Julie M. Tarara

Assessing the impact of temperature on grape phenolic metabolism.

This study assessed the impact of fruit temperature on the phenolic metabolism of grape berries (Vitis vinifera L. cv. Merlot) grown under field conditions with controlled exposure to sunlight. Individual cluster temperatures were manipulated in situ. Diurnal temperature fluctuation was damped by daytime cooling and nighttime heating of clusters. Daytime-only and nighttime-only temperature controls were applied for comparison. Berry temperatures were recorded continuously to compare the chemical data. Samples collected at véraison indicated that damping the diurnal temperature fluctuation advanced the onset of ripening. Those berries were larger (double-damped: 0.753+/-0.015gberry(-1) vs control: 0.512+/-0.034gberry(-1)) and more colored than all others. Development of phenolic metabolites was followed by two reversed-phase high performance liquid chromatography methods and gel permeation chromatography. These methods provided information on anthocyanins, proanthocyanidins, flavonols, flavan-3-ol monomers, and polymeric material. Damping the diurnal temperature fluctuation reduced proanthocyanidin mean degree of polymerization (double-damped: 21.8+/-1.0 vs control: 28.0+/-1.7). Proanthocyanidin accumulation at véraison was linearly related to heat summation over the developmental period with nighttime heating yielding the highest concentration and daytime cooling yielding the lowest (night-heat: 1.46+/-0.13mgberry(-1) vs day-cool: 0.97+/-0.09mgberry(-1)). Damping the diurnal temperature fluctuation had a marked effect on the rate of fruit development whereas total heat summation had more of an effect on phenolic metabolism alone. The results provide insight on the direct effect of temperature on phenolic metabolism.

Impact of diurnal temperature variation on grape berry development, proanthocyanidin accumulation, and the expression of flavonoid pathway genes

Little is known about the impact of temperature on proanthocyanidin (PA) accumulation in grape skins, despite its significance in berry composition and wine quality. Field-grown grapes (cv. Merlot) were cooled during the day or heated at night by +/–8 °C, from fruit set to véraison in three seasons, to determine the effect of temperature on PA accumulation. Total PA content per berry varied only in one year, when PA content was highest in heated berries (1.46 mg berry−1) and lowest in cooled berries (0.97 mg berry−1). In two years, cooling berries resulted in a significant increase in the proportion of (–)-epigallocatechin as an extension subunit. In the third year, rates of berry development, PA accumulation, and the expression levels of several genes involved in flavonoid biosynthesis were assessed. Heating and cooling berries altered the initial rates of PA accumulation, which was correlated strongly with the expression of core genes in the flavonoid pathway. Both heating and cooling altered the rate of berry growth and coloration, and the expression of several structural genes within the flavonoid pathway.

Dynamic thermal time model of cold hardiness for dormant grapevine buds

BACKGROUND AND AIMS Grapevine (Vitis spp.) cold hardiness varies dynamically throughout the dormant season, primarily in response to changes in temperature. The development and possible uses of a discrete-dynamic model of bud cold hardiness for three Vitis genotypes are described. METHODS Iterative methods were used to optimize and evaluate model parameters by minimizing the root mean square error between observed and predicted bud hardiness, using up to 22 years of low-temperature exotherm data. Three grape cultivars were studied: Cabernet Sauvignon, Chardonnay (both V. vinifera) and Concord (V. labruscana). The model uses time steps of 1 d along with the measured daily mean air temperature to calculate the change in bud hardiness, which is then added to the hardiness from the previous day. Cultivar-dependent thermal time thresholds determine whether buds acclimate (gain hardiness) or deacclimate (lose hardiness). KEY RESULTS The parameterized model predicted bud hardiness for Cabernet Sauvignon and Chardonnay with an r(2) = 0·89 and for Concord with an r(2) = 0·82. Thermal time thresholds and (de-)acclimation rates changed between the early and late dormant season and were cultivar dependent but independent of each other. The timing of these changes was also unique for each cultivar. Concord achieved the greatest mid-winter hardiness but had the highest deacclimation rate, which resulted in rapid loss of hardiness in spring. Cabernet Sauvignon was least hardy, yet maintained its hardiness latest as a result of late transition to eco-dormancy, a high threshold temperature required to induce deacclimation and a low deacclimation rate. CONCLUSIONS A robust model of grapevine bud cold hardiness was developed that will aid in the anticipation of and response to potential injury from fluctuations in winter temperature and from extreme cold events. The model parameters that produce the best fit also permit insight into dynamic differences in hardiness among genotypes.

Biochar produced from anaerobically digested fiber reduces phosphorus in dairy lagoons.

This study evaluated the use of biochar produced from anaerobic digester dairy fiber (ADF) to sequester phosphorus (P) from dairy lagoons. The ADF was collected from a plugged flow digester, air-dried to <8% water content, and pelletized. Biochar was produced by slow pyrolysis in a barrel retort. The potential of biochar to reduce P in the anaerobic digester effluent (ADE) was assessed in small-scale filter systems through which the effluent was circulated. Biochar sequestered an average of 381 mg L P from the ADE, and 4 g L ADF was captured as a coating on the biochar. There was an increase of total (1.9 g kg), Olsen (763 mg kg), and water-extractable P (914 mg kg) bound to the biochar after 15 d of filtration. This accounted for a recovery of 32% of the P in the ADE. The recovered P on the biochar was analyzed using P nuclear magnetic resonance for P speciation, which confirmed the recovery of inorganic orthophosphate after liquid extraction of the biochar and the presence of inextractable Ca-P in the solid state. The inorganic phosphate was sequestered on the biochar through physical and weak chemical bonding. Results indicate that biochar could be a beneficial component to P reduction in the dairy system.

Warm spring temperatures induce persistent season-long changes in shoot development in grapevines

BACKGROUND AND AIMS The influence of temperature on the timing of budbreak in woody perennials is well known, but its effect on subsequent shoot growth and architecture has received little attention because it is understood that growth is determined by current temperature. Seasonal shoot development of grapevines (Vitis vinifera) was evaluated following differences in temperature near budbreak while minimizing the effects of other microclimatic variables. METHODS Dormant buds and emerging shoots of field-grown grapevines were heated above or cooled below the temperature of ambient buds from before budbreak until individual flowers were visible on inflorescences, at which stage the shoots had four to eight unfolded leaves. Multiple treatments were imposed randomly on individual plants and replicated across plants. Shoot growth and development were monitored during two growing seasons. KEY RESULTS Higher bud temperatures advanced the date of budbreak and accelerated shoot growth and leaf area development. Differences were due to higher rates of shoot elongation, leaf appearance, leaf-area expansion and axillary-bud outgrowth. Although shoots arising from heated buds grew most vigorously, apical dominance in these shoots was reduced, as their axillary buds broke earlier and gave rise to more vigorous lateral shoots. In contrast, axillary-bud outgrowth was minimal on the slow-growing shoots emerging from buds cooled below ambient. Variation in shoot development persisted or increased during the growing season, well after temperature treatments were terminated and despite an imposed soil water deficit. CONCLUSIONS The data indicate that bud-level differences in budbreak temperature may lead to marked differences in shoot growth, shoot architecture and leaf-area development that are maintained or amplified during the growing season. Although growth rates commonly are understood to reflect current temperatures, these results demonstrate a persistent effect of early-season temperatures, which should be considered in future growth models.

Net carbon exchange in grapevine canopies responds rapidly to timing and extent of regulated deficit irrigation

Whole-canopy net CO2 exchange (NCEC) was measured near key stages of fruit development in grapevines (Vitis vinifera L. cv. Cabernet Sauvignon) that were managed under three approaches to regulated deficit irrigation (RDI): (1) standard practice (RDIS), or weekly replacement of 60-70% of estimated evapotranspiration for well watered grapevines; (2) early additional deficit (RDIE), or one-half of RDIS applied between fruit set and the onset of ripening (veraison), followed by RDIS; and (3) RDIS followed by late additional deficit (RDIL), or one-half of RDIS applied between veraison and harvest. Summed between fruit set and harvest, nearly 40% less irrigation was applied to RDIE vines and ~20% less to RDIL vines than to those continuously under RDIS. After ~5 weeks of additional deficit, NCEC in RDIE vines was 43-46% less per day than in RDIS vines. After RDIL vines had been under additional water deficit for ~3 weeks, NCEC was ~33% less per day than in RDIS vines. Instantaneous rates of NCEC responded rapidly to irrigation delivery and elapsed time between irrigation sets. Concurrent single-leaf measurements (NCEL) reflected the relative differences in NCEC between irrigation treatments, and were linearly associated with NCEC (r2=0.61). Despite halving the water applied under commercial RDI, mid-day stomatal conductance values in RDIE and RDIL of ~50-125mmolm-2s-1 indicated that the additional deficit imposed only moderate water stress. There was no effect of additional deficit on yield or berry maturity.

Diurnal Temperature Range Compression Hastens Berry Development and Modifies Flavonoid Partitioning in Grapes

Temperatures during the day and night are known to influence grape berry metabolism and resulting composition. In this study, the flavonoid composition of field-grown Vitis vinifera L. cv. Merlot berries was investigated as a function of diurnal temperature range (DTR). The DTR was compressed by cooling berries during the day and heating them at night. Before veraison, there were minor differences in proanthocyanidin (PA) composition in the skins and seeds due to temperature treatments, most notably a decrease in gallate-esterification of seed flavan-3-ols with compressed DTR. Compressing the DTR significantly hastened berry development and the inception of veraison. Treatments imposed after veraison had minimal impact on skin and seed PAs; however, compressed DTRs favored the partitioning of anthocyanins and flavonols toward B-ring di-substitution. Compressing the DTR of grape berries had a consistent effect on berry development and partitioning of flavonoid metabolites while total flavonoid content was not significantly altered.

MODELING SEASONAL WINE GRAPE DEVELOPMENT USING A MIXTURE TECHNIQUE

Biological growth data typically display an increasing sigmoidal pattern over time. Grape development is no exception and shows a similar general trend. A detailed examination of the growth process in grapes, however, reveals a few systematic deviations from this pattern. Specifically, grape development is often characterized by localized areas of growth plateaus leading to an overall growth pattern referred to as a double sigmoidal curve. Capturing and characterizing these local changes in growth is important as they represent important phases in grape development such as veraison. This paper utilizes a model adapted from the technique of mixture models to estimate the growth curve of grapes. The resulting model provides a more accurate description of the growth process and has parameter estimates directly related to the various phases of grape development. The model is demonstrated using data collected from an experimental trellis tension monitoring system in the Chardonnay grape varietie.

Use of Cordon Wire Tension for Static and Dynamic Prediction of Grapevine Yield

An automated system was used during three growing seasons to monitor the change in tension (ΔT) in the load-bearing wire of a trellis to estimate yield in vineyards. Actual yield varied nearly four-fold among the three study years, but in each year the fruit was uniformly distributed along the length of the wire. The automated sensor detected sequential harvests up to ~12 m to either side of the sensor, or 24 m total wire length, in a nonlinear fashion. Yield was predicted statically from ΔT at the lag phase (L) of berry growth (ΔTL) and dynamically from continuous output of ΔT. Relationships between ΔTL and yield were linear. Estimated yield was not sensitive to the date of ΔTL, within 10 days. In using the ratio between the current year ΔT and that of a specific previous year, the differences between estimated and observed yields depended upon the choice of predictor year(s), where years with similar ΔT were the most accurate. Across an estimation interval of L to harvest, the precision of dynamic estimates was determined by the similarity in the day-to-day shapes of the double-logistic curves of ΔT over time. Due to a catastrophic frost in the second year of the study, an extremely small crop and an uncharacteristic growth curve made it difficult to predict yield either statically or dynamically. In practice, the method requires a grower to collect multiple years of growth curves from which to build a robust linear relationship between ΔTL and yield (static estimates), or to apply an average of multiple years’ ΔT values dynamically.