Graduate Thesis Or Dissertation
 

Impact of Nitrogen Use in Grapevines: Vine Physiology, Fruit Quality, and Mycorrhizal Symbiosis

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  • Nitrogen (N) is the most important nutrient to manage in the overall wine production system, since N has a large influence on vine productivity and fruit quality in the vineyard and also on fermentation kinetics and fermentation-derived aromas in the winery. Previous studies investigated the influence of either vineyard N use or winery N supplementation on must composition, fermentation, and wine quality. Yet, N management in both the vineyard and winery has not been examined simultaneously in prior work, even though this knowledge can help viticulturists and winemakers work together to attain the desired wine quality or style while at the same time maintaining vine health and minimizing the environmental impact of wine production. Additionally, N fertilizer use in other crops can reduce root colonization by arbuscular mycorrhizal fungi (AMF) and alter plant P status, but whether N addition at the moderate rates typically used in viticulture would alter AMF colonization and function in grapevines was not known. We conducted experiments in Chardonnay between 2016 and 2018 and in Pinot noir between 2017 and 2019 in the Willamette Valley, OR, to understand how vineyard N application to the soil or to the foliage would affect vine growth, yield, fruit quality, and mycorrhizal colonization; and how vineyard N use alters must composition and fermentation rates as compared to N use in the winery. Five treatments, including no vineyard or winery N addition (No N), application of N in the vineyard to either the soil or to the foliage (Soil N and Foliar N), and addition of either diammonium phosphate or an amino-N to musts in the winery (+ DAP and + Org N) were examined. In both Chardonnay and Pinot noir vineyards, soil N application at moderate rates (45 to 67 kg N/ha) increased vine N status and yeast assimilable nitrogen (YAN) the first year it was applied, and subsequently increased vegetative growth in the second and third year after experiments began. Soil N application improved yield in Chardonnay also beginning in the second year, but did not affect yield in Pinot noir. Soil N fertilization reduced root colonization by AMF and arbucules in Chardonnay vines in the latter two years of the experiment, and reduced vine P status. In Pinot noir vines, however, even though soil N application reduced AMF colonization, vine P status was only altered slightly. Foliar N application at lower rates than Soil N (22 to 25 kg N/ha) did not alter vine growth or yield in either variety, and only affected vine N status slightly. Foliar N, however, increased must YAN just as effectively as Soil N in Pinot noir, but it was less effective than Soil N in Chardonnay. The addition of DAP or Org N in the winery boosted must YAN to similar levels as were achieved with the Soil N and Foliar N treatments in both varieties. Among N treatments, only soil N application in the vineyard resulted in more rapid fermentation in Chardonnay, but both vineyard N applications accelerated fermentation in Pinot noir. In addition to the field experiments, two greenhouse experiments were undertaken to better understand how N use in grapevines affects AMF symbiosis and their function in nutrient uptake. In both studies, vines were destructively harvested at the end of the growth cycle to determine biomass and accurately assess vine nutrient uptake. The first greenhouse trial examined the interactive effects of N and P supply on AMF colonization, vine growth and nutrient uptake in Pinot noir grapevines. This experiment utilized a 4 × 3 × 2 factorial design, with four N rates (0, 3, 6, and 12 mM N as NH4NO3), three P rates (0, 1, and 2 mM P as KH2PO4), and two AMF treatments (mycorrhizal and non-mycorrhizal). A soil with moderate P availability was used to avoid P deficiency in the non-mycorrhizal vines, and thus the non-mycorrhizal and mycorrhizal vines would reach similar level of growth and vine N uptake can be compared without the interference of large biomass difference. The vines were grown in the experimental soil for 6 weeks and supplied with a half-strength complete nutrient solution before fertilized at varying N and P rates. Results of this study showed that N application improved vine N uptake owing to the increase in biomass, but AMF did not enhance vine N acquisition at any N or P level. The AMF suppressed shoot growth at the two intermediate N levels (3 and 6 mM N), concurrent with an increased arbuscular frequency in roots. However, the shoot growth did not differ between mycorrhizal and non-mycorrhizal vines at the lowest or highest N rates (0 and 12 mM N), where arbuscule frequency was lower in comparison to the two moderate N rates. The percent of total root colonization by AMF (including hyphae, arbuscules and vesicles) was reduced at the lowest N rate (0 mM N) as compared to other three N treatments (3, 6, and 12 mM N), indicating that AMF may have been limited by the lack of N in this treatment. Phosphorus input did not affect vine growth or total AMF colonization in roots, but arbuscular colonization were suppressed slightly with higher P input. The subsequent greenhouse trial examined whether AMF would enhance vine N uptake when N in soil was organic, as opposed to the inorganic N used in the first greenhouse trial. Pinot noir vines were grown with or without AMF, in the same soil type with a greater amount of sand added to reduce native organic N levels in the soil. Within each AMF group, vines were assigned to seven different N treatments; including no N addition, NH4NO3 applied at 3 and at 6 mM N, glycine applied at 3 and at 6 mM N, and leaf litter applied at 10 and at 20 g. Vines were grown in the experimental soil for 4 weeks and supplied with a half-strength, complete nutrient solution before receiving N treatments. All of the N treatments increased the growth of shoots and roots as compared to vines that received no N after starting the experiment. Vine growth and N uptake increased with the increasing rate of material supplied for each type of N tested, but N uptake was not enhanced in any treatment by AMF. Vine N uptake increased to a greater extent when N was supplied as NH4NO3 or glycine than when litter was the source of N. Shoot growth was reduced by AMF in vines supplied with 6 mM N as NH4NO3, but not in any other N treatments. The percent of total root colonization by AMF (including hyphae, arbuscules and vesicles) as well as the level of arbuscules were again reduced at the lowest N rate (0 mM N) as compared to all other N treatments. Arbuscular frequency was also lower in roots in both leaf litter treatments at the end of the experiment compared to NH4NO3 and glycine treatments, although they were just as high midway through the experiment. The evidence provided from the two greenhouse studies conducted here indicate that AMF do not improve N acquisition by grapevines. This was true over a wide range of available N levels tested with an inorganic N source, but also when N supply was provided from two different organic N sources, glycine and leaf litter. Yet, evidence from both the field experiments and greenhouse experiments showed that N supply has a significant impact on root colonization by AMF. This impact was more evident for arbuscules in roots as opposed to total root colonization by any fungal structures in roots. Arbuscules are the primary site of nutrient transfer in AMF symbiosis, and regulating their development is a critical point of control by both symbiotic partners to ensure that they each benefit from the current set of conditions. Because grapevines did not gain a benefit in terms of N uptake from AMF, it is somewhat surprising that the use of N fertilizer suppressed arbuscules in the field and that both high and low N suppressed arbuscules in greenhouse. These results indicate that N plays a role in the development or maintenance of arbuscules in grapevine roots even if AMF do not improve vine N uptake. One interpretation of these findings is that at very low N, arbuscules are suppressed due to their own N-limitation, and perhaps some competition with the plant for N, while at higher N arbuscules are suppressed by crosstalk in the regulatory pathways that maintain N and P homeostasis. In addition, young vines appear to allocate carbon to support AMF even at the cost of reducing shoot growth, when N supply is moderate and soil P is not limiting vine growth. Finally, in actual vineyards, it is important to consider that N fertilizer use can suppress AMF and potentially reduce other benefits that are derived from AMF, such as P and Zn uptake and possible alleviation of drought stress.
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  • Pending Publication
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  • 2020-12-10 to 2023-01-11

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