2007 was an abnormally wet spring in western Kansas. Creeks were at or above their banks for much of late spring and early summer. As summer progressed, creek water receded to low levels. Trees near creeks were monitored to determine the effects of decreasing water availability on leaf-level processes. Shallow-rooted trees were expected to be affected to a greater extent than deep-rooted trees. To test this hypothesis, trees were monitored weekly during the transition from saturated soils to drier soils during the 2007 growing season. Shallow-rooted honeysuckle (Lonicera tatarica) plants were compared to deep-rooted American elm (Ulmus americana) and hackberry (Celtis occidentalis) trees. Leaves were monitored for changes in stomatal conductance, transpiration, δ¹³C, δ¹⁵N, leaf temperature, and heat losses via latent, sensible, and radiative pathways. These changes were monitored weekly and were related to changes in soil water potential.

Results/Conclusions

Soil water potentials around the shallow roots of Lonicera significantly decreased as the creek receded. In contrast, soil water potentials remained near zero at deeper rooting depth. Despite being rooted at the drier shallow depths, Lonicera plants used water more freely compared to the deeper-rooted Celtis and Ulmus plants. Lonicera had significantly greater leaf transpiration rates and lower leaf δ¹³C compared to the deep-rooted species. Leaf temperatures in Lonicera were significantly lower than the other species, making rates of sensible heat loss lower. Moreover, leaves of Lonicera were significantly smaller than Celtis and Ulmus, creating a correspondingly smaller boundary layer and a lower resistance to heat and water loss. δ¹⁵N was significantly higher in Lonicera leaves compared to Celtis and Ulmus. Heavy nitrogen is likely the result of fertilizer runoff in the creeks. It was concluded that high stomatal conductances and increased ability to take up nitrate from creek waters might help explain the invasive success of Lonicera tatarica in riparian systems.