Int. J. Plant Sci. 163(4):559–566. 2002.
䉷 2002 by The University of Chicago. All rights reserved.
1058-5893/2002/16304-0007$15.00
ARBUSCULAR MYCORRHIZAL FUNGI ENHANCE SEEDLING GROWTH IN TWO
ENDANGERED PLANT SPECIES FROM SOUTH FLORIDA
Jack B. Fisher1,*,† and K. Jayachandran‡
*Fairchild Tropical Garden, Coral Gables, Miami, Florida 33156, U.S.A.; †Department of Biological Sciences, Florida International University,
Miami, Florida 33199, U.S.A.; and ‡Department of Environmental Studies and Southeast Environmental Research Center,
Florida International University, Miami, Florida 33199, U.S.A.
Arbuscular mycorrhizal fungi (AMF) are reported and described in the fine roots of two federally listed
endangered plant species: Amorpha crenulata Rydb. (Fabaceae) (crenulate lead plant or lusterspike indigobush)
and Jacquemontia reclinata House ex Small (Convolvulaceae) (beach jacquemontia or beach clustervine). Wildgrown plants have typical Arum-type arbuscular mycorrhizae. Seedlings of these species were grown in pots
with various native soil treatments under greenhouse conditions. Native mixed AMF from soil and roots
growing in the natural communities pine rockland and beach back dune, respectively, were multiplied on
Sudan grass and pigeon pea nurse cultures. Native sandy soil is low in available phosphorus (P), ranging from
8–18 ppm at the surface 0–5 cm to 2 ppm at 70 cm. AMF significantly increased the dry weight and total P
content of seedlings growing on native soil. Additions of phosphate but without AMF also promoted seedling
growth. Soil microbe filtrate had no effect on J. reclinata but did increase growth of A. crenulata, possibly
by increased potential for Rhizobium inoculum for nitrogen-fixing nodules in this legume.
Keywords: arbuscular mycorrhizal fungi, endangered species, Amorpha crenulata, Jacquemontia reclinata,
phosphorus uptake.
Introduction
of AMF in their roots growing in the natural habitat and to
clarify the degree of benefit that these species derive from AMF
colonization. Other studies of endangered plants have found
that AMF vary in their significance to plant growth and survival. AMF were required for survival of seedlings of Astragalis
applegatei under nursery conditions (Barroctavena et al. 1998),
whereas Penstemon haydenii appeared to be little associated
with AMF under natural conditions (Flessner and Stubbendieck 1992). In a survey of endangered Hawaiian plants, Koske
and Gemma (1995) found a wide range of responsiveness in
seedlings inoculated with AMF and growing in artificial potting media. More recently, a survey of tropical and subtropical
native plants in Brazil found variation in responsiveness to
both AMF and added phosphorus fertilizer when these plants
were grown on infertile native soil (Siqueira and Saggin-Júnior
2001). They also found quite different responses among species
of the same genus. These results indicate that generalizations
regarding AMF dependency of endangered species are inappropriate. Each species must be investigated individually before decisions on its mycorrhizal requirement can be made and
implemented in restoration projects.
In the greater Everglades ecosystem, which includes the
coastal and pine rockland habitats of the two species under
study, phosphorus (P) is a significant pollutant (U.S. Fish and
Wildlife Service 1999). These habitats are all environments low
in available P. Consequently, restoration efforts must be mindful of keeping additions of P to a minimum. Colonization of
roots by AMF increases the uptake of P and allows plants to
thrive in soils with low levels of available P (Smith and Read
1997). In the Everglades context, we designed our research to
verify that plant growth in native soils that are low in available
Two rare plant species growing in the subtropical region of
southeast Florida are listed as endangered, and restoration actions have been recommended (U.S. Fish and Wildlife Service
1999). Jacquemontia reclinata House ex Small (Convolvulaceae) (beach jacquemontia or beach clustervine) grows in seven
small isolated populations along the Atlantic Ocean coast behind sand dunes and in the transitional zone to coastal pineland and hammock. Fewer than 733 plants remain, with most
in two large populations, making this one of the most endangered plants in Florida (Lane 2001). Anthropogenic activities
such as coastal development have eliminated most of this
coastal habitat.
Amorpha crenulata Rydb. (Fabaceae) (A. herbaceae Walter
var. crenulata [Rydb.] Isely) (crenulate lead plant or lusterspike
indigobush) grows in six sites (including one not protected) in
the highly endangered pine rockland community that has
largely been destroyed by farming and urbanization of metropolitan Miami. More than 1000 plants exist mainly in two
populations (Fisher 2000).
As part of the effort to better understand the biology of
these endangered species and to improve success in restoration
efforts, we examined the role of arbuscular mycorrhizal fungi
(AMF) in the species’ growth, since it is widely known that
AMF develop symbiotic relationships with most vascular
plants (Smith and Read 1997). We sought to verify the presence
1
Author for correspondence; telephone 305-665-2844; fax 305665-8032; e-mail [email protected].
Manuscript received July 2001; revised manuscript received November 2001.
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560
P is enhanced by AMF. We also use the addition of P (in the
form of phosphate) to the native soil as a standard to evaluate
the effect of AMF on plant growth. Since additions of fertilizer
will not be advisable, the P equivalence of AMF treatment will
be a valuable index for restoration managers to consider.
Because of the extreme rarity of these endangered plants and
their habitats, there is an urgency to apply botanical and horticultural research to the pressing needs of conservation (St.
John 1993; Affolter 1997). Our findings will aid in planning
future restoration strategies and improving methods of propagating plants used for restoration. For convenience, only the
generic name is used when referring to these two species when
there is no ambiguity.
Material and Methods
Habitat
The research site for Jacquemontia is a nature preserve at
Crandon Park on the northern end of Key Biscayne, a barrier
island in Miami–Dade County, Florida. The plant community
is a mix of back dune species (e.g., Cocoloba uvifera [L.] L.,
Uniola paniculata L., and Caesalpinia bonduc [L.] Roxb.) and
coastal pine rockland species (e.g., Myrica cerifera L., Pithecellobium keyense Britton ex Britton & Rose, and Sabal palmetto [Walter] Lodd. ex Schult. & Schult. f).
The research site for Amorpha is a remnant of undisturbed
natural pine rockland vegetation in Tropical Park, Miami–Dade County, Florida. The overstory is the Dade County
slash pine, Pinus elliottii Engelm. var. densa Little & Dorman.
The following plants grow within 10 m of the collection site:
Pithecellobium keyense Britton ex Britton & Rose, Quercus
virginiana Mill., Rhus copallinum L., Sabal palmetto (Walter)
Lodd. ex Schult. & Schult. f., Serenoa repens (Bart.) Small,
and Smilax auriculata Walter.
Soil
Soil samples for physicochemical analysis were collected
within 50 cm of the plant. Soil analysis was carried out by a
reputable local commercial testing service. For both species,
soil used to fill pots for greenhouse experiments was dug from
5–20-cm depths in nearby identical habitats but in areas free
of the endangered species. Soil was sieved through 6-mm mesh
to remove stones and large root fragments.
Root Samples
Soil and larger surface roots were carefully excavated at the
base of wild plants. The finest feeder roots with clear organic
connection to the mother plant were fixed in 70% ethanol.
Root samples of experimental plants were weighed before being fixed in ethanol. Each root sample was cleared in KOH,
bleached with ammoniated H2O2, and stained with trypan blue
in acidic glycerol (Brundrett et al. 1996) to determine presence
of AMF.
AMF Inoculum
Nurse cultures of native AMF from each of the two habitats
were maintained separately in 4-L pots containing fresh, unpasteurized soil from the native habitat of the species of interest. Host plants were pigeon pea and Sudan grass. Nurse
cultures were at least 12 wk old before use. The inoculum
samples showed heavily colonized root fragments and many
AMF spores. Soil and root fragments were mixed well and
used as a mixed AMF inoculum. A part of the same inoculum
was steam pasteurized for 2 h one time and used as an inoculum control for all treatments except treatment 2 (table 1).
Greenhouse Study
Seeds were collected from cultivated plants in the ex situ
conservation collection at Fairchild Tropical Garden. Seeds
were surfaced sterilized with 1.0% sodium hypochlorite solution, scattered on the surface of new inorganic Perlite in
plastic pots, and placed under periodic mist watering. Seedlings
at the cotyledon or first true leaf stage were transplanted into
6.4 # 25-cm plastic pots (D40 Deepots, Stuewe and Sons),
each filled with 600 g of native sandy soil (for Jacquemontia)
that was steam pasteurized twice (brought to 90⬚C on the first
and third days). For Amorpha, pots were filled with 300 g of
native sandy soil mixed with 300 g of sieved natural limestone
gravel that was similarly steam pasteurized. Inclusion of gravel
gave a better-drained mix that was more like the natural site.
A layer of paper towel prevented loss of soil from bottom
drainage holes.
The treatment numbers and compositions are noted in table
1. Each pot received 20 g of either fresh or steam pasteurized
inoculum. Soil filtrate consisted of 50 mL per pot of a soil
solution derived from 300 g of fresh soil shaken in 2 L of
distilled water and filtered through Whatman no. 1 filter paper.
Phosphate treatments consisted of five treatments on alternating weeks beginning 3–4 wk after transplanting. This brought
the total available P additions (in the form of KH2PO4) to the
Table 1
Treatments Used in Pot Experiments
Treatment
1
2
3
4
5
6
Description
Control
AMF + microbes
5 ppm available P
10 ppm available P
20 ppm available P
Filtrate (microbes only)
Note.
Contents of pot
Pasteurized
Pasteurized
Pasteurized
Pasteurized
Pasteurized
Pasteurized
soil
soil
soil
soil
soil
soil
+
+
+
+
+
+
pasteurized inoculum
live inoculum
pasteurized inoculum
pasteurized inoculum
pasteurized inoculum
pasteurized inoculum
+
+
+
+
PO4 additions
PO4 additions
PO4 additions
soil filtrate
Soil and AMF from the native habitat of each species. See details in “Material and Methods.”
FISHER & JAYACHANDRAN—ENDANGERED PLANT ARBUSCULAR MYCORRHIZAE
pot to 5, 10, and 20 ppm (based on 600 g of total soil).
Treatments were as follows: control (soil + steamed inoculum),
AMF (soil + fresh inoculum), filtrate (control + soil filtrate),
and phosphorus (control + added KH2PO4). Since we wanted
to relate effects of AMF inoculation (which included soil microbes) to additions of PO4, we did not include soil filtrate
(treatment 6) to the PO4 treatments (treatments 3–5).
In one Amorpha experiment (fig. 3B), 50 mL of Hoagland’s
nutrient solution (made without PO4) was added three times
to all pots because the seedlings became chlorotic from apparent nitrogen deficiency. All other plants were purposely not
fertilized with Hoagland’s in order to stress the plants nutritionally as would be the case in natural habitats.
561
Each treatment was replicated in eight to 10 pots. The pots
each had one seedling and were randomly arranged in frames
and grown on benches in a glasshouse under ca. 50% shade.
Experiments were repeated twice, starting during the months
of May and June. Cross contamination was prevented by separation of pots and care in watering.
Plant height from cotyledonary node to shoot apex was measured at irregular intervals, but variations due to branching in
Amorpha and the twining habit of Jacquemontia limited the
usefulness of these measurements. At the end of the experiment, fresh and dry weights of roots and shoots were determined and used to evaluate treatment response. A small fresh
root sample was also fixed in ethanol after its fresh weight
Fig. 1 Experimental plants and roots cleared and stained with trypan blue. A–C, Amorpha plants after 21 wk. A, Representative plants (from
left to right: control, AMF, P, and filtrate treatments). B, AMF in cortex of Amorpha. C, Arbuscules in cortical parenchyma of Amorpha. D–F,
Jacquemontia plants after 16 wk. D, Representative plants (from left to right: control, filtrate, AMF, and P at 5, 10, and 20 ppm). E, AMF in
root, vesicles dark. F, Arbuscules in cortical parenchyma. a, arbuscule; h, hypha; v, vesicle. Bars p 50 mm in B and E; 100 mm in C and F.
INTERNATIONAL JOURNAL OF PLANT SCIENCES
562
was a yellow-orange sand; available P p 4–8 ppm and
pH p 7.3–7.4. Organic matter was 4%–8%.
AMF Colonization
Wild-collected roots of both species had many septate and
presumably saprophytic fungi on their surfaces. Similar surface
fungi also occurred irregularly in most of the experimentally
treated plants, although at lower density. Nonseptate (rare and
irregular septa) hyphae were observed in the root cortex of
wild-collected and experimental plants. Defining arbuscules
and vesicles were observed attached to these nonseptate
hyphae.
In both species, most AMF hyphae were found in the longitudinal intercellular spaces of the cortex, mainly from the
midcortex to the endodermis (fig. 1B, 1E). Single arbuscules
filled individual cells (fig. 1C, 1F) and were concentrated in
younger regions of fine roots. Vesicles tended to occur in older
regions of fine roots (fig. 1E).
Roots of Jacquemontia were difficult to clear and observe
because of scattered pigmented epidermal cells (gray cells in
fig. 1E) and laticifers in the cortex of even the thinnest roots.
Root hairs occur irregularly (in surface patches) in both
species.
Fig. 2 Dry weight of Jacquemontia plants after 16 wk of growth;
see table 2 for significant differences among treatments. A, Experiment
started in late June; no Hoagland’s addition. B, Another experiment
started in early May; no Hoagland’s addition.
was measured. The final dry weight of the root was calculated
based on the addition of the sample’s proportion of the whole
root system. Phosphorus content of tissues was determined
from pulverized dried tissues of all replicates. Digestion and
analysis of total P followed the dry combustion and colorimetric method (Solorzano and Sharp 1980).
Statistical analysis was carried out using SPSS Base 10.0
statistical software (SPSS, Chicago). Differences between all
treatment means of dry weight and P concentrations were
tested with a one-way ANOVA. The data were natural log
transformed if homogeneity of variances could not be assumed
(Levene statistic). A post hoc comparison of the differences
between means was made using either a conservative Bonferroni test if the Levene statistic indicated homogeneity of variances or a Games-Howell test if variances were not homogeneous even after transformation.
Results
Soils
The native beach back dunes site of Jacquemontia had deep
(150 cm) sandy soil. In the surface 0–5 cm (three samples,
n p 3), P (weak Bray test) p 8–18 ppm and pH p 7.3–7.5.
At 5–10 cm depth (n p 3), P p 4–10 ppm and pH p 7.6–7.7.
At 70 cm depth (n p 1), P p 2 ppm and pH p 8.1. Organic
matter declined from 7% near the surface to 1% at 70 cm
depth.
The native pine rockland site of Amorpha had shallow sandy
soil over a bed of oolitic limestone. The surface 0–5 cm was
a white to gray sand (n p 3); P (weak Bray test) p 8 ppm and
pH p 6.8–7.3. The soil at 5–20 cm depth (in scattered pockets)
Growth Effects of AMF
Jacquemontia. The two experiments had similar results
(figs. 1A, 2) after 16 wk of growth. The later experiment produced somewhat smaller plants, possibly because it was started
almost 2 mo later (in late June) and was exposed to less sunlight because of increased cloudiness in the later rainy season
(fig. 2). Table 2 shows the treatment effects on growth that
have potential ecological significance: promotion of shoot and
root dry weight (biomass) by AMF versus control (treatment
1 vs. treatment 2), promotion by AMF versus soil filtrate (treatment 2 vs. treatment 6), and equivalence of AMF effect to level
of added phosphate (treatment 2 vs. treatments 3–5). Except
Table 2
Comparison of Dry Weights in Treatments with
Potential Ecological Significance
Jacquemontia:
Figure 2A:
Root
Shoot
Figure 2B:
Root
Shoot
Amorpha:
Figure 3A:
Root
Shoot
Figure 3B:
Root
Shoot
AMF 1 control
(2 vs. 1)
AMF 1 filtrate
(2 vs. 6)
AMF p ppm P
(2 vs. 3, 4, 5)
ns
+
ns
+
ns (5, 10, 20)
5, 10, 20
+
+
+
+
20
10, 20
+
+
+
+
20
10, 20
+
+
ns
ns
10 only
10 only
Note. Two replicate experiments for each species; ns p not significantly different (5% level); + p significant difference; 10 only p
only one concentration used in this experiment.
FISHER & JAYACHANDRAN—ENDANGERED PLANT ARBUSCULAR MYCORRHIZAE
563
Table 3
Ratio of Root : Shoot Dry Weights
Treatment
Jacquemontia:
Figure 2A
Figure 2B
Amorpha:
Figure 3A
Figure 3B
1
2
3
4
5
6
ANOVA
0.88A
1.06ABCE
0.56A
1.49ABE
0.50A
0.78ACDE
0.52A
0.52CDE
0.53A
0.59ACDE
0.98A
0.99ABCDE
ns
s
2.28A
2.99A
1.55A
1.57AB
4.10A
…
2.63A
0.63B
2.41A
…
2.80A
2.31AB
ns
s
Note. Two replicate experiments for each species; ratios with same letters are not significantly different; s p significant difference at 5%
level; ns p not significantly different; ellipses indicate treatment not done.
for the roots in figure 2A, AMF promoted growth more than
control and more than filtrate (non-AMF microbes). This AMF
promotion was equivalent to the addition of phosphate at various levels (available P p 5–20 ppm). The base level of available P in the pasteurized soil was 10 ppm.
The ratio of shoot to root dry weight was calculated for all
plants. Table 3 shows that the root : shoot ratio was either
equivalent for all treatments (fig. 2A in table 3) or various for
all treatments (fig. 2B in table 3) depending on the experiment.
However, the root weight data may be overestimated. While
washing soil from the roots, we found that it was impossible
to remove all soil without the loss of fine roots. Small particles
of sand and organic matter were bound to the surface of all
roots by fungal hyphae, as seen with magnification. Treatments
2 and 6 were especially problematic, although saprophytic fungal hyphae occurred in all treatments. Much of this unwashed
soil detached after drying and was separated from the roots
with a brush. Nevertheless, treatment 2 roots were never completely free of dark particles, presumably overestimating root
weight.
Amorpha. The unpotted plants are shown in figure 1D.
Plants inoculated with AMF (treatment 2) were larger than control (treatment 1) and soil filtrate (treatment 6) in one experiment
(fig. 3A in table 2) and only larger than the control in the other
(fig. 3B in table 2). The effect on dry weight of AMF is equal
to that of added available P at 10 and 20 ppm (treatments 4
and 5). We had problems with soil attachment similar to but
not as extreme as Jacquemontia. For the root : shoot ratios, there
were no significant differences among treatments in one experiment (fig. 3A in table 3). AMF was smaller than in the control
in the other experiment (fig. 3B in table 3).
The number of root nodules was counted for each plant in
one experiment (fig. 3A), and there were no significant differences among treatments (numbers are not shown). However,
there was a moderate positive linear relationship between nodule number and shoot dry weight (linear regression, adjusted
r 2 p 0.379), with the greatest number of nodules in treatment
2 (mean p 3.1, n p 10). The mean nodule number was 2.3
in treatment 6 and 1.2 in treatment 1.
Jacquemontia. Because of low dry weights per shoot, pairs
of plants were pooled for P analysis, but care was taken to
record the replicate numbers and their pooled weights for later
calculation of total shoot P. Thus, most P calculations are based
on n p 4 or 5. Both shoot total P and tissue concentration
were increased by AMF and additions of PO4 (fig. 4). In both
experiments, AMF was equivalent to added available P at 20
ppm. Statistical analysis revealed that AMF inoculation significantly increased both tissue P concentrations and uptake
per shoot compared with control and microbial filtrate treatments (table 4).
Amorpha. In treatment 1 in figure 1A, only two plants
were large enough for a P assay using our techniques because
of the small size of plants. In the remaining treatments, eight
to 10 plants were assayed by pooling pairs of replicates; thus,
only four to five values were obtained per treatment. There
was no statistical difference between AMF and control and
filtrate treatments (table 4). In figure 5, the PO4 addition had
Phosphorus Uptake Effects of AMF
We chose to analyze the concentration of P in only shoot
tissues because of the unreliable determination of root weights
(especially in treatment 2). Concentration of P in the tissue
(mg/0.1g) and total shoot P (mg/shoot) were calculated.
Fig. 3 Dry weight of Amorpha plants after 21 wk of growth; see
table 2 for significant differences among treatments. A, Experiment
started in late May; no Hoagland’s addition. B, Another experiment
started in early May; Hoagland’s solution added three times.
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INTERNATIONAL JOURNAL OF PLANT SCIENCES
Fig. 4 Effect of treatments on the phosphorus concentration and
total content in shoots of Jacquemontia; pairs of replicate plants were
pooled for P analysis so that each bar is the mean of four samples;
measurements made after 16 wk of growth. A, Experiment started in
late June. B, Another experiment started in early May.
a significant effect to increase both shoot total and tissue concentrations of P compared with AMF and filtrate. The tissue
concentration of P in AMF was significantly less than control
but equal to filtrate in figure 5 and table 4. Plants grown with
higher available P (10 and 20 ppm) had more P in both tissues
and per shoot than those with AMF and filtrate.
Discussion
We report for the first time that both of these endangered
species have a symbiotic association with AMF in their wild
habitats. The fungi form typical Arum-type arbuscules within
cortical parenchyma cells of roots (Smith and Smith 1997).
This is expected since many of the associated plants growing
nearby have been shown to be mycorrhizal, e.g., Serenoa
(Fisher and Jayachandran 1999), Zamia (Fisher and Vovides
2002), Uniola (Sylvia et al. 1993), and Myrica (Semones and
Young 1995). Other species in the same genus or family are
also colonized by AMF, e.g., Convolvulaceae: Jacquemontia
(Koske and Gemma 1990; Koske et al. 1992) and Ipomoea
(O’Keefe and Sylvia 1993) and Fabaceae-Papilonoideae:
Amorpha (Wilson and Hartnett 1998), Cajanus (Olsen and
Habte 1995), and Pithecellobium (Herrera and Ferrer 1980).
The soil in both habitats is relatively low in available P (8–18
ppm at the surface 5 cm and 2–8 ppm at greater depths). Both
species have feeder roots near the surface (0–10 cm) during
the rainy season (June–November), which is when roots were
collected to verify presence of AMF. Tap roots grow deeper
but were not exposed or studied in detail at protected sites.
The Hawaiian endemic Jacquemontia sandwicensis, two introduced species of Ipomoea, and several species of Fabaceae
were all growing in the same coastal strand community in
Hawaii and were all colonized by AMF (Koske and Gemma
1990, Koske et al. 1992). In J. sandwicensis, AMF hyphae
were present on the surface of rhizomes collected from the
wild (Koske and Gemma 1990).
In Jacquemontia reclinata, AMF clearly promote seedling
growth and P uptake by shoots when grown on these native
soils with low to moderate levels of available P. The growth
of Ipomoea batatas was also promoted by AMF (O’Keefe and
Sylvia 1993). We found that root measurements were unreliable because of difficulty in cleaning soil particles off roots.
This surface rhizosphere sheath may have been associated with
the AMF hyphae (St. John et al. 1984) or other soil microorganisms. The inconsistent and nonsignificant variations in
root : shoot ratio were likely due to this difficulty. Our observation that more soil particles adhere to AMF roots compared
with control roots suggests that AMF extend their hyphal network beyond the P depletion zone, which increases nutrient
uptake from these poor soils.
In Amorpha, which is a nitrogen-fixing legume, AMF significantly promoted growth as did high available P. In one
experiment (fig. 3B), soil filtrate had an effect equivalent to
AMF, possibly by promoting Rhizobium inoculation, although
this was only weakly supported by differences in nodule numbers. However, we found no support for a positive AMF effect
on P accumulation in the shoot. The filtrate was equivalent to
AMF, while the control had greater P accumulation (fig. 5A).
It is possible that P accumulated at higher concentrations in
roots than in shoots, but we did not collect data on this. The
interaction between AMF and nitrogen-fixing nodules (which
require high levels of P) is complex and appears to be complimentary in noncrop woody legumes such as Cajanus (Olsen
and Habte 1995) and Acacia (Martin-Laurent et al. 1999).
The growth of Amorpha canescens, a prairie species, was significantly promoted 6 wk after inoculation with native AMF
(Wilson and Hartnett 1998).
Both habitats (coastal and pine rocklands) are fire prone.
Seedlings of both endangered species form a taproot system,
and mature plants survive and resprout from the rootstock
after wild fires or artificial mowing (U.S. Fish and Wildlife
Service 1999). However, the relationship between mycorrhizal
colonization and postfire responses is unknown for these
species.
Restoration of these two U.S. federally listed species was
proposed and includes artificial outplanting to augment the
few remaining populations and to introduce new populations
into historically appropriate habitats that are now protected
(U.S. Fish and Wildlife Service 1999). Our demonstration that
AMF occur in and promote growth of these species will aid
in developing best methods to produce the propagules used in
FISHER & JAYACHANDRAN—ENDANGERED PLANT ARBUSCULAR MYCORRHIZAE
565
Table 4
Comparison of Shoot Phosphorus Levels in Biologically Significant Treatments
Jacquemontia:
Figure 4A:
P total
P concentration
Figure 4B:
P total
P concentration
Amorpha:
Figure 5A:
P total
P concentration
Figure 5B:
P total
P concentration
AMF 1 control
(2 vs. 1)
AMF 1 filtrate
(2 vs. 6)
AMF p ppm P
(2 vs. 3, 4, 5)
+
+
+
+
20
20
+
+
+
+
20
20
ns
ns
ns
ns
5, 10
5
?
?
ns
ns
Only 10
Only 10
Note. Two replicate experiments for each species; ns p not significantly different (5% level);
+ p significant difference; ? p sample size too small.
restoration efforts. Plants of the endangered legume Astragalis
applegatei survived on artificial, sterilized potting medium
(peat + perlite) only if inoculated with native soil containing
AMF (Barroetavena et al. 1998). Inoculated plants had both
mycorrhizae and nodules, both of which were absent in control, uninoculated plants. In experimental seedlings and cuttings grown on artificial media, Hawaiian plants inoculated
with a species of Glomus formed mycorrhizae and were “usually larger” than control plants that were not inoculated
(Koske and Gemma 1995). Thus, inoculation of nursery stock
with AMF can promote growth and substitute for additions
of phosphate on native soils. However, acceptance of phosphate fertilization is very unlikely for plants grown for Everglades ecosystem restoration since P is such a significant pollutant in these habitats (U.S. Fish and Wildlife Service 1999).
The use of native AMF is an ecologically sound method for
conservation horticulture and will be a valuable tool in future
restoration plans.
We presume that nursery-grown seedlings may have improved survivorship when they are later outplanted if they are
first colonized by AMF. This was demonstrated with Uniola
in dune restorations of a similar habitat in south Florida (Sylvia
1989; Sylvia et al. 1993). However, promotion of growth of
potted plants by AMF does not necessarily indicate improved
survivorship. Of two Hawaiian species with increased survival
due to AMF inoculation, one had significantly larger seedlings,
but the other was not significantly different in size from the
control plants (Koske and Gemma 1995). Therefore, the hypothesis of AMF-enhanced survival in Jacquemontia and
Amorpha seedlings must still be tested in situ under natural
field conditions.
Fig. 5 Effect of treatments on the phosphorus concentration and
total content in shoots of Amorpha; measurements made after 21 wk
of growth. A, Experiment started in late May; pairs of replicate plants
were pooled for P analysis so that each bar is the mean of five samples.
B, Another experiment started in early June; in treatment 1, only two
plants were measured; in treatments 2–4, eight to 10 plants were
measured.
Acknowledgments
We thank Elena Pinto-Torres, Paul Fenster, and Marianne
Vanevic for technical assistance and Carl Lewis for helpful
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comments on the manuscript. The Montgomery Botanical
Center permitted use of its pine rockland site. We appreciate
the cooperation of the Natural Areas Management of Miami–
Dade County Park and Recreation Department, which allowed
collections under permit 12. Research was supported in part
by U.S. Fish and Wildlife Service grant 1448-40181-99-G-173
and by Florida Department of Agriculture and Consumer Services contract 5619. This article is Southeast Environmental
Research Center contribution 168 and Florida International
University Tropical Biology Program contribution 46.
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