Re-centering the hidden half of plant–plant interactions: moving beyond root biomass to architectural-chemical-microbial traits framework

Abstract

Plant–plant interactions are central to understanding species coexistence, community assembly and succession, as well as ecosystem function. Yet empirical studies of plant interactions continue to privilege aboveground responses and whole-plant biomass, leaving the subterranean dimension comparatively underexamined. Even when roots are considered, interaction strength is often inferred from standing root biomass. This practice risks collapsing a multidimensional suite of mechanisms—spatial pre-emption, resource foraging strategies, chemically mediated interference, and microbially shaped feedbacks—into a single outcome variable. As a result, biomass-based inference may obscure whether interactions are competitive or facilitative, and why they vary across contexts and shape coexistence. To substantiate this argument, we conducted a targeted survey of 346 peer-reviewed articles on plant–plant interactions retrieved from the Web of Science, which revealed a prevailing emphasis on aboveground responses and root biomass. We therefore argue that the field must move from an aboveground-anchored narrative to an explicitly belowground-informed framework. Additionally, root biomass should be complemented by architectural and chemical root traits, evaluated within their environmental and biotic context. We outline a framework integrating root architectural and chemical traits, as well as rhizospheric microbes for root–root interactions, emphasizing context dependence. We then identify a focused set of testable predictions, and propose minimum reporting recommendations that balance feasibility and mechanistic insight. Re-centering root interactions in this way should improve the interpretability and comparability of plant-plant interaction studies, and strengthen predictions of community dynamics under global change.