Litter-fall and litter decomposition in a low Mediterranean shrubland

Annual production of litter by Cistus incanus (L.) and Myrtus communis (L.) and decomposition dynamics of leaf litter of these species was studied in a Mediterranean shrubland. Myrtus and Cistus produced 472 and 429 g dry weight litter m-2 year-1, respectively. Leaves were the predominant litter component for both species. The average decay constant of Myrtus and Cistus litters enclosed in litter bags, calculated over the whole study period (38 months), was 0.71 year-1 and 0.31 year-1 respectively. In green leaves the N content differed during growth seasons for both species, whereas the content of Ca, Mg, P, K, and Na did not show significant changes. Abscised leaves had lower N, P and K contents than green leaves, evidencing that a nutrient translocation before abscission occurred from senescent leaves. The nutrient contents of the leaves at abscission time, generally higher in Cistus than in Myrtus, allowed us to estimate the annual nutrient input to the soil. Phosphorus and K more than N were rapidly released by the decomposing litters after exposure. Nutrient limitation, in particular P, might be considered the main growth limiting factor for Myrtus and Cistus. Both species were adapted to recovery and rapidly recycle P more than N and K in the living biomass through retranslocation from green leaves before abscission and/or a high release rate from the decomposing litter. The former strategy was better used by Cistus, the latter by Myrtus.