Morphological and anatomical responses of Lythrum salicaria L (purple loosestrife) to an imposed water gradient

Morphological and anatomical responses of Lythrum salicaria L. to an imposed water gradient were assessed under greenhouse conditions. Nine-week-old seedlings were exposed to three levels of water availability for an 8-wk period. Fresh and dry mass of the shoot, root, and entire plant, shoot fresh:dry mass ratios, root:shoot fresh mass ratios, and root:shoot dry mass ratios were not significantly affected by water availability. Total fresh:dry mass ratios were significantly lower in the dry treatment compared with the wet, while root fresh:dry mass ratios were significantly greater in the intermediate and wet treatments. Total stem diameter and porosity was generally higher in submersed portions of hooded stems and roots, while tissue density was generally lower under these conditions. Stem diameter excluding the phellem did not differ among treatments. The total root diameter to diameter excluding phellem showed significant increases with increasing water availability. Adventitious and lateral roots in primary growth from all plants possessed an endodermis with Casparian bands and subsequently suberin lamellae and a modified, uniseriate hypodermis. Submerged stems and roots in secondary growth possessed a multilayered, lacunate polyderm, while nonsubmerged stems and roots had a compact, multilayered polyderm. Fluorescent properties of walls of some cells in the root and stem polyderm indicate that these cells share features with endodermal cells.