Spatial and Temporal Variation of Roots, Arbuscular Mycorrhizal Fungi, and Plant and Soil Nutrients in a Mature Pinot Noir (Vitis vinifera L.) Vineyard in Oregon, USA

Abstract

The spatial and temporal development of grapevine roots and associated mycorrhizal fungi was studied in 1999 and 2000 in a 21-year-old, Pinot Noir (Vitis vinifera L.) vineyard located on a Jory soil (Palehumult, silty clay loam) in Oregon, USA. The density of woody roots and fine (primary) roots deemed to be physiologically active (based on color and cellular integrity) were determined at monthly intervals in the weed-free, vine row and in the alleyway between rows at two depths (0–50 and 50–100 cm). The majority of fine roots were growing in the vine row at 0–50 cm depth. Fine root density did not change dramatically over the 1999 or 2000 seasons until the time of fruit harvest in the fall. Apparently, new root growth kept pace with turnover (death) prior to harvest, but new root growth surpassed turnover in the fall after fruit harvest. Colonization of fine roots by arbuscular mycorrhizal fungi (AMF) was consistently high in the vine row at 0–50 cm depth, but was lower in roots growing in the alleyway, and in roots below 50 cm. The proportion of fine roots containing arbuscules (the site of nutrient exchange in arbuscular mycorrhizas) was also greatest for roots growing in the vine row at 0–50 cm depth. Arbuscular colonization of these roots increased prior to budbreak in the spring, reached a high level (50–60% root length) by early summer, and remained high until after the time of leaf senescence in late fall. Arbuscular colonization decreased rapidly by December of 1999 when November rainfall exceeded 200 mm, but did not decline by December of 2000 when November rainfall was below 80 mm. The availability of important plant nutrients in the soil, with the exception of Mg and Zn, was higher in the upper 50 cm of the soil profile where the majority of roots were found. In addition, available nitrate and phosphate were higher in the vine row than in the alleyway soil. Seasonal changes in leaf nutrient concentrations of Pinot Noir confirmed findings in other cultivars, but fluctuations of N, P, and K concentrations in fine roots over the season suggested that fine roots may play a role in nutrient storage, as well as nutrient uptake, in grapevines. Grapevines grown in Oregon direct significant resources to roots and AMF after fruit harvest and substantial post-harvest nutrient uptake may extend into the early winter.