Contents lists available at ScienceDirect Ecological Engineering journal homepage: www.elsevier.com/locate/ecoleng Plant species efect on CO 2 and CH 4 emissions from pilot constructed wetlands in Mediterranean area Carmelo Maucieri a, ⁎ , Maurizio Borin a , Mirco Milani b , Giuseppe L. Cirelli b , Antonio C. Barbera b,c a Department of Agronomy, Food, Natural Resources, Animals and Environment – DAFNAE, University of Padua, Agripolis Campus, Viale dell’Università 16, Legnaro, PD, Italy b Department of Agriculture, Food and Environment – Di3A, University of Catania, Via Valdisavoia 5, Catania, CT, Italy c Trees and Timber Institute, National Research Council of Italy (CNR-IVALSA), Via Paolo Gaifami 18, Catania, CT, Italy ARTICLE INFO Keywords: Arundo donax L. Phragmites australis (Cav.) Trin. ex Steud. Chrysopogon zizanioides (L.) Roberty Mischantus x giganteus Greef et Deu. CO 2(eq) balance ABSTRACT The aim of this research was to evaluate the role of constructed wetland (CW) horizontal sub-surface fow pilot- plant beds vegetation, comparing four perennial herbaceous plant species with an unvegetated bed, on carbon dioxide (CO 2 ) and methane (CH 4 ) emissions, and CO 2(eq) budgets. The research was conducted from April 1 st to November 30 th in 2012 and 2013 in a pilot plant located in San Michele di Ganzaria (Sicily, Italy) that treated urban wastewaters, studying Phragmites australis (Cav.) Trin. ex Steud. (common reed), Arundo donax L. (giant reed), Chrysopogon zizanioides (L.) Roberty (vetiver) and Miscanthus x giganteus Greef et Deu. (miscanthus). Results showed a greater aboveground biomass yield in the second experimental year than the frst one for all species except vetiver, which showed a 10.5% reduction. Considering CWs gases emission, a signifcantly higher CO 2 emission (+52.5%) was monitored in 2013 than 2012 whereas CH 4 had the opposite trend (−97.0%). Seasons and plant species infuenced gases emission. The lower CO 2 emission (median value 5.2 g m −2 d −1 ) was monitored during the spring seasons when instead was monitored the highest CH 4 emission (median value 0.232 g m −2 d −1 ). Opposite CO 2 and CH 4 emissions were found in fall. A. donax, M. giganteus and P. australis determined signifcantly higher (2.9 times) CO 2 emission than C. zizanioides and unvegetated bed. Vegetated beds showed a positive CO 2(eq) total balance with the best results calculated for A. donax whereas, as expected, it was negative for the unvegetated bed, with a cumulative CO 2(eq) emission of 6.68 kg m −2 . Obtained results confrm the active and key role of plant species used in the CW systems and indicate A. donax as the most environmentally friendly species to use under Mediterranean climate conditions, followed by P. australis. 1. Introduction Constructed wetlands (CWs) are natural-like systems widely used for wastewater treatment (Barbera et al., 2009; Vymazal, 2013; Tamiazzo et al., 2015; Pappalardo et al., 2016). CWs carbon (C) cycle contribute to the global greenhouse gases (GHGs) balance through carbon dioxide (CO 2 ) and methane (CH 4 ) emissions. In particular, ve- getated CW beds can act as CO 2 sinks by photosynthetic CO 2 assim- ilation from the atmosphere or as a source of CO 2 through respiration (Maucieri et al., 2014a; Picek et al., 2007) and/or organic matter fer- mentation (CH 4 )(Brix et al., 2001). Søvik et al. (2006) reported that the question then arises if CWs, used to protect freshwater ecosystems, are a solution to an environmental problem or if they replace one problem with another by reducing water pollution, but at the same time in- creasing GHGs emission. Pan et al. (2011), in an estimated life-cycle GHGs emission study concluded that a vertical subsurface fow CW emitted only about 50% of CO 2(eq) with respect to a conventional system to remove 1 kg of BOD. Mitsch et al. (2013) showed that most wetlands are net C sinks providing many ecosystem services in addition to C sequestration; also considering the savings that wetlands give us from fossil fuel consumption for the ecosystem services (e.g. water quality improvement) their service as carbon sinks is even greater. The presence of plants is one of the most conspicuous features of these systems and distinguishes them from unplanted soil flters or la- goons (Vymazal, 2011). As reviewed by Maucieri et al. (2017) several studies confrm the role of vascular plants in CWs on GHGs fux by their presence, phenology, density and species composition. Indeed, plant species with diferent anatomy and physiology and so diferent oxygen (Wigand et al., 1997) and exudate release levels (Ström et al., 2003) determine diferent CO 2 :CH 4 ratio emission and global warming po- tential (GWP), given that CH 4 has, for a 100 year time horizon with inclusion of climate–carbon feedbacks, a 34 times higher efect on GWP https://doi.org/10.1016/j.ecoleng.2019.04.019 Received 2 December 2018; Received in revised form 14 April 2019; Accepted 15 April 2019 ⁎ Corresponding author. E-mail address: carmelo.maucieri@unipd.it (C. Maucieri). Ecological Engineering 134 (2019) 112–117 Available online 17 May 2019 0925-8574/ © 2019 Elsevier B.V. All rights reserved. T