There is growing observational evidence that disk evolution is stellar-mass dependent. In this talk,
I will show that these dependencies extend to the atomic and molecular content of disk atmospheres.
I will summarize the main results from a unique dataset of high-resolution Spitzer/IRS spectra from
8 very low-mass star and brown dwarf disks. I will present the first detections of ionized neon,
molecular hydrogen, carbon dioxide, and water in these disks and discuss implications for the heating
and ionization of disk atmospheres. Finally, I will show that BD disks have on average higher
C2H2/HCN and HCN/H2O line flux and column density ratios than T Tauri disks. I will speculate on the
implications of these trends for the O/C ratio in inner disks and the bulk composition of rocky planets.
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