Using isotope tracing to track ammonium and nitrate uptake, scientists found that wheat dominates nitrogen capture in calcareous (alkaline) soils, while microbes compete more effectively in acid soils. These findings uncover how soil chemistry shapes short-term nitrogen dynamics in agricultural systems and offer new insight into improving nitrogen use efficiency in crop production.
Nitrogen is one of the most limiting nutrients for plant growth worldwide. Plants absorb nitrogen primarily as ammonium (NH₄⁺) and nitrate (NO₃⁻), but soil microorganisms depend on the same forms for growth and metabolism. This overlap creates direct competition in the rhizosphere—the narrow zone surrounding plant roots where biological activity is intense. Soil pH is a major regulator of nitrogen availability. In acidic soils, nitrification is inhibited, often leading to ammonium accumulation. In alkaline or calcareous soils, higher nitrification rates increase nitrate availability. Because different crops prefer different nitrogen forms—wheat generally favors nitrate—pH-driven changes in nitrogen chemistry may alter plant–microbe competition. Despite its importance, this regulatory role of soil pH has remained insufficiently understood.
A study (DOI: 10.48130/nc-0025-0016) published in Nitrogen Cycling on 15 January 2026 by Ting Lan’s team, Sichuan Agricultural University, demonstrates that soil pH fundamentally regulates short-term nitrogen competition between wheat and soil microorganisms by reshaping nitrogen transformation processes and altering the balance of inorganic nitrogen acquisition in agricultural soils.
To investigate how soil pH regulates nitrogen dynamics and plant–microbe competition, the study combined measurements of gross nitrogen transformation rates with 15N isotope tracing in wheat grown in contrasting acid and calcareous soils. Gross mineralization, nitrification, and immobilization rates were first quantified to characterize background N cycling, followed by 15NH₄⁺ and 15NO₃⁻ labeling to trace uptake and assimilation by wheat and soil microorganisms at multiple time points (4, 24, and 48 h). The results showed that gross mineralization and nitrification rates were significantly higher in the calcareous soil–wheat system—by nine-fold and two-fold, respectively—compared with the acid soil system, while exchangeable NH₄⁺ concentrations were lower in calcareous soil and NO₃⁻ concentrations were similar between soils. In contrast, inorganic N immobilization rates were higher in acid soil (10.41 vs 6.92 mg kg⁻¹ d⁻¹), although these values may be slightly overestimated due to methodological assumptions. Isotope tracing further revealed that wheat 15N uptake patterns differed between soils: in calcareous soil, 15NH₄⁺ uptake increased over time and exceeded 15NO₃⁻ uptake at 48 h, whereas in acid soil, uptake of both forms was initially similar but shifted toward greater 15NO₃⁻ uptake at 48 h. Microbial 15N assimilation declined over time in both systems and showed no sustained preference for either N form. Early after labeling (4 h), microbes assimilated more 15N than wheat, indicating strong initial competition; however, by 48 h, wheat 15N recovery surpassed microbial recovery in both soils. Overall, while soil pH significantly altered microbial 15N assimilation and gross N transformation rates, total wheat 15N uptake rates remained relatively similar between soils, highlighting that pH-driven shifts primarily influenced microbial dynamics rather than plant uptake capacity.
In conclusion, this study highlights soil pH as a key regulator of short-term nitrogen competition between wheat and soil microorganisms, with important implications for nutrient management in agricultural systems. Wheat showed a competitive advantage in calcareous soils with higher nitrification rates, whereas microbial immobilization was stronger in acid soils. These findings suggest that nitrogen fertilizer strategies should be adapted to soil pH conditions. Integrating pH management, optimized fertilization timing, and soil carbon regulation may enhance nitrogen use efficiency, sustain crop productivity, and reduce environmental risks associated with nitrogen losses.
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References
DOI
10.48130/nc-0025-0016
Original Souce URL
https://doi.org/10.48130/nc-0025-0016
Funding information
This work was supported by the National Natural Science Foundation of China (Grant No. U22A20562).
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