  Historically, multiple populations in Globular Clusters (GCs) have been
mostly studied from ultraviolet and optical filters down to stars that are more
massive than ~0.6 solar masses. Here we exploit deep near-infrared (NIR)
photometry from the Hubble Space Telescope to investigate multiple populations
among M-dwarfs in the GC NGC6752. We discovered that the three main populations
(A, B and C), previously observed in the brightest part of the color-magnitude
diagram, define three distinct sequences that run from the main-sequence (MS)
knee towards the bottom of the MS (~0.15 solar masses). These results, together
with similar findings on NGC2808, M4, and omega Centauri, demonstrate that
multiple sequences of M-dwarfs are common features of the color-magnitude
diagrams of GCs. The three sequences of low-mass stars in NGC6752 are
consistent with stellar populations with different oxygen abundances. The range
of [O/Fe] needed to reproduce the NIR CMD of NGC6752 is similar to the oxygen
spread inferred from high-resolution spectroscopy of red-giant branch (RGB)
stars. The relative numbers of stars in the three populations of M-dwarfs are
similar to those derived among RGB and MS stars more massive than ~0.6 solar
masses. As a consequence, the evidence that the properties of multiple
populations do not depend on stellar mass is a constraint for the formation
scenarios.
