02167naa a2200265 a 450000100080000000500110000800800410001902400460006010000200010624501650012626000090029152012980030065000090159865000220160765000220162965000220165165000110167365000290168465000250171365000130173870000180175170000250176970000220179477300850181620935992018-07-26       2018    bl uuuu     u00u1 u    #d7 ahttps://doi.org/10.1002/2017JG0041032DOI1 aDAVIDSON, E. A.  aNitrogen fixation inputs in pasture and early successional forest in the Brazilian Amazon regionbevidence from a claybox mesocosm study.h[electronic resource]  c2018  aThe role of biological nitrogen fixation (BNF) during secondary forest succession and in tropical pastures has been investigated and debated for several decades. Here we present results of a replicated experimental study in a degraded cattle pasture of eastern Amazonia using mass balance and a 15N tracer in lined soil pit mesocosms with three treatments: (1) plant-free control plots, (2) pasture grass Brachiaria brizantha, and (3) regrowth of early successional secondary forest species. Accumulation of N in grass biomass slightly exceeded estimates of net N mineralization from the plant-free control plots but was within the margin of error, so inputs of BNF may not have been needed. In contrast, the secondary forest vegetation accumulated about 3 times as much biomass N annually as the net N mineralization estimate, suggesting at least some role for BNF. Based on isotopic and mass measurements of N-fixing species, BNF was estimated to contribute at least 27 ± 3% of mean annual plant uptake in the secondary forest regrowth vegetation plots. Although BNF is probably important for recuperation of tropical secondary forests following land use change, the majority of the N taken up by both grasses and secondary forest regrowth arose from mineralization of the stocks of soil N.  aClay  aForest succession  aNitrogen fixation  aTropical pastures  aArgila  aFixação de nitrogênio  aFloresta secundária  aPastagem1 aMARKEWITZ, D.1 aFIGUEIREDO, R. de O.1 aCAMARGO, P. B. de  tJournal of Geophysical Research: Biogeosciencesgv. 123, n. 2, p. 712-721, 2018.