Bingbing Han

Soil pH management underpins sustainable agriculture globally, yet the intrinsic effects of pH change on soil organic carbon (SOC) accrual and crop yields remain obscured by concomitant shifts in other soil properties. Here, using two complementary global field datasets, we disentangle pH‐specific contributions to SOC accrual and yield gains under organic substitution regimes (partial replacement of synthetic fertilizers with organic amendments). Organic substitution consistently shifted soil pH toward neutrality. Quantitative partitioning revealed that pH amelioration independently accounted for 15.0%, 9.2%, and 4.1% of SOC accrual in acidic, neutral, and alkaline soils, respectively, effects primarily mediated by enhanced microbial biomass. The pH amelioration‐shared SOC accrual underpinned yield gains of 8.6%, 5.1%, and 8.1% across the three pH categories. These benefits were sustained over extended organic substitution durations, with the most pronounced effects in acidic soils. Spatially, pH‐driven yield gains peaked at 9.9% in Africa. Our findings underscore that integrating proactive pH management into organic substitution strategies advances both soil carbon sequestration and global food security.

Mitigating reactive nitrogen losses is essential for sustainable agriculture. However, predicting the benefits of substituting synthetic fertilizers with organic amendments remain unreliable because conventional approaches treat soil nitrogen processes in isolation. Here, we adapt a synchrony metric from community ecology to quantify the coordination among nitrogen processes. Using 2,235 global paired observations (organic vs. synthetic), we find that the synchrony metric predicts nitrous oxide (N₂O) and ammonia (NH₃) emissions more accurately than individual processes alone. Specifically, synchrony deviations in nitrification and denitrification account for half of global N₂O variability, while synchrony deviations in mineralization and immobilization explain over one-third of NH₃ variability. Projections indicate that leveraging organic substitution could achieve the greatest N₂O reductions in European croplands (−40.7%) and the highest NH₃ mitigation in Africa croplands (−46.1%). These findings establish process synchrony as a mechanistic framework for improving nitrogen gas loss models and inform targeted organic amendment strategies.

The stability of soil organic carbon (SOC) is fundamental to the integrity of agricultural carbon credits but remains challenging to verify and predict. A persistent methodological challenge lies in isolating the specific effect of soil pH amelioration from confounding factors like organic matter inputs. Here, by applying bivariate linear mixed‐effects modelling to a global synthesis of 180 field trials, we quantitatively disentangled the effects of pH amelioration on SOC components across a stability continuum from bulk soils to aggregate fractions. The results showed that pH amelioration enhanced bulk SOC stocks by 18%–20%, with mineral‐associated organic carbon and microbial necromass carbon significantly increasing by 11%–15% and 12%–19%, respectively. Simultaneously, pH amelioration restructured soil architecture toward enhanced aggregate stability, preferentially enriching carbon within microaggregates (by up to 44% in alkaline soils). Structural equation modelling confirmed that this process is hierarchically driven by pH‐induced shifts in microbial biomass and aggregate stability. The pH amelioration‐shared increment in particulate organic carbon and mineral‐associated organic carbon tended to attenuate with prolonged experimental duration, while that in microbial necromass carbon remained invariant. Across organic substitution types, pH amelioration under manure substitution significantly increased all carbon components, while straw substitution exhibited a weaker pH amelioration‐shared effect on particulate organic carbon increment compared to biochar and manure. Our findings suggest that pH amelioration is a fundamental process that engineers persistent carbon sinks by directing carbon flow into mineral‐stabilized and physically protected pools. This work repositions precision pH management as an essential ecological engineering strategy and provides a mechanistic foundation for transitioning carbon credit protocols from stock‐based accounting to stability‐centric verification.

Anthropogenic nitrogen enrichment is widely expected to suppress symbiotic nitrogen fixation in terrestrial ecosystems. Nevertheless, observed symbiotic nitrogen fixation responses remain incompletely explained by exogenous nitrogen inputs, climate, and edaphic factors. In this meta-analysis, we integrate 908 globally distributed field measurements to identify the key predictors that improve simulation of symbiotic nitrogen fixation responses to nitrogen enrichment. On average, symbiotic nitrogen fixation declines by 33.0% upon nitrogen enrichment, with the reduction being more pronounced in non-croplands than croplands. Models considering only environmental factors overestimate symbiotic nitrogen fixation decline relative to observations. The better performance of plant traits like plant growth and biomass allocation (shoot:root ratio) partially buffer symbiotic nitrogen fixation suppression under nitrogen enrichment. Integrating both environmental factors and plant performance traits improves predictive accuracy of symbiotic nitrogen fixation responses by 42.7% and brings the simulated symbiotic nitrogen fixation reductions into close agreement with observations. The alterations in plant performance traits are thus critical for explaining variability in terrestrial symbiotic nitrogen fixation responses, and incorporating plant trait dynamics in Earth System Models can quantitatively partition the compensatory symbiotic nitrogen fixation supported by nitrogen-fixing plant growth from the direct negative impact of nitrogen inputs.

Symbiotic nitrogen (N) fixation (SNF), replenishing bioavailable N for terrestrial ecosystems, exerts decisive roles in N cycling and gross primary production. Nevertheless, it remains unclear what determines the variability of SNF rate, which retards the accurate prediction for global N fixation in earth system models. This study synthesized 1230 isotopic observations to elucidate the governing factors underlying the variability of SNF rate. The SNF rates varied significantly from 3.69 to 12.54 g N m⁻² year⁻¹ across host plant taxa. The traits of host plant (e.g. biomass characteristics and taxa) far outweighed soil properties and climatic factors in explaining the variations of SNF rate, accounting for 79.0% of total relative importance. Furthermore, annual SNF yield contributed to more than half of N uptake for host plants, which was consistent across different ecosystem types. This study highlights that the biotic factors, especially host plant traits (e.g. biomass characteristics and taxa), play overriding roles in determining SNF rate compared with soil properties. The suite of parameters for SNF lends support to improve N fixation module in earth system models that can provide more confidence in predicting bioavailable N changes in terrestrial ecosystems.

Nitrous oxide (N₂O) is a potent greenhouse gas, and its mitigation is a pressing task in the coming decade. However, it remains unclear which specific process between concurrent nitrification and denitrification dominates worldwide N₂O emission. We snagged an opportunity to ascertain whence the N₂O came and which were the controlling factors on the basis of 1315 soil N₂O observations from 74 peer‐reviewed articles. The average N₂O emission derived from nitrification (N₂O_n) was higher than that from denitrification (N₂O_d) worldwide. The ratios of nitrification‐derived N₂O to denitrification‐derived N₂O, hereof N₂O_n:N₂O_d, exhibited large variations across terrestrial ecosystems. Although soil carbon and nitrogen content, pH, moisture, and clay content accounted for a part of the geographical variations in the N₂O_n:N₂O_d ratio, ammonia‐oxidizing microorganisms (AOM):denitrifier ratio was the pivotal driver for the N₂O_n:N₂O_d ratios, since the AOM:denitrfier ratio accounted for 53.7% of geographical variations in N₂O_n:N₂O_d ratios. Compared with natural ecosystems, soil pH exerted a more remarkable role to dictate the N₂O_n:N₂O_d ratio in croplands. This study emphasizes the vital role of functional soil microorganisms in geographical variations of N₂O_n:N₂O_d ratio and lays the foundation for the incorporation of soil AOM:denitrfier ratio into models to better predict N₂O_n:N₂O_d ratio. Identifying soil N₂O derivation will provide a global potential benchmark for N₂O mitigation by manipulating the nitrification or denitrification.

Aim: The accumulation of microbial necromass carbon has gained increasing attention due to its slow decomposition. However, it remains unclear what induces the accumulation of microbial necromass carbon via reiterated community turnover on large spatial scales. This study explores the characteristics of soil necromass carbon accumulation in terrestrial ecosystems.Location: Global.Time Period: Contemporary (1999–2022).Major Taxa Studied: Soil microorganisms.Methods: A dataset was compiled using 993 observations from 82 peer‐reviewed papers on the effects of coefficients of microbial necromass accumulation (hereafter NAC) in equilibrium. Linear mixed‐effect models and structural equation models were used to ascertain the controlling factors of the NAC.Results: The average NAC was higher in croplands (28.2) and forests (26.8) than in grasslands (21.1). Edaphic factors seemingly affected the NAC, which was lower in soils with high pH and clay content on a global scale. Biotic factors, particularly those related to living microorganism abundance and microbial biomass nitrogen content, were the pivotal drivers of NAC and accounted for approximately 43.6% of its geographic variability. More organic carbon was likely to be preserved in soil with a higher NAC, regardless of ecosystem type.Conclusions: Novel findings regarding the overriding controls for the living microorganism abundance and microbial biomass nitrogen that drive the NAC highlight an urgent need for viable strategies to manipulate microbial attributes for enhancing carbon sequestration.