Effects of nutrient supply and nutrient ratio on diversity–productivity relationships of phytoplankton in the Cau Hai lagoon, Vietnam

Diversity and productivity of primary producers are known to be influenced simultaneously
by resource availability and resource ratio, but the relative importance of these
two factors differed among studies and so far only entire phytoplankton communities
were investigated which might ignore specific nutrient requirements and stoichiometric
plasticity of different functional groups. We measured nutrient availability (DIN, total N
[TN], total P [TP]), nutrient imbalance (TN:TP, DIN:TP, N:Pseston), species richness, and
abundance of the whole phytoplankton community, as well as those specific for cyanobacteria,
diatoms, and dinoflagellates in Cau Hai lagoon in Vietnam. We determined the
correlation among these variables, using structural equation modeling. The models applied
to the whole phytoplankton community indicated that the nutrient availability
(particularly TP and DIN) drove variation in phytoplankton abundance and richness, and
that abundance also depended on species richness. The models applied to different
functional groups differed considerably from the entire community and among each
other, and only a part of the models was significant. The relationship between nutrient
availability (mainly TP) and abundance was driven by cyanobacteria, and the relationship
between nutrient imbalance (only with N:Pseston) and species richness was driven
by diatoms. Remarkably, the positive relationship between species richness and abundance,
as consistently observed for the whole phytoplankton community, was only observed
for one of the three functional groups (diatoms), indicating that resource
complementarity occurs particularly among species of different functional groups. Our
results emphasized that nutrient availability (TP and to a lesser extent DIN) as well as
nutrient imbalance (albeit only with N:Pseston as proxy) were driving factors for the phytoplankton
community in the Cau Hai lagoon and hence alterations in both of these
factors leading to a shift in phytoplankton species composition and productivity.

Publication year:2019

Keywords:abundance, functional groups, phytoplankton, resource availability, resource ratio, richness

CSS-citation score:1

Accessibility:Open