Stoichiometric constraints on phytoplankton resource use efficiency in monocultures and mixtures

Franziska Frank,Maren Striebel,Michael Danger,Helmut Hillebrand

doi:10.1002/lno.11415

Abstract

AbstractA central concept for understanding the mechanisms linking diversity and primary production or more general, ecosystem functioning, is resource use efficiency (RUE). It quantifies the amount of biomass production over time relative to unit resource supplied, that is, represents a quota of matter use efficiency. Given anthropogenic alterations of biogeochemical cycles, the consequent changes in supply rate and especially supply ratio of nutrients will change. Using four species of freshwater phytoplankton, and their mixture, we asked how the RUE for nitrogen and phosphorus depends on the stoichiometry of resource supply and how this differs between single species and their mixture. We conducted a factorial laboratory experiment spanning 25 different nutrient supply treatments with differing absolute and relative nitrogen (N) and phosphorus (P) concentrations. N and P supply increased biomass production and decreased C : nutrient ratios and RUE for the respective nutrient, but always significantly affected by the supply of the respective other nutrient. Biomass peaked at molar N : P supply ratios above the Redfield ratio (18–22). Species tended to respond similarly to the resource gradients. Consequently, mixtures outperformed the component species only during early growth responses, but not regarding maximum biomass and RUE. Bioassays performed at the end of the main experiment revealed predominance of N‐limitation, but again strongly depending on the interaction between both nutrient gradients. Our study suggests that stoichiometric constraints of resource incorporation and RUE need to be accounted for when studying the response of phytoplankton to natural and anthropogenic variation in resource availability.

Highlights

resource use efficiency (RUE) has been defined as the production realized per unit of the Resource use efficiency & stoichiometry limiting resource (Chapin 1997; Nijs and Impens 2000)
Bringing RUE into a multiple resource limitation perspective, metacommunity models (Gross and Cardinale 2007; Hodapp et al 2016) and experiments (Gamfeldt and Hillebrand 2011; Hillebrand and Lehmpfuhl 2011; Gülzow et al 2019) have shown that the stoichiometry of resource supply alters the efficiency of using available resources
Algal stoichiometry During exponential growth, nutrient incorporation reflected mainly the absolute availability of the respective nutrient, that is, C : N decreased and N : P increased with Nsupply, C : P decreased with Psupply (Table 2, Supporting Information Fig. A2)

Summary

Introduction

How efficiently limiting nutrients are taken up and used for production, especially in context with biodiversity, has recently been assessed in terms of resource use efficiency (RUE), both in field situations (Ptacnik et al 2008; Filstrup et al 2014; Verbeek et al 2018; Hodapp et al 2019) and experimental resource gradients (Cardinale et al 2009a; Hillebrand and Lehmpfuhl 2011). Changes in the balance of resource ratios occur either naturally depending on the species present and their differences in uptake preferences and nutrient recycling (Sterner 1990; Elser and Urabe 1999; Evans-White and Lamberti 2006; Danger et al 2007; Plum et al 2015), or due anthropogenic changes in relative nutrient availability (e.g., Elser et al 2009) with variable effects over spatiotemporal scales (Elser et al 2009; Beusen et al 2016; Greaver et al 2016; Yan et al 2016)

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