Wednesday, 14 January 2015

How do plants cope with changing temperature?

By Dr Lindsey Atkinson (@LJA_1)


Plants have evolved many specialised adaptations to enable them to live in a wide range of conditions but what happens when their environment changes?

Plants are sessile organisms, literally rooted to the spot, so if the conditions where they live become unfavourable they cannot move to a more favourable area.  For instance, they may be subject to changes in water or nutrients supply, light or temperature:  here I want to focus on temperature in particular. Plants experience climate with some seasonal variation but they may also be exposed to short-term fluctuations in temperature due to local weather conditions. These changes in temperature impact on the plant’s growth, function and development (phenology). In the long term adaptation may occur, or there may be a change in the range in which the species can live. However, in the short term, plants need to adjust to the local conditions to ensure survival, growth and ultimately reproduction.

It is important to understand how plants will respond to climate change as this will have impacts on biodiversity and also on crop productivity and quality, and hence food security.   In addition plants are major determinants of CO2 turnover in the atmosphere (Schimel et al. 2001) through the processes of photosynthesis and respiration.  Both of these processes are sensitive to temperature, with rates increasing with increased temperature. However, there may be an adjustment in the rate of the process to compensate for the initial change in temperature; this is known as acclimation and may moderate the response.

We can use our knowledge of how changing temperatures will affect photosynthesis and respiration at the leaf level of individual leaves to scale these processes up to predict the responses of ecosystems to global change.  For example, we incorporated thermal acclimation of respiration into a coupled-global climate vegetation model. The results indicated that while incorporating acclimation of respiration had little effect on predicted global atmospheric CO2 levels, the response varied between biomes which could have land use management implications (Atkin et al. 2008).


Arabidopsis thaliana  grown at 23oC in
controlled environment conditions
Even in a warmer world plants may experience a sudden drop in temperature: this could occur in the autumn at the onset of winter, or due to a late cold-spell in spring.  We wanted to know whether plants could continue to grow in these conditions so we grew Arabidopsis thaliana plants at 23oC and then shifted them to 5oC (Atkinson et al., 2014):  following the shift the growth rate was initially reduced to less than one third of that of warm grown plants.  However, growth subsequently recovered with the development of new leaves in the new conditions after about 14 days.  These new leaves had a cold phenotype which was important in the recovery in carbon metabolism in the cold.  The development of the new tissues was supported initially by use of stored nitrogen and relocation from pre-existing tissues but later by nitrogen obtained from the growth medium. This indicates that both the nitrogen status of the plant and the external nitrogen supply may be important in the acclimation of photosynthesis and respiration in the cold. 

The paper is available online at http://onlinelibrary.wiley.com/doi/10.1111/pce.12460/abstract

References
Atkin OK, Atkinson LJ, Fisher RA, Campbell CD, Zaragoza-Castells J, Pitchford JW, Woodward FI, and Hurry VM (2008) Using temperature-dependent changes in leaf scaling relationships to quantitatively account for thermal acclimation of respiration in a coupled global climate-vegetation model.   Global Change Biology 14: 1-18 
Atkinson LJ, Sherlock DJ and Atkin OK (2014) Source of nitrogen associated with recovery of relative growth rate in Arabidopsis thaliana acclimated to sustained cold treatment. Plant, Cell and Environment Article first published online: 7 Dec 2014 | DOI: 10.1111/pce.12460
Schimel DS, House JI, Hibbard KA et al. (2001) Recent patterns and mechanisms of carbon exchange by terrestrial ecosystems.  Nature, 414, 169–172.

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