The University of Southampton

Tag: CO2

We need to change today, not the day after tomorrow…

Posted on by Alexandra Loveridge

The evidence for global environmental change is overwhelming. Increased levels of CO2 and other pollutants in the atmosphere cause constant and gradual increases in the average global temperature.  This is largely the fault of human activity through the burning of fossil fuels and the release of greenhouse gases. Carbon dioxide is long lived in our atmosphere and so these changes will continue happening for a long time even if we stop producing greenhouse gases.

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A tree line so straight it could have been drawn on with a ruler.

 

Have you ever gone to the mountains and wondered why there is a distinct sequence in the types of trees you see: deciduous, evergreen, then a well defined tree line above which there are rarely any trees?

This is because most plants can only live in very specific conditions. But global change will increase the amount of CO2 in the atmosphere, which warms the environment…

 

 

What does global environmental change mean for plants in the future?

 

 

 

Firstly, there will be a higher rate of photosynthesis under increased CO2. Rubisco, a key part of the photosynthetic process that fixes CO2, evolved at a time when there was a higher proportion of CO2 in the atmosphere. Under today’s much lower CO2 levels, this enzyme is far less efficient because Rubisco also fixes oxygen, wasting energy. So for plants, more CO2 in the environment means more photosynthesis, right?

Not necessarily true! Bowes (1993) suggested that at high levels of CO2 for a long time some plants may decrease the number of pores (stomata) that absorb CO2 on their leaves and the rate of photosynthesis may actually decrease. As well as this, changes to precipitation and nutrient supply may stop plants from reaching their full photosynthetic potential.

Secondly, rates of growth increase when plants are subjected to higher levels of CO2. Taylor et al. (1994) found that leaves and roots were bigger under higher levels of CO2 and also found that individual cells in the roots got larger too. However, some plants are already living on the edge of their physiological limits and cannot adapt. This may lead to some species dying out if they cannot adapt to the conditions quickly enough.

The UK: a future tropical paradise? Quite unlikely…

Finally plants will need to be hardier to withstand increased temperatures and occurrences of extreme weather events… Some plants have found a clever way to get around the warming problem. In the mountains, trees have gradually been moving higher up to avoid the warmer temperatures (Thuiller et al., 2005). As well as this, species such as mangroves are also shifting north (Field, 1995). This change in latitude is called a range shift. This doesn’t, however, mean that the future beaches around Britain will be warm and sunny and covered in palm trees unfortunately…

 

These changes will have a huge impact on society through reduced food security, changes to our water and power supplies, and may even impact on our health.

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Its not the end of the world quite yet!

How do you think we can reduce these risks? What can people do to reduce their impact on the planet? Leave your thoughts and comments below!

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All photographs taken by Sophie Loveridge.

 

References

  • Monleon, V. and Lintz, H. (2015). Evidence of Tree Species’ Range Shifts in a Complex Landscape. PLOS ONE, 10(1), p.e0118069.
  • Field, C. (1995). Impact of expected climate change on mangroves. Hydrobiologia, 295(1-3), pp.75-81.
  • Bowes, G. (1993). Facing the Inevitable: Plants and Increasing Atmospheric CO2. Annual Review of Plant Physiology and Plant Molecular Biology, 44(1), pp.309-332.
  • Thuiller, W., Lavorel, S., Araujo, M., Sykes, M. and Prentice, I. (2005). Climate change threats to plant diversity in Europe. Proceedings of the National Academy of Sciences, 102(23), pp.8245-8250.
  • 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), pp.1761-1774.


Plant Pores: How Carbon Dioxide Changes Stomata

Posted on by Alexanda Hewitt

 

Humans change the world around them. From farms to factories, that’s all on us. But what about a deeper level of change, happening to the parts of arguably our most important friends on this planet. The plants.

All types of plant have small holes, or pores, on their leaves called stomata. Each individual stoma is bound by a pair of cells called guard cells (see Figure 1), that help to control the uptake and release of gases (most importantly carbon dioxide (CO2) and water vapour) between the inside of the leaf and the atmosphere(1). This gas exchange as it were is regulated by the number of stomata that form on the leaf (the stomatal density) and by how open (the aperture) the stomatal pores are kept by the guard cells. The stomatal density and aperture are themselves influenced by environmental conditions such as light intensity and CO2 concentration(1).

Figure 1: A microscope image of a stoma. The pore is visible in the centre of the image, whilst the two guard cells (although they look like one circular cell surrounding the pore) can be seen either side of the pore(2).
Figure 1: A microscope image of a stoma. The pore is visible in the centre of the image, whilst the two guard cells (although they look like one circular cell surrounding the pore) can be seen either side of the pore(2).

CO2 concentration in the atmosphere is particularly important for modern day plants as although CO2 levels have fluctuated considerably over the last 400 million years(3), in the last 250 years they have risen by nearly 40%, a significant increase at a fast rate(4). Plants have thus had to go from living in some relatively low CO2 environments to living in a higher CO2 one(3). Experimental CO2 increases have shown to change the stomatal density by different amounts in different types of plant, but with an average of an 11% reduction with a doubling of the CO2 concentration, regardless of the starting density of the stomata(1). Furthermore, higher than normal CO2 levels in the atmosphere result in the closure of stomatal pores in plants(5).

These changes generally lead to a decrease (of between 21% and 40% in some studies(6)) in the amount of gas exchange between the plant and the atmosphere(1) but even this has other influences acting on it. The response to CO2 changes has been shown to be significantly stronger in younger trees, in non-evergreen trees and in trees that do not have enough water compared to those that do not have enough nutrients(6). This however, seems to be affected by the length of time that the leaves are in the higher than normal CO2 conditions with some leaves returning to a “normal” stomatal density after 2 years in a higher CO2 environment(7).

What does any of this actually do to the plant though? In some cases there has been an increased maximum rate of photosynthesis (the process by which plants make sugar from CO2 and water) at these higher CO2 levels(1). However, other studies have shown plants with the highest stomatal densities obtained the highest gas exchange rate and rate of photosynthesis, contrary to the previous results(8). Effectively we need more experiments to take place to get an accurate answer. What we do know is that we are changing the stomata on plants, be it for better or worse is yet to be decided.

 

References

  1. Hetherington AM, Woodward FI. The role of stomata in sensing and driving environmental change. Nature. 2003 Aug 21;424(6951):901-8.
  2. Ferry RJ. Stomata, Subsidiary Cells, and Implications. North American native orchid journal. 2008:168.
  3. Woodward FI. Do plants really need stomata?. Journal of Experimental Botany. 1998 Mar 1:471-80.
  4. Singh UB, Ahluwalia AS. Microalgae: a promising tool for carbon sequestration. Mitigation and Adaptation Strategies for Global Change. 2013 Jan 1;18(1):73-95.
  5. Engineer CB, Hashimoto-Sugimoto M, Negi J, Israelsson-Nordström M, Azoulay-Shemer T, Rappel WJ, Iba K, Schroeder JI. CO2 sensing and CO2 regulation of stomatal conductance: advances and open questions. Trends in plant science. 2016 Jan 31;21(1):16-30.
  6. Medlyn BE, Barton CV, Broadmeadow MS, Ceulemans R, De Angelis P, Forstreuter M, Freeman M, Jackson SB, Kellomäki S, Laitat E, Rey A. Stomatal conductance of forest species after long‐term exposure to elevated CO2 concentration: A synthesis. New Phytologist. 2001 Feb 1;149(2):247-64.
  7. Ainsworth EA, Rogers A. The response of photosynthesis and stomatal conductance to rising [CO2]: mechanisms and environmental interactions. Plant, cell & environment. 2007 Mar 1;30(3):258-70.
  8. Woodward FI, Lake JA, Quick WP. Stomatal development and CO2: ecological consequences. New Phytologist. 2002 Mar 1;153(3):477-84.

 

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