The University of Southampton

Tag: nutrients

Plants in Elevated CO2: Stimulated Photosynthesis, Good News or Bad News?

Posted on by Jiahuan Gu

Climate change, I believe people are familiar with this word, although some of them may not believe it, it is the truth that is happening right now.

Since the Industrial Revolution, a large amount of CO2 has been released into the atmosphere due to the burning of fossil fuel. Human has obtained great development from Industrial Revolution and we are living a better life. However, the increasing concentration of CO2 in the atmosphere is warming our planet! We already know that the high temperature, extreme weather and sea level rise are the horrible consequences of climate change, but what about the impacts on plants?

Plants are the major terrestrial carbon sink. They absorb CO2 and water as raw materials, use sunlight as the energy source, release O2 and store sugars in organs as products, which support the plant growth and fix carbon in the wood and leaves. This process happens in the tiny chloroplast inside the cells of leaves and is called photosynthesis, which is a crucial chemical reaction on the earth, as oxygen is essential to human life.

The process of Photosynthesis

The process of Photosynthesis. (Patrickodonkor, 2017)

It seems that the increasing atmospheric concentration of CO2 provides the plants more CO2 input. Will it stimulate the photosynthesis process of plants? Probably. Some studies show that plants increase the photosynthesis rate in the elevated CO2 concentration, and especially, more evidence is found for the C3 plants (plants grow in the cool, wet climate) (Kirschbaum, 2004).

Although the plants may be happy with taking in more carbon for their growth and development, the Rubisco, which is the most abundant protein playing a role in the photosynthesis, seems unhappy with the elevated CO2. The activity of Rubisco decreases, and the Rubisco content shows a 20% drop in the elevated CO2 condition (Long et al., 2004). Such change is the acclimation of plants to the changing environmental condition, and the elevated CO2 decreases the photosynthesis capacity in long term.

However, even with the acclimation of photosynthesis capability, significant enhancement of carbon uptake has been found in the Free-Air Carbon dioxide Enrichment (FACE) studies of plants grow in the exposure to the CO2 concentration of estimated mid-century scenario (Leakey et al., 2009). This may be a good news, as the plants absorb more CO2, they can somewhat offset the greenhouse emissions and slow down the climate change. Moreover, the dry matter production and seed yield of C3 plants also slightly increased, although it is not as significant as the increase of carbon uptake (Long et al., 2004).

Another general finding of plant’s response to elevated CO2 is the increasing nitrogen use efficiency of photosynthesis. As the Rubisco decreases, less nitrogen is needed and the C: N ratio increases (Drake, Gonzàlez-Meler and Long, 1997). That is to say, the elevated CO2 reduce the nitrogen content in plant tissue and thus fewer nutrients are provided by the plants (Cotrufo, Ineson and Scott, 1998). People have to consume more food than before to obtain the same amount of nutrients!

Can you accept this trade off?

[493 words]

 

Reference

  • Cotrufo, M., Ineson, P. and Scott, A. (1998). Elevated CO2 reduces the nitrogen concentration of plant tissues. Global Change Biology, 4(1), pp.43-54.
  • 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.
  • Kirschbaum, M. (2004). Direct and Indirect Climate Change Effects on Photosynthesis and Transpiration. Plant Biology, 6(3), pp.242-253.
  • Leakey, A., Ainsworth, E., Bernacchi, C., Rogers, A., Long, S. and Ort, D. (2009). Elevated CO2 effects on plant carbon, nitrogen, and water relations: six important lessons from FACE. Journal of Experimental Botany, 60(10), pp.2859-2876.
  • Long, S., Ainsworth, E., Rogers, A. and Ort, D. (2004). RISING ATMOSPHERIC CARBON DIOXIDE: Plants FACE the Future. Annual Review of Plant Biology, 55(1), pp.591-628.
  • Patrickodonkor, (2017). Process of photosynthesis. [online] YouTube. Available at: https://www.youtube.com/watch?v=krat2mnM1M0 [Accessed 19 Mar. 2017].


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.

[486]