Can peatland plants take up organic nitrogen?
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.
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.