Expl Agric. (2010), volume 46 (3), pp. 381–391 C  Cambridge University Press 2010 doi:10.1017/S0014479710000013 IMPROVING THE DEVELOPMENT OF COFFEA ARABICA AFTER CHANGING THE PATTERN OF LEAF GAS EXCHANGE BY WATERING CYCLES By PAULA NOVAES†,‡, JO ˜ AO PAULO SOUZA§,¶ and CARLOS HENRIQUE BRITTO ASSIS PRADO† †Universidade Federal de S˜ ao Carlos, Departamento de Botˆ anica, Laborat´ orio de Fisiologia Vegetal. Via Washington Luis, km 235, 13565–905, S˜ ao Carlos-SP, Brazil and §Universidade Federal de Goi´ as, Departamento de Ciˆ encias Biol´ ogicas. Avenida Dr. Lamartine Pinto de Avelar, 1120, 75704-020, Catal˜ ao-GO, Brazil (Accepted 13 January 2010; First published online 15 March 2010) SUMMARY Hardening of Coffea arabica saplings by watering cycles (WCs) might be a suitable practice to achieve higher tolerance to low leaf water potential ( leaf ) before transplanting to the field. As a consequence, hardening could promote growth and biomass gain during the initial development of C. arabica in the field. Thus, the less interrupted initial growth in a changing environment should confer higher flowering intensity in hardened than in control plants. The aim of this work was to verify if leaf gas exchange and  leaf behaviour of C. arabica saplings grafted on C. canephora showed consistent alterations during hardening by WCs and if this was effective to improve vegetative and reproductive growth under field conditions. For these reasons, saplings of the Mundo Novo cultivar of C. arabica grafted on C. canephora were submitted to seven WCs over 35 days. Each WC was completed when net photosynthesis was close to zero. The pattern of leaf gas exchange, mainly stomatal conductance (g s ), was modified permanently after three WCs and the new pattern of leaf gas exchange could result in a more positive water balance and less interrupted development of C. arabica saplings in the field, particularly due to permanent low values of g s . After field transplantation, hardened plants showed greater height and stem diameter, more leaves and branches, and superior biomass production in leaves, stem and roots than control plants in dry and wet periods. The number of flowers was also significantly higher in hardened than in control plants. On the other hand, similar values were found between control and hardened plants in the leaf area ratio and the shoot/root ratio. Therefore, previous hardening by WCs was effective in improving leaf gas exchange, vegetative and reproductive development under field conditions and maintained the original biomass partitioning among the main plant compartments in dry and wet periods. INTRODUCTION Hardening by watering cycles (WCs) decreases leaf osmotic potential, stomatal conductance (g s ) and growth (Ackerson and Hebert, 1981a; b; Franco et al., 2002). Stomatal responses to leaf water potential ( leaf ) can be modified when young plants are subjected to WCs (Ackerson, 1980; Brown et al., 1976; Jones and Turner 1978). Hardening improves tolerance to lower values of  leaf and increases water use efficiency (WUE) (B˜ anon et al., 2006; S´ anchez-Blanco et al., 2004). The maintenance ‡Corresponding author: paulanovaes.botanica@gmail.com ¶Current address: Programa de P´ os-Graduac ¸˜ ao em Ecologia e Conservac ¸˜ ao de Recursos Naturais, Universidade Federal de Uberl˜ andia, 38400-902, Uberl˜ andia – MG, Brazil