Global warming is an increasing problem in today’s society. Thus, it is important to know how plants, specifically those that are cultivated for human consumption, react to rising average temperatures. This experiment tested how the leaf size of a common crop plant, Raphanus sativus (radish), is affected by two different temperatures. It is hypothesized that as temperature rises, the leaf size will increase, giving the leaf greater ability to cool via transpiration because of an larger surface area for stomatal conductance. This hypothesis was tested by growing two samples of plants in separate incubators. One sample was grown at a normal atmospheric temperature, and the other at a temperature 6 degrees Celsius higher. The average leaf area of each sample was measured using the Leaf Area Meter. Comparing the average leaf sizes of the group of radishes grown in warmer versus cooler temperatures showed a significant increase in both growth rates and final leaf sizes for the plants grown in the warmer incubator. Therefore, radishes clearly show phenotypic plasticity of their leaf sizes in response to changing temperatures. This morphological adaptation may increase the plant’s physiological fitness in its new environment, giving hope that common crop plants can make some adaptations to the world’s changing climate, mitigating some of the negative effects of global warming for those who rely on such crops for subsistence

Fleming, Matthew

McCormack, Michael

English

Pepperdine Digital Commons

Pepperdine UniversityPepperdine Digital CommonsAll Undergraduate Student Research Undergraduate Student Research10-1-2012Effect of Ambient Air Temperature on Leaf Size inRaphanus sativusMatthew FlemingPepperdine UniversityMichael McCormackPepperdine UniversityFollow this and additional works at: http://digitalcommons.pepperdine.edu/sturesearchPart of the Plant Biology CommonsThis Research Poster is brought to you for free and open access by the Undergraduate Student Research at Pepperdine Digital Commons. It has beenaccepted for inclusion in All Undergraduate Student Research by an authorized administrator of Pepperdine Digital Commons. For more information,please contact Kevin.Miller3@pepperdine.edu.Recommended CitationFleming, Matthew and McCormack, Michael, "Effect of Ambient Air Temperature on Leaf Size in Raphanus sativus" (2012).Pepperdine University, All Undergraduate Student Research. Paper 50.http://digitalcommons.pepperdine.edu/sturesearch/50Eﬀect	  of	  Ambient	  Air	  Temperature	  on	  Leaf	  Size	  in	  Raphanus	  sa)vus	  	  Ma7hew	  Fleming,	  Michael	  McCormack	  Pepperdine	  University,	  Malibu,	  CA,	  90263	  	  IntroducLon	  Ambient	  temperatures	  have	  a	  major	  impact	  on	  plant	  physiology.	  	  This	  fact	  is	  especially	  relevant	  to	  humans	  because	  global	  warming,	  caused	  by	  the	  accumula<on	  of	  anthropogenic	  greenhouse	  gases,	  is	  predicted	  to	  cause	  a	  signiﬁcant	  rise	  in	  temperatures	  over	  the	  next	  several	  decades.5	  Par<cularly	  impacted	  will	  be	  subsistence	  farmers	  in	  third	  world	  countries	  who	  have	  liAle	  access	  to	  the	  knowledge	  and	  resources	  needed	  to	  adapt	  agriculture	  to	  consistently	  rising	  temperatures.	  	  Thus,	  the	  livelihood	  of	  many	  subsistence	  farmers	  may	  rely	  on	  the	  ability	  of	  common	  agricultural	  staples	  to	  adapt	  their	  morphologies	  and	  physiologies	  to	  these	  changing	  condi<ons.	  	  Leaf	  size	  is	  extremely	  important	  to	  the	  physiological	  health	  of	  plants.	  	  The	  coupling	  of	  a	  leaf	  to	  its	  external	  temperature,	  rela<ve	  humidity,	  and	  CO2	  concentra<ons	  are	  all	  dependent	  upon	  leaf	  size	  -­‐	  making	  the	  ability	  of	  plants	  to	  adjust	  this	  phenotypic	  trait	  crucial	  to	  their	  ability	  in	  adap<ng	  to	  rising	  global	  temperatures.4	  	  Because	  of	  these	  issues,	  we	  wish	  to	  inves<gate	  the	  phenotypic	  plas<city	  of	  leaves	  in	  the	  face	  of	  rising	  temperatures.	  Raphanus	  sa)vus	  (the	  radish	  plant)	  was	  chosen	  to	  study	  the	  eﬀects	  of	  how	  warmer	  temperatures	  aﬀect	  leaf	  size.	  	  Raphanus	  sa)vus	  is	  an	  excellent	  model	  organism	  for	  such	  studies	  because	  of	  its	  sensi<vity	  to	  environmental	  stress,	  short	  culture	  <me,	  and	  small	  size.3	  	  24	  radish	  plants	  were	  cul<vated	  in	  separate	  pots	  ﬁlled	  with	  vermiculite.	  	  These	  plants	  were	  divided	  into	  two	  groups	  of	  12.	  	  One	  group	  was	  grown	  in	  a	  lower	  temperature	  environment,	  and	  the	  other	  group	  was	  raised	  in	  an	  environment	  several	  degrees	  Celsius	  higher	  to	  approximate	  the	  eﬀects	  of	  global	  warming.	  	  Otherwise	  all	  other	  poten<al	  environmental	  variables	  were	  held	  constant	  between	  the	  two	  groups.	  	  Leaf	  sizes	  were	  measured	  twice	  over	  a	  period	  of	  two	  weeks	  from	  ﬁrst	  plan<ng.	  	  H:	  As	  temperature	  increases,	  leaf	  size	  will	  increase	  in	  order	  to	  cope	  with	  rising	  temperature	  because	  of	  enhanced	  transpira<on	  cooling.	  	  H0:	  As	  temperature	  increases,	  leaf	  size	  will	  not	  increase.	  Materials	  and	  Methods	  To	  perform	  the	  experiment,	  two	  plant	  incubators	  were	  used.	  Both	  incubators	  were	  set	  to	  the	  same	  environmental	  condi<ons	  with	  the	  excep<on	  of	  temperature.	  A	  photoperiod	  of	  12	  hours	  was	  chosen	  for	  the	  plants.	  The	  ﬁrst	  incubator	  was	  set	  at	  lower	  temperatures	  with	  day	  temperatures	  at	  23.8	  degrees	  Celsius	  and	  night	  temperatures	  of	  20.7	  degrees	  Celsius.	  The	  second	  incubator	  had	  temperatures	  6	  degrees	  Celsius	  greater	  than	  the	  ﬁrst,	  with	  day	  temperatures	  of	  29.8	  degrees	  Celsius	  and	  night	  temperatures	  of	  26.7	  degrees	  Celsius.	  	  Two	  separate	  poWng	  trays	  of	  R.	  sa)vus	  were	  obtained,	  each	  with	  12	  small	  plan<ng	  pots.	  	  Each	  of	  the	  total	  24	  pots	  were	  ﬁlled	  with	  vermiculite	  and	  placed	  in	  their	  respec<ve	  tray.	  A	  pen	  was	  used	  to	  create	  holes	  in	  the	  vermiculite	  in	  which	  to	  place	  the	  seeds.	  Once	  each	  of	  the	  24	  pots	  contained	  a	  planted	  R.	  sa)vus	  seed,	  the	  pots	  were	  watered.	  Each	  pot	  was	  watered	  to	  satura<on	  of	  	  the	  vermiculite,	  with	  the	  extra	  water	  leY	  in	  the	  boAom	  of	  each	  tray	  in	  order	  to	  keep	  the	  vermiculite	  hydrated.	  Both	  trays	  were	  labeled	  as	  either	  normal	  or	  high	  temperature	  samples	  and	  placed	  in	  their	  respec<ve	  incubator.	  	  Throughout	  the	  experiment,	  the	  plants	  were	  monitored	  and	  watered	  as	  needed	  in	  order	  to	  ensure	  all	  plants	  maintained	  the	  same	  levels	  of	  hydra<on.	  	  Data	  was	  ﬁrst	  collected	  on	  the	  tenth	  day	  aYer	  plan<ng	  the	  seeds	  because	  at	  this	  point	  there	  was	  appreciable	  growth	  for	  several	  of	  the	  plants	  in	  both	  groups.	  	  The	  leaves	  of	  each	  plant	  were	  traced	  on	  a	  piece	  of	  paper	  and	  cut	  out.	  The	  paper	  cut	  outs	  were	  placed	  in	  the	  Leaf	  Area	  Meter	  for	  measurement	  and	  the	  data	  was	  recorded.	  	  An	  unpaired	  T-­‐test	  was	  performed	  on	  the	  data	  to	  decide	  whether	  the	  results	  were	  signiﬁcant.	  For	  the	  ﬁnal	  data	  collec<on,	  four	  days	  aYer	  the	  ﬁrst,	  the	  leaves	  were	  cut	  oﬀ	  of	  each	  plant	  with	  scissors	  and	  placed	  in	  the	  Leaf	  Area	  Meter.	  The	  data	  was	  handled	  in	  the	  same	  way	  as	  the	  ﬁrst	  day	  of	  collec<on.	  The	  average	  size	  of	  each	  tray	  for	  both	  days	  of	  collec<on	  was	  calculated	  and	  ploAed	  over	  <me	  to	  obtain	  the	  average	  growth	  rate	  for	  the	  two	  groups	  of	  plants.	  	  Results:	  Figure	  2:	  A	  comparison	  of	  the	  mean	  leaf	  sizes	  for	  both	  high	  temperature	  and	  low	  temperature	  groups	  with	  standard	  error	  bars.	  	  “Day	  1”	  is	  the	  	  ﬁrst	  day	  the	  leaves	  were	  measured	  (Day	  10	  from	  ﬁrst	  plan<ng),	  “Day	  5”	  is	  the	  ﬁnal	  measurement	  of	  the	  leaves	  (Day	  14	  from	  ﬁrst	  plan<ng).	  High	  Temperature	  Low	  Temperature	  Total	  Leaf	  Count	   19	   14	  Mean	  Leaf	  Area	  (cm2)	  1.62	   2.22	  Standard	  Devia<on	  (cm2)	  0.598	   0.797	  High	  Temperature	  Low	  Temperature	  Total	  Leaf	  Count	   20	   14	  Mean	  Leaf	  Area	  (cm2)	  1.72	   2.90	  Standard	  Devia<on	  (cm2)	  0.72	   0.970	  Table	  1:	  Data	  from	  the	  ﬁrst	  measurement	  of	  the	  leaf	  areas	  of	  both	  High	  Temperature	  and	  Low	  Temperature	  groups	  Table	  2:	  Data	  from	  the	  second	  and	  ﬁnal	  measurement	  of	  the	  leaf	  areas	  of	  both	  High	  Temperature	  and	  Low	  Temperature	  groups	  Mean	  Diﬀerence	  =	  0.597	  cm2	  t-­‐probability	  =	  0.020	  Mean	  Diﬀerence	  =	  1.17	  cm2	  t-­‐probability	  =	  0.000287	  	  Figure	  1:	  High	  Temperature	  vs.	  Low	  Temperature	  Trays	  with	  weeds	  blocked	  out	  (at	  ﬁnal	  measurement)	  a)	  Radish	  Plants	  grown	  in	  high	  temps.	  b)	  Radish	  Plants	  grown	  in	  low	  temps.	  	  b)	  a)	  0	  0.5	  1	  1.5	  2	  2.5	  3	  3.5	  0	   5	   10	   15	  Mean	  Leaf	  Size	  cm^2	  Days	  Rate	  of	  Leaf	  Growth:	  High	  Temperature	  vs.	  Low	  Temperature	  Low	  Temp	  High	  Temp	  Figure	  3:	  a	  comparison	  of	  mean	  area	  leaf	  growth	  rates	  between	  radishes	  grown	  in	  the	  high	  and	  low	  temperature	  groups,	  the	  accelerated	  growth	  rate	  of	  the	  high	  temperature	  group	  is	  clearly	  seen	  Abstract:	  Global	  warming	  is	  an	  increasing	  problem	  in	  today’s	  society.	  Thus,	  it	  is	  important	  to	  know	  how	  plants,	  speciﬁcally	  those	  that	  are	  cul<vated	  for	  human	  consump<on,	  react	  to	  rising	  average	  temperatures.	  This	  experiment	  tested	  how	  the	  leaf	  size	  of	  a	  common	  crop	  plant,	  Raphanus	  sa)vus	  (radish),	  is	  aﬀected	  by	  two	  diﬀerent	  temperatures.	  It	  is	  hypothesized	  that	  as	  temperature	  rises,	  the	  leaf	  size	  will	  increase,	  giving	  the	  leaf	  greater	  ability	  to	  cool	  via	  transpira<on	  because	  of	  an	  larger	  surface	  area	  for	  stomatal	  conductance.	  	  This	  hypothesis	  was	  tested	  by	  growing	  two	  samples	  of	  plants	  in	  separate	  incubators.	  One	  sample	  was	  grown	  at	  a	  normal	  atmospheric	  temperature,	  and	  the	  other	  at	  a	  temperature	  6	  degrees	  Celsius	  higher.	  The	  average	  leaf	  area	  of	  each	  sample	  was	  measured	  using	  the	  Leaf	  Area	  Meter.	  	  Comparing	  the	  average	  leaf	  sizes	  of	  the	  group	  of	  radishes	  grown	  in	  warmer	  versus	  cooler	  temperatures	  showed	  a	  signiﬁcant	  increase	  in	  both	  growth	  rates	  and	  ﬁnal	  leaf	  sizes	  for	  the	  plants	  grown	  in	  the	  warmer	  incubator.	  	  Therefore,	  radishes	  clearly	  show	  phenotypic	  plas<city	  of	  their	  leaf	  sizes	  in	  response	  to	  changing	  temperatures.	  	  This	  morphological	  adapta<on	  may	  increase	  the	  plant’s	  physiological	  ﬁtness	  in	  its	  new	  environment,	  giving	  hope	  that	  common	  crop	  plants	  can	  make	  some	  adapta<ons	  to	  the	  world’s	  changing	  climate,	  mi<ga<ng	  some	  of	  the	  nega<ve	  eﬀects	  of	  global	  warming	  for	  those	  who	  rely	  on	  such	  crops	  for	  subsistence.	  Works	  Cited:	  1.	  	  Craker	  LE,	  Seibert	  M,	  Cliﬀord	  JT.	  1982.	  	  “Growth	  and	  Development	  of	  the	  Radish	  (Raphanus	  sa)vus	  L.)	  Under	  Selected	  Light	  Environments.”	  Annals	  of	  Botany.	  51(1):	  59-­‐64.	  	  2.	  Gates	  DM,	  	  Alderfer	  R,	  Taylor	  E.	  1968.	  “Leaf	  temperatures	  	  of	  desert	  plants.”	  Science.	  159:	  994-­‐995	  3.	  Kosta-­‐Rick	  R	  and	  Manning	  WJ.	  1993.	  	  “Radish	  (Raphanus	  sa<vus	  L.):	  a	  model	  for	  studying	  plant	  responses	  to	  air	  pollutants	  and	  other	  environmental	  stresses.”	  Environmental	  	  Pollu)on.	  82(2):107-­‐38.	  4.	  Parkhurst	  	  DF	  and	  Loucks	  OL.	  1972.	  	  “Op<mal	  Leaf	  Size	  in	  Rela<on	  to	  Environment.”	  	  Journal	  of	  Ecology.	  60(2):	  505-­‐537.	  5.	  Yirka,	  Bob.	  2012.	  "New	  simula<on	  predicts	  higher	  average	  Earth	  temperatures	  by	  2050	  than	  other	  models."	  Natural	  Climate	  Change.	  5:	  256-­‐260.	  Discussion:	  In	  our	  experiment	  we	  found	  that	  temperature	  is	  a	  strong	  determiner	  of	  leaf	  size	  in	  R.	  sa)vus.	  One	  explana<on	  for	  an	  advantage	  that	  plants	  gain	  by	  growing	  larger	  leaves	  is	  that	  they	  allow	  for	  greater	  transpira<on	  rates	  which	  are	  a	  method	  by	  which	  the	  plant	  cools	  itself	  and	  regulates	  its	  temperature.	  	  According	  to	  Gates,	  leaves	  with	  greater	  surface	  area	  can	  increase	  the	  temperature	  of	  the	  air	  above	  the	  leave,	  resul<ng	  in	  higher	  transpira<on	  rates	  due	  to	  an	  increased	  temperature	  directly	  over	  the	  plant’s	  stomata.2	  	  Our	  results	  would	  seem	  to	  validate	  this	  conclusion	  because	  the	  radishes	  grown	  in	  the	  warmer	  environments	  had	  signiﬁcantly	  larger	  average	  leaf	  sizes	  than	  the	  group	  grown	  in	  lower	  temperatures.	  	  However,	  the	  radishes	  in	  our	  experiment	  were	  not	  limited	  by	  water	  availability,	  a	  crucial	  component	  of	  the	  trade-­‐oﬀ	  involved	  in	  cooling	  by	  way	  of	  transpira<on.	  	  Therefore,	  it	  would	  be	  worthwhile	  to	  inves<gate	  how	  radishes	  deal	  with	  the	  trade-­‐oﬀs	  involved	  with	  increasing	  need	  to	  cool	  via	  transpira<on	  along	  with	  limited	  water	  resources.	  	  In	  a	  similar	  experiment	  by	  Cracker,	  Siebert,	  and	  Cliﬀord,	  it	  was	  found	  that	  input	  of	  solar	  radia<on	  plays	  the	  most	  important	  role	  in	  leaf	  development	  of	  R.	  sa)vus.1	  	  Because	  radia<on	  levels	  were	  held	  constant	  in	  our	  experiment,	  it	  would	  also	  be	  valuable	  to	  do	  further	  research	  into	  how	  temperature	  and	  radia<on	  levels	  interact	  to	  inﬂuence	  leaf	  development.	  	  Conclusions:	  • Radish	  plants	  grown	  in	  higher	  temperatures	  (day	  at	  29.8	  °C,	  night	  at	  26.7	  °C)	  had	  signiﬁcantly	  larger	  leaf	  areas	  than	  those	  grown	  in	  lower	  temperatures	  (day	  at	  23.8	  °C,	  night	  at	  20.7	  °C).	  • 	  Along	  with	  having	  larger	  leaf	  sizes,	  the	  leaves	  of	  radishes	  grown	  in	  higher	  temperatures	  had	  faster	  growth	  rates	  • The	  total	  number	  of	  leaves	  for	  radishes	  grown	  in	  higher	  temperatures	  was	  also	  larger	  than	  the	  number	  of	  leaves	  counted	  on	  the	  radishes	  grown	  in	  lower	  temperatures	  • Further	  research	  should	  be	  done	  on	  how	  other	  environmental	  factors	  interact	  with	  temperature	  to	  aﬀect	  leaf	  size,	  con<nued	  study	  could	  also	  focus	  on	  the	  physiological	  beneﬁts	  and	  trade-­‐oﬀs	  associated	  with	  larger	  leaf	  size	  in	  radishes	  • The	  ability	  of	  the	  radish	  to	  adapt	  to	  rising	  temperatures	  demonstrates	  that	  at	  least	  one	  common	  crop	  plant	  can	  change	  along	  with	  the	  climate,	  giving	  hope	  that	  other	  common	  staples	  may	  be	  similarly	  plas<c	  in	  their	  response	  to	  warming.	  Acknowledgements	  We	  would	  like	  to	  thank	  the	  Natural	  Science	  Division	  for	  suppor<ng	  this	  project,	  and	  Dr.	  Davis	  for	  his	  help	  in	  both	  seWng	  up	  the	  experiment	  and	  analyzing	  the	  results.	  	  We	  would	  also	  like	  to	  thank	  Kevin	  Ko,	  for	  his	  help	  in	  seWng	  up	  the	  project	  and	  con<nuing	  to	  oﬀer	  support	  even	  when	  not	  required.	  Kevin	  Ko	  

Effect of Ambient Air Temperature on Leaf Size in Raphanus sativus

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Effect of Ambient Air Temperature on Leaf Size in Raphanus sativus

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