Arbuscular Mycorrhizal Fungi and Grapevines: Boosting Nutrition, Resilience, and Yield
- Stanislav M.
- 39 minutes ago
- 10 min read
Arbuscular mycorrhizal fungi (AMF) are beneficial soil microorganisms that form symbiotic “fungus-root” associations with plants – including grapevines (Vitis vinifera).
In this mutualistic partnership, the fungus (especially species like Rhizophagus intraradices, formerly Glomus intraradices) colonizes vine roots and extends a network of microscopic hyphae into the soil. The grapevine supplies the fungus with sugars, and in return the AMF greatly enhances the plant’s ability to absorb hard-to-acquire nutrients (particularly phosphorus and micronutrients) and water.
This relationship is widespread and natural in vineyards – most grapevines in the field host AMF in their roots, which act as a living extension of the root system. Research has shown that this symbiosis can significantly improve grapevine performance, from better vine growth and drought tolerance to higher yields and transplant success. Below, we summarize how AMF (with a focus on R. intraradices) benefits grapevines and provide practical guidance for leveraging this fungus in vineyard management, particularly in North American growing conditions.
Enhanced Nutrient Uptake
Phosphorus (P) is a critical macronutrient for vines, yet in many soils P is present in forms that are not easily accessible to roots. R. intraradices addresses this by sending out extremely fine hyphae that explore a much greater soil volume than roots alone, scavenging phosphate ions beyond the root depletion zone. The fungus effectively acts as a living pipeline for phosphorus: it transports P back to the root and delivers it to the plant at specialized root structures called arbuscules. Mycorrhizal grapevines often show dramatically higher P uptake and tissue P levels than non-mycorrhizal vines – for example, one experiment found foliar P content almost doubled in AMF-inoculated grapevines compared to uninoculated controls (with associated increases in zinc, copper, and iron in the leaves as well). AMF hyphae also secrete enzymes and organic acids that help solubilize bound phosphates in the soil, further boosting nutrient availability. Notably, the benefits of AMF are greatest in low-P conditions: in nutrient-poor soils, a well-colonized vine can thrive where it might otherwise suffer P deficiency, sometimes reducing the vine’s external P fertilizer needs by an order of magnitude. (Conversely, in very high-P soils grapevines tend to down-regulate mycorrhizal colonization, as the plant doesn’t need the extra help.) In essence, R. intraradices serves as a natural biofertilizer, greatly extending the grapevine’s nutrient foraging ability in the soil.
Arbuscular Mycorrhizal Fungi and Improved Water Uptake and Drought Resilience
Beyond nutrients, R. intraradices symbiosis also enhances the vine’s water uptake and drought tolerance. The fungal hyphal network can access water from soil pores too small for roots, effectively increasing the absorptive surface area for water. In drought-prone regions or during dry spells, mycorrhizal vines consistently maintain better water status than their non-mycorrhizal counterparts. For instance, in controlled experiments, grapevines inoculated with AMF showed significantly less negative leaf water potential (indicating less water stress), higher stomatal conductance, and higher photosynthesis rates under drought compared to uninoculated vines. Part of this improved drought resilience comes indirectly from better nutrition – AMF-inoculated vines had superior P status, which helps sustain root growth and stomatal function during water stress. Additionally, the fungus can alter root system architecture and deposit glomalin (a fungal glycoprotein) in soils, which improves soil structure and moisture retention around the roots. The overall outcome is that AMF-colonized grapevines are more “drought-avoidant,” sustaining higher tissue water content and physiological activity under water-limited conditions than vines without AMF. This trait is increasingly valuable as many wine regions face greater water scarcity or rely on deficit irrigation.
Climate‑change context for AMF adoption
—A recent Chilean review highlights that Vitis vinifera production is already constrained by declining irrigation water (an estimated 95 % of vineyards report shortages) and mounting disease pressure as temperatures rise. The authors conclude that arbuscular mycorrhizal fungi (AMF) can serve as a “biotechnological tool” to buffer both abiotic stress (by improving water and P/N uptake and sustaining photosynthesis during drought) and biotic stress (by triggering mycorrhiza‑induced resistance against trunk pathogens, nematodes and viruses). They also stress the importance of sourcing locally adapted AMF isolates to protect native biodiversity and maximise symbiotic efficiency under regional soil–climate conditions.
Key Benefits of AMF for Grapevine Health and Productivity
By partnering with AMF, grapevines reap a range of growth and health benefits.
Agronomic studies comparing mycorrhizal and non-mycorrhizal vines have documented the following improvements:
Vigor and Nutrient Status: Mycorrhizal vines develop more robust root systems and canopies thanks to improved nutrition. In one trial, R. intraradices-inoculated Cabernet Sauvignon vines had ~75% greater root dry weight than uninoculated vines, along with nearly double the leaf P concentration and 2–3× higher leaf nitrogen. These nutrient boosts translate into greener leaves (higher chlorophyll) and a more vigorous vine canopy.
Better Transplant Success: AMF inoculation helps young vines overcome transplant shock. In a study with micropropagated grapevine plantlets, those treated with R. intraradices had almost double the survival rate after weaning compared to controls, and showed faster growth (greater height, biomass, leaf area) within the first two months. Establishing mycorrhizae early ensures the vine quickly regains nutrient and water uptake capacity in field conditions, leading to higher transplant success.
Stress Tolerance (Drought, Nutrient, Disease): Mycorrhizal symbiosis makes vines more resilient to environmental stresses. As noted, AMF-colonized vines maintain higher stomatal conductance and hydration under drought stress. In low-fertility soils, AMF help buffer nutrient deficiencies so vines are less likely to exhibit stress symptoms. There is even evidence that AMF can induce resistance to certain root pathogens – for example, vineyards with healthy AMF populations have shown lower incidence of “black foot” root disease, as the fungal symbiosis improves root health and defensive capacity. Overall, AMF acts as a biostimulant, helping vines tolerate drought, nutrient scarcity, and some diseases more effectively.
Higher Yields and Fruit Quality: Perhaps most importantly for growers, AMF can boost crop productivity. In field trials, grapevines inoculated with AMF produced significantly more grape clusters per vine and higher overall yield than non-inoculated vines. In one two-year study on Cabernet Sauvignon, mycorrhizal vines yielded about 25–30% more fruit (by weight) compared to controls. Crucially, this yield increase comes without sacrificing fruit quality. Mycorrhizal vines in the same study also had higher concentrations of phenolic compounds in the grapes – including ~25% more skin anthocyanins – which enhance wine color, flavor, and antioxidant content. Other trials similarly report equal or improved grape quality (e.g. balanced sugars and acids, nutrient-rich must) in AMF-treated vines. The net effect is that a well-colonized vine can ripen a full crop with adequate sugar while also improving flavor and metabolite profiles, meaning growers get both more fruit and better fruit.
AMF in Low-Phosphorus Vineyard Soils (North America)
Many vineyard soils in North America have inherently low available phosphorus, making AMF symbiosis especially valuable. Regions such as parts of Washington and Oregon (with volcanic or weathered soils), coastal California, British Columbia’s Okanagan, and even certain Ontario vineyards often report low soil P levels or tightly bound P that vines can’t easily access. In these low-P scenarios, grapevines rely heavily on mycorrhizal fungi to meet their P needs. Vines in “low P” blocks can maintain adequate tissue P and show no deficiency symptoms largely because of AMF foraging. Field observations back this up: for example, researchers in Oregon’s Willamette Valley noted that low soil P availability did not translate to low vine P status where AMF were present, underscoring that native mycorrhizae were helping vines get by. That said, AMF are not a panacea for extreme depletion – if soil P drops below critical thresholds (e.g. <5 ppm extractable P), even mycorrhizal vines may become P-deficient and struggle with stunted growth and poor fruit set. In such cases, growers should consider both inoculating with AMF and applying modest P inputs to build soil fertility. The key point is that R. intraradices is most beneficial in P-impoverished soils – under those conditions, inoculation can dramatically improve vine P uptake and growth, whereas in high-P soils the vine gains little extra from the fungus. Relying on AMF for phosphorus not only supports vine nutrition but also has environmental benefits, potentially reducing the need for heavy P fertilizer applications (and thus lowering the risk of phosphate runoff into waterways).
Application: Inoculation Timing and Methods
When and How to Inoculate:
The optimal time to introduce R. intraradices into a vineyard is at planting or during early root development. For new vineyard establishments, this means inoculating young vines (dormant rooted cuttings or potted nursery vines) at transplanting. Growers can apply granular or powdered AMF inoculum in the planting hole, dust it directly on the roots, or dip vine roots in an AMF spore slurry immediately before planting. These methods ensure the fungus comes into direct contact with roots and colonization begins promptly. Nursery propagation offers another opportunity: mixing AMF into potting media when raising grapevine cuttings will pre-colonize roots so that vines are mycorrhizal by the time they go into the field. This approach has been shown to boost subsequent field performance of vines by jump-starting the symbiosis. If planting into fumigated or sterilized soil (for instance, replanting an old vineyard site that was treated for nematodes), inoculation at planting is critical – otherwise the soil has virtually no beneficial fungi and vines will remain non-mycorrhizal for an extended period. Field trials in Oregon have demonstrated that grapevines in fumigated plots had negligible AMF colonization unless they were deliberately inoculated at planting. In contrast, planting into older vineyard soil with an intact native AMF community is more forgiving, as indigenous fungi will often colonize new vines on their own (though supplementing with a robust inoculant can still enhance colonization levels and early growth).
In established vineyards: Introducing AMF after vines are already planted is more challenging, but there are methods to do so. One approach is to apply granular inoculum in furrows or holes near the vine root zone (to get spores closer to roots). Another strategy is injecting liquid mycorrhizal inoculum through drip irrigation systems, which can distribute the propagules to the root vicinity. Additionally, using mycorrhizal cover crops or companion plants in the vine rows can help spread AMF to grape roots over time. Many grasses and legumes commonly used as cover crops are good hosts for AMF; planting these in row middles or undervine can act as a “living reservoir” of mycorrhiza that gradually transfer to the vines. (Note: avoid non-mycorrhizal covers like mustards in areas where you want to promote AMF, as Brassica species do not host AMF and can even suppress them.) While post-planting inoculation is possible, it may take longer to see effects than early-life colonization, and success can be variable. Thus, integrating AMF at the start of a vineyard’s life is ideal for maximum benefit.
Compatibility with Other Inputs and Sustainable Practices
One advantage of R. intraradices is that it is generally compatible with typical vineyard inputs and sustainable farming practices. It thrives alongside organic matter additions like compost or mulches, which improve soil structure and provide resources for the fungi. Moderate use of fertilizers is also fine – growers often continue normal nitrogen and potassium fertilization, but can reduce phosphorus inputs when AMF are active, since the fungi make soil P more available (allowing cost savings and avoiding nutrient imbalances).
It is recommended to avoid excessive P fertilization, as high soil P will chemically satisfy the vine and actually suppress mycorrhizal colonization, negating the benefits. Similarly, be cautious with certain agricultural chemicals: soil fumigants or fungicides with broad antifungal activity can harm AMF propagules. If a fungicide treatment is needed, using primarily foliar fungicides or timing soil-directed fungicides when AMF are less active can mitigate negative impacts. Always check product labels for AMF safety if planning a concurrent inoculation.
Combining with biostimulants:
AMF inoculation can be part of a broader biofertility program in the vineyard. Researchers have found synergies between AMF and other beneficial microbes. For example, the beneficial rhizobacterium Bacillus subtilis is often applied in vineyards for biocontrol and growth promotion, and it pairs well with R. intraradices. Co-inoculating grapevines with AMF plus B. subtilis has shown significantly greater plant growth than using either alone – the AMF boosts nutrient and water uptake while the bacterium produces growth-stimulating compounds and helps suppress soil pathogens, together resulting in healthier, more vigorous vines. Other inoculant fungi like Trichoderma can also coexist with AMF, targeting different aspects of plant health. The key is that a diverse, microbially rich soil tends to support robust AMF function rather than hinder it. Just take care to avoid highly fungicidal treatments around the same time as applying AMF, as noted above, so you don’t inadvertently kill your beneficial fungi.
Best practices to support AMF: Once you’ve established mycorrhizal fungi in your vineyard, certain practices will help them flourish. Keeping some form of cover crop or vegetation year-round provides continuous host roots for the fungi, preventing starvation during fallow periods. Minimizing deep or frequent tillage is important, as intensive soil disturbance can break the hyphal networks and reduce AMF effectiveness (switching to no-till or shallow cultivation systems is more AMF-friendly). Many growers using AMF also adopt organic or sustainable viticulture methods that naturally align with nurturing soil biology – for instance, using compost, reducing synthetic fertilizers, and employing deficit irrigation, which can even stimulate greater AMF colonization in vines. With proper management, inoculated vines can achieve over 50% of fine roots colonized by AMF within a year or two. Growers should essentially treat the mycorrhiza as an extension of the vine’s own roots: feed it, protect it, and it will reward you with ongoing improvements in vine health and productivity. In practical terms, leveraging R. intraradices in vineyards offers a science-backed route to stronger, more resilient grapevines that produce high-quality fruit sustainably – a win-win for both vineyard performance and soil ecosystem health.
References:
Trouvelot, S., Bonneau, L., Redecker, D., van Tuinen, D., Adrian, M., & Wipf, D. (2015). Arbuscular mycorrhiza symbiosis in viticulture: a review. Agronomy for Sustainable Development, 35, 1449‑1467. https://doi.org/10.1007/s13593‑015‑0329‑7 link.springer.com
Krishna, H., Singh, S.K., Minakshi, G., Patel, V.B., Khawale, R.N., Deshmukh, P.S., & Jindal, P.C. (2006). Arbuscular‑Mycorrhizal Fungi Alleviate Transplantation Shock in Micro‑propagated Grapevine (Vitis vinifera L.). Journal of Horticultural Science & Biotechnology, 81(2), 259‑263. https://doi.org/10.1080/14620316.2006.11512059 researchgate.net
Schreiner, R.P., Tarara, J.M., & Smithyman, R.P. (2007). Deficit irrigation promotes arbuscular colonization of fine roots by mycorrhizal fungi in grapevines (Vitis vinifera L.) in an arid climate. Mycorrhiza, 17(7), 551‑562. https://doi.org/10.1007/s00572‑007‑0128‑3 pubmed.ncbi.nlm.nih.gov
Schreiner, R.P., & Mihara, K.L. (2009). The diversity of arbuscular mycorrhizal fungi amplified from grapevine roots (Vitis vinifera L.) in Oregon vineyards is seasonally stable and influenced by soil and vine age. Mycologia, 101(5), 599‑611. https://doi.org/10.3852/08‑169 pubmed.ncbi.nlm.nih.gov
Massa, N., Bona, E., Novello, G., et al. (2020). AMF communities associated to Vitis vinifera in an Italian vineyard subjected to integrated pest management at two different phenological stages. Scientific Reports, 10, 9197. https://doi.org/10.1038/s41598‑020‑66067‑w pubmed.ncbi.nlm.nih.gov
Fattahi, M., Nasrollahpourmoghadam, S., & Mohammadkhani, A. (2021). Comparison of effectiveness of arbuscular mycorrhiza fungi (AMF) on Vitis vinifera under low‑irrigation conditions. Agricultural Science Digest, 41(Special Issue), 119‑128. https://doi.org/10.18805/ag.D‑253 arccjournals.com
Aguilera, P., Ortiz, N., Becerra, N., et al. (2022). Application of Arbuscular Mycorrhizal Fungi in Vineyards: Water and Biotic Stress Under a Climate Change Scenario – New Challenge for Chilean Grapevine Crop. Frontiers in Microbiology, 13, 826571. https://doi.org/10.3389/fmicb.2022.826571
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