Effects of mixing radiata pine needles and understory litters on decomposition and nutrients release

A microcosm experiment was conducted to understand the impacts of mixing radiata pine ( Pinus radiata D. Don) needle litter and understory ( gorse - Ulex europaeus L., broom - Cytisus scoparius L., bracken Pteridium aquilinum L., and lotus - Lotus pedunculatus L.) litter materials on decomposition and nutrient release dynamics. Mixing of pine needle litter with understory litter material had significant impacts on both the rate of decomposition and nutrient release patterns of pine litter as well as that of the understory species. Incubation in microcosms over 10 months resulted in significantly lower mass loss of radiata pine needle litter mixed with broom and lotus litters (35.8 +/- 8.4 and 41.3 +/- 0.8%, respectively) than pure pine needle litter (63.5 +/- 2.3%). Mixing with pine needle litter significantly increased the mass loss of broom (53.1 +/- 6.1%) compared to that of pure broom (30.2 +/- 1.0%). Significant transfers of nutrients, especially of magnesium and potassium, were observed in litter mixture treatments. Concentration of K in litter materials was found to be the most limiting factor for the decomposing microorganisms in the present study. The findings of this study suggest that management of understory litter composition via weed control could be used to manipulate carbon turnover and nutrient release in the forest floor. Also, initial selection of understory species will be important and could be managed.