Can peatland plants take up organic nitrogen?

Background/Question/Methods

Total Dissolved Nitrogen (TDN) in peat porewater is usually dominated by organic over inorganic ammonium and nitrate forms. Although uptake of organic N has been shown in other ecosystems, no studies have been published where organic N uptake was examined across multiple species in bogs. To test whether peatland plants can take up organic N, we applied dual-labelled (¹³C and ¹⁵N) glycine to the surface layer of the peat at two sites and sampled above and below ground plant tissues for C and N content and d¹³C and d¹⁵N, 48 – 72 hours later. One site was the Mer Bleue bog in eastern Ontario, Canada comprising a mixture of hummocks and lawns with shrubs, sedges and mosses. The other was the Torehape peatland in the North Island, New Zealand which was dominated by restiad plants and a sedge.

Results/Conclusions

Organic nitrogen dominated TDN in the peat porewaters, with an average of 93% at Mer Bleue and 50% at Torehape. In the Mer Bleue peat porewater, glycine was the most abundant amino acid. Nearly all plant species showed significant evidence of ¹⁵N uptake in foliar tissues, but without any significant uptake of ¹³C. Greater enrichment of ¹⁵N occurred in the root tissues at both sites, with some evidence of ¹³C enrichment. The absence of significant ¹³C uptake, along with ¹⁵N, in the foliar and root tissues suggests that a cleavage between C and N in the glycine occurs in the soil or in the plant roots and that the ¹⁵N may have been accessed in the inorganic forms. Alternatively, ¹³C has been lost from the plant through respiration, leaving the residual ¹⁵N.We conclude that these peatland plants can take up organic N, such as glycine, but that the C and N are decoupled in the process.