Resource-use efficiency drives overyielding via enhanced complementarity
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ECOSYSTEM ECOLOGY – ORIGINAL RESEARCH
Resource‑use efficiency drives overyielding via enhanced complementarity Norman W. H. Mason1 · Kate H. Orwin2 · Suzanne Lambie1 · Deanne Waugh3 · Jack Pronger1 · Carlos Perez Carmona4 · Paul Mudge1 Received: 12 August 2019 / Accepted: 12 August 2020 © Springer-Verlag GmbH Germany, part of Springer Nature 2020
Abstract Overyielding, the primary metric for assessing biodiversity effects on ecosystem functions, is often partitioned into “complementarity” and “selection” components, but this reveals nothing about the role of increased resource use, resource-use efficiency, or trait plasticity. We obtained multiple overyielding values by comparing productivity in a five-species mixture to expected values from its component monocultures at a) six levels of nitrogen addition (spanning 0–500 kg N ha –1 year–1) and b) across four seasons. We also measured light, water, and nitrogen use, resource-use efficiency, and three functional traits—leaf nitrogen content, specific leaf area, and leaf area ratio—n mixtures and monocultures. We found strong evidence for non-transgressive overyielding. This was strongest in spring, with mixture productivity exceeding expected values by 20 kg dry matter h a–1 day–1. Peak overyielding was driven by enhanced complementarity, with the two non-N2-fixing forb species far exceeding expected productivity in mixtures. Peak overyielding also coincided with higher water use in the mixture than for any monoculture, and enhanced mixture-resource-use efficiency. There was only weak evidence that trait plasticity influenced overyielding or resource use. Our findings suggest that when complementarity drives overyielding in grassland mixtures, and this is made possible both by increased water use and enhanced efficiency in water, nitrogen, and light use. Our results also suggest that mixtures offer a viable compromise between productivity, resource-use efficiency, and reduced environmental impacts (i.e., nitrate leaching) from intensive agriculture. Keywords Agriculture · Forage · Functional diversity · Functional groups · Nutrient addition
Introduction
Communicated by Katherine Gross. Electronic supplementary material The online version of this article (https://doi.org/10.1007/s00442-020-04732-7) contains supplementary material, which is available to authorized users. * Norman W. H. Mason [email protected] 1
Landcare Research, Private Bag 3127, Hamilton 3240, New Zealand
2
Landcare Research, PO Box 40, Lincoln 7640, New Zealand
3
DairyNZ, Private Bag 3221, Hamilton 3240, New Zealand
4
Institute of Ecology and Earth Sciences, University of Tartu, 50407 Tartu, Estonia
Overyielding—i.e., greater biomass production in mixtures relative to monocultures of their component species—has been the primary metric for examining plant biodiversity effects on ecosystem functions this century (Isbell et al. 2018). Two types of overyielding are broadly recognised: non-transgressive—when mixtures exceed expected yield based on the sown proport
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