Design, technical specification, and operation of growth chambers with a computer-controlled system for regulating relative humidity suitable for ecophysiological experiments with bryophytes

The control and precise definition of the humidity conditions in experiment s on bryophyte performance under controlled conditions is important. Howeve r, this aspect is often neglected in ecophysiological and ecological resear ch. The construction, operation and application of growth chambers with a c omputer-controlled regulation of ambient relative humidity (RH) is describe d and the chamber performance is characterized. The chambers have moist roc kwool at the bottom and are fitted with Plexiglas plates, one fan and one R H sensor each. Evaporation from the plant material and the moist substrate give an increased relative humidity within the chamber and a stable RH is o btained by removing excess humidity. The RH is monitored and controlled by a fan which starts and draws humid air out of the chamber at user-selected RH levels. Horizontal light gradients were found to be small when neutral f ilters were used on the lids. Chamber temperature followed the temperature of the surroundings, with a lag in temperature drop during night. The stabi lity of the RH levels is dependent on the difference in humidity between ch amber and external environment and this gave diurnal humidity fluctuations in chambers regulated at levels near the extremes of a wide humidity gradie nt. More constant RH levels were obtained with a shorter RH range and optim um performance of the regulation system was obtained when the difference in RH between chamber and the surroundings was moderate. Thus, optimal perfor mance and the widest range of applications can be achieved when humidity an d temperature of the external environment can be controlled. Temperature di fferences among chambers were small and did not affect the humidity gradien t. The system permits a convenient and accurate regulation of RH with a sho rt- and long-term stability and reliability.