The world’s getting warmer and more filled with carbon dioxide as all our natural storage of
carbon is being lit up and dispersed in our atmosphere along with all the other junk we’ve
been pumping into it for the last hundred years or so. Things are definitely changing, and not
just for us! Plants are everywhere and definitely contribute to keeping us alive with their nifty
ability to produce oxygen, food, and carbon storage. These plants depend on a stable,
suitable environment for them to grow and reproduce, and if their habitats are changing
across the globe, we should probably be worried. While we’re bracing ourselves for the
extinction of species, flooding of our coasts, and other symptoms of the incoming
anthropogenic apocalypse, ecologists are wondering how phenolic compounds are affected
by rising CO2 and temperature levels! Neat! Wait, what? Why?
What even are phenolic compounds?
Phenolic compounds are a broad group of carbon-based byproducts of certain
photosynthetic pathways that are used in plant defense, structure, communication between
plants, and attractingsbeneficial microbiota. Still confused, I don’t blame you one bit! They’re produced
during everyday life for plants, but especially when life gets rough. Studies have shown that when
plants are stressed they sacrifice periods of growth for producing lots of these phenolics, which are
used to toughen themselves up so they stay strong and unappealing to potential herbivores
(Johnson et al. 2018, Zvereva et al., 2006). Phenolics are also neat in that some of them can attract
beneficial microorganisms such as Rhizobium and Agrobacteria when they’re released into the soil
(Battacharya et al. 2010). That way they can help themselves out by calling their friends who give
them nutrients! Like these Rhizobia!
Phenolic compounds are a broad group of carbon-based byproducts of certain
photosynthetic pathways that are used in plant defense, structure, communication between
plants, and attractingsbeneficial microbiota. Still confused, I don’t blame you one bit! They’re produced
during everyday life for plants, but especially when life gets rough. Studies have shown that when
plants are stressed they sacrifice periods of growth for producing lots of these phenolics, which are
used to toughen themselves up so they stay strong and unappealing to potential herbivores
(Johnson et al. 2018, Zvereva et al., 2006). Phenolics are also neat in that some of them can attract
beneficial microorganisms such as Rhizobium and Agrobacteria when they’re released into the soil
(Battacharya et al. 2010). That way they can help themselves out by calling their friends who give
them nutrients! Like these Rhizobia!
Why should we care about phenolics? They don’t really sound like they help us out much.
Well, they do in small quantities--they probably can impede cancer development to an extent and are
common in the plant-based foods we eat (Stich H. F., 1991), but this isn’t really why scientists are
interested in them. You see, they’re more interested in how they benefit the plant and why a plant
might produce them. We touched on this earlier but it has a lot to do with plant stress. These
compounds are particularly useful to plants when they’re being eaten, and plants can even recognize
when they’re being attacked and synthesize these in self-defense! (Battacharya et al. 2010). The idea
is that if plants are producing these, they aren’t producing as many carbon-based compounds to help
them grow. Scientists have linked increased phenolics to the decreased growth rate in plants,
suggesting a survival trade-off (Johnson et al. 2018). By keeping an eye on the concentration of
phenolic compounds, scientists can sort of quantify plant stress, and that can be an important variable
to measure in experiments because of the implications it might have on environmental suitability for
the plants that live there.
common in the plant-based foods we eat (Stich H. F., 1991), but this isn’t really why scientists are
interested in them. You see, they’re more interested in how they benefit the plant and why a plant
might produce them. We touched on this earlier but it has a lot to do with plant stress. These
compounds are particularly useful to plants when they’re being eaten, and plants can even recognize
when they’re being attacked and synthesize these in self-defense! (Battacharya et al. 2010). The idea
is that if plants are producing these, they aren’t producing as many carbon-based compounds to help
them grow. Scientists have linked increased phenolics to the decreased growth rate in plants,
suggesting a survival trade-off (Johnson et al. 2018). By keeping an eye on the concentration of
phenolic compounds, scientists can sort of quantify plant stress, and that can be an important variable
to measure in experiments because of the implications it might have on environmental suitability for
the plants that live there.
To recap, plants produce phenolic compounds for a lot of reasons, but mainly for self-preservation in
the face of danger and scientists can analyze them to see how stressed plants are in their
environments.
the face of danger and scientists can analyze them to see how stressed plants are in their
environments.
These scientists looking at phenolic concentrations tend to be asking the same question: how does the
concentration of phenolic compounds change with increasing carbon dioxide and temperature?
concentration of phenolic compounds change with increasing carbon dioxide and temperature?
By artificially increasing temperature and carbon dioxide, scientists can simulate the conditions of the
future, as these factors are very likely to increase in the near future due to human activity. So that’s
what scientists did! That’s what a lot of scientists did. Not just to look at phenolic concentration, but
several other factors that might be influenced by CO2 and temperature increases like growth rate,
leaf size, and other plant morphological traits. Hundreds of studies like this analyzing several species
of plants have been conducted throughout recent years, and along the way, have been compiled by
other scientists into meta-analyses. These meta-analyses look at all the data studies like this have
collected into one place and draw their own conclusions. What these scientists have learned will
shock you (maybe)!
future, as these factors are very likely to increase in the near future due to human activity. So that’s
what scientists did! That’s what a lot of scientists did. Not just to look at phenolic concentration, but
several other factors that might be influenced by CO2 and temperature increases like growth rate,
leaf size, and other plant morphological traits. Hundreds of studies like this analyzing several species
of plants have been conducted throughout recent years, and along the way, have been compiled by
other scientists into meta-analyses. These meta-analyses look at all the data studies like this have
collected into one place and draw their own conclusions. What these scientists have learned will
shock you (maybe)!
Generally speaking, these meta-analyses have recognized common trends among phenolic
concentration in elevated carbon dioxide and temperature.
1.) Phenolic concentration increases with increasing carbon dioxide (Bezemer et al., 1998; Johnson et al., 2018; Zvereva et al., 2006)
2.) Phenolic concentration decreases with decreasing temperature (Lemoine et al., 2017)
3.) Increasing temperature and carbon dioxide cancel each other out with regard to phenolic
concentration (Veteli et al., 2007, Zvereva et al., 2006)
concentration in elevated carbon dioxide and temperature.
1.) Phenolic concentration increases with increasing carbon dioxide (Bezemer et al., 1998; Johnson et al., 2018; Zvereva et al., 2006)
2.) Phenolic concentration decreases with decreasing temperature (Lemoine et al., 2017)
3.) Increasing temperature and carbon dioxide cancel each other out with regard to phenolic
concentration (Veteli et al., 2007, Zvereva et al., 2006)
The first trend was actually hypothesized in the ‘80s in the Carbon/Nutrient-Balance Hypothesis, which
proposes that when plants have access to more CO2, they’re able to synthesize more secondary
compounds like phenolics. (Bryant et al., 1983) While this hypothesis was proven to be false for most
other secondary compounds, it actually held true for phenolics in a recent meta-analysis! (Robinson
et al., 2012) The other two trends are only fairly recently observed but present interesting implications
given the additive effect between temperature and CO2 with regard to phenolic concentration.
proposes that when plants have access to more CO2, they’re able to synthesize more secondary
compounds like phenolics. (Bryant et al., 1983) While this hypothesis was proven to be false for most
other secondary compounds, it actually held true for phenolics in a recent meta-analysis! (Robinson
et al., 2012) The other two trends are only fairly recently observed but present interesting implications
given the additive effect between temperature and CO2 with regard to phenolic concentration.
Here are a couple of figures that help explain the results!
This figure from Zvereva et al. 2006 demonstrates these principles firsthand, as elevated CO2 has a
positive impact on phenolics, elevated temperature has a negative impact on phenolics, and both of
them elevated together is slightly positive, suggesting an additive effect. It should be noted that these
only pertain to green tissues, although plants may be concentrating phenolics in these because they
are more susceptible to herbivory.
positive impact on phenolics, elevated temperature has a negative impact on phenolics, and both of
them elevated together is slightly positive, suggesting an additive effect. It should be noted that these
only pertain to green tissues, although plants may be concentrating phenolics in these because they
are more susceptible to herbivory.
This figure from Robinson et al. 2012 examines the displays several plant responses to elevated CO2.
Among several other functional traits, it appears that total phenolics increase with rising CO2,
supporting the first trend listed! This meta-analysis actually referenced the one from the previous
figure (Zvereva et al. 2006), and the blue dots represent results that are similar to those found in their
meta-analysis (Robinson et al. 2012). Another aspect of this figure we’ll come back to later is the fact
that nitrogen levels expressed in plants decrease across the board with rising CO2.
Among several other functional traits, it appears that total phenolics increase with rising CO2,
supporting the first trend listed! This meta-analysis actually referenced the one from the previous
figure (Zvereva et al. 2006), and the blue dots represent results that are similar to those found in their
meta-analysis (Robinson et al. 2012). Another aspect of this figure we’ll come back to later is the fact
that nitrogen levels expressed in plants decrease across the board with rising CO2.
We know that phenolic concentrations are influenced by temperature and carbon dioxide, so what?
These results basically mean that plants will invest more energy into these phenolics, but at this point,
we can’t say for sure whether this means plants are stressed or that increased carbon allows them to
synthesize more of these. If plants make a trade-off between growth and phenolic concentrations as
Johnson et al. (2018) suggest, it can be inferred that plants are increasingly favoring bunkering down
and slowing down their growth rates as a survival strategy over, say, banking everything into growing
like mad. I mean I don’t blame them, playing it safe is probably more likely to provide benefits in the
long run while minimizing the risk of croaking early.
we can’t say for sure whether this means plants are stressed or that increased carbon allows them to
synthesize more of these. If plants make a trade-off between growth and phenolic concentrations as
Johnson et al. (2018) suggest, it can be inferred that plants are increasingly favoring bunkering down
and slowing down their growth rates as a survival strategy over, say, banking everything into growing
like mad. I mean I don’t blame them, playing it safe is probably more likely to provide benefits in the
long run while minimizing the risk of croaking early.
What does this mean in terms of plant defense?
As CO2 concentrations and temperature increase in the near future, plants are more likely to invest
into phenolics maybe at the cost of growth. An increase of phenolic concentrations in plant tissues
combined with lowered nitrogen values as suggested by Robinson et al. (2012) ultimately lead to a
decreased palatability of plants to the organisms that consume them. This is because of the toxicity
of phenolic compounds to most organisms (Battacharya et al. 2010) in addition to how nitrogen tends
to be a limiting growth factor for most herbivores, especially insects (Zvereva et al. 2006). Because
plants are becoming less nutritious for herbivores, you might think this is good news for plants, but
you’d be wrong!
into phenolics maybe at the cost of growth. An increase of phenolic concentrations in plant tissues
combined with lowered nitrogen values as suggested by Robinson et al. (2012) ultimately lead to a
decreased palatability of plants to the organisms that consume them. This is because of the toxicity
of phenolic compounds to most organisms (Battacharya et al. 2010) in addition to how nitrogen tends
to be a limiting growth factor for most herbivores, especially insects (Zvereva et al. 2006). Because
plants are becoming less nutritious for herbivores, you might think this is good news for plants, but
you’d be wrong!
Because these herbivores need to eat more than they would to satisfy their nutritional requirements!
It’s not like the herbivores really benefit all that much from this arrangement though, reducing the
quality of their food is associated with a loss in fitness (Zvereva et al. 2006). If the increasing
concentration of phenolic compounds is linked with decreased growth rates in the plants that produce
them, elevated CO2 concentrations create a lose-lose situation for both the plants and the herbivores
that eat them. While this shift in resources might open some opportunities for new organismal niches
in a few circumstances, this is generally bad news for ecosystem productivity. While temperature
seems to limit phenolic concentrations, this might not be able to compensate for the reduced nitrogen
concentrations in plants to the herbivores that consume them.
quality of their food is associated with a loss in fitness (Zvereva et al. 2006). If the increasing
concentration of phenolic compounds is linked with decreased growth rates in the plants that produce
them, elevated CO2 concentrations create a lose-lose situation for both the plants and the herbivores
that eat them. While this shift in resources might open some opportunities for new organismal niches
in a few circumstances, this is generally bad news for ecosystem productivity. While temperature
seems to limit phenolic concentrations, this might not be able to compensate for the reduced nitrogen
concentrations in plants to the herbivores that consume them.
So, what’s next?
In my opinion, more research should be done to confirm or dispel a link between growth rate and
phenolic concentrations in plants and the effect of temperature on nitrogen concentrations in the
environment. Otherwise, society should do what it can to limit its release of CO2 into the atmosphere.
I can’t promise whether the outcome for plants and the world that depends on them will be good or
not but I feel like this is a problem worth digging deeper on!
phenolic concentrations in plants and the effect of temperature on nitrogen concentrations in the
environment. Otherwise, society should do what it can to limit its release of CO2 into the atmosphere.
I can’t promise whether the outcome for plants and the world that depends on them will be good or
not but I feel like this is a problem worth digging deeper on!
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TL;DR: Carbon dioxide and temperature are increasing throughout the world. Phenolics are
compounds that help plants out, particularly when they’re stressed by herbivory. Studies show that
phenolic concentrations increase with increasing CO2 but decrease with temperature. Increasing
phenolic concentrations in tandem with decreased nitrogen in plants also due to climate change could
be bad news for ecosystems. To fix this we need to better understand the relationship between
phenolics and growth rate and temperature and nitrogen concentrations.
compounds that help plants out, particularly when they’re stressed by herbivory. Studies show that
phenolic concentrations increase with increasing CO2 but decrease with temperature. Increasing
phenolic concentrations in tandem with decreased nitrogen in plants also due to climate change could
be bad news for ecosystems. To fix this we need to better understand the relationship between
phenolics and growth rate and temperature and nitrogen concentrations.
-
References:
Bezemer, T. M. and Jones, T. H. 1998. Plant–insect herbivore interactions in elevated atmospheric CO2: quantitative analyses and guild effects. Oikos 82:212–222.
Bryant JP, Chapin FS III, Klein DR. 1983. Carbon/nutrient balance of boreal plants in relation to vertebrate herbivory. Oikos 40: 357–368.
Zvereva, E. L., and M. V. Kozlov. 2006. Consequences of simultaneous elevation of carbon dioxide and temperature for plant‐herbivore interactions: A metaanalysis. Global Change Biology 12:27–41.
Lemoine, N. P., Doublet, D., Salminen, J.-P., Burkepile, D. E., and Parker, J. D. (2017). Responses of plant phenology, growth, defense, and reproduction to interactive effects of warming and insect herbivory. Ecology 98, 1817–1828.
Bhattacharya A, Sood P, Citovsky V. The roles of plant phenolics in defence and communication during Agrobacterium and Rhizobium infection. Mol Plant Pathol 2010; 11:705–19.
Veteli TO, Kuokkanen K, Julkunen‐Tiitto R et al. (2002) Effects of elevated CO2 and temperature on plant growth and herbivore defensive chemistry. Global Change Biology, 8, 1240–1252.
Stich, H. F. The Beneficial and Hazardous Effects of Simple Phenolic Compounds Mutat. Res., Genet. Toxicol. 1991, 259, 307– 324 DOI: 10.1016/0165-1218(91)90125-6
