Water-related Phenomena in Winter Buds and Twigs of Picea abies L. (Karst.) until Bud-burst: A Biological, Histological and NMR Study

This paper investigates the uptake, transport, state and self-diffusion of water in twigs and buds ofPicea abies L. (Karst.) trees in winter until reactivation in spring. The presence or absence of xylem in embryonic shoots, as well as the intensity and type of bud dormancy were also studied. Three clones of P. abies were grown in a forest in north-eastern France. The clones differed in their timing of bud-burst, with the two clones from the Vosges showing different degrees of early bud-burst and the clone from Poland showing late bud-burst. One-bud cuttings grown in standard forcing conditions showed a great difference in dormancy between the two provenances, but only a small difference between the two Vosges clones. Earliness of bud-burst was not strongly linked to the intensity of dormancy. A dye experiment combined with light microscopy indicated increased velocity of water transport in stems up to a maximum in April, initial entry of water into embryonic shoots, protoxylem differentiation in embryonic shoots from April, and then, shortly before bud-burst, water transport through the newly-formed protoxylem almost up to the meristem. Nuclear magnetic resonance measurements of the transverse relaxation time (T2) and the self-diffusion coefficient of water confirmed these observations and showed water availability in embryonic shoots. The sequence of water-related phenomena occurring in early spring was the same in the three clones, but was earliest in the Vosges clone with the earliest bud-burst and latest in the Polish clone with late bud-burst. The results imply that this sequence of water-related phenomena leads to bud-burst.