Study site and design
Our study was situated at the Niagara College Teaching Vineyard, a 16.2-ha operational vineyard situated at the Daniel J. Patterson Campus in Niagara-on-the-Lake, Ontario, Canada (43.1522° N, 79.1652° W). The vineyard is situated in the Niagara-on-the-Lake Regional Appellation, which is in turn nested within the Niagara Peninsula Appellation. Soils at the site are classified as imperfectly drained silty clays (to 40-100 cm depth) over clay loam till mixed with poorly drained lacustrine heavy clay. The farm is under commonly employed vineyard management systems, which includes applications of calcium nitrate and/ or muriate of potash and/ or sulphate of potash magnesium (K-Mag; 22-10.8-22), applied uniformly across the farm in mid-June. Liquid calcium (8-0-0-10) is also applied as a foliar spray early in each growing season. In mid- June of each year cover crops are planted in every second row with 65% annual rye, 20% crimson clover and 15% eco-till radish through deep ripping, discing and harrowing passes. At the site there is 7.26-cm diameter tile drainage installed in every other row, and the site is not irrigated.
Our study was conducted over a 1-week period between July 1st and 7th, 2021, when vines were in the fruit setting/ berry development phenological stage (Coombe, 1995). We selected a total of 15 individual ‘Chardonnay’ vines (“Dijon Clone 76”) for functional trait analyses, which were distributed evenly across five different planting rows spaced 15-20 m apart (corresponding to an even 10 interceding planting rows). These sampling rows run parallel to one another, and broadly follow a soil compaction gradient that runs along a northwest to southeast orientation in the vineyard. This gradient is related to the vineyard’s imperfectly drained soils and hydrology. Generally, northwest areas and planting rows are well drained by mid- to late- May. By comparison, areas and planting rows in the southeast remain poorly drained for roughly an additional month, drying by mid- to late-June. Since farm machinery is required for foliar applications and cover crop plantings across the entire vineyard in mid- June, southeast areas of the vineyard therefore experience enhanced mechanical compaction every year in early late Spring/ early summer. Soil bulk density was collected for each sampled vine (described below) to a 10 cm depth, using a 1 cm diameter core borer, and varied significantly across rows (Analysis of Variance (ANOVA)F 4, 10=5.84, p <0.001), with rows 1 through 5 expressing bulk density values of 1.36±0.12 (S.D.) g cm-3, 1.58±0.08 g cm-3, 1.67±0.09 g cm-3, 1.64±0.1 g cm-3, and 1.72±0.1 g cm-3, respectively.
Within each sampling row, three individual vines situated 13-15 m away from one another were chosen for leaf trait measurements. Each of the 15 vines chosen for our study, was between 1.5-2 cm in resprout diameter and free of any pest, pathogen, or mechanical damage. On each plant, we selected three recently developed and fully expanded leaves that were free of any damage or disease, and situated on the upper-most cane in full-sun conditions. This nested study design therefore resulted in leaf traits being measured on 45 leaves from 15 individual vines that were of the same size, age, rootstock and pruning regimes, which were in turn situated within five distinct sample rows.