Benefits and costs of mycorrhizal associations vary along the acquisitive–conservative plant strategy spectrum

Abstract

The acquisitive–conservative spectrum of plant strategies is a well-supported interspecific trade-off axis: Compared to acquisitive species that prioritize resource allocation to functions promoting carbon fixation, conservative species tend to grow slower because a larger amount of resources is allocated to functions promoting survival. However, mycorrhizal allocation—potentially beneficial or costly to the plant—has not been fully integrated into this framework. We developed a model predicting plant growth along a soil fertility gradient, incorporating mycorrhizal allocation. Plant strategies are defined using the acquisitive–conservative spectrum, while mycorrhizal fungal strategies are defined based on how beneficial fungi are to plants and their sensitivity to soil fertility. Our results predict that conservative species exhibit greater mycorrhizal allocation under optimality than acquisitive species when paired with similar fungi in the same environment. This allocation difference across plant strategies becomes more prominent for plant associations with ectomycorrhizal versus arbuscular mycorrhizal fungi. Mycorrhizal allocation improves conservative species' growth across broader ranges of fungal strategies and soil fertilities, even to the point that they can achieve growth rates comparable to or exceeding those of acquisitive species in infertile soils when acquisitive species' mycorrhizal interactions (fungal strategy or allocation) are suboptimal. Our findings highlight broader ecological and evolutionary implications of trade-offs in mycorrhizal allocation for plant resource allocation. Ecologically, variation in mycorrhizal costs and benefits along the acquisitive–conservative spectrum can affect plant coexistence. Evolutionarily, greater opportunities to benefit from mycorrhizae may select for more optimized plant–mycorrhizal relationships, especially for conservative species.