Michael E. Van Nuland, Ian M. Ware, Joseph K. Bailey, and Jennifer A. Schweitzer
Plants take up nutrients from the soil to grow and build important structures like leaves and roots. As plants interact with their environment (including the soil bacteria and fungi that live belowground), these nutrients eventually cycle back belowground to create a feedback loop. These feedback loops can effectively lock plants and soils into different nutrient cycles: plant populations in fertile soils have nutrient-rich leaves that decompose quickly and return lots of nutrients back to the soil, whereas plants in nutrient-poor soils have less-nutritious leaves that do not add much nutrients belowground, thus perpetuating the infertile conditions. While these types of nutrient feedbacks have been well-studied from an ecological perspective, here we show their importance for understanding plant evolutionary processes.
We first measured leaf nutrients, growth traits, and soil chemistry in different populations of Populus angustifolia, a dominant tree that grows along riverbanks throughout the Rocky Mountains. We observed that the populations had different levels of soil nitrogen (N). In addition, the N-rich populations had higher nutrient concentrations in their leaves and larger growth traits compared to populations in N-poor soils, suggesting that these populations are locked into different nutrient cycles. To understand whether these nutrient feedback loops had evolutionary consequences, we grew genetic clones from each population in a greenhouse environment. Here, plants were inoculated with the various soil biotic communities from the different populations to see if their fitness changed depending on which group of microorganisms they interacted with. Much like how sports teams receive a boost from their home fans, Populus trees from nutrient-rich soils grew best with their “home” soil microbes. This suggests that these plants are adapted to, and have coevolved with, their soil microbes under their N-rich nutrient cycles. In addition, these home-team dynamics seem to reinforce the feedback loops by adjusting soil nutrient levels according to whether the plants and microbes came from fertile or infertile soil conditions. Overall, these results show that the way plants interact with their soil environment is directly connected to the way they evolve, and vice versa.
This paper is part of the cross-journal Special Feature: Eco‐Evolutionary Dynamics Across Scales.