PARENT SESSION
Contributed Oral Session 16: Photosynthesis and Water Relations: Conductivity; Stress
Monday, August 8, 8:00 AM - 11:30 AM, Meeting Room 524 A, Level 5, Palais des congrès de Montréal

Light requirements for a xeric sedge in a Juniperus woodland.

Wayne, E.¹, Van Auken, O.¹, ¹ The University of Texas at San Antonio, San Antonio, TX

ABSTRACT- Carex spp. are widespread throughout the world including portions of the United States, but most occur at high latitude or high elevation. In addition, most occur in mesic communities. However, Carex planostachys (cedar sedge) occurs in the understory of some xeric Juniperus woodlands of central Texas. Standing crop biomass of C. planostachys was measured and varied spatially (one way ANOVA, p < 0.05), ranging from 28.0 ± 7.4 g⋅m^-2 below the canopy, to 111.6 ± 13.9 g⋅m^-2 at the canopy edge to 5.8 ± 3.6 g⋅m^-2 in the intercanopy. Leaf xylem water potential also varied spatially (one way ANOVA, p < 0.001), ranging from -2.8 ± 0.1 MPa below the canopy to -4.2 ± 0.2 MPa at the canopy edge. Photosynthetic active radiation (PAR)did not vary spatially (one way ANOVA, p > 0.05), ranging from 318 ± 132 mol⋅m^-2⋅s^-1 below the canopy to 762 ± 279 mol⋅m^-2⋅s^-1 at the canopy edge. Instantaneous net photosynthesis varied spatially (ANCOVAR, p < 0.05), ranging from 4.0 ± 0.9 mol CO₂⋅m^-2⋅s^-1 below the canopy to 5.4 ± 0.8 mol CO₂⋅m^-2⋅s^-1 at the canopy edge. Dark respiration did not vary (one way ANOVA, p > 0.05), ranging from -0.56 ± 0.22 mol CO₂⋅m^-2⋅s^-1 to -0.95 ± 0.24 mol CO₂⋅m^-2⋅s^-1. Light saturation was between 300 — 600 mol⋅m^-2⋅s^-1 (PAR). Light compensation values were between 8 and 11 mol⋅m^-2⋅s^-1 (PAR). Carex planostachys appears to survive in a xeric J. ashei understory. Spatial differences in C. planostachys growth and physiology appear related to available light and soil moisture. It seems well adapted to the low light environment of Juniperus woodlands.

Key words: Juniperus, Carex planostachys, physiology, understory