Role of allelopathy of Phragmites australis in its invasion processes Md. Nazim Uddin a, ⁎, Randall William Robinson a , Andrew Buultjens b , Md. Abdullah Yousuf Al Harun a , Shahana Haque Shampa c a Department of Ecology and Environmental Management, College of Engineering & Science, Victoria University, St Albans Campus, Melbourne, VIC 8001, Australia b Department of Microbiology and Immunology, Faculty of Medicine, Dentistry and Health Science, The University of Melbourne, Parkville, Melbourne, VIC 3010, Australia c Department of Geography & Environment, National University, Gazipur, 1704 Dhaka, Bangladesh abstract article info Article history: Received 24 May 2016 Received in revised form 17 October 2016 Accepted 19 October 2016 Available online xxxx Allelopathy is one of the mechanisms that help to explain the invasion success of some plant species. Invasion of Phragmites australis through allelopathy is not robust enough to provide reliable information that could integrate the existing knowledge to sound on-ground reality. This study analysed the chemical characteristics of soil and water and monitored both over four seasons taking into consideration the phenological cycle of P. australis in the field. A series of bioassays has been conducted to test phytotoxicity using field concentrations of allelochemicals on different plant species in laboratory. Significant changes in soil and water chemistry were ob- served in invaded area compared to uninvaded area. Soil-water (rhizosphere and surface) and whole plant- leachate significantly inhibited germination and α-amylase activity of Lactuca sativa as well as the adventitious root formation of Phaseolus aureus. Seasonal impact on allelopathic interference of P. australis in terms of germi- nation and growth of L. sativa, Melaleuca ericifolia, and Poa labillardierei showed distinct but inconsistent varia- tion. Soil biota played an important role in reducing the phytotoxicity in natural soil. In addition, P. australis infested soil showed a lower arbuscular mycorrhizal fungus inoculum potential in terms of Zea mays roots colo- nization. A synthesis from field studies and associated laboratory experiments may provide a more logical under- standing towards invasion mechanisms of P. australis through allelopathy, leading to more realistic management decisions. © 2016 Elsevier B.V. All rights reserved. Keywords: Allelopathy Invasion Phenolics Phragmites australis Soil biota 1. Introduction Biological invasion by non-native species is a worldwide phenome- non that threatens to dramatically change communities and ecosystems (Alvarez and Cushman, 2002; Mack et al., 2000). Allelopathy, the release of phytotoxins by plants, has been proposed as an alternative theory for the success of many invasive plants (Callaway and Aschehoug, 2000; Callaway et al., 2008; Donnelly et al., 2008; Ens et al., 2009). There are some important methodological aspects of allelopathy which are crucial to be addressed in determining the impacts. One aspect of allelopathy presently not generally addressed is phytotoxicity assessment in rela- tion to field concentration of phytotoxins released from the allelopathic plants. Most of the research works performed on phytotoxic assess- ments are carried out in the laboratory and greenhouse using only plant extracts that makes difficult to show functional importance in na- ture (Mallik, 2000; McNaughton, 1968). In this background, more eco- logical realistic experiments are needed to understand the allelopathic functional activities occurred in natural ecosystems though due to complexity in natural system it is nearly impossible to demonstrate al- lelopathy (Harper, 1975). In addition, field chemistry associated with soil and water seem to be the key in determining the qualitative and quantitative availability of allelochemicals in vicinity of neighbouring species and is critically important to provide the better understanding in allelopathy (Callaway et al., 2004; Inderjit, 2001, 2005) and suppres- sion of germination, growth and establishment of the associated species in fields (Lambers et al., 2008). As interactive effects of plants, water, and soil are not independent in natural ecosystems, it is essential to in- tegrate them in experiments on biological invasion of any wetland inva- sive species through considerations of natural allelochemical concentration in bioassays for allelopathy (Inderjit and Nilsen, 2003). With these complex interactions, these studies were designed to find out the role of allelopathy in invasion of Phragmites australis using field concentrations of allelochemicals that almost reflects the complex- ity of the ‘natural’ ecosystem. A ubiquitous wetland plant, Phragmites australis, has been consid- ered one of the most invasive species in the world (Fell et al., 1998; Uddin et al., 2012), however, the origin and original distribution of the species is still unclear (Plut et al., 2011). It is a perennial graminaceous plant, 3 to 4 m tall, which reproduces mainly through rhizomes and, at low frequency, through seeds. This large wetland grass grows in all temperate zones of the world, and is especially common in North Journal of Experimental Marine Biology and Ecology 486 (2017) 237–244 ⁎ Corresponding author. E-mail addresses: Nazim.Uddin@vu.edu.au (M.N. Uddin), randall.robinson@vu.edu.au (R.W. Robinson), abuultjens@student.unimelb.edu.au (A. Buultjens), harunkb@yahoo.com (M.A.Y. Al Harun), shampa_nazim@yahoo.com (S.H. Shampa). http://dx.doi.org/10.1016/j.jembe.2016.10.016 0022-0981/© 2016 Elsevier B.V. All rights reserved. Contents lists available at ScienceDirect Journal of Experimental Marine Biology and Ecology journal homepage: www.elsevier.com/locate/jembe