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Sep 15, 2022

Arbuscular Mycorrhizal Fungi, known as AMF, has an interesting an important relationship with plants, grapevines included. AMF helps vines take up mineral nutrients, creates a layer of protection from pathogens by occupying plant cells, and seems to improve soil structure and water movement.  In turn, grapevines supply carbohydrates to the fungus. Scientists believe the pant calculates the value of giving carbon in exchange for nutrients provided by the AMF.

Tian Tian, Viticulture Farm Advisor, Cooperative Extension Kern County, UC Cooperative Extension studies this super host relationship between grapevines and AMF to determine how farmers can cultivate this natural alliance.

She also covers how different Nitrogen applications impact wine flavor. A winemaker can create tropical notes or clean flavors in Chardonnay through soil, foliar or winery applications of Nitrogen.


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Craig Macmillan  0:00  

Today is Dr. Tian Tian Viticultural Farm Advisor with Corporate Extension, Kern County, part of the UC Corporate Extension system. Dr. Tian, thank you for being with us today.


Dr Tian Tian  0:11 

Thanks for having me.


Craig Macmillan  0:12 

Can you tell us a little bit what's your role as a Viticulture Farm Advisor? That's a term that we hear but we don't always know kind of what it means.


Dr Tian Tian  0:19 

My title is a Viticulture Farm Advisor. So there's a three components involved in my job extension, research and education. So a lot of times what we do is we help growers to solve problems, through farm calls and to find better solutions for their problems through a research project. And if they are something, knowledge have been obtained through research or other sources, we communicate with growers and to inform them the availability of those knowledge. And the meanwhile, education is occurred during this process. Specifically for Kern County, this is a big area for grape production. So 60% of the grape in the county are table grapes, and close to 30% are wine grapes, and 10% is a rasin grapes. The nature of my work, I work close with table grape growers, then to help them to solve the production issues they may have. And they're teaching me a lot of things along the way.


Craig Macmillan  1:20 

I'm sure. I'm sure. So you have a role directly with farmers.


Dr Tian Tian  1:25 

Yeah, yeah, it's way, a lot of times we find those research questions in the vineyard and a grower call us to say, for example, last year, was it delayed, the spring grows, a lot of them are observed. Stunted growth, and they're just wondering what's happened. And then that is actually as a start off me to look into what it is the reasons lead to the problem. And next year, what can we do better. And then, early this year, when we have our annual meeting and a rower come and they just say, Okay, now we know how there's some practice we can use to avoid the problem again, and how to adjust our practice based on the weather we got in certain years. And what other things we should taking, taking consideration when making management practices. All of those has been a really beneficial for both sides. I learned a lot from them, and then they actually benefited from the extension work were doing.


Craig Macmillan  2:25 

That's really great. And I'm glad that that exists. And I'm glad you're on the job there in Kern. And prior to that you have done a lot of research in the area of arbuscular mycorrhizal fungi. And also in terms of the effects of nitrogen, either as fertilizer or natural uptake, into vines and impacts on buying productivity and also on wine quality and all of that. Mycorrhizal fungi are something that a lot of us hear about. We're aware of. We know they're important. It's part of the soil biome, but I think a lot of us can use at least a refresher course. What exactly are arbuscular mycorrhizal fungi? What is the role that they play in the soil microbiome?


Dr Tian Tian  3:05 

That's a really good question. Actually. I feel arbuscular mycorrhizal fungi is probably a one group of the fungus were no more than a lot of other groups. The reason for that is arbuscular mycorrhizal fungi actually form the fungal structure inside of the critical cell of grapevine roots. And it's probably something happened million years ago that grapevine just decided they really liked this a friend. So for a lot of roots, we have looking at 80, let me say 60 to 95% of the root cells are a critical cells are colonized by arbuscular mycorrhizal fungi. And so it's kind of a reflection about how how tight those association is. So in terms of what does the fungus do, there's a main, the three main roles we know. The top is to help the plants to take mineral nutrients from the soil. So especially those fully mobile ones and the ones we know more than others is a phosphorus. So it's in the vineyard where you have low phosphorus availability, the day you fumigat it and then just kill that AMF inoculum and your ends up with a stunted vine because phosphorus deficiency and it has been observed in the past. But once you innoculate with AMSF they're improving the efficiency of obtain those fully mobile nutrients. And the second thing we believe or it needs more research into the area is because they have a lot of fungal structure is a high fast growing in the soil. So they improve the aggregation of the soil and then improve the water movement in the soil. So that is, that is a new area where or kind of the newer research or dive into it is maybe the grapevines are also say creating a lot of the, let's say sugar or other compounds a carbohydrate compounds through AMF hyphae. And so it's influencing the soil microbial community in that way. So it is a really interesting fungus where they have part leaving the plants and apart out of the plants, and also there have a critical contribution to grapes. But it's a fair trade when the AMF is working hard to grow the hyphae through to explore the soil for those mineral nutrients. And the grapevines are supply carbohydrate to those fungus as well. So what they caught is a fair trade market. In other crop, what they find is actually the plants were reward the AMF be able to deliver the more resources they need.


Craig Macmillan  5:54 

So are AMF actually do they play the role of kind of an extension of the roots? They're bringing resources to the root?


Dr Tian Tian  6:03 

Yeah, kind of you can understand that way they consider the the high face or extension of the roots. But there's other arguments is a hybrid much stronger as compared to a roots. So what is probably not a really close analogy. So what we find is the root length off a grapevine is kind of the distance your walk your dog in a day, but the length of the hyphae the vine can hold is the probably the lens you can kind of make a circle around the earth for at least one circle. So yeah, because there's lower construction cost, if you have thinner hyphae compare with grapevine roots, which is thicker as compared to grass and as a crop. But that data is only opt in to from our greenhouse trial. It's does not necessarily mena its representing what happened in the natural environment.


Craig Macmillan  7:03 

How do you study the stuff in the natural environment? This seems really hard. You're talking about things that are finer and sounds like very fragile, even compared to roots. And if you're growing things in like a clay, clay loam soil, it seems like it'd be hard to tease these little bits out or to study how things moved or anything. How do you do it in the field?


Dr Tian Tian  7:22 

Yeah, so in the field, what our focus is we focus on the roots, it is really difficult to get even in the greenhouse where the vines growing in a confined space, but those hyphae are really hard to pick up from the soil. And then to find them to isolate them and to evaluate them is really difficult. But there's a certain protocol can be used to study that area. It's just not that what I did for my PhD. My PhD advisor was left with all those. So what my my PhD work focused is I'm looking into arbusbular actually living in the roots, they were formed a tree like a beautiful structure called arbusbular actually living in the roots, they were formed a tree like a beautiful structure called el bosque, you're the frequency of those albacore show up and the intensity of their basket or, or even the size of them are a reflection of the nutrient exchange between the two partners. So what I did is we're we're collecting rock samples, both in the field and also in the greenhouse to clean it up, and then to stain the roots and a molded glass plate, and then to look under scope. So we could say how different treatment has effect, basically, the association of grapevines and arbuscular mycorrhizal fungi. But in addition to that, we'll look into plant grows, plant nutrient status and to track it during the season. And so in our list work, give us some idea about what happening. It's a big complicated puzzle and a wedge, I find it's really fascinating, but may allow it to make it a different area to study albacore. The frequency of those arbuscular show up and the intensity of their arbuscular or, or even the size of them are a reflection of the nutrient exchange between the two partners. So what I did is we're we're collecting root samples, both in the field and also in the greenhouse to clean it up, and then to stain the roots and mount it on a glass plate, and then to look under scope. So we could say how different treatment has effect, basically, the association of grapevines and arbuscular mycorrhizal fungi. But in addition to that, we'll look into plant grows, plant nutrient status and to track it during the season. And so in our list work, give us some idea about what happening. It's a big complicated puzzle and a which, I find it's really fascinating, but may allow it to make it a different area to study.


Craig Macmillan  9:01 

Right, right. Right, right. This is a silly question, I guess. But there's no silly questions. So is it fair to say that more AMF is better for crop?


Dr Tian Tian  9:12 

That's actually a really good question. We're trying to find the answer is not an optimal level. It's like wow, what my wines are 80% of the fine roots of my vine our colonized and away call it good. It's more complicated than that. If we're thinking about a question like this is first if you like you're in your vineyard, and you do your leaf petiol or leaf blade and nutrient test your phosphorus or has never been really a problem. So for us, that's an indication that the vines, the association between mycorrhizal and the grapevines are working and then so if that does not really work, and the way you're using the test you say a phosphorus is a probably mineral nutrient or tell you how good the bond is. And another thing is grapevine we consider it as a super host. They love AMF. So listen, it's how it happened is glorified probably pretty efficient in terms of fixed cover so they can afford to allocate those were like to contribute to the AMF to you know, to establish a good relationship. And another thing for plants is they need to consider if I give the carbon to the it's not that smart of the process, but that's how we think that's happened is the grapevine so will have a way to semi calculate how much carbon you get or how much things like nutrient you can get from that. So what they find is with the amount of carbohydrate they supply, and it's more efficient to allow the fungus to do the job to get the bio nutrients. And then there's other benefits off AMF is there whilst they occupied the cells and a lot of time the the pathogens are hard to get into the into the roots and to serve as a layer of protection. That is area more research is dive into under to say how good it works. So in general, I would think not exactly more AMF is better. Its the plant make it's a choice that based on the situation. But for other samples I have a look at in Oregon and the roots are colonized really well. With that being said, Oregon is an area where we have more radical soil where the availablity is relatively low. And so that's maybe why we say a really high colonization rate. I'm curious to see what happened California.


Yeah, absolutely. And that was leads to my next question is as far as we know right now what are the conditions that promote AMF populations?


Well we find is in general adding AMF is a different story if you're have you have no fumigation going on your vineyard is relatively healthy on a you don't run into other issues it is really not clear to us if you're inoculated certain you wouls day more beneficial AMF will lead to a better growth. That part of the data or is to your liking because if you apply to to the greenhouse it does not representing what happened in the field if you put in the field it is just really hard to do that you probably need to mix your soil with also inoculum right and and now there's a some product say you can mix it in the liquid and then there were significantly increase the amount of colonization but there's so many different ways to look at the fungus so it's added to a lot of vague area what we're gonna be doing. So but in general, what we're finding is if you have have legume as your cover crop legume is a host for AMF and so they're able to increase kind of both of the AMF population. So if you are thinking about to grow a new you establish a new vineyards and the you have the history nutrient limitation, I will just say use legume would be a good choice. And on the other hand mustard is not AMF host but it has been using cover crop some people were saying it's were released some of the compounds that were feter nemotodes so that's a totally different story. Yeah, so for me the best way it's not really add more AMF and the vine will bemore healthy. A lot of time what happened is in the vineyard there the vines and afff are both pretty happy and they have a good relationship. Actually we tried really hard to to increase nitrogen fertilization rate and able to shake that relationship a little bit so they're bonds are pretty tight and then it's if you are not running into a huge issue that is maybe it's the AMF inoculation and potential is low or that's a certain things in the vineyard and welcome to discuss that was me however interested know. And then the last thinkg that happens, you really it's I want to say most of the time, the AMF in your soil will be sufficient to help your vines to get the fully mobile nutrients like phosphorus, Zinc, copper from the soil.


Craig Macmillan  14:31 

Are there ways that I can test to see whether I've hit that threshold?


Dr Tian Tian  14:37 

There's a test you can run to see the inoculum potential and then just to say feel filled is a safe, but generally that is happens normally in a research lab. Yeah, there's not any commercial lab I know of there were collector root, route samples, because that's a tedious process. You're collecting the routes and the unit to pick only the fine routes, not all the woody roots you can, the AMF does not live there. Then you need to clean them really well, stain it at a look at it under the scope and evolve in like way, we have a great system and then to great how much the roots got colonized. So while the way we're used mostly to say where a problem occurred is look at leaf petiol and leaf blade, phosphorous status and I felt that's the most easiest way you can now if there's a problem. But the threshold if a nutrient is deficient or sufficient, that's another another topic.


Craig Macmillan  15:36 

There's kind of a proxy variable there that I can actually look at my soil phosphorus, it's maybe not mobile, then I can then look at what the what the deficiencies are, sufficiency are in the vine and say, hey, you know, I'm guessing that I don't have a lot of mycorrhizal activity here. arbuscular mycorrhizal activity here because I'm not seeing that phosphorus moving, there's plenty there, but it's not moving into the plant. So that seems like a good kind of guide. What things can go or do if anything to encourage AMF in their soil? Assume its there, relationship with the grapevine. Maybe I'm not seeing the kind of transport that I think I would like to see which would make sense what can I do to help move that process along recurs as populations?


Dr Tian Tian  16:18 

Okay, so that's kind of a dive into a really good question. So a lot of times, people weill think AMF is able to assess a different pool of phosphorus as compared to grapevine, that's really not true for AMF or they're assessing all the inorganic phosphorus in the soil. So a lot of times the availability of phosphorus in the soil is changing based on the soil pH if you have a really low pH soil you're probably outline prior to planting to bring up the pH and a like that. But there's no really a particular thinkg you're really do in the vineyard to bolster up the AMF population as long as you have a good canopy growth canopy create a couple of hydrate without carbohydrate AMF wont. It's it's a kind of both it's a fair market trade thing. If the grapevine is because in some of the experimental way wrong and the way keep the nitrogen rate really low so the vines are not really growing and we have say the arbuscular frequency in the fine roots are decreasing. Our understanding of that is so the grapevine says I tried really hard but I just cannot supply the carbohydrate you be happy with. So AMF just said okay, you know what I will do what I can do I'm not as happy as when you give me more but I will do what the job I can possibly offer right. Well you have a decent Canopy Growth and your nitrogen is kind of in the middle they reach you know a happy relationship is, yeah, you know what I am ready to share with my carbohydrate and AMF say okay, I'll give you the maximum benefits. But if you are in the vineyard you have really high nitrogen status which mainly happens in research not really I've noticed that you weren't dump a lot of nitrogen if that happens. And so the vines say maybe I have you know enough ability to grow the roots I think our be less dependent on AMF or the nitrogen you add in actually is regulating some part of AMF and AMF is okay, I feel my function our association our relationship is affected the cell that I decided to colonize les. So actually there's quite a bit of research going on to tease this apart out but so far we don't know which is a key part that is playing in terms of how AMF and the plants out there are regulating each other.


Craig Macmillan  18:44 

So we know a little bit but we don't know if mentioned Oregon soils and so at this point, what do we know about AMF and soil and other particular soil that seems to do well and you find it more frequently here there's others were really shows up at all.


Dr Tian Tian  18:57 

Yeah, well I was thinking about this question because when we're thinking about soil type that's including a lot of things the texture the pH the organic matter the so so I'm am still really learning about California to the soil here and then I haven't got to dive into the roots yet. So what happened in Oregon is there some more clay and loam soil there generally with AMF of the hyphae of the fungus are pretty powerful in terms of explore the soil and a few have little pore and the roots cannot grow and lead and the hyphae. So when we grow plants in the greenhouse where we have have soil and have sand and the AMF of colonization is about 75 to 95 even 100. And that is a similar to what we got from field where we have more clay loam soil. So I would say soil texture or soil type may have some effects, but I'm not so clear on how big the impact is. In terms of the lifecycle, or the impact of AMF I found the plants.


Craig Macmillan  20:04 

So moving to California, welcome, very glad to have you as a farmer advisor in Kern County, and you've been doing some research here recently. That's kind of exciting. Would you want to tell us a little bit a little bit about that things related to nitrogen fertilization and things related to wind quality and nitrogen uptake? You've done some interesting stuff on that.


Dr Tian Tian  20:23 

My Nitrogen work is also work I did in in Oregon, and my colleague, Dr. Matthew, Fidelibus in Cardiac Center, and he's doing more work in table grapes. Than they have a bigger project to find a more efficient way and easier way to look into plant to vine nutrient need and how you're going to fertilize. So for my work in Oregon, is to start with a simple question. If you want to add in nitrogen, should you add it in the vineyard or in the winery. Because nitrogen is a essential nutrient for the grapevines but also essential nutrients for the yeast, you can either adding nitrogen to the soil or to the foliage in the vineyard, or you can just keep the nitrogen low in the vineyard and then the added in the winery. And in the winery you can have a two form of nitrogen you can add a one is diammonium phosphate, and then or you can add organic and supplements like those those products and have a lot of people are selling. At the beginning of the research is we want to find a which one relates to about her wine quality in chardonnay and also in Pinot Noir. What previous work in Oregon what my PhD advisor Dr. Paul Schreiner did is he find that maintaining a low nitrogen status in Oregon vineyard is not a bad idea. The yield is less responsive to nitrogen status as compared to the canopy grows the vegetative growth, if you're changing nitrogen application rate, you're saying the response pretty significantly. And then so that is one benefits. And second is from the wines they made they point to the low nitrogen wise actually gave more floral aromas. And then the color is darker. So it's related to a better quality in the sense of you know, sensory and appearance of the wine and all those things. They think lower nitrogen may be the way to go. But that research is did in our research farm where they have put the device in 50 gallon big pots, so they can control the fertilization. It's not really a commercial production setting. So my PhD work is to focus on okay, let's think about that were to add in nitrogen and water to relate to. So what we actually find is adding nitrogen to the soil in the vineyard affected the wine sensory quality more than other treatments, where you've highlighted in the trial, and we say a more clear in fact, in shadow neck than Pinot Noir. The reason is not really a varietals, only varieties are different. It's also because the Chardonnay block where you'd have lower nitrogen depth status to start with. Yeah, so what we're finding is if you're adding nitrogen to the soil, and then the finish wine, the Chardonnay, we're have more tropical aroma, the pashion fruit trait that is a famous for sauvignon blanc producing New Zealand. So a lot of people like those more fruity drink wine, but if you wanted to Oak Chardonnay, and then to maintain a more, the winemaker calls it clean characteristics, and then data where bring more potential during the aging process. We say the soil aliance brings more the rather fruit characters, like a berry, like the cherry, and the plum, or it's kind of in that category, I need to go back to dive into my own notes. But what what generally we find is soil nitrogen application in the bigger cause and effect on the wine thatn foliar application in the vineyard or adding nitrogen in the winery.


Craig Macmillan  24:10 

In a positive way?


Dr Tian Tian  24:11 

Well, we were considered as winemaker can use it as a tool to make wines in a different style. So if you want your wines to be more fruity or have these and that characters, there's a something you could do just kind of just other just a practice you're already using in the vineyard and to achieve that.


Craig Macmillan  24:31 

You talked about two topics here. And so I'm gonna ask the same question regarding the kind of both of them is it what is the one thing that you would advise or would recommend to a grape grower regarding AMF and maybe soil health just kind of in general?


Dr Tian Tian  24:46 

Wow. Theres so many things. But in general what I, I have been thinking about this question a lot because now soil health is a big topic, no matter whichever area would dive into and not only grower, consumer wants to have a fruit a coming from, a vineyard that is more sustainable operated. One advice I would have is adding organic matter back to this compost is good. There's a lot of things, it does not need to be so fancy. And it'll work kind of increase the if organic matter basically adding food to the soil microbe microbial community, right, there's different parts, and each of them are playing a role. And we do a lot of bio genome kind of study, who is there, but what they're doing is a series of things we don't know. And so that is a good thing. And the second is, so I'm only allowed to say one thing?


Craig Macmillan  25:47 

Go ahead and say a second thing.


Dr Tian Tian  25:51 

Okay. So the second thing I always think is just look at do your leaf petiol or blade, nutrient. The threshold stablished by research. That's a lot of work into it, but it is representing a limited number of vineayrd. If you have a record for your own vineyard, you want to feel more comfortable about how you manage the nutrition.


Craig Macmillan  26:15 

Now that said, just do one thing I'm going to now I have to ask a follow up question. What's your recommendation for how to add organic matter? What do you think are the best ways to do that?


Dr Tian Tian  26:24 

Well, a good question. Actually, I was thinking about I would dive more into that as a research trial. So a lot of growers in our region do, they were just lay on the compost kind of on the surface around the vine. So there's a benefit is actually like, yeah, slowly releasing fertilizer. But some people will say add the planting, you can incorporate it into the soil a little bit, or even after planting, you can incorporate it into the soil. Yes, you're improve part of the roots, but you're also adding nutrients back to the soil where the roots can easily access. The answer is I'm not so sure what is a best idea. And also, now they have a liquid for an organic fertilizer on the market and so there is another way other than to use a compost, there's another form of fertilizer you can add and that is organic certified and then provide organic matter to the soil.


Craig Macmillan  27:16 

Now going back to nitrogen, what is one thing that you would recommend to grape grower regarding their nitrogen management?


Dr Tian Tian  27:23 

Oh, okay, monitored closely, and they don't fertilize too much. But as of this year, the fertilizer price is increased to 30 to 40%. I think over fertilization is really not an option. But it's more like I feel growers like to take care of babies, you'll you look at their needs, and then you you know, you do the physical exam, to understand what's happening, and then you'll fertilize it based on that. Block to block may be different. And the variety to a variety can be different. And then the more you know about them, and then the more you can help them to gather to the level of of canopy growth and the fruit quality you're shooting for.


Craig Macmillan  28:05 

And that's gonna have everything to do with taking those petiol and leaf blade samples and keeping records and then comparing them to what your outcomes are.


Dr Tian Tian  28:13 

Not only that, it's also including looking at the vineyard and to walk through to to look at the canopy. If you're thinking about a petiol nutrient test, they're testing concentration, right, and then the threshold established our concentration. But how the concentration of those nutrients is decided by the canopy size. Okay, the vine grows, have some ideas on aware, research are looking into easier ways to monitor in vine rows so you can compare a year to a year. And a lot of times it catches the onset of the problem is really important. And then we're always learning I feel agriculture is a learning business. Every year we'll learn something new and next year we're doing something better.


Craig Macmillan  28:58 

That is very wise. Where can people find out more about you and your work?


Dr Tian Tian  29:02 

Welcome to visit the UCC Kern website and then also feel free you can find my email my phone there and then feel free to call or email and I'm happy to help if there's any anything I could do to make your life happier and you will be happier.


Craig Macmillan  29:18 

And then we will have links to those things in the show notes. I want to thank our guest today Dr. Tian Tian Viticulture Farm Advisor, Cooperative Extension, Kern County UC Cooperative Extension, thank you so much for taking the time to do this interview. And thank you for sharing your knowledge. I think you're gonna be a real benefit to the region. And we really appreciate you having this job.


Dr Tian Tian  29:35 

Thank you. That is a so fun to chat about my research work and all those interesting things. The grape world is happening.


Craig Macmillan  29:44 

It is a really, really fun and I think that's why people like this podcast, especially me, this is so much fun for me. Anyway, enough about that, you know, thank you so much.


Dr Tian Tian  29:55 

Thanks for having me.


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