Leaf litter decomposition and nutrient release under nitrogen, phosphorus and nitrogen plus phosphorus additions in a savanna in central Brazil

Abstract

The aim of this study was to determine leaf decomposition rates and nutrient release in a cerrado sensu stricto under nitrogen (N), phosphorus (P) and N plus P additions. The experiment was carried out in an area located in the Ecological Reserve of the Instituto Brasileiro de Geografia e Estatística, near Brasília (15° 56’ S, 47° 53’ W). Between 1998 and 2006, 100 kg ha-1year-1of N (N treatment), P (P treatment) and N plus P (NP treatment) were applied to 16 225 m2 plots, arranged in a completely randomized design. Litterfall was collected at the end of dry season (September 2006) and oven dried (60 °C) for 72 h. Litter bags with 10 g of leaf litter were incubated in situ for 453 days to determine decomposition rate. Nitrogen and P concentrations and mass loss were measured during the incubation process. Decomposition rates of leaf litter in N plots did not differ in relation to those in control plots. Leaf litter decomposition rates increased in P (+ 18.6 %) and NP (+ 27.4 %) plots, where there was a greater N (in NP plots) and P (in P and NP plots) initial concentration in litter relative to the control plots (p < 0.05). Leaf litter in the N treatment had the highest N mass loss, and together with NP treatment, the smallest P mass loss. Nitrogen addition increased N mass loss, while the combined addition of N and P resulted in an immobilization of N in leaf litter. When the nutrients are supplied separately, there is greater mass loss of N with N addition, and greater mass loss of P with P addition compared to that observed when N and P are supplied together. The results indicate that if the availability of P is not increased proportionally to the availability of N, the losses of N are intensified during the decomposition process.