Nutrient dynamics in litter mixtures of four Mediterranean maquis species decomposing in situ Giulia Maisto, Anna De Marco, Angela Meola, Ludovica Sessa, Amalia Virzo De Santo * Department of Structural and Functional Biology, University Federico II Napoli, Via Cinthia, Napoli I-80126, Italy article info Article history: Received 5 August 2010 Received in revised form 11 November 2010 Accepted 17 November 2010 Available online 1 December 2010 Keywords: Litter decomposition Manganese Lignin Interactions among litters Non-additive effects of litter mixing abstract In natural conditions, litters shed from different species become mixed with each other, and decompose together. Most studies deal with decomposition of individual species; few studies investigate the influence of litter mixing on decomposition and nutrient dynamics; the results are contradictory as positive, negative, or no effect, of litter mixing have been observed. In this study we test the hypothesis: i) that litter mixing in the Mediterranean maquis, a nutrient poor, high diversity ecosystem, produces non-additive effects on nutrient dynamics; ii) that the effects vary with the composition in species of the mixture and with the relative amount of the species component the mixture. Two types of 3-species mixtures were set up; one contained three sclerophylls, Phillyrea angustifolia, Pistacia lentiscus and Quercus ilex; the other contained the first two species with the mesophyll Cistus. Litterbags, containing monospecific litters and even and uneven mixtures, were incubated under natural condition in situ; even mixtures had the 3 species in equal proportion, whereas uneven mixtures had one of the species as dominant (50%) and the other two species in equal proportion (25%:25%). Litterbags were retrieved after 92, 188 and 403 days; litters from the mixtures were separately analyzed for mass loss and content of nitrogen (N), potassium (K), sodium (Na), calcium (Ca), magnesium (Mg), manganese (Mn), iron (Fe), copper (Cu), and zinc (Zn). Results indicate that mixing influences the dynamics of N, Mn, Ca, Mg, Fe, Cu and Zn, but scarcely affects the dynamics of K and Na. The comparison of observed to expected values for changes of nutrients in litterbags indicates the occurrence of non-additive effects of litter mixing on movements of N, Fe, Cu, and Zn to or from the litterbags containing the mixtures. The effects depend on the composition in species of the mixture, whereas the relative amount of the species component the mixture is not relevant. Ó 2010 Elsevier Ltd. All rights reserved. 1. Introduction Litter decomposition is a fundamental process in ecosystem functioning as it regulates the cycle of matter, CO 2 release into the atmosphere, carbon sequestration in the soil and nutrients miner- alization. The rate of decomposition is largely determined by litter chemistry, particularly lignin concentration and nutrient level. In the early stages of decomposition, nutrient-rich litters decompose faster than nutrient-poor litters. As litter decomposes, concentra- tions of lignin and nitrogen increase (Berg and McClaugherty, 2008) and litters with low initial nitrogen concentration may accumulate more nitrogen than those with a high level (Berg and Staaf, 1981; Hobbie and Vitousek, 2000); moreover nitrogen accumulation in litter may be enhanced by high N availability in the surrounding environment, as in the case of high soil N levels (Berg and Ekbohm, 1983; Virzo De Santo et al., 1998). Limitation posed by litter chemical composition may be mitigated by nutrient availability in the soil; thus mountain birch leaf litter incubated at nutrient-poor tundra sites decomposed less than at nutrient-richer forest sites (Sjögersten and Wookey, 2004). The onset of net loss of lignin mass identifies the start of late stages in which lignin and modified lignin-like humification products dominate litter decomposition (Fogel and Cromack, 1977; Berg et al., 1993) up to a limit value; the limit value of decomposition, i.e. the litter remains, that have an extremely low decomposition rate, are related to litter concentra- tion of N, Mn, and Ca (Berg, 2000; Berg et al., 2003) which are nutrients regulating the lignin-degrading microflora (Eriksson et al., 1990). The role of Mn deserves a particular attention. The most efficient degraders of lignin are white-rot fungi producing manganese peroxidase (MnP) that is able to degrade lignin in vitro (Hofrichter et al., 2001). Mn availability has been found to limit lignin degradation in needle litter of Norway spruce (Berg, 2000), in leaf litter of common oak (Davey et al., 2007) and in several pine needle litters (Berg et al., 2007, 2010; Virzo De Santo et al., 2009). * Corresponding author. Tel.: þ39 081 679113; fax: þ39 081 679233. E-mail address: virzo@unina.it (A. Virzo De Santo). Contents lists available at ScienceDirect Soil Biology & Biochemistry journal homepage: www.elsevier.com/locate/soilbio 0038-0717/$ e see front matter Ó 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.soilbio.2010.11.017 Soil Biology & Biochemistry 43 (2011) 520e530