Leaf growth, senescence and decomposition of Juncus maritimus Lam. in a coastal Mediterranean marsh Margarita Mene ´ ndez * Departament d’Ecologia, Facultat de Biologia, Universitat de Barcelona, Av. Diagonal 645, E-08028 Barcelona, Spain 1. Introduction Primary production in brackish and salt marshes is dominated by emergent macrophytes (Mitsch and Gosselink, 2007). When these plants senesce, soluble organic compounds are rapidly leached from tissues. This labile soluble organic matter is a considerable energy source for microorganisms in the marsh and the adjacent estuary (Wilson et al., 1986). Juncus maritimus is widely distributed in Europe, West Africa and North Asia and commonly occurs along the littoral salt marshes on permanently wet soils. This species is an important component of halophyte meadows in Mediterranean salt and brackish marshes. In spite of its wide distribution and potential importance in the trophic structure of marsh and estuarine ecosystems, only one reference was found concerning J. maritimus decomposition (Alvarez et al., 2001), which was reported in two temporary lagoons in the Don ˜ ana National Park (southern Spain). In general, plant litter breakdown in marshes is examined by placing clipped air-dried leaves in litterbags on the sediment surface or in the water column and following their rate of decay (Valiela et al., 1985; Tanaka, 1991; Kuehn and Suberkropp, 1998). Newell (1993) emphasized that experiments designed to study the breakdown of marsh plants should simulate the conditions of natural decomposition. However, most previous research on litter decay in estuarine systems has been conducted with plant material collected before natural senescence and death. This approach fails to characterize the initial decay phase while leaves are still attached to the plant. Moreover, this material has often been manipulated (e.g., oven-dried, air-dried, ground) prior to sub- mergence. In combination, these manipulations impact on the previously active microbial inhabitants of litter, and this impact receive little to no attention in most litter decay studies. According to Mitsch and Gosselink (2007), epiphytic algae and bacteria growing on decomposing leaves and on the lower parts of grass culms in salt marshes also form part of the detrital mixture, which is then consumed by meiofauna (such as nematodes and ciliates), gastropods and amphipods. In marsh environments, metazoans, such as nematodes and ciliates, are abundant and have been assigned a key role in transferring organic matter from primary producers and decomposers to top predators (Lillebø et al., 1999; Riera and Hubas, 2003). Moreover, bacterial grazers, such as protozoans and nematodes, stimulate bacterial activity and decomposition (Freckman, 1988; Alkemade et al., 1992a, 1993; Griffiths, 1994; Mamilov et al., 2000). In spite of this evidence, to Aquatic Botany 89 (2008) 365–371 ARTICLE INFO Article history: Received 28 August 2007 Received in revised form 28 March 2008 Accepted 7 April 2008 Available online 12 April 2008 Keywords: Meiofauna Fungus Nutrient Plant litter Juncus maritimus ABSTRACT In this study, the growth, senescence, leaf loss and nutrient dynamics of Juncus maritimus were followed to examine litter decay in a Mediterranean coastal marsh. Decomposition was studied in dead leaves still attached to the plant and in leaves placed in litterbags (detached leaves/litter) on the sediment surface. The dynamics of fungi, meiofauna and epiphytes associated with detached litter were also followed. No significant differences were observed between decay rates in dead leaves attached to plants (0.0017 day À1 ) and detached leaves (0.0015 day À1 ) in litter bags. The percentage of ash-free dry weight lost was inversely proportional to the C:N and C:P ratios in plant detritus during decay, indicating N and P limitation for the decomposer community inhabiting decaying J. maritimus litter and uptake of these nutrients from the environment. Water availability and high temperatures on the sediment surface increased the density of meiofauna and epiphyton and decreased fungal biomass during the first 20 days of the experiment. The density of ciliates and nematodes in decomposing litter was inversely related to the C:N ratio and directly related to the percentage of AFDW lost. On the basis of these observations, it was concluded that meiofauna are primary colonizers of J. maritimus leaf litter. ß 2008 Elsevier B.V. All rights reserved. * Tel.: +34 934021510; fax: +34 934111438. E-mail address: mmenendez@ub.edu. Contents lists available at ScienceDirect Aquatic Botany journal homepage: www.elsevier.com/locate/aquabot 0304-3770/$ – see front matter ß 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.aquabot.2008.04.006