Response of biological and physical proxies of soil biocrusts to land-use succession in Khanghah-Sorkh watershed, West Azerbaijan province

Introduction
Sustainable ecosystems fundamentally support biogeochemical cycles and maintain terrestrial equilibrium. However, extensive conversion of rangelands to rainfed agriculture has severely compromised soil surface integrity, triggering accelerated degradation trajectories. Biological soil crusts (biocrusts) function as critical ecological engineers, yet their integrated biological and physical proxies remain inadequately monitored across sequential land-use transitions. Elucidating the precise responses of these functional components to anthropogenic disturbances is paramount for designing targeted rehabilitation interventions. Consequently, this investigation specifically evaluated the sensitivity of six key biocrust proxies, encompassing exopolysaccharide concentrations, basal microbial respiration rates, biocrust thickness, gravimetric moisture content, mean weight diameter, and geometric mean diameter of soil aggregates, across three distinct land-use categories: natural rangeland, actively cultivated rainfed fields, and recently abandoned rainfed land. Situated within a representative cold semi-arid watershed, the research tested the primary hypothesis that conversion to conventional rainfed farming precipitates rapid biocrust collapse, whereas short-term passive abandonment fails to catalyze substantial functional recovery. By systematically quantifying these highly responsive indicators, the study establishes a rigorous diagnostic protocol for early-stage soil degradation assessment. Ultimately, these findings will inform evidence-based land management frameworks and promote sustainable restoration paradigms in ecologically fragile dryland environments globally.
 
Materials and Methods
The field investigation was executed within the Khanqah Sorkh watershed, a cold semi-arid region experiencing pronounced seasonal moisture deficits and alkaline loam-clay soils. A systematic random-compound sampling design was implemented to capture spatial heterogeneity across three land-use types: reference rangeland, active rainfed agriculture, and two-to-three-year abandoned fields. Twelve independent composite samples per land-use category were meticulously extracted from the upper two-centimeter biocrust horizon using sterilized tools to prevent cross-contamination. Exopolysaccharides were quantified via the phenol-sulfuric acid colorimetric assay, with absorbance measured at 490 nanometers. Basal microbial respiration was determined through closed-system alkali absorption, wherein evolved carbon dioxide was trapped in sodium hydroxide and subsequently titrated with standardized hydrochloric acid. Biocrust thickness was recorded using a high-precision digital caliper across five micro-sites per plot. Soil moisture was established gravimetrically after oven-drying at 105 degrees Celsius for twenty-four hours. Aggregate stability was assessed via dry sieving through a nested series of standard sieves, enabling precise computation of mean weight diameter and geometric mean diameter. Data normality and homogeneity of variance were rigorously verified prior to statistical processing. One-way analysis of variance coupled with Tukey’s honest significant difference test was employed at a ninety-five percent confidence level to detect inter-treatment disparities. All laboratory procedures adhered strictly to internationally recognized soil analytical protocols to ensure reproducibility. Quality control measures included duplicate analyses for ten percent of samples and calibration against certified reference materials. Statistical computations were performed using specialized analytical software, guaranteeing robust parameter estimation. This methodological framework effectively isolates land-use effects from extraneous environmental noise factors.
 
Results and Discussion
One-way ANOVA demonstrated highly significant land-use effects (p<0.001) on all six biocrust proxies, with F-values ranging from 27.71 (biocrust thickness) to 101.51 (GMD). Natural rangelands exhibited maximum values across all indicators: gravimetric moisture (9.39±1.78%), exopolysaccharide concentrations (0.15±0.02 mg g⁻¹), basal microbial respiration (0.21±0.02 mg CO₂ g⁻¹ day⁻¹), biocrust thickness (11.42±4.14 mm), mean weight diameter (1.69±0.08 mm), and geometric mean diameter (1.14±0.03 mm). Conversion to active rainfed agriculture precipitated substantial declines: exopolysaccharides decreased 27% (to 0.11±0.01 mg g⁻¹), respiration 29% (to 0.15±0.02 mg CO₂ g⁻¹ day⁻¹), thickness 55% (to 5.16±1.17 mm), MWD 17% (to 1.41±0.07 mm), and GMD 15% (to 0.97±0.03 mm). Abandoned rainfed lands (2–3 years post-cultivation) showed negligible recovery: exopolysaccharides (0.07±0.02 mg g⁻¹), respiration (0.11±0.01 mg CO₂ g⁻¹ day⁻¹), and thickness (4.23±1.15 mm) remained statistically equivalent to active rainfed soils (Tukey's HSD, p>0.05). Pearson correlation analysis revealed strong interdependencies among proxies: EPS–BMR (r=0.866), EPS–moisture (r=0.844), BMR–MWD (r=0.676), and MWD–GMD (r=0.880; all p<0.001). These quantitative patterns confirm that passive abandonment fails to restore biocrust functionality within short management timeframes. The integrated assessment of these highly responsive indicators provides a robust diagnostic framework for early detection of soil surface degradation and for evaluating restoration efficacy in semi-arid landscapes where moisture limitation and anthropogenic pressures converge.
 
Conclusion
This investigation conclusively demonstrates that sequential land-use transitions from intact rangelands to cultivated fields and subsequently abandoned plots trigger profound, multi-dimensional degradation of biological and physical soil surface proxies. All measured indicators exhibited extreme sensitivity to agricultural conversion, with active cultivation causing immediate functional collapse across exopolysaccharide concentrations, microbial respiration, crust thickness, moisture retention, and aggregate stability metrics. Critically, two to three years of passive abandonment failed to initiate meaningful ecological recovery, as structural indices and metabolic activities remained statistically indistinguishable from actively managed degraded soils. This evidence unequivocally confirms that natural succession processes are insufficient to restore biocrust-mediated ecosystem services in semi-arid environments within short, management-relevant timeframes. Strong functional correlations among proxies highlight the mechanistic coupling between biological activity and physical structure in surface soil communities. Consequently, land management paradigms must urgently shift from passive conservation toward active ecological engineering approaches. We recommend implementing targeted biotechnological interventions, particularly in recently abandoned fields, to stimulate polymeric secretion and accelerate structural rehabilitation. Additionally, integrating these six validated proxies into routine soil monitoring protocols will enable early detection of degradation thresholds and precise evaluation of restoration efficacy. Future research should prioritize long-term field trials assessing intervention scalability and economic viability to establish standardized guidelines for sustainable dryland management worldwide.