Lateral water exchange between shelf-margin upwelling and Kuroshio waters influences phosphorus stress in microphytoplankton

Abstract

Phosphorus stress in microphytoplankton was investigated in an upwelling system and an adjacent segment of the Kuroshio Current in the southern East China Sea. In June, August, and September 2007, 3 cruises were conducted, and alkaline phosphatase activity (APA) and the maximum quantum efficiency of photosynthesis (F v /F m ) were measured along a cross-shelf cruise track from the mid-shelf to the Kuroshio Current. In June and August, values of APA ranged from 1.41 to 9.56 pmol PO 4, and those of F v /F m ranged from 0.28 to 0.45 in surface waters. In September, a strong salinity front appeared between the upwelling zone and Kuroshio waters. Low APA values of 1.23 to 8.08 pmol PO 4 3 -(µg chl a) -1 min -1 were observed in the upwelling region, and high values of 34.9 to 77.6 pmol PO 4 3 -(µg chl a) -1 min -1 were observed in Kuroshio waters. A significant correlation between the APA and F v /F m only occurred in September, and a possible event of phosphate stress in Kuroshio waters was supported by high APA values and changes in the microphytoplankton species composition. Our results suggest that phosphorus stress in microphytoplankton is related to the magnitude of horizontal water exchange between the Kuroshio and upwelling waters.

Alkaline phosphatase activity at the southwest coast of India: A comparison of locations differently affected by upwelling

“…Interestingly, when APA at 5-m layer alone was considered, the values were 0.51 μM P h −1 nearshore and 2.23 μM P h −1 offshore. Similar results have also been observed by Liu et al (2010) in the lateral water exchange between shelf margins during upwelling in Kuroshio waters. Off Kochi there was no difference in APA between near and offshore waters both being around 5.2 μM P h −1 (Fig.…”

“…The APA depends on the availability of inorganic P in surface water, where phytoplankton dominates. Both in laboratory cultures and natural communities of phytoplankton, AP production is associated with low P which is greatly repressed when P is sufficient (Dyhrman and Ruttenberg, 2006;Kobori and Taga, 1979;Liu et al, 2010;Nausch, 1998;Ruttenberg and Dyhrman, 2005). Measurement of AP activity (APA) is done by addition of artificial substrates like para-nitrophenol phosphate (pNPP) to samples.…”

“…Several reports show that bacteria, fungi, protozoa and algae have the ability to secrete phosphatases at the cell surface or release them into their environments. In both free and organismassociated forms, AP is considered to be responsible for the generation of inorganic P from organic P in natural environments (Kwon et al, 2011;Liu et al, 2010;Nausch and Nausch, 2006). The APA depends on the availability of inorganic P in surface water, where phytoplankton dominates.…”

Joint effect of freshwater plume and coastal upwelling on phytoplankton growth off the Changjiang River

“…Besides the nutrient-replete CJ plume, in the ECS Liu et al (2010 explored the P stress of microphytoplankton by using APA and the maximum quantum efficiency of photosynthesis (Fv / Fm) assay. Similarly, the expression of APA was blocked on the surface of the upwelling region, and high APA was recorded on the surface of the CJ plume fringe.…”

Sequence diversity and expression levels of Synechococcus phosphate transporter gene in the East China Sea

“…The increase in fluorescence intensity during the incubation period was converted to an increase in 3-OMF using a standard curve constructed with purified 3-OMF (Sigma-Aldrich). The measured APA was expressed on a per cell basis as fmol PO 4 3− cell −1 min −1 (Liu et al, 2010).…”