Seasonal and multi-annual patterns ofPhragmites australisdecomposition in a wetland of the Adriatic area (Northeast Italy): a three-years analysis

Abstract

-Wetlands are one of the most biologically productive ecosystems, in which reedbeds of Phragmites australis are an essentially detritus-based system where litter decomposition is a fundamental process. This study represents a three year dataset describing cyclic trends of Phragmites australis leaf litter breakdown in a temporary and managed environment. For three years, 45 days field experiments were seasonally performed, using leaf bag technique within a large managed temporary pond (Natural Reserve of the Isonzo River Mouth, Northeast Italy), in order to analyze spatial and temporal variation in decomposition processes, to search for patterns on seasonal and inter-annual time scale and to infer the relevance of the main environmental features (physical and chemical) on decomposition dynamic. During the three years of analysis, decay rates (k) ranges were 0.0066-0.0075 days −1 in autumn, 0.0108-0.0158 days −1 in spring and k = 0.0168 days −1 in summer. Average mass loss per day % range was 0.97-1.31% in autumn, 1.12-2.04% in spring and 1.79-2.06% in summer. A well-defined seasonal cycle was observed through the study years as result of the drought-reflooding dynamic and the highest percentage (91.1%) of the average mass loss per day % variability was explained above all by rainfall, temperature and conductivity. Key-words:Leaf bag / wetland / seasonal dynamic / temporary pond / decomposition rate Résumé -Schémas saisonnier et pluriannuel de décomposition de Phragmites australis dans une zone humide de la région adriatique (Italie du Nord) : une étude de trois ans. Les zones humides sont parmi les écosystèmes les plus productifs, dont les roselières à Phragmites australis constituent un système basé essentiellement sur les détritus, où la décomposition de la litière représente un processus fondamental. Cette étude analyse un ensemble pluriannuel de données qui décrit les tendances cycliques relatives à la décomposition de Phragmites australis dans un milieu temporaire d'eau douce sujet à la gestion. Pendant trois ans, 45 jours d'expériences sur le terrain ont été effectués de façon saisonnière, en utilisant la technique du sac de feuilles dans un grand étang temporaire géré (Réserve Naturelle de l'embouchure de la rivière Isonzo, Italie du Nord), afin d'analyser les variations spatiales et temporelles dans les processus de décomposition, à la recherche de modèles à l'échelle temporelle saisonnière et inter-annuelle et d'en déduire la pertinence des principales caractéristiques environnementales (physiques et chimiques) sur la dynamique de la décomposition. Au cours des trois années d'analyse, les taux de décomposition (k) étaient 0,0066-0,0075 jours −1 à l'automne, 0,0108-0,0158 jours −1 au printemps et k = 0,0168 jours −1 en été. La perte moyenne de masse par jour était de 0,97 à 1,31 % en automne, 01,12 à 02,04 % au printemps et de 1,79 à 2,06 % en été. Un cycle saisonnier bien défini a été observé au cours des années d'études résultant de l'alternance assec-mise en eau. Le pourcentage le plus élevé (...

Seasonal patterns of Phragmites australis breakdown in a karstic freshwater system (Doberdò Lake, Northeast Italy) in relation to water level fluctuations, environmental features, and macrobenthic invertebrate communities

“…This can also be observed for a nearby area, a managed freshwater temporary pond at the mouth of the Soc ˇa River (Fig. 1; Table 7), where Bertoli et al (2016) used the same approach as we did. However, the k values for Doberdo `Lake appear to agree with the measures for P. australis leaf decomposition reported by Dolinar et al (2016) for Cerknica Lake, though they used a different methodological approach.…”

“…These rates are consistent with the literature on the decomposition of P. australis (Table 7). However, it is difficult to draw comparisons because each study was carried out in different conditions (i.e., environment, season, hydrologic regime, depth, different types of leaf bag mesh size) so that decomposition rates could be affected by a variety of factors such as geographical context and experimental conditions (Bedford, 2005;Sangiorgio et al, 2008a;Quintino et al, 2009;Bertoli et al, 2016).…”

“…The leaf bag technique (Petersen & Cummins, 1974) was used to study organic matter decomposition processes. Leaf bags were prepared by adapting the protocol reported by Basset et al (2006) and used in previous studies in other freshwater environments (Ruzic ˇet al, 2013;Bertoli et al, 2015;Bertoli et al, 2016;Bertoli et al, 2018). Leaves of Phragmites australis were chosen as it is one of the most abundant plant species in the Doberdo `polje and dominates the riparian vegetation.…”

“…Litter breakdown has been widely studied in lotic environments (Diez et al, 2002;Mene ´ndez et al, 2003;Pinna et al, 2004;Sangiorgio et al, 2006), lakes (Hietz, 1992;Gupta et al, 1996;Kara ´di-Kova ´cs et al, 2015;Raposeiro et al, 2016), and transitional aquatic ecosystems such as coastal lagoons and river mouths (Rossi & Costantini, 2000;Sangiorgio et al, 2004;Bayo et al, 2005;Sangiorgio et al, 2008a, b). However, increasing attention has also been directed at decomposition dynamics in temporary freshwater bodies with seasonally fluctuating water levels (Bedford, 2005;Vo ¨llm & Tannenberger, 2014;Gingerich et al, 2015;Bertoli et al, 2016). Studies on litter breakdown in karst systems have been reported: several investigated lotic environments (Tanaka et al, 2006;Martı ´nez et al, 2015) and the relationship between calcite deposition and litter breakdown in travertine systems (Casas & Gessner, 1999;Carter & Marks, 2007;Belanc ˇic ˇet al, 2009;Milis ˇa et al, 2010).…”

“…Water level variations, together with the intensity, timing, and extent of flood/drought, affect sedimentation and erosion of alluvial sediments, primary production, vegetation, animal life cycles (i.e., spawning of fish and nesting of birds), mineralization, turnover rate, interaction among species, and decomposition dynamics (Boulton & Brock, 1999;Gabers ˇc ˇik et al, 2003;Dinka et al, 2008;Dolinar et al, 2016). Particularly interesting among these factors is organic matter decomposition: plant breakdown is a fundamental process in the metabolism of all wetlands (Webster et al, 1995;Wallace et al, 1997;Eid et al, 2014;Bertoli et al, 2016) as it provides for the maintenance of nutrient status and constitutes a basis for defining wetland properties (Fennessy et al, 2008;Dolinar et al, 2016). In this setting, reedbed detritus decomposition has been widely studied.…”