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Mon May 27, 2019, 01:26 PM

Climatic controls of decomposition drive the global biogeography of forest-tree symbioses.

The paper I'll discuss in this post is this one: Climatic controls of decomposition drive the global biogeography of forest-tree symbioses.

The lead authors are T. W. Crowther, of ETH is Switzerland, J. Liang, who apparently holds a dual appointment at Research Center of Forest Management Engineering of State Forestry and Grassland Administration, Beijing Forestry University, Beijing, China and Purdue University, and K. G. Peay at Stanford University.

The data was collected by multiple other authors from around the world and by appeal to data produced by an international consortium of scientists (of which I was unaware), GFBI, the Global Forest Biodiversity Initiative.

The existence of the GFBI is a wonderful thing; there are people who are fighting what we are doing to the planet, and, of course, many of us, a minority perhaps, wish them well. The international rise and celebration of ignorance, left and right, has made focus on biodiversity in forests a somewhat quixotic enterprise, but that's just my opinion. (I would love, absolutely love to be proved wrong, although I have the unfortunate experience of having been right about more things than I would have liked, at least where climate change is connected, climate change being the focus of this paper. We hit 415 ppm this year and are doing nothing, absolutely nothing practical to address it, and, no, Musk worship and battery worship won't cut it.)

The reference for the paper is Nature 569, 404–408 (2019).


Even a cursory study of biochemistry can inspire a sense of awe for the dance of elements by which living things exist. In recent times many of us think about carbon and hydrogen, but the extreme stability of dinitrogen, the main constituent of our dying planetary atmosphere, places powerful energy constraints on the availability of fixed nitrogen. Other critical elements include phosphorous, the key to nucleic acids, protein signaling and the energetics of all living things, and many minor elements including, interestingly one of the only two elements in the 5th period of periodic table to be essential to life, molybdenum, the other such element being iodine.

Dinitrogenase, the protein that fixes nitrogen from the air, has a molybdenum coordinating center which is the catalytic site. (Interestingly this element may play a role in low energy catalysts to replace the energy consuming Haber Bosch process, which consumes about 2% of the world energy supply: New process could slash energy demands of fertilizer, nitrogen-based chemicals

(The mindless acceptance of "could" statements, as having more value than "is" or "are" statements are part of the reason that climate change is accelerating. This is not a criticism of Dr. Carter, who is a certifiable genius of the first order, but rather a reflection of how people interpret "could" statements as being equivalent to "problem solved."

I had an opportunity, after one of her lectures, during Q&A to ask Dr. Carter what it is about molybdenum, to which she kind of shrugged and said, "It's the energy of the d-orbitals, I guess." In any case, life understood the energy minimization associated with molybdenum and nitrogen before Dr. Carter did.

Many of us are aware of the symbiont role played by organisms in such species as peas and soybeans where nitrogen fixation is concerned, and this was the basis for crop rotation before the industrialization of agriculture in the "green revolution" of the mid 20th century which, unlike the "green revolution" advertised in the late 20th and early 21st century, worked. The food supply increased to levels sufficient to support billions of more human lives, albeit at the cost of considerable expense to the environment.

But the paper focuses on the environment.

From the introductory text:

Microbial symbionts strongly influence the functioning of forest ecosystems. Root-associated microorganisms exploit inorganic, organic2 and/or atmospheric forms of nutrients that enable plant growth1, determine how trees respond to increased concentrations6 of CO2, regulate the respiratory activity of soil microorganisms3,8 and affect plant species diversity by altering the strength of conspecific negative density dependence9. Despite the growing recognition of the importance of root symbioses for forest functioning1,6,10 and the potential to integrate symbiotic status into Earth system models that predict functional changes to the terrestrial biosphere10, we lack spatially explicit quantitative maps of root symbioses at the global scale. Quantitative maps of tree symbiotic states would link the biogeography of functional traits of belowground microbial symbionts with their 3.1 trillion host trees11, which are spread across Earth’s forests, woodlands and savannahs.

The dominant guilds of tree root symbionts—arbuscular mycorrhizal fungi, ectomycorrhizal fungi, ericoid mycorrhizal fungi and nitrogen-fixing bacteria (N-fixers)—are all based on the exchange of plant photosynthate for limiting macronutrients. Arbuscular mycorrhizal symbiosis evolved nearly 500 million years ago, and ectomycorrhizal, ericoid mycorrhizal and N-fixer plant taxa have evolved multiple times from an arbuscular-mycorrhizal basal state. Plants that are involved in arbuscular mycorrhizal symbiosis comprise nearly 80% of all terrestrial plant species; these plants principally rely on arbuscular mycorrhizal fungi for enhancing mineral phosphorus uptake12. In contrast to arbuscular mycorrhizal fungi, ectomycorrhizal fungi evolved from multiple lineages of saprotrophic ancestors and, as a result, some ectomycorrhizal fungi are capable of directly mobilizing organic sources of soil nutrients (particularly nitrogen)2.

So it turns out that these symbiotic relationships are as important for phosphorous as they are for nitrogen. (By the way, we are mining the hell out of the world's phosphorous for our industrial agriculture and for the all important task of keeping the grass nice on golf courses.)

Later, the authors discuss the known role of temperature to the mycorrhizal species:

One of the earliest efforts16 to understand the functional biogeography of plant root symbioses categorically classified biomes by their perceived dominant mycorrhizal type, and hypothesized that seasonal climates favour hosts that associate with ectomycorrhizal fungi (owing to the ability of these hosts to compete directly for organic nitrogen). By contrast, it has more recently been proposed that sensitivity to low temperatures has prevented N-fixers from dominating outside of the tropics, despite the potential for nitrogen fixation to alleviate nitrogen limitation in boreal forests15,17...

...To address this, we compiled a global ground-sourced survey database to reveal the numerical abundances of each type of symbiosis across the globe. Such a database is essential for identifying the potential mechanisms that underlie transitions in forest symbiotic state along climatic gradients18,19.

We determined the abundance of tree symbioses using an extension of the plot-based Global Forest Biodiversity (GFB) database that we term the GFBi; this extended database contains over 1.1 million forest inventory plots of individual-based measurement records, from which we derive abundance information for entire tree communities (Fig. 1).

The authors used "training sets" to generate the "artificial intelligence" tools to process their data.

A picture from the paper:

The caption:

The global map has n = 2,768 grid cells at a resolution of 1° × 1° latitude and longitude. Cells are coloured in the red, green and blue spectrum according to the percentage of total tree basal area occupied by N-fixer, arbuscular mycorrhizal (AM) and ectomycorrhizal (EM) tree symbiotic guilds, as indicated by the ternary plot.

They find that only a small number factors control decomposition of forest litter and turnover of essential nutrients:

The caption:

a–c, Partial feature contributions of different environmental variables to forest symbiotic state. Each row plots the shape of the contribution of the four most-important predictors of the proportion of tree basal area that belongs to the ectomycorrhizal (a), arbuscular mycorrhizal (b) and N-fixer (c) symbiotic guilds (n = 2,768). Variables are listed in declining importance from left to right, as determined by the increase in node purity (inc. node purity), and with points coloured with a red to green to blue gradient according to their position on the x axis of the most-important variable (left-most panels for each guild), allowing cross-visualization between predictors. Each panel lists two measures of variable importance; inc. node purity (used for sorting) and percentage increase in mean square error (% inc. MSE) (see Supplementary Information). The abundance of each type of symbiont transitions sharply along climatic gradients, which suggests that sites near the threshold are particularly vulnerable to switching their dominant symbiont guild as climate changes. Warmest and wettest quarter, the warmest and wettest quarters of the year, respectively.

a, Biome level summaries of the median ± 1 quartile of the predicted percentage of tree basal area per biome for ectomycorrhizal, arbuscular mycorrhizal and N-fixer symbiotic guilds (n = 100 random samples per biome). b, The dependency of decomposition coefficients (k, solid and dotted lines; in the region between the solid lines, the model transitions abruptly between dominant symbiotic status) on temperature and precipitation during the warmest quarter with respect to predicted dominance of mycorrhizal symbiosis. The transition from arbuscular mycorrhizal forests to ectomycorrhizal forests between k = 1 and k = 2 is abrupt, which is consistent with positive feedback between climatic and biological controls of decomposition.

Their software tools predict the types of symbiotic relationships that dominate forests.

The caption:

a–c, Maps (left) and latitudinal gradients (right; solid line indicates median; coloured ribbon spans the range between the 5% and 95% quantiles) of the percentage of tree basal area for ectomycorrhizal (a), arbuscular mycorrhizal (b) and N-fixer (c) symbiotic guilds. All projections are displayed on a 0.5°-by-0.5° latitude and longitude scale. n = 28,454 grid cells.

Some disturbing stuff, at least to me, since while I encourage other people to not worry and be happy in order to embrace popular trends, I do worry and am not happy and my thoughts are perhaps, unpopular and unpleasant:

To illustrate the sensitivity of global patterns of tree symbiosis to climate change, we use the relationships that we observed for current climates to project potential changes in the symbiotic status of forests in the future. Relative to our global predictions that use the most-recent climate data, model predictions that use the projected climates for 2070 suggest that the abundance of ectomycorrhizal trees will decline by as much as 10% (using a relative concentration pathway of 8.5 W per m2) (Supplementary Fig. 24). Our models predict that the largest declines in ectomycorrhizal abundance will occur along the boreal–temperate ecotone, where small increases in climatic decomposition coefficients cause abrupt transitions to arbuscular mycorrhizal forests (Fig. 2a, b). Although our model does not estimate the time lag between climate change and forest community responses, the predicted decline in ectomycorrhizal trees corroborates the results of common garden transfer and simulated warming experiments, which have demonstrated that some important ectomycorrhizal hosts will decline at the boreal–temperate ecotone under altered climate conditions24.

But again, don't worry, be happy. If our boreal forests die off, maybe, just maybe, we can have new kinds of forests, maybe even steel forests. It's a transition, just like the swell transition we're undergoing from coal to gas while we wait, like Godot, for the grand so called "renewable energy" nirvana that has not come, is not here, and will not come.

But anyway, who cares? Forests are not popular really. On the right, no matter how much real estate and how many crops in the red states are destroyed by extreme weather events there is no willingness to acknowledge that climate change is real.

On the left, we plan to cover all of our pristine forests with access roads to our wind turbine laced industrial parks so we can drive through the industrial parks where the forests used to be with diesel trucks and of course, our swell Tesla electric cars.

Either way the forests, and the atmosphere lose.

And sorry, the forests are in no position to mitigate climate change.

History will not forgive us; nor should it.

I trust you're having a wonderful Memorial Day holiday.

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Reply Climatic controls of decomposition drive the global biogeography of forest-tree symbioses. (Original post)
NNadir May 2019 OP
ffr May 2019 #1
NNadir May 2019 #2

Response to NNadir (Original post)

Mon May 27, 2019, 02:39 PM

1. Off the subject of Memorial Day holiday

If you look out how we react to anything as a species you will see that we do so slowly. There is a segment of the population that once born feels that whatever traditions they were accustomed to growing up are those that should remain in place until they die. That segment of traditionalists do not care about the future, future generations or anyone other than themselves. And somehow, people continue to elect such people who gravitate to one political party exclusively.

So your conclusion that forests be damned and history will not forgive us, is quite accurate. But try not to lump those who are making sacrifices that do look after the better interests of the planet and oppose the traditionalists, in with those that don't. Change is difficult for our species. We marvel at our steel and cement deserts as something to be viewed, while universally treasure all that with which we have not touched.

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Response to ffr (Reply #1)

Mon May 27, 2019, 03:40 PM

2. I must be missing something, since I'm not sure what you're trying to advise me to do.

Exactly who am I "lumping" with whom?

Who exactly are these people "making sacrifices" who I addressed in the OP?

Admittedly, as a cynic who earned his cynicism, since, in general, a cynic is nothing more than an idealist worn down by reality, I'm not all that prone, especially at my age, to taking advice, but I am interested in understanding what you are trying to say.

If I am being advised to embrace optimism, let me say this; there are two kinds of optimism, blind optimism, and hopeful optimism. The former can be, and in my view with respect to climate change especially, is toxic and extremely destructive and dangerous. The latter is an understanding that even if something is improbable but good, it remains possible. I see very little of the latter, but the world is awash in the former. I hope that will change, but I do not expect it will, hence my prediction about history.

We're at 415 ppm of the dangerous fossil fuel waste carbon dioxide in the atmosphere and we're still reciting dogma, left and right.

As for change, I do not agree it happens slowly. I lived through unbelievable and rapid change. The world I live in is nothing like the world into which I was born. I may as well have moved to a different planet, because I am very much on a very different planet than the one into which I was born.

I'm so old that I come from a time when liberalism involved giving more attention to human poverty than worshiping electric cars depending on human slavery to operate. When I was a kid, slavery was generally agreed to be a bad thing. That's how old I am.

This is the magnitude, for just one example, of the change I have seen in a single lifetime.

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