Abstract
The northern Adriatic is highly productive and shallow area characterized by numerous spatio-temporal gradients (e.g. nutrients, salinity, temperature). It is strongly influenced by numerous freshwater inputs, mainly from Po river. Its current systems as well as Po river, generates gradients of phosphate availability with an expressed N/P imbalance and phosphate limitation. A number of recent studies characterized these gradients as major factors affecting abundance and composition of microphytoplankton communities. Focus of this study is on two Leptocylindrus species, Leptocylindrus aporus (F.W. French & Hargraves) D. Nanjappa & A. Zingone 2013 and Leptocylindrus hargravesii D. Nanjappa & A. Zingone 2013. Species belonging to Leptocylindrus genus are frequently observed and have high abundances and also high contributions to the microphytoplankton community in this area. We focused on their morphological and physiological responses to phosphate limitation in situ and also performed in vitro experiments. In this study we report data on species specific growth rates under phosphorus (P) deplete and P rich conditions, localization and characteristics of alkaline phosphate activity, phosphate uptake rates as well as their morphological differences in P deplete versus P rich conditions. Our in vitro experiments showed that both Leptocylindrus species morphologically reacted similarly to phosphorus depletion and showed significantly elongated pervalvar axis in P depleted conditions if compared to P rich conditions. Also average chain lengths increased when in P depleted conditions. Two previously mentioned adaptations indicate their tendency to increase cellular surface areas available for alkaline phosphatase. Chlorophyll fluorescence of both species significantly decreased in P depleted medium. Although both species morphologically reacted similarly, our experiment demonstrated significant differences in physiological reactions to P depleted conditions.
Highlights
French & Hargraves 1986 was raised to species level as L. aporus
Leptocylindrus cultures CIM869 and CIM874 were taxonomically identified with light microscopy and DNA barcoding as L. aporus and L. hargravesii respectively
L. aporus and L. hargravesii are fairly new species and in our long term dataset they are combined within Leptocylindrus spp
Summary
Leptocylindrus Cleve, 1889 (Bacillariophyta, Leptocylindraceae) is a genus of centric diatoms. Cells contain various numbers of plastids which are of variable s hape[1] Their simplicity results in significant difficulties for the identification (to species level) by light microscopy. Some phytoplankton species are highly sensitive to phosphorus (P) availability, which affects physiological performance and biochemistry (e.g. photosynthetic efficiency, biovolume, growth...) It affects the composition and abundance of marine phytoplankton c ommunities[4,14,15]. We focus on two Leptocylindrus species, L. aporus and L. hargravesii Both are new to the Adriatic Sea and one of them is only recently described. We report data on species specific growth rates under different nutrient regimes, phosphate uptake rates, alkaline phosphatase activity, localization and activation patterns and characteristics of alkaline phosphatase activity, P uptake dynamics and changes in the lipid composition as well as their morphological reactions to phosphate limited conditions
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