A device for studying the influence of declining water table on poplar growth and survival

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.