Root nutrient acquisition strategies change emergent properties at the community and ecosystem scales

Background/Question/Methods

Plant individual performance, community assemblage and ecosystem functions hinge on plant-plant interactions, of which the interaction between belowground roots is a major component. Analyses of how plants forage for belowground resources generally assume that the rooting system of an individual plant is spatially optimized to acquire soil nutrients from a “commons” pool available to all individual plants. While this commons assumption is a reasonable simplification, analyses of belowground interactions may be improved if we can incorporate the diversity of nutrient acquisition strategies that characterize plants in natural environments. Central to this question is the distinction between the commons nutrient pool vs. pools that can be privately accessed by individual plants; such common vs. private strategies of nutrient acquisition lead to fundamentally different dynamics and predictions.  We developed a novel individual-based plant model capable of considering both common and private acquisition strategies, including the private strategies of root priming and root-microbe symbioses. To capture the complexity of root interactions, we also consider strategies of plant-plant interaction including ‘Aggressive Hawk’, ‘Optimization Dove’ and ‘Avoidance’, which enables us to evaluate different game theoretical situations. 

Results/Conclusions

We found that – with or without competition with neighbors – the inclusion of private nutrient acquisition strategies shifted fine roots towards surficial soil layers with high organic nitrogen content. Specifically, when plants compete for a common resource we found an Evolutionary Stable Strategy (ESS) that favors a medium degree of plant-plant aggressiveness in root system overlap. However, when we added private strategies, this ESS shifted from aggressive towards optimization at the individual and community levels. This study implies the importance of private nutrient acquisition strategies in response to changes in global biogeochemical cycling, including CO₂ enrichment. Based on our model results, we will examine the local conditions under which plants would deploy different private strategies, and their implication on plant nutrient limitation.