Plant progress takes a heavy toll on the soil – supposedly – with it?

Guest contribution by Henry Gillard

[This originally arrived as a tip/suggestion for a post. The author was encouraged to turn it into a complete post. Be gentle~cr ]

I hate reading academic papers. Too often the grammar is appalling; The goals of the work described are unclear. The bulk of the paper is a thicket of technical terminology. The abstract of what was found is incomprehensible (and at times the abstract seems barely related to the main body of the paper).

Occasionally, just occasionally, I read something in an academic paper that makes me smile. It has a ring of truth expressed in plain language. I came across such a statement yesterday and I feel the need to make it available to a wider audience.

It started with a typically breathless, alarming warning from Stanford University:

“Stanford research has shown that increased levels of carbon dioxide, which leads to increased plant growth, place a surprisingly large burden on another large carbon sink: the soil.”

The claim is in a 29-03-2021 report; https://news.stanford.edu/2021/03/24/one-earths-biggest-carbon-sinks-overestimated/?utm_source=Stanford+Report&utm_campaign=1a26a66d1f-EMAIL_CAMPAIGN_2021_03_26_03_m9

The report summarizes a paper published earlier this week (24-03-2021) in Nature and adds comments from two of the co-authors.

The lead author reveals one of his secrets: “When plants increase biomass, carbon storage in the soil usually decreases.”

Wow! Who would have thought? As a plant grows, it extracts nutrients and carbon from the soil and converts them into roots, stems, flowers and seeds. This sounds like something I learned in biology class from Mr. Collins at the age of 11, but Mr. Collins wasn’t a fellow at Lawrence Livermore National Laboratory doing this research as a postdoctoral fellow at Stanford University, so maybe I have him all undervalued those years ago.

The lead study author, who is both Michelle and Kevin Douglas Provostial (whatever that is) Professor at the Stanford School of Earth, Energy & Environmental Sciences and Senior Fellow at the Stanford Woods Institute for the Environment, admits, “It has proven it is much more difficult than expected to increase both plant growth and carbon in the soil. “At this point it would have been helpful if he had given us some insight into his theory of how the plant interacts with the air and the soil and what he expected. But he did not do it. See my first grumpy remarks above about failure to specify goals.

Desperate for the lighting from the Stanford report, I followed the link https://www.nature.com/articles/s41586-021-03306-8 to the original Nature article. Let me quote verbatim the entire abstract except for removing the references. Read it slowly and enjoy.

abstract

Terrestrial ecosystems remove around 30 percent of the carbon dioxide (CO2) released by human activities each year. The persistence of this carbon sink, however, depends in part on how stocks of plant biomass and soil organic carbon (SOC) respond to future increases in atmospheric CO2. Although plant biomass often increases in experiments with increased CO2 (eCO2). It has been observed that the SOC increases, remains unchanged or even decreases. The mechanisms that drive this variation between experiments are still poorly understood, leading to uncertainties in climate projections. Here we have synthesized data from 108 eCO2 experiments and found that the effect of eCO2 on SOC stocks can best be explained by a negative relationship to plant biomass: When plant biomass is strongly stimulated by eCO2, SOC storage decreases; Conversely, SOC storage increases when the biomass is weakly stimulated. This tradeoff appears to be related to plant nutrient uptake, where plants increase their biomass by breaking down the soil for nutrients, thereby reducing SOC storage. Overall, we found that the SOC stocks in grasslands (8 ± 2 percent) increase with eCO2, but not in forests (0 ± 2 percent), although the plant biomass increases less in grassland areas (9 ± 3 percent) than in forests (23 ± 2 percent). Ecosystem models do not reproduce this tradeoff, which means that the projections of the SOC may need to be revised.

I find it wonderfully funny to read: “(Of) increases in experiments with increased CO2 (eCO2), it has been observed that SOC (organic carbon in the soil) increases, remains unchanged or even decreases. Little is known about the mechanisms that drive this variation across experiments.”

Oops. You let the cat out of there! I can almost hear her say, “We have these prestigious jobs and we paid all the money and we did all this work, but we don’t understand what’s going on.” Maybe I’m cynical, but I really wonder if this will be their justification for asking for more scholarships for more work. Anyway, I made a smile out of it, and I hope you did too.

Seriously, what worries me most is that the authors seem drawn to a broad causal link between the concentration of eCO2 and the change in SOC, with the former influencing the latter through the mechanism of plants “polluting the soil for nutrients dismantle”. It’s really a shame they didn’t explicitly understand how eCO2, SOC and the plants interact over both a single growing season and over a longer period of time. The key failure in their model (if we can call it such honorable) is that it fails to attempt to explain How The SOC can go up at all when plants grow. Mere correlation does not mean causality. And “increase, stay the same, or even decrease” doesn’t even mean correlation.

My interpretation of this interaction – based on the notes I made in Arthur Collins’ biology class in 1965 – is:

• high eCO2 initially stimulates plant growth;
• Plants absorb CO2 from the air to build their (carbon-based) biomass.
• The healthy, growing plants take up SOC (soil organic carbon) for the same purpose.
• therefore the SOC concentration decreases;
• When the nutrients are depleted, a plant’s growth slows down so the plant has to extract less SOC from the soil.
• When plants die, they decay and their components become part of the soil.

The consequence of a falling SOC concentration – all other things being equal – is that the soil will have more capacity in the future to absorb more CO2, using the same mechanisms that have always existed.

Looking at their numbers: With increased eCO2:

• The SOC stocks in the grasslands increase by 8 ± 2 percent
• The SOC stocks in the forests increase by 0 ± 2 percent
• Plant biomass increases by 9 ± 3 percent in grasslands
• Plant biomass increases in forests by 23 ± 2 percent

To my interpretation:

• Meadows do not produce biomass as efficiently as forests
• Grassland biomass increases by 9%: the process stimulates the initial SOC depletion and subsequent replenishment by a net 8%
• Forest biomass increases by 23%: the process stimulates the initial SOC depletion and subsequent replenishment by a net 0%

According to the figures of the study, planting one hectare of trees absorbs more CO2 than planting one hectare of maize. Crucially, during the study period, the forests tend to keep the SOC concentration unchanged while the grasslands increase it. If we look at the sum of the increase in biomass + increase in SOC for grasslands compared to forests, they are not that different: 8 + 9 versus 23 + 0. Is that surprising? Not for me. If there was a big difference, I suspect that whoever does better would have completely colonized the other in the course of Earth’s existence.

The Nature paper and the Stanford report on it do not deal with what has happened over the decades. Their key view seems to be short-term: “When plant biomass is strongly stimulated by eCO2, the SOC storage decreases. Conversely, the SOC storage increases when the biomass is weakly stimulated. So if there is a lot of extra CO2 in the air, the SOC will go down because the plants are growing fast, and if the plants have little extra CO2 in the air, don’t grow so much so the SOC will rise rather than fall.

In addition, the authors implicitly believe that SOC is extracted from the soil Of course bad for failing to see the benefits of converting SOC into additional wheat, rice and other crops to feed a growing world population. But let’s not get distracted from the topic.

So does this mean that planting trees to reduce CO2 is a waste of time and money?

If you think climate alarmism is unfounded, your answer is definitely “yes”. So let me ask the question only to those who believe it makes sense to reduce atmospheric CO2.

Look at the paper. Look at the numbers. Make up your own mind. I won’t tell you what to think.

If you think the concerns in the paper are legitimate, ask yourself what you are going to do. Are you writing to your local mayor urging him not to waste public money on his virtuous tree-planting initiative? (Every city seems to have such a scheme). And are you risking the wrath of the greens, the hippies and the media? You may not be able to be convinced by this paper.

Or, if you think the report has questionable methodology, is poorly written, and contains inconclusive conclusions, then write to Stanford University asking them not to waste their money in making another grant to these people ?

Or won’t you do anything?

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