ECO-PHYSIOLOG-ICAL STUDIES ON PIST1A STuATlOTES. L. with sp eo ia l referenoe to i t s ooourrenoe on the Volta Lake in Ghana.

ABSTRACT

The oreation o f the Volta Lake in Ghana provides favourable conditions fo r rapid weed growth,, The present report represents an attempt to in v e s t ig a te the in te ra c t ion between one o f the economically important weeds on the Lake, P is t ia s t r a t io t e s , L ., an  the physicochemical condition o f i t s environment in the f i e l d and laboratory, P is t ia is represented in most reaches o f the Lake but only sheltered bays and es tu arie s in the south are oharaoterized by luxuriant veg etation o f the species. Distribution and growth o f the plant within these areas are con tro lled to some extent by the pH and mineral composition o f lake water. Under laboratory oonditions, marked influence is exerted by substrate pH and nutrient content on the ve g etative reproduction and growth or the plant. Occurrence o f optimum v e g e ta t iv e growth a t low to ta l nutrient content and pH 5»0 is r e f le c te d in the tendenc3r shown by ro s e tte s to grow la r g e r in areas o f the Lake characterised by comparatively low degree o f m ineralization, and pH. Growth of the plant has been observed to a l t e r the pH and mineral content of the substrate under f i e l d and laboratory conditions. The nature o f th is change in the f i e l d depends on the cover o f vegetation. Stranded ro s e tte s which have become rooted in the drawdown area o f the Vo lta Lake are capable o f regenerating and may reco lonize the lake surfaceo Results o f these in v e stigation s have been discussed with reference to methods of con tro llin g the plant,,