using a portable assimilation chamber. Prediction of Pn was satisfactory under normal conditions of air temperature (T,), vapour pressure deficit (VPD) and I, in
glasshouse production. Discrepancies between measured and estimated rates of Pn occurred under high I, (more than 700 pm01 photon m -2s-1),T, (over25”C) andVPD (morethan 1.5kPa),and can possibly be attributed to effects of stomata1 closure on the net photosynthetic rate.