The Direct and Interactive Effects of Warming and Species Interaction on Plant Functional Traits

Abstract

Global climate change is a threat that continues to affect nearly every ecosystem on the planet through warmer temperatures, changes in precipitation patterns, and many other manifestations of a warmer world. Warming directly and indirectly affects plants and ecosystem functioning. In the natural world, both the direct and indirect effects of warming impact plant communities and the ecosystem functions simultaneously. Here, we conducted an experiment to determine how the direct and indirect effects of warming impacts plant functional traits in an alpine ecosystem. We leveraged an existing warming experiment in the Upper Gunnison Valley Basin in Colorado, USA. The ongoing 6-year study elevates plot temperatures using open-top warming chambers and manipulates species composition by removing the dominant plant species at a high and low elevation to evaluate the direct and indirect effects of warming on ecosystem structure and function. We sampled plant species from within the plots to answer a series of interrelated questions focused on how shifts in warming and species interactions alters plant functional traits: (1) How does warming directly alter plant functional traits? (2) How does removing the dominant species alter plant functional traits by shifting species interactions? (3) Will warming and species removal interact synergistically to alter plant traits? We hypothesized that: (1) Warming will shift the individual and community-wide traits to be more conservative by exacerbating water-stress in a moisture-limited environment. (2) Removing the dominant species will shift the plant community to be more acquisitive as the remaining plants are released from competitive pressure. (3) Warming and species removal will have counteractive effects on plant functional traits, possibly neutralizing the simulated effects of climate change on plant communities when both treatments occur simultaneously. Our results confirmed that warming and species removal have opposing effects on community shifts, though not in the direction that was expected. By comparing trait values within a species across the warming and removal treatments, we did not see overall shifts in most traits. The shifts in communities are therefore driven by shifts in the relative abundance of species as climate change selects for plant species that are best adapted to warmer environments in the absence of the dominant species, creating winners and losers in the plant community. From our results, it is evident that direct and indirect effects of climate change counteract each other rather than amplify each other. Functional traits of plants remain an effective lens through which we can observe the pathways through which climate change drives shifts in ecosystem structure and function.

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