Seasonal and Diurnal Water Relations of Selected Forest Species

Abstract

Leaf diffusive conductance, leaf water potential, and leaf osmotic potential measurements were made on one tree species and three woody brush species on north and south aspects in the Priest River Experimental Forest of northern Idaho. Douglas maple (Acer glabrum) and western white pine (Pinus monticola) occurred on both aspects. Sitka alder (Alnus sinuata) and mallow ninebark (Physocarpus malvaceus) occurred only on north and south aspects, respectively. Physocarpus on the south aspect attained osmotic and leaf water potentials near ‐30 bars and daytime leaf diffusive conductances (reciprocal of resistance) near 0.3 cm/s. The Pinus on this site attained osmotic and leaf water potentials near °25 bars and leaf diffusive conductances near 0.06 cm/s. Osmotic potential and leaf water potential decreased to a minimum specific to each deciduous species as the season progressed. The Alnus and Acer species exhibited osmotic potentials near ‐16 bars with the Acer leaf water potential decreasing further to near ‐20 bars. The Pinus maintained a uniform osmotic potential between ‐20 and ‐25 bars throughout the year. Leaf diffusive conductance appeared to be controlled during the day by a combination of atmospheric demand, soil moisture availability, and plant adaptation to water stress. Stomatal control of leaf water potential was evident in Pinus on both aspects and in the brush species on the north but not on the south aspect.