Pepperdine University is one located in one of the most diverse places of the world. It is located in the Mediterranean which occupies less than 5% of the earth\u27s landmass and is only found in five areas which includes California. On the campus there are several canyons. One of the canyons is called Winter Canyon. The canyon contained a plant called Malosma laurina which is located in a riparian environment and a chaparral environment. The plant grows in both areas however, our hypothesis was that the dry plants\u27 leaves would demonstrate more plasticity. The soil humidity was also measured to compare the difference between the two and there was a significant difference. The average humidity for the wet soil was 43.5% and the dry was 22.5%. Our hypothesis was proven to be true after analyzing the results of the instron machine. The tensile strength was higher among dry leaves

Candelore, T.

Despenza, N.

Garrison, L.

Hinther, L.

English

Pepperdine Digital Commons

Pepperdine UniversityPepperdine Digital CommonsAll Undergraduate Student Research Undergraduate Student Research1-1-2010Tensile Strength of Malosma Laurina Leaves in Wetand Dry ConditionsT. CandelorePepperdine UniversityN. DespenzaPepperdine UniversityL. GarrisonPepperdine UniversityL. HintherPepperdine UniversityFollow this and additional works at: http://digitalcommons.pepperdine.edu/sturesearchPart of the Plant Biology CommonsThis Article is brought to you for free and open access by the Undergraduate Student Research at Pepperdine Digital Commons. It has been acceptedfor inclusion in All Undergraduate Student Research by an authorized administrator of Pepperdine Digital Commons. For more information, pleasecontact Kevin.Miller3@pepperdine.edu.Recommended CitationCandelore, T.; Despenza, N.; Garrison, L.; and Hinther, L., "Tensile Strength of Malosma Laurina Leaves in Wet and Dry Conditions"(2010). Pepperdine University, All Undergraduate Student Research. Paper 23.http://digitalcommons.pepperdine.edu/sturesearch/23Tensile	  Strength	  of	  Malosma	  Laurina	  Leaves	  in	  Wet	  and	  Dry	  Condi7ons	  Abstract:	  	  Pepperdine	  University	  is	  one	  located	  in	  one	  of	  the	  most	  diverse	  places	  of	  the	  world.	  It	  is	  located	  in	  the	  Mediterranean	  which	  occupies	  less	  than	  5%	  of	  the	  earths	  landmass	  and	  is	  only	  found	  in	  ﬁve	  areas	  which	  includes	  California.	  On	  the	  campus	  there	  are	  several	  canyons.	  One	  of	  the	  canyons	  is	  called	  Winter	  Canyon.	  The	  canyon	  contained	  a	  plant	  called	  Malosma	  laurina	  which	  is	  located	  in	  a	  riparian	  environment	  and	  a	  chaparral	  environment.	  The	  plant	  grows	  in	  both	  areas	  however,	  our	  hypothesis	  was	  that	  the	  dry	  plants'	  leaves	  would	  demonstrate	  more	  plas7city.	  The	  soil	  humidity	  was	  also	  measured	  to	  compare	  the	  diﬀerence	  between	  the	  two	  and	  there	  was	  a	  signiﬁcant	  diﬀerence.	  The	  average	  humidity	  for	  the	  wet	  soil	  was	  43.5%	  and	  the	  dry	  was	  22.5%.	  Our	  hypothesis	  was	  proven	  to	  be	  true	  aOer	  analyzing	  the	  results	  of	  the	  instron	  machine.	  The	  tensile	  strength	  was	  higher	  among	  dry	  leaves.	  	  Material	  &	  Methods:	  	  We	  went	  to	  Winters	  Canyon	  to	  collect	  samples	  in	  the	  	  riparian	  and	  chaparral	  environments	  of	  the	  plant,	  Malosoma	  laurina.	  Our	  leaves	  were	  placed	  in	  a	  plas7c	  bag	  to	  prevent	  dehydra7on.	  The	  instron	  machine	  was	  used	  to	  test	  the	  tensile	  strength.	  The	  leaf	  measurements	  were	  made	  by	  using	  a	  digital	  vernier	  caliber	  then	  clamped	  in	  the	  instron	  so	  the	  leaf	  would	  lie	  laterally	  to	  be	  centered.	  Con7nuous	  and	  increasing	  force	  was	  applied	  to	  transverse	  leaf	  area	  un7l	  leaf	  ripped.	  The	  instron	  soOware	  was	  used	  to	  calculate	  to	  transverse	  area	  that	  underwent	  the	  force	  of	  the	  system	  and	  Young's	  modulus.	  The	  moisture	  of	  the	  soil	  was	  also	  measured	  in	  both	  environments	  and	  compared.	  The	  device	  was	  a	  called	  a	  soil	  moisture	  probe.	  Discussion:	  Upon	  measuring	  strength	  of	  the	  leaves	  from	  the	  wet	  and	  dry	  samples	  of	  Malosma	  laurina,	  the	  leaves	  of	  the	  wet	  sample	  were	  shown	  to	  exhibit	  greater	  resistance	  to	  breakage.	  On	  average,	  the	  wet	  leaves	  broke	  at	  a	  force	  approximately	  3	  7mes	  greater	  than	  those	  of	  the	  dry	  samples.	  It	  was	  determined	  using	  the	  instron	  machine	  that	  this	  was	  due	  to	  the	  extension	  of	  the	  wet	  leaves	  as	  they	  were	  pulled	  apart.	  The	  leaves	  stretched	  and	  this	  enabled	  it	  to	  resist	  greater	  force	  before	  breaking.	  The	  dry	  leaves	  were	  shown	  to	  beak	  at	  a	  greater	  tensile	  strain	  on	  average	  compared	  to	  the	  wet	  leaves,	  and	  this	  demonstrated	  that	  these	  leaves	  resisted	  stretching	  more,	  yet	  s7ll	  broke	  at	  a	  weaker	  force.	  We	  had	  to	  reject	  our	  hypothesis	  because	  the	  wet	  leaves,	  not	  the	  dry,	  in	  fact	  demonstrated	  greater	  strength	  by	  resis7ng	  breakage	  7ll	  a	  much	  greater	  force.	  	  	  The	  soil	  moisture	  data	  demonstrated	  that	  the	  water	  levels	  near	  the	  stream	  were,	  on	  average,	  more	  saturated	  with	  water	  than	  that	  on	  the	  ridges.	  However,	  the	  wet	  soil	  showed	  much	  more	  variability	  which	  can	  be	  explained	  because	  of	  the	  high	  sand	  content	  of	  the	  soil	  near	  the	  stream	  which	  doesn’t	  hold	  water	  well.	  	  Conclusion:	  	  S7ll,	  the	  dry	  plants	  were	  deﬁnitely	  less	  hydrated	  than	  the	  wet	  plants.	  	  One	  possible	  explana7on	  was	  that	  the	  ﬁber-­‐strengthening	  of	  xylem	  was	  simply	  gene7cally-­‐governed	  over	  centuries	  of	  selec7ve	  adapta7on	  which	  wouldn’t	  change	  in	  a	  single	  genera7on	  due	  to	  an	  environmental	  factor.	  The	  extra	  water	  hydra7on	  within	  leaves	  of	  the	  wet	  plant	  enabled	  xylem	  vessels	  to	  become	  more	  plas7c	  and	  ﬂexible	  than	  those	  of	  the	  dry	  plant.	  Because	  of	  this	  extra	  ﬂexibility,	  it	  was	  able	  to	  resist	  greater	  pulling	  force.	  	  For	  future	  experiments,	  we	  would	  need	  to	  collect	  many	  more	  samples	  of	  leaves,	  and	  stems,	  and	  test	  for	  strength.	  In	  addi7on,	  the	  soil	  moisture	  probe	  would	  have	  to	  be	  repaired	  because	  the	  broken	  probe	  demonstrated	  measuring	  problems	  which	  had	  to	  be	  addressed	  in-­‐situ.	  Furthermore,	  the	  test	  area	  would	  need	  to	  be	  expanded	  to	  include	  a	  wider	  collec7on	  of	  smaller	  systems	  and	  samples.	  25.450 7 6.237 .0004 16.181 34.718Mean Diff. DF t-Value P-Value 95% Low er 95% UpperWet, DryPaired Means ComparisonHypothesized Difference = 151015202530354045505560Wet DryBox PlotDry	  Leaves	   Maximum	  Load	  (N)	  1	   12.12149	  2	   17.05282	  3	   18.31295	  4	   6.41919	  5	   12.79910	  6	   14.38367	  7	   11.30113	  9	   14.17522	  10	   11.89157	  11	   15.16461	  Maximum	   18.31295	  Mean	  	   13.36217	  Minimum	   6.41919	  Standard	  Devia7on	  3.326	  Maximum Load	  (N)	  1	   37.38889	  2	   42.31786	  3	   54.36862	  4	   33.93885	  5	   35.34615	  6	   46.55944	  7	   49.54084	  9	   15.58039	  Maximum	   54.36862	  Mean 	   39.38013	  Minimum	   15.58039	  Standard Deviation	  11.978	  Candelore,	  T.,	  Despenza,	  N.,	  Garrison,	  L.,	  Hinther,	  L.	  “The	  chaparral	  plant	  community	  of	  southern	  California	  must	  be	  resistant	  to	  mul7ple	  stress	  factors,	  including	  protracted	  summer	  drought,	  periodic	  wildﬁres,	  and,	  in	  some	  regions,	  freezing	  air	  temperatures”	  (Langan,	  1997,	  433).	  “Xylem	  must	  withstand	  both	  the	  mechanical	  stresses	  associated	  with	  nega7ve	  pressure	  as	  well	  as	  the	  risk	  of	  air	  entering	  the	  hydraulic	  pathway”	  (Jacobsen,	  2005,	  546).	  Thus,	  tradeoﬀs	  between	  biological	  costs	  and	  beneﬁts	  exist	  and	  vary	  amongst	  chaparral	  species.	  	  In	  order	  to	  overcome	  greater	  nega7ve	  pressures	  and	  resist	  collapse	  of	  conduits,	  plants	  exhibit	  a	  higher	  degree	  of	  cavita7on	  resistance	  in	  the	  form	  of	  thicker	  vessel	  walls	  rela7ve	  to	  lumen	  diameter,	  and	  denser	  xylem	  (Jacobsen,	  2005,	  549).	  	  A	  greater	  thickness	  to	  diameter	  ra7o,	  or	  young’s	  modulus,	  indicates	  increased	  strength	  of	  cells	  against	  implosion	  under	  nega7ve	  pressure	  (Jacobsen,	  2005,	  547).	  Furthermore,	  studies	  performed	  on	  leaf	  tensile	  proper7es	  in	  Cape	  Town	  have	  demonstrated	  that	  there	  is	  a	  posi7ve	  correla7on	  between	  %lignin/unit	  cross-­‐sec7onal	  area	  and	  tensile	  strength	  of	  hydrated	  leaves	  (Hedderson,	  2008).	  Thus,	  in	  order	  to	  overcome	  possibly	  arduous	  periods	  of	  drought	  chaparral	  species	  tend	  to	  invest	  in	  xylem	  density	  and	  ligniﬁca7on	  in	  order	  to	  increase	  cavita7on	  resistance,	  but	  must	  be	  cau7ous	  as	  doing	  so	  also	  decreases	  hydraulic	  conductance.	  	  Malosma	  Laurina	  (previously	  known	  as	  Rhus	  Laurina)	  has	  deep	  roots,	  the	  largest	  vessel	  diameters	  reported	  for	  chaparral	  plants,	  and	  maintains	  a	  high	  seasonal	  water	  poten7al	  (Langan,	  1997,	  426).	  	  M.	  Laurina’s	  deep	  root	  system	  contributes	  to	  it’s	  highly	  nega7ve	  water	  poten7als.	  	  Researchers	  have	  shown	  that	  M.	  Laurina	  has	  weak	  stems	  (Low	  Modulus	  of	  Rupture	  (MOR))	  compara7vely,	  low	  transverse	  ﬁber	  wall	  area,	  and	  vessels	  that	  are	  predominantly	  surrounded	  by	  ﬁbers	  (Jacobsen,	  2005,	  554).	  Hence,	  M.	  Laurina	  must	  spend	  a	  fair	  amount	  of	  its	  cellular	  energy	  on	  overcoming	  such	  compara7vely	  nega7ve	  water	  poten7als	  due	  to	  its	  basal	  burl,	  and	  possible	  ensuing	  drought	  induced	  cavita7on.	  Leaves	  were	  collected	  from	  M.	  Laurina	  growing	  near	  a	  stream	  in	  Winter	  Canyon	  in	  Malibu,	  California	  on	  the	  campus	  of	  Pepperdine	  University.	  To	  measure	  the	  tensile	  strength	  of	  leaves	  the	  instron	  in	  the	  Natural	  Science	  Division	  of	  Pepperdine	  University	  was	  u7lized.	  	  Each	  obtained	  young’s	  modulus	  from	  leaves	  in	  the	  riparian	  group	  and	  leaves	  in	  the	  non-­‐riparian	  subset	  were	  tested	  for	  a	  sta7s7cal	  diﬀerence	  with	  a	  t-­‐test.	  	  Introduc7on:	  Dry	  Leaves	   Wet	  Leaves	  Pepperdine	  University	  	  24255	  Paciﬁc	  Coast	  Hwy.	  Malibu,	  CA	  90263	  Literature Cited Jacobsen L. Anna., “Do Xylem Fibers Affect Xylem Vessel Cavitation Resistance”.	  2005,	  549. Langan S. J., “Xylem Dysfunction Caused by Water Stress and Freezing in Two Types of Co-occurring Chaparral Shrubs”.	  1997,	  426 

Tensile Strength of Malosma Laurina Leaves in Wet and Dry Conditions

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Tensile Strength of Malosma Laurina Leaves in Wet and Dry Conditions

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