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Tag: CO2

Stomata – an ancient insight into a modern problem

Posted on by Anonymous

Findings from a pharaoh

What can an Egyptian pharaoh from 1300 BC tell us about how plants will respond to 21st century environmental change?

Olive leaves in Tutankhamun’s tomb allowed Beerling & Chaloner to show that the number of stomata declined in response to increasing CO2. Photo credit – Discovery Times Square Museum (Available: http://www.discoverytsx.com/exhibitions/kingtut).
Olive leaves in Tutankhamun’s tomb allowed Beerling & Chaloner to show that the number of stomata declines in response to increasing levels of carbon dioxide.
Photo credit – Discovery Times Square Museum (Available: http://www.discoverytsx.com/exhibitions/kingtut).

 

When Howard Carter discovered King Tutankhamun’s tomb in 1922, the boy pharaoh’s treasures captivated the world. Amidst such splendor, olive leaves found in the burial chamber were overlooked. But, in 1993, two botanists, David Beerling and William Chaloner decided to compare these leaves with their modern counterparts. They found that olive leaves grown today have 33% fewer stomata (tiny ‘pores’ on the leaf surface) than they did in 1300 BC. Beerling & Chaloner linked this decline in stomata to increasing carbon dioxide (CO2) levels.

Stomata – microscopic pores on the surface of a leaf let plants ‘breathe’.
Photo credit – University of California Museum of Paleontology’s Understanding Evolution (http://evolution.berkeley.edu).

 

Powerful pores

Stomata (singular – stoma) are vital to plant function. Plants use these pores to ‘breathe’. Stomata allow CO2 to enter a leaf, where it is used in photosynthesis to generate sugars, which the plant needs to survive and grow. The trade-off is stomata also let water escape. Plants, therefore, need to balance CO2 gain and water loss.

Stomata control a vital trade-off between carbon dioxide gain and water loss.
Photo credit – University of California Museum of Paleontology’s Understanding Evolution (http://evolution.berkeley.edu).

 

Rising CO2 – a certainty in an uncertain world

CO2 is the most well known of the greenhouse gases. These gases trap the Sun’s heat within Earth’s atmosphere, causing our planet to warm up. We produce CO2 every day when we burn oil, gas and coal to drive our cars, heat our homes and power our factories.

This has caused CO2 levels to increase by 40% since the industrial revolution started in 1750 (IPCC, 2014). CO2 levels are predicted to increase more rapidly in the future as populations and economies grow (IPCC, 2014).

With some exceptions (Bettarini et al., 1998), most scientists agree that this rise in CO2 will cause a decline in stomatal density (Woodward & Kelly, 1995; Lin et al., 2001). Paoletti et al. (1998) showed that stomata numbers will decline until CO2 levels reach 750 μmol mol-1.

But, how will this change impact plant function?

Some plants naturally have few stomata because they have a change in the gene that controls stomatal development (Gray et al., 2000). As CO2 levels rise, each stoma will be able to bring in more CO2. So, a leaf will need fewer stomata to bring in the same amount of CO2.

A leaf with fewer stomata will lose less water. As a result, the plant will have a higher water use efficiency and so has an advantage over others (Drake et al., 1997). With time, CO2 will act as a selection pressure and these plants will become more common.

Stomatal density will decline as CO2 levels rise. Photo credit - University of California Museum of Paleontology's Understanding Evolution (http://evolution.berkeley.edu).
Stomatal density will decline as carbon dioxide levels rise.
Photo credit – University of California Museum of Paleontology’s Understanding Evolution (http://evolution.berkeley.edu).

 

Future plants will be better able to conserve water, making them more tolerant to periods of water stress (Woodward, 1987). This is just as well as droughts are predicted to become more common (IPCC, 2014). It will also mean we will be able to grow the same amount of crops, but using less water (Drake et al., 1997).

Stomata transfer water from the land to the atmosphere. If plants have fewer stomata, less water will be transferred, which will cause increased air temperatures and runoff (Kürschner et al., 1997).

The olive leaves from King Tut’s tomb showed that stomata respond to CO2 levels. With rises in CO2 predicted for the 21st century, perhaps the insights provided by these leaves are the boy pharaoh’s most valuable treasure.

 

References

Beerling, D.J. & Chaloner, W.G. (1993) Stomatal density responses of Egyptian Olea europaea L. leaves to CO2 change since 1327 BC. Annals of Botany. 71(5), 431-435.

Bettarini, I., Vaccari, F.P. & Miglietta, F. (1998) Elevated CO2 concentrations and stomatal density: observations from 17 plant species growing in a CO2 spring in central Italy. Global Change Biology. 4(1), 17-22.

Drake, B.G., Gonzàlez-Meler, M.A. & Long, S.P. (1997) More efficient plants: a consequence of rising atmospheric CO2? Annual review of plant biology. 48(1), 609-639.

Gray, J.E., Holroyd, G.H., Van Der Lee, F.M., Bahrami, A.R., Sijmons, P.C., Woodward, F.I., Schuch, W. & Hetherington, A.M. (2000) The HIC signalling pathway links CO2 perception to stomatal development. Nature. 408(6813), 713-716.

IPCC (2014) Summary for Policymakers. In: Pachauri. R.K. & Meyer, L.A. (eds.) Climate Change 2014: Synthesis Report. Contribution of Working Groups I, II and III to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change. IPCC, Geneva, Switzerland, pp. 1-31.

Kürschner, W.M., Wagner, F., Visscher, E.H. & Visscher, H. (1997) Predicting the response of leaf stomatal frequency to a future CO2-enriched atmosphere: constraints from historical observations. Geologische Rundschau. 86(2), 512-517.

Lin, J., Jach, M.E. & Ceulemans, R. (2001) Stomatal density and needle anatomy of Scots pine (Pinus sylvestris) are affected by elevated CO2. New Phytologist. 150(3), 665-674.

Paoletti, E., Nourrisson, G., Garrec, J.P. & Raschi, A. (1998) Modifications of the leaf surface structures of Quercus ilex L. in open, naturally CO2-enriched environments. Plant, Cell & Environment. 21(10), 1071-1075.

Woodward, F.I. & Kelly, C.K. (1995) The influence of CO2 concentration on stomatal density. New Phytologist. 131(3), 311-327.

Woodward, F.I. (1987) Stomatal numbers are sensitive to increases in CO2 from pre-industrial levels. Nature. 327(6123), 617-618.

 

Word count: 499



Plants – The Power of Adaptation in the Fight Against Climate Change

Posted on by Craig Turner
The adaptive power of plants could be crucial in sustaining the future of our planet! (Source: About Lifting)
The adaptive power of plants could be crucial in sustaining the future of our planet!
(Source: Aboutlifting.com)

 

From giant redwoods to small bonsai trees, all plants are bracing for a future of increasing global CO2 emissions.

FACT! In 2015, we as humans pumped out 36.3 GIGATONNES of CO2 into our atmosphere (GCP, 2016).

The Dilemma: Though rising atmospheric CO2 is almost always seen as a bad thing, the astute readers among you may ask: “isn’t that a good thing for plants, seeing as how they need CO2 to photosynthesise (convert CO2 gas into sugar for food)?”

The answer is a bit more complex than yes or no.

Studies have shown that in the short-term, increased CO2 concentrations:

  • Improve the efficiency of plant water use (Drake et al., 1997).
  • Increase the rates of photosynthesis (Drake et al. 1997).
  • Increase plant growth and productivity (Raschi et al., 1997).

 

… But.

Over longer timescales (days to weeks), the photosynthetic capabilities of plants can decrease because of a process called ACCLIMATISATION. To put it briefly, acclimatisation is when there is a build-up of leaf carbohydrates, such as sugars and starch, which triggers a decrease in the amount of RUBISCO enzyme (the enzyme responsible for upholding photosynthesis) in plants (Cheng et al., 1998).

Is the future all DOOM and GLOOM?

Encouragingly, the future looks somewhat optimistic…

A study using natural springs, which already emit high concentrations of CO2, found that over multiple generations, the “spring” plants that live there have become adapted to the elevated CO2 concentrations we can expect in the future, through the power of GENE EXPRESSION (Watson-Lazowski et al., 2016).

 

“Spring” and “non-spring” Plantago lanceolata plants from the Bossoleto natural spring in Italy. (Source: Herbalism)
“Spring” and “non-spring” Plantago lanceolata plants from the Bossoleto natural spring in Italy.
(Source: dspermaculture.wordpress.com)

 

Interestingly, the populations of “spring” and “non-spring/control” plants were genetically identical but over 800 genes were expressed differently between the two. Gene expression is kind of like a plug switch, genes can be turned on or off depending on the plant’s needs in order better suit its environment; it is thought that CO2 was directly regulating these changes in gene expression (Watson-Lazowski et al., 2016).

Differences in gene expression resulted in “spring” plants NOT BECOMING ACCLIMATISED to elevated CO2 conditions. In fact, the “spring” plants were able to photosynthetically fix carbon faster and produce larger carbon pools, they then used this additional carbon to enhance their growth through greater respiration (release of energy from carbon) (Watson-Lazowski et al., 2016).

Gene expression also caused the “spring” plants to increase their STOMATA (leaf pores used for gas exchange) index by 5.2% in elevated CO2 conditions, perhaps as an adaptive response (Watson-Lazowski et al., 2016). This contradicts previous studies that predict stomata numbers should have decreased.

What does this mean?

Well, it means that ability of plants to change their gene expression could be the underlying factor that enables future generations to adapt to rising atmospheric CO2. Questions as to whether this stark change in gene expression is capable in all plants and whether it is enough to enable them to fully adapt to future CO2 concentrations is yet to be tested; but this study shows that in the battle against climate change, plants may have a fighting chance!

References:

  1. CHENG, S. MOORE, B. & SEEMAN, J. (1998) Effects of short- and long-term elevated CO2 on the expression of ribulose-1,5-bisphosphate carboxylase/oxygenase genes and carbohydrate accumulation in leaves of Arabidopsis thaliana (L.) Heynh. American Society of Plant Physiologists. 116 (2). pp. 715-723.
  2. DRAKE, B. GONZALEZ-MELER, M. & LONG, S. (1997) More efficient plants: a consequence of rising atmospheric CO2. Annual Review of Plant Physiology & Plant Molecular Biology. 48. pp. 609-639.
  3. GLOBAL CARBON PROJECT, 2016. Global Carbon Budget. [pdf] Futurearth. Available at: http://www.globalcarbonproject.org/carbonbudget/16/files/GCP_CarbonBudget_2016.pdf.
  4. RASCHI, A. MIGLIETTA, F. TOGNETTI, R. & VAN GARDINGEN, P. (1997) Plant Responses to Elevated CO2: Evidence from Natural Springs. New York: Cambridge University Press.
  5. WATSON-LAZOWSKI, A. LIN, Y. MIGLIETTA, F. EDWARDS, R. CHAPMAN, M. & TAYLOR, G. (2016) Plant adaptation or acclimation to rising CO2? Insight from first multi-generational RNA-Seq transcriptome. Global Change Biology. 22 (11). pp. 3760 – 3773.

 

Word Count: 498

 



UK Food in a climate crisis?

Posted on by Phoebe O'Brien

British food security is under threat due to Climate change.

If you haven’t heard of ‘climate change’ you‘ve either been living under a rock for the last 30 years or getting yourself elected as leader the free world. But not much has changed, Winter’s a little warmer, summer’s a little wetter? We’ve heard of extreme weather conditions in some far corners of the globe but unless you’ve been planning a trip there, it’s unlikely to affect our everyday lives. But behind supermarkets sliding doors lurks a real peril, one directly impacting Britons at their most vulnerable part, our Achilles heel, our pockets. As crop production is jeopardised, already inflated prices are set to rise, correlating with the environmental changes induced by human pollution (Lobell, 2007).

Figure 1. A familiar slight, well stocked fruit and veg for public consumption. But for how long? (WordShore (flickr), 2016)
Figure 1. A familiar slight, well stocked fruit and veg for public consumption. But for how long? (WordShore (flickr), 2016)

Food security is perhaps the most important commodity provided by the planet. At a glance the effects of climate change, seem on the whole, to be exactly what farmers are looking for in terms of improving yield from their crops. It’s wet, hot, there’s more CO2, more decomposition and available nutrients, just what plants need right? But this is not always the case, although higher CO2 levels does stimulate plant growth, it is counteracted by the increase in temperature and ozone, a molecule with harmful effects on plant tissue(Hogsett, et al 1997). Warming decreases the quality of the crops produced, grains are less dense and seeds contain less oil, as well as favouring growth and proliferation of weeds into new areas, due to the differences in how they photosynthesise (Fuhrer, 2003. Martre, 2017).

Figure 2. The graph from DEFRA (Department for Environmental Food and Rural Affairs) shows billions of pounds worth of imported food, especially fruit and vegetables. (Source: DEFRA Food Statistics Pocketbook 2016)
Figure 2. This graph from DEFRA (Department for Environmental Food and Rural Affairs) shows billions of pounds worth of imported food, especially fruit and vegetables. (Source: DEFRA Food Statistics Pocketbook 2016)

It is no secret that as a nation we currently import almost half of our food and animal feed from overseas (Ruiter et al 2015). In response to huge population increases of 3 Million on average every decade since the baby boomers of the 50s(Humby, 2016) and market for year-round exotic produce. But tropical regions are likely to suffer much more, even a slight temperature increase interfering with developmental and growth processes beyond already stretched thresholds, meaning production in these areas will fall hugely(Challinor, 2008). Excess precipitation, effectively drowning roots and drought adding another uncertain dimension to the mix(Amedie, 2013).

“[In staples like wheat, maize and barley] warming has resulted in annual combined losses of $5 billion per year, as of 2002” -Lobell, 2007

Environmental change is going to effect everyone in one way or another, we rely on plants for food, clothing, oxygen, medicine and much more. Prices of everyday commodities reflect the quantity and quality of production processes. The result is innumerable aspects of our lives being changed, in some way by the unsustainable practices we are complicit to on a daily basis(Lepetz et al., 2009).

Research into genetic modification of crop plants provides some relief in the challenges ahead, improving crop plant coping mechanisms and yield potential (Martre et al 2017), as well as a decrease in the consumption of animal products due to their high carbon footprint and inefficiency(Ruiter et al 2015). For now it will be a 4p increase in a farmhouse loaf and 10p extra for sunflower oil, but immediate action is necessary to prevent a large-scale food shortage in the near future.

[500 words]

References:

Amedie, F.A., (2013). Impacts of Climate Change on Plant Growth, Ecosystem Services, Biodiversity, and Potential Adaptation Measure. , pp.1–61.

Challinor, A.J. & Wheeler, T.R., (2008). Crop yield reduction in the tropics under climate change: Processes and uncertainties. Agricultural and Forest Meteorology, 148(3), pp.343–356.

Fuhrer, J., (2003). Agroecosystem responses to combinations of elevated CO2, ozone, and global climate change. Agriculture, Ecosystems and Environment, 97(1–3), pp.1–20.

Hogsett, W.E., J.E. Weber, D. Tingey, A. Herstrom, E.H. Lee and J.A. Laurence. (1997). An approach for characterizing tropospheric ozone risk to forests. Environmental Management 21:105-120.

Humby, P. (2016). Overview of the UK population: February 2016. [ONLINE] Available at: https://www.ons.gov.uk/peoplepopulationandcommunity/populationandmigration/populationestimates/articles/overviewoftheukpopulation/february2016. [Accessed 13 March 2017].

Lepetz V., Massot, M. & Schmeller, D.S., & Clobert, J., (2009). Biodiversity monitoring: some proposals to adequately study species’ responses to climate change. Biodiversity and Conservation 18, 3185- 3203

Lobell, D.B. & Field, C.B., (2007). Global scale climate–crop yield relationships and the impacts of recent warming. Environmental Research Letters, 2(1), p.14002.

Martre, P., Yin, X. & Ewert, F., (2017). Modeling crops from genotype to phenotype in a changing climate. Field Crops Research, 202, pp.1–4. Available at: http://linkinghub.elsevier.com/retrieve/pii/S0378429017300242.

Ruiter, H. de et al., (2015). Global cropland and greenhouse gas impacts of UK food supply are increasingly located overseas. Journal of The Royal Society Interface, 13(114). Available at: http://rsif.royalsocietypublishing.org/content/13/114/20151001.abstract.

WordShore (flickr), (2016), Fruit (WordShore)[ONLINE]. Available at: https://hiveminer.com/Tags/hebrides,solas [Accessed 15 March 2017].



Plants Revealed to be More Efficient at Higher CO2 Levels

Posted on by Erin Blandford

As we enjoy a varied diet of carbohydrates, proteins and fats, for plants it is the gas carbon dioxide (CO2), water and sunlight (figure. 1).

Figure. 1 Pedunculate Oak Tree; a temperate plant species that could be impacted by changing atmospheric conditions.
Figure. 1 Pedunculate Oak Tree in sunlight (Lind).

It is not just CO2 use which is made more efficient at elevated CO2 levels, water efficiency is greater as less water is lost from leaf pores; stomata. FACE (Free-Air CO2 Enrichment) experiments with soybean show that leaf pore conductance is not adapted to elevated CO2 but rather maintain decreased conductance. Furthermore, this increase in water efficiency is consistent between the leaf and canopy levels (Leakey et al, 2009).

 

It was also thought that higher CO2 levels lead to increased efficiency of nitrogen, a mineral required for growth, as plants grown at these levels do not have as much nitrogen present. These high CO2 grown plants also have a greater biological mass than those grown at normal CO2 conditions. However these CO2 levels where not found to affect levels of biological mass attained over plant lifetime which indicates that an accelerated period of growth that used up nitrogen reserves (Coleman et al, 1993). Increased CO2 levels are thought to contribute to increased uptake of nitrogen by plant roots rather than increased plant efficiency regarding nitrogen. Further FACE experiments at three separate forest locations showed that increased biological mass corresponded to increased nitrogen uptake from the soil. However this is limited to areas where nitrogen soil supply exceeds demand and is therefore unlikely to be seen in all plants worldwide (Finzi et al, 2007).

 

These FACE experiments are advantageous as they allow CO2 to be applied to a specific area of a wide range of ecosystems from desert to tropical forest. Trees as tall as 25m can be used in these experimental plots which can be as large as 30m in dimeter (Norby and Zak, 2011).

 

Figure.1 Atmospheric carbon dioxide (CO2) levels from 1950-2010 (IPCC, 2013)
Figure.2 Atmospheric carbon dioxide (CO2) levels from 1950-2010 (IPCC, 2013)

Scientists have been documenting rising atmospheric CO2, which is associated with planetary warming, for almost 70 years now, since 1950 (figure. 2). It is widely accepted that this change in CO2 has arisen from human industrialisation. While it seems that plants can positively cope with this change this conclusion must not be taken at face value and further studies must be undertaken.

 

 

 

  • Coleman, J.S., McConnaughay, K. D. M and Bazzaz, F. A. (1993). Elevated CO2 and Plant Nitrogen-Use: is reduced Tissue Nitrogen Concentration Size Dependent?. Oecologia. 93, 195-200.
  • Drake, B. G., Gonzalez-Meler, M. A and Long, S. P. (1997). More Efficient Plants: a Consequence of Rising Atmospheric CO2. Ann. Rev. Plant. Physiol. 48, 609-639.
  • Finzi, A. C., Norby, R. J., Calfapietra, C., Gallet-Budynek, A., Gielen, B., Holmes, W. E., Hoosbeek, M. R., Iversen, C. M, Jackson, R. B., Kubiske, M. E, Ledford, J., Liberloo, M., Oren, R., Polle, A., Pritchard, S., Zak, D. R., Schlesinger, W. H and Ceulemans, R. (2007). Increased in Nitrogen Uptake rather than Nitrogen-Use Efficiency support higher rates of Temperate Productivity under Elevated CO2. PNAS. 104 (35), 14014-14019.
  • IPCC, 2013: Summary for Policymakers. In: Climate Change 2013: The Physical Science Basis. Contribution of Working Group I to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change [Stocker, T.F., D. Qin, G.-K. Plattner, M. Tignor, S. K. Allen, J. Boschung, A. Nauels, Y. Xia, V. Bex and P.M. Midgley (eds.)]. Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA.
  • Leakey, A. D. B., Ainsworth, E. A., Bernacchi, C. J., Rogers, A., Long, S.P and Ort, D. R. (2009). Elevated CO2 Effects on Plant Carbon, Nitrogen and Water Relations: six important lessions from FACE. Journal of Experimental Botany. 60 (10), 2859-2876.
  • Lind, J. © Photo of Pedunculate Oak Tree. Available: http://www.arkive.org/pedunculate-oak/quercus-robur/image-A20783.html. Last accessed 20th March 2017.
  • Norby, R. J and Zak, D. R. (2011). Ecological Lessons from Free-Air CO2 Enrichment (FACE) Experiments. Annual Review of Ecology, Evolution and Systematics. 42. 181-203.

[480 words]



Climate Change IS happening, and it’s set to starve the planet… (The opposite of FAKE NEWS!)

Posted on by Anonymous

With the large scale funding cuts of the Environmental Protection Agency in the USA, the current rapid rates of climate change and CO2 release show no hope of stopping.

But seeing as though plants breathe using CO2 (through the process of photosynthesis), and use carbon in their growth, surely the increased amounts of CO2 being pumped into our atmosphere is a good thing for plants?  As studies have shown; perhaps not…

Plants require very specific environmental conditions to function efficiently, and any changes in these conditions can be detrimental.  Although it has been shown that increased CO2 initially causes an increase in the rate of photosynthesis and growth of leaves and roots (Taylor et al 1994), generally, in the long-term, the stimulation of photosynthesis is actually suppressed!

This is mainly due to negative effects on the plants function, such as the build-up of excess starch (sugars) in leaves via increased photosynthesis, hindering breathing of CO2 via pores; called the stomata (Makino & Mae 1999), and increased CO2 also causes the stomata to partially close (Singh 2009), resulting in an inability to respire efficiently (Ryan 1991).

The mechanism for respiration in a plant leaf, through the stomata.
The mechanism for gas exchange in a plant leaf, through the stomata.  Source: Understanding Evolution

The failure to respire efficiently can cause the death of many food crops globally that are vital to feeding our populations!

Increased environmental CO2 also results in global warming due to increased reflection of the Sun’s radiation back to the Earth’s surface; and a temperature increase of 2-3⁰C over the next 30-50 years (IPCC 2007) is predicted to cause problems for our crops.  For example, warmer temperatures affect plants mainly when they are developing, and this has been shown to reduce the numbers of our food crop plants by 80%-90% (Hatfield & Prueger 2015), having dire consequences for our food supplies!

The global change in surface temperature from 1901-2012. A worrying trend that is set to worsen... Source: National Snow & Ice Data Center
The global change in surface temperature from 1901-2012. A worrying trend that is set to worsen… Source: National Snow & Ice Data Center

Climate change is also set to increase the frequency of extreme weather events (Rosenzweig et al 2001). With increased storms and flooding drowning plants in some areas, and in other areas increased drought, resulting in a lack of water for plants to function with, which they rely heavily on for processes such as photosynthesis, vital for growth and survival.  The equation for photosynthesis is shown below, in case you have forgotten…

 

The equation for photosynthesis, showing how carbon dioxide and water are transformed into oxygen and sugars through the light energy from the sun hitting the chlorophyll pigments in the plants cells.
The equation for photosynthesis, showing how carbon dioxide and water are transformed into oxygen and sugars through the light energy from the sun interacting with the chlorophyll pigments in the plants cells.

 

With increasing global temperatures, drought affected areas will increase from 15.4% to 44.0% by 2100 (Li et al 2009) – resulting in less land to grow crops, which will be disastrous for our food security, along with the fact that the number of suitable growing days per year for our crops will decrease by 11% by the year 2100 (Mora et al 2015)!

A sunny day on a Californian beach? Not exactly… This is Californian farmland suffering from a severe drought – completely unusable!
A sunny day on a Californian beach? Not exactly… This is Californian farmland suffering from a severe drought – completely unusable! Source:  New York Times

 

With the saying “Feed the World” becoming more and more poignant, our future looks bleak, as we are set to have less food security per person than ever before due to the detrimental effects that climate change will have on plant function. Also, plants not only provide food, but are also at the heart of our medicines and resources! So maybe Donald Trump ought to reconsider his views on climate change before threatening his new healthcare system before it has begun.

Word Count: 500

 

References:

Hatfield, J. and Prueger, J. (2015). Temperature extremes: Effect on plant growth and development. Weather and Climate Extremes, 10, pp.4-10.

IPCC, (2007). Climate Change 2007: Impacts, Adaptation and Vulnerability. New York: Cambridge University Press, p.17.

Li, Y., Ye, W., Wang, M. and Yan, X. (2009). Climate change and drought: a risk assessment of crop-yield impacts. Climate Research, 39, pp.31-46.

Makino, A. and Mae, T. (1999). Photosynthesis and Plant Growth at Elevated Levels of CO2. Plant and Cell Physiology, 40(10), pp.999-1006.

Mora, C., Caldwell, I., Caldwell, J., Fisher, M., Genco, B. and Running, S. (2015). Suitable Days for Plant Growth Disappear under Projected Climate Change: Potential Human and Biotic Vulnerability. PLOS Biology, 13(6), p.e1002167.

Rosenzweig, C., Iglesius, A., Yang, X., Epstein, P. and Chivian, E. (2001). Climate change and extreme weather events – Implications for food production, plant diseases, and pests. Global Change & Human Health, 2(2), pp.90-104.

Ryan, M. (1991). Effects of Climate Change on Plant Respiration. Ecological Applications, 1(2), pp.157-167.

Singh, S. (2009). Climate change and crops. 1st ed. Berlin: Springer, pp.5-6.

Taylor, G., Ranasinghe, S., Bosac, C., Gardner, S.D.L. and Ferris, R. (1994). Elevated CO2 and plant growth: cellular mechanisms and responses of whole plants. Journal of Experimental Botany, 45, pp.1761-1774.



Crops and Climate Change: the good, the bad and the ugly truth

Posted on by Anonymous

New Year, New Hope? But 2017 began with Britain being hit with a vegetable shortage!

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(Independent, 2017)                                                    (The Guardian, 2017)

But apart from halting our “clean eating” resolutions…..

Is a courgette shortage really the end of the world?

Well, probably not! But globally, food security is no laughing matter.

 And what is the cause you may ask? Climate change, of course!

The evidence for climate change is overwhelming.

The Earth’s average temperature has increased by 0.85°C between 1980-2012 (IPCC, 2014). This may seem insignificant, yet, it has severe consequences, such as the ice caps melting, sea levels rising and increased occurrence of extreme weather events (Overpeck and Cole, 2006).

3

Globally averaged combined land and ocean surface temperature (IPCC, 2014)

Humans are to blame.

Since the industrial revolution, burning of fossil fuels has increased emissions of carbon dioxide (CO2) and other greenhouse gases (GHGs) These GHGs act as a blanket, trapping energy in the atmosphere, causing Earth’s temperature to rise (IPCC, 2014).

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Global Human CO2 Emissions, IPCC, 2014

The good?

Higher CO2 levels increase plant photosynthesis (Pospisilova and Catsky, 1999). Photosynthesis depends on an enzyme called Rubisco, which evolved at higher prehistoric CO2 levels, therefore has higher activity when CO2 increases (Bowes, 1996). This increases plant growth, thereby increasing crop yield, in a phenomenon termed “CO2-fertlisation” (Allen, 1990).

This is particularly pronounced plants categorised at C3 , which includes major crops such as rice, wheat and soybean. Increasing CO2 to 550pm causes 10-20% increase in C3 crop yield, but only 0-10% increase plants categorised as C4, which includes the crops maize and sorghum (Schmidhuber and Tubiello, 2007).

CO2 enters plants through stomata (plant pores), therefore, at higher CO2 levels the stomata need not open as often, termed reduced stomatal conductance. This decreases the amount of water lost through the pores in the process of transpiration, thereby increasing the water efficiency of the plants (Drake et al., 2007).

The bad?

So, is climate change good for plants if it causes increased growth and higher water efficiency? Well no, it was never going to be that simple…

Extreme weather events negatively impact food security, both directly by reduced yields from damaged crops but also indirectly by increasing the chance of landslides and soil erosion, thereby reducing the land available for agriculture (Cerri et al., 2007).

This issue is becoming more urgent as global population increases at an unprecedented rate, increasing the demand for food (MA, 2005).

Food security issues are not only concerned with the quantity of food but also the quality, as globally many people suffer from malnutrition (MA, 2005). Elevated CO2 decreases the zinc, iron, and protein content in wheat, barley, and rice (Myers et al., 2014).

 5

The two-fold effect of increased CO2 form increased carbon emissions; most likely the negative effect will outweigh the positive effect. 

The ugly truth

Unfortunately, it is predicted the losses will outweigh any gains from CO2 fertilisation.

Ultimately, lack of food could see increased prices for consumers in the developed world whilst the developing world will suffer with food shortage and malnutrition.

Lack of courgettes may seem a trivial matter but is it just one more sign that we getting closer to the tipping point of our planet’s ability to cope with climate change.

Word count: 499

References

Allen, L.H. Jr. (1990). Plant responses to rising carbon dioxide and potential interactions with air pollutants. J. Environ. Qual, 19: 15-34.

Bowes G. (1996) Photosynthetic responses to changing atmospheric carbon dioxide. pp. 387-407. In: N.R. Baker (ed.). Photosynthesis and the Environment. Advances in Photosynthesis, Vol. 5, Kluwer, Dordrecht

Cerri, C. E.P., Sparovek, G., Bernoux, M., Easterling, W.E., Melillo, J. M., and Cerri C. C. (2007). Tropical Agriculture and Global Warming: Impacts and Mitigation Options. Sci. Agric., 64(1): 83-89.

Drake, B.G., Gonzàlez-Meler, M.A. and Long, S.P., 1997. More efficient plants: a consequence of rising atmospheric CO2? Annual review of plant biology, 48(1): 609-639.

IPCC. (2014) Climate Change 2014: Synthesis Report. Contribution of Working Groups I, II and III to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change. R.K. Pachauri and L.A. Meyer (eds.). IPCC, Geneva, Switzerland, pp. 151.

Millennium Ecosystem Assessment (2005). Ecosystems and Human Well-being: Synthesis. Island Press, Washington, DC.

Myers SS, Zanobetti A, Kloog I, et al. (2014). Rising CO2 threatens human nutrition. Nature. 510(7503): 139-142.

Overpeck, J.T. and Cole, J.E. (2006). Abrupt change in Earth’s climate system. Annual Review of Environment and Resources, 31: 1-31.

Pospisilova, J. and Catsky, J. (1999). Development of water stress under increased atmospheric CO2 concentration. Biologia Plantarum, 42: 1-24.

Schmidhuber, J. and Tubiello, F.N. (2007). Global food security under climate change. Proc. Natl. Acad. Sci. USA, 104(50): 19703-8.



How do you like your toast in the morning? Without the worry of food security?

Posted on by Imogen Vieten

80% of human calorie intake comes from 6 major crops including – maize, wheat and rice1. For all people, at all times to have physical and economic access to sufficient food needed for a balanced diet2–food security, the production and distribution of these crops is vital.

Present day representation of global vulnerability to food insecurity8. Explore scenarios of Greenhouse gas emissions and adaptation to climate change impacts on food security by clicking on the link: http://www.metoffice.gov.uk/food-insecurity-index/ Present day representation of global vulnerability to food insecurity3. Explore scenarios of Greenhouse gas emissions and adaptation to climate change impacts on food security by clicking on the image.

A growing human population increases pressure to enhance crop production. 1 billion ha of land will be converted by 2050 for agriculture, reducing absorption of atmospheric carbon dioxide by plants2 and restoration of gaseous balance in the atmosphere, with fewer plants to act as a CO2 ‘sink’.

Human induced climate change is negatively affecting ecosystems, crop yield and production. Since the industrial revolution greenhouse gas emissions have risen, with atmospheric CO2 levels currently at 406.42ppm4, meaning plants are growing in conditions not experienced for 26 million years5.

Impacts of future climate change are predicted to be severe, varying between regions, through changes in temperature, precipitation and increases in extreme weather events. Methods of crop production such as sustainable intensification are needed to increase yields and overcome threats to livelihoods and food security2.

Will increased CO2 result in higher crop yields?

During photosynthesis plants use CO2, water and light to produce oxygen and carbohydrates for growth. Efficiency of this depends on the enzyme Rubisco, which functions better in high CO2, shown experimentally to increase photosynthesis by 58%5. There is evidence that the number and size of individual cells increase in elevated CO26, showing species specific adaptive ability7,  indicating potential to increase crop yield. However other climatic stresses will have negative effects.

The temperature dependant action of Rubisco may become less efficient with rising global temperatures. Furthermore in the long term, plants can acclimatise as additional carbohydrates produced from photosynthesis cannot be used5.

During extended periods of high CO2 exposure the number of stomata- pores used in gaseous exchange in leaves, may decrease indicating that photosynthetic rate will too7.

How will crop production be affected?

For sustainable intensification sufficient water and nutrients8 are required, which will be threatened by increased extreme weather events- from drought affecting water supply to storms where heavy downpours can wash away top soil, reducing land fertility.

Threats to global productivity and changes in yield could have impacts worldwide8. If production decreases, prices of grain products and meat reliant on grain as a feedstock will increase8. Furthermore lower agricultural output, especially in the developing world, leads to lower incomes, with the poorest suffering the most.

High CO2 can decrease food quality with a decline in protein, nitrogen, zinc and iron concentrations in crops9, potentially causing adverse health effects, and necessitating consumption of greater quantities.

Securing the future

FACE (Free-air concentration enrichment) experiments expose crops to elevated CO2 to examine responses and adaptions of ecosystems. Research to develop climate resilient crop varieties to better cope with heat, drought and salinity is also being conducted.

By adapting farming mechanisms and increasing yield and tolerance of essential crop species to environmental extremes, can we ensure food security? Yes, the time to act is now!

 

Discover more about how farmers may adapt their practices to a changing climate in the video ‘Feeding Nine Billion’10

 

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References

  1. Campell, N,A., Reece, J, B., Urry, L,A., Cain, M,L., Wasserman, S, A., Minorsky, P, V., Jackson, R, B. (2015). Seed Plants. In: Wilbur, BBiology A Global Approach. 10th ed. Essex: Pearson. p707.
  2. Sunderland, T., Powell, B., Ickowitz, A., Foli, S., Pinedo-Vasquez, M., Nasi, R. and Padoch, C. (2013). Food security and nutrition: The role of forests. Center for International Forestry Research. Discussion Paper, p1-20.
  3. Met Office. (2017).Food Insecurity Climate Change. Available: http://www.metoffice.gov.uk/food-insecurity-index/. Last accessed 18th March 2017.
  4. CO2 (2017). Earth’s CO2 home page. Available: https://www.CO2.earth/earths-CO2-main-page. Last accessed 20th March 2017.
  5. Drake, B, G. and Gonzàlez-Meler, M, A. (1997). More Efficient Plants: A Consequence of Rising Atmospheric CO2?.Annual Review of Plant Physiology and Plant Molecular Biology. 48, p609-639.
  6. Taylor, G., Ranasinghe, S., Bosac, C., Gardner, S and Ferris, R. (1994). Elevated CO2 and plant growth: cellular mechanisms and responses of whole plants. Journal of Experimental Botany. 45 (Special Issue). P 1761-1774
  7. Long, S, P., Ainsworth, E, A., Rogers, A. and Ort, D, R. (2004). Rising Atmospheric Carbon Dioxide: Plants FACE the Future.Annual Review of Plant Biology. 55, p591-628.
  8. Nelson, G, C., Rosegrant, M, W., Koo, J., Robertson, R., Sulser, T., Zhu, T., Ringler, C., Msangi, S., Palazzo, A., Batka, M., Magalhaes, M., Valmonte-Santos, R., Ewing, M. and Lee, D. (2009). Climate Change: Impact on Agriculture and Costs of Adaptation.International Food Policy Research Institute. Available at: http://www.fao.org/fileadmin/user_upload/rome2007/docs/Impact_on_Agriculture_and_Costs_of_Adaptation.pdf. Last accessed 19th March 2017
  9. Myers, S., Zanobetti, A., Kloog, I., Huybers, P., Leakry, A., Bloom, A., Carlisle, E., Dietterich, L., Fitzgerald, G., Hasegawa, T., Holbrook, N., Nelson, R., Ottman, M., Raboy, V., Sakai, H., Sartor, K., Schwartz, J., Seneweera, S., Tausz, M. and Usui, Y. (2014). Increasing CO2 threatens human nutrition. Nature, 510, p139-142
  10. Fraser, E. (2014). Feeding Nine Billion Video 6: Climate Change and Food Security. Available: https://www.youtube.com/watch?v=cYq2elstFWQ. Last accessed 18th March 2017.


Bloom and Bust

Posted on by Lauren Furmidge
‘Blue Marble’ –Earth as seen by Apollo 17 (NASA/ Apollo 17 Crew, 1972)

 

In 1972, one of the most iconic photographs of the Earth was taken from space.  The ‘Blue Marble’ snapped by the astronauts aboard Apollo 17 shows an Earth with deep blue oceans but very little greenery on the land. Now photographs of the Earth from space look very different, with luscious green patches where there was once dull brown.  The spreading and growing of green vegetation is a result of rising CO2 levels in the Earth’s atmosphere.  The Earth has undergone an increase of 18 square kilometres of new vegetation between 1982 and 2009 (Keenan et al., 2016).

 

Since the Industrial Revolution, the burning of fossil fuels such as coal and oil by humans has caused an enormous rise in atmospheric CO2 from 280ppm to over 400ppm today, inducing disastrous effects on the environment such as climate change (Khatiwala et al., 2009).

So if increases in CO2 are so bad, why is a boom in plant growth occurring?

 

Plants use CO2 in photosynthesis; a process in which plants use CO2, water and light from the sun to produce sugars for growth and oxygen which they give off.  The increased rates of photosynthesis are down to a chemical called Rubisco, which helps incorporate CO2 into the photosynthesis process.  Rubisco first evolved long, long ago- far before humans began affecting the world.  At this point in history CO2 levels were much greater than during recent times.  This means that Rubisco is less efficient at lower CO2 levels.  As humans have begun to disturb these lower CO2 concentrations and caused them to rise, Rubisco works better meaning plants are able to photosynthesise at a greater rate, which increases their growth (Taylor et al., 1994).

 

Sun through leaves (Shuttershock, 2013)
Sun through leaves (Shuttershock, 2013)

 

Although this appears to be all good news for the plants, rising atmospheric CO2 levels also bring negative effects, one of them being climate change.  With increasing CO2 comes increases in temperature which can negatively impact plants.  Plants require an optimum temperature in order to survive well and if they are not able to shift their ranges, they will suffer the effects of warmer, dryer environments which are ultimately inhospitable (Hatfield and Prueger, 2015).  So whilst plants prosper in the short term, when temperatures get too high they languish.

Also, there is evidence that rising CO2 reduces the ability of stomata- small pores on plants- to conduct CO2 and perform transpiration- the removal of water-, ultimately leading to reduced photosynthesis (Drake et al., 1997).

 

Although rising CO2 has turned the brown swathes of Earth captured in the ‘Blue Marble’ into luscious green, behind this initial bloom lurks an ominous truth. If humans continue to fuel rising CO2 levels, plants will suffer and food crops will fail. Global temperature increases, rainfall changes and extreme weather events- droughts and floods- jeopardise the functions of plants, ultimately devastating them.

 

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References

Drake, B.G., Gonzalez-Meler, M.A., Long, S.P.,1997. More efficient plants: a consequence of rising atmospheric CO? Annu. Rev. Plant Physiol. Plant Mol. Biol. 48, 609 – 639.

Hatfield, J.L. and Prueger, J.H., 2015. Temperature extremes: effect on plant growth and development. Weather and Climate Extremes, 10, pp.4-10.

Keenan, T.F., Prentice, I.C., Canadell, J.G., Williams, C.A., Wang, H., Raupach, M. and Collatz, G.J., 2016. Recent pause in the growth rate of atmospheric CO2 due to enhanced terrestrial carbon uptake. Nature communications, 7.

Khatiwala, S., Primeau, F. and Hall, T., 2009. Reconstruction of the history of anthropogenic CO2 concentrations in the ocean. Nature, 462(7271), pp.346-349.

NASA/ Apollo 17 Crew., 1972., ‘Blue Marble’ –Earth as seen by Apollo 17. [Photograph]

Shuttershock., 2013., Sun through leaves. [Photograph]

Taylor, G., Ranasinghe, S., Bosac, C., Gardner, S.D.L. and Ferris, R., 1994. Elevated CO2 and plant growth: cellular mechanisms and responses of whole plants. Journal of Experimental Botany, 45(Special Issue), pp.1761-1774.

 

 



Could Climate Change STARVE us?

Posted on by Anonymous

The planet needs YOUR help!

We all have been alarmed and warned about rising sea temperatures, melting sea ice and glaciers, but the main problem is that we could describe them on and on.. Therefore, one of the greatest challenges the earth faces in this day and age is CLIMATE CHANGE.

A photo to show the loss of vegetation as a result of climate change (http://ayalim.org/israeli-plant-species-resistant-to-climate-change/)
A photo to show the loss of vegetation as a result of climate change  Available at:(http://ayalim.org/israeli-plant-species-resistant-to-climate-change/)

An unprecedented ↑ in atmospheric CO2 and temperature can shockingly lead to:

  • Species extinction
  • Collapsing ecosystems and food chains and as a result, foreseeable shortages of food and water to the increasing global population.

One of the toughest tasks this century, is predicting the response of plants to global climate change. Thus, what is essentially happening to our plants through this unpredictable change?

Many studies have observed:

Plants will thrive with an established elevation in CO2 and temperature…

  • As more CO2 = more fixation = more photosynthesis

Bisgrove and Hadley (2002) suggest that a “doubling in carbon dioxide level can increase plant growth by as much as 50%”

  • More heat = advanced growth and seed germination

 

HOWEVER…

Agriculture sustains almost all life-forms on Earth, meaning adverse conditions, can restrict crop plants in reaching their full genetic potential of producing a high yield (Anjum et al., 2014).

(1) Heat waves, extreme temperature events are projected to become more intense, more frequent and longer lasting to what is currently been observed in recent years (Hatfield and Prueger, 2015). Consequently, when a drought occurs where the levels of heat are extreme, the growth of a plant will rapidly decrease due to the high level of moisture loss. Furthermore, although water is essential for the functioning of virtually every plant on the planet, too much water (as a result of a storm… which we all can undeniably find exciting!) can in fact reduce the amount of oxygen in the soil, making a plant more susceptible to disease.

NOTE: Remember to stop and think, ‘this storm is not only damaging our plants, but in fact our livelihoods!’

(2) In addition, there is abundant evidence that in the long term, plants will begin to acclimate to a rise in CO2 levels. Therefore, the photosynthetic capacity becomes inhibited due to the plants being unable to utilise the additional carbohydrate that is accompanied with photosynthesis (Drake et al., 1997).

(3) Shockingly, crops of the future that are grown in a high- CO2 environment, will have decreases in the concentrations of zinc, iron and protein in grains of wheat, barley and rice (Myers et al., 2014) meaning the food in which we eat will be much less nutritious. Considering most people depend on these grains for their source of zinc and iron this can be detrimental to human health.

percentage
A graph to show the result in % reduction of nutrients from certain crops in an expected level of CO2 by 2050. (Source: NATURE)

 

If we continue to actively contribute to a world of increasing CO2 and temperature, not only are the plants on our Earth disturbed but if you stop and think: YOU yourself can be hugely affected.

A question of thought, who knows what this may cause to our future health and livelihoods?

 

 

References:

  • Anjum, N., Gill, S. and Gill, R. (2014). Plant adaptation to environmental change. 1st ed. Wallingford: CABI.
  • Bisgrove, R. and Hadley, P. (2002) Gardening in the Global Greenhouse: The Impacts of Climate Change on Gardens in the UK. Technical Report. Oxford: UKCIP.
  • Drake, B., Gonzalez-Meler, M. and Long, S. (1997). MORE EFFICIENT PLANTS: A Consequence of Rising Atmospheric CO2?. Annual Review of Plant Physiology and Plant Molecular Biology. 48(1), pp.609-639.
  • Hatfield, J. and Prueger, J. (2015). Temperature extremes: Effect on plant growth and development. Weather and Climate Extremes, 10, pp.4-10.
  • Myers, S., Zanobetti, A., Kloog, I., Huybers, P., Leakey, A., Bloom, A., Carlisle, E., Dietterich, L., Fitzgerald, G., Hasegawa, T., Holbrook, N., Nelson, R., Ottman, M., Raboy, V., Sakai, H., Sartor, K., Schwartz, J., Seneweera S., Tausz, M. and Usui, Y. (2014). Increasing CO2 threatens human nutrition. Nature, 510(7503), pp.139-142.

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Are plants on their way to killing us?

Posted on by Charlotte Alanine

          Have you ever noticed how much easier it is to breathe on a jog through a luscious park or a woodland compared to the inner city? This is because the air we breathe comes from the photosynthetic process plants provide. In this reaction, plants extract energy from carbon dioxide (CO2) combined with sunlight as well as other organic soil materials and release Oxygen (O2) as a by-product which we then benefit from.

 

         Photosynthesis under increasing CO2

          Each year since 1959, approximately half of the CO2 emissions we produce linger in our atmosphere (Le Quéré, et al., 2009). With atmospheric levels of CO2 on the rise as a result of our activities, the logical outcome would be that plants have additional CO2 to photosynthesise, allowing for more oxygen for us, right? Indeed, short-term increases have no negative impacts on photosynthesis. In fact, a study suggested they became more efficient at recycling CO2 (Besford, et al., 1990) as demonstrated in the positive feedback photosynthesis and growth of P.cathayana (Zhao, et al., 2012). However, under long-term carbon dioxide exposure, plants lost all photosynthetic gain (Besford, et al., 1990). Other studies have investigated the effects of increasing CO2 levels on plants and it has recently been found that previous models may have overestimated  the ability of plant “sinks” to make use of the additional human-related carbon. A “sink” is a location where carbon dioxide accumulates and is absorbed by plants much like running water down a sink.

 

From carbon sinks to carbon sources

        In 1991, Arp projected that plants in the field would not experience a decrease in photosynthetic abilities as a result of atmospheric CO2 increase. However, more recently in 2015, Wieder et al. reported that photosynthetic processes were limited by nutrient availability, in which phosphorus and nitrogen (Aranjuelo, et al., 2013) were the main limiting factors.

Figure 1. Modelling of changes in mean terrestrial carbon storage from an initial record 1860-1869 (top) to the 2100 projection with limited nitrogen and phosphorus (bottom). Source: Wieder et al. (2015)
Figure 1. Modelling of changes in mean terrestrial carbon storage from an initial record 1860-1869 (top) to the 2100 projection with limited nitrogen and phosphorus (bottom). Source: Wieder et al. (2015)

          In addition, their models projected that by 2100, plants which were once considered sinks may actually be turning into carbon sources (fig.1). This means they could be emitting more carbon than they absorb as a result of increasing carbon dioxide in the air in combination with the insufficient amounts of other organic materials (nitrogen, phosphorus, minerals, etc.) necessary for photosynthesis and consequently accelerating the rate of climate change which is bad news for us. Plants will essentially be slowly suffocating us as we rely on them for clean air.

 

 

 

A threat to food security

          Likewise, as a result of intensifying agriculture, soils are becoming increasingly eroded. For one, this means they are unable to store and process atmospheric carbon as efficiently and there is a lack of nutrients made available to plants (Lal, et al., 2008). This, coupled with the higher concentrations of CO2, poses a great threat to major crop plants such as oilseed rape (Franzaring, et al., 2011) and wheat (Uddling, et al., 2008). In laboratory studies, these crop plants tended to reduce the quality and quantity of their seeds in high concentrations of CO2.

          Emissions are not only posing a threat to a plant’s capacity to recycle air but also put our food security at risk.

References

Aranjuelo, I., Cabrerizo, P., Arrese-Igor, C. & Aparicio-Tejo, P., 2013. Pea plant responsiveness under elevated [CO2] is conditioned by the N source (N2 fixation versus NO3 – fertilization). Environmental and Experimental Botany, Volume 95, pp. 34-40.

Arp, W., 1991. Effects of source-sink relations on photosynthetic acclimation to elevated CO2. Plant, Cell and Environment, Volume 14, pp. 869-875.

Besford, R., Ludwig, L. & Withers, A., 1990. The Greenhouse Effect: Acclimation of Tomato Plants Growing in High CO2, Photosynthesis and Ribulose-1, 5-Bisphosphate Carboxylase Protein. Journal of Experimental Botany, 41(8), pp. 925-931.

Franzaring, J., Weller, S., Schmid, I. & Fangmeier, A., 2011. Growth, senescence and water use efficiency of spring oilseed rape (Brassica napus L. cv.Mozart) grown in a factorial combination of nitrogen supply and elevated CO2. Environmental and Experimental Botany, Volume 72, pp. 284-296.

Lal, R. et al., 2008. Soil erosion: a carbon sink or source?. Science, 319(5866), pp. 1040-1042.

Le Quéré, C. et al., 2009. Trends in the sources and sinks of carbon dioxide. Nature geoscience, 2(12), pp. 831-836.

Uddling, J. et al., 2008. Source-sink balance of wheat determines responsiveness of grain production to increased [CO2] and water supply. Agriculture, Ecosystems and Environment, Volume 127, pp. 215-222.

Wieder, W., Cleveland, C., Smith, W. & Todd-Brown, K., 2015. Future productivity and carbon storage limited by terrestrial nutrient availability. Nature, 8(6), pp. 441-445.

Zhao, H. et al., 2012. Sex-related and stage-dependent source-to-sink transition in Populus cathayana grown at elevated CO2 and elevated temperature. Tree Physiology, Volume 32, pp. 1325-1338.

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