Aquatic Botany 53 (1996) 151-162 Influences of water depth and substrate nitrogen on leaf surface area and maximum bed extension in Nymphaea odorata M. Sinden-Hempstead * , K.T. Killingbeck Department of Biological Sciences, University of Rhode Island. Kingston, RI 02881, USA Accepted 15 December 1995 Abstract Relationships among water depth, substrate nitrogen, and leaf surface area in the floating-leaved macrophyte Nymphaea odorata Aiton (fragrant waterlily) were studied in seven ponds in Rhode Island, USA. Beds of N. odorata in ponds that varied three- to seven-fold in depth, total area, water-column phosphorus and nitrogen, transparency, and chlorophyll content grew to strikingly similar water depth maxima (1.9-2.2 m; coefficient of variation 5%) suggesting a significant effect of water depth on N. odorata growth. Surface areas of leaves growing within N. odorata beds were not influenced by water depth, yet leaves growing at the pondward perimeter of beds were up to 74% larger than mid-bed leaves. Water depth was not significantly correlated with the mean surface area of these bed-edge leaves (r = 0.28, P > 0.05) but 71% of the variance in surface area of mid-bed and bed-edge leaves was accounted for by the concentration of ammonium-nitrogen in the corresponding substrates (R* = 0.71, P < 0.001). Leaf size of N. odorata was also related to pond trophic state, probably as a result of the inherent linkage between trophic state and nutrient dynamics. We conclude that both water depth and substrate nitrogen are instrumental in limiting growth of N. odorata. Kcwords: Leaf surface area; Nitrogen; Substrate; Trophic state; Water depth; Nymphma odmta 1. Introduction Communities that inhabit the shorelines of lentic bodies of water are ordered into zones dominated by plants with distinctly differing growth forms and life history strategies (Mitsch and Gosselink, 1986). Species that occupy these zones are ultimately * Correspondingauthor. 03043770/%/$15.00 8 1996 Elsevier Science B.V. All rights reserved PII SO304-3770(96)01020-O