Short-term plant-soil feedback experiments cannot predict the competitive outcome of long-term field experiments

Causal sequences or "feedback" between plants and soil microbial communities play an important role
in plant community structure.
To predict this synergistic coexistence, the researchers conducted short-term, pairwise experiments based on mathematical theories — measuring how the two plants responded to growing in the
soil in which they were grown.
But does it really work?

Utah State University ecologist Noelle Beckman and his colleagues Ray Dybzinski of Loyola University Chicago and David Tilman of the University of Minnesota measured plant-soil feedback from six perennial prairie grasses in a short-term greenhouse study and said their findings were inconsistent
with those of long-term experiments conducted at the Cedar Creek Ecosystem Science Preserve in Minnesota.
They reported their findings
in the October 8, 2022 issue of the journal Ecology.
Their research was supported
by the National Science Foundation.

Beckman, an assistant professor in USU's Department of Biology and USU's Center for Ecology, said, "As the theory of bidirectional feedback measures advances, the number of short-term experiments has exploded
.
" "However, few studies have linked
pairwise comparisons of plant growth in short-term experiments to predictions of coexistence with the results of competitive interactions in the field.
"

Plant-soil feedback, she said, is expected to change
with nutrient availability.

Dybzinski, assistant professor at LUC's Institute for Environmental Sustainability, said: "The pairwise feedback measure is only valid if two species exhibit internal equilibrium, but this condition holds only for
two of the four possible outcomes of species interactions.
" "To make predictions using all four possible outcomes, you need to measure plant biomass in uncultured soil, which is methodologically challenging and therefore rarely done
.
"

In their short-term experiment, the team measured plant-soil feedback under low and high nitrogen availability in a greenhouse study using soil
monoculture from the field.

"Our study provides important insights
into the use of short-term greenhouse experiments to predict paired competition outcomes at different nitrogen levels," Beckman said.
"Our results show that we still have a lot to learn about these feedbacks, and that we can specifically extrapolate the results
of long-term coexistence from short-term experiments.
"

Journal Reference:

1. Noelle G.
   Beckman, Ray Dybzinski, David Tilman.
   Short‐term plant– soil feedback experiment fails to predict outcome of competition observed in long‐term field experiment.
   Ecology, 2022; DOI: 10.
   1002/ecy.
   3883