Growth and nutrient uptake capacity of two co-occurring species, Ulva prolifera and Ulva linza

This study was designed to evaluate interspecific physiological differences in growth and nutrient uptake of two co-occurring species, Ulva prolifera and Ulva linza, in laboratory conditions. Growth-testing results showed that U. prolifera grew faster than U. linza in a range of temperature (8–30 °C) and irradiance (50–500 μmol photon m−2 s−1). Nitrate (NO3−) and ammonium (NH4+) enrichment had far more effect on growth of U. prolifera (max. 13.1 and 16.9% d−1) than on U. linza (max. 9.8 and 11.6% d−1). The Vmax values of NO3− and NH4+ uptake by U. prolifera (124.25 and 284.60 μmol g−1 DM h−1) were higher than those by U. linza (109.13 and 250.25 μmol g−1 DM h−1), and the Ks values for U. prolifera were much lower than those for U. linza during the 3-h testing period. Significant difference in the Vmax/Ks values indicated that U. prolifera had an apparent competitive advantage over U. linza to uptake and stock nitrogen (NO3− and NH4+) from the water column. There was no distinct difference in phosphate uptake between the two species. The results of this investigation revealed that distinct interspecific physiological traits in growth and nutrient uptake might be key factors to determine the species dominance patterns in green tides in the Yellow Sea.

► Ulva prolifera has higher growth rates than Ulva linza under the same condition.
► Nitrogen enrichment had far more effect on U. prolifera than on U. linza.
► Algal physiological traits might determine the species dominance patterns in blooms.