Abstract
Despite the sophistication of contemporary growth chambers, growing conditions cannot be uniformly controlled during experiments. Uniformity trials with bean (Phaseolus vulgaris cv. Spartan) and maize (Zea mays cv. Golden Bantam) in the McGill University Phytotron identified three significant sources of variability. First, not even two identically programmed chambers of the same model and from the same manufacturer provide identical growing environments. Second, programmed environmental conditions are not precisely maintained over time even in a single chamber. Third, the growing environment within a chamber has a consistent pattern of spatial variability with poor growth in the chamber corners and best growth in the center. The importance of these effects varies with species and with the parameters measured, but none can be entirely avoided. Good experimental design with replication of treatments across chambers and blocking within chambers can minimize the negative impact of these sources of uncontrolled experimental variability.
Highlights
The increasing popularity of growth chambers in the last 20 years has been encouraged by two factors: (i) the ability to simulate a wide variety of growth conditions independent of conditions prevailing outdoors, and (ii) the widely held perception that growth conditions can be precisely and uniformly controlled in commercially available chambers
Beans The analysis of variance with repeated measurements (ANOVAR) on height of beans reveals that three betweensubject effects are statistically significant (Table 1)
Our results indicate that experiments using even the most sophisticated of contemporary chambers can still not be assumed to be free of uncontrolled variations in growing conditions
Summary
The increasing popularity of growth chambers in the last 20 years has been encouraged by two factors: (i) the ability to simulate a wide variety of growth conditions independent of conditions prevailing outdoors, and (ii) the widely held perception that growth conditions can be precisely and uniformly controlled in commercially available chambers. In a uniformity trial with bean, Potvin and Tardif (1988) recognized three potential sources of variability in growth chamber experiments: variation within chambers over time (problems of temporal replication), variation between chambers, and the interaction of these two effects. When lettuce was grown in a series of trials involving growth chambers in several laboratories, more variability was found among repetitions within a laboratory than among laboratories (Hammer et al 1978). Such variability in growth chamber experiments has been recognized for a long time (Langhans 1978), but its implications for experimental design in controlled environments are still too often ignored
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