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Environmental characterisation

• Light, air temperature, VPD (Vapour Pressure Deficit) are measured every minute (values averaged and recorded every 15 minutes). Measurements are taken at 6 points in the greenhouse at plant level. Light and VPD mapping is carried out several times a year to precisely characterise the climatic gradients in the greenhouse. The experimental design and data analysis must take these gradients into account.

• The temperature of organs is measured every minute (values averaged and stored every 15 minutes) on 8 plants distributed in the greenhouse according to the gradients described above. This gives access to the temperature actually experienced by different plant organs (leaves, meristems). For example, the temperature of the leaves and the air can vary by more than 8°C.

The temperature of the meristematic zone of studied organs is measured with fine copper-constantan thermocouples

• Impact of plant movement : Plant movement can potentially impact plant growth. The growth of plants placed on the conveyor is compared with those that are not moving.

Control of soil water status

• The relevant physiological variable for soil water status is water potential but the variable for control is water content. Pots and plants are weighed several times a day (depending on evaporative demand). The volume of water in the soil is determined by the total weight minus the weight of the pots, dry soil and the estimated weight of the plant.
  Soil water content is determined by dividing the volume of water by the weight of dry soil. The water potential of the soil is calculated via a water release curve.

• A sub-sample of plants is weighed continuously. Transpiration is calculated every 15 minutes.

Measurement of leaf area and plant biomass

The images are taken on 2 axes (top and side view). These images are analysed to separate the plant from the rest of the image (segmentation process). The result is shown below. The predicted biomass correlates very well with the measured biomass (see example below).

Plant architecture and individual organs

More sophisticated image analysis is being developed to individualise organs and determine their geometry.

Efficiency of radiation use

Measurements of intercepted radiation and estimated biomass could be used to calculate radiation use efficiency (under development).