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Initial chemistry and decay dynamics of deciduous leaf litter
from a long-term soil-warming study in the Northeastern US
Lauren Wind
Allegheny College
520 North Main Street, Meadville, PA 06335
Advisor: Jerry Melillo
Marine Biological Laboratory
7 MBL Street, Woods Hole, MA 02543
SES 2013
Abstract
Global warming has the potential to affect terrestrial ecosystems in many ways
including the cycling of carbon. This study focuses on how in situ soil warming affects
the carbon and nitrogen chemistry and decay rates of litter from heated and control forest
plots. The effect of exogenous nitrogen inputs on litter decay was also studied. The leaf
litter chemistry between the heated and control plots are significant when studying litter
decomposition, and understanding why decay rates differ among species. Observed
changes in carbon fractions and mass loss depended more on litter type then whether it
was from the control or heated plot. There is an average 24.7% increase in initial nitrogen
content of the heated litter compared to the control. Decay rates increased with the heated
litter, and also with nitrogen addition but it was not significant. Red maple litter has the
highest soluble carbon content, which led to having the most mass loss. This suggests that
in a warmer world, red maple trees may have an advantage. Future investigation is
needed to continue to study the decay rates between the heated and control litter because
23 days of decomposition was not enough time to find significance.
Keywords: Harvard Forest, litter quality, leaf litter decomposition, lignin, cellulose,
nitrogen addition, carbon fractionation
Introduction
Global warming, a component of climate change, affects many of the Earth’s
ecosystems (Solomon et al., 2007). In 2012, terrestrial ecosystems removed 23% of total
carbon dioxide emissions in the atmosphere (Global Carbon Project, 2013). Forests are
major carbon pools, but by 2100, there may be a 15% carbon pool loss in forests globally
(Davidson et al., 2006). This loss may be significant because we rely on forests as carbon
sinks with global carbon emissions on the rise. Forests have been studied for years to see
how carbon storage pools, nutrient cycling, and soil respiration relate to one another. Yet,
the effects of global warming on these interrelated processes are just beginning to be
studied.
Land feedbacks are important to consider when hypothesizing what may happen in a
warmer world. With an increase in global carbon emissions and a decrease in forest
capacity as carbon sinks, there may be an overall greater increase in atmospheric carbon
and accelerated global warming. This increased warming may also accelerate the leaf
litter decomposition process in the forest (Fierer et al., 2005). A self-reinforcing feedback
will start to form with this faster decomposition due to the increase in temperature from
carbon emissions resulting in more atmospheric carbon dioxide accelerating further
warming (Davidson et al., 2006).
Climate, N fertilization, and species composition are among the major factors that
affect decomposition rates. Designed to explore the effects of increasing temperatures
from global warming, a long- term soil warming experiments have been implemented at
the Harvard Forest, in Petersham MA by Jerry Mellilo and his research team (Mellilo et
al. 2011). Melillo and colleagues have found that over the first decade of soil warming,
soil carbon stocks decreased by 11.3% and inorganic nitrogen availability to plants
increased by 12.7% over ten years in warmed soil plots (Melillo et al., 2002). Increasing
soil temperatures not only changes carbon and nutrient availability within the soil, but it
may also alter the chemistry of leaf litter across different species.
Being able to compare different leaf litter types which have grown in warmed soils to
ones grown in ambient, or controlled, soils can add new information about how global
warming is changing the chemistry of forest ecosystems. Variable leaf litter species are
commonly compared by ratios of percent lignin to percent nitrogen in relation to overall
litter decay rates (Melillo et al., 1982). Comparing carbon fraction from litter grown in
warmed and ambient soils may help determine if soil warming affects the chemistry of
litter and their inputs back into the soil from decomposition.
Nutrients are effectively cycled within a forest ecosystem through leaf litter
decomposition (Melillo et al., 1982). Chemical differences between warmed and control
leaf litter may affect the decay rate within the forest. Leaf litter with more complex
carbon compounds such as lignin has a slower decay rate because the carbon ring
structure found in its phenolic structures are hard for microbes to break down (Allen,
1974). Leaf litter with more nitrogen tends to decay faster because nitrogen is often a
limiting nutrient in the decay process (Aber and Mellilo, 1991).
Another factor affecting forest litter decomposition, besides its initial carbon and
nitrogen chemistry, is additional nitrogen inputs from a variety of sources, including
precipitation (Magill et al., 2000). This added nitrogen has the potential to accelerate
litter decay.
Here I present the results of a study looking at the effects of soil-warming on leaf
litter decay rates for four major deciduous tree species found on the Harvard Forest
warming plots. I tested three hypotheses. First, the initial chemistry (carbon compounds
and nitrogen concentration) differs between leaf litter types collected from warmed
verses ambient plots. Second, decay rates of litter types are dependent on their initial
quality. And third, decay rates of litter types are accelerated by external nitrogen supply.
This study hopes to explore the dynamics of litter chemical structures and find patterns in
how this affects decomposition. A greater understanding of changes in litter quality in a
warmer world would help us to predict how litter decomposition and carbon cycling will
be affected by global climate change.
Materials and Methods
1.1 Field Collections
At the Harvard Forest, since 2003, Jerry Melillo and his research team have been
heating a large plot (30m x 30m) of land using heating cables beneath the surface to
increase the soil temperature by 5˚ C throughout the year (Melillo et al., 2011). There is
also a control plot located next to it. Ongoing experiments from these plots are
quantifying the effects of soil warming on the rates plant and soil carbon storage, soil
respiration, soil nitrogen nutrient availability and microbial community composition. The
four most dominate tree species (greatest to least) found there are, written as common
and (Latin) names, red and black oak (Quercus veluntina), red maple (Acer rubrem),
yellow and black birch (Betula lenta), and white ash (Fraxinus americana) (Table 1). The
oak and birch species are grouped together because they are ecologically similar.
From both the heated and controlled plots, I randomly collected fresh leaf litter of the
above oak, maple, birch, and ash trees. I chose these species because the literature
indicated that chemically they differ in initial carbon-to-nitrogen ratios (Aber and
Melillo, 1991). I put the litter, separated by species, into paper bags and air dried them at
room temperature. I then took subsamples of the air dried litter and oven dried them at
50˚C for 48 hours to find an air-to-oven dry baseline correction factor.
1.2 Incubation Experiment
I incubated the four litter types from the heated and control plots in aerated four
water baths containing a soil inoculum to introduce soil microbes. Two of the water
baths contained added nitrogen and two did not. I considered each water bath a unique
treatment: 1 – litter from control plot with 10mg/L N addition; 2 – litter from control plot
with no N addition; 3 – litter from heated plot with 10mg/L N addition; and 4 – litter
from heated plot with no N addition. I expected 30-40% mass loss from the 23 day
decomposition (Saruyildiz, 2003). In order to have enough material at the end of
decomposition for final analyses, I started with 4 grams of the dried litter and placed it in
10cm by 10cm 1mm2 mesh bags. All mass loss sampling was performed in triplicate. I
randomly suspended the bags of litter from wooden dowels for 23 days in 60 liters of 26-
27˚Cwarm, aerated water baths in a dark environment. The purpose of this was to speed
up the rate decomposition relative to what occurs in the field. I took initial and final water
samples of the different treatments for nutrient analyses of ammonium and nitrate. I
sampled for mass loss at 7, 14 and 23 days. Each sampling day, I removed all remaining
mass from each litter bag and dried them for 48 hours at 50˚C. After oven-drying, I
weighed the samples to record mass loss.
1.3 Litter Chemistry Analysis
The triplicates of the remaining litter from each species and treatment were
composited and ground in a Wiley Mill (20 size mesh). For initial, 7, 14 and 23 (referred
to as final from here on) samples of litter were measured for CHN using a Perkin Elmer
CHN elemental analyzer.
I performed sequential extractions on the initial and final litter composites to
gather carbon fraction information. The extraction procedure included a hot water
extraction and a sulfuric acid extraction (Allen et al. 1974; Dubois et al., 1956; Effland,
1977). The hot water extraction removed sugars, starches tannin and phenolics. The
extract was assayed for tannins and phenolics. The residual was extracted with sulfuric
acid to extract the celluloses. The residual contained acid insoluble lignin and ash.
I placed approximately 1 gram of dried ground litter into a BD 20 tube and added
80 mL of DI water. The tubes sat in a block digester at 100˚C for 3 hours. Using pre-
ashed and weighed Gooch fritter filters, I filtered the samples, diluted the filtrate to 250
mL, and saved it for the tannin and phenolic assays.
Using the Folins-Denis method from Allen et al. 1974 , I diluted the filtrates
100:1 and found percent tannin of the litter through colorimetric assay. I added 2.5 mL of
the Folins-Denis reagent to 35 mL of water and 2 mL of diluted sample. Then after 3
minutes, I added 10 mL of 1M Sodium Bicarbonate. I measured the absorbances on a
Shimadzu Spectrometer at 760 nm, integrated the absorbances using a tannin standard
curve, and used Equation 1 to solve for percent tannin. Using the Dubois et al. method, I
performed a phenol-sulfuric assay to find sugar concentration of the litter. I added 84 uL
of 90% phenol and 5 mL of 99% Sulfuric Acid to 2 mL of the 100:1 diluted sample. I
used a single sample Perkin Elmer Spectrometer to measure the absorbances at 490nm
and integrated the sugar concentrations of the samples from a dextrose standard curve.
(1) Tannin (mg)* extract volume (ml) * 10-3
* 100 = % Tannin
Sample (g) * aliquot volume (ml) mg
To determine the acid insoluble lignin content of the litter, I reference the Effland,
1977 method. I placed 400 mg of the dried litter residue from the first soluble extraction
in a BD 20 tube. I added 3 mL of 72% Sulfuric Acid to each sample and let them sit in a
30˚C water bath for 1 hour. Then I added 84 mL of DI water to each sample and
autoclaved the samples for one hours at 120˚C. I filtered the solution through pre-ashed
and weighed Gooch fritted filters. I weighed these filters after 50˚C oven drying, and
again after 450˚C ashing to find the lignin and ash content of the litter. The initial and
final litter composites were analyzed using the same extraction methods.
Results
3.1 Leaf Litter Chemistry
Initial CHN results show that for three of the four litter types (oak, maple and
birch) there is no significant difference, 0.99% change in carbon content, between the
heated and control litter types; white ash is the exception (Figure 1). The heated litter has
on average a 24.67 % increase in N overall, than compared to the control litter. The
heated red maple litter has less than half percent N then the oak, birch, and ash species
(Figure 2).
After decomposition, there is a 1.16% increase in carbon content in the heated
litter compared to the control litter (Figure 3). Following the same trend in the initial litter
chemistry, red maple has 6.5 % and 5.39% less carbon, respectively, in the control and
heated litter after decomposition. The difference in N content after decomposition is
insignificant, less than 1%, between heated and control litter (Figure 4).
Initial chemical analyses show that percent lignin (L) and nitrogen (N) in the
litter vary between species (Table 1). For the control litter, red and black oak has the
highest L:N ratio followed by red maple, yellow and black birch, and white ash. The L:N
ratio decreases in litter from the heated plot. For the heated-plot litter, red maple has the
highest L:N ratio followed by yellow and black birch, red and black oak, and white ash.
After decomposition, the ratio of L:N in all litter types and treatments increased
anywhere between 4% and 220%, but the most change of L:N in the litter types was
observed in the no N addition treatments (Table 2).
The initial and final litter specie carbon fractions appear in Table 3 and Figure 5
and 6. Initially, red maple has 32.85% less lignin content compared to the other litter
types. The difference in percent lignin between heated and control litter, for red maple
and red and black oak is less than 1%. Yellow and black birch and white ash show about
a 5% difference between heated and control litter lignin. The red maple counteracts its
low lignin percent with the having a 45.75% increase in soluble content (sugars and
starches, tannin, and phenolics) compared to the other litter types. After decomposition,
on average the soluble content in every litter type and treatment decreased 35.87% and
their lignin content increased 29.51%. The polar extraction assays showed that red maple
litter has twice the amount of tannin than the other species. The heated red maple litter
has 1.56% more tannin than the control, but for the other species their control litter has
1.60% more tannin than their heated litter. Percent phenolic in the control litter is more
than the heated litters by almost 2.5 fold (Table 3 and Figure 5). Compared to final litter
chemistry, the tannins decreased but it was only significant for the red maple litter
treatments. The phenolics decreased by 2.51% after decomposition in all only the control
litter and increased by 1.20% in the heated litter. These results are important, yet
statistically insignificant.(Table 3).
Percent cellulose is also accounted for through extraction. Initially, in the control
litter, white ash has the most cellulose followed by yellow and black birch, red and black
oak, and red maple. Litter from the heated plot showed a similar trend. After
decomposition, every litter species and treatment decreased in percent cellulose except
for red maple from the heated plot, irrespective of treatment. In litter from the heated
plot, red maple’s percent cellulose increased 3.36% with N addition and increased
10.16% without N addition. The cellulose to lignin (C:L) ratio and the holocellulose
lignin quotient (HLQ) decreased in every litter type and treatment after decomposition
(Table 2).
3.2 Mass Loss through Decomposition
After 23 days of decomposition, litter from the heated plot lost 3.26% more
mass, by a pooled mass loss mean for the litter types in each plot, then the litter from the
control plots for the four litter types without N addition and had the least biomass
remaining (Figure 9). Red maple litter lost 36.5% mass after decomposition, as much as
17% more mass than the other litter types. The red and black oak species lost the least
mass, 19.5%, and the yellow and black birch and white ash lost 22.5% and 23.5%
respectively (Figures 7, 8, &9). Decay rates of the litter seem to be species dependent;
independent of whether the litter was heated or N was added. The common pattern is the
low-lignin, red maple litter decays faster than the yellow and black birch and white ash
which have similar decay rates, and the high- lignin red and black oak decays the slowest
(Maple> Birch≈ Ash >Oak).
3.3 Nitrogen Addition Effects on Decomposition
When 10mg N /L was added during the decomposition process, we see no
significant effects of nitrogen additions on the rate of decomposition between control and
heated litter types (Figure 10). After 23 days of decomposition, litter from the heated plot
lost an average of 3.50% more mass than the litter from the controls plots for the four
litter types with N addition. When N is added, decay rates increase 3% from the no N
treatment.
Percent original nitrogen remaining was calculated to compare where the
nitrogen goes after decomposition. The control litter contained more percent original N
remaining than the heated litter for every litter type and treatment. With no N addition,
the control litter types increased in percent original N remaining, except for the yellow
and black birch and white ash. The heated litter species only increased in percent original
N remaining for the red maple litter. All other litter types decreased in percent original N
remaining in both treatments over the decomposition time.
Red and black oak only increased in percent original N remaining for the control
N addition treatment. The heated red and black oak litter decreased by as much as 40%
original N remaining (Figure 11). Yellow black birch and white ash followed similar
patterns to the red black oak, only increasing percent original N remaining in the control
N addition treatment (Figures 13 & 14). Red maple litter showed as much as 9-42%
increase in original N remaining for each treatment (Figure 12). The N addition
treatments had an average of 25.7% more original N remaining than the no N addition
treatments.
3.4 Leachate Analysis
Nutrient analysis on the water from the four treatments included ammonium
(NH4+
) and nitrate (NO3-
). In the N addition treatments, ammonium concentration
decreased an average of 245.55 uM over the decomposition time. In the no-N addition
treatments, ammonium concentration increased an average of 52.65 uM (Table 4). Nitrate
concentration decreased an average of 30.87 uM in the N addition treatments. In the no N
addition treatments, nitrate concentration increased an averaged of 0.16 uM (Table 4).
Discussion
This litter chemistry experiment is the first to compare carbon fractions between
heated and control leaf litter at the Harvard Forest. Red maple litter, which decomposed
the fastest over the 23-day decomposition, had the highest concentration of hot-water-
soluble compounds, including sugars and starches that are easily metabolized by
microbes. The microbial biomass is likely to have been N or P limited, which would have
contributed to the slower decay rates of the high C quality oak, ash, and birch litter
(Fierer et al., 2005). At the end of the 23 days decomposition, the hot-water-soluble
compounds in the red maple litter decreased 34 %, the most of any litter type. As the
percent soluble decreased in every litter type and treatment after decomposition, the
percent lignin increased an average of 30%. Lignin is the slowest carbon fraction to
decompose because of its carbon ring structures, and this is proven true from the results
seen in both the heated and control litter (Figure 6) (Allen et al., 1974).
It is important to compare the C and N litter quality because it can show
significant differences between litter types, and more importantly the difference in heated
and control litter (Aber et al., 1990). The heated red maple litter has up to a 44% increase
in % L: N compared to the other heated and control species because it has the lowest
percent lignin and nitrogen in its initial results. Butler et al. (2012) found opposite results,
where the heated red maple trees had the most foliar nitrogen. Although this is different,
the growth rate of red maple trees had an increased N content which is comparable to the
litter decay rates found in this study (Butler et al., 2012). Initial leaf litter carbon content
may be sensitive to temperature when comparing percent lignin among litter types,
which was also found in the Berbeco et al. (2012) study when looking at the initial
percent lignin in woody debris in the same heated plots at the Harvard Forest (Berbeco et
al., 2012).
The evidence of an increase in initial nitrogen content, which was found in the
heated litter, is supported by the Butler et al. (2012) paper, where soil warming affecting
the N cycle was studied. Butler found that with the induced soil warming, there is an
increase in available nitrogen in the soil, which leads to an increase in tree growth and
foliar nitrogen content in the same plot where the heated litter was collected from at the
Harvard Forest (Butler et al., 2012). Comparable to other soil warming experiments,
increases in vegetative growth, leaf litter and plant N content have been found during
induced artificial warming (Arft et al., 1999, Dukes et al., 2005, Melillo et al., 2002, and
Wan et al., 2005). A study in the US Great Plains found that soil warming increases net N
mineralization because it increases N turnover rates, and stimulates plant N uptake (Wan
et al., 2005). Butler et al. (2005) and Melillo et al. (2002) also found an overall increase
in net N mineralization in the heated plots, which may account for the higher initial N
content in the heated litter than the control litter.
From the initial leaf litter chemistry results, the percent lignin to N ratio can be
used as a predictor of decay rate of deciduous litter (Melillo et al. 1982).The control % L:
N ratios are greater than ones found in the Harvard Forest study in 1990 with the same
species, but the trend across litter types is similar (Aber et al., 1990) (Table 2). After 23
years, the increase observed in % L: N ratios in the control litter may be attributed to an
overall decrease in nitrogen content of the control leaf litter and a decrease in carbon
storage that terrestrial ecosystems over the years (Global Climate Project, 2013). In this
study, the %L: N ratios did not significantly predict the decay rate of the litter types.
However in a laboratory decomposition study by Sariyildiz et al. (2003), %L and %N
content of oak and beech litter species in a deciduous forest did significantly predict mass
loss over twelve months (Sariyildiz et al., 2003).
The nitrogen content in the initial litter is often considered a rate-controlling
factor on litter decay rate (Aber and Melillo, 1991, Knorr et al., 2005). After
decomposition with no N addition, the decay rates were highest in the heated litter. I
found the most decay in the red maple, which is related to also having the highest percent
solubles and lowest percent lignin from the initial litter types. The other litter types
decayed less, on average 22% mass loss and they had similar carbon fractions. I
hypothesize that due to similar initial nitrogen content, the litter did not have enough time
to reach the mineralization stage of decomposition to give significant and different
biomass loss results. Melillo et al. (1982) found significant differences in decay rates
during a twelve month decomposition study for the ash, birch, and maple litter, and this
supports the hypothesis that more time is needed in this decomposition experiment to find
significant changes in decay rates between the heated and control litter (Melillo et al.,
1982). The C:N ratio decreases during decomposition because there is less carbon in the
litter after decomposition and more nitrogen from immobilization (Melillo et al., 1984).
Knorr et al. (2005) completed a meta- analysis on litter decomposition and found that
litter decay under 24 months exhibited a 7% percent mass loss, whereas litter decay over
24 months inhibited 18% mass loss (Knorr et al., 2005). This supports a hypothesis that
the mass loss seen in this experiment is from the rapid decay of cellulose, which
decreased an average of 5% across litter types and treatments, and the lignin had not
started accumulating yet. Looking at the short term, global warming will increase decay
rates due to the increase in initial N content of material, but on a long term scale, effects
of warming may not be as noticeable (Field et al., 2007).
I observed net increases in percent original N remaining in the control litter after
decomposition. In the field one might suggest the additional nitrogen mass comes from
nitrogen fixation, fertilization, through fall, dust, green litter, or immobilization (Melillo
et al., 1982). But these litter treatments had no nitrogen addition and were not
contaminated within the incubation chamber. This may suggest that the microbes on the
litter in the incubation bins were readily competing against each other for the leached
nitrogen from the surrounding leaves, and had more N mass after decomposition.
Immobilization could have also occurred due to the labile carbon fractions in the leachate
(Magill et al., 2000).
Since the start of the initial soil warming experiment in 2003, Melillo and his
research team have seen significant effects in the N cycles, like increases in net
mineralization and nitrification, and the N content of the foliar species (Butler et al.,
2012). When the heated and control litter types decomposed in a 10 mg N/ L eutrophic
environment, I saw no statistical significance between these decay rates of the N addition
litter and the no N addition litter treatments which is comparable to the results found in
the Knorr et al. (2005) meta-analysis (Knorr et al., 2005). Although an N addition
laboratory litter decomposition study which had a similar experimental design to this
study found that when N is added, mass loss increases without affecting dissolved
organic carbon (DOC) leaching rates (Magill et al., 2000). A warming experiment in a
California grassland agrees with Magill, and saw an increase in decay rates when N was
added (Hugh et al., 2005). From past literature, we know soil warming will effect N
cycling and increase soil N availability in terrestrial ecosystems (Butler et al., 2012). N is
increasing in terrestrial ecosystems and that may affect the overall decay rates of leaf
litter decomposition.
In order to find long term effects of soil warming on litter decomposition, this
experiment must be continued for a longer period of time. I attribute the close relation of
the heated and control litter mass loss to there being not enough time to see the effects of
immobilization during decomposition in the 23 day incubation. I also expect the initial L:
N ratios will become significant in predicting decay rates, if carbon fractions are
performed in triplicate and an ANOVA statistical analysis is run on the results. I also
suggest following the Magill et al. (2005) leachate analysis, where the DOC, DON, and
respiration rates were found for each litter type and treatment. This will improve the
experiment by giving data that can compare and quantify litter quality to the amount of
DOC leached into the soil, the effects of N on leaching rates, and the rates of carbon
released during decomposition (Magill et al., 2005). In order to do this, keep in mind
each litter type must be incubated in separate incubation bins.
By examining the leaf litter chemistry, decay rates, and effects of N addition, we
can better predict how terrestrial ecosystems will respond to global warming, a
component of climate change. Initial leaf litter chemistry is important in knowing what to
expect during the decomposition of different leaf litter types. Although the carbon
fractions between litter types were significantly different, the initial heated and control
litter was not. The heated litter had a significantly greater initial N content when
compared to the control litter. The heated litter had greater decay rates, and particularly
the red maple litter may have a competitive advantage in a warmer world due to its low
litter quality (Butler et al., 2012). When N is added, the C:N ratio in litter decreases and
this may accelerate the decomposition process. Decay rates and N addition are important
to think about when coupled with heated litter for ecosystem nutrient cycling and the
implications of what may come in a warmer, non-nitrogen limited world.
Acknowledgments
Special thanks to Jerry Melillo, Will Werner, and Ken Foreman for help designing the
experiment and interpreting its results. Also thanks to Rich McHorney, Alice Carter,
Fiona Jevon, Sarah Nalven, Kelsey Gosselin, and Rich Bowden for advice and helping
with the execution of this experiment. Thank you to Ken Foreman, SES, MBL, and the
Ecosystems Center for making this project possible.
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Press, Cambridge, United Kingdom and New York, NY, USA.
Wan, S., Hui, D., Wallace, L., and Luo, Y. 2005. Direct and indirect effect of
experimental warming on ecosystem carbon processes in a tallgrass prarie. Global
Biogeochemical Cycles. 19:GB2014.
(2013, November 19). Global carbon budget. Globalcarbonproject.org. Retrieved
December 16, 2013 from http://www.globalcarbonproject.org/carbonbudget
/13/hl-full.htm.
Table 1. Initial percent lignin and nitrogen for each of the four litter species in the
warmed and control plots.
Plot Litter Species % Lignin % N % L:N
Control Red Black Oak 31.05 0.72 43.00
Red Maple 22.63 0.51 44.46
Yellow Black Birch 29.43 0.89 33.22
White Ash 32.82 1.01 32.40
Warmed Red Black Oak 32.82 1.27 25.90
Red Maple 22.88 0.54 42.21
Yellow Black Birch 33.47 1.23 27.32
White Ash 29.89 1.26 23.65
Aber et al., 1990 Red Oak 26.70 0.83 32.17
Red Maple 17.30 0.66 26.21
Paper Birch 20.70 0.90 23.00
Table 2. Percent lignin to nitrogen ratios, cellulose to lignin ratios, and also HLQ in the
initial and final litter species and treatment types.
Plot Treament Species Initial Final Initial Final Initial Final
Control Nitrogen Addition Red Black Oak 43.00 48.43 1.03 0.62 0.51 0.28
Red Maple 42.51 57.76 1.23 0.26 0.55 0.18
Yellow Black Birch 33.22 46.39 1.19 0.41 0.54 0.23
White Ash 32.40 34.79 1.22 0.57 0.55 0.27
No Nitrogen Addition Red Black Oak 43.00 72.82 1.03 0.31 0.51 0.19
Red Maple 42.51 64.78 1.23 0.38 0.55 0.22
Yellow Black Birch 33.22 54.03 1.19 0.49 0.54 0.25
White Ash 32.40 63.80 1.22 0.27 0.55 0.17
Warmed Nitrogen Addition Red Black Oak 25.90 33.40 1.00 0.64 0.50 0.28
Red Maple 42.22 43.99 1.05 0.48 0.51 0.25
Yellow Black Birch 27.33 48.23 1.10 0.30 0.52 0.19
White Ash 23.65 42.00 1.25 0.51 0.55 0.26
No Nitrogen Addition Red Black Oak 25.90 56.86 1.00 0.56 0.50 0.26
Red Maple 42.22 53.37 1.05 0.67 0.51 0.29
Yellow Black Birch 27.33 42.99 1.10 0.71 0.52 0.29
White Ash 23.65 42.16 1.25 0.54 0.55 0.26
% Lignin: Nitrogen %Cellulose: Lignin HLQ
Table 3. Carbon fraction break down for each litter type and treatment. All parts of the
carbon fractions were scaled up to the percent of the initial litter quantity.
Table 4. Initial and final nutrient concentrations (uM) for all four litter treatments.
Initial Final
Treatment NH4 uM NO3 uM NH4 uM NO3 uM
Control: N Addition 563.67 35.00 318.33 8.42
Control: No N Addition 16.07 0.10 68.85 0.12
Warmed: N Addition 532.33 35.60 290.56 0.44
Warmed: No N Addition 13.78 0.05 66.30 0.34
Figure 1. The initial percent carbon for red and black oak, red maple, yellow and black
birch and white ash litter types in the control and warmed plots.
45.50
46.00
46.50
47.00
47.50
48.00
48.50
49.00
49.50
Red Black Oak Red Maple Yellow BlackBirch
White Ash
%C
of
leav
es
%C of Initial Litter
Control
Warmed
Figure 2. The initial percent nitrogen for red and black oak, red maple, yellow and black
birch and white ash litter types in the control and warmed plots.
0
0.2
0.4
0.6
0.8
1
1.2
1.4
Red Black Oak Red Maple Yellow BlackBirch
White Ash
%N
of
Litt
er
%N of Initial Litter
Control
Warmed
Figure 3. The final percent carbon for red and black oak, red maple, yellow and black
birch and white ash litter types in the control and warmed plots with no addition nitrogen.
45
46
47
48
49
50
51
Red Black Oak Red Maple Yellow BlackBirch
White Ash
%C
of
leav
es
%C of Final Litter (No N addition)
Control
Warmed
Figure 4. The final percent nitrogen for red and black oak, red maple, yellow and black
birch and white ash litter types in the control and warmed plots with no addition nitrogen.
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
Red Black Oak Red Maple Yellow BlackBirch
White Ash
%N
of
leav
es
%N of Final Litter (No N addition)
Control
Warmed
Figure 5. Initial carbon fractions in all litter species in the N addition treatment. C is the
control litter and W is the warmed litter.
0%10%20%30%40%50%60%70%80%90%
100% Initial Carbon Fractionation Comparison
% Sugars andStarch% Tannin
% Phenolics
% Cellulose
% Lignin
% Ash
Figure 6. Final carbon fractions in all litter species in the N addition treatment. C is the
control litter and W is the warmed litter.
0%
10%
20%
30%
40%
50%
60%
70%
80%
90%
100%
Final Carbon Fractionation Comparison
% Sugars andStarch% Tannin
% Phenolics
% Cellulose
% Lignin
% Ash
Figure 7. The overall percent biomass loss in oak, maple, birch, and ash litter species in
the control and warmed plots with nitrogen addition.
0%
5%
10%
15%
20%
25%
30%
35%
40%
45%
50%
Red Black Oak Red Maple Yellow BlackBirch
White Ash
% B
iom
ass
Lost
Mass Loss After 23 Days (N addition)
Warmed
Control
Figure 8. The overall percent biomass loss in oak, maple, birch, and ash litter species in
the control and heated plots with no nitrogen addition.
0%
5%
10%
15%
20%
25%
30%
35%
40%
45%
50%
Red Black Oak Red Maple Yellow BlackBirch
White Ash
% B
iom
ass
Lost
Mass Loss After 23 Days (No N addition)
Warmed
Control
Figure 9. The difference shown for percent biomass remaining between the heated and
control red and black oak, red maple, yellow and black birch, and white ash litter types
during decomposition with no N added.
50%
60%
70%
80%
90%
100%
0.00 5.00 10.00 15.00 20.00
% B
Iom
ass
Re
mai
nin
g
Time (days)
Oak Heated: No NAddition
Control: No NAddition
50%
60%
70%
80%
90%
100%
0.00 5.00 10.00 15.00 20.00
% B
iom
ass
Re
mai
nin
g
Time (days)
Maple
Heated: No NAddition
Control: No NAddition
50%
60%
70%
80%
90%
100%
0.00 5.00 10.00 15.00 20.00
% B
iom
ass
Re
mai
nin
g
Time (days)
Birch Heated: No NAddition
Control: No NAddition
50%
60%
70%
80%
90%
100%
0.00 5.00 10.00 15.00 20.00
% B
iom
ass
Re
mai
nin
g
Time (days)
Ash Heated: No NAddition
Control: No NAddition
Figure 10. The difference shown for percent biomass remaining between the heated and
control red and black oak, red maple, yellow and black birch, and white ash litter types
during decomposition with N addition.
50%
60%
70%
80%
90%
100%
0.00 5.00 10.00 15.00 20.00
% B
Iom
ass
Re
mai
nin
g
Time (days)
Oak
Control: NAddition
Heated: NAddition
50%
60%
70%
80%
90%
100%
0.00 5.00 10.00 15.00 20.00
% B
iom
ass
Re
mai
nin
g
Time (days)
Maple
Control: NAddition
Heated: NAddition
50%
60%
70%
80%
90%
100%
0.00 5.00 10.00 15.00 20.00
% B
iom
ass
Re
mai
nin
g
Time (days)
Birch
Control: N Addition
Heated: N Addition
50%
60%
70%
80%
90%
100%
0.00 5.00 10.00 15.00 20.00
% B
iom
ass
Rem
ain
ing
Time (days)
Ash
Control: NAddition
Heated: NAddition
Figure 11. The relationship of % Original N Remaining of red and black oak during
decomposition.
0%
20%
40%
60%
80%
100%
120%
140%
160%
0 5 10 15 20 25
% O
rigi
nal
N R
em
ain
ing
Time (days)
Red Black Oak
Control: N addition
Control: No N addition
Warmed: N addition
Warmed: No N addition
Figure 12. The relationship of % Original N Remaining of red maple, yellow and black
during decomposition.
0%
20%
40%
60%
80%
100%
120%
140%
160%
0 5 10 15 20 25
% O
rigi
nal
N R
em
ain
ing
Time (days)
Red Maple
Control: N addition
Control: No N addition
Heated: N Addition
Heated: No N Addition
Figure 13. The relationship of % Original N Remaining of yellow and black birch during
decomposition.
0%
20%
40%
60%
80%
100%
120%
140%
160%
0 5 10 15 20 25
% O
rigi
nal
N R
em
ain
ing
Time (days)
Yellow Black Birch
Control: N addition
Control: No N addition
Warmed: N addition
Warmed: No N addition
Figure 14. The relationship of % Original N Remaining of white ash during
decomposition.
0%
20%
40%
60%
80%
100%
120%
140%
160%
0 5 10 15 20 25
% O
rigi
nal
N R
em
ain
ing
Time (days)
White Ash
Control: N addition
Control: No N addition
Warmed: N addition
Warmed: No N addition
