Horizon 1 1 17 ACL : Articles dans des revues avec comité de lecture répertoriées par l'AERES Science of the Total Environment 142202 [ p.] Canopy soil Epiphytes Leaves Litter Bryophytes N-15(2) Terrestrial LIDAR GUYANE FRANCAISE ZONE TROPICALE 2021 fdi:010080461 ENG Science of the Total Environment 0048-9697 ISI:000593987500031 10.1016/j.scitotenv.2020.142202 https://www.documentation.ird.fr/hor/fdi:010080461 https://www.documentation.ird.fr/intranet/publi/2021/01/010080461.pdf 754 Horizon (IRD) Biological nitrogen fixation (BNF) isa fundamental part of nitrogen cycling in tropical forests, yet little is known about the contribution made by free-living nitrogen fixers inhabiting the often-extensive forest canopy. We used the acetylene reduction assay, calibrated with N-15(2), to measure free-living BNF on forest canopy leaves, vascular epiphytes, bryophytes and canopy soil, as well as on the forest floor in leaf litter and soil. We used a combination of calculated and published component densities to upscale free-living BNF rates to the forest level. We found that bryophytes and leaves situated in the canopy in particular displayed high mass-based rates of freeliving BNF. Additionally, we calculated that nearly 2 kg of nitrogen enters the forest ecosystem through free-living BNF every year, 40% of which was fixed by the various canopy components. Our results reveal that in the studied tropical lowland forest a large part of the nitrogen input through free-living BNF stems from the canopy, but also that the total nitrogen inputs by free-living BNF are lower than previously thought and comparable to the inputs of reactive nitrogen by atmospheric deposition. 082 ; 084 ; 074 UR253 / UR123