Carbon isotope composition of sugars in grapevine, an integrated indicator of vineyard water status.

Photosynthetic carbon isotope composition (delta(13)C) was measured on sugars in mature fruits from field-grown grapevines. Sugar delta(13)C and summer predawn leaf water potential were significantly correlated. The survey of different vineyards during four growing seasons showed that sugar delta(13)C in must at harvest varied from -20 per thousand to -26 per thousand when conditions during berry maturation varied from dry to wet. This range allows a very sensitive detection of grapevine water status under natural conditions. However, local differences due to soil capacity to supply water to grapevines are maintained, whatever the annual water balance. Leaf nitrogen content variations of field-grown grapevines did not change delta(13)C values. Genetic variability of delta(13)C between 31 grapevine varieties for delta(13)C was observed. Must sugar delta(13)C can be used to characterize vineyards for their soil structural capacity to provide water to grapevines. It was concluded that isotope carbon composition in grapevine measured on sugars at harvest can be applied to compare the capacities of vineyard soils and canopy management to induce mild water stress in order to produce premium wines.