title: Slowing of nitrogen cycling and increasing nitrogen use efficiency following afforestation of semi-arid shrubland.
abstract: Nitrogen (N) and water availability are important factors affecting ecosystem productivity that can be influenced by land-use change. We hypothesized that the observed increase in carbon (C) sequestration associated with afforestation of semi-arid sparse shrubland must also be associated with an increase in N input. We tested this hypothesis by reconstructing the ecosystem N budget of two ecosystems, a semi-arid shrubland and a nearby planted pine forest, using measurements augmented with literature-based estimates. Our findings demonstrate that, contrary to our hypothesis, massive C sequestration by the pine forest could be accounted for without a change in the net N budget (i.e., neither elevated N inputs nor reduced N losses). However, in comparison to the shrubland, the forest showed an almost tripling in aboveground N use efficiency (NUE; 235 vs. 83 kg dry mass kg(-1) N) and a doubling in ecosystem level C/N ratio (16 vs. 8, for the forest and shrubland, respectively). Nitrogen cycling slowed in the forest compared to the shrubland: net N mineralization rates in soils decreased by approximately 50%, decomposition rates decreased by approximately 20%, and NO(x) loss decreased by approximately 64%. These adjustments in N cycling provide a possible basis for increased NUE and subsequent C sequestration without net change in the overall N budget, which should be addressed in future investigations.
authors: Department of Environmental Sciences and Energy Research, Weizmann Institute of Sciences, 76100, Rehovot, Israel. imgelfand@gmail.com
authors: I
authors: I
authors: Gelfand
authors: J M
authors: JM
authors: Grünzweig
authors: D
authors: D
authors: Yakir
mesh_terms: D018533:Biomass; D002244:Carbon / Q000378:metabolism; D017753:Ecosystem; D009584:Nitrogen / Q000378:metabolism*; D058458:Nitrogen Cycle; D028223:Pinus / Q000254:growth & development / Q000378:metabolism; D027824:Rosaceae / Q000254:growth & development / Q000378:metabolism; D014197:Trees / Q000254:growth & development / Q000378:metabolism
chemical_list: D002244:Carbon; D009584:Nitrogen