Growth responses of Nymphoides indica seedlings and vegetative propagules along a water depth gradient

Abstract

Seedlings and vegetative propagules of Nymphoides indica (L.) O. Kuntze, a species with floating leaves, were grown in a concrete tank at 17, 35, 75, 105 and 140 cm below the surface of the water. The total biomass, relative growth rate (RGR), net assimilation rate (NAR), specific leaf area (SLA), leaf area ratio (LAR) and leaf weight ratio (LWR) were measured or calculated for both seedlings and vegetative propagules. At the end of the experiment, the total biomass for seedlings and vegetative propagules was similar at all depths. Overall, RGR values were higher for seedlings (54.3–64.3 mg g −1 day −1) than for vegetative propagules (41.4–57.1 mg g −1 day −1). Before reaching maximum RGR, LAR and NAR values were generally higher for seedlings. After reaching maximum RGR, LAR values remained higher for seedlings, but NAR values became higher for vegetative propagules. Growth strategies for seedlings and vegetative propagules differed in shallow (17 and 35 cm) and deep (105 and 140 cm) water. Before maximum RGR were reached, LAR values of seedlings in shallow water (8.4–10.9 m 2 kg −1) were higher than those in deep water (4.1–6.8 m 2 kg −1). NAR values, on the other hand, were lower in shallow water (5.8–8.0 g m −2 day −1) than in deep water (10–13 g m −2 day −1). After reaching maximum RGR, LAR values were similar at all water depths, but NAR values remained lower in shallow water. Before maximum RGR were reached, LAR values of vegetative propagules were higher in shallow water (7.0–7.9 m 2 kg −1) than in deep water (5.8–6.4 m 2 kg −1). NAR values, however, were higher in deep water (4.4–6.8 m 2 day −1). After reaching the maximum RGR, LAR values became higher in deep water and NAR values were highest in deep water and also at the shallowest water depth.