r/min for 10 min. After centrifugation, we transferred the supernatant to other centrifuge tubes. Then, the absorbance was measured by a UV-vis spectrophotometer detector (UV2300, Techcomp, Shanghai, China) (Ritchie, 2006). It was ensured that the samples were handled in the dark to prevent chlorophyll decomposition. The chlorophyll content was calculated using the following formula:

$$Chl = (11.0935 \ OD$$

where Chla is the chlorophyll a content (μg/cm²); OD₆₆₅ is the absorbance value of the extract at 665 nm; V is the volume of 95.00% ethanol (mL); and s is the area of cyanobacteria crusts (cm²).

The thickness of the biocrusts was measured by the vernier caliper. The biocrusts coverage was investigated by employing the point-intercept method with a 25 cm×25 cm gridded quadrat (Belnap et al., 2001).

2.6.2 Soil nutrients and enzyme activities

Soil organic matter (SOM) was determined by the dichromate redox titration method (Nelson and Sommers, 1982). Soil total nitrogen (TN) was determined by the Kjeldahl method following H₂SO₄ catalyst digestion. Soil NH₄⁺-N and NO₃⁻-N were extracted by KCl solution and determined by segmented flow analysis. Soil total phosphorus (TP) content was determined by the alkali fusion-Mo-Sb anti-spectrophotometric method. Soil available phosphorus (AP) was determined by the sodium hydrogen carbonate solution-Mo-Sb anti-spectrophotometric method (Carter and Gregorich, 2007).

Soil sucrase activity was determined using the 3-5 dinitrosalicylic acid colorimetric method (Guan, 1986). Soil sucrase activity was expressed as milligrams of glucose consumed in 1 g of soil after 24 h. Soil alkaline phosphatase activity was determined using the disodium phenyl phosphate colorimetric method (Guan, 1986). Soil alkaline phosphatase activity was expressed as milligrams of phenol released in 1 g of soil after 24 h. Soil urease activity was determined using the method used by Yang et al. (2007). Urease activity was expressed as milligrams of NH₃-N in 1 g of soil after 24 h. Soil catalase activity was determined using the method of Jin et al. (2009).

2.6.3 Plant nutrients and root morphology

Plant N content was determined by phosphoric acid-perchloric acid decoction and Kjeldahl method. Plant P content was determined by molybdenum-antimony antisorbent absorbance photometry. Plant K content was determined by flame atomic absorption spectrophotometry. Plant root morphology indicators, including total root length, total surface area, total volume, and average diameter were scanned using an Epson Perfection V700 Photo scanner (Epson (China) Co. Ltd., Beijing, China) and analyzed by WinPHIZO software.

2.7 Statistical analysis

Data were organized and analyzed using Excel v.2019 and SPSS v.26.0 softwares. To clarify the development process of artificial cyanobacteria crusts in cropland and their effects on soil nutrients, soil enzyme activities, and plant growth, we performed one-way analysis of variance (ANOVA) for cyanobacteria crusts biomass, thickness, coverage, soil organic matter, N and P contents, soil enzyme activity, plant biomass, root indices, and plant N, P, and K contents under different treatments. The data were subjected to the test of normal distribution and the test of homoscedasticity before ANOVA. Levene's test was utilized to test for ANOVA. Multiple comparisons were performed using the least significant difference test (α=0.05) in case of ANOVA alignment and the Tamhane's T2 test in case of ANOVA disagreement. Origin v.2023 software was used for graphing.

3.1 Artificial cyanobacteria crusts

There was a sharp increase in the biomass of artificial cyanobacteria crusts after 5 d of inoculation (Fig. 2 [FIGURE:2]). Biomass of artificial cyanobacteria crusts reached 22.21 μg chla/cm² on the 18th d, which was 8.0 times higher than that of the control. Compared with the initial inoculum, the biomass of artificial cyanobacteria crusts increased by 2.7 times. Similar to the control, no obvious cyanobacteria crust formation was observed in chemical fertilizer treatment.

Total coverage of biocrusts was 59.60% with a thickness of 3.74 mm on the 18th d of inoculation (Table 1 [TABLE:1]). Cyanobacteria crust biomass, coverage, and thickness did not change significantly on the 50th d of inoculation (Table 1). Total coverage of biocrusts was 73.46% with a thickness of 3.80 mm on the 50th d of inoculation (Table 1).

Fig. 2 Biomass of cyanobacteria crusts under different fertilizer treatments. Bars are standard errors.

Table 1 Biomass, coverage, and thickness of artificial cyanobacteria crusts in cropland

Inoculation days Cyanobacteria biomass (μg chla/cm²) Cyanobacteria crust coverage (%) Moss crust coverage Thickness (mm) 18 22.21±2.27a 56.13±9.00a 3.47±1.09a 3.74±0.20a 50 22.35±0.89a 66.93±7.36a 6.53±0.44a 3.80±0.09a

Note: Different lowercase letters within the same column indicate significant differences between two inoculation days at P<0.05 level. Mean±SD.

3.2 Soil nutrients dynamics

Figure 3 [FIGURE:3] showed soil nutrient changes after inoculation cyanobacteria crusts. Artificial cyanobacteria crusts did not show a significant effect on soil SOM and TN in the first 30 d of inoculation compared with control. However, artificial cyanobacteria crusts significantly increased soil SOM and TN on the 50th d of inoculation (Fig. 3a and f). Artificial cyanobacteria crusts had no significant effect on soil AP and TP throughout the growth period of Pak-choi (Fig. 3b and c). Artificial cyanobacteria crusts significantly reduced soil NH₄⁺-N content compared with control on the 30th d of inoculation. Still, there was no significant difference in NH₄⁺-N content between artificial cyanobacteria crusts and control on the 50th d of inoculation (Fig. 3d). Soil NO₃⁻-N content was significantly increased by 7.0 times in artificial cyanobacteria crusts compared with control on the 30th d of inoculation, and with the growth of Pak-choi, NO₃⁻-N content of artificial cyanobacteria crusts surface soil gradually decreased, but was always significantly higher than that of control (Fig. 3e).

Fig. 3 Dynamics of soil nutrient content in the 0–2 cm soil layer of different fertilizer treatments. (a), soil organic matter (SOM); (b), available phosphorus (AP); (c), total phosphorus (TP); (d), NH₄⁺-N; (e), NO₃⁻-N; (f), total nitrogen (TN). Different lowercase letters within the same day of treatment indicate significant differences among different fertilizer treatments at P<0.05 level. Bars are standard errors.

3.3 Soil nutrient distribution in different soil layers

Soil nutrient content of artificial cyanobacteria crusts was increased in the 0–2 cm soil layer, and the extent of its effect was related to nutrient type (Fig. 4 [FIGURE:4]). Artificial cyanobacteria crusts significantly increased soil SOM, NO₃⁻-N, and TN contents in the 0–2 cm soil layer by 26.44%, 106.46%, and 26.44%, respectively, and had no significant effect on soil SOM, TN, and NO₃⁻-N contents in the 2–10 cm soil layer and AP, TP, and NH₄⁺-N contents in the 0–10 cm soil layer on the 50th d of inoculation. Chemical fertilizers significantly increased soil SOM, TP, and TN contents in the 0–2 cm soil layer and AP contents in the 0–5 cm soil layer on the 50th d of plant growth.

3.4 Soil enzyme activities

Artificial cyanobacteria crusts significantly increased soil enzyme activities in the 0–2 cm soil layer (Fig. 5 [FIGURE:5]). Artificial cyanobacteria crusts significantly increased soil sucrase, alkaline phosphatase, urease, and catalase activities in the 0–2 cm soil layer by 29.72%, 29.39%, 53.77%, and 21.37% compared with control, respectively, and increased soil alkaline phosphatase activity by 62.78% in the 2–5 cm soil layer. Urease activity in the 0–2 cm layer with chemical fertilizer was significantly increased by 69.70%, and soil sucrase activity in the 2–10 cm layer was also significantly increased.

Fig. 4 Soil nutrient contents in different soil layers during plant harvesting. (a), SOM; (b), AP; (c), TP; (d), NH₄⁺-N; (e), NO₃⁻-N; (f), TN. Different lowercase letters within the same soil layer indicate significant differences among different fertilizer treatments at P<0.05 level. Bars are standard errors.

Fig. 5 Soil enzyme activities in different soil layers during plant harvesting. (a), catalase; (b), alkaline phosphatase; (c), urease; (d), sucrase. Different lowercase letters within the same soil layer indicate significant differences among different fertilizer treatments at P<0.05 level. Bars are standard errors.

3.5 Plant growth dynamics

The promotion of plant growth by artificial cyanobacteria crusts was more obvious in the later growth stages (20 d after inoculation) (Fig. 6 [FIGURE:6]). Plant height, leaf width, and leaf number of plants treated with chemical fertilizer were higher than artificial cyanobacteria crusts and control in the first 20 d of plant growth. However, the plants treated with artificial cyanobacteria crusts began to grow rapidly on the 20th d of plant growth, and the height and leaf width of the plants treated with artificial cyanobacteria crusts were gradually higher than chemical fertilizers on the 40th d of plant growth. Compared with control, plant height, leaf width, and leaf number of artificial cyanobacteria crusts were significantly increased by 242.86%, 229.03%, and 114.29% when the plants were harvested, respectively. Pak-choi fresh and dry weights of artificial cyanobacteria crusts were 14.0 and 18.0 times higher than those of control, respectively. There was no significant difference between artificial cyanobacteria crusts and chemical fertilizer in plant height, leaf width, plant fresh weight, and dry weight. The leaf number in plants of artificial cyanobacteria crusts was significantly lower than that of chemical fertilizer (Table 2 [TABLE:2]; Fig. 7 [FIGURE:7]).

Fig. 6 Growth dynamics of plants under different fertilizer treatments. (a), plant height; (b), leaf width; (c), leaf number. Bars are standard errors.

Table 2 Growth indices of Pak-choi under different fertilizer treatments during plant harvesting

Treatment Plant height (cm) Leaf width (cm) Leaf number Plant fresh weight (g) Plant dry weight (g) Control 4.9±1.02b 3.1±0.80b 7±0.97c 4.24±1.81b 0.67±0.38b Chemical fertilizer 15.5±0.80a 9.5±0.50a 17±1.98a 58.31±15.77a 12.76±3.31a Artificial cyanobacteria crusts 16.8±1.31a 10.2±1.38a 15±1.59b 65.46±14.77a 12.85±3.15a

Note: Different lowercase letters within the same columns indicate significant differences among different fertilizer treatments at P<0.05 level. Mean±SD.

Fig. 7 Growth status of Pak-choi under different fertilizer treatments during plant harvesting. (a), control; (b), chemical fertilizer; (c), artificial cyanobacteria crusts.

3.6 Nutrient content in the aboveground plants

Artificial cyanobacteria crusts were able to significantly increase plant nutrient uptake (Fig. 8 [FIGURE:8]). Compared with control, P and K contents in the aboveground plants of artificial cyanobacteria crusts increased by 47.64% and 43.41%, respectively, but did not affect N content. In comparison with chemical fertilizer, artificial cyanobacteria crusts increased N content of the aboveground plants by 26.22%, but P content decreased by 22.59%.

Fig. 8 Contents of nitrogen (N), phosphorus (P), and potassium (K) in Pak-choi under different fertilizer treatments. Different lowercase letters within the same nutrient indicate significant differences among different fertilizer treatments at P<0.05 level. Bars are standard errors.

3.7 Morphology of plant roots

Artificial cyanobacteria crusts significantly promoted plant root growth (Table 3 [TABLE:3]). Compared with control, artificial cyanobacteria crusts significantly increased dry weight, total root length, total surface area, total volume, and average diameter of Pak-choi root by 700.00%, 258.93%, 356.67%, 503.13%, and 216.67%, respectively. Root dry weight of artificial cyanobacteria crusts was significantly lower than that of chemical fertilizer, while there were no significant differences between the two in the other root morphology indices.

Table 3 Root morphology of Pak-choi under different fertilizer treatments

Treatment Root dry weight (g) Total root length (cm) Total surface area (cm²) Total volume (cm³) Average diameter (mm) Control 0.09±0.07c 77.02±17.20b 17.70±4.56b 0.32±0.09b 0.30±0.06b Chemical fertilizer 0.93±0.25a 271.77±42.80a 84.59±12.80a 2.14±0.40a 0.99±0.10a Artificial cyanobacteria crusts 0.72±0.02b 276.45±50.50a 80.83±16.40a 1.93±0.60a 0.95±0.20a

Note: Different lowercase letters within the same column indicate significant differences among different fertilizer treatments at P<0.05 level. Mean±SD.

4 Discussion

Severe wind erosion from cropland, especially in winter and spring in arid and semi-arid areas, threatens the sustainable development of agriculture production and ecological environment (Gomes et al., 2003). As a biological measure that can improve soil structure and increase soil stability (Belnap and Lange, 2003; Gao et al., 2017), artificial cyanobacteria crusts offer a promising alternative for sustainable wind erosion management. However, it is not clear how long it takes to form cyanobacteria crusts with wind erosion control capacity after inoculation in cropland.

The results of this field experiment showed that coverage, thickness, and biomass of the cyanobacteria crusts on the 18th d of inoculation were 56.13%, 3.74 mm, and 22.21 μg chla/cm², respectively. Our previous study demonstrated that crusts with these characteristics can withstand wind erosion at wind speeds of up to 13.0 m/s in controlled tests (Huang et al., 2023), thereby confirming their protective capacity. Moreover, the plants achieved a certain degree of coverage on the 18th d of inoculation, which offered some protection against wind erosion. Thus, the cyanobacteria crusts that formed on the 18th d of inoculation in this study are likely to be effective in controlling wind erosion.

Cyanobacteria crust demonstrated sustained soil enhancement capabilities through photosynthesis (Zaady et al., 2000; Guan et al., 2020), atmospheric N conversion (Belnap and Lange, 2003), and secretion of polysaccharides (Mugnai et al., 2018). In our study, on the 50th d of inoculation, artificial cyanobacteria crusts remained and increased SOM and N contents, and stimulated key enzymatic activities for nutrient cycling. In addition, our findings demonstrated that artificial cyanobacteria crusts substantially improved Pak-choi development, with pronounced biomass accumulation observed in both aboveground and root systems. The observed growth promotion likely stems from cyanobacteria crust-mediated modifications to rhizosphere dynamics, particularly through soil nutrient enrichment and optimized plant nutrient acquisition (Godínez-Alvarez et al., 2012). Such rhizospheric improvements create favorable conditions for photosynthetic assimilation and subsequent biomass partitioning (Zaady et al., 2000; Belnap and Lange, 2003).

Experiments monitoring Pak-choi growth revealed that artificial cyanobacteria crusts began enhancing plant development after 20 d of inoculation, aligning with their biological formation period of 15–20 d after inoculation (Lan et al., 2017; Mugnai et al., 2018). This delay reflects the time required for crust stabilization. As cyanobacteria crusts developed, their benefits including soil nutrient enrichment and gradual growth promotion became measurable over time. During harvesting, Pak-choi with cyanobacteria crusts produced biomass equivalent to crops receiving 700 kg/hm² of standard N-P-K fertilizer. This result demonstrated that optimized cyanobacteria applications could reduce chemical fertilizer dependency while maintaining yield integrity.

High yields of cropland were closely related to chemical fertilizer, and fertilizer application brought about 33.00%–66.00% yield increases (Cassman et al., 1998). However, the widespread use of chemical fertilizer caused serious problems, such as reduced productivity of soils, environmental pollution, development of pest resistance, and reduction in food safety (Lin et al., 2020). Results of this study showed that in addition to wind erosion prevention, artificial cyanobacteria crusts can promote crop growth. Thus, the application of artificial cyanobacteria crusts provides a new, environment-friendly idea for chemical fertilizer reduction, and agricultural sustainable development in arid and semi-arid areas. However, cyanobacteria crust in different growth stages may have different effects on soil nutrients and plant growth (Weber et al., 2022). In our study, we used Pak-choi, which has a short growth period, as the indicator plant, hence, whether artificial cyanobacteria crusts exert similar effects on the long-term growth plant still needed further study.

Water is a fundamental resource for the metabolism of cyanobacteria (Rippin et al., 2017). A lack of water may affect the survival rate of soil cyanobacteria (Ayuso et al., 2017). Thus, soil moisture is an important factor influencing the formation of artificial cyanobacteria crusts (Rossi et al., 2022). It is noteworthy that this study was carried out in August and September, which is the monsoon season in the wind-water erosion crisscross area of the Loess Plateau. The soil moisture conditions may be more favorable for the formation of artificial cyanobacteria crusts. Temperature is significant for the growth and reproduction of soil algal cells (Lu et al., 2022). However, wind erosion generally occurs in winter and spring, and low temperatures can limit the formation of artificial cyanobacterial crusts. Therefore, it is worthwhile conducting verification in winter and spring. Meanwhile, we propose exploring cyanobacterial species that can adapt to cold environments for inoculation as one approach to solve this problem.

Ecological constraints always exhibit in arid and semi-arid areas, such as low soil fertility, frequent droughts, land degradation, loss of biodiversity, leading to the decline of agricultural productivity (Gaur and Squires, 2018). Artificial cyanobacteria crusts, an effective strategy for wind erosion prevention and soil enhancement, are widely used in desertified areas (Chen et al., 2006; Kheirfam and Asadzadeh, 2020). However, cropland faces distinct challenges, i.e., wind erosion primarily occurs in winter and spring (Gomes et al., 2003), necessitating rapid crust establishment to achieve timely protection. Our study demonstrates that artificial cyanobacteria crusts can be formed on the 18th d of inoculation, which not only can prevent wind erosion but also exert certain benefits for plant growth. These results will benefit soil quality in arid and semi-arid areas. Integration with modern irrigation infrastructure renders cyanobacteria crust practically viable for widespread agricultural adoption. Moreover, compared with desertified areas, cropland soil has better nutrient and water status (Zhang et al., 2019). All these provide more favorable conditions for the formation of artificial cyanobacteria crusts. Additionally, as native soil microorganisms, cyanobacteria inoculants enhance biodiversity without ecological risks (Darby et al., 2007; Lan et al., 2022), differentiating it from invasive bioengineering methods. Therefore, we recommend that artificial cyanobacteria crusts could be inoculated in cropland in arid and semi-arid areas of the world during fallow periods and at the time of planting to prevent wind erosion and to promote plant growth.

5 Conclusions

Wind erosion presents a major threat to agricultural sustainability in semi-arid areas, accelerating soil degradation and contributing to adverse atmospheric effects. Our research results showed that the surface coverage of artificially inoculated cyanobacteria crusts reached 56.13% on the 18th of inoculation, offering a viable solution to mitigate wind erosion in vulnerable agricultural systems.

The introduction of cyanobacteria crusts substantially enhanced soil nutrient quality, increased plant biomass, and elevated nutrient levels in crops. Compared with control, inoculation with cyanobacteria crusts increased SOM, TN, and NO₃⁻-N in surface soils, alongside boosting enzymatic activity. Additionally, cyanobacteria crusts showed marked improvements in Pak-choi growth indices, including fresh weight, plant height, leaf width, and leaf number. Importantly, P and K contents in Pak-choi with cyanobacteria crusts far exceeded those of control. These results validate the viability of using cyanobacteria crusts as a tool to combat wind erosion in arid and semi-arid areas. Furthermore, the biomass-enhancing potential of artificial cyanobacteria crusts offers a novel approach for reducing reliance on chemical fertilizers and promoting sustainable agricultural development in arid and semi-arid areas.

Conflict of interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgments

This work was supported by the National Key Research and Development Program of China (2022YFF1300802) and the National Natural Science Foundation of China (42377357).

Author contributions

Conceptualization: ZHAO Yunge
Methodology: ZHAO Yunge, ZHOU Nan
Formal analysis: JING Haimeng, ZHOU Nan, TANTAI Yu
Writing - original draft preparation: JING Haimeng
Writing - review and editing: JING Haimeng, ZHAO Yunge
Funding acquisition: ZHAO Yunge
Resources: ZHAO Yunge
Supervision: ZHAO Yunge
Data curation: ZHOU Nan
Investigation: JING Haimeng, ZHOU Nan, TANTAI Yu
Project administration: ZHOU Nan
Validation: JING Haimeng, ZHOU Nan
Visualization: JING Haimeng

All authors approved the manuscript.

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Appendix

Table S1 BG11 nutrient solution concentration

Chemical composition Concentration (g/L) NaNO₃ 1.5 K₂HPO₄•3H₂O 0.04 MgSO₄•7H₂O 0.075 C₁₀H₁₄N₂Na₂O₈ 0.01 CaCl₂•2H₂O 0.036 C₆H₈O₇ 0.006 C₆H₄O₇•xFe•yNH₃ 0.006 NaCO₃ 0.02

Note: The composition of A5 solution concentration is shown in Table S2.

Table S2 A5 solution concentration

Chemical composition Concentration (g/L) H₃BO₃ 2.86 MnCl₂•H₂O 1.81 ZnSO₄•7H₂O 0.222 CuSO₄•5H₂O 0.079 Na₂MoO₄•2H₂O 0.39 Co(NO₃)₂•6H₂O 0.049