Early terrestrial ecosystems
The advent of land plants had important consequences for energy
and nutrient fluxes among terrestrial and freshwater ecosystems29,55
and hence for the evolution of animal groups that live in these
habitats. The vegetational changes of the Silurian and Devonian also
had a major impact on the atmosphere and other aspects of the
global environment. The evolution of roots is thought to have been
an important factor in the reduction of atmospheric CO2 concentrations
through increased weathering of Ca–Mg silicate minerals
brought about by mechanical disruption and soil acidification56,57.
Accelerated weathering has also been linked to the formation of
Devonian and Early Carboniferous marine black shales58, but this
requires further investigation in view of similar deposits earlier and
later in the geological record. Root-like impressions have been
recognized in Late Silurian palaeosols59, but the earliest unequivocal
evidence comes from Early Devonian vascular plants26, which have
modified prostrate stems bearing rhizoids resembling those of living
bryophytes. More substantial roots capable of anchoring large trees
evolved independently in several groups during the Middle to Late
Devonian.