Environmental and Experimental Botany 75 (2012) 258–267 Contents lists available at ScienceDirect Environmental and Experimental Botany j o ur nal homep age : www.elsevier.com/locate/envexpbot Restricted root-to-shoot translocation and decreased sink size are responsible for limited nitrogen uptake in three grass species under water deficit V. Gonzalez-Dugo c,1,2 , J.L. Durand a,∗,2 , F. Gastal a,2 , T. Bariac b,2 , J. Poincheval a,2 a Unité de Recherche Pluridisciplinaire Prairies et Plantes Fourragères, INRA, BP6, F-86600 Lusignan, France b UMR 7618 BIOEMCO, Université Pierre-et-Marie-Curie–CNRS–INRA, Centre de recherche INRA–INA PG, Bâtiment EGER, 78850 Thiverval-Grignon, France c Instituto de Agricultura Sostenible – CSIC, Alameda del Obispo, s/n 14004, Córdoba, Spain a r t i c l e i n f o Article history: Received 8 July 2010 Received in revised form 11 July 2011 Accepted 13 July 2011 Keywords: Dactylis glomerata Festuca arundinacea Growth Lolium multiflorum Nitrogen concentration Split-root a b s t r a c t Earlier studies showed that water deficit reduces nitrogen (N) uptake and N nutrition index of grasses. So far, the main effect of water deficit on N uptake and N nutrition status was ascribed to the alteration of the transpiration-dependent transport of mineral N in the soil solution. A split-root experiment was performed to determine whether plant and/or solution water potential could alter N uptake and allo- cation, independently of N fluxes in the soil solution. The split-root experiment allowed to manipulate separately the water and the N status of the root environment and of the plant, by various combina- tions of addition of polyethylene glycol 6000 (PEG) and mineral N on half or on the entire root system. Tall fescue, Italian ryegrass and cocksfoot, known for their contrasted sensitivities to water deficit, were studied. The addition of PEG largely reduced water and N uptake of the roots on which it was applied (half or entire root system). A significant accumulation of N was observed on the roots to which PEG was added, particularly in cocksfoot and tall fescue, hypothetically contributing to the alteration of N uptake. Cocksfoot displayed a high plasticity in N allocation to leaves related to sheaths, allowing the maintenance of N concentration and therefore its N status despite the reduction in N uptake. By contrast, leaf N concentration and N status of tall fescue and Italian ryegrass was more sensitive to water deficit, similarly to observations of the effect of drought in field studies. Therefore, it is concluded that the effect of soil solution potential on N uptake and plant N allocation may also contribute to the observed effect of drought on N status of grass crops, additionally to the effect of drought on the transfer of mineral N in the soil solution to the root surface. However, the importance of this physiological effect varies among species. © 2011 Elsevier B.V. All rights reserved. 1. Introduction It has repeatedly been observed that soil water deficit alters crop nitrogen (N) nutrition, even if mineral N is fully available in the soil, leading to a lower shoot N concentration, a lower crop N status, and therefore to a crop N deficiency (Lemaire and Denoix, 1987; Onillon et al., 1995; Gonzalez-Dugo et al., 2005, 2010). Once soil water deficit is removed, N uptake is restored if N is still available in the soil (Buljovcic and Engels, 2001; Gonzalez-Dugo et al., 2005). Crop N uptake is regulated by N availability at the root surface, which depends on soil water content and on soil water movement through both mass flow and diffusive water fluxes (Gonzalez-Dugo ∗ Corresponding author. Tel.: +33 5 49 55 60 94; fax: +33 5 49 55 60 68. E-mail address: jldurand@lusignan.inra.fr (J.L. Durand). 1 Present address. 2 With the technical collaboration of G. Bardou b , P. Biron b , L. Cousson a , A. Eprinchard a , G. Millet a , P. Richard b , J.-P. Terrasson a (see Appendix A). et al., 2010; Durand et al., 2010). Garwood and Williams (1967) demonstrated the interaction between local water and N content of soil layers and the growth of perennial ryegrass in the field, by injecting nutrients at controlled depths in soil. During soil water deficit, the decline in soil N supply to roots may induce a crop N deficiency that contributes, together with the direct effect of plant water deficit per se, to the overall resulting effect of soil water deficit on crop growth (Gonzalez-Dugo et al., 2010). However, in addition to the effect of the water-dependent trans- port of mineral soil N to the root surface, water deficit also has major physiological effects on N uptake and N economy of the plant. By experimentally manipulating root water uptake and plant water fluxes independently of N availability at root surface (PEG, split-root experiments), several studies showed that a reduction in plant water uptake may limit N uptake (Nicolas et al., 1985; Larsson, 1992; Buljovcic and Engels, 2001; Cayet, 2001). Further- more, beyond affecting N uptake, water deficit may also alter N assimilation and N allocation between plant organs. Water deficit alters nitrate reductase activity (Larsson, 1992, Azedo-Silva et al., 0098-8472/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.envexpbot.2011.07.009