Abstract
Riparian poplar forests are declining downstream from many dams in the western prairie regions of North America. Drought-induced seedling and sapling mortality caused by abrupt drops in water table level following river flow regulation may be contributing to this forest decline. Here we describe a device, the rhizopod, for studying the influence of a changing water table on poplar seedling survival and growth. Seeds of a natural poplar hybrid (Populus deltoides x P. balsamifera) were planted in five rhizopods and treated to water table declines of 0, 1, 2, 4, or 8 cm day(-1). Each rhizopod consisted of 15 growth tubes connected to a central water reservoir through which the water level was regulated. Seedling survival was over 90% in rhizopods in which water table declined by 0, 1 or 2 cm day(-1), but was reduced to about 40% and less than 25% in rhizopods in which the water table level declined by 4 and 8 cm day(-1), respectively. Maximum shoot height, leaf number, and leaf area were observed in the rhizopod with a constant water table and decreased progressively with increasing rates of water table decline. Maximum root mass and length were observed in plants subjected to declines in water table level of 0 and 1 cm day(-1), respectively.
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