Linking nitrogen and phosphorus dynamics in litter production and decomposition during secondary forest succession in the eastern Amazon

Land-use change, including tropical deforestation for agriculture and subsequent agricultural abandonment, may change the stoichiometry of nutrient cycling in tropical secondary forests relative to mature forests. While phosphorus (P) is conservatively cycled in these mature forests, nitrogen (N) losses during an agricultural phase may provoke conservative N cycling processes in young secondary forests. Here we explore differences in nutrient cycling properties among secondary and mature forests of the eastern Amazon, including litter nutrient concentrations and rates of litter production and decomposition. In a chronosequence of successional forest age, N production in litterfall and N loss during litter decomposition were low in young forests but increased with increasing forest age, whereas P was conservatively cycled in all forest ages. Litter N concentration was positively correlated with the rate of mass loss in a litterbag study and with a mass balance estimate of litter decomposition based on annual litterfall and litter stock measurements. Therefore, while P is conservatively cycled and may limit or co-limit productivity in these forests, variation in N content of litter among forest successional stages may be related to differences in decomposition rates and mean residence times of litter, thus linking N availability with rates of litter decomposition and P cycling.