Historically, ecosystems in the southwestern United States derived much of their nitrogen (N)
from N-fixation in biological soil crusts. Today, these regions have highly reduced crust
cover, and atmospheric deposition may be the dominant source of N. This study investigates
the effects of increased nitrogen deposition on nitrogen uptake, photosynthesis, and growth
of the two main forage grasses on the Colorado Plateau, galleta (Hilaria jamesii [Torr.]
Benth.) and Indian ricegrass (Oryzopsis hymenoides,[Roemer & JS Schultes] Ricker ex …

Rising atmospheric N deposition will impact ecosystems worldwide. This study investigated
the effects of spring and summer NH4+ and NO3–inputs on 2 rangeland grasses (C3 and
C4) on the Colorado Plateau. Both grasses took up N derived from NH4+ or NO3–in spring,
but only the C3 grass increased in cover, while a summer-active annual invader had the
greatest growth response overall to summer-applied NO3–. Simultaneously declining N
inputs from biological crusts in spring and increasing atmospheric N deposition at any time …