MONDAY, SEPTEMBER 23, 2024. BY STAN GRANT, VITICULTURIST.
“Out of sight, out of mind” is an old saying that can apply to grapevine roots. Roots exist and function in the invisible world below ground, where their activities are fundamental to overall vine growth, health and productivity. That being so, root health and functioning are evident in the growth and condition of grapevine canopies (Figure 1). In this article, we will consider grapevine roots and root systems, as well as how rootstocks can influence them.
Figure 1. The condition of grapevine canopies reflects the health and functioning of their supporting root system. Photo: Progressive Viticulture, LLC©.
What Roots Do
Roots extend within the upper part of the vineyard soil, which is appropriately named the root zone. In so doing, they anchor grapevines in place, as well as mine water and mineral nutrients. These root functions are well known.
There are equally important root functions that are less familiar. Roots, especially older woody roots, store nutrient reserves. Carbohydrates and some mineral nutrients, including nitrogen, are among the nutrients stored in woody root tissues. These nutrients are remobilized to support early season shoot growth until shoots develop sufficient leaves and photosynthetic capacity to sustain themselves. Later in the growing season, under stressful conditions stored carbohydrate reserves may supplement other sources.
While old roots are important, young roots are where the action is. The sections of young roots immediately behind the root tips are the primary sites of water and mineral nutrient uptake. Hormones that promote shoot growth and development are synthesized in root tips and subsequently translocated to shoots. In addition, root tips exude organic compounds and nutrients into the soil adjacent to them (the rhizosphere) to encourage the growth of microorganisms beneficial to vines. In season, we can enhance the activities of young roots with certain stimulatory materials applied through drip irrigation, including some fertilizers formulated with organic compounds.
Grapevine Root Systems and Methods for Their Characterization
Compared to other cultivated plants, grapevine root systems are extensive, their root densities (roots per unit soil volume) are comparatively low and their root numbers slowly decrease as they radiate away from vine trunks. In their natural habitats, these attributes allow vine roots to extend among the roots of neighboring plants and effectively compete with them for soil resources.
The extensive, low density properties of grapevine root systems, however, make them challenging to study. The excavation of entire well-established grapevine root systems is seldom practical, and it is even less so when several vines are involved for rootstock comparisons. Consequently, few researchers have done so. Instead, most researchers have evaluated portions of grapevine root systems and drew inferences about them from their observations.
The oldest and most common method involves counts and size classification of roots within grids on exposed walls of trenches positioned at some specified distance from vines. Usually, trenches are positioned parallel to the vine row (Figure 2). This appears to be a valid approach, as root densities in trenches made parallel and perpendicular to vine rows differed negligibly, at least in deep, fairly uniform soils. An alternative but less common method for characterizing grapevine root systems involves auger borings made at specific distances from trunks and between specific depths below the soil surface.
Figure 2. Grapevine roots exposed on the wall of a trench oriented parallel with a vine row. Photo: Progressive Viticulture, LLC©.
Rhizotrons are a more recent method of characterizing grapevine root systems. These are clear, often tubular devices containing cameras that allow nearly continuous monitoring of roots adjacent to them. While their limited fields of view restrict their capacities for broad characterization of root systems, their steady monitoring facilitates documentation of root growth and development.
Grapevine Root System Distribution
University of California viticultural researchers conducted an extensive study of published research and concluded that all rootstock varieties have similar vertical and horizontal root distributions. Therefore, the differences between rootstock influences on grapevines growth and productivity must reside in other factors, such as their interactions with scion varieties, water and mineral nutrient uptake capacities, root life spans and root system densities. Before exploring these possibilities in the next section of this article, we will consider general aspects of grapevine root distribution, which again, are somewhat independent of rootstock.
While grapevines have deep root systems that can extend 20 feet or more below the soil surface, on average, 63% of grapevine roots reside in the top 24 inches of soil and 80% reside in the upper 40 inches of soil. The concentration of roots in upper root zones is largely due to greater aeration and fertility in topsoils compared to subsoils.
As noted above, grapevine root systems spread extensively horizontally. Consequently, there is substantial root system overlap between adjacent vines within vineyard rows regardless of vine spacing. Simultaneously, the angle of primary roots at the base of trunks becomes increasingly downward oriented, roots penetrate more deeply, and root systems become progressively denser as vines are spaced more closely together.
Soil conditions, unlike rootstock, influence grapevine root distribution. Soil structure and stoniness are among root distribution altering factors. Compact subsoil layers or the presence of a water table can alter the depth of grapevine roots (Figure 3). If berms are present in rows of vines, roots will be most concentrated in them.
Figure 3. A subsurface hardpan restricts the extent of grapevine roots to the depth of the topsoil. Photo: Progressive Viticulture, LLC©.
It follows that soil management actions which modify soil conditions can also influence root distribution. For instance, clean cultivation and permanent cover crops decreased grapevine roots in the top 8 to 12 inches of vineyard soils. Root pruning and intense competition for soil resources, respectively, were likely causes.
Rootstocks and Grapevine Root System Density – Influences on Grapevine Growth Capacity
Two studies conducted with irrigated vines on well-drained soils in warm areas (Fresno County, California and the Mildura region, Australia) provide insight into the basis for rootstock influences on grapevine growth capacity. They involved Thompson Seedless vines on their own roots and on Ramsey rootstock (a.k.a. Salt Creek).
In both studies, vines on Ramsey had denser root systems than vines on their own roots. In the US study, vines on Ramsey produced more structural roots, more root tips, and left more root casings than own-rooted vines at nearly all depths and distances from trunks. In the Australian study, vines on Ramsey had more fine roots (≤ 0.5 mm) and higher root densities than own-rooted vines on three alkaline soils (pH ≈ 8.5) of differing textures. In addition, on coarse and moderately coarse soils, the density of vine roots on Ramsey decreased more slowly at radial distances away from the vine trunks than did own-rooted Thompson Seedless vines.
In these instances, the denser root systems of vines on Ramsey exploited a larger portion of root zones than own-rooted vines, thereby providing greater access to soil water and mineral nutrients. Further, the greater number of root tips of vines on Ramsey gave them greater uptake capacity. At the same time, the numerous root tips of Ramsey produce and export more growth stimulating hormones (cytokinins) towards shoots than less invigorating rootstocks, such as 1613C.
Roots are one of the grapevine growth balance factors (Figure 4). Accordingly, vines with denser root systems and their comparatively high level of root activity are associated with greater overall growth, including growth of leaves and berries. This is the basis for the documented enhancing influence of Ramsey on the growth and fruit production capacity of the vines grafted to it.
Figure 4. A grapevine growth balance triangle illustrating the importance of root growth to both leaf and berry growth. Photo: Progressive Viticulture, LLC©.
Rootstocks and Grapevine Root System Density – More Comparisons Under Specific Soil Conditions
South African researchers studied Chenin blanc grapevines on different rootstocks. The studies included four experiments under a range of growing conditions. Some of the rootstocks included are familiar in California, but others are not. The differing growing conditions for the four experiments included non-irrigation on a structureless (massive) soil; sprinkler irrigation on a sandy soil; a moderately alkaline, saline, and sodic sandy clay soil; and an acid, organic soil with a fluctuating water table that limited the depth of roots to about 5.0 to 6.5 feet below the soil surface. Across all locations, increasing shoot growth (fresh shoot weight or dormant cane mass) was associated with increasing root density (Figure 5A).
A Napa Valley study involving Cabernet Sauvignon on different rootstocks found a similar relationship between pruning weights and root density. Only one of the South African trials involved fruit yield measurements and they, too, were positively correlated with root densities (Figure 5B).
Figure 5. Chenin blanc shoot mass (A) and fruit yield (B) as functions of rootstock root densities. Data Source: Swanepoel and Southey, 1989.
Rootstock influences and soil conditions had interactive effects on root system densities. As such, soil conditions ought to be a factor in rootstock selection for vineyard planting. Of the tested rootstocks, Ramsey and 99R appeared best adapted for sprinkler-irrigated Chenin blanc vineyards on sandy soils, while 140R appeared best adapted for dry farmed vineyards. For both saline and sodic soils, 1103P and 216-3 Castel appeared most suitable; for acidic organic soils, 1103P appeared most suitable.
Conclusions
Grapevine roots may be out of sight, but, given their importance to vine growth capacity, health and productivity, they should never be out of mind. As much as practical, we ought to maximize the volume of vineyard soil amenable to roots, which favors an extensive root system. In this regard, preplant activities are particularly important. These may include soil amending, deep cultivation, water table control measures, and berm making.
Just as significant, prior to planting, we ought to select a rootstock well adapted to vineyard soil conditions. This includes the inherent ability of the rootstock to develop dense root systems which permeate the maximum volume of the root zone prepared prior to planting. Such a rootstock will further enhance a vine’s capacity for growth, fruit production and ripening. Identifying such rootstocks may require investigations of vineyards with high-capacity vines on similar soils and discussions with other growers and advisers, as happens in the Lodi Rootstock Research Focus Group.
This article is based on a report for the Lodi Winegrape Commission Grapevine Rootstock Research Focus Group.
References and Further Reading
Bauerle, TL, Smart, DR, Bauerle, WL, Stockert, C, and Eissenstat, DM. 2008. Root foraging in response to heterogeneous soil moisture in two grapevines that differ in potential growth. New Phytologist. 179, 857-866.
Daulta, BS, and Chauhan, KS. 1980. Varietal variations in root growth of some grape varieties. Prog. Hort. 12, 37-39.
Eissenstat, DM, Bauerle, TL, Comas, LH, Lasko, AN, Neilsen, D, Neilsen, GH, and Smart, DR. 2006. Seasonal patterns of root growth in relation to shoot phenology in grape and apple. Acta Hort. 721, 21-26.
Eissenstat, D, Lakso, A, Smart, D, Bauerle, T, and Comas, L. Undated. Root dynamics in grape. Unpublished report.
Freeman, B, and Smart, RE. 1976. Research note: a root observation laboratory for studies with grapevines. American Journal of Enology and Viticulture. 27, 36-39.
Grant, S. The ultimate goal of vineyard soil management: optimized root zone function. Lodi Winegrape Commission Coffee Shop Blog. December 20, 2021.
Grant, S. The many uses and some misuses of gypsum in vineyards. Lodi Winegrape Commission Coffee Shop Blog. November 18, 2019.
Grant, S. Root zones and rhizospheres: considering the above and below ground grapevine. Wine Business Monthly. February, 2019. 154-158.
Grant, S. Grapevine shoots and roots: interconnectedness of the above and below ground grapevine. Wine Business Monthly. February, 2019. 148-152.
Grant, S. Evaluating vineyard soils in trenches. Lodi Winegrape Commission Coffee Shop Blog. February 17, 2016.
Grant, S. Selecting a rootstock for a winegrape vineyard. Lodi Winegrape Commission Coffee Shop Blog. October 07, 2016.
Grant, RS, and Matthews, MA. 1996. The Influence of phosphorus availability and rootstock on root system characteristics, phosphorus uptake, phosphorus partitioning, and growth efficiency. American Journal of Enology and Viticulture. 47: 403-409.
Harmon, FN, and Snyder, E. 1934. Grape rootstock distribution studies. Proc. Amer. Soc. Hort. Sci. 32:370-373.
Kocsis, L, and Tarczal Molinar Kocsisne, G. 2016. Grape rootstocks-scion interaction on root system development. Acta Horticulturae. 1136, 27-31.
Keller, M. 2010. The science of grapevines. Academic Press, Burlington, MA.
Killham, K. 1994. Soil Ecology. Cambridge University Press, Cambridge.
Lanyon, DM, Cass, A, and Hansen, D. The effect of soil properties on vine performance. CSIRO Land and Water Technical Report No 34/04. Oct. 2004.
McKenry, MV. 1984. Grape root phenology relative to control of parasitic nematodes. American Journal of Enology and Viticulture. 35, 206-211.
Morano, L, and Kliewer, WM (a). 1994. Root distribution of three grapevine rootstocks grafted to Cabernet Sauvignon grown on a very gravelly clay loam soil in Oakville, California. American Journal of Enology and Viticulture. 45, 345-348.
Morano, L, and Kliewer, WM (b). Effects of rootstocks and spacing on root distribution. Practical Winery and Vineyard. pp. 40-43. Jul/Aug 1994.
Morlat, R, and Jacquet, A. 2003. Grapevine root system and soil characteristics in a vineyard maintained long-term with and without interrow sward. American Journal of Enology and Viticulture. 54, 1-7.
Mullins, MG, Bouquet, A, and Williams, LE. 1992. Biology of the grapevine. Cambridge University Press, Cambridge, UK.
Nagarajah, S. 1987. Effects of soil texture on the rooting patterns of Thompson Seedless on own roots and on Ramsey rootstock in irrigated vineyards. American Journal of Enology and Viticulture. 38, 54-59.
Perry, RL, and Lyda, SD. 1983. Root distribution of four Vitis cultivars. Plant and Soil. 71, 63-74.
Richards, D. 1983. The grape root system. In Janick, J (Ed.). Hort. Rev., Vol. 5. John Wiley and Sons, Hoboken, NJ.
Skene, KGM, and Antcliff, AJ. 1972. A comparative study of cytokinin levels in bleeding sap of Vitis vinifera (L.) and the two grapevine rootstocks, Salt Creek and 1613. J. Exp. Bot. 23, 283-293.
Smart, DR, Schwass, E, Lasko, A, and Morano, L. 2006. Grapevine rooting patterns: a comprehensive analysis and a review. American Journal of Enology and Viticulture. 57, 89-104.
Southey, JM, and Archer, E. 1988. The effect of rootstock cultivar on grapevine root distribution and density. In van Zyl, J (Ed.). The grapevine root and its environment. Tech. Comm. 215. Dept. Agric. Water Supply, Pretoria.
Southey, JM. 1992. Root distribution of different grapevine rootstocks on a relatively saline soil. S. Afr. J. Enol. Vitic. 13, 1-9.
Swanepoel, JJ, and Southey, JM. 1989. The influence of rootstock on the rooting pattern of the grapevine. S. Afr. J. Enol. Vitic. 10:23-28.
van Huyssteen L. 1988. Soil preparation and grapevine root distribution – a qualitative and quantitative assessment. pp. 1-15. In The Grapevine Root and Its Environment. JL Van Zyl (Ed.). Department of Agriculture and Water Supply, Pretoria, South Africa.
van Huyssteen L. 1988. Grapevine root growth in response to tillage and root pruning practices. pp. 44-56. In The Grapevine Root and Its Environment. JL Van Zyl (Ed.). Department of Agriculture and Water Supply, Pretoria, South Africa.
Williams, LE, and Smith, RJ. 1991. The effect of rootstock on the partitioning of dry weight, nitrogen, and potassium, and root distribution of Cabernet Sauvignon grapevines. American Journal of Enology and Viticulture. 42,118-122.
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