Leaf Size and Biomass Allocation in Thelypteris dentata, Woodwardia virginica, and Osmunda regalis in Central Florida

6 Pages·1997·3.2 MB·English

by  Ingrid Bartsch

Leaf and Biomass
Size
Allocation
in Thelypteris
Woodwardia
Osmunda
dentata, and
virginica,
regalis in Central Florida
Bartsch
Ingrid
Environmental Science and Policy Program
University of South Florida, Tampa, FL 33620
Lawrence
John
Department
of Biology
and
length weight, the greatest specific leaf area (area:we
mass and
Thelypteris dentata exhibited charac
leaflet:stalk. leaf
tolerant strategy, whereas W. virginica and O. regalis exhibited
a
commonly
associated with competitive plants.
Life-history characteristics of seed plants have been used to identify strategies
that have evolved to environmental characteristics. In the three-strategy,
fit
C-S-R model proposed by Grime
(1979), plants exist in particular places at par-
ticular times as a result of reaching an equilibrium between the intensities of
numerous
and
disturbance, competition. Autecological studies of plant
stress,
species have allowed plant ecologists to generate a of morphological, phys-
list
and with main
iological, life-history attributes associated the three, strategies;
One
competitive, and ruderal (Grime 1988). characteristic
stress-tolerant, et
al.,
used to distinguish between these strategies growth, with the most rapid rates
is
generally found environments with abundant resources and relatively low
in
may
disturbance, although plant species differ widely in their relative rate of
biomass production, even when grown as isolated individuals under productive
conditions (Garnier, 1991). There are also differences in the grovirth of individual
may mechanism whereby
plants and of plant populations, which be a species
and
with more monopolize suppress
resources
competitive rapidly
strategies
the growth and regeneration of neighboring plants (Grime et 1988).
al.,
A
second used distinguish plant strategies are those
suite of characteristics to
related to the size and composition of supporting and photosynthetic structures.
Biomass allocation typically defined in terms of leaf, stem, and root weight
is
ratios and allocation leaves and stems of particular importance (Lambers
to is
and
Poorter, 1992). Patterns, as well as shifts in allocation patterns, reflect se-
may
lective pressures and be a measure of the adaptive significance associated
Some
even
with specific plant structures (Harper, 1977). ratios are plastic, in
response small conditions (Dong, 1995). Therefore, leaves
to differences in local
AMERICAN FERN VOLUME NUMBER
JOURNAL:
87
2
may
barometer
represent a particularly sensitive for assessing plant strategies
used to adapt and succeed under, existing environmental conditions.
to,
Plant strategies have been proposed for a number of herbs, trees and shrubs,
and
bryophytes, lichens (Grime 1988) but type of analysis has not
et this
al.,
been The and among
applied to ferns. great variety in leaf sizes textures ferns
has been used to qualify species as more primitive or recently evolved (Gifford
may
and and
Foster, 1989) also suggests that leaves provide excellent models
determining
for life-history strategies appropriate for different environments.
and
Certainly, the reproductive physiological differences that distinguish ferns
make
from other plants such an analysis desirable.
We
examined
the sizes of leaves of three fern species that have contrasting
We
how
grow
leaf forms but in similar determined biomass was
habitats. divid-
ed within on which
the focusing function photosynthetic
leaf, leaflets, as units,
and which
leaf have both photosynthetic and support Under-
stalks, functions.
was
lying our investigation the question of whether these species exhibit similar
under
strategies apparently similar environmental conditions in freshwater,
for-
ested
habitats.
A
clearly defined, monospecific population each was
of of the three species
selected in the Ecological Research Area, a 220-ha tract of land located in Hills-
borough
County, west central Florida (28°05' N, 82°20' W) The
in July 1994.
populations
of Thelypteris dentata and Woodwardia
(Forssk.) John
E. St. virgin-
m
ica (L.) Sm. were approximately 50 from each wetland
other in a forested
dominated by elm {Ulmus
americana and oak [Quercus
L.) Michx.).
laurifolia
The Osmunda
population of was km
regalis located approximately away,
L.
1
but
in a similar Nomenclature
habitat. follows Wunderlin
that of
(1982).
The
density (number
of leaves
of leaves per square meter) each species
for
was
calculated
in three areas of each population. Twenty over the
five leaves,
range
size represented, were
collected between
to establish the relationship
length and weight
during
leaf growth. Their length was measured within hours
2
and
after collection the weight of and measured
leaflets leaf stalks after drying
A
60°C
at for 2 days. curve-fitting procedure (DeltaGraph was used de-
to
3.5)
termine
the relationship between and
length
weight.
Ten
leaves of dentata and
T. W. virginica and 10 clumps were
of O. regalis
randomly
by
selected throwing
marker
a The were
into the population. leaves
clipped
at the surface and placed
in a labeled plastic bag. The length and area
each was
of measured
leaf within 2 hours of Each was then
collection.
leaf
separated and
into
leaflets leaf stalks (petioles), placed in individual, labeled
aluminum
containers, dried 60°C and
at for 2 days, weighed.
Two
were
ratios
calculated, both
reflecting relative contributions of energy
invested
in photosynthetic
versus support were
tissue. Leaf length:mass ratios
calculated using
the and
total leaf length dry mass, and were
leaflet:stalk ratios
calculated using the dry mass
of leaflets to the dry mass of The specific
stalks.
leaf area area/dry was
(leaf weight)
also determined.
BARTSCH AND
LAWRENCE: AND
LEAF BIOMASS
SIZE
72
Table
1. Leaf characteristics (mean and standard deviations with sample size in parentheses) of The
lypteris dentata. Wood.vardia and Ostnunda
vi,'ginica, regalis in west central Florida.
Characteristic
T. dentata W. virginica O. regalis
Leaves m^
per ±
18 5 16
(3) i
Leaf length (cm)
19.6(10)
:
Dry
weight of leaves 0.06 ±0.06 ±
(g) (10) 2.06 1.21 (10) 2.22 t
22.4(10)
showed
All three species considerable
variation in leaf characteristics (Table
had
1). Thelypteris dentata the densest population of leaves, but the leaves were
considerably smaller and lighter than those of the two other species. Thelypteris
had
dentata also the greatest within species variation in leaf length and weight.
The
was
specific leaf area (area:weight) of dentata twice that of W. virginica.
T.
Leaf area was not measured in O. regalis, as the instrument used to measure the
was
areas unavailable.
The
between and mass was
relationship leaf length for a range of leaf sizes
not linear (Fig. but was most highly correlated with a parabolic curve. Thus,
1),
and more
dentata W. virginica devoted energy to increasing leaf length (or
T.
height) early in their development while continuing to increase in biomass later
in their development.
The was and more
ratio of leaf length:mass significantly higher variable for
dentata than were more con-
T. for the other species (Fig. Leaflet:stalk ratios
2).
between and were
sistent populations than length:mass ratios generally highest
which showed two
for dentata, also greater variation that the other species
T.
(Fig.
3).
Discussion
Osmunda
The Woodwardia and
populations of Thelypteris dentata, virginica,
showed could
regalis and intraspecific variation in leaf characteristics that
inter-
had
be the result of different adaptive strategies. Thelypteris dentata the greatest
variation both terms of being different from the other
in leaf characteristics, in
two species, as well as having high variability within the population. Thelyp-
and
teris dentata an introduced species in Florida, whereas W. virginica O.
is
may
due
Some be
regalis are native differences in characteristics
to this area.
to this, although we cannot determine whether dentata is different from the
T.
native plants because introduced, as we have neither other populations nor
is
it
other introduced with which compare our data.
species to
Although our observation that
three species,
variation in leaf size exists for all
mass expansion
plants invest more biomass height than leaf early in leaf
in leaf
canopy within
suggests grow equalize the height of the
that these ferns so as to
new when
growth shading
the The canopy impacts
population. height of the
AMERICAN FERN JOURNAL: VOLUME NUMBER
87
2
{
wardia
virginica.
from
standing
{dead
litter leaves) influences the density, and growth rate
size,
of emerging shoots (Ekstam, much
1995). Thelypteris dentata does not produce
biomass, and decompose
leaves
quickly once they become brown and Sim-
dry.
O. grows clumps
ilarly, rega/js in that are slightly more elevated and where drier
conditions and
increased oxidation promote
higher decomposition.
rates of
However,
W. virginica has high biomass
production, creating dense that
litter
does decompose
not as rapidly and which may
emerging
affect the size of
Thelypteris dentata more
allocates energy producing
to photosynthetic leaf
material than
supporting
leaf material. This evident not only from the data
is
on
ratios of length:weight and
leafletsdeaf stalks but also from the qualitatively
nature
fragile of these
leaves. Thelypteris dentata also has a higher specific leaf
may
and
area capture more
by
light displaying These
leaves horizontally. leaf
adaptations
are indicative of a
stress-tolerant strategy (Grime 1988). Fur-
et
al.,
BARTSCH AND
LAWRENCE: AND
LEAF BIOMASS
SIZE
Ml
O D
DE WOV, OSRE
V
1600
1400
1200-
E 1000-
1
600-
t
i J
jfc
::
Fig. 2. Ratios of leaf length to leaf b Tbelypteris dentata (THDE),
f
we
thermore, have not observed spore production in dentata in nearly three
T.
years of monitoring this population, and lack of investment to reproduction
is
another measure (Grime
of a stress-tolerant strategy et 1988).
al.,
Woodwardia and number
virginica O. regalis exhibit a of the characteristics
associated with competitive plants including robust and mesophytic leaves, a
rapidly ascending monolayer canopy, and high investment in support tissue to
provide height growth which increases competitive effectiveness for radiation
(Grime
et 1988). not possible to quantify competitive interactions in the
al., is
It
absence of shared environmental (Mitchell-Olds, 1987) but likely
effects is
it
due
that intraspecific competition for light resources occurs in both populations
to the high density of leaves in W. virginica and the clumped growth of O.
regalis.
Competitive plants also tend to have high turn-over rates for leaves since, in
a competitive situation, the ability to redistribute resources from old leaves to
new
may Some
and
better placed ones be crucial (Grime 1979). of the leaves
measured in study may have been produced different times during the
this at
season, serving different functions as environmental conditions changed over
The and
time. value of a leaf varies with developmental age (Harper, 1989),
its
we
cannot assume leaves were necessarily older leaves in the case
that larger
of these
ferns.
Although there a growing body of research related to fern populations
is
(Werth and be need fundamental studies
Cousens, 1990) there continues to a for
such within
as these build our understanding about basic characteristics this
to
group versus native
of plants. In addition to identifying strategies for exotic
ferns, future research related to plant strategies should strive to include allo-
cation to reproductive as well as vegetative structures since plant strategies re-
populations (growth)
flect a trade-off between efficiencies in maintaining local
VOLUME NUMBER
AMERICAN FERN JOURNAL: 87
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thde WOVI
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10-1
^
8-
«j
7-
E
5
6-
.
.^
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n«
I .
te
i
™l
'M
1
and expanding Our
populations (reproduction). study does not include repro-
ductive allocation, because only W. virginica produced although both
sori,
T.
and
dentata O. regalis are capable of producing sori and viable spores. This
raises interesting questions about the absolute and
relative allocation to repro-
among
duction and between between produce
ferns, particularly species that
and
similar fertile vegetative leaves (where sori are borne on "normal" leaves)
versus those that produce modified leaves resembling bearing
fertile stalks
sori.
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