okay um so as don said i'm going to be talking about niche properties and niche construction by the fungus uh soilless pungence and there we go so i think today what i'm going to try and do is argue that one of the major gaps in our understanding of fungal community ecology is really a lack of detailed information about the details of individual species and uh you know we're all aware and we've seen lots of examples of um how high-throughput sequencing has really revolutionized our understanding of fungal communities and how it's getting exponentially easier and cheaper with time and as a result i think we know a lot about overall changes in community composition sort of similar to this cartoon i've showed you on the left here so we do a lot of sequencing uh we can look at samples from habitat one and habitat two um and we can compare the differences in composition and we often uh you know make hypotheses about um you know what sort of environmental filters might be determining membership across these two different habitat types um and so i guess i would argue that in some ways we know a lot about um sort of these overall changes in community structure much more than we do about why those changes occur at say the individual species level and you know this is can pose some difficulties because we know that within the you know species that co-occur in the same site of the same sample or the same habitat are actually often doing so even if they're responding to very different environmental cues that have brought them to that particular place and so even though we tend to treat you know communities as real things uh somewhat akin to if you're familiar the arguments of of uh clements one of the earliest early very influential ecologists who kind of thought of communities as sort of a super organism where all the individual species kind of function to support the whole in reality i think that they're often much more like this uh there was a concurrent ecologist named henry gleason who argued that really uh communities don't exist in a real way they're just really the sum of all these individualistic species responses um and so if we know that species are responding very individualistically to different environmental conditions this can cause some problems if we're trying to use these top-down approaches to predict you know what a fungal community might look like in the future um and you know as a mycologist i really like this overall kind of top-down approach but um i often feel like i i want some more details about the fine-grained biology of individual fungal species and so you know my goal for this talk then is really to try and uh start building uh motivating myself and maybe other people to start thinking about how we can build a bottom-up approach to fungal community ecology that's rooted in the details of individual species of fungi and so today um what i am going to do uh is um try and uh give this uh give a talk kind of using three vignettes that illustrate what i think can be gained from this approach um and so i'll be using um talking about three different uh what i'll call niche axes um relating to uh dispersal uh and recruitment uh of fungi uh some critical soil macronutrients nitrogen and phosphorus and then i want to talk a little bit about overall community composition and chemistry in the soils and i really want to follow these studies through with a single organism and this is the ectomycorrhizal fungus soilus pungents you can see this really charismatic photo of it right here i love betsy's photos of all these different cultures and hopefully suelis strikes you as being equally charismatic and ultimately what i want to do is try and use this information that we can glean about these different niche axes to then try and connect it with what uh what we know about where this organism occurs in the environment and you know this is going to be an imperfect story since this is kind of a new endeavor for me trying to think about things through this lens um what i'm really hoping to do is show you that by going into a deep dive on a single species i think this actually helps us in the long run to be able to generalize out a mechanism when we think about what's going on in entire fungal communities okay so i want to start by talking about dispersal so this image on the left here shows point raised national seashore which is where i've been doing research for a while where sewell's pungence occurs this is just north of san francisco about 45 minutes to an hour and a half depending on traffic and really before going any further i need to acknowledge tom bruns who is gratefully here for really introducing me to this system as a doctoral student and all the work that he's done here which has made much of my work possible and you can see tom is here working on his gps unit with that hammer and uh i hate that zoom is off so if this joke was bad i don't know it but i'm assuming you're all laughing with me right now um and then this is me here um in san francisco where i'm sitting right now giving this talk and you know one of the reasons that uh working here has been so appealing is you can look in this picture on the right and you can see this very patchy kind of vegetation structure at the coast and in particular here there's really one species of pine which is pinus miracada or bishopine and this pine is really the only host for zoella's pungence in this area and really the most important ectomycorrhizal tree out in this coastal vegetation and it occurs in this primarily our muscular mycorrhizal vegetation matrix which is made up of things like bishop pine um and uh poison oak mostly as far as i can tell and uh or sorry of bacares piliolaris which is coyote brush not bishop uh and uh because uh so willis and other ectomycorrhizal fungi are obligate biotrophs um this is really an ideal landscape for trying to understand how soilless pungence disperses because we can find uh you know find its host pants in this landscape and study how it moves across this fragmented landscape and so um i've been studying dispersal of um ectomycorrhizal fungi in a number of ways but i want to show you some results from a recent paper that was led by one of my graduate students gabriel smith and so because uh swillows pungence and other ectomycorrhizal ectomycorrhizal fungi are host specific we know the location of potential propagule sources which is the pines as you can see kind of up at the top of this top left of this slide and we can measure how well these fungi disperse across this landscape by kind of going out and collecting soils bringing them back to the lab and then assaying the colonization of bait seedlings that are growing in the greenhouse like this and so we can look at you know the percentage of the root system that's occupied by these fungi and use molecular methods to characterize the diversity of these fungi and so in this cartoon in the bottom where the y-axis shows the percentage of seedlings that are colonized by em fungi uh the percentage of the root system or percentage of seedling sorry i should say and the x-axis shows a distance away from established pine trees if we see something like this like really no change in colonization of these pine seedlings with distance then this would suggest that there's really no dispersal limitation of these fungi and that wherever a pine seedling might establish this landscape it's going to be able to find its mutualistic partners however if you get something like this where you would see a decrease in the fraction of the seedlings that are colonized this indicates that there is probably dispersal limitation and that in establishing pine seedling might not be able to find fungal partners in certain parts of this landscape and what we see in reality is evidence for a fairly rapid decrease in the availability of ectomycorrhizal propagules which is consistent with this idea of dispersal limitation now of course we don't just want to know if fungi colonize these seedlings but also who colonizes them so we've used dna sequencing to characterize fungi from the individual root tips at these different sites and you know while this global model shows uh dispersal limitation uh what we see from sequencing uh are really two important things the first is that from a total ectomycorrhizal fungal community associating with bishop pine at this site which is probably close to 200 species there's really only about 20 species of ectomycorrhizal fungi that actually colonize these seedlings and out of that there's really only seven in this particular study that appeared with any sort of regular abundance so there's a very small fraction of the total electromycorrhizal fungal community that's actually very good at dispersing you also notice that these fungi individually show different dispersal patterns so some of these um like uh helbella vespertina and tomatella sablanosana disappear within a few meters of the forest edge uh whereas some of these like the left for terrestris um and suella's pungence because the star of our show they're able to colonize seedlings up to you know a few hundred meters to a kilometer away from the edge of the forest so they're dispersing quite well the second thing that you might be noticing is there's actually a pattern for a number of these fungi where they appear to peak in abundance farther away from the forest edge which seems sort of counter-intuitive and so you know we've been really curious about why you might see patterns like this all right and so i'll explore this maybe a little bit more of a deep dive into suelis so if you focus on solos puncheons uh we know uh from the figure i just showed you that colonization does peak at a distance and so one possibility here is that there's some sort of mechanism where it's spores tend to preferentially disperse long distances so they're preferentially deposited farther away from the forest edge than near to the forest edge but what we know from previous studies is that this actually isn't the case so we've gone out and used kind of spore trapping methods along with soilless pungen's specific quantitative pcr to count the number of spores that reach different areas away from the edge of established pines and you can see that here on the y-axis this is the spore deposition rate in terms of spores per square centimeter per day and again on the x-axis this is the distance away from established times um and so we know that the spores do kind of um monotonically decrease as you move away from the forest edge so we can rule out that as a potential explanation the thing we do actually know though and this comes from a study by peter kennedy uh is that swill is pungent is really a wimpy competitor and so what this figure shows is that um this is uh uh spore inoculations of soyuz pungents and two other ectomycorrhizal fungi onto bishop pine seedlings on the y-axis here you can see the fraction of the root biomass that was colonized and what you can see is for soils pungents when it's grown by itself it colonizes a fairly large fraction of the ceiling root system whereas uh when you co-inoculate it with either resin pokemon salibrosis or rise of pokemon oxidantalis who also were in this last figure i showed you but they totally exclude zoolous pungents from colonizing these and so it seems like this incredible dispersal ability that solus has solas pungence has comes at a competitive cost so you know despite like the fact that uh solas punjab is a poor competitor it's actually one of the most common fungi at point reyes in early successional settings and this figure shows what's known as a nestedness diagram from a study of a 10 year old tree or tree islands or tree patches and this figure i think is one of the more interesting parts of this particular study to me and what this figure shows is the matrix where the columns uh are fungi and the rows are tree patches and so you can go here and these pre-patches are kind of arranged these rows are arranged from sort of the largest tree patches down to the smallest tree patches here and you know everywhere you see a filled cell in this diagram this is where a particular fungus occurred on a particular tree island patch and so for example amanita franchetti here occurred really only on this one large tree island that i surveyed or tree patch that i serve it by contrast you can see the far left of this figure this is solace pungence and it was really present on every single tree island that i went out and surveyed all right and what this figure shows is that the communities that occur on these smaller tree islands are kind of a nested subset or a subset of the communities that occur on these larger tree islands but the reason i'm showing you this is because i think it says something about the importance of these competition colonization tradeoffs because we actually see this nested pattern repeated across studies and so this is the figure i just showed you from looking at a nestedness with these tree island patches arranged according to size this is the same figure this is the same kind of a figure from uh gabriel's paper that i was just talking about uh where these um uh these um locations are arranged uh from kind of closest to the forest edge to farthest away you can see that this nestedness pattern is repeated across this distance gradient um and um you know what we were able to do then in the same study is take a theoretical model that david tillman had developed about spatial competition which is based on an assumed dispersal competition trade-off and using uh this model we're able to recreate a nested pattern parameterize with a community with someone something like the community we see in this size gradient study and so what i think we see here is that you know sowellis is probably on an extreme end of being really good at competing and being terrible at competition but that this pattern really generalizes across the entire fungal community okay so just to wrap the uh this part of the talk um so solace is a great disperser as well as pungent is a great disperser i should say even compared with other willis in this particular system and i think by focusing on this as well as where we get all this really detailed information and since it's at the extreme end of this dispersal and competition spectrum i think we can actually help to generalize this competition composition trade-off to be something that is more applicable or widely applicable across the fungal community and more broadly there's this idea of a regeneration niche which grub in 1977 defined to include all the things that are necessary for successful reproduction and dispersal as well as the kinds of environments that favor recruitment and and i think that this regeneration niche actually then becomes a really important way in which um ectomycorrhizal fungi differentiate themselves and which hopefully you can see from these nestedness diagrams that we can use to understand patterns of fungal community composition across patterns of say habitat size or isolation or successional time okay so uh knowing about you know this dispersal and regeneration niche of this fungus i think helps to explain some of the patterns we see in ectomycorrhizal fungal community organization you know across spatial or temporal ingredients but next i want to talk about nutrients and this is often one of the things that people think about first when they begin to think about ectomycorrhizal fungi and so up until this point um i've been using the term niche or niche a bit vaguely and when there's well there's lots of different definitions of the term niche probably the one most like widely used as uh hutchinson's definition of the n-dimensional niche and there's a good summary quote uh describing this up above from from bob holt but essentially you can think of the niche as kind of an abstract space defined by different environmental axes um and so i put put one up here uh whoops and i've skipped ahead a little bit um sorry um and you know we know a lot about these for things like plants so i've got kind of a cartoon example here for say a pine um and this kind of uh area of you know if we know from physiological studies there's this area of temperature and rainfall where this pine we know is theoretically able to survive this is known as the fundamental niche if you go out in the environment and look for this pine you'd often find it in some subsped of the subset of the environmental conditions we think it can actually tolerate and this is known as the realized niche and the difference between these two is thought to result from competitive interactions that might exclude it from other areas that it might otherwise be able to occur in however this conceptualization of the niche treats biotic interactions as primarily negative despite the fact that we know that species are engaged in a large number of positive interactions such as of course ectomycorrhizal symbiosis and so a number of people myself included have kind of tried to incorporate this um into kind of niche models and the one that i've proposed is that you can think about the portion of the um this kind of fundamental niche space where a tree a species is able to grow in the absence of its positive interactions is its individualistic niche and then this you could also think of this mutualistic niche that defines the area of the environmental space it can occupy in the presence of mutualistic interactions which is often likely to be much larger due to the positive effects that mutualisms generally have on physiology okay so how can we go about trying to visualize this mutualistic niche so for ectomycorrhizal fungi as i said probably the most important niche dimensions are the host plants they can colonize uh but also the two key macronutrients that we think are the primary currencies they provide for their hosts so nitrogen and phosphorus so to try and test some of these ideas about this mutualistic niche a postdoc in my lab michael van newland and i designed an experiment to grow pine seedlings in a factorial continuous gradient of nitrogen and phosphorus concentrations and you can see an example of you know the experimental layout for one one replica of our study here and so we used uh seven different uh factorial combinations of increasing nitrogen and phosphorus concentrations so seven by seven uh a single replica of this experiment had 49 seedlings in it so we used an artificial soil so we could totally control nutrient inputs which we did by modifying this pine specific fertilizer called ingustad solution we kept the recipe sort of normal other than changing the nitrogen and phosphorus concentrations from 0.1 to about 6.4 times the normal concentrations used in in ingustan so to try and connect this back to the neutralistic niche concept we grew the seedlings either alone um inoculated with spores of swillous pungents uh inoculated with spores of fluff or terrestris one of these other common fungi at point rays or with spores of both of these fungi and we waited for about nine months and then harvested the seedlings weighed their biomass and measured the percentage of roots that were colonized by ectomycorrhizal fungi so i'm going to show you next is a diagram of the kind of data that i want to present at the bottom on the x and the y you can see this 7 by 7 combination of the n and the p treatments and so on the top left you can see it's n increases and p is going to stay the same if you kind of stay hug the axis there so you get your highest nitrogen to phosphorus ratios over there similarly kind of p increases across this axis and so over here we're going to get our our lowest uh end of p ratio so highest phosphorous lowest then and then in the middle kind of if you track the one to one this is going to be the area with the highest total nitrogen and phosphorus and then if you look up in the z plane this is where we're going to map performance either of the fungi or the plants and so what we're going to do is kind of use the data we get to map this response surface that charts fungal or plant fungal growth or plant growth across these gradients and then you can calculate the total volume occupied under that surface using something known as a convex hole and while biomass isn't a perfect representation of fitness or population dynamics we can use this as our best possible representation of the niche space that's occupied by each species so this is the niche space that we mapped out using this approach for soilus punjins and you can see there's a few things that uh jump out right away so first uh if you look kind of over here you'll see that colonization is lowest either when nutrients are kind of at their absolute low or over here where there's lots of nitrogen and not very much phosphorus so kind of high end of p ratios and then by contrast you can see that colonization is highest over here where phosphorus levels are very high but nitrogen levels are relatively low so n becomes the most limiting nutrient and this is where sowellus seems to do best and so it's actually the ratio of these two nutrients as well as the absolute magnitude of their concentrations but the ratios are really important that tend to predict a niche occupancy for this fungus so if we go to celepha this is where things get even more interesting you can kind of see that there's the exact opposite pattern and so you can see that its peak is where n is abundant so these are kind of the areas where our highest nitrogen levels and phosphorus is kind of over here at its lowest level so it kind of peaks over here when there's lots of nitrogen and not much phosphorus in the system and by contrast when there's a lot of phosphorus and not much and this is when it has its lowest colonization levels um and when you put both fungi together what you actually get is kind of maximal colonization across this surface which suggests that having multiple partners allows the plant some environmental flexibility um so unfortunately we didn't uh separate out fluffer terrestris and soils pundits colonization because this is already a lot of work so we don't know who was colonizing where but that would be an interesting next thing to try and do okay yeah so there you can see those those are the two areas where in general when there was a single species either uh soilless maybe failed to colonize over here and philippa failed to colonize over here but by having both of them together the plant is able to maintain maximal colonization levels so i want to turn out of the plant side and think about how this resource specialization from the fungi affects post plant growth and this figure is a little bit different because now we're comparing plant biomass uh uh between uh the control or these non-mycorrhizal plants with the colonized plants and so when you look at this figure uh the warm colors are gonna show where the the fungus improves plant growth or it expands the plant niche um and these cool colors show where it contracts the plant nature or reduces the plant niche or reduces plant growth relative to the control and so for so willis on the left here you can see that this is a somewhat complicated response surface but that in general plant biomass is most approved here kind of at the top right where p is abundant but nitrogen is limiting all right and this makes a lot of sense uh this reflects what we saw with the soulless colonization data to large in a large part all right and for telephone again uh we see the opposite pattern um whereas telephone seems to maximize plant growth uh when n is plentiful and p is limiting all right so this uh together this kind of suggests that um this niche specialization of the fungi is directly reflected in this mutualistic knit space that is able to be occupied by their plant host all right so the next part um maybe some of you are thinking this that this is what i expected is that because these two fungi have really complementary nutrient niches what it seems to suggest that the host could then maximize the environmental niche space it can occupy by having a diversity of partners and uh switching associations depending on the environmental context right okay so this is where uh if you thought that uh you were wrong um and i was incorrect and so we found something quite different so this is the figure that looks at uh plants growing with both the leftover trestress and soilless pungents and what we find actually is that having in this particular experiment having two partners tends to depress the benefits that you get from being uh mycorrhizal so over here in the this top left corner now what we see is that with fallopra terrestris we're actually able to maintain pretty comparable benefits um when phosphorus is limiting and there's lots of nitrogen it still seems to improve um plant growth but when you look over here at the place where the left or soilless tends to be the beneficial for the plant host that actually these benefits tend to get uh suppressed here in the presence of telephone and so this is probably because uh swollow's pundits is actually kind of a weak competitor and so in the presence of another fungus it's not really able to confer the benefits that might otherwise to the host and interestingly as well you can see that there's also this kind of exaggeration of this um of this kind of poor performance space here in the middle and this is where kind of neither n or p are limiting uh so these are kind of uh in kind of equal stoichiometry compared to what uh the plant probably needs which is actually quite interesting that um it's more about um which nutrient is is is or isn't limiting that determines uh you know when a fungus can actually be beneficial all right so it seems like these fungal interactions can actually have a negative effect on the host and complicate our understanding of functional complementarity so just to summarize while this is a really labor intensive thing to do it's possible to use these kinds of approaches to map out what we think of as niche space for symbiotic organisms and look for evidence of this mutualistic niche which we see i think in this particular study and i think doing this actually reveals some really informative things about the nature of the nutrient niche for sowellus and other fungi and so as i said first we see that absolute nutrient concentrations are of course important but really that also these relative concentrations and stoichiometry of nutrients are really important as well and what this means is that these two niche axes are interacting with each other and you can't understand a niche access alone so if we just measured you know soilless growth along an axis of nitrogen and tried to predict how it would uh it would do a different um when you had if you had different sort of levels of phosphorus you couldn't do it so you need to measure both of these axes at the same time um and then finally um we saw that even though there is interesting niche differentiation between these two fungi in a way that suggests functional complementarity in a very appealing way um in contrast with this kind of avatar view of the world where everything is functioning for the good of the whole we see that these interactions between an individual fungi are often antagonistic and need to be accounted for when we think about things like functional complementarity okay so hopefully it's quite obvious how um you know defining the nutrient niche space or the recruitment niche of solas pungence can determine you know help us understand what kinds of habitats it might occur in or where it might be beneficial so why is this important more broadly and the thing i'm going to argue is that this regeneration niche and this nutrient niche for as well as pundits actually dramatically influenced the rest of the environmental and microbial community through this process of niche construction okay so niche construction is the process by which an organism alters its own or another species local environment and thus changes the selective pressures that they or another organism experience so how does this apply to silva's punions well we know that based on this regeneration niche that soilless is one of the most common partners of pine seedlings establishing coastal scrub vegetation and we've shown in other experiments that the presence of soil with pungents is really critical for pine seedlings to be able to out-compete seedlings of this other really dominant muscular mycorrhizal shrub baccharis palularis that coyote bush um and so you know solo's punjin's dispersal ability uh can really help change the trajectory of the plant community by helping it uh you know helping its uh host plant establish and outcompete um and alcohol eat other plants and kind of transform the plant community and we know that the type of plant species and what root symbioses they have can lead to very different trajectories in the development of the overall soil chemistry at point reyes um really changing the soil nitrogen uh carbon concentrations of the two nations we this is from a study by a postdoc from my lab marie duhamel we looked at you know 20 years after fire what a change in vegetation from bacarists that say either bishopheim ceanothus or staying the same as baccarus would do to the soil chemistry and it has really extreme effects so you can often lead to i think we calculated this over the extent of a fire that had been there this can lead to changes in things like thousands of tons of carbon and hundreds of tons of nitrogen depending on which way these plant communities are shifting and we also know that the established of these different plant species and the changes in the soil environment change the selective environment for the rest of the microbial community and over the 20 years we've tracked these changes in plant communities and their effects on the overall soil microbial communities we see really different trajectories depending on which plant species established and how the environment's changed for the entire community of fungi bacteria and archaea not just direct to mycorrhizal fungi and this of course changes the feedback and it feeds back to change the fitness landscape for soilless pungence itself okay so hopefully i've convinced you that this bottom-up approach is an interesting and useful way to think about fungal communities and that a deep dive into the ecology of a single species can actually help us to make better broad generalizations about what's driving the community assembly for the entire fungal community and with that i will say thank you and i'd be happy to answer questions when it's time