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June 2017 WINES&VINES 55 PRACTICAL WINERY & VINEYARD GRAPEGROWING plants at regular intervals and demonstrated that shoot and root dry matter accumulation were related. Regulation of the shoot-to-root ratio is not imposed by morphology. There are, in gen- eral, an excess of potential meristems in both the shoot and root that are not activated and, in practice, the control of plant form is achieved by selected suppression of meristem growth. In 1983, R. Brouwer suggested that the rela- tive growth rate of various organs is a reflection of the environment in which the plant is grow- ing. In a specific environment, this results in a "functional equilibrium," in which root growth is limited by the supply of assimilates from the shoot, while shoot growth is limited by the sup- ply of nutrients from the roots. 2 The mutual dependence of shoot and root growth results in a balance in their develop- ment with a result that, under low fertility conditions and/or sites with limited water availability, root growth will be favored at the expense of shoot growth (see "Influence of Soil Fertility on Root and Shoot Distribution" on this page). Conversely, in shade, shoot growth will be favored over root growth. However, unlike the herbaceous plants used by R. Brouwer, fruit is a third important sink of grapevines and the most important compo- nent to the viticulturist. Approximately 20% of the final bunch dry weight has been accu- mulated by véraison. 25 The remaining 80% is accumulated from véraison to harvest, and during this period fruit is the dominant sink for carbohydrates. An inadequate leaf area or excessive yield (depending on the capacity of the site, variety and target soluble solids) will slow sugar ac- cumulation by the fruit 19 and deprive roots and shoots (in particular trunks) of the reserves necessary for spring growth. (See "Thinning and Trimming Impact on Soluble Solids and Titratable Acidity" on page 56.) The conservative nature of carbohydrate distribution between the various sinks was dem- onstrated by Stan Howell and colleagues. 6 In their experiments, a range of clusters from none to six were retained on pot-grown Seyval Blanc vines. Total cluster dry weight increased with the greater cluster number, but the shoot, leaf, wood and root dry weight decreased, with the result that the total vine dry weight remained the same regardless of the number of clusters on the vine. Their experiments demonstrated the conserva- tive nature of dry matter accumulation by vines and the effect that that over-cropping may reduce reserves in the shoot and root systems necessary for shoot development the following spring. (The figure "Influence of Site Capacity and Yield on Equilibrium" on page 57 conceptualizes this ef- fect using the grapevine triangle.) Pneumatic Stand for Foil Spinner Contact us today! 575 ird St. Bldg. A Napa CA 94559 707-255-6372 | napafermentation@aol.com www.napafermentation.com Takes 27-32 ml Capsules Spinner is 110v Table Top Unit INFLUENCE OF SOIL FERTILITY ON ROOT AND SHOOT DISTRIBUTION Root growth is favored over shoot growth in the unfertile site, while the reverse is true in a fertile site. The overall capacity of the vine may also be increased as fertility increases. Shoot Root Shoot Root Unfertile site Fertile site 21208 State Road 113, Knights Landing, CA Phone: 530-735-6821, Cell: 530-379-5007 www.guillaumenurseries.com Where Experience is a Tradition • ENTAV Licensee • 2010 Protocol material available • Certified virus and disease test protocol