A globally replicated experiment shows that long-term environmental filters constrain plant response to increased temperature and loss of foundation species

Background/Question/Methods

The functional properties of plants' roots, shoots, and leaves indicate resource use patterns of the whole plant and determine how plants interact with their neighbors, how they respond to changes in their environment, and how ecosystems cycle matter and energy. Here, we report on a globally coordinated experimental network where we manipulate temperature and remove the dominant plant species from a community at both high and low elevations. We ask how environmental context and the baseline trait composition of the plant community determine the relative influence of environmental change and species interactions on plant community structure and function. At each experimental location, at two sites separated by ~500 m of elevation, we set up thirty-two 4 m² plots in a 2 x 2 factorial design crossing warming with open-top greenhouse chambers (~2° C growing-season air warming; ~1° C topsoil warming) and removal of the most abundant plant species. We measured plant community composition, leaf and root plant traits (leaf mass:area ratio, root mass:length ratio, and leaf and root N and P), soil respiration, and total soil carbon in the experimental plots.

Results/Conclusions

After three years of warming and removal of dominant plant species at the experimental location in Colorado, plants with a lower leaf mass:area ratio increased disproportionately in relative cover in response to the removal of the dominant plant species; however, this response was observed only at the high-elevation site. Plants with a lower root mass:length ratio tended to increase in relative abundance in the absence of competition from the dominant species as well, again primarily at the high-elevation site, but the magnitude of this effect was weaker. The responses of soil carbon fluxes and storage, in contrast, were largely decoupled from both the aboveground and belowground plant trait response; the soil respiration rate and total soil carbon did not depend on plant species removal at either site, but respiration rate increased moderately with warming. Our results indicate that long-term environmental filtering for plants with particular trait syndromes caused by resource limitation, in this case water stress at the low elevation, may constrain the responses of plant communities to both anthropogenic environmental change and species loss. In coming years, our globally replicated experimental design will allow us to test the generality of this effect and its relationship with other environmental factors.