Annual and Seasonal Variations in Net Production, Biomass and Life Span of Floating Leaves in Brasenia schreberi J.F. GMEL.

Abstract

Quantitative observations on the seasonal changes in leaf life span, leaf. area and leaf mass of a floating-leaved aquatic macrophyte, Brasenia schreberi J. F. Gmel., were carried out from 1986 to 1988 in an irrigation pond in Matsue, Shimane Prefecture, Japan, using a non-destructive leaf-marking method. During those three years, the seasonal maximum leaf area index, seasonal maximum leaf mass, and annual net production changed considerably ; 0.90-1.36, 52.5-80.5g dry weight m-2 and 154.9-243.5 g dry weight m-2 yr-1, respectively. In contrast, the annual mean life span, turnover of leaves in number, and the annual net production to seasonal maximum biomass ratio (P/ Bmax ratio) were relatively constant around the values of 25-28 d, 6. 0-6.3 and 2.95-3.25 yr-1, respectively. While the net production (P<0.05) and leaf mass (P<0.005) of leaves had a significant linear relation to cumulative sunshine duration from 1 May to late Septem ber, there was no significant correlation between cumulative tempera ture and annual net production and leaf mass. Present result suggests that sunshine duration during the growing season is crucial for the leaf production of B. schreberi.