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

Grazielle Sales Teodoro, Hans Lambers, Diego L. Nascimento, Patrícia de Britto Costa, Denisele N. A. Flores-Borges, Anna Abrahão, Juliana L. S. Mayer, Alexandra C. H. F. Sawaya, Francisco Sérgio Bernardes Ladeira, Dalton Belchior Abdala, Carlos A. Pérez and Rafael S. Oliveira

a) Barbacenia tomentosa growing on their natural substrate of quartzite rock in campos rupestres; b) Root specialization - vellozioid roots - in B. tomentosa showing dense root hairs; c) Scanning electron micrograph of the root hairs of B. tomentosa; d) Rock slices, the fissures in the rocks represent the tunnels and channels resulting from root activities. A root can be viewed in this slice.
a) Barbacenia tomentosa growing on their natural substrate of quartzite rock in campos rupestres; b) Root specialization – vellozioid roots – in B. tomentosa showing dense root hairs; c) Scanning electron micrograph of the root hairs of B. tomentosa; d) Rock slices, the fissures in the rocks represent the tunnels and channels resulting from root activities. A root can be viewed in this slice.

Campos rupestres, grassy-shrubby mountaintop vegetation interspersed by rock outcrops in the cerrado domain in Brazil, is one of the most phosphorus (P)-impoverished ecosystems in the world. In this environment there are some species that colonize the bare rock. However, we know nothing about their root development in this hard substrate,  how plants can acquire nutrients or their influence on the weathering process.

Thus, we investigated the roots of two species (Barbacenia) from the Velloziaceae, an important family in campos rupestres. The two Barbacenia species colonize directly the quartzite rocks. We tested the hypothesis that Velloziaceae dissolve P from the rock, enhancing rock-biological weathering in campos rupestres thorough chemical and physical actions. For this, we investigated the roots and the rock substrate using different methods and we discovered a new root specialization.

The quartzite rocks in campos rupestres contained a low concentration of P in a matrix composed mainly of silica. Some Velloziaceae occur directly in the bare rocks, and proliferate their roots inside the rocks. The roots of these Barbacenia species release substances into the rocks called organic acids, which dissolve the quartzite and release soluble P, mostly from rare minerals containing rare earth elements such as cerium and yttrium.

This special root that we showed in Velloziaceae species has never been recorded before, and we coin the term “vellozioid roots” for this newly described structure. These roots are very effective at P acquisition in the hard substrate. These vellozioid roots play an important role in rock weathering, contributing to shaping the entire landscape of the campos rupestres, a biodiversity hotspot.

Read the paper in full here.

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