Adaptation to low light levels by Hydrilla

Abstract

Mature, apical stem sections of hydrilla (Hydrilla verticillata (L.F.) Royle) were collected at Orange Lake, Florida to determine their adaptability to low light levels. These plants were grown in controlled environment chambers at quantum flux densities varying from below the photosynthetic light compensation point to near light saturation. Growth ratesa expressed as fresh weight, dry weight and stem length, were measured over a 5-week period. Concomitantly, chlorophyll content, photosynthetic, photorespiratory, and respiratory characteristics were determined. The plants adapted their photosynthetic and respiratory characteristics to make more effective use of the lower light levels. Young shoots, developing from tubers, exhibited similar adaptations to low light. Tuber size influenced both shoot survival and shoot length when they were germinated and held in complete darkness. The largest tubers produced shoots that survived longer and had longer stems. The lowest light level to which hydrilla plants could adapt was 10 to 12 ..mu..einstein/m/sup 2/.sec. Below this quantum flux density the plants were incapable of increasing in dry weight.