9224: Wheat assimilation of carbon and nitrogen investigated by amendments of dual-labelled (13C and 15N) green manure

Larsen, Thomas; Magid, Jakob and Gorissen, Antonie (2006) Wheat assimilation of carbon and nitrogen investigated by amendments of dual-labelled (13C and 15N) green manure. [preprint]

Summary

Experimental data is still lacking for determining whether plant uptake of organic nitrogen in agricultural soils contributes substantially to the total nitrogen (N) uptake. Pulse-injection studies with duallabelled amino acids have confirmed that non-mycorrhizal crops possess the capacity to take up organic N but failed to quantify the uptake relative to total N uptake. In this study wheat uptake of organic N was investigated in combination with monitoring N-dynamics by adding dual-labelled green manure to soil with wheat plants. An advantage of using dual-labelled green manure as opposed to pulse injection of uallabelled amino acids is that the amino acids in the fertilizer are released gradually and naturally in the same time that N dynamics and assimilation can be monitored. The wheat plants were harvested after 27, 56, and 84 days after sowing and analyzed for 13C and 15N. A small, but significantly higher 13C signature was measured in roots from the labelled treatments at 27 days, which indicates uptake of organic N. From this value, the uptake of organic N was estimated to be minor and constitute between 1.5 % and 4.4 % of total root N. Wheat N derived from the green manure was for all three harvest dates 83.3% (±0.9) and 88.6% (±0.7) for roots and shoots, respectively. This significant difference that is very large compared to natural abundance studies might be explained by a differential assimilation of N forms in the different plant compartments. From the soil-plant system there was 11-13 % loss of green manure N and 51 % loss of green manure C within the initial 27 days after which there was little or no losses. These initial losses suggest a pre-emptive decoupling of dual-labelled molecules. In conclusion, the study supports the hypothesis that organic N uptake does not contribute substantially to N acquisition in agricultural crops.

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