Differential responses of macroinvertebrate ionomes across experimental N:P gradients in detritus-based headwater streams

Clay Prater,Lee M Demi,Punidan D Jeyasingh,Phillip M Bumpers,Amy D Rosemond

doi:10.1007/s00442-020-04720-x

Abstract

Diverse global change processes are reshaping the biogeochemistry of stream ecosystems. Nutrient enrichment is a common stressor that can modify flows of biologically important elements such as carbon (C), nitrogen (N), and phosphorus (P) through stream foodwebs by altering the stoichiometric composition of stream organisms. However, enrichment effects on concentrations of other important essential and trace elements in stream taxa are less understood. We investigated shifts in macroinvertebrate ionomes in response to changes in coarse benthic organic matter (CBOM) stoichiometry following N and P enrichment of five detritus-based headwater streams. Concentrations of most elements (17/19) differed among three insect genera (Maccaffertium sp., Pycnopsyche spp., and Tallaperla spp.) prior to enrichment. Genus-specific changes in the body content of: P, magnesium, and sodium (Na) in Tallaperla; P, Na, and cadmium in Pycnopsyche; and P in Maccaffertium were also found across CBOM N:P gradients. These elements increased in Tallaperla but decreased in the other two taxa due to growth dilution at larger body sizes. Multivariate elemental differences were found across all taxa, and ionome-wide shifts with dietary N and P enrichment were also observed in Tallaperla and Pycnopsyche. Our results show that macroinvertebrates exhibit distinct differences in elemental composition beyond C, N, and P and that the ionomic composition of common stream taxa can vary with body size and N and P enrichment. Thus, bottom-up changes in N and P supplies could potentially influence the cycling of lesser studied biologically essential elements in aquatic environments by altering their relative proportions in animal tissues.

Highlights

The biogeochemistry of stream ecosystems is currently being altered in myriad ways, including increases in alkalinity, heavy metals, and nutrients (Ferreira et al 2016; Kaushal et al 2018; Wurtsbaugh et al 2019)
We collected coarse benthic organic matter (CBOM) samples and macroinvertebrates as part of an experimental fivestream manipulative study conducted at the U.S.D.A Forest Service Coweeta Hydrological Laboratory, which serves as a long-term ecological research site in southwestern North Carolina, US
The relative proportions of other elements differed with Maccaffertium having the highest body content of most elements including Cd, Cu, Fe, S, and Si whereas Pycnopsyche showed the highest proportions of Ba, K, and Mn

Summary

Introduction

The biogeochemistry of stream ecosystems is currently being altered in myriad ways, including increases in alkalinity, heavy metals, and nutrients (Ferreira et al 2016; Kaushal et al 2018; Wurtsbaugh et al 2019). Nutrient loading can impact streams by altering the relative proportions of biologically essential elements in producer and consumer tissues and modifying their flows through aquatic foodwebs (Cross et al 2003; Singer and Battin 2007; EvansWhite et al 2009; Morse et al 2012; Johnson et al 2013). These changes can influence a variety of ecosystem functions including primary production, secondary production, decomposition rate, and whole-stream metabolism As these responses are collectively governed by bottom-up changes in elemental mass balance, it is critical to understand how N and P enrichment affects both organismal and ecosystem-level processes

Methods

Results

Conclusion