Response of juvenile plants of Myriophyllum elatinoides Gaudich. to shade in experimental culture

Abstract

Myriophyllum elatinoides is an aquatic submersed plant with erratic distribution in the irrigation systems of southern Argentina. Th especies usually occurs in channel sites with high light availability, suggesting a low tolerance to the reduced light conditions caused by water turbidity or shading. The aim of the present work was to study the response of this species to shading in experimental culture. Buds contained in 400 cm3 pots were introduced in tanks with water (150 l; 12 plants/tank), under artificial light supply (113.86 μE m-2 s-1 just below water surface; 16/8 plants/tank). Shade treatments were assayed by installing a geotextile material just over the tanks. Treatments were: high shade (86% reduction in PAR radiation), low shade (41% reduction) and full light, resulting a complete randomised design with three replicates. At 35 days, significant reductions were observed at both shade levels for stem length, plant total length, number of branches per plant, below and above ground plant weight. At the end of the experiment (78 days), the percentages of reduction varied between 70 and 97% for all the measured parameters. The effect of treatments on plant chlorophyll a and b and total chlorophyll is discussed. Results showed that shade stress produced in M. elatinoides none of the typically-observed morphological responses of most of submersed plants to shade, but clear deletereous effect at both shade levels.