Effects of nitrogen and phosphorus on the abundance and cell size of planktonic nanoflagellate communities

Danielle Goeldner Pereira,Gustavo Mayer Pauleto,Fábio Amodêo Lansac-Tôha,Luis Mauricio Bini,Luiz Felipe Machado Velho

doi:10.1590/s2179-975x2013005000009

Danielle Goeldner Pereira, Gustavo Mayer Pauleto + Show 3 more

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https://doi.org/10.1590/s2179-975x2013005000009

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Abstract

AIM: We experimentally investigated the effects of nutrients (Nitrogen and Phosphorus) enrichment on the density, biomass, and cell size of pigmented and heterotrophic plankton nanoflagellates communities. METHODS: The experiment was done in mesocosms in a tropical reservoir during a 19-day period. Four different treatments were carried out: Control (non-nutrient addition - C), phosphorus additions (P), nitrogen addition (N) and phosphorus + nitrogen addition (N + P). Each treatment was performed in triplicate, sorted randomly, thus giving a total of 12 experimental carboys, which were placed transversely in the middle of the reservoir. RESULTS: In general, pigmented and heterotrophic nanoflagellates fractions responded to nutrient addition, increasing densities and biomass values at the fertilized treatments. Opposed to expected, enriched treatments resulted in a slight decrease in mean cell size of the pigmented fraction. Moreover, in nutrient-rich treatments, pigmented nanoflagellates had higher relative abundance than in the control. CONCLUSIONS: Our results indicate that: i) the density and biomass of nanoflagellates responded to the nutrient enrichment, mainly when N and P were added together; ii) the pigmented and heterotrophic fractions showed distinct time responses to fertilization; iii) the growth of nanoflagellate community seems to be co-limited by N and P; iv) the nutrient enrichment led to a greater pigmented than heterotrophic fraction contribution; and v) among the analyzed variables, nanoflagellate densities seem to be more sensitive to changes in nutrient availability than biomass or mean cell size.

Highlights

The effects of nutrient fertilization and the importance of bottom-up control on aquatic communities are both current subjects of discussion (Auer et al, 2004; Samuelsson et al, 2006)
The density, biomass, and mean cell size of the nanoflagellate community were affected by nutrient addition, paralleling results obtained in several experimental studies (Jansson et al, 1996; Gilbert et al, 1998; Simek et al, 2003)
The increase in the abundance of PNF and HNF as a response to the increase in nutrient availability is frequently reported in non-manipulative studies (Gasol et al, 1995; Hwang and Heath, 1997; Hobbie et al, 1999; Auer and Arndt, 2001; Samuelsson et al, 2002, 2006; Auer et al, 2004) showing the influence of the lake trophy on the abundance and biomass of distinct compounds of the planktonic food web

Summary

Introduction

The effects of nutrient fertilization and the importance of bottom-up control on aquatic communities are both current subjects of discussion (Auer et al, 2004; Samuelsson et al, 2006). Studies on planktonic communities have shown that eutrophication leads to an increase in the abundance of classical grazing food web, and affects the microbial food web components such as bacteria and protozoan communities (Sipura et al, 2005; Pagioro et al, 2005; Samuelsson et al, 2006). Regarding the nutrient effects on the abundance of different fractions of plankton communities, some studies observed that, in general, the autotrophic fraction dominated at oligotrophic conditions, and the heterotrophic contribution increased with increase in trophic status of the ecosystems (Auer et al, 2004; Samuelsson et al, 2006). More resources lead to a replacement of smaller by bigger individuals in distinct fractions of microbial communities (Kress et al, 2005; Sabetta et al, 2005; Sipura et al, 2005; Samuelsson et al, 2006)

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