Assessment of cardinal temperatures of Egeria najas Planchon and its potential growth in a tropical floodplain lagoon.

Knowledge of the factors controlling the growth of macrophytes is essential to forecasting their spatial distribution and management. Based on growth rates (µ), this study describes the cardinal temperatures of Egeria najas, and evaluates its growth potential. Cultures at 4 temperatures (15, 20, 25 and 30 °C) were monitored for 48 days. Plant growth was fitted to a logistic model to obtain growth rates (µ15: 0.02; µ20: 0.05; µ25: 0.10; µ30: 0.04 day−1) which were used for parameterization of the optimal temperature function, obtaining the cardinal temperatures (lower basal temperature: 5 °C; optimum temperature: 26.3 °C; upper basal temperature: 31.7 °C). Using the water temperature of the Óleo Lagoon (a tropical floodplain lagoon from which E. najas was harvested) and optimum temperature function, the seasonal variation of the E. najas µ was calculated. This procedure predicted that the highest µ are expected between September and April (rainy season); however, on average, the µ was higher between April and October (dry season). Although the temperature is of paramount importance for the growth of this species (Q10: 4.39), in aquatic environments with small thermal variations, turbidity and nutrient scarcity can decisively interfere with the growth of submerged macrophytes. [ABSTRACT FROM AUTHOR]