Lugli, Laynara F.Rosa, Jessica S.Andersen, Kelly M.di Ponzio, RaffaelloAlmeida, Renata VPires, MariaCordeiro, Amanda L.Cunha, Hellen F.V.Martins, Nathielly P.Assis, Rafael LMeir, Patrick2023-04-060028-646Xhttp://hdl.handle.net/1885/288169Soil nutrient availability can strongly affect root traits. In tropical forests, phosphorus (P) is often considered the main limiting nutrient for plants. However, support for the P paradigm is limited, and N and cations might also control tropical forests functioning. We used a large-scale experiment to determine how the factorial addition of nitrogen (N), P and cations affected root productivity and traits related to nutrient acquisition strategies (morphological traits, phosphatase activity, arbuscular mycorrhizal colonisation and nutrient contents) in a primary rainforest growing on low-fertility soils in Central Amazonia after 1 yr of fertilisation. Multiple root traits and productivity were affected. Phosphorus additions increased annual root productivity and root diameter, but decreased root phosphatase activity. Cation additions increased root productivity at certain times of year, also increasing root diameter and mycorrhizal colonisation. P and cation additions increased their element concentrations in root tissues. No responses were detected with N addition. Here we showed that rock-derived nutrients determined root functioning in low-fertility Amazonian soils, demonstrating not only the hypothesised importance of P, but also highlighting the role of cations. The changes in fine root traits and productivity indicated that even slow-growing tropical rainforests can respond rapidly to changes in resource availability.This research was supported by the Brazilian National Council for Scientific and Technological Development(CNPq) through the Science Without Borders Program grant number 206826/2014-1 and UK’s Natural Environment Research Council (NERC), grant number NE/L007223/1; CAQ acknowledges the support from CNPq/LBA 68/2013 research grant 458020/2013-3. PM also acknowledges support fromARC, DP170104091 and LF acknowledges the support of the European Research Council grant ERC-SyG-2013-610028. This paper is number 801 on the BDFFP seriesapplication/pdfen-AU© 2021 The Authors New Phytologist © 2021 New Phytologist FoundationAmazon rainforestarbuscularmycorrhizafine root productivitylarge-scalenutrient fertilisation experimentmultiplenutrient limitationphosphatase enzymeroot morphology202110.1111/nph.171542022-01-23