Abstract
Arboreal termites are widely recognized for the ecological functions of their conspicuous nests, yet their interactions with the underlying soil remain poorly understood. Here, we provide the first comprehensive characterization of the hypogeal constructions associated with the arboreal termite Constrictotermes cyphergaster and evaluate their effects on soil properties across two contrasting pedological contexts in a semiarid environment in Brazil. We documented a consistent subterranean system composed of a central chamber and radiating tunnels connected to arboreal nests by a single gallery, revealing a poorly recognized vertical extension of the colony. The architecture of these hypogeal structures was independent of arboreal nest size, suggesting a functionally regulated subterranean component. By comparing soils collected from hypogeal constructions, soil beneath nests, and surrounding soil controls, we show that termite activity modifies soil chemistry and physical structure, but in a context-dependent manner. In hydromorphic Stagnosol soils, termite constructions increased porosity and pH, and base cation concentrations, indicating effects on soil structure and biogeochemistry cycling. In nutrient-poor Regosol soils, termite influence was primarily expressed through the accumulation of organic matter and nitrogen. Across both soil classes, hypogeal chambers exhibited higher nutrient content, revealing these structures as biogeochemical hotspots. Our findings demonstrate that C. cyphergaster functions as a dual-strata ecosystem engineer, integrating arboreal and subterranean environments through a cryptic yet ecologically consequential hypogeal system. These results redefine the ecological footprint of arboreal termites and highlight their potential role in enhancing soil functioning in semiarid landscapes.