Effects of water stress and nocturnal temperature on carbon allocation in the perennial grass, Leymus chinensis

Water deficit and high temperature often occur simultaneously, but their effects on plants are usually investigated separately. The aim of this study was to test how interactions between water stress and nocturnal warming affect carbon allocation in the perennial grass, Leymus chinensis. Plant biomass, dry mass allocation, C-14 partitioning and carbon isotope composition (delta(13)C) were measured. Severe and extreme water stress during nocturnal warming decreased the allocation of dry mass and C-14 partitioning below ground to the roots, but moderate water stress significantly increased the below-ground allocation of dry mass and C-14, especially at the lower night temperature. The delta(13)C values were more positive at day/night temperatures of 30/20degreesC than at 30/25degreesC, and greater in the roots than in the leaves. By plotting the delta(13)C values of the leaves against the delta(13)C values of the roots, the slopes of regressions were steeper at low than at high night temperature, also indicating that nocturnal warming reduces carbon allocation below ground to the roots. The results suggest that nocturnal warming may weaken acclimation during water stress in this species by regulating carbon allocation between source and sink organs.