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

Abstract

The control and precise definition of the humidity conditions in experiments on bryophyte performance under controlled conditions is important. However, this aspect is often neglected in ecophysiological and ecological research. The construction, operation and application of growth chambers with a computer-controlled regulation of ambient relative humidity (RH) is described and the chamber performance is characterized. The chambers have moist rockwool at the bottom and are fitted with Plexiglas plates, one fan and one RH sensor each. Evaporation from the plant material and the moist substrate give an increased relative humidity within the chamber and a stable RH is obtained 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 filters were used on the lids. Chamber temperature followed the temperature of the surroundings, with a lag in temperature drop during night. The stability of the RH levels is dependent on the difference in humidity between chamber and external environment and this gave diurnal humidity fluctuations in chambers regulated at levels near the extremes of a wide humidity gradient. More constant RH levels were obtained with a shorter RH range and optimum performance of the regulation system was obtained when the difference in RH between chamber and the surroundings was moderate. Thus, optimal performance and the widest range of applications can be achieved when humidity and temperature of the external environment can be controlled. Temperature differences among chambers were small and did not affect the humidity gradient. The system permits a convenient and accurate regulation of RH with a short- and long-term stability and reliability.