Influence of insulating dead leaves and low temperatures on water balance in an Andean giant rosette plant

. The influence of insulating dead leaves on water balance in Espeletia timotensis Cuatr., an Andean caulescent giant rosette plant, was studied under field and laboratory conditions. Removal of the dead leaf layer surrounding the stem changed the pattern of diurnal stem temperature variation and produced transient and permanent effects on water balance. The pattern of liquid water flow resistance increase at low stem temperatures suggested that much of the water flow in the stem was through living membranes, probably those of the pith cells. The pith was determined to be an important source of stored water for daily transpirational needs. The lethal effects of dead leaf removal were attributed to one or more of the following causes: (1) inhibition of pith recharge by subfreezing stem temperatures; (2) embolisms in stem xylem; (3) freezing injury to pith tissue. The results suggested that an insulating layer of marcescent leaves and the presence of an internal water reservoir closer to the rosette than the soil water are important adaptations for maintenance of a favourable water balance in tropical alpine habitats where freezing temperatures occur regularly but last only a few hours.