The soil moisture percentage (Figure 2A) indicates that, at five of the nine sampling points under biological soil crusts (Crust), the moisture content was significantly higher compared to the soils without biological soil crusts (Non-Crust). Conversely, at the remaining four points, Non-Crust soils exhibited significantly higher moisture levels. However, when analyzing the data globally (Figure 2E), there is a 2.1% increase in moisture in Non-Crust soils compared to Crust soils, but this difference is not statistically significant. Some types of crusts in sandy soil can reduce rapid water infiltration and help retain soil moisture (Navas et al. 2021). Similarly, Cerdà (1998) notes that soils under BSC tend to maintain more stable moisture levels than Non-Crust soils, likely due to differences in infiltration rates and reduced soil erodibility under BSCs. Additionally, studies suggest that in extreme environments, microorganisms within BSCs can absorb water as an adaptation mechanism to withstand desiccation. In particular, mosses, a key component of many BSCs, are poikilohydric organisms, meaning they can survive extreme dehydration and rehydrate when water becomes available, which may explain the moisture levels observed in BSC-covered soils (Nuñez 2013). However, it is important to acknowledge that the initial water content in crusted soils might influence the observed moisture differences, rather than solely reflecting the effects of BSCs. To minimize this uncertainty, future studies should include sampling across different seasons to assess moisture variations under diverse climatic conditions.

Figure 2

The pH values obtained are generally classified as strongly acidic. Significant differences were observed at four of the nine sampling points (Figure 2B), with three points exhibiting higher pH values in Non-Crust soils. However, when considering all sampling points collectively, no statistically significant differences were detected (Figure 2F). Although the overall acidity is evident, previous studies present differing perspectives. For instance, Kakeh et al. (2018) report no significant differences in pH between soils with and without BSC. In contrast, Wu et al. (2013) suggest that microbial respiration within BSCs may contribute to a reduction in soil pH, which aligns with the lower pH values observed at three of the four significantly different sampling points.

The total nitrogen content in the soil (Figure 2C) is generally low. Significant differences were observed at four of the nine sampling points, with Crust soils exhibiting higher nitrogen levels at three of these points. However, when analyzing the average data (Figure 2G), Crust soils contain 15.3% more nitrogen than Non-Crust soils, although this difference is not statistically significant. Plata (2019) reports higher total nitrogen percentages in soils with BSC, while Toledo (2012) also notes significantly higher nitrogen levels in BSC soils compared to Non-Crust soils. The observed increase in nitrogen content in some samples may be attributed to microorganisms within the BSC, such as cyanobacteria, which facilitate nitrogen fixation in the soil (García 2019).

The organic carbon content in the soil (Figure 2D) is generally low. Significant differences were found at five of the nine sampling points, with Crust soils exhibiting significantly higher organic carbon content. Additionally, Figure 2H indicates that the organic carbon content in Crust soils is 27.4% higher compared to Non-Crust soils, though this difference is not statistically significant. Studies by Kakeh et al. (2020) and Plata (2019) also, report higher amounts of organic carbon in soils with BSC. Nuñez (2013) studied three different types of BSC and similarly found higher organic carbon levels in soils with BSC. This is supported by Ayala et al. (2018), which affirms that BSCs provide valuable environmental services through carbon sequestration.

Urease enzyme activity (Figure 3A) shows significant differences at four of the nine sampling points, with two points exhibiting higher activity in Crust soils and two in Non-Crust soils. On average (Figure 3D), Crust soils show an 8.5% increase in urease activity compared to Non-Crust soils; however, this difference is not statistically significant. Sun et al. (2020) reported higher enzyme activity in BSC soils compared to Non-Crust soils, though the differences were not significant. In contrast, Xu et al. (2022) found a significant increase in urease activity in BSC soils compared to Non-Crust soils, with a more pronounced effect in hostile environments. Urease activity is highly site-dependent and influenced by factors such as organic carbon content and soil moisture (Rodríguez and Merchancano 2018).

Figure 3

The enzymatic activity of protease (Figure 3B) showed no significant differences at six of the nine sampling points. Among those with significant differences, only one of the three points exhibited higher enzymatic activity in Crust soils. Additionally, Figure 3E shows that protease activity is 18.7% higher in Crust soils compared to Non-Crust soils; however, this difference is not statistically significant. These results indicate that BSCs did not have a significant impact on protease enzymatic activity.

The enzymatic activity of β-glucosidase (Figure 3C) showed significant differences at only two of the nine sampling points, with higher enzymatic activity in Crust soils at both points. On average (Figure 3F), β-glucosidase activity in Crust soils was 11.1% higher compared to that in Non-Crust soils, though this difference was not statistically significant. Miralles et al. (2012) reported significantly higher β-glucosidase activity in soils with BSC. Similarly, Xu et al. (2022) observed a 48.4% increase in β-glucosidase activity in BSC soils, demonstrating a significant difference compared to Non-Crust soils. β-glucosidase activity is strongly associated with organic carbon content (Orellana 2019), which aligns with the results showing higher organic carbon in Crust soils (Figure 2D).

The results obtained for nitrogen-fixing bacteria (Figure 4A) reveal four significant differences out of the nine sampling points, with all significant differences showing higher counts in Crust soils compared to Non-Crust soils. Additionally, on average (Figure 4D), the number of colony-forming units in Crust soils is 41.9% higher than in Non-Crust soils, with this difference being statistically significant. Zhao et al. (2019) found a correlation with the results obtained in this study, demonstrating a higher presence of nitrogen-fixing bacteria in soils with Biological Soil Crust (BSC). The presence of BSC may promote the growth of nitrogen-fixing bacteria due to the presence of aerobic and microaerophilic bacteria that constitute the BSC (Castillo-Monroy and Maestre 2011). Furthermore, Huang et al. (2011) mention that microorganisms within BSCs function as diazotrophic communities. The dominant morphological group in BSCs whether cyanobacteria, mosses, or lichens can influence their development and ecological functions. However, since no taxonomic identification was performed in this study, these remain as possible explanations rather than definitive conclusions.

Figure 4

The results for cellulolytic bacteria at each sampling point did not show any significant differences (Figure 4B). On average (Figure 4E), cellulolytic bacteria in Crust soils were 50.5% more abundant than in Non-Crust soils, although this difference was not statistically significant. The abundance of cellulolytic fungi showed four significant differences out of the nine sampling points, with two of these differences being higher in Crust soils (Figure 4C) and the remaining two in Non-Crust soils. Conversely, the overall presence of cellulolytic fungi (Figure 4F) was 96% higher in Non-Crust soils than in Crust soils. Biological soil crusts did not significantly affect microorganisms involved in the carbon cycle. One possible explanation is that in extreme environments, microorganisms responsible for decomposing environmental cellulose are significantly reduced (Soares et al. 2012). Another possible explanation could relate to a study examining the contribution of microorganisms in BSCs over time, which shows greater bacterial diversity and abundance compared to fungi at certain times, suggesting that when bacterial populations are higher than fungal populations in BSCs, the crust might be relatively young (Zhao et al. 2019).

The principal component analysis (PCA) included the first three axes, which together explained 65.2% of the variance (Figures 5A and 5B). The PCA indicates a correlation among the variables of moisture, nitrogen percentage, and carbon. However, no clear trend is observed in the behavior of these variables between Crust and Non-Crust points, no single trend is observed. Similarly, Avellaneda et al. (2012) reported an inverse relationship between urease and protease, consistent with the present study (Figures 5A and 5B). The authors suggest that when urease is activated within the same microbial morphotype, protease remains inactive.

Figure 5

When analyzing the overall data for physicochemical variables (Figures 2D to 2H), enzymatic activities (Figures 3D to 3F), and microorganisms (Figures 4D to 4F) in relation to soil quality in Crust and Non-Crust samples it was observed that, although only the nitrogen-fixing bacteria showed a significant individual result (Figure 4A) and an average increase (Figure 4D) in Crust soils, there was a general trend indicating an increase in total nitrogen, organic carbon, urease, and β-glucosidase in Crust soils compared to Non-Crust soils. This suggests that biological soil crusts (BSCs) contribute properties that enhance soil fertility, conservation, and restoration, as discussed in review articles by García (2019) and Castillo-Monroy et al. (2011). These studies highlight that BSC significantly contributes to nitrogen fixation in arid and semi-arid ecosystems, similar to the conditions of the present study, and that BSCs in hot deserts (>25°C) tend to be more efficient than those in cold climates. Recent studies by Gorji et al. (2021) corroborate the findings of this study, reinforcing the importance of BSC in arid ecosystems for soil fertility.

The results indicate that soils with biological soil crusts (BSC) exhibit significant ecological benefits. Moisture levels were significantly higher in BSC soils at five out of nine sampling points, suggesting enhanced water retention. In terms of pH, four samples showed significant differences, with three indicating lower values in soils with BSC. Total nitrogen tended to be higher in soils with BSC, as three out of four significant differences pointed to increased nitrogen content, accompanied by a notably greater abundance of nitrogen-fixing bacteria compared to soils without crust. Although organic carbon content displayed an upward trend in five of the nine sampling points, these differences were not statistically significant. Additionally, enzymatic activities-specifically urease and β-glucosidase-were elevated in BSC soils, further suggesting a positive impact on soil quality.

These findings demonstrate that the evaluated BSC possesses beneficial properties for soils in extreme, vegetation-sparse, and erosion-affected environments, underscoring its potential for soil recovery and protection in degraded landscapes. To gain a broader understanding of BSC behavior, it is recommended to extend this research to diverse environmental conditions across Colombia and Latin America. Future studies should also monitor factors such as crust age, conservation status, and soil depth variations, while expanding the analysis of associated microbial diversity.

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.