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Data from: Urine is an important nitrogen source for plants irrespective of vegetation composition in an Arctic tundra: insights from a 15N-enriched urea tracer experiment
Cite as:
2017-06-19T17:34:35.000+0200 Barthelemy, Hélène; Stark, Sari; Michelsen, Anders; Olofsson, Johan; 10.5061/dryad.52qh9
1. Mammalian herbivores can strongly influence nitrogen (N) cycling and herbivore urine could be a central component of the N cycle in grazed ecosystems. Despite its potential role for ecosystem productivity and functioning, the fate of N derived from urine has rarely been investigated in grazed ecosystems. 2. This study explored the fate of <sup>15</sup>N-enriched urea in tundra sites that have been either lightly or intensively grazed by reindeer for more than 50 years. We followed the fate of the <sup>15</sup>N applied to the plant canopy, at 2 weeks and 1 year after tracer addition, in the different ecosystem N pools. 3. <sup>15</sup>N-urea was rapidly incorporated in cryptogams and in aboveground parts of vascular plants, while the soil microbial pool and plant roots sequestered only a marginal proportion. Further, the litter layer constituted a large sink for the <sup>15</sup>N-urea, at least in the short term, indicating a high biological activity in the litter layer and high immobilization in the first phases of organic matter decomposition. 4. Mosses and lichens still constituted the largest sink for the <sup>15</sup>N-urea 1 year after tracer addition at both levels of grazing intensity demonstrating their large ability to capture and retain N from urine. Despite large fundamental differences in their traits, deciduous and evergreen shrubs were just as efficient as graminoids in taking up the <sup>15</sup>N-urea. The total recovery of <sup>15</sup>N-urea was lower in the intensively grazed sites, suggesting that reindeer reduce ecosystem N retention. 5. <i>Synthesis</i> The rapid incorporation of the applied <sup>15</sup>N-urea indicates that arctic plants can take advantage of a pulse of incoming N from urine. In addition, δ <sup>15</sup>N values of all taxa in the heavily grazed sites converged towards the δ <sup>15</sup>N values for urine, bringing further evidence that urine is an important N source for plants in grazed tundra ecosystems.