PHOTOSYNTHESIS AND WATER RELATIONS OF ALMOND TREE CULTIVARS GRAFTED ON 2 ROOTSTOCKS

Five cultivars of Prunus amygdalus Batsch (Ferragnes, Ferrastar, Marco na, Garrigues, and Non Pareil) grafted on two different rootstocks (Ga rrigues and GF677), and two cultivars (Ferraduel and Casa Nova) grafte d on GF677, were grown for three years under rainfed conditions in an orchard in northeast Portugal. Net photosynthetic rate (P-N), leaf con ductance for water vapour (g(s)), leaf water potential (Psi), instanta neous water use efficiency (WUE), and internal CO2 concentration (C-i) were measured at three periods of the growing season: spring, summer (June or July) and late summer (September) over two years. Ferraduel, Ferrastar, and Marcona presented the best performance in the periods w hen environmental conditions were not very hard (May or September). Ca sa Nova and Non Pareil were well adapted to high air evaporative deman d, preventing the increase of leaf temperature (T-l). Ferrastar, altho ugh having a good performance in May and September, did well adapt to hard climatic conditions in June 1994. In the following year, although it presented the highest T-l, the values were not limiting (30.6 +/- 2.1 degrees C), and P-N was only decreased from May to July. Marcona w as highly dependent on T-l, but prevented its increasing. Garrigues sh owed lower PN in most measurement periods. GF677 frequently induced th e highest P-N, WUE, and Psi P. P-N was mainly dependent on T-l, radiat ion, C-i, month, and year. WUE depended on the same factors. Psi depen ded mainly on g(s), air temperature, month, and year.