TY - JOUR
T1 - Urine is an important nitrogen source for plants irrespective of vegetation composition in an Arctic tundra
T2 - insights from a 15N-enriched urea tracer experiment
AU - Barthelemy, Hélène
AU - Stark, Sari
AU - Michelsen, Anders
AU - Olofsson, Johan
N1 - CENPERM[2018]
PY - 2018/1
Y1 - 2018/1
N2 - 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. This study explored the fate of 15N-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 15N applied to the plant canopy, at 2 weeks and 1 year after tracer addition, in the different ecosystem N pools. 15N-urea was rapidly incorporated in cryptogams and in above-ground parts of vascular plants, while the soil microbial pool and plant roots sequestered only a marginal proportion. Furthermore, the litter layer constituted a large sink for the 15N-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. Mosses and lichens still constituted the largest sink for the 15N-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 15N-urea. The total recovery of 15N-urea was lower in the intensively grazed sites, suggesting that reindeer reduce ecosystem N retention. Synthesis. The rapid incorporation of the applied 15N-urea indicates that arctic plants can take advantage of a pulse of incoming N from urine. In addition, δ15N values of all taxa in the heavily grazed sites converged towards the δ15N values for urine, bringing further evidence that urine is an important N source for plants in grazed tundra ecosystems.
AB - 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. This study explored the fate of 15N-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 15N applied to the plant canopy, at 2 weeks and 1 year after tracer addition, in the different ecosystem N pools. 15N-urea was rapidly incorporated in cryptogams and in above-ground parts of vascular plants, while the soil microbial pool and plant roots sequestered only a marginal proportion. Furthermore, the litter layer constituted a large sink for the 15N-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. Mosses and lichens still constituted the largest sink for the 15N-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 15N-urea. The total recovery of 15N-urea was lower in the intensively grazed sites, suggesting that reindeer reduce ecosystem N retention. Synthesis. The rapid incorporation of the applied 15N-urea indicates that arctic plants can take advantage of a pulse of incoming N from urine. In addition, δ15N values of all taxa in the heavily grazed sites converged towards the δ15N values for urine, bringing further evidence that urine is an important N source for plants in grazed tundra ecosystems.
U2 - 10.1111/1365-2745.12820
DO - 10.1111/1365-2745.12820
M3 - Journal article
SN - 0022-0477
VL - 106
SP - 367
EP - 378
JO - Journal of Ecology
JF - Journal of Ecology
IS - 1
ER -