The University of Southampton

Tag: Carbon Dioxide

Popeye didn’t cause the spinach shortage: why the effects of global environmental change on plant function is a double-edge sword

Posted on by Anonymous

Climate change – a myth? We have all heard of it and its impending threat to our global environment. However, what we should ask ourselves is how are plants affected by our planet’s increasing temperatures, carbon dioxide (CO2) levels and the increasing frequency and intensity of severe weather changes?

Diagram illustrating some factors mentioned that are linked to climate change and their impact on several biological processes carried out in plants
Diagram illustrating some factors mentioned that are linked to climate change and their impact on several biological processes carried out in plants (Source: (Kallarackal and Roby, 2012))

Plants play a critical role in pulling CO2 out of the atmosphere. This uptake of CO2 during photosynthesis is a major pathway by which carbon can be stored (Tkemaladze and Makhashvili, 2016). Carbon dioxide is predicted to increase to approximately 1000 ppm by 2100. Since the beginning of the Industrial Revolution approximately 200 years ago average global temperatures have increased by 0.85°C and by the end of the century temperature is projected to rise by approximately another 4°C (IPCC, 2013).  Some would assume this to be beneficial to plants due to these warmer temperatures and increased levels of gas as it should, in theory, encourage growth. However, it is not as straight forward as this.

The enzyme rubisco is the key to this photosynthetic process by fixing CO2. Drake et al. (1997) states that the increased levels of CO2 will allow greater fixation by plants and, therefore, result in increased growth. However, Bisgrove and Hadley (2002) found that long-term exposure to elevated levels of CO2 caused an accumulation of carbohydrates in plant tissues, which in turn reduced the rate of photosynthesis. Furthermore, although plants initially respond positively to increasing temperature, this will eventually plateau or even decline after reaching the optimum range for some species. Plants may experience an increased rate of respiration leading to death; illustrating the world’s plants can easily lose their ability to act as a global carbon sink, becoming instead yet another carbon source (Mellilo et al., 1990; Hawkins et al., 2008).

Moreover, another consequence of global environmental change is a change to global weather patterns. Many do not connect climate change with uncharacteristic weather events, however, there is no doubt that climate change affects their intensity and frequency. Thus, in the future, we can expect to experience more frequent periods of drought, floods and storms (Frich et al., 2002). For example, during the past winter, there was snow escape in Spain as we witnessed a window to our future in the form of the courgette and spinach crisis, which caused havoc and rationing in British supermarkets. Yet these changing weather patterns will have a much larger impact than just a blow to spiralizer sales.

 

The heavy snowfall the province of Murcia in Spain experienced this winter ruining many crops.
The province of Murcia in Spain experienced heavy snowfall this winter ruining many crops (Source:http://edition.cnn.com/2017/02/03/europe/lettuce-shortage-europe/)

Stated above are only a few effects global climate change has on our planet’s plants. Plants have an essential regulatory role in the control of our planet’s climate: they did yesterday, they do today and they most certainly will in the future. If we continue to allow the CO2 level to increase at the rate it is currently we will suffer dramatic consequences. It not only will affect the Earth’s vegetation such as forests and plants, but will also have a knock-on effect on global food production, therefore, affecting our wellbeing.

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References

Bisgrove, R. and Hadley, P. (2002). Gardening in the global greenhouse: The impacts of future landuse and climate on the red list status of the Proteaceae in the cape floristic region, South Africa. Global Change Biology, 69, pp.79-91.

Drake, B., Gonzàlez-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.

Frich, P., Alexander, L., Della-Marta, P., Gleason, B., Haylock, M., Klein Tank, A. and Peterson, T. (2002). Observed coherent changes in climatic extremes during the second half of the twentieth century. Climate Research, 19, pp.193-212.

Hawkins, B., Sharrock, S. and Havens, K. (2008). Plants and climate change; which future? Richmond, UK: Botanic Gardens Conservation International, pp.98.

IPCC (2013) Climate Change 2013: The Physical Science Basis.Intergovernmental Panel on Climate Change, Cambridge, UK.

Kallarackal, J. and Roby, T. (2012). Responses of trees to elevated carbon dioxide and climate change. Biodiversity and Conservation, 21, pp.1327-1342.

Melillo, J., Callaghan, T., Woodward, F., Salati, E. and Sinha, S. (1990). Effects on Ecosystems, in Climate Change: The IPCC Scientific Assessment, edited by J. Houghton, G. Jenkins, J. Ephraums, Cambridge University Press, Cambridge, pp.283−310.

Tkemaladze, G. and Makhashvili, K. (2016). Climate changes and photosynthesis. Annals of Agrarian Science, 14, pp.119-126.



What can an Egyptian King tell us about climate change?

Posted on by Carla Broom

Our plants are hugely affected by carbon dioxide levels in our atmosphere. Green plants absorb CO2 to produce sugars for growth (and oxygen for us!) in a process known as photosynthesis, meaning CO2 levels can hugely affect plant function.

All green flowers take in carbon dioxide and convert it to sugars and oxygen
All green plants absorb CO2 and produce sugars and oxygen

CO2 levels are currently at 406 parts per million (ppm), which may not seem high, but have risen 21% over the last 230 years (Woodward, 1987). This fluctuated constantly throughout time, varying from 280 to 370ppm over the last 24 million years (Van Der Burgh et al, 1993), but now for the first time exceeds 400ppm (Khatiwala et al, 2009).

CO2, oxygen and water are absorbed and released through small pores on the underside of leaves known as stomata, protected by guard cells which open and close the pore. This is affected by conditions such as hormones, light, and- you guessed it- atmospheric CO2 concentration. Stomata allow plants to survive stress, for example retaining water during extreme heat and drought (Hetherington & Woodward, 2003).

Microscope image of two kinds of stomata on the underside of leaves
Microscope image of stomata on the underside of leaves (Hetherington & Woodward, 2003)

How do we investigate change in stomata over time? We can find out what plants were like thousands of years ago- that’s where the Egyptian King Tutankhamun comes in. Olive leaves from his tomb (from 1327 BC) were taken, and the amount of stomata on the underside counted and compared to Egyptian olive samples from 332BC, 1818AD, 1978AD and 1991AD (Beerling & Chaloner, 1993a).

The tomb of King Tutankhamun, with ancient olive leaves around the headpiece
The tomb of King Tutankhamun, with olive leaves around the headpiece (Beerling & Chaloner, 1993a).

As CO2 increases, the number of stomata decrease (Beerling & Chaloner, 1993a). This is also seen in other species, such as oak (Van der Burgh et al, 1993) and pine (Van de Water et al, 2007), but their methods weren’t as creative! The first ever study to show this change found a 40% decrease in number of stomata over the last 230 years (Woodward, 1987).

Why does this happen? CO2 affects the genetic make-up of plants, reducing the number of cells developing into stomata. Plants are likely adapting to rising temperatures and CO2 levels by decreasing the amount of pores to reduce water loss, improving their water use efficiency (Beerling & Chaloner, 1993b).

Is this change a problem for plants? The short term effects of more CO2 can be beneficial, increasing photosynthesis and growth and therefore  yield (Osborne et al, 1997), however the long term effects are not so good. Fewer stomata decreases CO2 uptake, reducing growth and leading to higher atmospheric CO2 (Reddy et al, 2004). Although the plants retain more water, if CO2 levels and temperature decrease again, plants with fewer stomata will have reduced water use efficiency (Woodward, 1987) as they will not be able to exchange as well. Less sugar production also reduces metabolism, therefore CO2 intake is inhibited even further (Flexas & Medrano, 2002) in a cycle known as negative feedback; a reduction in one factor causes a further reduction in something else.

This shows us that plants have changed greatly over thousands of years to adapt to the increasing carbon dioxide levels around them, which could have long-term negative effects on both plants and other life. The environment around us is changing with the atmosphere, and human-caused CO2 increase should not be ignored as it affects many things, no matter how small.

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References

Beerling, D. J., Chaloner, W. G. 1993 a. Stomatal Density Responses of Egyptian Olea europaea L. Leaves to CO2 Change to 1327BC. Annals of Botany, 71: 431-435

Beerling, D. J., Chaloner, W. G. 1993 b. Evolutionary Responses of Stomatal Density to Global CO2 Change. Biological Journal of the Linnean Society, 48: 343-353

Flexas, J., Medrano, H. 2002. Drought Inhibition of Photosynthesis in C3 Plants: Stomatal and non-Stomatal Limitations Revised. Annals of Botany, 89(2): 183-189

Hetherington, A. M., Woodward, F. I. 2003. The Role of Stomata in Sensing and Driving Environmental Change. Nature, 424: 901-908

Khatiwala, S., Primeau, F., Hall, T. 2009. Reconstruction of the History of Anthropogenic CO2 Concentrations in the Ocean. Nature, 462: 346-350

Osborne, C. P., Drake, B. G., LaRoche, J., Long, S. P. 1997. Does Long Term Elevation of CO2 Concentration Increase Photosynthesis in Forest Floor Vegetation? (Indiana Strawberry in a Maryland Forest). Plant Physiology, 114(1): 337-344

Reddy, A. R., Chaitanya, K. V., Vivekanandan, M. 2004. Drought-Induced Responses of Photosynthesis and Antioxidant Metabolism in Higher Plants. Journal of Plant Physiology, 161(11): 1189-1202

Van Der Burgh, J., Visscher, H., Dilcher, D., Kürschner, W. M. 1993. Paleoatmospheric Signatures in Neogene Fossil Leaves. Science, 260(5115): 1788-1790

Van de Water, P. K., Leavitt, S. W., Betancourt, J. L. 2007. Trends in Stomatal Density and 13C/12C Ratios of Pinus flexilis Needles During the last Glacial-Interglacial Cycle. Science, 264: 239-243

Woodward, F. I. 1987. Stomatal Numbers are Sensitive to Increases in CO2 from pre-Industrial Levels. Nature, 327: 617-618



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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