The University of Southampton

Tag: global change

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.

 

 



A global invasion: Are all islands doomed?

Posted on by Cerridwen Richards
gannet
Islands: perfect breeding locations, or death traps?

Rats are definitely troublesome vermin. They raid our houses, they steal our food and they carry diseases. Not many of us would welcome a rat into our home, and a rat invasion is bad news everywhere, especially on islands.

Rats are non-native species to island ecosystems as seas and oceans act as barriers which hinder their dispersion. Unfortunately, by joining us for free boat trips, rats have successfully overcome this dispersion barrier, and incorporated themselves as unwelcome members of island communities. Today, rats have invaded up to 90% of the world’s islands (Towns et al., 2009). They are such effective invaders because they eat anything and everything, and can adapt quickly to new environments (Jones et al., 2008). The problem is that they change island communities and ecosystem functioning in the process…

No hope for seabirds?

Previously, islands were perfect habitats for nesting seabirds due to their lack of terrestrial predators (Latorre et al., 2013). Now, rat invasions are considered one of the largest threats to seabird breeding colonies (Jones et al., 2008). Once introduced, rats feed on the eggs and chicks of seabirds because they have no defensive strategies (Latorre et al., 2008). The result is the decline and local extinctions of seabird populations (Towns et al., 2009), but what is the consequence for island communities and ecosystems?

rats
Without defensive strategies, rats make easy meals out of seabird eggs and chicks

What if seabirds disappear from islands?

Seabirds provide key ecosystem services through two particular actions (Towns et al., 2009):

  1. Soil modification – By burrowing and nesting, seabirds change the soil environment for plants and     invertebrates.
  2. Soil fertilisation – Feeding at sea and depositing waste on land adds marine derived nutrients and minerals to the soil making it more productive.

 

On rat-invaded islands without the seabirds, these services are no longer provided. This has caused a change in the below-ground invertebrate community and the decline in numbers of several invertebrate groups including centipedes, ants, wasps and snails (Fukami et al., 2006; Towns et al., 2009).

Do rats only bring destruction?

rat-invasion
Rats predate on island-nesting seabirds resulting in the shift of above ground plant biomass (Fukami et al., 2006)

Although seabirds bring vital nutrients to the soil, they also cause considerable disturbance through:

  • Constantly changing the soil moisture by burrowing;
  • Trampling the soil and therefore preventing seedling growth;
  • Making the soil more acidic by creating waste (Fukami et al., 2006).

 

As mentioned before, rats feed on seabirds causing a negative indirect effects on the underground invertebrate community, but believe it, or not, they can actually have positive effects for islands. How? Well, it all occurs above ground. Introducing rats alleviates the three negative effects of seabirds on plants and soil (Fukami et al., 2006). The result is an increase in the amount and growth of ground-level plants on rat-invaded islands.

What can be done?

The effects of human-caused introductions of rats are undeniable. They reduce seabird populations, and indirectly influence above- and below-ground communities, ultimately resulting in changes to how island ecosystems function across the world (Fukami et al., 2006). Rat eradication programmes are vital if we want to restore island ecosystems and communities to their natural state.

 

References

Fukami, T., Wardle, D., Bellingham, P., Mulder, C., Towns, D., Yeates, G., Bonner, K., Durrett, M., Grant-Hoffman, M. and Williamson, W. (2006). Above- and below-ground impact of introduced predators in seabird-dominated island ecosystems. Ecology Letters, 9(12), pp.1299-1307.

Jones, H., Tershy, B., Zavaleta, E., Croll, D., Keitt, B., Finkelstein, M. and Howald, G. (2008). Severity of the effects of invasive rats on seabirds: a global review. Conservation Biology, 22(1), pp.16-26.

Latorre, L., Larrinaga, A. and Santamaria, L. (2013). Rats and seabirds: effects of egg size on predation risk and the potential of conditioned taste aversion as a mitigation method. PLoS ONE, 8(9), p.e76138.

Towns, D., Wardle, D., Mulder, C., Yeates, G., Fitzgerald, B., Parrish, G., Bellingham, P. and Bonner, K. (2008). Predation of seabirds by invasive rats: multiple indirect consequences for invertebrate communities. Oikos, 118(3), pp.420-430.

 

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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.

Word Count: 469

 

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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