Specialized roots of Velloziaceae weather quartzite rock while mobilizing phosphorus using carboxylates

Campos rupestres is an extremely phosphorus (P)-impoverished rocky ecosystem in Brazil. Velloziaceae is an important plant family in this environment, and some species colonize exposed quartzite rock. However, we know virtually nothing about their root development and nutrient acquisition within the rock outcrops and their possible role in rock weathering and landscape formation. We tested the hypothesis that Velloziaceae dissolve P from the rock, enhancing rock weathering. The study was carried out with two Barbacenia species (Velloziaceae) that colonize quartzite rocks. We assessed the root specializations and exudates, and determined the mineralogical composition of the rocks. The quartzite rocks contained a low concentration of total P in a matrix composed predominantly of silica. Using transmission electron microscopy, we show root growth perpendicular to the rock-bedding planes. A micro-XRF set-up at the XRF beamline of a synchrotron evidenced root-associated rock dissolution. The investigated roots show novel morphological and physiological specializations, coined vellozioid roots, which are highly effective at P acquisition. These carboxylate-releasing roots function like other specialized roots in nutrient-depleted soils. The rocks represent a barrier for most species, but due to their chemical and physical actions inside the rocks, vellozioid roots play a pivotal role in rock weathering, contributing to shaping the campos rupestres landscapes.

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