Respiration costs associated with nitrate reduction as estimated by ¹⁴CO₂ pulse labeling of corn at various growth stages
2010
Gavrichkova, Olga | Kuzyakov, Yakov
Utilization of nitrogen in the form of either nitrate (NO ₃ ⁻ ) or ammonium (NH ₄ ⁺ ) ions may affect the carbohydrate metabolism and energy budget of plants. Recent studies showed that greater expenses of NO ₃ ⁻ to NH ₄ ⁺ reduction mostly occur in the roots and during darkness. Fertilization of corn with ¹⁵N-labeled nitrate and ammonium, combined with pulse labeling of plants in a ¹⁴CO₂ atmosphere at the V6 and V8 growth stages, allowed us to evaluate the effect of N form on the CO₂ efflux from soil. NH ₄ ⁺ oxidation was inhibited by adding dicyandiamide. In respect to ammonium, nitrate addition increased root-derived CO₂ efflux from corn by 2.6 times at stage V6 and by 1.8 times at stage V8. The time of peak ¹⁴CO₂ efflux from soil also differed between two growing stages: at V6, efflux peaked only on the second day after pulse labeling, while at V8 this occurred within the first 6 h. The strong effect of NO ₃ ⁻ and NH ₄ ⁺ on root respiration requires considering the N form in the soil and the nitrate reduction site location in a plant when modeling soil respiration changes and when separately estimating individual CO₂ sources that contribute to the total soil CO₂ efflux.
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