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

Abstract

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.

Recent advances and future research in ecological stoichiometry

“…We highlighted the lack of ES studies in terrestrial ecosystems in a previous review to evaluate topics such as the GRH, relationships of elemental stoichiometry with trophic web function and species composition in ecosystems and communities (Sardans et al, 2012). Several recent studies have provided further evidence that changes in the N:P ratios of media (water or soil) or food affect the structure of food webs in terrestrial ecosystems (Fanin et al, 2013;Zechmeister-Bolstenstren et al, 2015;Paseka and Grunberg, 2019) and other studies have observed this link in aquatic ecosystems (Plum et al, 2015;Sitters et al, 2015;Lee et al, 2017;Zhao et al, 2018b;Nhu et al, 2019). Shifts in organismic stoichiometry throughout trophic webs due to changes in excreted stoichiometry and/or resource use (nutrients, light, water) have provided new insights into the changes in community composition, dynamics, and functionality in freshwater and marine ecosystems (Glibert et al, 2011;Hillebrand and Lehmpfuhl, 2011;Hessen et al, 2013;Plum et al, 2015;Galbraith and Martiny, 2015;Vanni and McIntyre, 2016;Filipiak, 2016;Moorthi et al, 2017;Vanderploeg et al, 2107;Branco et al 2018;Moody et al, 2018;Mousing et al, 2018;Prater et al, 2018;Spilling et al, 2019;Tanioka and Matsumoto, 2019).…”

“…The link between N:P ratios and diversity in freshwater ecosystems, particularly in lakes, has been well studied, providing clear pathways to account for this link. For example, diversity and N:P ratios tend to be negatively correlated in marine plankton (He et al, 2013) and coastal lagoon phytoplankton (Nhu et al, 2019), which has been attributed to lower rates of transfer of matter and energy along short trophic webs under P limitation (Elser et al, 2010). However, resource stoichiometry is not a unique factor of community diversity.…”

Combined effect of warming, nutrients, and species pool size on the seasonal variability of phytoplankton composition: A modeling perspective

“…While modeling studies applying this theory to planktonic communities mostly relied on food web dynamics and stoichiometry (e.g., Morozov et al 2019; Sandhu et al 2020), our results suggest that the inclusion of temperature effects could be important in further exploration of the paradox. Besides nutrient loads, nutrient supply ratios can affect phytoplankton community composition, partly due to resource use complementarity among different functional groups (Nhu et al 2019). Based on the decisive role of the N/P ratio in the presented simulations, our model further suggests that it might additionally affect phytoplankton community responses to rising mean temperatures, which is an under‐researched aspect.…”

Ecological stoichiometry influences phytoplankton alpha and beta diversity rather than the community stability in subtropical bay

“…In contrast, He et al ( 2013 ) found that the N:P ratio was negatively correlated with the phytoplankton diversity index in the spring near Weizhou Island in the northern South China Sea. N:P ratios were also negatively correlated with species richness of the entire phytoplankton community in the Cau Hai Lagoon in Vietnam (Nhu et al, 2019 ). A possible explanation for these inconsistent results is that the positive correlation between the N:P ratio and phytoplankton diversity in our study was based on evaluation of samples collected on a spatio‐temporal scale (different sites, four seasons), whereas the results from the other studies were obtained during one individual season or several months within a short time period.…”