Consequently, they are widely used by plant biologists. However, their application has some drawbacks as well. First, conditions in growth chambers are generally the furthest away from those in the field, not only becauseenvironmental values are often programmed within a relatively small diurnal range, but also with regard to the absolute values of, for example, light and temperature, at which they operate (Garnier and Freijsen 1994). Second, although growth chambers
enable a strong temporal control over conditions, spatial variability is often larger than anticipated and higher than
those measured in experimental gardens. For example, light intensity may vary from place to place in the growth chamber (Granier et al. 2006) and can be especially lower close to the walls (Fig. 2a). Another often ignored gradient relates to the vertical light profile: the closer the plants grow to the lamps, the higher the light intensity. For rosette species like Arabidopsis this is not a point of concern, but erect species may experience substantial gradients, especially when they grow over 40 cm tall (Fig. 2b). As growing taller is inevitably connected to development, plants that are older or in later stages of development often experience significantly higher light regimes than younger ones; despite this, differences in plant characteristics are then often associated with development and not with changed light conditions. Adjusting lamp height to a fixed distance relative to the top of the shoot may partly mitigate the fact that plants that grow faster because of, for example, a higher nutrient supply, will by consequence also grow faster because they experience higher light levels and higher temperatures. These examples illustrate that even in controlled environments it is not easy to separate different environmental/developmental responses from each other