Journal of Threatened Taxa |
www.threatenedtaxa.org | 26 September 2020 | 12(13): 16831–16839
ISSN 0974-7907 (Online) | ISSN 0974-7893
(Print)
doi: https://doi.org/10.11609/jott.6205.12.13.16831-16839
#6205 | Received 21 May 2020 |Finally
accepted 01 September 2020
Leaf nutrients of two Cycas
L. species contrast among in situ and ex situ locations
Thomas E. Marler
1 & Anders J. Lindström 2
1 Western Pacific Tropical Research
Center, University of Guam, Mangilao,
Guam 96923, USA.
2 Nong Nooch
Tropical Botanical Garden, 34/1 Sukhumvit Hgy, Najomtien, Sattahip, Chonburi, 20250, Thailand.
1 marler.uog@gmail.com
(corresponding author), 2 ajlindstrom71@gmail.com
Editor: Anonymity requested. Date of publication: 26 September 2020 (online & print)
Citation: Marler, T.E. & A.J.
Lindstrom (2020). Leaf nutrients of two
Cycas L. species contrast among in situ and ex situ locations. Journal of Threatened Taxa 12(13): 16831–16839. https://doi.org/10.11609/jott.6205.12.13.16831-16839
Copyright: © Marler & Lindstrom 2020. Creative Commons Attribution 4.0
International License. JoTT allows unrestricted use, reproduction, and
distribution of this article in any medium by providing adequate credit to the
author(s) and the source of publication.
Funding: U.S.
Forest Service (13-DG-11052021-210 and 17-DG-11052021-217).
Competing interests: The authors declare no competing interests.
Author details: Thomas Marler is a
terrestrial ecologist who has conducted plant physiology research in
Micronesia, Philippines, and Thailand for 29 years. Anders Lindström is curator of the Living Plant Collections
at Nong Nooch Tropical
Botanical Garden, member of IUCN Cycad Specialist Group, and cycad taxonomist.
Author contribution: Development
of concepts for experimental methods was shared by both authors, TEM was responsible
for all data collection, entry, and analysis.
Both authors shared the authoring and editing role.
Acknowledgements: This work was supported by the
U.S. Forest Service under agreements 13-DG-11052021-210 and 17-DG-11052021-217.
Abstract: An understanding of leaf nutrient
relations is required for tree conservation and horticulture success. The study of cycad leaf nutrient dynamics has
expanded in recent years, but direct comparisons among reports remains
equivocal due to varying sampling protocols.
We used Cycas micronesica K.D. Hill and
Cycas nongnoochiae K.D. Hill trees to
determine the influence on leaf nutrient concentrations of in situ versus ex
situ locations and orientation of leaves within the tree canopy. Nitrogen, phosphorus, and potassium
concentrations of leaves from ex situ plants exceeded those from in situ
plants, and the differences were not explained by soil nutrient
differences. Calcium concentrations of
leaves varied among the site pairs, with differences primarily explained by
soil calcium. Magnesium concentrations
of leaves were not different among all location pairs even though soil
magnesium concentrations varied among the sites more than any of the other
elements. Differences in leaf
macronutrient concentrations among four C. micronesica
provenances were minimal when grown in a common garden. Lateral orientation of leaves did not
influence any of the essential elements for either of the species. These findings indicate that the lateral
orientation of cycad leaves does not influence leaf nutrient concentrations,
leaf nutrient relations of cycad plants in managed ex situ settings do not
align with leaf nutrient relations in habitat, and these differences are not
explained by soil nutrition for most elements.
We suggest that leaf nutrient concentrations should be determined in all
niche habitats within the geographic range of a cycad species in order to fully
understand the leaf physiology of each species.
Keywords: Cycad, Cycas micronesica, Cycas nongnoochiae, Guam,
plant nutrients.
Introduction
Cycads comprise a severely threatened plant group (Fragniere et al. 2015).
The need for more applied research to inform cycad conservation and
horticultural decisions has been recognized (Norstog
& Nicholls 1997; Cascasan & Marler 2016). The
literature on cycad leaf nutrient relations is insufficient, and a need to
standardize sampling protocols among various studies and taxa has been
discussed (Marler & Lindström
2018). Toward that end, we have recently
shown that plant size (Marler & Krishnapillai 2018a), position of leaflet along the rachis
(Marler & Krishnapillai
2019a), incident light, and leaf age (Marler & Krishnapillai 2019b) are plant traits that should be
recorded to ensure repeatable methods in cycad leaf nutrient studies. Additionally, the nutrient status of the
soils directly subtending a cycad plant differs from that of the bulk community
soil (Marler & Krishnapillai
2018b; Marler & Calonje
2020), so sampling of soil directly beneath plants from which leaf samples are
collected is needed to adequately interpret research results. Details on these influential plant traits and
soil properties are missing from the methods of most published reports on cycad
leaf nutrients (Grove et al. 1980; Watanabe et al. 2007; Álvarez-Yépiz et al. 2014; Marler & Ferreras 2015, 2017; Krieg et al. 2017; Zhang et al. 2015,
2017, 2018).
Several questions concerning cycad leaf nutrient
relations remain unanswered. For
example, the influence on leaf nutrients of lateral orientation of leaves
within the canopy has not been studied.
Similarly, we are not aware of any reports which include a comparison of
leaf nutrients between cultivated plants and in situ plants. Therefore, the plasticity of intra-specific
leaf nutrient relations among various growing conditions is not known.
Cycas micronesica is listed as Endangered (Marler
et al. 2010) and Cycas nongnoochiae is listed
as Vulnerable (Hill 2010) by the International Union for Conservation of Nature
Red List of Threatened Species. Threats
to C. nongnoochiae are more typical of global
threats, and include plant collecting, loss of habitat, and fire damage. The acute threat to C. micronesica
is damage from invasive non-native insect species. Cycas micronesica
leaves persist for many years and the native range includes Palau, Yap, Guam,
and Rota Islands (Hill 1994). Cycas nongnoochiae leaves are usually replaced annually and
the endemic range includes two adjacent mountains in central Thailand (Hill
& Yang 1999; Marler et al. 2018). Both species are arborescent.
We used these two cycad species to answer the
following questions: (1) Do leaf macronutrient concentrations differ among ex
situ versus in situ locations? (2) Does the provenance influence leaf
macronutrient concentrations when grown in a common garden? (3) Does the
lateral orientation of the large pinnately compound leaves of arborescent cycad
plants influence leaf mineral and metal concentrations?
Materials and Methods
Habitat relations study
An ex situ collection of Guam, Rota, and Yap C. micronesica genotypes was established in Angeles City,
Philippines (15°09’N). The plants were
grown in full sun and were maintained with no plant competition, but were not
provided irrigation or fertilizer. An ex
situ collection of Guam, Palau, Rota, and Yap C. micronesica
genotypes and C. nongnoochiae genotypes was
established at Nong Nooch
Tropical Botanical Garden (NNTBG) in Chonburi, Thailand (12°46’N). The C. micronesica
plants were grown under shade cloth with ≈50% sunlight transmission and
received irrigation as needed, but no fertilization. The C. nongnoochiae
plants we sampled were managed in a landscape setting with tree canopy
cover. They were irrigated as needed,
but did not receive fertilization.
We collected samples from two ex situ garden locations
and four in situ locations to compare leaf nutrient concentrations for five C.
micronesica and one C. nongnoochiae
location pairs. Cycas micronesica provenances included Guam, Palau and
Yap. We could not include the Rota
provenance because there were no healthy trees for in situ Rota habitats due to
non-native insect herbivore infestations.
For each in situ locality we documented canopy cover with a
spherical densiometer (Forest Densiometers,
Bartlesville, OK, USA). The densiometer was positioned at the horizontal plane located
at the tip of the tallest leaf of each plant for each determination. We limited the replications to plants close
to full sun conditions to match the Philippine ex situ replications, and close
to 50% openness to match the Thailand ex situ replications. We also recorded the height of each
replication from the location that was sampled first for each paired site. These data were used to locate replications
with similar heights from the second location for each pair of locations. The dates of sample collection for the two
locations in each pair were restricted to less than one month apart to ensure
no seasonal effects would complicate the findings. There were eight replications for the Guam and
Yap site pairs, and six replications for the Palau site pair.
(1) In situ C. nongnoochiae
leaves were sampled in Tak Fa, Thailand on 17
June 2013 (15°19’N), and the canopy openness ranged from 45% to 60%. Ex situ leaves were sampled at NNTBG on 24
June 2013, and the plants were selected to match the same canopy openness. (2) Ex situ leaves from Guam C. micronesica trees were sampled in Thailand on 11 August
2013 and Philippines on 30 August 2013.
Matching in situ C. micronesica leaves
were sampled in an east Guam habitat on 06 September 2013 (13°27’N). All unprotected in situ localities throughout
Guam were severely threatened by several non-native insect pests, so we used a
semi-managed plot in which imidacloprid was used to provide systemic tree protection. The imidacloprid applications began in 2007
and were repeated every 3–4 months.
These in situ plants exhibited minimal infestations of the non-native
insect herbivores. Moreover, they
received no management protocols other than the pesticide applications. The densiometer was
used to select appropriate trees with ≈50% sunlight for the Thailand samples
and full sun for the Philippine samples.
(3) In situ C. micronesica leaves were
sampled in Ngellil Island, Palau on 20 May 2017
(7°20’N). The densiometer
was used to select trees with ≈50% sunlight. Matching ex situ leaves from Palau
C. micronesica trees were sampled in Thailand
on 07 June 2017. There were no Palau genotypes in the Philippine ex situ collection. (4) Ex situ leaves from Yap C. micronesica trees were sampled in Thailand on 18 Jan
2018 and Philippines on 26 January 2018. Matching in situ C. micronesica leaves were sampled in Yap on 04 February
2018 (9°31’N).
Leaflets from the youngest leaves on plants with no
visible active leaf growth were sampled.
Trees with no signs of recent reproductive events were selected. Leaflets were collected from basal, midpoint,
and apical locations on each leaf, and one leaf from each cardinal direction
was sampled per plant. All leaflets were
homogenized into one sample per replicate.
The tissue was dried at 75 °C and milled to pass
through 20-mesh screen. Total nitrogen
was determined by dry combustion (FLASH EA1112 CHN Analyzer, Thermo Fisher, Waltham, Mass, U.S.A.) (Dumas 1831). Samples were also digested by a microwave
system with nitric acid and peroxide, then phosphorus, potassium, calcium, and
magnesium were quantified by inductively coupled plasma optical emission
spectroscopy (Spectro Genesis; SPECTRO Analytical Instruments, Kleve, Germany)
(Hou & Jones 2000).
Common garden study
We used C. micronesica
plants growing in homogeneous conditions at NNTBG to determine the influence of
provenance on leaf macronutrient concentrations. Provenances were Guam, Palau,
Rota, and Yap. Sampling was conducted on 07 June 2017. The plants were growing in homogeneous
constructed mineral soil medium in raised beds underneath shade cloth with ≈50%
sunlight transmission. For each
replicate, leaves from the youngest flush that were oriented north, east,
south, and west were selected and leaflets were harvested from base, midpoint,
and apex of each rachis. Leaflets from
the three rachis locations and four cardinal directions were combined into one
sample for each replice. Six homogeneous trees of each species were
selected within the height range 1.0–1.6 m.
Macronutrients were determined as previously described.
Leaf orientation study
The influence of leaf orientation within the canopy on
essential element concentrations in leaf tissue of C. micronesica
and C. nongnoochiae trees was determined at Nong Nooch Tropical Botanical
Garden. We restricted the sampling to C.
micronesica plants from Guam. Sampling was conducted on 18 January
2018. The plants were growing in
homogeneous constructed mineral soil medium in raised beds underneath shade
cloth with ≈50% sunlight transmission.
For each replication, leaves from the youngest flush that were oriented
north, east, south, and west were selected and leaflets were harvested from
base, midpoint, and apex of each rachis.
The three rachis locations were combined into one sample for each
cardinal direction for each replication.
Six homogeneous trees of each species were selected within the height
range 1.0–1.3 m. Macronutrients were determined as previously described. In addition, the nutrients boron, copper,
iron, manganese, sulfur, and zinc were digested and
determined by spectroscopy as described for the macronutrients.
Soil analyses
A soil sample was collected beneath each sampled tree
and combined into a composite sample for each location. The soil cores were 15cm in depth and were
positioned at half the length of the longest leaves. There were four cores
positioned in cardinal directions for each tree. The soil was combined and homogenized for one
analysis per sampling date per location.
Total nitrogen content was determined by dry combustion. Extractable
essential nutrients other than phosphorus were quantified following digestion
with diethylenetriaminepentaacetic acid (Berghage et
al. 1987), and total metals were quantified following digestion with nitric
acid (Zheljazkov et al. 2002). Analysis was by inductively coupled plasma
optical emission spectrometry. Available
P was determined by the Olsen method (Olsen et al. 1954) for every site except
for the Yap site. A modified Truog method (Hue et al. 2000) was used for the acid Yap
soils.
Statistics
Macronutrient concentrations from each of the location
pairs were subjected to t test to compare in situ and ex situ
locations. Macronutrients from plants in
the common garden setting were subjected to a one-way ANOVA (PROC GLM, SAS
Institute, Cary, Indiana) to compare provenances. The leaf orientation data were subjected to
one-way ANOVA to determine the influence of lateral orientation on leaf
traits. The two species were analyzed separately.
Means separation was conducted with Tukey’s HSD test for each response
variable that was significant.
Results
Habitat relations
Soil chemistry varied substantially among the in situ
and ex situ locations (Table 1). Our two
ex situ location differences were greatest for nitrogen and phosphorus and
moderate for magnesium and zinc. Elements that exhibited the greatest range
among the in situ locations were calcium, iron, manganese, phosphorus, and
zinc. The mean of the in situ locations
exhibited greater concentrations of every reported element than the mean of the
ex situ locations.
Green leaf nitrogen concentration was significantly
greater in the ex situ locations than the in situ locations for all six habitat
pairs (Table 2). The paired comparison
that exhibited the greatest difference was the Palau C. micronesica
genotype, with nitrogen in leaves from the in situ site exhibiting a 44%
increase above that from the ex situ site.
Green leaf phosphorus concentration was also greater in the ex situ
locations than the in situ locations for all six habitat pairs (Table 3). The location differences for C. nongnoochiae leaf phosphorus exceeded the location
differences for all C. micronesica site
pairs. The Palau C. micronesica plants exhibited the greatest difference
between the two locations for the five C. micronesica
site pairs, with the ex situ site exhibiting leaf phosphorus that was double
that of the in situ site. The patterns
for green leaf potassium concentration were similar to those for leaf
phosphorus (Table 4). The in situ C.
nongnoochiae leaf potassium concentration was
one-fourth that of the ex situ leaf concentration. The Palau C. micronesica
plants again exhibited the greatest difference between the two locations, with
the ex situ plants exhibiting a 75% increase above that of the in situ plants.
Green leaf calcium concentration was significantly
different for all six location pairs (Table 5).
In contrast to nitrogen, phosphorus, and potassium, the in situ locations
exhibited greater leaf calcium concentration than the ex situ locations for C.
nongnoochiae and the Guam and Palau genotypes
of C. micronesica. The Yap C. micronesica
trees, however, exhibited greater leaf calcium concentration in the in situ locations
for both site pairs. Green leaf
magnesium concentration was similar for each of the six location pairs (Table
6). The leaf magnesium concentration of C.
nongnoochiae trees was less than that of the five
C. micronesica location pairs. The plasticity of magnesium concentration
appeared to be highly constrained with a homeostasis among numerous settings.
The behavior
of the macronutrients separated into three general groups with regard to our
paired site approach. The first group
was comprised of nitrogen, phosphorus, and potassium where the ex situ plants
universally exhibited greater leaf concentrations than the in situ plants and
the differences could not be explained by differences in soil chemistry. The second group was comprised of the single
element calcium where the soil calcium concentrations appeared to control of
leaf calcium concentrations within the context of our methods. The third group was comprised of the single
element magnesium where constrained variability caused no differences in leaf
concentrations among all site pairs despite extreme differences in soil
magnesium concentrations.
The influence of provenance
Differences in leaf macronutrient concentrations among
the four C. micronesica provenances were not
different for nitrogen (P=0.372), phosphorus (P=0.656), potassium
(P=0.551), or calcium (P=0.654) when they were grown in a common
garden setting (Figure 1). In contrast,
leaf magnesium concentration was greater for the Guam, Rota, and Palau
provenances than for the Yap provenance (P=0.037, Figure 1).
The influence of leaf orientation
Differences among the C. micronesica
leaves that were oriented north, east, south, or west were not significant for
any of the measured nutrient concentrations.
These Guam-sourced trees produced leaves with nutrients in the following
order of concentration: N (25.29 mg·g-1) > K (18.09 mg·g-1)
> Ca (5.85 mg·g-1) > Mg (4.22 mg·g-1) > P (2.34
mg·g-1) > S (1.12 mg·g-1) > Fe (71.44 µg·g-1)
> B (43.39 µg·g-1) > Mn (36.55 µg·g-1) > Zn
(32.49 µg·g-1) > Cu (7.66 µg·g-1). The differences among the C. nongnoochiae leaves that were oriented north, east,
south, or west were not significant for any of the measured nutrient
concentrations. This Thailand endemic
species produced leaves with nutrients in the following order of concentration:
N (29.98 mg·g-1) > K (18.29 mg·g-1) > P (3.36 mg·g-1)
> Ca (3.15 mg·g-1) > Mg (2.49 mg·g-1) > S (1.35
mg·g-1) > Fe (76.42 µg·g-1) > Mn (68.58 µg·g-1)
> Zn (28.03 µg·g-1) > B (25.64 µg·g-1) > Cu
(9.69 µg·g-1).
Discussion
We have used several approaches to examine Cycas
leaf macronutrient plasticity, and our results indicate that plasticity of C.
micronesica and C. nongnoochiae
leaf concentrations of nitrogen, phosphorus, potassium, and calcium is largely
determined by the growing environment.
For nitrogen, phosphorus and potassium, the benign growing conditions of
a managed garden versus the competitive conditions of a biodiverse forest
community appeared to be a mitigating factor.
For calcium, soil content variation appeared to be the mitigating
factor. In contrast, leaf concentrations of magnesium were primarily under
genetic control and were relatively unresponsive to variation in the growing
environment.
Variability in leaf macronutrient concentrations among
the various ex situ plants was generally less than that among the matched in
situ plants. These observations support
the interpretation that environmental variables of the growing site were more
important for determining green leaf nutrient relations than genetic
differences among provenances of C. micronesica. The same phenomenon was reported for Quercus
variabilis Blume where differences in tissue
macronutrient concentrations among various provenances disappeared when plants
from each of the provenances were grown in a common garden (Lei et al. 2013).
We are aware of only three other reports in which
cycad leaf nutrients were studied in more than one location. Marler & Ferreras (2015) determined leaf nutrient relations of Cycas
nitida K.D. Hill & A. Lindstr.
plants from four Philippine in situ localities with contrasting soil
chemistry. The green leaf nitrogen
relations were similar to our results with minimal differences among the
localities, but the phosphorus concentrations varied 1.7-fold and the potassium
concentrations varied 2.6-fold among the localities. Leaf nutrient relations of several cycad
species were studied in two managed botanic gardens in China. In the first report from this work (Zhang et
al. 2015), there were four species that were included from both gardens. In the second report from this work (Zhang et
al. 2017), no information was provided concerning leaf nutrient concentrations
of individual species, so a comparison of species between the two sites was not
possible. Tissue sampling of the two
garden sites was separated by two to three years in these studies, so a direct
comparison with our methods which minimized the time separation effects is
difficult because we ensured that each pair of sites were sampled on dates that
were separated by less than one month.
Despite these limitations, the four species that were studied in both
gardens exhibited inconsistent leaf nutrient concentrations with regard to
corresponding soil nutrients (Zhang et al. 2015), a result that did not
corroborate our findings for calcium.
Leaf calcium concentration in three of the four species was greater in
the garden site with less soil calcium concentration. A contrast in soil sampling methods may
explain the differences, in that we obtained our soil samples directly beneath
the sampled trees while Zhang et al. (2015) examined general soil samples from
each garden. Thus our soil data were
from the substrates in which the plants we examined were growing, an approach
that is required to ensure accuracy (Marler & Krishnapillai 2018b; Marler &
Calonje 2020).
Our results and other reports indicate much is left to be learned about
site-to-site differences in cycad leaf nutrient relations.
The Thailand garden exhibited greater leaf
concentrations than the Philippine garden for most macronutrients. We did not
collect samples for the purpose of comparing these two garden settings, however
future research may be guided by two influential factors that differed between
these gardens. First, the Thailand
garden plants received irrigation as needed, but the Philippine garden plants
were rain-fed and received no supplemental irrigation after they had become
established. Leaf water relations may
exert a profound effect on leaf physiology for various cycad species (Zhang et
al. 2018), and the relatively greater water stress in the Philippine garden may
explain the generally lower leaf nutrient concentrations. Second, the Thailand garden plants were
cultured under 50% shade cloth and the Philippine garden plants were cultured
in full sun. Incident light influences
leaf nutrient relations for C. micronesica (Marler & Krishnapillai
2019b), and the generally lower leaf nutrient concentrations in the Philippine
garden may have been explained by the full sun growing conditions.
Why would the managed gardens produce plants with
greater leaf macronutrient concentrations than the in situ plants when the soil
nutrient status was not an explanatory factor and the plants in our two gardens
received no supplemental fertilizer? We
suggest the greater nitrogen, phosphorus, and potassium concentrations in the
garden plants resulted from the profound inter-specific competition of the
typical species rich cycad habitat versus the lack of inter-specific
competition due to weed control in the garden settings. Manipulative studies have shown that greater
plant species richness leads to decreased leaf macronutrient concentrations,
indicating more efficient use of the leaf nutrients in the biodiverse settings
(Lü et al. 2019).
Cycas plants are responsive to containerized competition studies
(Marler 2013; Marler et al.
2016). Species richness studies using
sympatric species from the habitats of each model cycad species may answer
these questions about greater leaf macronutrient concentrations in managed
garden settings.
One of the factors that governs global leaf nitrogen
and phosphorus variation is latitude. Both of these leaf nutrients are found in
greater concentrations with greater latitude (Reich & Oleksyn
2004; Han et al. 2005). Our range of
7°20’N (Palau) to 14°07’N (Rota) for the C. micronesica
provenances revealed no observable influence of latitude on leaf nitrogen or
phosphorus concentration.
The collective results and observations indicate that
the study of cycad leaf nutrient relations is a field of study that is in its
infancy. The addition of more relevant
reports is important for improving terrestrial plant conservation because
cycads are one of the most threatened groups of plants worldwide (Fragniere et al. 2015).
That reports are accumulating in the literature is encouraging, but
appropriate sampling methods must be used to gather useful information. From the information known to date, such
methods must assess plant size, position of leaflet along the rachis, incident
light, and leaf age or description of the sequence of leaf flushes sampled (Marler & Krishnapillai 2018a,
2019a,b). Herein we have shown that the
lateral direction of a Cycas leaf within the canopy did not influence
the 11 minerals and metals measured, and our findings indicate the omission of
this sampling information from many past reports on cycad leaf tissue analyses
may be acceptable.
What are some of the areas of study that are
needed? More multi-species studies are
needed from robust botanic garden collections to more fully understand the
genetic controls over cycad leaf nutrient status and whether these leaf
physiology traits are correlated with phylogeny. To our knowledge, ours is the first
provenance study for any cycad species, so more provenance studies are needed
on indigenous species with wide geographic ranges and multiple niche areas of
occupancy. The influence of season on
cycad leaf nutrient status has not been studied to our knowledge, and this
needs to be corrected. The single study
that revealed leaflet location along the rachis strongly influenced leaf
nutrient status was conducted with a species with ≈2 m mature leaf lengths (Marler & Krishnapillai
2019a). The range in mature length of
the cycad pinnately compound leaf is immense among the described species (Norstog & Nicholls 1997). Future research should exploit this range in
mature leaf length to determine if the influence of position along the rachis
is an allometric phenomenon such that differences along the rachis are
restricted to species that produce large leaves. The mobilization and resorption of leaf
elements during the senescence process is an important plant behavior. We are
aware of only three reports that describe nutrient resorption traits for
cycads, and all three reports used Cycas species (Marler
& Ferreras 2015, 2017; Marler
& Krishnapillai 2018a). Most botanic gardens manicure their plants
such that old leaves are removed prior to becoming unsightly during senescence,
so studying nutrient resorption dynamics may be difficult in most ex situ
settings. Curators may want to
reconsider the use of this practice for cycad plants that are not positioned in
the public areas as a means of enabling more nutrient resorption research in ex
situ locations.
In summary, the paucity of cycad research is a
limitation for conservation of this threatened plant group. The recent reports on leaf nutrient content
have been conducted without sufficient sampling conformity. We have shown that the orientation of leaves
on two arborescent cycad species did not influence leaf nutrient
concentrations, so the omission of this information from past reports may be acceptable. We are the first to report that a
representative cycad species expresses heterogeneous leaf macronutrient
relations among in situ versus ex situ locations, and the differences in soil
macronutrient concentrations did not explain most of this heterogeneity. We are also the first to report leaf nutrient
concentrations of cycad plants derived from multiple provenances and grown in a
common garden setting. The controls over
nitrogen, phosphorus, potassium, and calcium concentrations appear to be influenced
primarily by environmental factors whereas the controls over magnesium
concentration appear to be primarily influenced by genetic factors. We suggest that leaf nutrient concentrations
should be determined in all niche habitats within the geographic range of a
cycad species in order to fully understand the leaf physiology of each species.
Table 1. Chemical elements of soils subtending Cycas
micronesica or Cycas nongnoochiae
plants in various locations.
|
Off-site |
Off-site |
in situ |
in situ |
in situ |
in situ |
Substrate property |
Philippines |
Thailand |
Yap |
Guam |
Palau |
Thailand |
Nitrogen (mg·g-1) |
1.3 |
4.3 |
5.2 |
10.2 |
13.4 |
4.9 |
Phosphorus (μg·g-1) |
92.7 |
9.5 |
14.2 |
50.1 |
62.5 |
45.8 |
Potassium (μg·g-1) |
76.7 |
64.4 |
99.5 |
406.6 |
511.2 |
273.8 |
Calcium (mg·g-1) |
0.9 |
1.1 |
2.1 |
11.9 |
12.9 |
10.1 |
Magnesium (μg·g-1) |
96.3 |
141.6 |
1292.2 |
543.4 |
1112.7 |
1021.2 |
Manganese (μg·g-1) |
19.1 |
18.7 |
14.3 |
143.2 |
56.1 |
15.5 |
Iron (μg·g-1) |
8.4 |
11.5 |
328.7 |
15.7 |
20.7 |
7.3 |
Copper (μg·g-1) |
1.2 |
1.8 |
3.9 |
1.5 |
2.2 |
0.9 |
Zinc (μg·g-1) |
9.9 |
5.5 |
8.8 |
39.6 |
8.7 |
2.8 |
Table 2. Green leaf nitrogen concentration (mg·g-1)
of Cycas micronesica and Cycas nongnoochiae plants in various locations. Ex situ sites
included Chonburi, Thailand (curated by Nong Nooch Tropical Botanical Garden) and Angeles City,
Philippines (curated by University of Guam).
Cycas Genotype |
Site |
Ex situ |
In situ |
t |
p |
C. nongnoochiae |
Thailand |
25.63±1.22 |
29.88±1.52 |
2.224 |
0.043 |
Guam C. micronesica
|
Philippines |
16.89±2.11 |
23.15±2.56 |
4.569 |
<0.001 |
Guam C. micronesica
|
Thailand |
18.95±1.99 |
25.14±3.02 |
3.435 |
0.004 |
Palau C. micronesica
|
Thailand |
20.46±2.04 |
29.51±2.99 |
8.320 |
<0.001 |
Yap C. micronesica |
Philippines |
21.12±2.14 |
26.89±2.01 |
3.849 |
0.002 |
Yap C. micronesica |
Thailand |
24.26±2.24 |
30.23±2.35 |
5.407 |
<0.001 |
Table 3. Green leaf phosphorus concentration (mg·g-1)
of Cycas micronesica and Cycas nongnoochiae plants in various locations. Ex situ sites
included Chonburi, Thailand (curated by Nong Nooch Tropical Botanical Garden) and Angeles City,
Philippines (curated by University of Guam).
Cycas Genotype |
Site |
In situ |
Ex situ |
T |
P |
C. nongnoochiae |
Thailand |
1.31±0.06 |
3.44±0.41 |
11.997 |
<0.001 |
Guam C. micronesica
|
Philippines |
1.77±0.13 |
2.04±0.21 |
2.152 |
0.048 |
Guam C. micronesica
|
Thailand |
1.91±0.14 |
2.34±0.21 |
2.114 |
0.026 |
Palau C. micronesica
|
Thailand |
1.45±0.16 |
2.94±0.18 |
15.395 |
<0.001 |
Yap C. micronesica |
Philippines |
1.61±0.21 |
2.39±0.22 |
3.394 |
0.004 |
Yap C. micronesica |
Thailand |
1.68±0.24 |
2.47±0.25 |
3.989 |
0.001 |
Table 4. Green leaf potassium concentration (mg·g-1)
of Cycas micronesica and Cycas nongnoochiae plants in various locations. Ex situ sites
included Chonburi, Thailand (curated by Nong Nooch Tropical Botanical Garden) and Angeles City,
Philippines (curated by University of Guam).
Cycas Genotype |
Site |
In situ |
Ex situ |
t |
p |
C. nongnoochiae |
Thailand |
4.41±0.39 |
18.19±2.19 |
12.227 |
<0.001 |
Guam C. micronesica
|
Philippines |
11.79±0.55 |
16.14±1.62 |
5.413 |
<0.001 |
Guam C. micronesica
|
Thailand |
12.57±0.66 |
18.02±1.88 |
6.382 |
<0.001 |
Palau C. micronesica
|
Thailand |
10.45±1.35 |
18.29±1.38 |
9.128 |
<0.001 |
Yap C. micronesica |
Philippines |
12.49±2.12 |
16.88±2.05 |
4.710 |
<0.001 |
Yap C. micronesica |
Thailand |
14.92±2.63 |
18.86±2.11 |
3.719 |
0.002 |
Table 5. Green leaf calcium
concentration (mg·g-1) of Cycas micronesica
and Cycas nongnoochiae plants in various
locations. Ex situ sites included Chonburi, Thailand (curated by Nong Nooch Tropical Botanical
Garden) and Angeles City, Philippines (curated by University of Guam).
Cycas Genotype |
Site |
In situ |
Ex situ |
t |
P |
C. nongnoochiae |
Thailand |
7.02±0.76 |
3.24±0.44 |
4.425 |
<0.001 |
Guam C. micronesica
|
Philippines |
18.48±2.01 |
6.85±0.77 |
5.103 |
<0.001 |
Guam C. micronesica
|
Thailand |
15.98±1.45 |
6.11±0.72 |
5.339 |
<0.001 |
Palau C. micronesica
|
Thailand |
19.94±2.33 |
6.96±0.92 |
12.287 |
<0.001 |
Yap C. micronesica |
Philippines |
3.32±1.16 |
6.22±1.29 |
2.567 |
0.022 |
Yap C. micronesica |
Thailand |
3.12±1.01 |
5.91±1.22 |
2.290 |
0.038 |
Table 6. Green leaf magnesium
concentration (mg·g-1) of Cycas micronesica
and Cycas nongnoochiae plants in various
locations. Ex situ sites included Chonburi, Thailand (curated by Nong Nooch Tropical Botanical
Garden) and Angeles City, Philippines (curated by University of Guam).
Cycas Genotype |
Site |
In situ |
Ex situ |
t |
P |
C. nongnoochiae |
Thailand |
2.56±0.22 |
2.42±0.26 |
0.571 |
0.289 |
Guam C. micronesica
|
Philippines |
4.46±0.53 |
5.22±0.87 |
0.858 |
0.202 |
Guam C. micronesica
|
Thailand |
4.52±0.55 |
5.32±0.89 |
0.764 |
0.457 |
Palau C. micronesica
|
Thailand |
6.95±1.85 |
5.48±1.68 |
1.123 |
0.288 |
Yap C. micronesica |
Philippines |
3.22±0.46 |
3.08±0.21 |
0.721 |
0.483 |
Yap C. micronesica |
Thailand |
3.66±0.78 |
3.41±0.69 |
0.555 |
0.587 |
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