title: Submerged plant survival strategies in relation to disturbance and stress in artificial channels of Britain and Argentina
Creators: name: Sabbatini, Mario Ricardo
Publisher: name: University of Glasgow
Year: 1996
Subjects: subject: Botany

description: The aim of this thesis was to make a functional analysis of submerged aquatic plants in relation to management and environmental factors in artificial systems of Britain and Argentina. In Britain, low-lying plains must have artificial drainage systems to avoid flooding and maintain optimum soil conditions. In Argentina, there are several irrigation districts for agricultural use and two of the most important are the Valle Inferior del Rio Colorado (VIRC) and the Valle inferior del Rio Negro (IDEVI). One of the main problems in these channel networks are the growth of submerged weeds which cause a great deal of damage by blocking the flow of water. The abundance of submerged weeds were surveyed during 1992 and 1993 in drainage channels located in geographically-distinct areas of Britain and in 1993/1994 in drainage and irrigation channels of VIRC and IDEVI. Environmental and management data were recorded and indices of disturbance and stress constructed from combined data for each site surveyed. In Britain, a species ordination using Canonical Correspondence Analysis (CCA) showed that the combined disturbance variable explained more of the variability that did stress. Two main groups of species could be distinguished using cluster analysis (TWINSPAN: Two way indicator species analysis). The larger group appear to be those better-adapted to habitats with low disturbance constraints (e.g.. Myriophyllum spicatum and Potamogeton pectinatus). The smaller group comprised species which tended to occur in sites with higher disturbance (e.g.. regular cutting) such Callitriche stagnalis. In Argentina, the same analysis that above showed that each variable (disturbance and stress) explained about half of the constrained variation. Four TWINSPAN species groups were separate in VIRC and IDEVI showing different tolerance to disturbance and stress. Since the species groups were indicative of different combination of stress and disturbance, each plant community may be defined as different functional groups. When data from Britain and Argentina were analysed together, stress appears as an important factor in determining species variation in Argentina, Ruppia maritima being the species most tolerant, especially to water conductivity. Disturbance explained variation in both countries, Chara contraria, Potamogeton crispus, P. pusillus and the moss Rynchostegium riparioides being the most tolerant, especially to management, water velocity and water fluctuation. Plants were also classified in functional terms on the basis of plant morphological traits, and this study found a relationship between these attributes and the stress and disturbance variables. This suggests the possibility of determined functional groups in submerged vegetation from classic-standardised ecological measures as for example plant length or plant weight. The inverse relationship between shoot length and total PAR was found in plants of Potamogeton pectinatus growing in drainage and irrigation channels of VIRC and IDEVI, showing that the condition of light-limitation for plant growth is frequent in these channels. Specimens of P. pectinatus from the area of VIRC, were grown under laboratory conditions in order to determine its tolerance to disturbance (cutting) and stress (shade). Results suggest that the species has the stress element in its established-phase strategy, and an intermediate tolerance to disturbance. A field experiment was performed in the Solway drainage area, NW England, to examine the response of populations of Callitriche stagnalis and Potamogeton crispus to disturbance treatments (manual cutting and dredging) and stress treatments (shade). Results showed that, although the survival strategy of both plants is essentially similar (competitive-disturbance tolerators: CD) C. stagnalis was the more competitive of the two species, while P. crispus tolerated disturbance and stress better.