PARENT SESSION
Oral Session #22: Plant function and response to stress. Presiding: K. Miyanishi.
Tuesday, August 7, 2001. 8:00 AM to 11:45 AM. Hall of Ideas P&Q.
Physiologic response of Carex planostachys (Cyperaceae) along a woodland to intercanopy patch gradient.
Wayne, E1, Van Auken, O1, Barnes, P2, 1 2
ABSTRACT- Juniperus ashei woodlands with associated intercanopy patches dominate the southern Edwards Plateau region of central Texas. Beneath these woodland canopies occur a xeric sedge, Carex planostachys (Cyperaceae), however this sedge does not occur in the intercanopy patches. Temporal and spatial changes in surface light levels and surface soil moisture were studied along with stress induced physiologic changes in C. planostachys. Light levels ranged from 296.8±143.8 
mol⋅m-2⋅s-1 (canopy) to 1824±31.0 mol⋅m-2⋅s-1 (patch) during summer and 39.2±7.2 mol⋅m-2⋅s-1 (canopy) to 561.6±257.1 mol⋅m-2 ⋅s-1 (patch) during winter. Gravimetric soil moisture ranged from 20.0±1.9% (canopy) to 22.8±1.1% (patch) during summer and 57.8±6.7% (canopy) to 43.6±1.0% (patch) during winter. Predawn xylem water potential (
p) of C. planostachys ranged from -6.5±0 MPa during summer to -0.1±0 MPa during winter. In addition, sedges that were watered with the equivalent of 2.54 cm of rainfall bi-monthly during summer were maintained at a p of -0.5±0 MPa. Carex planostachys also appears to reach a stable photosynthetic rate at low light levels (400 to 600 mol⋅m-2⋅s-1). In these Juniperus communities a gradient appears to exist with surface soil moisture higher and light levels lower under the woodland and the reverse trend in intercanopy patches. These gradients may facilitate the growth and survival of C. planostachys beneath the Juniperus woodland and exclude it from intercanopy patches.
KEY WORDS: Carex Planostachys, Juniperus, Water potential, Light saturation