Abstract Coffea canephora plants (clone INCAPER-99) were submitted to low N (LN) or high N (HN) applica- tions and two watering regimes (daily irrigation and irrigation every 5 days for a month). Although water po- tential was not altered significantly by N, HN plants showed higher relative water content than did LN plants under water deficit. Only HN plants exhibited some abili- ty for osmotic adjustment. Plants from both N treatments increased their cell wall rigidity under drought, with a more pronounced augmentation in HN plants. In well- watered plants, carbon assimilation rate increased with increasing N while stomatal conductance did not respond to N supply. Under drought conditions, carbon assimilation decreased by 68–80% compared to well- watered plants, whereas stomatal conductance and tran- spiration rate declined by 35% irrespective of the N applications. Stable carbon isotope analysis, combined with leaf gas exchange measurements, indicated that re- gardless of the watering treatments, N increased the long- term water use efficiency through changes in carbon as- similation with little or no effect on stomatal behaviour. Keywords Carbon isotope composition · Coffee · Drought · Water deficit · Water use efficiency Introduction Plants may delay the onset of dehydration effects through a range of physiological strategies. For instance, both a decrease and an increase in the bulk modulus of elasticity (ε) may contribute to drought tolerance, for dif- ferent reasons. Decreased ε (higher elasticity) can lead to maintenance of cell turgor because the wall accommo- dates the smaller cell volume during dehydration. In- creased ε (lower elasticity) tends to favour maintenance of symplast volume rather than turgor by itself (Kramer and Boyer 1995). Osmotic adjustment has also been con- sidered as an adaptation to water deficit, by which a net increase of solute concentration in cells may help to maintain turgor, enabling plants to sustain metabolic activity, growth and productivity (Turner 1997). The nitrogen (N) status of a plant has a significant im- pact on its water relations (Morgan 1986; Tan and Hogan 1995). However, the N status has variable effects on plant water relations. For example, Morgan (1986) found that in wheat a greater amplitude of osmotic adjustment was associated with low N supply after withholding watering, while opposite responses in corn (Bennett et al. 1986) and tomato (García et al. 1996) have been ob- served. Furthermore, while N or water deficits usually decrease the rate of carbon assimilation (A), N limitation per se may affect stomatal behaviour in different ways; both increases (e.g., Livingston et al. 1999) and decreas- es (e.g., Lima et al. 1999) in stomatal conductance (g s ) have been noted. In part, fluctuations in environmental conditions at the time of measurements mask the effects of water stress and N nutrition on leaf gas exchange. Measurements of stable carbon isotope ratio (δ 13 C) of leaves can provide a useful long-term indicator of photo- synthetic performance and plant metabolism (Farquhar et al. 1989), not being affected by the prevailing conditions at the sampling time. The model developed by Farquhar et al. (1982) links δ 13 C to C 3 photosynthesis through the ratio of intercellular to ambient CO 2 concentration. Leaf δ 13 C is thus related to the ratio of A and g s , in such a way that it can be used to indicate the long-term water use efficiency (WUE) (Farquhar et al. 1989). Prolonged droughts severely restrict the mobility of N through dehydrated soil, and thus co-occurrence of water deficits and N limitations are common. Although the physiological responses of plants to either water or N stress have been extensively investigated, relatively few F.M. DaMatta ( ✉ ) · R.A. Loos · E.A. Silva · M.E. Loureiro Departamento de Biologia Vegetal, Universidade Federal de Viçosa, 36571–000 Viçosa, MG, Brazil e-mail: fdamatta@ufv.br Fax: +55-31-38992580 C. Ducatti Centro de Isótopos Estáveis Ambientais, Departamento de Física e Biofísica, Universidade do Estado de São Paulo, 18618–000 Botucatu, SP, Brazil Trees (2002) 16:555–558 DOI 10.1007/s00468-002-0205-3 ORIGINAL ARTICLE Fábio M. DaMatta · Rodolfo A. Loos Emerson A. Silva · Marcelo E. Loureiro Carlos Ducatti Effects of soil water deficit and nitrogen nutrition on water relations and photosynthesis of pot-grown Coffea canephora Pierre Received: 17 May 2001 / Accepted: 1 July 2002 / Published online: 13 August 2002 © Springer-Verlag 2002