Long‐term, amplified responses of soil organic carbon to nitrogen addition worldwide

Abstract

Soil organic carbon (SOC) is the largest carbon sink in terrestrial ecosystems and plays a critical role in mitigating climate change. Increasing reactive nitrogen (N) in ecosystems caused by anthropogenic N input substantially affects SOC dynamics. However, uncertainties remain concerning the effects of N addition on SOC in both organic and mineral soil layers over time at the global scale. Here, we analysed a large empirical data set spanning 60 years across 369 sites worldwide to explore the temporal dynamics of SOC to N addition. We found that N addition significantly increased SOC across the globe by 4.2% (2.7%–5.8%). SOC increases were amplified from short‐ to long‐term N addition durations in both organic and mineral soil layers. The positive effects of N addition on SOC were independent of ecosystem types, mean annual temperature and precipitation. Our findings suggest that SOC increases largely resulted from the enhanced plant C input to soils coupled with reduced C loss from decomposition and amplification was associated with reduced microbial biomass and respiration under long‐term N addition. Our study suggests that N addition will enhance SOC sequestration over time and contribute to future climate change mitigation.

Decrease in soil pH has greater effects than increase in above‐ground carbon inputs on soil organic carbon in terrestrial ecosystems of China under nitrogen enrichment

“…Furthermore, the current meta‐analysis (Figure 2b) and other meta‐analyses (e.g. Lu, Guo, et al., 2021; Lu, Hou, et al., 2021; Xu et al., 2021) found that N‐addition actually increases rather than reduces the SOC concentration despite increased inputs of labile C into soil. Clearly, the inputs of plant C may be not a primary determinant of below‐ground C budget, suggesting an alternative explanation for increased SOC concentration under N enrichment.…”

“…We used the Web of Science (WoS, before December 2020) to select peer‐reviewed publications reporting effects of N‐addition on C‐related variables, and changes in soil pH. The search terms were selected based on similar meta‐analysis (Lu, Guo, et al., 2021; Lu, Hou, et al., 2021; Xu et al., 2021), and the keywords selected for online searching were ‘(nitrogen deposition OR nitrogen addition OR nitrogen enrichment OR nitrogen application OR nitrogen fertilization) and (soil organic carbon OR dissolved organic carbon OR microbial biomass carbon OR aboveground biomass OR litter OR root OR respiration OR microbe OR extracellular enzyme OR pH)’.…”

“…To determine whether the response of soil C‐related processes to N enrichment was dependent on ecosystem types or fertilization regimes, all data were divided into three subgroups according to ecosystem type (natural forest, grassland, plantation or cropland), experimental N‐addition level (low [≤50 kg N ha –1 year –1 ], medium [51 − 100 kg N ha –1 year –1 ] or high [>100 kg N ha –1 year –1 ]) and experimental duration (≤5, 6–10 or ≥11 year). The thresholds were those used in other meta‐analyses (Song et al., 2019; Xu et al., 2021). In addition, we calculated the difference in soil pH (ΔpH) between the N‐addition treatment and the control, and then divided the difference into three levels based on the average soil pH decline value (0.5 unit) across China (Guo et al., 2010) (i.e.…”

“…Averill & Waring, 2018; Geng et al., 2021; Lu, Guo & Hou, 2021; Lu, Vitousek, et al., 2021) and syntheses (e.g. Deng et al., 2018; Xu et al., 2021) have demonstrated that N enrichment can promote an accumulation of soil organic C (SOC), the underlying mechanisms for this remain unclear, resulting in a wide debate about the interrelationships between plant and soil C dynamics under N enrichment (Liu & Greaver, 2010; Xu et al., 2021; Ye et al., 2018).…”

Sensing of Soil Organic Matter Using Laser-Induced Breakdown Spectroscopy Coupled with Optimized Self-Adaptive Calibration Strategy

“…Soil functions as the largest carbon pool, and soil organic matter (SOM) plays a vital role in ecosystem, agricultural and land management [1][2][3][4][5]. Therefore, developing fast, efficient and accurate SOM content measurement methods is important for both agricultural production and environmental management.…”