No evidence of positive feedback between litter deposition and seedling growth rate in Neotropical savannas

Plant-soil feedbacks are important drivers of ecosystem dynamics and have been hypothesized to affect woody encroachment in savannas. Woody encroachment is expected to increases savanna soil fertility through deposition of organic matter, favoring further establishment of woody individuals. In this context, we tested if litter input promotes forest seedling growth in dystrophic savanna soils, and if this was accompanied by an increase in microbial activity. In a glasshouse experiment, we planted woody seedlings of three forest species in savanna soils either mixed or not (control) with litter from closely related savanna or forest species (10 species). We evaluated the growth of the woody seedlings as well as the response of the soil microbiota activity and biomass to litter addition. Litter addition had either no effect or negative effects on seedling growth, and different seedling species responded differently to litter addition. However, we did find microbial activity to increase in response to litter addition, especially through the input of litter rich in phosphorus (P) and carbon (C). Our results indicate that litter input does not favor woody seedlings growth in savanna soil. Instead, litter input showed a potential to hinder seedling growth, especially of fast-growing species. Furthermore, litter input consistently increased soil microbiota activity, mainly through the input of P and C, highlighting the importance of energy and P in the nutrient dynamics of Cerrado. Thus, our results did not support the hypothesis that litter deposition triggers a positive feedback with woody encroachment via increased seedling growth.