Wenhua Chang

Alpine wetlands on the Qinghai-Tibet Plateau are increasingly degraded, with potentially important consequences for soil nitrogen (N) cycling and ecosystem functioning. However, how degradation restructures enzyme-mediated soil N cycling and its functional potential remains poorly understood. To address this gap, we conducted a three-year field investigation across 2019 to 2021 four degradation stages (i.e.non-degraded (ND), lightly degraded (LD), moderately degraded (MD), and heavily degraded (HD)) in the Gahai Wetland. We quantified four key soil N-cycling enzymes, including urease, protease, nitrate reductase, and nitrite reductase, and developed a nitrogen cycling functional potential (NCFP) index to characterize shifts in the relative balance between hydrolytic and reductive N-cycling functions potentials. Our results showing that 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. Enzyme responses were strongly pathway specific: urease and nitrate reductase activities increased with degradation, whereas protease and nitrite reductase activities declined. Consequently, NCFP index shifting from slightly positive values in ND and LD to negative values in MD and HD, indicating a reorganization of N-cycling functional potential from a relative hydrolytic bias toward a relative reductive bias. Interannual hydroclimatic variability further modified this pattern; notably, exceptionally wet conditions in 2021 shifted NCFP index toward negative values across all degradation stages. Redundancy analysis and piecewise structural equation modeling showed that soil water content, and organic carbon were the primary regulators of NCFP index. Alpine wetland degradation reorganized the relative configuration of hydrolytic and reductive N-cycling potentials rather than uniformly suppressing N cycling, and this functional balance was jointly regulated by long-term degradation and short-term hydrological variability. Overall, the 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.

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.

Nitrogen (N) cycling in alpine wetlands plays a crucial role in global nitrogen cycling and its balance. Although the mechanisms underlying the net nitrogen mineralization rate (Rmin) in degraded soils of alpine wetlands have been extensively studied, research on the effects of temperature and humidity on the Rmin process under different vegetation degradation gradients remains limited. Alpine wet meadows with different vegetation degradation conditions (i.e. undegraded (UD), lightly degraded (LD), moderately degraded (MD), and heavily degraded (HD) were selected to examine effects of temperature, soil moisture, and their interactions on soil net N mineralization. The results indicated that vegetation degradation significantly inhibited the Rmin process, with its rate remaining constant or gradually decreasing as degradation severity increased. Soil moisture significantly affects Rmin. Within the moisture range of 20%–60% FC, Rmin increases with increasing humidity, but decreases gradually beyond 60% FC. Additionally, reduced moisture significantly affects Rmin in soils with different degrees of vegetation degradation. Temperature also significantly affects Rmin. The Q10 values for the four levels of degraded soil are 1.73–2.37 (UD), 0.82–2.98 (LD), 0.93–2.30 (MD), and 1.12–2.10 (HD), respectively. The growth rate of Rmin at all moisture levels decreases with increasing temperature, and the soil nitrogen mineralization process is most sensitive in the 15°C–25°C temperature range. Temperature changes have a greater impact on nitrogen mineralization in MD sites than in UD, LD, and HD sites. Overall, temperature and moisture exhibit synergistic and antagonistic effects on soil nitrogen mineralization, with temperature effects being more pronounced. The optimal temperature for Rmin among the four degradation levels is 20.50–25.00°C, and the optimal moisture condition is 50.00–69.52% FC. These findings provide crucial scientific evidence for understanding soil nitrogen dynamics on the Tibetan Plateau and formulating targeted management measures.

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.