Sediment chemistry and flooding exposure: a fatal cocktail forPhragmites australisin the Mediterranean basin?

Abstract

The common reed die-back syndrome was formerly reported mostly in Central Europe and more recently in the Mediterranean basin. This study investigates a case of reed die-back in Central Italy through a Geographic Information System (GIS) diachronic survey and the analysis of macromorphological and ecological parameters. Data were recorded during field activities on ten plots randomly distributed according to two ecological statuses, permanently and temporarily flooded. Culm density, height and diameter, clumping habit, flowering head and dead apical bud number and rate were measured; for each plot, chemical parameters of sediments were analyzed. Information on interstitial waters for the flooded plots was also provided. Floristic-vegetational features of the reed-bed community such as the total vegetation cover, the species composition and abundance were estimated. Univariate and multivariate analyses were used to demonstrate differences between morphological traits of flooded and emerged stands and their relationships with the chemical features of sediment. Macromorphological traits differed according to the ecological status, with flooded stands showing patterns related to poor health status of Phragmites australis, such as high rates of clumping habit and dead apical bud rate, high culm density and, to a lesser extent, low culm diameter and flowering head rate. Sulfates were relatively abundant in the sediment of flooded stands and, together with some heavy metals, resulted in some of the mentioned traits. Our results showed a relationship between reed die-back and prolonged flooding and highlighted the potential role of some chemical parameters in affecting the growth of permanently flooded reeds.

Oomycete Communities Associated with Reed Die-Back Syndrome

“…Even if this species sometimes shows an expansive behavior ( Bertness et al, 2002 ; Foggi et al, 2011 ), since the 1950s an irreversible retreat of the population known as reed die-back syndrome (RDBS) has been observed from several wetlands of northern and central Europe (for a review, see van der Putten, 1997 ). In Italy, it was first detected in a brackish lagoon ( Fogli et al, 2002 ), and recently in freshwater lakes ( Gigante et al, 2011 , 2014 ; Lastrucci et al, 2016a ). Typical symptoms of RDBS include reduced plant height, weaker culms, abnormal rhizomes, formation of clumps ( Armstrong et al, 1996 ; Fogli et al, 2002 ), and eventually retreat of the population ( van der Putten, 1997 ).…”

“…Some of the possible abiotic and biotic causes of reed decline has been widely investigated ( Brix, 1999 ; Fogli et al, 2002 ). Among the abiotic factors, prolonged submersion of the plant appears to have dramatic consequences; Lastrucci et al (2016a) demonstrated the existence of a relationship between reed die-back and permanent-artificially induced flooding conditions. Several macromorphological traits associated with RDBS (such as clumping habit, reduced culm height or diameter, high rate of dead buds, see Gigante et al, 2011 , 2014 ; Lastrucci et al, 2016a for details) were significantly more often observed in permanently flooded stands than in the emerged stands.…”

“…Among the abiotic factors, prolonged submersion of the plant appears to have dramatic consequences; Lastrucci et al (2016a) demonstrated the existence of a relationship between reed die-back and permanent-artificially induced flooding conditions. Several macromorphological traits associated with RDBS (such as clumping habit, reduced culm height or diameter, high rate of dead buds, see Gigante et al, 2011 , 2014 ; Lastrucci et al, 2016a for details) were significantly more often observed in permanently flooded stands than in the emerged stands. Furthermore, even if P. australis can tolerate high concentrations of heavy metals ( Bonanno and Lo Giudice, 2010 ), some studies have highlighted their negative effect on plant fitness, suggesting a role in the RDBS ( Gigante et al, 2014 ; Lastrucci et al, 2016a ).…”

“…Several macromorphological traits associated with RDBS (such as clumping habit, reduced culm height or diameter, high rate of dead buds, see Gigante et al, 2011 , 2014 ; Lastrucci et al, 2016a for details) were significantly more often observed in permanently flooded stands than in the emerged stands. Furthermore, even if P. australis can tolerate high concentrations of heavy metals ( Bonanno and Lo Giudice, 2010 ), some studies have highlighted their negative effect on plant fitness, suggesting a role in the RDBS ( Gigante et al, 2014 ; Lastrucci et al, 2016a ). Cd and Co, for example, seemed to be related to some traits associated with the die-back symptoms in Montepulciano ( Lastrucci et al, 2016a ).…”

Plant–environment interactions through a functional traits perspective: a review of Italian studies

“…Studies related to growth form and performance of Phragmites australis found significant differences in attributes according to site-specific ecological status. Flooded stands or sites with permanent submersion were characterized by high rates of clumping habit and dead apical bud, and lower culm diameters, showing clear signs of plants dieback (Lastrucci et al 2016(Lastrucci et al , 2017. Other studies addressed the growth response of a rare fern, Marsilea quadrifolia, and a widespread opportunistic species, Vallisneria spiralis, respectively to sediment trophic level and physicochemical water features, demonstrating a certain capacity of both species to grow under varying levels of nutrients in water and sediment (Bolpagni & Pino 2017;Bolpagni et al 2015).…”