Ecophysiology of Two Native Invasive Woody Species and Two Dominant Warm-Season Grasses in the Semiarid Grasslands of the Nebraska Sandhills

Authors

Kathleen D. Eggemeyer, University of Nebraska-Lincoln
Tala Awada, University of Nebraska-LincolnFollow
David A. Wedin, University of Nebraska-LincolnFollow
F. Edwin Harvey, University of Nebraska-LincolnFollow
Xinhua Zhou, University of Nebraska-LincolnFollow

Document Type

Article

Date of this Version

9-18-2006

Citation

International Journal of Plant Sciences (2006) 167(5): 991-999.

Comments

Copyright 2006, University of Chicago. Used by permission.

Abstract

Populations of Pinus ponderosa and Juniperus virginiana are expanding into semiarid Sandhills grasslands in Nebraska. To evaluate the physiological basis of their success, we measured the seasonal course of leaf gas exchange, plant water status, and carbon isotope discrimination in these two native trees and two native C₄ grasses (Schizachyrium scoparium and Panicum virgatum). Compared to the trees, grasses had higher net photosynthetic rates (A_net) and water use efficiency (WUE) and more negative predawn and midday water potentials (Ψ) in June and July. While leaf Ψ and rates of leaf gas exchange declined for all four species during August, the Ψ_mid of the grasses were significantly more negative than those of the two trees. The deeply rooted trees maintained water status during summer, in contrast to the grasses, which senesced. Juniperus virginiana in particular was well adapted to xeric conditions, with low stomatal conductance, high WUE, and positive A_netat low Ψ. The highest values of A_netwere observed in May for J. virginiana and in May and September for P. ponderosa. Both species maintained low but positive A_net throughout the winter at temperatures above 0°C. Leaf carbon isotopic signature differed between tree and grass species but did not exhibit significant within species seasonal variability. The semiarid grassland climate of Nebraska does not appear to limit P. ponderosa and J. virginiana, which use growth during the non-growing season and access to deep soil moisture to compensate for growing-season drought.