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Foliar Nutrition of Serianthes nelsonii Seedlings as a Conservation Tool

DOI:10.21273/HORTSCI16391-21
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Thomas E Marler at University of Guam
Thomas E Marler
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Conservation of the endangered Serianthes nelsonii is constrained by lack of research. Transplanted containerized plants die in the competitive in situ environment. This study determined if foliar applications of nutrient solution could replace edaphic fertilizer applications for mitigating competition for soil nutrients. Weekly sprays with 0.1× Hoagland solution were compared with weekly drenches of 0.5× Hoagland solution. Plants receiving edaphic or foliar nutrition were not different in height, and height growth was 72% above that of control plants. Similar results were obtained for stem diameter and leaf number. Leaf nutrient concentrations were not different for the two nutrition treatments, but stem nutrient concentration differences were dependent on the element. Stem copper, nitrogen, phosphorus, potassium, and zinc concentrations were not different for edaphic vs. foliar nutrition. Contrarily, stem boron, calcium, iron, magnesium, and manganese concentrations were greater in plants receiving edaphic nutrients. The results indicate nutritional needs of recently out-planted plants may be supplied directly to leaves to mitigate below-ground competition for nutrient resources.
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HORTSCIENCE 57(3):389–390. 2022. https://doi.org/10.21273/HORTSCI16391-21
Foliar Nutrition of Serianthes nelsonii
Seedlings as a Conservation Tool
Thomas E. Marler
Western Pacific Tropical Research Center, University of Guam, Mangilao,
GU 96923
Additional index words. conservation biology, endangered plants, Guam, nutrient resorption
Abstract. Conservation of the endangered Serianthes nelsonii is constrained by lack of
research. Transplanted containerized plants die in the competitive in situ environ-
ment. This study determined if foliar applications of nutrient solution could replace
edaphic fertilizer applications for mitigating competition for soil nutrients. Weekly
sprays with 0.1× Hoagland solution were compared with weekly drenches of 0.5×
Hoagland solution. Plants receiving edaphic or foliar nutrition were not different in
height, and height growth was 72% above that of control plants. Similar results were
obtained for stem diameter and leaf number. Leaf nutrient concentrations were not
different for the two nutrition treatments, but stem nutrient concentration differences
were dependent on the element. Stem copper, nitrogen, phosphorus, potassium, and
zinc concentrations were not different for edaphic vs. foliar nutrition. Contrarily,
stem boron, calcium, iron, magnesium, and manganese concentrations were greater in
plants receiving edaphic nutrients. The results indicate nutritional needs of recently
out-planted plants may be supplied directly to leaves to mitigate below-ground com-
petition for nutrient resources.
Conservation of the endangered S. nelsonii
has suffered from a history of limited research
(Marler et al., 2021). A chronic conservation
failure has been mortality of container-grown
plants after transplanting to in situ forests.
Limited root growth at the time of transplant-
ing (Marler, 2019) and competition for resour-
ces in this biodiverse setting (Marler and
Musser, 2015) have been identified as causes
of in situ seedling mortality.
Mineral nutrients are derived from the
soil, and soil-applied fertilizers form the
foundation of horticultural mitigation of defi-
ciencies. Under some conditions, these added
nutrients may become unavailable to the
managed plants due to soil characteristics or
plant competition. Foliar applications and
trunk injections of nutrients have been used
to mitigate these conditions. This study deter-
mined if foliar applications of nutrient solu-
tions to S. nelsonii seedlings could generate
growth and tissue concentrations similar to
soil-applied solutions.
Methods
The study was conducted in a conserva-
tion nursery in Angeles City, Philippines.
The seedlings were sourced from urban street
trees on Rota Island, and original provenance
was not known. The seedlings were initially
grown in tubes (5-cm diameter, 12-cm depth)
and were 27.8 ± 1.1 cm tall (mean ± SE)with
a basal diameter of 5.1 ± 0.2 mm at the initia-
tion of the study. Seedlings were bare-rooted
on 5 Nov. 2017 and planted individually in
2.6-L containers in a medium composed of
one-third loam soil and two-thirds quarried
river sand. The soil ensured a suite of nutrients
to sustain limited growth of control plants, and
the sand ensured adequate drainage in the con-
tainers. This substrate was impoverished, as
indicated by soil analyses that revealed total
nitrogen was 4.9 ± 0.2 mg·g
1
, available phos-
phorus was 5.9 ± 0.5 mg·kg
1
, and excha-
ngeable potassium was 29.6 ± 1.6 mg·kg
1
(mean ± SE,n=4).
The plants were sorted into three treat-
ments. Control plants received no nutritional
applications. Plants in the foliar treatment
received weekly sprays of 0.1 × Hoagland
solution. Every fully expanded leaf was
sprayed using the standard horticultural pro-
tocol of application until initial runoff. Plants
in the soil-applied treatment received weekly
drenches of 0.5 × Hoagland solution. Each
container received 200 mL of solution. Daily
irrigation using deep well water was provided
with care to refrain from wetting the leaf sur-
faces. Initial plant height and basal stem
diameter were measured. The plants were
grown under 50% shadecloth and rainfall
protection until 15 Jan. 2018.
Ending height, basal stem diameter, and
leaf number were measured. The terminal 15
cm of each stem was pruned and separated
into stem and leaf tissues. All tissue was
washed four times in reverse osmosis water
to remove all nutrients adhering to the organ
surfaces. Nutrient concentrations were quan-
tified using previously described methods
(Marler, 2021). The tissue was dried at 75 C
for 24 h and milled to pass through 20-mesh
screen. Total carbon and nitrogen were deter-
mined by dry combustion (FLASH EA1112
CHN Analyzer; Thermo Fisher, Waltham,
MA). Samples were digested by a microwave
system with nitric acid and peroxide, then
boron, calcium, copper, iron, magnesium, man-
ganese, phosphorus, potassium, and zinc were
quantified by inductively coupled plasma opti-
cal emission spectroscopy (Spectro Genesis;
SPECTRO Analytical Instruments, Kleve,
Germany).
Each response variable was subjected to
one-way analysis of variance (Proc GLM;
SAS Institute, Cary, NC). Growth was calcu-
lated as the difference in height and stem
diameter from the initial to the final measure-
ments. Tukey’s honestly significant differ-
ence was used for pairwise comparisons for
significant response variables.
Results
Growth was similar for plants receiving the
two nutrient application treatments (Fig. 1).
The increase in height was 72% above, increase
in diameter was 29% above, and ending leaf
number was 64% above that of control plants.
Leaf nutrient concentrations were not dif-
ferent between the two nutrition treatments,
but one or both treatments exhibited leaf con-
centrations greater than control plants for eight
of the 11 nutrients (Table 1). The exceptions
were boron, carbon, and copper.
Stem nutrient concentration differences
were heterogeneous among the nutrients
(Table 1). Stem boron, copper, nitrogen, phos-
phorus, potassium, and zinc concentrations
were not different for edaphic vs. foliar nutri-
tion. In contrast, stem calcium, iron, magne-
sium, and manganese concentrations were
greater in plants receiving edaphic applica-
tions than plants receiving foliar applications.
As expected, most of the nutrients in stems of
the plants receiving edaphic applications were
greater than stems of control plants. In addi-
tion, eight of the 11 nutrients exhibited greater
stem concentrations for the foliar application
treatments than for the control treatment.
Discussion
The results indicate nutritional needs of
recently out-planted S. nelsonii plants may be
supplied as sprays to aboveground organs to
mitigate the below-ground competition for
nutrient resources. Phosphorus and potassium
limit in situ S. nelsonii productivity more than
other nutrients based on leaf stoichiometry
(Marler, 2021). Plants receiving the foliar appli-
cations exhibited leaves with 56% greater phos-
phorus and 35% more potassium than control
plants. More importantly, plants receiving foliar
applications exhibited stems with 75% more
phosphorus and 45% more potassium than con-
trol plants, indicating efficient mobilization of
foliar-applied nutrients into the stem tissue.
Nitrogen, phosphorus, potassium, and zinc
are resorbed in senescing S. nelsonii leaves
more efficiently than other nutrients (Marler,
2021). Although the control plants in this study
exhibited leaf mortality, no leaf mortality
Received for publication 18 Nov. 2021. Accepted
for publication 17 Dec. 2021.
Published online 28 January 2022.
T.E.M. is the corresponding author. E-mail:
marler.uog@gmail.com.
This is an open access article distributed under the
CC BY-NC-ND license (https://creativecommons.
org/licenses/by-nc-nd/4.0/).
HORTSCIENCE VOL. 57(3) MARCH 2022 389
occurred in the nutrient application treatments.
The substantial increase in stem concentrations
of these nutrients deserves further study, as the
results indicate translocation from leaf to stem
occurred in the absence of leaf senescence. The
observation that leaf longevity increased in
plants receiving either nutrient treatment also
deserves further study as one approach for
increasing plant productivity.
The mechanistic details of these plant beha-
viors may be more fully understood with more
refined methods; for example, use of solution
applications that ensure homogeneous total
nutrient applications between the two treat-
ments. Moreover, endorsement of this conserva-
tion protocol requires repeating the methods in
situ. One caveat of my methods is that rainfall
was excluded from the experimental plants. This
is not feasible in a forest setting. Rainfall may
affect the results in two ways. First, tissue con-
centrations may be less than reported here if
nutrients are washed off by rainfall before
absorption into the laminae. Second, tissue con-
centrations may be more than reported here if
some surface nutrients are washed into the soil
where they may be absorbed by the roots. More-
over, plant responses to horticultural manipula-
tions may be affected by con- and interspecific
competition, so the efficacy of this newly
described management protocol in situ is not
known until it is repeated in a competitive forest.
This study adds to a growing body of
adaptive management lessons that inform
conservation decisions for this endangered
endemic tree species (Marler et al., 2021).
For example, treatments that increase relative
root growth in a container nursery appear to
be mandatory to improve posttransplant sur-
vival, and two protocols have been identified
to achieve this goal (Marler, 2019; Marler
and Callaway, 2021). As a late successional
species, studies indicate shade is mandatory
for germination and growth of seedlings and
saplings (Marler et al., 2015). Grafting scions
on congeneric rootstocks may be used to mit-
igate the constrained seed supply (Marler,
2017).
Literature Cited
Marler, T.E. 2017. Asexual reproduction to propel
recovery efforts of the critically endangered
Håyun Lågu tree (Serianthes nelsonii Merr.).
Trop. Conserv. Sci. 10:1–10, https://doi.org/
10.1177/1940082917697707.
Marler, T.E. 2019. Repetitive pruning of Serianthes
nursery plants improves transplant quality and
post-transplant survival. Plant Signal. Behav.
14:E1621246, https://doi.org/10.1080/15592324.
2019.1621246.
Marler, T.E. 2021. Leaf elemental concentrations,
stoichiometry, and resorption in Guam’scoastal
karst forests. Diversity (Basel) 13:545, https://
doi.org/10.3390/d13110545.
Marler, T.E. and R.M. Callaway. 2021. Talking
with strangers: Improving Serianthes transplant
quality with interspecific companions. Forests
12:1192, https://doi.org/10.3390/f12091192.
Marler, T.E., A.N. Cascasan, and J.H. Lawrence.
2015. Threatened native trees in Guam: Short-
term seed storage and shade conditions influence
emergence and growth of seedlings. HortScience
50:1049–1054.
Marler, T.E., C. Musser, A.N.J. Cascasan, G.N. Cruz,
and B.E. Deloso. 2021. Adaptive management
lessons for Serianthes nelsonii conservation.
Horticulturae 7:43, https://doi.org/10.3390/horti
culturae7030043.
Marler, T. and C. Musser. 2015. Potential stressors
leading to seedling mortality in the endemic
Håyunlågutree(Serianthes nelsonii Merr.) in the
island of Guam. Trop. Conserv. Sci. 8:738–744.
0
10
20
30
40
2
3
4
5
6
0
2
4
6
8
10
12
14
)mc( thgieh ni htworG
Growth in stem diameter (mm)
Leaf number
ABC
a
a
b
a
a
b
a
a
b
Fig. 1. Size of Serianthes nelsonii seedlings as influenced by nutrition treatments. Blue = control; green = edaphic nutrition; yellow = foliar nutrition.
(A) Increase in stem height; (B) increase in stem diameter; (C)final leaf number. Bars with same letters are not different. Mean ± SE,n=8.
Table 1. Foliar and stem nutrient concentrations of Serianthes nelsonii seedlings as influenced by
edaphic versus foliar nutrition. Mean ± SE,n=8.
Nutrient Control Edaphic nutrition Foliar nutrition F
2,21
P
Leaf
Boron 33.1 ± 1.6 a
z
35.1 ± 1.9 a 35.7 ± 1.7 a 0.726 0.496
Calcium 10.6 ± 0.5 b 12.1 ± 0.6 ab 12.8 ± 0.8 a 4.997 0.017
Carbon 447 ± 3 a 452 ± 2 a 450 ± 2 a 1.474 0.252
Copper 2.5 ± 0.3 a 2.9 ± 0.3 a 3.1 ± 0.3 a 1.209 0.318
Iron 38.8 ± 2.8 b 59.1 ± 4.2 a 57.1 ± 5.3 a 7.772 0.003
Magnesium 2.1 ± 0.1 b 2.9 ± 0.1 a 2.8 ± 0.1 a 19.557 <0.001
Manganese 24.1 ± 1.9 b 32.4 ± 3.4 a 33.9 ± 3.5 a 3.547 0.047
Nitrogen 15.1 ± 1.0 b 22.5 ± 1.5 a 21.2 ± 1.2 a 9.976 <0.001
Phosphorus 1.6 ± 0.1 b 2.6 ± 0.1 a 2.5 ± 0.1 a 30.798 <0.001
Potassium 11.2 ± 0.4 b 14.8 ± 0.5 a 15.1 ± 0.6 a 21.904 <0.001
Zinc 20.4 ± 1.9 b 36.6 ± 2.5 a 36.4 ± 2.8 a 14.847 <0.001
Stem
Boron 9.7 ± 0.3 b
z
11.7 ± 0.7 a 10.4 ± 0.5 ab 10.265 <0.001
Calcium 15.1 ± 1.1 a 14.7 ± 0.3 a 11.7 ± 0.2 b 8.480 0.002
Carbon 426 ± 1.8 a 427 ± 2 a 433 ± 3 a 3.369 0.058
Copper 3.1 ± 0.3 a 4.0 ± 0.8 a 3.9 ± 0.3 a 1.452 0.257
Iron 42.8 ± 2.5 a 44.5 ± 3.5 a 29.4 ± 1.2 b 3.986 0.034
Magnesium 2.4 ± 0.1 b 3.1 ± 0.2 a 2.5 ± 0.1 b 11.089 <0.001
Manganese 5.2 ± 0.3 b 6.8 ± 0.4 a 5.1 ± 0.4 b 6.345 0.007
Nitrogen 5.7 ± 0.6 b 8.8 ± 1.0 a 8.7 ± 0.4 a 6.725 0.006
Phosphorus 1.6 ± 0.2 b 2.7 ± 0.1 a 2.8 ± 0.1 a 21.821 <0.001
Potassium 10.4 ± 0.1 b 14.9 ± 0.8 a 15.1 ± 0.7 a 18.672 <0.001
Zinc 24.1 ± 1.4 b 37.5 ± 4.3 a 34.5 ± 2.7 a 5.481 0.012
z
Means within a row not followed by the same letter are significantly different at P#0.05.
390 HORTSCIENCE VOL. 57(3) MARCH 2022
... In situ S. nelsonii trees are primarily limited by phosphorus (P) and secondarily limited by potassium (K) [15]. To my knowledge, only one study has been published regarding the use of horticultural fertilization methods for S. nelsonii plants [16]. In this study, foliar sprays of dilute nutrient solutions were employed to successfully supply leaves with essential plant nutrients. ...
... This prediction was shown to be true by quantifying carbon dioxide efflux and nitrogen release from litter incubated in native soil [23]. A complete nutrient solution may be sprayed on S. nelsonii foliage to improve plant nutrition [16]. The current study expands our understanding of this subject by revealing the utilitarian benefits of P-only fertilizers for mitigating P deficiency. ...
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Repetitive pruning of Serianthes nursery plants improves transplant quality and post-transplant survival
Article
Information on the best methods for producing endangered Serianthes nelsonii plants for use in species recovery projects is lacking. Plants of this species behave similarly in a nursery setting to plants of the congeneric Serianthes grandiflora and Serianthes kanehirae. Container-grown plants of these two species were repeatedly pruned in the nursery to determine if a more favorable root:shoot ratio would result, then to determine if performance after out-planting would benefit from the enhanced root growth. Repetitive pruning increased absolute root dry weight 43% to 61% and root:shoot ratio 55% to 56% above that of control plants that were not pruned. One year after out-planting, the pruned plants were greater in shoot dry weight and plant height than the control plants. More importantly, control plants exhibited 70% to 80% mortality, but the pruned plants exhibited 100% survival. This new knowledge from two surrogate species indicated that repetitive pruning of S. nelsonii plants in conservation nurseries would greatly increase the quality of the resulting transplants and therefore nurseries may add pruning as a prescribed production protocol to improve species recovery success.
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