The responses of soil nitrogen component dynamics and enzyme activities to vegetation degradation in wet meadows ecosystems remain unclear. This study employed a combination of field surveys and laboratory experiments to investigate soil nitrogen components and nitrogen cycling enzyme activities under different intensities of vegetation degradation and during the vegetation growth season in a wet meadow on the Qinghai–Tibetan Plateau. The aim was to explore the responses of soil nitrogen components and nitrogen cycling enzyme activities to vegetation degradation and their interrelationships. The results showed that vegetation degradation significantly reduced TN, NH₄⁺-N, MBN, PRO, and NiR, and increased NO₃⁻-N, URE, and NR. Soil nitrogen components and enzyme activities exhibited seasonal fluctuations across different degradation levels during the growing season. The Pearson correlation analysis revealed a significant positive correlation between temperature, moisture, nitrogen fractions, and nitrogen cycle-related enzyme activities, as well as between the nitrogen fractions and the enzyme activities themselves. Partial Least Squares Path Modeling (PLS-PM) elucidated the relationships between soil properties and nitrogen components under different degradation levels, explaining 78% of the variance in nitrogen components. Degradation level, growth season, and soil physical properties had indirect associations with nitrogen components, whereas soil enzyme activities exerted a direct positive influence on nitrogen components. Our research revealed the universal impact mechanism of environmental factors, soil characteristics, and vegetation degradation on nitrogen cycling in a wet meadow, thereby making a significant contribution to the restoration and maintenance of functional integrity in alpine wetland ecosystems.

Alpine wetlands on the Qinghai–Tibet Plateau are increasingly degraded, threatening soil nitrogen (N) cycling and ecosystem functioning. However, how degradation restructures enzyme-mediated soil N cycling and its functional balance remains poorly understood. To address this gap, we conducted a three-year field investigation across four degradation stages (non-degraded, lightly degraded, moderately degraded, and heavily degraded wetlands) in the Gahai Wetland. We quantified four key soil N-cycling enzymes, namely urease, protease, nitrate reductase, and nitrite reductase, and developed a nitrogen cycling functional balance (NCFB) index to assess shifts in the coordination between hydrolytic and reductive functions. Degradation-induced drying and nutrient depletion reduced soil water content, soil organic carbon, total nitrogen, ammonium availability, and microbial biomass N, while increasing soil temperature and nitrate accumulation. Degradation increased urease and nitrate reductase activities but decreased protease and nitrite reductase activities, indicating enzyme-specific restructuring of soil N cycling. Most enzyme activities peaked in mid-growing season, whereas nitrate reductase peaked later. Soil N cycling shifted from a relatively coordinated state in non-degraded wetlands toward greater functional imbalance in degraded wetlands. This reorganization was strongly modulated by hydroclimatic variability, with drier conditions amplifying degradation, induced divergence in enzyme activities. Redundancy analysis and piecewise structural equation modeling showed that soil water content, organic carbon, inorganic N availability, and microbial biomass N were the primary regulators of enzyme variation and N-cycling functional imbalance. Overall, this study provides new insight into mechanisms of soil N-cycling destabilization in degraded alpine wetlands and informs wetland restoration under a drier future climate.

Alpine wetlands on the Qinghai–Tibet Plateau are increasingly degraded, threatening soil nitrogen (N) cycling and ecosystem functioning. However, how degradation restructures enzyme-mediated soil N cycling and its functional balance remains poorly understood. To address this gap, we conducted a three-year field investigation across four degradation stages (non-degraded, lightly degraded, moderately degraded, and heavily degraded wetlands) in the Gahai Wetland. We quantified four key soil N-cycling enzymes, namely urease, protease, nitrate reductase, and nitrite reductase, and developed a nitrogen cycling functional balance (NCFB) index to assess shifts in the coordination between hydrolytic and reductive functions. Degradation-induced drying and nutrient depletion reduced soil water content, soil organic carbon, total nitrogen, ammonium availability, and microbial biomass N, while increasing soil temperature and nitrate accumulation. Degradation increased urease and nitrate reductase activities but decreased protease and nitrite reductase activities, indicating enzyme-specific restructuring of soil N cycling. Most enzyme activities peaked in mid-growing season, whereas nitrate reductase peaked later. Soil N cycling shifted from a relatively coordinated state in non-degraded wetlands toward greater functional imbalance in degraded wetlands. This reorganization was strongly modulated by hydroclimatic variability, with drier conditions amplifying degradation, induced divergence in enzyme activities. Redundancy analysis and piecewise structural equation modeling showed that soil water content, organic carbon, inorganic N availability, and microbial biomass N were the primary regulators of enzyme variation and N-cycling functional imbalance. Overall, this study provides new insight into mechanisms of soil N-cycling destabilization in degraded alpine wetlands and informs wetland restoration under a drier future climate.

Alpine wetlands on the Qinghai–Tibet Plateau are increasingly degraded, threatening soil nitrogen (N) cycling and ecosystem functioning. However, how degradation restructures enzyme-mediated soil N cycling and its functional balance remains poorly understood. To address this gap, we conducted a three-year field investigation across four degradation stages (non-degraded, lightly degraded, moderately degraded, and heavily degraded wetlands) in the Gahai Wetland. We quantified four key soil N-cycling enzymes, namely urease, protease, nitrate reductase, and nitrite reductase, and developed a nitrogen cycling functional balance (NCFB) index to assess shifts in the coordination between hydrolytic and reductive functions. Degradation-induced drying and nutrient depletion reduced soil water content, soil organic carbon, total nitrogen, ammonium availability, and microbial biomass N, while increasing soil temperature and nitrate accumulation. Degradation increased urease and nitrate reductase activities but decreased protease and nitrite reductase activities, indicating enzyme-specific restructuring of soil N cycling. Most enzyme activities peaked in mid-growing season, whereas nitrate reductase peaked later. Soil N cycling shifted from a relatively coordinated state in non-degraded wetlands toward greater functional imbalance in degraded wetlands. This reorganization was strongly modulated by hydroclimatic variability, with drier conditions amplifying degradation, induced divergence in enzyme activities. Redundancy analysis and piecewise structural equation modeling showed that soil water content, organic carbon, inorganic N availability, and microbial biomass N were the primary regulators of enzyme variation and N-cycling functional imbalance. Overall, this study provides new insight into mechanisms of soil N-cycling destabilization in degraded alpine wetlands and informs wetland restoration under a drier future climate.

Alpine wetlands on the Qinghai–Tibet Plateau are increasingly degraded, threatening soil nitrogen (N) cycling and ecosystem functioning. However, how degradation restructures enzyme-mediated soil N cycling and its functional balance remains poorly understood. To address this gap, we conducted a three-year field investigation across four degradation stages (non-degraded, lightly degraded, moderately degraded, and heavily degraded wetlands) in the Gahai Wetland. We quantified four key soil N-cycling enzymes, namely urease, protease, nitrate reductase, and nitrite reductase, and developed a nitrogen cycling functional balance (NCFB) index to assess shifts in the coordination between hydrolytic and reductive functions. Degradation-induced drying and nutrient depletion reduced soil water content, soil organic carbon, total nitrogen, ammonium availability, and microbial biomass N, while increasing soil temperature and nitrate accumulation. Degradation increased urease and nitrate reductase activities but decreased protease and nitrite reductase activities, indicating enzyme-specific restructuring of soil N cycling. Most enzyme activities peaked in mid-growing season, whereas nitrate reductase peaked later. Soil N cycling shifted from a relatively coordinated state in non-degraded wetlands toward greater functional imbalance in degraded wetlands. This reorganization was strongly modulated by hydroclimatic variability, with drier conditions amplifying degradation, induced divergence in enzyme activities. Redundancy analysis and piecewise structural equation modeling showed that soil water content, organic carbon, inorganic N availability, and microbial biomass N were the primary regulators of enzyme variation and N-cycling functional imbalance. Overall, this study provides new insight into mechanisms of soil N-cycling destabilization in degraded alpine wetlands and informs wetland restoration under a drier future climate.

Climate warming and atmospheric nitrogen deposition are altering carbon (C), nitrogen (N), and phosphorus (P) cycling in alpine wetlands. However, how these drivers jointly reorganize microbial communities and their biogeochemical cycling potential remains poorly understood, particularly in cold, nutrient-limited alpine wetlands. We conducted a four-year field experiment combining open-top chamber warming and nitrogen addition. Soil physicochemical measurements were integrated with shotgun metagenomic sequencing to assess microbial community structure and the functional potential associated with C, N, and P cycling. The results showed that archaeal and bacterial community composition remained stable following warming and nitrogen addition, whereas fungal composition changed. Functional gene richness was positively correlated with archaeal and bacterial richness but was not correlated with fungal richness, indicating asynchronous responses between taxonomic–functional dimensions. Warming and nitrogen addition did not consistently increase the overall abundance of C, N, and P cycling functional genes. Instead, they induced pathway-specific responses: compensatory shifts among C fixation pathways, decreases in complex C degradation genes, increases in nitrification genes, and decreases in genes associated with P acquisition and homeostatic regulation. Soil moisture and enzyme activities were significantly correlated with C, N, and P cycling genes. These findings highlight domain-specific taxonomic responses and process-specific re-organization of microbial functional potential and emphasize the importance of hydro-thermal constraints when predicting alpine-wetland biogeochemical responses to future warming and increasing N inputs.