Phosphorus addition drives carbon sink, but multiple nutrients drive carbon loss

Abstract

Forest productivity and respiration are key components of the carbon cycle that can be affected by nutrients. This work aimed to directly identify through nutrient manipulation experiment, which specific elements limit these processes. The experiment was installed in May 2017 in a tropical forest in the Central Amazon, the collections covered a period from 2017 to 2019. Total net primary production increased by 15,6 % with phosphorus addition alone, driven by the increase in litter productivity (19%) and fine root productivity (29,4%). The addition of nutrients did not affect wood productivity during the studied period. In contrast to NPP, the components of respiration responded to various combinations of nutrients, an interaction between phosphorus and cations was observed in leaf respiration and an interaction between nitrogen and cation affected autotrophic and heterotrophic soil respiration. Ecosystem respiration was not affected by phosphorus addition, since stem respiration decreased by 12% with phosphorus addition, and on the other hand, the addition of the same element increased heterotrophic respiration by 13%, so that the flows compensated. In summary, it appears that rapid productivity responses did not come with a high autotrophic respiration cost. The results of the present thesis will demonstrate that Earth System Models must incorporate P cycles and potential P limitation to capture the global carbon cycle.