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Key functional root traits, including mycorrhizal association and root diameter, can help project ecosystem processes like root turnover and soil carbon sequestration. It is less clear, however, how such traits relate to variations in soil biology and chemistry. Here, we examined the impact of tree species with varied root traits on soil properties and rhizoplane bacterial composition, focusing specifically on mycorrhizal association type and root diameter. Within a long-term common garden in central Pennsylvania, USA, we selected three arbuscular mycorrhizal (AM) and three ectomycorrhizal (EM) tree species and assessed changes in (1) soil and leaf chemistry and (2) bacterial composition along fine absorptive roots, through 16S rRNA gene sequencing. AM trees increased soil pH and soil available nitrogen relative to EM trees, and mycorrhizal association type was significantly associated with rhizoplane-associated bacterial composition. Absorptive root diameter did not clearly explain soil variability but was associated with changes in the composition of rhizoplane-associated bacteria. Tree-mediated shifts to soil properties were linked to mycorrhizal association type, whereas rhizoplane recruitment of bacteria was linked to both mycorrhizal type and root diameter. This has implications for predicting changes in biogeochemical processes following shifts in tree species composition.

Vegetative groundcover and rootstock selection are popular growth control practices for fruit and nut crops. Theoretically, plant potential growth rate should influence competitive effectiveness; however, it is unclear if rootstock vigor alters crop productivity when groundcover is present. In a humid-climate vineyard we grew young grapevines on low- and medium-vigor rootstocks with and without groundcover. Vegetative growth was determined on dormant stems; yield was determined at harvest. Roots were extracted with soil cores and distribution, morphology, and mycorrhizal colonization were determined. Resource competition was assessed by water and nutrient depletion in vines and soil. Compared to vines on low-vigor rootstocks, vines on medium-vigor rootstocks exhibited greater reductions in vegetative (40% vs 19%) and reproductive (22% vs 0%) growth by presence of groundcover. Irrespective of rootstock vigor, grapevine root systems coped with competition by increasing specific root length, decreasing absorptive root diameter, and redistributing roots deeper. Competition for nutrients was the apparent main cause of growth reductions with groundcover; however, mechanisms for differential rootstock responses remain unclear. This study suggests that in a wet year, young grapevines grafted on low-vigor rootstocks may be more tolerant of groundcover competition than those on medium-vigor rootstocks; however, both rootstocks cope with a similar root response.

A traditional crop load regulation technique, cluster thinning (CT), was compared to a more innovative technique, early leaf removal (ELR) applied either at trace bloom (TBLR) or fruit set (FSLR), on high-yielding and vigorous Vitis vinifera cv. Gruner Veltliner. Treatment effects on key production parameters, Botrytis bunch rot, tolerance to winter temperatures, and production costs were evaluated and compared to an untreated control over two years. Compared to CT, we hypothesized that ELR would improve fruit composition, reduce Botrytis bunch rot, and decrease grower costs. Yield regulation imposed by CT was significantly higher (39.3%) than that of TBLR (12.6%) or FSLR (13.3%), but neither CT nor ELR consistently improved fruit chemistry. Our results suggest that the number of leaves removed (five) at trace bloom or fruit set was insufficient to induce a carbohydrate-limiting response, as ELR vines did not have lower fruit set or bud fruitfulness. Concurrently, TBLR and FSLR vines did not show recovery mechanisms such as greater production of lateral leaves or higher shoot efficiency. Although the overall level of bunch rot severity was lower than 5%, ELR consistently decreased bunch rot intensity (TBLR, FSLR) and severity (FSLR). TBLR also improved bud freezing tolerance during vine acclimation in both years. CT was the most expensive treatment, and the lack of a consistent improvement in fruit chemical composition or tolerance to winter temperatures indicated that Gruner Veltliner can properly ripen more than one cluster/shoot.

Excessive precipitation events have greatly increased in several grape growing regions due to human-caused climate change. These heavy downpours result in a myriad of problems in the vineyard including soil aggregate breakdown, soil runoff, nutrient leaching, excessive vine vegetative growth, and diseased fruit. The negative impacts of excessive precipitation events on vineyards are exacerbated by the maintenance of bare soil under the vines. Exposure of bare soil results in soil erosion and runoff which pollutes nearby watersheds; raindrops weaken and break apart soil aggregates, leading to increased soil erosivity and contributing to the formation of surface crusts. In addition to excessive precipitation events, some grape growing regions can be characterized by fertile soils. The availability of ample water and nutrients can lead to highly vigorous vines with shoot growth continuing through harvest. Long shoots and large leaves result in shaded fruit, a humid vine microclimate, and excessive cluster rot. In this review, we examined how either natural (i.e., resident) or seeded under-vine vegetation (UVV) can help mitigate many of the problems associated with excessive precipitation. Through providing vegetative coverage to reduce the force of raindrops, increasing soil organic matter and enhancing soil microbial diversity, UVV can reduce the soil degradation and off-site impacts caused by excessive precipitation events. Through competition for soil resources, UVV can reduce excessive vegetative growth of vines and decrease cluster rot incidence and severity, although grapevine response to UVV can be highly variable. We discussed recent advances in understanding below and aboveground vine response and acclimation to UVV and presented current evidence of factors influencing the impact of UVV on vine growth and productivity to assist practitioners in making informed decisions and maximize the ecosystem services provided by UVV.

The influence of cultural and environmental factors on the sensory and chemical profiles of wines has been the subject of research investigation for many years, and an examination of these relationships can help determine whether wine regional trends exist. The present study investigated the chemical and sensory factors that drive regional differences in Pennsylvania Grüner Veltliner wines through a controlled winemaking study across two vintages in 2018 and 2019. Descriptive analysis was used to identify key sensory attributes of Pennsylvania Grüner Veltliner. Intensities of these attributes were evaluated in wines vinified under identical conditions from grapes harvested across nine Pennsylvania vineyards. Chemical profiles of finished wines were examined through volatile, phenolic, and color analyses. Significant sensory differences were found between wine regions, with some trends consistent across both vintages, however, regionality based on compositional analyses was less clear. As the first study to examine Pennsylvania Grüner Veltliner wines sensorially, results revealed sensory characteristics that can be useful for wineries and their tasting room staff in marketing these lesser-known white wines to wine consumers as the variety grows in popularity in the state.

Late-season bunch rot causes significant crop loss for grape growers in wet and humid climates. For 3 years (2016 to 2018), we integrated prebloom mechanized defoliation (MD) in the fruit zone and bloom gibberellin (GA) applications, either alone or in combination, into the bunch rot control program of Vignoles, a commercially valuable grape variety that is highly susceptible to bunch rot. We hypothesized that both treatments would decrease bunch rot through modification of cluster architecture or fruit zone microclimate compared with vines treated with the standard chemical control program. Grapevines were trained to two popular training systems, four-arm Kniffin (4AK) and high-wire bilateral cordon (HWC). Treatment responses varied between training systems. MD, alone or in combination with GA, reduced bunch rot incidence and severity every year on 4AK-trained vines, an effect attributed mainly to fruit zone improvements. Conversely, MD alone did not reduce bunch rot incidence on HWC-trained vines, despite significant improvements in cluster architecture (reduced number of berries per cluster and cluster compactness). GA applications were more effective than MD at reducing cluster compactness, regardless of training system. As a result, GA reduced bunch rot incidence and severity when applied alone or with MD on 4AK- and HWC-trained vines. All treatments positively improved fruit-soluble sugar concentration on both training systems, while positive effects on titratable acidity were more consistent across training systems with MD.

Fruit-zone leaf removal is typically applied in cool and humid regions to improve grape and wine quality, while reducing disease pressure. When fruit-zone leaf removal is applied early in the season, before bloom [early leaf removal (ELR)], it also reduces fruit-set, cluster compactness, and susceptibility to bunch rot, a complex disease that involves fungi (Botrytis cinerea, Aspergillus sp., Penicillium sp.) and bacteria (Acetobacter sp.). Over 2 years (2015–16), we tested whether ELR applied mechanically [mechanical defoliation at stage E-L 18 (MD-I)] would mimic the effects of a hand removal [hand defoliation of the first six basal leaves and laterals at stage E-L 18 (Coombe, 1995) (HD-I)] with respect to ‘Riesling’ (Vitis vinifera) production parameters, canopy density and cluster sunlight exposure, fruit composition, and bunch rot control. We also compared the effects of mechanical defoliation applied either at prebloom (MD-I) or at fruit-set [mechanical defoliation at stage E-L 27 (MD-II)]. In both years, fruit-zone leaf removal, regardless of method and timing, reduced yield, cluster weight, and berries per cluster, while maintaining fruit composition and bud fruitfulness as compared with nondefoliated vines (control, C). In 2015, HD-I vines had a lower percentage of clusters infected by bunch rot as compared with the C and MD-II vines. However, severity of bunch rot was low in all treatments, and there was not significant treatment effect on bunch rot severity in either year. ELR consistently shortened cluster length, offsetting much of the intended cluster loosening effect induced by a lower number of berries per cluster—that would have reduced bunch susceptibility to late seasons rots. Despite removing only half the leaf area of HD-I, MD-I successfully mimicked the canopy improving effects of HD-I in terms of fewer interior clusters and leaves, fewer cluster-shading layers, and greater light available to clusters and leaves as compared with C vines.

Field studies were conducted in 2014 and 2015 on Vitis vinifera cvs. Lemberger and Riesling and on interspecific hybrid cvs. Noiret and Traminette to evaluate the effectiveness of two sprayable products for reducing postbudburst freeze damage without impacting grape production, fruit composition, wine chemistry, or sensory perception. The treatments consisted of a) one application of a vegetable oil-based adjuvant (Amigo) during the dormant season to delay budburst and reduce the chance of frost damage; and b) application of a potassium fertilizer (KDL) within 24 hrs before a predicted frost event to increase plant freeze resistance. Amigo oil application significantly delayed budburst in Lemberger and Riesling in both years (six to 11 days), but the delay was less pronounced in Noiret and Traminette (two to four days). A frost event (minimum temperature −3°C) occurred in late spring 2015 in the Noiret and Traminette vineyard. At that time, the percentage of buds that had reached budburst was no longer lower in the Amigo oil-treated vines than other treatments. Neither Amigo oil nor KDL reduced freeze damage and crop loss in the hybrid cultivars. The lower osmotic potential of Noiret KDL-treated leaves compared to the control did not translate into increased freeze resistance under our experimental conditions. The delay in budburst in Amigo oil-treated vines did not impact fruit composition at harvest in any of the cultivars tested or the sensory perception of Riesling wines. Amigo oil applied at 10% concentration caused, however, phytotoxic effects (i.e., reduced cluster weight and bud survival). Further studies are needed before Amigo oil can be recommended as a frost-avoidance strategy.

Rotundone was recently identified as the compound that imparts the black pepper aroma in several winegrape cultivars. This two-year study aimed to identify the presence of rotundone in Noiret (interspecific hybrid of Vitis) and to determine the impact of fruit-zone leaf removal on rotundone concentrations in fruit and wine. The relationship between the intensity of black pepper aroma and rotundone concentration in Noiret wine was also explored. An undefoliated control (CON) was compared to a maintained fruit-zone sunlight exposure (MSE) treatment, where leaves were periodically removed from the fruit-zone. The influence of timing of fruit-zone leaf removal was assessed in a separate experiment by comparing preveraison leaf removal (LR) and postveraison leaf removal (PVLR) treatments. MSE vines had greater fruit-zone sunlight exposure compared to the CON throughout the season in 2015, both at the pre- and postveraison stages, but in 2014, only after veraison. PVLR increased fruit-zone sunlight exposure during ripening compared to LR in 2015 only. Rotundone could not be quantified in Noiret berries sampled before or at veraison (limit of quantitation = 0.16 μg/kg). Rotundone concentrations in harvested fruit and wines did not differ between treatments in 2014, but were significantly higher in MSE than in CON in 2015 (1.98 versus 1.28 μg/kg). PVLR temporarily increased rotundone concentration compared to LR, but differences disappeared by harvest. Black pepper aroma intensity, as determined by a sensory panel, was positively correlated (p = 0.023, r = 0.791) with rotundone concentration in wines made from imposed viticulture treatments, providing evidence that black pepper notes in Noiret are positively related to concentration of rotundone in the wine.

The sesquiterpenoid rotundone is the compound responsible for the “black pepper” aroma of many plant species, including several economically important wine grape varieties. Since its identification in wine in 2008, there has been an increased interest in understanding how individual climatic or cultural factors affect the accumulation of rotundone in grapes and subsequently the level of wine “pepperiness.” However, no study has assessed climatic and viticultural factors together to identify which variables have the strongest influence on rotundone accumulation. Our study aimed to fill this knowledge gap by developing a predictive model that identified factors that explain rotundone concentrations in Noiret (Vitis sp.) grapes at harvest. Over the 2016 and 2017 seasons, we measured 21 viticultural, meso- and microclimatic variables and concentrations of rotundone in Noiret wine grapes at seven vineyards in the northeastern U.S. Vineyard growing degree days (GDDv) and the amount of solar radiation (cumulative solar exposure; CSEv) accumulated from the beginning of fruit ripening to harvest were the variables best correlated (r = 0.70 and r = 0.74, respectively) with rotundone concentrations. Linear correlations between microclimatic parameters and rotundone concentrations were weaker, but overall rotundone was negatively correlated with low (30°C) berry temperatures. Using the 2-year data set we were able to develop a four-variable model which explained more than 80% of the variation in rotundone concentration at harvest. The model included weather [growing degree days during fruit ripening (GDDv)] and plant-related variables (concentrations of phosphorus and calcium in the leaf petiole, and crop load). The model we developed could be used by wine producers to identify sites or cultural practices that favor rotundone accumulation in Noiret grapes after performing a model validation with an additional, external data set. More broadly, the statistical approach used here could be applied to other studies that also seek to assess the effects of multiple factors on a variable of interest under varying environmental conditions.

Soil carbon may be enhanced in agroecosystems by increasing root density throughout the soil profile. In vineyards and orchards, groundcovers that grow concurrently with the grapevines directly increase shallow root biomass and may induce deeper rooting of the fruit crop. We examined root distributions and soil properties associated with soil carbon in a vineyard that varies in groundcover and rootstock management practices. In comparison to an herbicide control, the grass groundcover substantially increased root biomass inputs in shallow soil zones ( 40 cm). Collectively, our results suggest that undervine groundcovers can substantially increase shallow soil carbon, but the potential for increases beyond the groundcover root zone remains unclear.

Spring frosts and subsequent crop losses threaten the economic sustainability of fruit crop producers all over the world. This study used a controlled-freezing technique to impose a post-budburst freezing stress to grapevine shoots forced from one-node cuttings [‘Albariño’, ‘Cabernet Franc’, ‘Cabernet Sauvignon’, and ‘Pinot Grigio’ (Vitis vinifera)] and whole plants [‘Noiret’ (Vitis hybrid)]. Our goal was to investigate the incidence of freeze injury among cultivars, stage of phenological development, and a potassium salt-based fertilizer (KDL) with potential cryoprotectant activity. Among the V. vinifera cultivars, the incidence of mortality of shoots exposed to −3.5 °C was highest for ‘Albariño’ (71%) and lowest for ‘Cabernet Sauvignon’ (51%). Cuttings sprayed with KDL 24 hours before cold temperature exposure exhibited 16% lower shoot mortality and lower osmotic potential (Ψs) (−0.92 MPa) than the unsprayed cuttings (−0.77 MPa). However, application of KDL did not impact shoot mortality for whole ‘Noiret’ vines. Mortality for ‘Noiret’ shoots greatly increased with the advancement of phenological development, ranging from 10% in wooly buds to 78% in shoots ≈10-cm long. The practical significance of KDL remains questionable; cultivar selection still appears to be a more reliable method for avoiding spring frost, by planting late bursting cultivars in more frost-prone areas.

Cover crops limit canopy growth in fruit crops to varying magnitudes but mechanisms are poorly understood. Root responses of mature grapevines to understory grass were evaluated in a temperate, humid region of USA. We hypothesized that mature grapevines competing with understory grass would show deeper root distribution with deeper use of soil water but only modest reductions in nitrogen and phosphorus uptake. Root responses assessed included vertical distribution of absorptive root length, mycorrhizal fungal colonization and total vine root length. Extractable soil nitrogen and phosphorous, soil moisture, grapevine nutrient status, and grapevine depth of water uptake were also assessed. In response to cover crop, the well-established grapevines maintained canopy growth, had modest (17 %) reductions in fruit biomass production and exhibited little evidence of restricted uptake of water and nitrogen, despite marked shifts toward deeper grapevine root distribution and a 63 % decreased overall absorptive root length. Mycorrhizal colonization of the grapevines was unaffected by presence of a cover crop. Cover crop competition affected grapevine access to phosphorus more than water or nitrogen. These results illustrate that grapevine root systems are capable of acclimating to understory grass competition, but specific resource limitations are strongly context dependent.

Background and Aims The objective of this study was to assess the effect of root pruning (RP) and annual under-trellis cover crops (UTCC) on vegetative growth and physiological processes in Cabernet Franc (Vitis vinifera L.) grapevines grafted on 3309C rootstock. Methods and Results Five root-zone management treatments, namely under-trellis vegetation-free strip control (C), RP and three distinct annual UTCC [annual ryegrass (AR), buckwheat, (BW) and turnip (TP)] were evaluated and compared over three seasons in a vigorous vineyard in the Northeastern USA. Root pruning had the greatest impact in reducing grapevine size; AR reduced the duration of shoot growth 2 out of 3 years. Competition between grapevine and AR and BW fine roots resulted in a lower grapevine fine root production in shallow soil layers and in a decrease in fine root lifespan. Conclusions Root pruning was effective in reducing grapevine size for 3 years; RP effectiveness, however, may vary greatly depending on site conditions. Annual UTCC hold potential for reducing grapevine size in vigorous plantings in regions with ample precipitation. Appropriate choice of cover crop species, however, remains unclear. Significance of the Study This work demonstrates that root-zone management practices impact grapevine vegetative growth and induce changes in root morphological traits.