Resource-enhancing global changes drive a whole-ecosystem shift to faster cycling but decrease diversity.

Anu Eskelinen,W Stanley Harpole,Risto Virtanen,Susan Harrison,Kelly Gravuer,Yann Hautier

doi:10.1002/ecy.3178

Abstract

Many global changes take the form of resource enhancements that have potential to transform multiple aspects of ecosystems from slower to faster cycling, including a suite of both above- and belowground variables. We developed a novel analytic approach to measure integrated ecosystem responses to resource-enhancing global changes, and how such whole ecosystem slow-to-fast transitions are linked to diversity and exotic invasions in real-world ecosystems. We asked how 5-yr experimental rainfall and nutrient enhancements in a natural grassland system affected 16 ecosystem functions, pools, and stoichiometry variables considered to indicate slow vs. fast cycling. We combined these metrics into a novel index we termed "slow-fast multifunctionality" and assessed its relationship to plant community diversity and exotic plant dominance. Nutrient and rainfall addition interacted to affect average slow-fast multifunctionality. Nutrient addition alone pushed the system toward faster cycling, but this effect weakened with the joint addition of rainfall and nutrients. Variables associated with soil nutrient pools and cycling most strongly contributed to this antagonistic interaction. Nutrient and water addition together, respectively, had additive or synergistic effects on plant trait composition and productivity, demonstrating divergence of above- and belowground ecosystem responses. Our novel metric of faster cycling was strongly associated with decreased plant species richness and increased exotic species dominance. These results demonstrate the breadth of interacting community and ecosystem changes that ensue when resource limitation is relaxed.

Highlights

There is substantial evidence that anthropogenic global changes can modify plant community productivity, diversity, and trait composition in natural ecosystems (Stevens et al 2004, Bobbink et al 2010, Harrison et al 2015, Alstad et al 2016, Franklin et al 2016)
Using a novel analytic framework designed to measure transitions of ecosystems from slow to fast cycling, we demonstrate that resource-enhancing global changes can concordantly alter ecological functions, pools, and stoichiometry variables both above- and belowground, and result in a whole-ecosystem transition from slower to faster cycling in a natural grassland ecosystem
We demonstrate that this transition is associated with increased dominance by exotic species and loss of plant diversity in our system, suggesting that resource-enhancing global changes have the potential to simultaneously reduce diversity and alter ecosystem functioning

Summary

Introduction

There is substantial evidence that anthropogenic global changes can modify plant community productivity, diversity, and trait composition in natural ecosystems (Stevens et al 2004, Bobbink et al 2010, Harrison et al 2015, Alstad et al 2016, Franklin et al 2016). These shifts in aboveground communities are likely to modify multiple ecosystem functions and processes simultaneously and alter linkages between above- and belowground subsystems (Wardle et al 2004, De Deyn et al 2008). Global changes that increase limiting resources for plant and microbial growth

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Conclusion