Phragmites die–back: bud and root death, blockages within the aeration and vascular systems and the possible role of phytotoxins

Abstract

S I' M M h R YDie-back and healthy stands oi Phragmites australu (Cav.) Trin. ex Steud. in the UK and Hungary were compared in terms of stand architecture, plant morphology and anatomy, sediment redox potential and sulphide le\-els, plant resistance to internal Poiseuille gas flow, and convecti\-e flow characteristics of culms. Compared with healthy sites, die-back sites were characterized by lower sedmient redox potentials, and in Hungary by \-ery high sulphide levels. Plants at die-back sites showed a markedly clumped distribution, with fewer new shoots and fewer old flower heads than those at healthy sites, a high incidence of dead and decaying rhizomes and roots, and dead 'o\'er\vintering' and 'growing season' buds, and occasional prematurely senesced culms. Dead and stunted ad\'entitious roots with short peg-like laterals were very common, and there was abnormal hgnification and suberization within the cortex and epidermis/hypodermis of adventitious root apices, and in the epidermis of lateral roots. Callus was found blocking the internal aeration pathways m root aerenchyma, root-rhizome junctions, rhizome nodes and the bases of buds and culms. Blockages of the \ ascular elements of both x>-lem and phloem m rhizomes and roots were also common. At the die-back sites, callus accounted {or a greater resistance to gas Row from the dead aerial culms into the rhizome system. Compared with healthy culms, prematurely senesced culms from die-back sites exhibited smaller potentials for aerating the rhizome s\stem by humidityinduced con\ection.It is suggested that die-back in Phragnutes might be brought about and perpetuated at least partly b\" phytotoxins which induce (a) blockages within the aeration pathways due to callus development, (h) stunting oi roots and the de\'elopment of abnormal root wall Hgnification and suberisation causing interference with water and mineral absorption, and (c) internal blockages causing interference with vascular transport. A tentati\-e scheme for Phragmites die-back is presented.

The Fate of 15 N-Nitrate in Healthy and Declining Phragmites australis Stands

“…The main factors regulating which of the two nitratereducing processes will be favored are the concentrations and ratios of available electron donors and acceptors [20,27]. Aerenchymatous plants create an oxic-anoxic interface in the root zone by releasing oxygen into this zone [2,22]. The release of oxygen by the roots may stimulate nitrification [5,9,19] and, subsequently, denitrification after diffusion of nitrate into the reduced zone of the sediment.…”

“…Eutrophication could lead to anoxia in the below ground growing parts of P. australis because the increased litter production may result in an increase of decomposition activity in the sediment compartment. Also, it has been shown that at the die-back sites, aeration by plants was affected negatively due to blockages in the aerenchymatous tissue [2].…”

Phragmites die‐back: toxic effects of propionic, butyric and caproic acids in relation to pH

“…Symptoms of die-back in reed beds include a clumped habit, stunting and death of shoots and roots, premature senescence, death of buds and rhizomes, impeded diffusive and convective aeration of the underground parts due to occlusions of callus, blockages within vascular systems and lignification and suberization of surface layers of laterals and apices of adventitious roots *Author for correspondence (fax 01482 465458 ; e-mail w.armstrong!biosci.hull.ac.uk). (Armstrong et al, 1996a ;Armstrong et al, 1996c,d ;Kohl et al, 1996 ;Rolletschek et al, 1998). Other symptoms include weakened culms (Klo$ tzli 1971 ;Sukopp et al, 1975 ;Sukopp & Markstein, 1989), altered ratios of various amino acids and ratios of amino acids : sugars in culm bases (Kohl & Henning, 1987 ;Kohl et al, 1998) and lower levels of starch in rhizomes (Cizkova et al, 1996b).…”

“…Growth of Phragmites can be poor when cultivated in sediments containing an organic layer of rotting rhizomes and roots of the plant (Armstrong et al, 1996c). Bud death and reed decline have been associated at Lake Ferto in Hungary with high levels of sulphide : up to 4 mM (128 ppm) (Armstrong et al, 1996a) and at Rozmberk West, an anthropogenically induced eutrophic site in the Czech Republic, with a strongly reducing organic layer in the surface of the lake sediment (Cizkova et al, 1996a) and with high levels of some organic acids in interstitial waters, including acetic (H. Cizkova, pers. comm.).…”

“…In addition, we have previously suggested that the accumulation of sediment phytotoxins such as lower volatile monocarboxylic acids and\or sulphide generated by the decay of (i) the underground parts of the reed and\or (ii) organic deposits produced under eutrophic conditions might play a crucial part in a die-back syndrome (Armstrong et al, 1996a). Factors initiating greater than normal death of Phragmites might, directly or indirectly, promote higher levels of phytotoxins in sediments and at the same time make the plant more susceptible to phytotoxin damage, for example, through impedence of plant and rhizosphere aeration, and thus begin an accelerating cycle of death and decay.…”