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Mass and Nutrient Loss of Leaf Litter Collecting in Littertraps:
An In Situ and Ex Situ Study
Cassie Corrigan and Maren Oelbermann
Abstract: In forest ecosystems, litterfall collected in trapping devices is exposed to periods of wetting and
drying, which may initiate the first stages of decomposition. This could lead to an underestimation of organic
matter and nutrient input due to leaching or an overestimation due to immobilization. The objectives of this study
were to quantify changes in mass and nutrient stocks of sugar maple (Acer saccharum Marsh.), basswood (Tilia
americana L.), and beech (Fagus grandifolia Ehrh.) leaves under in situ conditions and to quantify changes in
leaf mass and nutrient stocks and leachate concentration when exposed to different quantities of moisture
(high ⫽100 mm, medium ⫽60 mm, and low ⫽30 mm) under ex situ conditions. Results from this study
showed that sugar maple and basswood had a significantly greater (P⬍0.05) mass loss than beech in the in situ
and ex situ study. Nutrient stocks either decreased significantly (P⬍0.05) or remained the same, depending on
species in the in situ study. Similar results were observed in the ex situ study, in which carbon, nitrogen,
phosphorus, and potassium stocks decreased significantly (P⬍0.05) with increasing exposure to moisture, but
calcium and magnesium stocks showed less pronounced changes. Mean concentrations of dissolved organic
carbon, dissolved organic nitrogen, and ammonium were significantly different (P⬍0.05) between species and
moisture treatments, whereas nitrite showed no such differences. Results from this study suggested that the
collection of leaf litter should take place frequently during the peak leaf abscission period and during periods of
high precipitation. This would provide a more accurate quantification of the quantity of nutrients entering the
forest ecosystem in the within-system pathway between live vegetation and the forest floor detritus pool. In
addition, more frequent litterfall collection may also minimize litter decomposition and nitrification. FOR.SCI.
59(4):484 – 493.
Keywords: deciduous forest zone, dissolved inorganic nitrogen, dissolved organic carbon, dissolved organic
nitrogen, leaching, littertraps
MAJOR SOURCES OF NUTRIENT INPUT in forest eco-
systems are derived from throughfall, stemflow,
and litterfall (Pedersen and Bille-Hansen 1999).
Although senesced leaf litter is nutrient-poor because of
nutrient retranslocation and leaching (Hagen-Thorn et al.
2006), litterfall contributes the greatest input of nutrients
(Ukonmaanaho and Starr 2001) to within-system pathways
between live vegetation and the forest floor detritus pool.
For example, Salazar et al. (2011) found that in deciduous
tree species, up to 50% of the nitrogen (N) and 1% of
phosphorus (P) can be retranslocated from leaves and that
the process of retranslocation of P may begin as early as June
in the north temperate zone (Staaf and Stjernquist 1986).
Nutrient input from litterfall in forest ecosystems is eval-
uated through biweekly or monthly collection of leaves and
small branches (⬍2 mm diameter) by open traps installed
underneath the forest canopy (Corrigan and Oelbermann
2010). However, between sampling periods, litterfall may
be exposed to precipitation, leading to the wetting and
drying of leaves, which thus may initiate the first stages of
decomposition (Ukonmaanaho and Starr 2001, Corrigan
and Oelbermann 2010). During the early stages of leaf litter
decomposition, the majority of mass and nutrients may be
lost due to leaching from rainfall, dew, mist, and/or fog
(Prescott 2005, Tietema and Wessel 1994). After leaching,
there may be an absolute increase in mass due to immobi-
lization and subsequent mass loss due to mineralization
(Berg and Eckbohm 1983, Upadhyay and Singh 1989).
Gessner and Konstanz (1989) found that up to 33% of leaf
mass may be lost due to leaching in addition to the loss of
nutrients such as P and potassium (K). For example, Taylor
and Parkinson (1988) determined that aspen (Populus
tremuloides Michx.) leaves lost 14% of their mass during
the early phase of decomposition as a result of leaching.
Salamanca et al. (2003) found that precipitation leached
labile compounds from leaf litter and noted that this occurs
because freshly abscised leaves have a higher concentration
of inorganic nutrients in their intercellular spaces.
Although nutrients lost from leaching and decomposition
of senescent leaves are returned to the forest soil, in litterfall
studies this may not provide an accurate quantification,
leading to an underestimation of the actual quantity of
carbon (C) and nutrients cycling within forest ecosystem
pathways due to mineralization (Ukonmaanaho and Starr
Manuscript received February 17, 2012; accepted September 3, 2012; published online November 8, 2012; http://dx.doi.org/10.5849/forsci.12-016.
Cassie Corrigan (ccorrigan@uwaterloo.ca), University of Waterloo, Waterloo, Ontario, Canada. Maren Oelbermann (moelbermann@uwaterloo.ca), Univer-
sity of Waterloo, Environment and Resource Studies, Waterloo, Ontario, Canada.
Acknowledgments: We thank the Natural Sciences and Engineering Research Council of Canada, the Canadian Foundation for Innovation, the Ontario
Research Fund, and the University of Waterloo for providing financial assistance and research infrastructure to carry out this work. We also thank the Laurel
Creek Nature Centre for granting access to the study site for the in situ experiment and for granting permission to collect leaves for the ex situ experiment.
We also thank the anonymous reviewers for their comments.
Copyright © 2013 by the Society of American Foresters.
484 Forest Science 59(4) 2013
2001, Corrigan and Oelbermann 2010) or an overestimation
due to immobilization. The objectives of this study were
to quantify changes in leaf mass (%) and nutrient stocks
(g m
⫺2
) of sugar maple (Acer saccharum Marsh.), Ameri-
can basswood (Tilia americana L.), and American beech
(Fagus grandifolia Ehrh.) leaves under in situ conditions.
We also determined changes in mass and nutrient stocks of
sugar maple, basswood, and beech leaves when exposed to
different quantities of moisture under ex situ conditions. In
addition, we quantified changes in leachate concentration
(mg l
⫺1
) as a result of exposing leaves to different quantities
of moisture (ex situ). It was hypothesized that leaves ex-
posed to higher moisture levels would have a greater mass
and nutrient loss, which would correspond to greater lea-
chate concentrations, and that this would differ among spe-
cies. Results from this study contribute to the current gap in
the literature on the potential role of precipitation in leach-
ing nutrients during the initial phase of decomposition in
litterfall studies. This study also contributes to the future
design of litterfall and decomposition studies and will help
in the calibration of empirical decomposition models.
Materials and Methods
Study Site
The in situ study was conducted at the Laurel Creek
Nature Centre (LCNC) (43°27⬘N, 80°22⬘W). Materials for
the ex situ study were also collected at the LCNC. The
LCNC is located in the peninsular region of southern On-
tario, Canada, which has a climate modified by the Great
Lakes. The climate is temperate with hot and humid sum-
mers and cold winters and a mean annual frost-free period
of 134 days, a mean annual precipitation of 820 mm, and a
mean annual temperature of 7.2° C (Environment Canada
2006). The LCNC is located 317 m above sea level.
The predominant vegetation includes sugar maple (Acer
saccharum Marsh.), bitternut hickory (Carya cordiformis
[Wangenh.] K. Koch), American basswood (Tilia ameri-
cana L.), American beech (Fagus grandifolia Ehrh.), and
eastern white cedar (Thuja occidentalis L.) interspersed
with trembling aspen (Populus tremuloides Michx.), white
elm (Ulmus americana L.), red osier dogwood (Cornus
stolonifera Michx.), and Canada yew (Taxus canadensis
Marsh.) (Oelbermann and Gordon 2000). The soil is a
gray-brown Luvisol, which developed on a well-drained
fine sand, loam, and silt loam forming part of the Waterloo
Moraine. The parent material of the soil is lacustrine fine
and very fine sand. The A-horizon consists of a fine sandy
loam with a pH of 6.9 (Tupman et al. 2004).
This study site was chosen for the in situ and ex situ
experiments because the LCNC represented typical forest
vegetation in this region of southern Ontario and is similar
to forest ecosystems extending to the eastern United States
and north to the Great Lakes-St. Lawrence forest region
(Watkins 2006). The specific tree species used in the in situ
and ex situ experiments included sugar maple, American
basswood, and American beech. These species were chosen
because they are the most representative within this forest
region and have also been the featured species in numerous
litterfall studies.
Experimental Design and Analysis
In Situ Study
A total of nine study plots (28 m ⫻30 m) were randomly
selected in the LCNC. Within each study plot, a 10 ⫻10 m
net (0.01 ⫻0.01 m mesh size, Vantage Utility netting,
VN1250; Vantage Ltd., Mississauga, ON, Canada) was
suspended above the ground for leaf collection. Freshly
fallen, undamaged, and naturally abscised leaves from sugar
maple, basswood, and beech were collected over a 2-day
period in mid-October 2007 (peak of autumnal litterfall) for
the in situ and ex situ experiments. Leaves were collected
daily to ensure that no exposure to precipitation occurred.
The collected leaves for the ex situ experiment were stored
in a cooler and transported immediately to the University of
Waterloo, Waterloo, ON, Canada.
A portion (500 g fresh weight) of the collected litter was
dried at 65° C for 48 hours, weighed, and analyzed for
nutrient concentration (C, N, P, K, calcium [Ca], and mag-
nesium [Mg]) for baseline (control) comparisons. For the
in situ experiment, three litter decomposition bags per tree
species (n⫽3) were randomly placed under the forest
canopy. The litterbags were constructed of netting with a
0.01 ⫻0.01 m mesh size. Each litterbag had a 0.45 m
2
area
and was suspended 0.4 m above the forest floor. A total of
200 g (fresh weight) of leaves for each sugar maple, bass-
wood, and beech was placed in the litterbags. Each litterbag
was covered with netting to minimize leaf loss or addition
during the study period. Leaves were left in situ during the
last 14 days of October, which is representative of the
maximum litterfall period in this region of southern Ontario.
During this time, the total amount of precipitation was 23.2
mm, with a mean daily maximum temperature of 16.1° C
and a mean daily minimum temperature of 6.9° C.
After 14 days, leaves were collected, weighed for fresh
weight, dried at 65° C for 48 hours, and weighed for dry
weight. Dried leaves for the baseline (control) comparisons
and those from the 14-day experiment were ground in a
Kinematica Polymix plant grinder (Px-MFC 90D; Kine-
matica, Lucerne, Switzerland) followed by grinding in a
Retsch ball mill (model MM200; Retsch, Haan, Germany).
The ground samples were analyzed for C and total N using
a Costech 4010 Elemental Analyzer (Costech, Cernusco,
Italy); P was analyzed using a Technicon Autoanalyzer II
(Technicon Industrial Systems, Tarrytown, NY), and K, Ca,
and Mg were analyzed using a Varian AA-20 atomic ab-
sorption spectrophotometer (Varian, Santa Clara, CA). The
percent change in dry weight was determined as the percent
difference between the baseline dry weight (defined as the
dry weight of freshly abscised leaf litter) and the dry weight
of leaf litter after the 14-day litterbag experiment.
Ex Situ Study
In the laboratory, Vantage utility netting was secured on
top of a plastic tank (0.32 ⫻0.27 ⫻0.12 m). For each
species and treatment, there was a replicate of three plastic
tanks (n⫽3). A total of 20 g of fresh leaves per treatment
and per species was placed on top of the utility netting. The
treatment consisted of leaves exposed to high (HI ⫽100
Forest Science 59(4) 2013 485
mm), medium (MED ⫽60 mm), low (LOW ⫽30 mm), and
no (CTRL ⫽0 mm) levels of moisture over a 14-day
experimental period. Water was applied using a small wa-
tering can. The 14-day experimental period represented the
minimum time that leaf litter typically accumulates in litter
traps before its collection. The amount of moisture applied
to the LOW treatment corresponded to that in the in situ
study. The ambient temperature (21° C) and relative humid-
ity (65%) were kept constant throughout the experiment.
On days 1, 10, and 14, leachate was collected 2 hours
after application of HI, MED, and LOW treatments. This
time was sufficient for the water to percolate through the
leaves and collect in the plastic tanks. Visual observations
showed that the leaf surface, between treatment applica-
tions, showed little water retention, which represented con-
ditions similar to those in the field. The collected leachate
was filtered immediately using a 1.5-
m pore size What-
man glass microfiber filter (934-AH) and was stored in the
dark at 4° C until further analysis. All leachate was analyzed
immediately after the last day of its collection (day 14 of the
experimental period).
On day 14, leaves from each treatment were prepared
and analyzed for nutrients as described for the in situ study.
The percent change in dry weight was determined as the
percent difference between the baseline dry weight (defined
as the dry weight of freshly abscised leaf litter) and the dry
weight of leaf litter after the 14-day litter trap experiment.
Leachate and water were analyzed for dissolved organic C
(DOC) using a Dohrmann Total Carbon Analyzer (DC190).
Total dissolved N (TDN) and dissolved inorganic N (DIN),
consisting of ammonium (NH
4
⫹
) and nitrate (NO
3
⫺
), were
analyzed using a Technicon Autoanalyzer II. Dissolved
organic N (DON) was calculated by subtracting NH
4
⫹
-N
and NO
3
⫺
-N from TDN (Campbell et al. 2000). All exper-
imental values for the ex situ experiment were corrected by
subtracting the concentration of the experimental leachate
from that of the water used in the treatment applications.
The quantity of water applied, representing HI, MED,
and LOW treatments, was determined from actual precipi-
tation data collected at this site over a 24-year period,
representing the peak litterfall period in this region of south-
ern Ontario. Precipitation data for the month of October,
from 1981 to 2005 (Environment Canada 2006) was divided
into three categories (HI, MED, and LOW). The mean value
within each category was used in the following equation to
quantify the daily volume of water application for each
treatment:
DAWW⫽DT ⫻TQ (1)
where DAQ
W
is the daily application quantity of water (ml)
assuming an equal amount of precipitation per day, DT is
the dimension of the tank (m
2
), and TQ is the treatment
quantity (mm) of moisture (HI, MED, and LOW). Ambient
temperature (21° C) and relative humidity (65%) were kept
constant throughout the experiment.
Water used to simulate the different quantities of mois-
ture was collected from natural rainfall events by placing a
large circular-shaped container (1.5 m diameter and 0.5 m
height) in an open area to avoid nutrient enrichment from
throughfall and stemflow. The rainfall collector was thor-
oughly cleaned before and after each collection. The col-
lected rainwater was frozen immediately, thawed in the
refrigerator, and kept at 4° C before and during its use in the
individual treatment applications.
Statistical Analysis
All data were examined for homogeneity of variance
using Levene’s test and found to have a normal distribution.
Our dependent variables (weight, nutrient stocks, and lea-
chate concentrations) were assessed by the Shapiro-Wilk
test and found to have a normal distribution. To quantify
differences within and between species nutrient concentra-
tions and between treatments for both in situ and ex situ
experiments, data were analyzed using the general linear
model (analysis of variance [ANOVA]) in SPSS (2009;
SPSS Science, Inc.). Significantly different main effects
were further tested using Tukey’s multiple comparison test
(Steel et al. 1997). Significant simple effects were tested
using the estimated marginal means function in SPSS. Dif-
ferences between control (before leaching) and after leach-
ing (treatment) in the in situ study were determined using a
ttest (Steel et al. 1997). Repeated measures of ANOVA in
SPSS were used to compare each of the measured parame-
ters of the leachate (DOC, DON, NH
4
⫹
, and NO
3
⫺
)be
-
tween treatments over the study period. Sampling time
(days 1, 10, and 14) was the repeated factor (within sub-
jects), and leachate (DOC, DON, NH
4
⫹
, and NO
3
⫺
) was the
main factor (between subjects) (Steel et al. 1997). Before
the statistical analysis, data for the leachate was corrected
with respect to nutrient values obtained from the rainwater.
For all statistical analyses, the threshold probability level for
determining significant differences was P⬍0.05.
Results
In Situ and Ex Situ Leaf Mass Change
Changes in leaf mass (actual percent weight) were sig-
nificantly different between species in the in situ study
(Table 1). The greatest loss in mass was observed in sugar
maple followed by basswood and beech. Interaction effects
Table 1. Actual percent weight change for sugar maple (A.
saccharum), basswood (T. americana), and beech (F. grandi-
folia) leaves after 14 days in an in situ experiment (nⴝ3) in
southern Ontario, Canada (nⴝ3) and changes after exposure
to different moisture levels for 14 days, using the same leaf
species in an ex situ experiment (nⴝ3).
Sugar maple Basswood Beech
...............(%) ...............
In situ 12.5
a
6.8
b
1.6
c
Ex situ
HI 13.2
A,a
13.3
A,a
3.2
A,b
MED 10.8
B,a
6.4
B,b
1.4
B,c
LOW 2.8
C,b
4.6
B,a
1.0
B,c
Values followed by the same upper case letters, comparing differences
between treatments HI, MED, and LOW within leaf species are not
significantly different at P⬍0.05 for the ex situ experiment. Values
followed by the same lower case letters, comparing differences between
leaf species for in situ and ex situ experiments, are not significantly
different at P⬍0.05.
486 Forest Science 59(4) 2013
of the actual percent weight change with respect to species-
by-moisture treatment was significant in the ex situ exper-
iment [F(6, 24) ⫽25.237, P⫽0.001]. Simple effects
showed that weight loss was significantly greater in the HI
treatment within species. Main effects showed that a signif-
icantly greater mass loss occurred in the HI and MED
treatments for sugar maple followed by basswood and beach
(Table 1). When HI, MED, and LOW treatments were
averaged, the greatest mass loss occurred in sugar maple
(8.9%) followed by basswood (8.1%) and beech (1.9%).
In Situ and Ex Situ Leaf Carbon and Nutrient
Stocks
Interaction effects of nutrient stocks (g m
⫺2
) with respect
to species-by-moisture treatment were not significant in the
in situ study. Main effects showed significant differences in
leaf C, N, Ca, and Mg stocks between species before leach-
ing (control) and showed significant decreases in leaf C, N,
K, Ca, and Mg stocks after leaching (treatment) (Table 2).
Within species, sugar maple had significantly lower C, N,
K, and Ca stocks after leaching (treatment) compared with
the control (Table 2). Basswood had significantly lower C,
K, Ca, and Mg stocks and beech had significantly lower N,
Ca, and Mg stocks after leaching than the control.
Interaction effects of nutrient stocks (g m
⫺2
) with respect
to species-by-moisture treatment were significant only for C
[F(6, 24) ⫽75.023, P⫽0.001] and N [F(6, 24) ⫽84.312,
P⫽0.001] in the ex situ experiment. Simple effects showed
that C and N stocks were significantly lower in the HI
treatment than in the control between species. Main effects
showed significant differences in leaf C and nutrient stocks
(N, Ca, and Mg) before leaching (CTRL) and in LOW,
MED, and HI treatments between species (Table 3). When
the influence of moisture level on leaves was compared,
results showed that the greatest loss of C and nutrient stocks
occurred in the HI treatment followed by the MED and
LOW treatments (Table 3). For example, C, N, and Mg
stocks for sugar maple followed a sequence of CTRL ⬎
LOW ⬎MED ⬎HI, whereas Ca stocks followed a se-
quence of CTRL ⬇LOW ⬇MED ⬎HI. For basswood, C
and N stocks followed a sequence of CTRL ⬎LOW ⬎
MED ⬎HI, whereas the sequence for Ca was CRTL ⬇
LOW ⬇MED ⬎HI and that for Mg was CTRL ⬎LOW ⬇
MED ⬎HI. Beech followed a sequence of CTRL ⬎
Table 2. Changes in sugar maple (A. saccharum), basswood (T. americana), and beech (F. grandifolia) leaf carbon and nutrient
stocks (g m
ⴚ2
) before leaching (control) and after leaching (treatment) over 14 days in an in situ experiment in southern Ontario,
Canada. Standard errors are given in parentheses (n ⴝ3).
Control Treatment
Sugar maple Basswood Beech Sugar maple Basswood Beech
.............................................(%).............................................
C 133.88 (3.24)
B,a
122.94 (2.14)
C,a
144.15 (2.62)
A,a
115.67 (2.49)
B,b
116.74 (0.96)
B,b
143.15 (2.09)
A,a
N 1.93 (0.05)
C,a
3.31 (0.07)
A,a
2.45 (0.11)
B,a
1.77 (0.03)
C,b
3.12 (0.14)
A,a
2.04 (0.03)
B,b
P 0.14 (0.03)
A,a
0.18 (0.02)
A,a
0.15 (0.03)
A,a
0.12 (0.03)
A,a
0.16 (0.03)
A,a
0.15 (0.03)
A,a
K 0.97 (0.11)
A,a
1.24 (0.21)
A,a
0.90 (0.02)
A,a
0.76 (0.01)
C,b
0.79 (0.01)
B,b
0.89 (0.01)
A,a
Ca 6.60 (0.21)
B,a
10.16 (0.76)
A,a
4.20 (0.09)
C,a
5.18 (0.11)
B,b
8.66 (0.47)
A,b
3.33 (0.06)
C,b
Mg 1.10 (0.02)
C,a
1.45 (0.06)
A,a
1.15 (0.03)
B,a
0.77 (0.05)
C,a
1.23 (0.02)
A,b
1.04 (0.04)
B,b
SEs are given in parentheses (n⫽3). Values followed by the same upper case letters, comparing differences between leaf species within the control or
treatment for each nutrient, are not significantly different at P⬍0.05. Values followed by the same lower case letters, comparing differences between the
control (before leaching) and the treatment (after leaching) within leaf species, are not significantly different at P⬍0.05.
Table 3. Changes in sugar maple (A. saccharum), basswood (T. americana), and beech (F. grandifolia) leaf C and nutrient (N, P,
K, Ca, and Mg) stocks when exposed to different moisture levels compared with a control in an ex situ experiment over 14 days.
C N P K Ca Mg
.......................................(gm
⫺2
) .......................................
Sugar maple
CTRL 93.84 (0.50)
B,a
1.69 (0.03)
C,a
0.43 (0.04)
A,a
0.21 (0.01)
B,a
4.60 (0.06)
B,a
0.79 (0.02)
C,a
HI 67.70 (0.80)
C,d
1.02 (0.02)
C,d
⬍0.01 ⬍0.01 4.09 (0.21)
B,b
0.50 (0.02)
B,d
MED 80.13 (0.08)
B,c
1.20 (0.02)
C,c
⬍0.01 ⬍0.01 4.18 (0.09)
B,a
0.59 (0.02)
C,c
LOW 88.60 (0.34)
B,b
1.45 (0.01)
C,b
0.37 (0.04)
A,a
0.20 (0.01)
B,a
4.54 (0.31)
B,a
0.69 (0.03)
B,b
Basswood
CTRL 97.94 (0.33)
B,a
3.48 (0.04)
A,a
0.16 (0.01)
B,a
0.69 (0.04)
A,a
7.87 (0.09)
A,a
1.07 (0.03)
A,a
HI 77.06 (0.63)
B,d
1.93 (0.06)
A,d
0.13 (0.01)
b
0.50 (0.01)
b
6.33 (0.19)
A,c
0.72 (0.08)
A,c
MED 79.49 (0.42)
C,c
2.26 (0.01)
A,c
0.13 (0.01)
b
0.64 (0.01)
a
7.19 (0.25)
A,a
0.91 (0.03)
A,b
LOW 86.22 (0.06)
C,b
2.65 (0.01)
A,b
0.15 (0.01)
B,a
0.69 (0.07)
A,a
7.58 (0.66)
A,a
0.91 (0.06)
A,b
Beech
CTRL 112.55 (0.37)
A,a
2.03 (0.01)
B,a
0.18 (0.02)
B
0.67 (0.02)
A
2.92 (0.17)
C,a
0.91 (0.05)
B,a
HI 96.67 (0.18)
A,d
1.42 (0.01)
B,d
⬍0.01 ⬍0.01 2.71 (0.20)
C,a
0.71 (0.01)
A,c
MED 99.56 (0.22)
A,c
1.58 (0.01)
B,c
⬍0.01 ⬍0.01 2.72 (0.18)
C,a
0.79 (0.03)
B,b
LOW 101.46 (0.53)
A,b
1.67 (0.01)
B,b
⬍0.01 ⬍0.01 2.74 (0.22)
C,a
0.86 (0.04)
A,a
SEs are given in parentheses (n⫽3). Values followed by the same upper case letters, comparing differences between leaf species, within CRTL, HI, MED,
and LOW treatments, are not significantly different at P⬍0.05. Values followed by the same lower case letter comparing differences between CRTL, HI,
MED, and LOW, within each leaf species for each are not significantly different at P⬍0.05.
Forest Science 59(4) 2013 487
LOW ⬎MED ⬎LOW for C and N stocks and CTRL ⬇
LOW ⬎MED ⬎HI for Mg stocks. Comparisons between
species for P and K nutrient stocks and within sugar maple
and beech were not possible because concentrations were
below the detection limit of the analytical equipment.
Ex Situ Leaf Leachate Concentration
Interaction effects of leachate concentrations (mg l
⫺1
)
with respect to species-by-moisture treatment were signifi-
cant only for DOC [F(4, 27) ⫽3.071, P⫽0.033]. Simple
effects showed that the DOC concentration was signifi-
cantly greater in the HI and MED treatments for sugar
maple and basswood. Main effects showed significantly
greater DON concentrations in the MED treatment for sugar
maple and beech (Table 4). In a comparison of differences
within species, basswood had a significantly greater DON
concentration in the HI treatment followed by the MED and
LOW treatments. When NH
4
⫹
was compared between spe-
cies, beech and basswood had a significantly greater con-
centration in the HI treatment, whereas sugar maple had a
significantly lower NH
4
⫹
concentration in the HI treatment.
No significant differences were observed for NO
3
⫺
concen-
tration between and within species.
Changes in leachate concentrations with time revealed
that DOC concentrations were significantly greater on day 1
for sugar maple in all treatments than on days 10 and 14, but
basswood and beech showed this tendency only in the HI
and MED treatments (Figure 1). However, DON concentra-
tions were significantly greater on day 14 in sugar maple
(HI and MED treatments), but the LOW treatment was
significantly greater on days 10 and 14 compared (Figure 2).
DON concentrations were significantly different only in the
MED treatment for basswood, whereas that for beech was
significantly greater on day 14 (HI) and on days 10 and 14
in the LOW treatment. Sugar maple and beech leaves pre-
sented a similar pattern for NH
4
⫹
concentration, with a
significantly greater concentration on day 10, whereas bass-
wood showed a significantly greater concentration on day
14 (Figure 3). However, NO
3
⫺
concentrations in sugar
maple and basswood were significantly greater on day 1
compared with those on days 10 and 14 in all treatments,
whereas that for beech was significantly lower on day 1
(Figure 4).
Discussion
In Situ and Ex Situ Leaf Mass Change
It was expected that exposure to moisture in the in situ
experiment would result in a decline in leaf mass and that
higher levels of moisture (HI) (ex situ experiment) would
lead to the greatest mass loss regardless of species. The
findings from the in situ experiment were similar to those of
Parsons et al. (1990), Huang and Schoenau (1997), and
Lensing and Wise (2006). Consistent with the ex situ ex-
periment, Knutson (1997) found increased leaf mass loss in
an Acer-Tilia-Quercus-dominated deciduous forest when
exposed to high levels of moisture. Wieder et al. (2009) and
Ventura et al. (2010) suggested that a higher mass loss with
increasing exposure to moisture may be related to enhanced
microbial activity on the leaf surface, initial litter solubility,
and/or the loss of particulate organic matter. The dissimilar
amount of mass loss between species (in situ and ex situ
studies) suggested that species may respond differently to
moisture (Pereira et al. 1998). This may be due to variations
in leaf chemical concentrations and physical quality (Wie-
der et al. 2009), such as leaf toughness and cuticle thickness
(Gallardo and Merino 1993), and the presence of cuticle and
epicuticular waxes that act as a barrier to water-soluble
compounds (Gessner and Konstanz 1989). Melillo et al.
(1982) and Joergensen and Meyer (1990) suggested that
variation in leaf chemical and physical characteristics may
affect overall mass loss during the initial stages of decom-
position. For example, the lower mass loss of beech leaves
in our study may be due to their waxy and thick cuticle, in
addition to a higher lignin/N ratio, rendering them more
resistant to decomposition (Pereira et al. 1998, Madritch and
Cardinale 2007, Page and Mitchell 2008). Jacob et al.
(2009) also observed a lower concentration of N, Ca, and
Mg and a lower density of microorganisms on the surface of
beech leaves. They suggested that these results may have
Table 4. Leachate concentrations of DOC, DON, NH
4
ⴙ
, and NO
3
ⴚ
expressed as a mean value of three different sampling points
(days 1, 10, and 14) over the entire 14-day ex situ experimental period for sugar maple (A. saccharum), basswood (T. americana),
and beech (F. grandifolia) leaves exposed to different levels of moisture.
DOC (mg C l
⫺1
)DON NH
4
⫹
NO
3
⫺
......................(mg N l
⫺1
) ......................
Sugar maple
HI 16.53 (5.66)
A,a
0.53 (0.11)
A,a
0.17 (0.06)
B,b
0.62 (0.08)
A,a
MED 12.33 (1.07)
A,a
0.72 (0.23)
A,a
0.19 (0.07)
A,b
0.56 (0.06)
A,a
LOW 3.63 (0.58)
A,b
0.25 (0.13)
A,b
0.43 (0.15)
A,a
0.64 (0.02)
A,a
Basswood
HI 6.78 (1.96)
B,a
0.54 (0.06)
A,a
0.64 (0.31)
A,a
0.47 (0.35)
A,a
MED 5.80 (0.81)
B,a
0.40 (0.08)
B,b
0.36 (0.27)
A,a
0.79 (0.26)
A,a
LOW 3.52 (0.29)
A,b
0.27 (0.01)
A,c
0.33 (0.27)
A,a
0.66 (0.25)
A,a
Beech
HI 2.18 (1.21)
C,a
0.46 (0.02)
A,b
0.30 (0.14)
A,a
0.60 (0.23)
A,a
MED 1.95 (0.32)
C,a
0.74 (0.22)
A,a
0.32 (0.13)
A,a
0.75 (0.26)
A,a
LOW 1.05 (0.33)
B,a
0.26 (0.05)
A,c
0.42 (0.15)
A,a
0.78 (0.30)
A,a
SEs are given in parentheses (n⫽3). Values followed by the same upper case letters, comparing differences between leaf species, within HI, MED, and
LOW treatments, are not significantly different at P⬍0.05. Values followed by the same lower case letter comparing differences between HI, MED, and
LOW treatments, within each leaf species for each leachate (DOC, DON, NH
4
⫹
, and NO
3
⫺
) are not significantly different at P⬍0.05.
488 Forest Science 59(4) 2013
led to a slower rate of decomposition and nutrient mineral-
ization (Jacob et al. 2009).
In Situ and Ex Situ Leaf Carbon and Nutrient
Stocks
In situ and ex situ leaf nutrient concentrations before
moisture exposure (control) showed substantial between-
species variation in litter chemistry, which was also ob-
served by Osono and Takeda (2004) and Wieder et al.
(2009). As a result of exposure to moisture in the in situ and
ex situ studies, nutrient stocks decreased significantly but
varied among species. This occurred because moisture is
considered to be the major factor in controlling litter de-
composition (Ibrahim et al. 2010), but differences in leaf
chemical and physical characteristics may affect the amount
of nutrient loss between species (Page and Mitchell 2008).
Variation in nutrient stocks between the in situ and ex
Figure 1. Concentration of DOC (mg l
ⴚ1
) in leachate from
sugar maple (A. saccharum) (a), basswood (T. americana) (b),
and beech (F. grandifolia) (c) leaves when exposed to HI, MED,
and LOW levels of moisture over 14 days. Letters above each
bar denote significant differences (P<0.05), comparing dif-
ferences between sampling dates and within each moisture
level (nⴝ3).
Figure 2. Concentration of DON (mg l
ⴚ1
) in leachate from
sugar maple (A. saccharum) (a), basswood (T. americana) (b),
and beech (F. grandifolia) (c) leaves when exposed to HI, MED,
and LOW levels of moisture over 14 days. Letters above each
bar denote significant differences (P<0.05), comparing dif-
ferences between sampling dates and within each moisture
level (nⴝ3).
Forest Science 59(4) 2013 489
situ studies were probably due to differences in environ-
mental conditions between the field and laboratory. Expo-
sure to moisture, including that of the LOW treatment, was
greater in the ex situ study compared with that in the field
study. Other factors such as temperature, which was kept
constant at 21° C in the ex situ environment compared with
a mean temperature of 16.1° C in the in situ study, was
probably more favorable for microbial activity, leading to a
greater loss in mass and nutrients (Qui et al. 2005).
Under ex situ conditions, significant losses in C and N
could already be observed at LOW levels of moisture in all
species. This result suggested that a small increase in mois-
ture availability provided a favorable environment for mi-
crobial activity when a sufficient amount of N was available
Figure 3. Concentration of NH4
ⴙ
(mg l
ⴚ1
) in leachate from
sugar maple (A. saccharum) (a), basswood (T. americana) (b),
and beech (F. grandifolia) (c) leaves when exposed to HI, MED,
and LOW levels of moisture over 14 days. Letters above each
bar denote significant differences (P<0.05), comparing dif-
ferences between sampling dates and within each moisture
level (nⴝ3).
Figure 4. Concentration of NO
3ⴚ
(mg l
ⴚ1
) in leachate from
sugar maple (A. saccharum) (a), basswood (T. americana) (b),
and beech (F. grandifolia) (c) leaves when exposed to HI, MED,
and LOW levels of moisture over 14 days. Letters above each
bar denote significant differences (P<0.05), comparing dif-
ferences between sampling dates and within each moisture
level (nⴝ3).
490 Forest Science 59(4) 2013
to mineralize leaf C (Berg and Eckbohm 1983). Manzoni et
al. (2010) also suggested that with time, a reduction in decom-
poser C-use efficiency may occur, leading to the leaching of
nutrients when exposed to high levels of moisture.
Losses of P and K, especially in sugar maple and beech,
were triggered with exposure to minimal amounts of mois-
ture. This may be due to initially low concentrations of P in
leaves (Moore et al. 2010), because most of the P is retrans-
located before leaf abscission (Duchesne et al. 2001). How-
ever, Rutigliano et al. (1998) and Ventura et al. (2010)
found that P that is not retranslocated may be rapidly
consumed by microbes. Ukonmaanaho and Starr (2001)
observed that K leached readily from litterfall, and Ru-
tigliano et al. (1998) found that beech leaves are especially
prone to K leaching. This leaching occurs because K is
highly mobile and not structurally bonded (Mahmood et al.
2009). For example, in a laboratory study, Moore (1996)
observed that the proportion of leaf K lost increased when
leaves were washed in deionized water.
The relatively small changes (sugar maple and bass-
wood) and lack of change (beech) in Ca stocks suggested
that this nutrient is not readily leached (Osono and Takeda
2004). A possible reason is that Ca is part of the structural
plant tissue and is relatively immobile during the first phase
of decomposition (Jacob et al. 2009). Ventura et al. (2010)
found that Ca was released more gradually and in smaller
quantities than N, P, and K, and the majority of this nutrient
was lost during the second phase of decomposition (Rees et
al. 2006), which, according to Osono and Takeda (2004),
occurs after 5 months. Similar to the results of our study,
Osono and Takeda (2004) observed that the Mg stock in
Acer rufinerve Siebold & Zucc. and Fagus crenata Blume
leaves decreased during the initial phase of decomposition
in a temperate Japanese forest, possibly because Mg occurs
in plant cells in solution rather than as part of the structural
plant tissue, allowing it to be readily leached during the
initial phase of decomposition (Osono and Takeda 2004).
In Situ Leachate Concentration
Water-soluble compounds are leached from leaves
within hours to days after exposure to water (Wallace et al.
2008); this may contribute up to 30% of the total C loss
from leaf litter (Magill and Aber 2000). Increasing exposure
to moisture resulted in greater DOC and DON concentra-
tions in the leachate in our study, which was also reported
by Michalizik et al. (2001), Schmidt et al. (2010), Artigas et
al. (2011), and Kammer and Hagedorn (2011).
The different species exhibited contrasting patterns of
DOC release, and the lower DOC concentration from beech
leaf leachate was similar to that reported by Hagedorn and
Machwitz (2007). Wieder et al. (2009) suggested that vari-
ation in DOC concentrations between species may be due to
differences in leaf chemical and physical qualities, in addi-
tion to differences in the initial carbon chemistry (Silveira et
al. 2011) or due to variation in the degree of water repel-
lency of the leaf cuticle (Czech and Kappen 1997, Wallace
et al. 2008). Wallace et al. (2008) found that leaves with a
high water repellency produced lower concentrations of
leachate. This finding suggested that DOC may be released
through complex interactions between microbial production
and consumption and exposure to moisture, which could
result in various amounts of DOC leached from different
species (Park et al. 2002).
Temporal trends of changes in DOC concentration were
similar to that reported by Hansson et al. (2010) and Magill
and Aber (2000). For example, Magill and Aber (2000)
found a high DOC concentration from sugar maple and red
maple (Acer rubrum L.) within the 1st week of leaching
followed by a rapid decrease. Similarly, Hansson et al.
(2010) observed an initially high DOC concentration from
Norway spruce (Picea abies L. [Karst.]) needles followed
by a quick decrease within the first 20 days of their 125-day
study. However, Magill and Aber (2000) noted that tempo-
ral changes in DOC concentration varied between species
and, similar to our study, found the least change in beech
leaves. They also noted that the overall amount of DOC
from beech leaves was lower compared with that from
maple leaves (Magill and Aber 2000). Kammer and Hage-
dorn. (2011) suggested that differences in DOC concentra-
tions between litter types may be due to different microbial
communities present on the leaves, which could be related
to differences in initial litter chemistry (Artigas et al. 2011)
and changes in substrate quality as decomposition proceeds
(Hansson et al. 2010). Hansson et al. (2010) found that the
degree of decomposition of the substrate is important in
controlling DOC production, and lower quantities of DOC
were released from more decomposed materials. Such dif-
ferences may be related to the different phases of litter
decomposition, for which losses of nutrients are more rapid
in the first phase of decomposition compared with that in
later phases (Kalbitz et al. 2007). Results from this study
suggested that leaves are an important source of DOC and
that they are readily metabolized by microbes while collect-
ing in litter traps, even when exposed to low amounts of
moisture.
Only a few studies have evaluated DON and DIN from
leached leaves. Aerts and de Caluwe (1997) found that up to
20% of the initial N was removed from Carex sp. when
immersed in distilled water for 96 hours. Thus, water may
be the major controlling agent of leaf DON leaching in
temperate forest ecosystems (Schmidt et al. 2010). How-
ever, the concentration of DON varied among species, and
its concentrations were lower compared with that of DIN
(Magill and Aber 2000), which was similar to the result in
the current study. Temporal trends in DON concentrations
were similar to that reported by Wallace et al. (2008) who
observed that the majority of DON was leached within the
first 6 days of exposure to moisture. Similar to the current
study, Hansson et al. (2010) did not detect a clear pattern of
increasing or decreasing DIN concentrations during the first
14 days of leaching. However, after 6 weeks of leaching
Hansson et al. (2010) observed a decrease in NH
4
⫹
and an
increase in NO
3
⫺
. On the basis of our results, this finding
suggested that collecting leaf litter from litter traps on a
2-week rotation probably does not initiate the process of
nitrification.
Forest Science 59(4) 2013 491
Conclusions
The present research showed that exposing leaves col-
lecting in littertraps to low levels of moisture can induce
initial stages of decomposition. Differences in environmen-
tal conditions, including greater exposure to moisture and
temperature, may lead to enhanced leaf microbial activity
and an increased loss of mass and nutrients under laboratory
conditions (ex situ study). Nonstructurally bonded nutrients
had the greatest loss with increasing moisture levels,
whereas structurally bonded nutrients such as Ca remained
more stable with increasing exposure to moisture. Our re-
sults also showed that the amount of mass and nutrient loss
varied among species, which may be due to differences in
initial leaf chemistry in addition to variation in physical
characteristics including leaf thickness and waxiness. Such
variation between species in chemical and physical charac-
teristics also influenced the concentration of leachate (DOC,
DON, and DIN) when exposed to different levels of mois-
ture. Temporal trends in DOC concentration showed a de-
crease in this leachate over the 14-day experimental period
for all species and corresponded to a pattern of an increasing
DON concentration with time. However, DIN did not show
a clear pattern, suggesting that nitrification may not have
taken place within the 14-day experimental period.
The loss in leaf mass and nutrient stocks at a low level of
moisture suggested that the collection of deciduous litterfall
should take place more frequently during the peak of leaf
abscission. To accurately quantify nutrient inputs via litter-
fall in the within-system pathway between live vegetation
and the forest floor detritus pool, more frequent litter col-
lection should also be considered during periods of high
precipitation. Future researchers should consider the inter-
action of various litter components and conduct leaching
studies using a mixture of leaves from a variety of species.
Because the leaching of DOC occurs almost immediately
after the first wetting of leaf tissue, it is imperative to collect
sufficient volumes of leachate to account for temporal
changes, especially in studies that take place over a period
longer than 14 days. Long-term studies will also provide
further insight into the temporal pattern of DIN and may
provide an opportunity to identify at what period nitrifica-
tion processes commence.
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