Photosynthetic and nutrient uptake physiology of Padina species in high and low nutrient waters in Bolinao, Pangasinan, Philippines

Abstract

Abstract The genus Padina (Dictyotales: Dictyotaceae) are ubiquitous tropical macroalgae found in a wide range of environmental conditions, but the physiological mechanisms that allow them to thrive in different light and nutrient conditions remain unclear. This study identified Padina species found at two contrasting sites in Bolinao, Pangasinan – turbid, high-nutrient waters at Rungos, and clear, low-nutrient waters at Patar, and compared their physiological responses. The examined parameters were growth rates, photosynthetic responses to varying irradiances (P-E curves), and NO3 - and NH4 + uptake kinetics. Different species were found at each site, i.e., Padina antillarum in Rungos and Padina minor in Patar. From the P-E curves, both species appeared to have “shade plant” characteristics with high α values, low compensation irradiances, and low saturation irradiances. Though P. antillarum had higher net productivity (Pmax=69.4 mg O2 gdw-1 h-1) than P. minor (Pmax=40.6 mg O2 gdw-1 h-1), their growth rates did not significantly differ. Their NO3 - uptake rates were similar, while the NH4 + uptake rate of P. minor (Vmax=249.60 μmol gdw-1 h-1) was double that of P. antillarum (Vmax=104.50 μmol gdw-1 h-1) during the first 30 min of exposure to NH4 +. These results suggest that each Padina species utilizes different strategies to survive in their respective habitats.