Ash Tree Leaf Litter (Fraxinus excelsior L.) Breakdown in Two Different Biotopes and Streams

© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim 1434-2944/04/5–612– 0508

TADEUSZ FLEITUCH1* and MARIA LEICHTFRIED2

1Institute of Nature Conservation, Polish Academy of Sciences, Pl 31–016 Cracow,Al. Mickiewicza 33, Poland; e-mail: [email protected]

2Biological Station Lunz, Institute of Limnology, Austrian Academy of Sciences,A-3293 Lunz/See, Seehof 4, Austria; e-mail: [email protected]

Ash Tree Leaf Litter (Fraxinus excelsior L.) Breakdownin Two Different Biotopes and Streams

key words: stream, leaf breakdown, biotopes, ash tree, chemical composition

Abstract

Coarse (0.5 mm) and fine (0.1 mm) mesh size bag methodology was used for comparing the breakdownof ash tree leaves (Fraxinus excelsior L.) in two biotopes (dry – terrestrial and wet – overflown streamzones) in two low order streams (the Oberer Seebach (OSB), Lower Austria and the Brzezowka stream(BRZ), Beskidy Mountains, southern Poland). In total, 96 bags were exposed in autumn 2000. Ash-freedry mass (AFDM) ranged in dry zones of both streams from 94–62% (OSB) and 85–53% (BRZ)respectively. The decomposition process was faster in wet zones: 96–33% (OSB) and 56–11% (B) during the study period. Significant differences in ash breakdown and its chemical content between stud-ied streams were found. Total organic carbon (TOC) and total nitrogen content (TN) of AFDM of littershowed increased differences with experiment duration between zones and between two bag types for bothstreams. The strongest increase of TOC and TN content (100% on average vs. initial content) for bag types,zones, and streams was observed in the first two weeks of the experiment. These results confirm the im-portance of chemical compounds for microbiological processes (biofilms) in different ecosystem biotopes.

1. Introduction

Organic matter is an essential resource in most aquatic and terrestrial ecosystems (ODUM

and DE LA CRUZ, 1963). Low order streams are typically heterotrophic; i.e. more energycomes from allochthonous sources than from autochthonous production (FISHER and LIKENS,1973; MINSHALL et al., 1983). Leaf breakdown, an important component of organic matterdynamics in lotic ecosystems (CUMMINS, 1974; GESSNER et al., 1999) has been widely exam-ined in streams (see reviews by ANDERSON et al., 1979 and BOULTON and BOON, 1991).

Riparian zones provide an ideal setting for the identification of factors that have a sig-nificant effect on organic matter breakdown because they contain a series of relatively dis-tinct zones that differ in abiotic and biotic factors across a relatively short distance(HUTCHENS and WALLACE, 2002). Most studies of leaf breakdown in riparian zones that haveincorporated biotopes (i.e. stream and terrestrial habitats) have been done in parts of streamdrainages that have relatively large, active floodplains (MERRITT and LAWSON, 1979, 1992).However, it is unclear whether riparian zones of mountain streams with little or no flood-plain development have such a wide range in leaf breakdown dynamics.

Differences in leaf processing rates among ecosystems and their biotopes have been attrib-uted mainly to physical factors such as temperature (see references in IRONS et al. 1994).Other important factors to consider are tree species and their nutrition quality (CUMMINS,

Internat. Rev. Hydrobiol. 89 2004 5–6 508–518

DOI: 10.1002/iroh.200410770

* Corresponding author

Ash Tree Leaf Litter Breakdown 509

© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

1974; LEICHTFRIED, 1998). The chemistry of leaf litter is fundamental to its decompositionand for cycling of nutrients in terrestrial (AERTS and DE CALUWE, 1997; HATTENSCHWILER

and VITOUSEK, 2000) and aquatic systems (ELWOOD, 1981; SUBERKROPP and CHAUVET, 1995;ROBINSON and GESSNER, 2000).

Although, emphasis on leaf decomposition research in streams has been laid on thedetermination of breakdown rates as a function of species (PETERSEN and CUMMINS, 1974;HILL et al., 1992), little is known about decomposition of common European ash tree (Frax-inus excelsior L.). This species is widespread through Europe except in far north, and south-ern half of Iberian Peninsula (WALLANDER, 2001). In central Europe, it occurs frequently inmountains, sporadically in woods of beech and spruce, up to 1700 m. The sun-loving treeprefers soils which are deep, fresh, and loose. Ash tolerates inundation for 40 days a year.In Central Europe the ash tree is associated with forests with high water tables often closeto ground level. This habitat requirement is reflected in high leaf water consumption. Theecology of ash tree has been described by WARDLE (1961) and WALLANDER (2001).

The main objective of this study was to examine the decomposition process of ash treeleaves in two biotopes, namely terrestrial (occasionally over flown or dry zones) and aquat-ic zones (permanently over flown or wet zones) with consideration of an effect of benthicmacroinvertebrate activity (coarse mesh bags) and without that activity (fine mesh bags).Thesecond objective was to determine the temporal variation of carbon and nitrogen concentra-tions associated with leaf breakdown in two mountain streams differing in geology andhydrological conditions. To our knowledge, decomposition of ash tree litter with its chemi-cal changes across different habitats has not been explored previously.

2. Study Area and Site Description

The studies were conducted concurrently in the Brzezowka stream (Southern Poland) andin the Oberer Seebach (Lower Austria). The Brzezówka stream (BRZ) is situated in theBeskid Wyspowy Mountains, which is a first order stream (STRAHLER, 1957) with a forestedcatchment area of 7.6 km2 (49o52Ń, 20o02É). The stream length is about 2 km and shows at

Table 1. Major physico-chemical data on the Brzezówka stream and Oberer Seebach.

Parameter Brzezówka stream Oberer Seebach

Geology Flysh rocks Karstic limestoneAltitude m a.s.l. 270 605Riparian vegetation Fagus silvatica L., Fraxinus Picea abies L.,

excelsior L., Salix spp, Fagus silvatica L.,Corylus avellana L., Fraxinus excelsior L.,

Quercus robur L. and Acer pseudoplatanus L.

Canopy Closed Mostly openMean stream width (m) 1.7 4.4Mean discharge (m3/s) 0.01 0.04Mean current velocity (cm/s) 10.5 4.5Mean water temperature (oC) 5.8 6.1Temperature range (oC) 1–15.5 4.5–6.8Mean conductivity (µS/cm) 390 237Total N (mg/l) 1.02 0.79Inorganic P (mg/l) 0.074 0.067Bed structure Stones, gravel Stones, gravel, sand, and mud

510 T. FLEITUCH and M. LEICHTFRIED


studied site a typical riffle-pool sequence. The mean width is 1.7 m and the mean depth is5.8 cm. The streambed consists mainly of stones (10–50 cm in diameter) and gravel.

The second site was chosen in an arm of the lower stretch at Oberer Seebach (OSB), asecond order alpine stream on the northern fringe of the Alps, near the town Lunz am See(Lower Austria) (47o51Ń, 5o04É). The stream length is about 7 km. The catchment area is20 km2. The mean width of the investigated stretch is 4.4 m and the mean depth is 17.9 cm.The streambed consists mainly of small stones (< 10 cm in diameter), gravel and sand.

The both streams are oligotrophic and their water flow is natural. The sites differ mainlyin altitude, catchment geology, canopy opening, bed structure, and stream hydrology. Theriparian canopy of the streams consists mostly of mixed deciduous trees with the presenceof European ash. Selected data from the streams are given in Table 1. More detailed descrip-tion of the study areas and streams are given by FLEITUCH (1992, 2001) and LEICHTFRIED

(1995).

3. Materials and Methods

Freshly fallen leaves of ash tree (Fraxinus excelsior L.) were collected concurrently from the twostreams and stored in the laboratory at 4.0 oC for 24 hours. They were then weighed into about 10–15 glots with accuracy of 0.01 g and enclosed in 10 × 25 cm nylon litter bags with 5 × 5 mm mesh size(coarse mesh bags – CMS) and 0.1 mm mesh size (fine mesh bags – FMS). The fine mesh size bagswere used in an attempt to minimize the influence of macro-invertebrates on leaf breakdown. In total,48 bags were prepared for each stream and divided into 4 sets as follows: 12 coarse mesh size and12 fine mesh size bags were exposed in riparian plot (dry zone), while 12 coarse and 12 fine bags inaquatic plot (wet zone). The extra collected fresh ash tree leaves were used for determination of wet/drymass coefficient and for estimation of initial ash free dry mass (AFDM) (CHERGUI and PATTEE, 1992).The bags with leaves were randomly exposed in selected grid-quadrates (24 per each zone), in 15 sec-tions with 2 m cross-sectional intervals, along 30 m stream stretch. The bags were tied in both habitatsto individual stones anchored into the bottom (the Brzezowka stream) and tethered to metal sticks (theOberer Seebach) on the end of September and exposed till November 2000. Three replicate bags of eachmesh size (coarse and fine) were then retrieved after 2, 4, 6 and 8 weeks after immersion at each studysite. Immediately following collection the individual litter bags were placed in plastic bags, stored in acooler and returned to the laboratory for processing and further analysis. In the laboratory, the leaveswere removed from the litter bags, rinsed with water through a 0.1 mm nylon net. The separated organ-ic material was freeze-dried at –50 oC for 24 hours. After freeze-drying, the leaves were weighed toobtain dry mass (DM) with an accuracy of 0.01 g. Two portions (ca. 1 g) of the dry remaining leaf ma-terial from each sample were ashed for 4 h at 500 oC to determinate AFDM (ash free dry mass) as anestimate of organic matter in each sample (CUFFNEY et al., 1990). The breakdown of leaves was per-formed as a percent of remaining AFDM equal to 100 percent decreased by percent loss AFDM on agiven time. Sub-samples of the material were used to estimate total organic carbon (TOC) and totalnitrogen (TN) with the use of a LECO CHN 600 analyser. Sub-samples of extra collected leaves wereused for determination of initial concentration (blank sample) for TOC and TN. Concurrently to thedates of experiments with leaf breakdown, the physical and chemical parameters of the stream waterwere measured: discharge, current velocity, conductivity, temperature, total nitrogen, and phosphorusconcentrations.

To assess the differences in leaf breakdown for each bag type (coarse or fine), two factors (streamand zone) ANCOVA with time intervals as co-variate was used. Moreover, % of leaf mass remainingwas regressed against time to fit the most significant model for each bag type and stream zone. Three-way factor ANOVA (with time as a nominal variable) was used to find differences for chemical param-eters: TOC and TN in ash leaves. Prior to all statistical analyses, the data were log-n transformed (ZAR,1984). The statistical calculations were done with the use of Systat software.



4. Results

4.1. Leaf Breakdown

Breakdown of ash leaves was higher in the wet zones of both study areas and bag types,than in dry zones (Fig.1). After 8 weeks of the exposition, the highest decomposition wasrecorded in wet zone, in coarse bags in the Brzezówka stream (% of remaining on the aver-age = 14,3%). In general, remaining AFDM ranged from 94–62% (Oberer Seebach) andfrom 85–53% (Brzezówka) in dry zones, and in the wet zones: 96–33% (OSB) and 56–11%(BRZ) during the study period. The differences in ash breakdown between zones (ANCOVAi.e. stream × zone interaction) in both streams and for each bag type were significant (Table 2). The patterns of leaf breakdown process differed according to type of zone. Thebest fitted model for this process was explained by a linear relationship for both streams andbags in the dry zones, and in the wet zones by the use of exponential model (Fig. 1, Table 3).

4.2. TOC and TN Concentrations

Total organic carbon (TOC, Fig. 2) and total nitrogen content (TN, Fig. 3) of ash littershowed increased differences between zones and between two bag types with experimentduration for both streams. The strongest increase of TOC and TN contents (100% on aver-age vs. initial content) for bag types, zones, and streams was observed in the first two weeksof the experiment (e.g. increase for TOC from 260 to 420 mg/g DW, for TN from 7 to22 mg/g DW in fine mesh bags in aquatic zones). Statistical differences for TOC were foundin coarse and fine bags (three way ANOVA) between streams and zones and for TN in fine

CMS

0

2 0

4 0

6 0

8 0

1 0 0

0 2 4 6 8 1 0

Week

% R

emai

nin

g (

AF

DM

)

OSB_DZ

OSB_WZ

BRZ_DZ

BRZ_WZ

OSB_DZ

OSB_WZ

BRZ_WZ

BRZ_DZ

FMS

0

2 0

4 0

6 0

8 0

1 0 0

0 2 4 6 8 1 0

Week

% R

emai

nin

g (

AF

DM

)

OSB_DZ

BRZ_DZ

BRZ_DZ

OSB_WZ

Figure 1. % of remaining of ash leaf litter in two biotopes: dry zone (DZ) and wet zone (WZ) in twobag types: coarse mesh bags (CMS) and fine mesh bags (FMS) in two streams: Oberer Seebach (OSB)and Brzezowka (BRZ). Regressions lines for terrestrial zones fitted by linear model (y = a + bx), fromaquatic zones fitted by exponential model (y = a + ex). R2 coefficients are given in the Table 3. All

regression significant at p < 0.05.



Tab

le 2

.R

esul

ts o

f 2

fact

ors

AN

CO

VA

(fa

ctor

s: s

trea

m a

nd z

one)

with

tim

e as

cov

aria

te f

or %

of

AFD

M r

emai

ning

(%

RE

M)

for

coar

se

(CM

S) a

nd f

ine

(FM

S) b

ags.

CM

S ba

gs%

RE

MFS

M b

ags

%R

EM

MA

IN E

FFE

CT

: ST

RE

AM

MA

IN E

FFE

CT

: ST

RE

AM

SSdf

MS

Fp

SSdf

MS

Fp

Eff

ect

0.12

7395

10.

1273

950

2.10

3132

NS

Eff

ect

0.02

5623

10.

0256

230

2.52

5351

NS

Err

or2.

4835

2441

0.06

0574

Err

or0.

3855

6338

0.01

0146

MA

IN E

FFE

CT

ZO

NE

MA

IN E

FFE

CT

ZO

NE

SSdf

MS

Fp

SSdf

MS

Fp

Eff

ect

0.85

2148

10.

8521

4819

.865

050.

0001

Eff

ect

0.08

7695

10.

0876

9510

.301

330.

001

Err

or1.

7587

7041

0.04

2897

Err

or0.

3234

9238

0.00

8513

INT

ER

AC

TIO

N S

TR

EA

M×

ZO

NE

INT

ER

AC

TIO

N S

TR

EA

M×

ZO

NE

SSdf

MS

Fp

SSdf

MS

Fp

Eff

ect

1.17

7749

30.

3925

8310

.683

130.

0001

Eff

ect

0.11

8152

30.

0393

840

4.83

8426

0.01

0E

rror

1.43

3169

390.

0367

48E

rror

0.29

3035

360.

0081

40



WZ/FMS

Time (week)

0 2 4 6 8

TO

Cm

g/g

150

200

250

300

350

400

450

500

DZ/CMS

0 2 4 6 8

TO

Cm

g/g

150

200

250

300

350

400

450

500OSBB

DZ/FMS

0 2 4 6 8

TO

Cm

g/g

150

200

250

300

350

400

450

500

Time (week)

0 2 4 6 8

TO

Cm

g/g

0

100

200

300

400

500WZ/CMS

Figure 2. Concentrations of total organic carbon (TOC) of ash litter in two biotopes: dry zone (DZ) andwet zone (WZ) in two bag types: coarse mesh bags (CMS) and fine mesh bags (FMS) in two streams:

Oberer Seebach (OSB) and Brzezowka (B). Bars with standard deviation (n = 3 for each bar).

Stream Zone Bag Model R2 pType

BRZ DZ CMS L 0.30 0.05BRZ DZ FMS L 0.73 0.01BRZ WZ CMS E 0.76 0.001BRZ WZ FMS E 0.81 0.001OSB DZ CMS L 0.51 0.01OSB DZ FMS L 0.63 0.01OSB WZ CMS E 0.53 0.01OSB WZ FMS E 0.63 0.01

Table 3. Regression results for ash tree breakdown (% of AFDM remaining) versus timefor two streams (BRZ – Brzezówka, OSB – Oberer Seebach), in two zones (DZ – dry zone,WZ – wet zone), and in two bag types (CMS – coarse and FMS – fine). For DZ linear model

(L) was used, and for WT exponential (E) regression model was used.



bags (three way ANOVA) between streams and zones (Table 4). Among two chemicalparameters and two bag types only one interaction (i.e. TN in CMS bags) of three effects(stream × zone × time) was significant at p < 0,01.

5. Discussion

In one of the most extensive studies of leaf breakdown in aquatic systems, PETERSEN andCUMMINS (1974) found that plants present a hierarchy of species in terms of processing ina continuum, grouped according to plant family. According to this continuum, the tree leaveswere placed into three processing groups: fast, medium and slow. The family Oleaceaebelongs to the medium – fast decomposing woody plant group (BOULTON and BOON, 1991).

The breakdown of ash tree leaves was relatively fast (sensu PETERSEN and CUMMINS,1974), especially in the first study period (i.e. 2–4 weeks after exposition, Fig. 1). This

DZ/ CMS

0 2 4 6 8

TN

mg/

g

10

20

30

40

OSBB

DZ/FMS

0 2 4 6 8

TN

mg/

g

10

20

30

40

WZ/CMS

Time (week)

0 2 4 6 8

TN

mg/

g

10

20

30

40WZ/FMS

Time (week)

0 2 4 6 8

TN

mg/

g

10

20

30

40

Figure 3. Concentrations of total nitrogen (TN) of ash litter in two biotopes: dry zone (DZ) and wetzone (WZ) in two bag types: coarse mesh bags (CMS) and fine mesh bags (FMS) in two streams:

Oberer Seebach (OSB) and Brzezowka (B). Bars with standard deviation (n = 3 for each bar).



CM

S ba

gs o

nly

TO

CT

N

Fact

ors:

SSdf

MS

Fp

Fact

ors:

SSdf

MS

Fp

STR

EA

M26

368.

191

2636

8.19

42.1

00.

0001

STR

EA

M2.

461

2.46

0.19

NS

ZO

NE

2412

7.10

124

127.

1038

.52

0.00

01Z

ON

E21

1.12

121

1.12

15.9

90.

001

TIM

E18

24.7

93

608.

260.

97N

ST

IME

184.

263

61.4

24.

650.

01ST

RE

AM

*ZO

NE

8886

.31

188

86.3

114

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0.00

1ST

RE

AM

*ZO

NE

0.20

10.

200.

01N

SST

RE

AM

*TIM

E56

62.3

83

1887

.46

3.01

0.05

STR

EA

M*T

IME

376.

393

125.

469.

500.

001

ZO

NE

*TIM

E18

78.4

33

626.

141.

00N

SZ

ON

E*T

IME

39.0

03

13.0

00.

98N

SST

RE

AM

*ZO

NE

*ST

RE

AM

*ZO

NE

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IME

4265

.69

314

21.9

02.

27N

ST

IME

214.

853

71.6

25.

420.

01E

rror

1691

1.16

2762

6.34

Err

or34

3.39

2613

.21

FMS

bags

onl

y

TO

CT

N

Fact

ors:

SSdf

MS

Fp

Fact

ors:

SSdf

MS

Fp

STR

EA

M54

73.7

61

5473

.76

12.9

40.

01ST

RE

AM

68.0

91

68.0

95.

630.

02Z

ON

E60

672.

371

6067

2.37

143.

390.

0001

ZO

NE

535.

991

535.

9944

.32

0.00

01T

IME

2915

.49

397

1.83

2.30

NS

TIM

E10

2.19

334

.06

2.82

NS

STR

EA

M*Z

ON

E50

5.07

150

5.07

1.19

NS

STR

EA

M*Z

ON

E12

2.71

112

2.71

10.1

50.

01ST

RE

AM

*TIM

E33

44.9

83

1114

.99

2.64

NS

STR

EA

M*T

IME

28.7

13

9.57

0.79

NS

ZO

NE

*TIM

E36

1.24

312

0.41

0.28

NS

ZO

NE

*TIM

E39

.74

313

.25

1.10

NS

STR

EA

M*Z

ON

E*

STR

EA

M*Z

ON

E*

TIM

E24

11.4

63

803.

821.

90N

ST

IME

45.3

13

15.1

01.

25N

SE

rror

1142

4.12

2742

3.12

Err

or32

6.56

2712

.09

Tab

le 4

.R

esul

ts f

or t

ree-

way

AN

OV

A (

fact

ors:

str

eam

, zon

e, a

nd t

ime)

for

tot

al o

rgan

ic c

arbo

n (T

OC

) an

d to

tal

nitr

ogen

(T

N)

in c

oars

e m

esh

bags

(C

MB

) an

d in

fin

e m

esh

bags

(FM

S) o

f as

h tr

ee l

eave

s un

der

stud

y. L

evel

of

sign

ific

ance

at

p<

0,05

, N

S –

non

sign

ific

ant.



process was fast despite low water temperatures and low nutrients concentration in bothstudy areas. It is possible that the use of freshly fallen leaves may have affected the break-down and may caused high leaching of the used material in wet zones (TAYLOR and BÄR-LOCHER, 1996; GESSNER et al., 1989, 1999). Besides, the rapid leaf decomposition (coarse-mesh bags) could be also explained by their potentially higher susceptibility to currentmotion, physical abrasion, and macroinvertebrate activity (MERRITT and LAWSON, 1992). Itseems that the higher litter breakdown in the Brzezówka stream (mainly for CMS bags) asin Oberer Seebach was caused also by higher water conductivity and nutrient concentrations(N and P, Table 1). Comparison of ash breakdown in different bags will be a subject of otherpublication which will consider also benthic invertebrates.

Carbon and nitrogen concentrations in the studied fresh ash tree leaves showed a similargradual increase (Figs. 2 and 3) typical of dead, decomposing plant material in both, aquat-ic and terrestrial ecosystems. This result may suggest that microbial colonization (biofilms)of the fresh leaves was not particularly hampered by the unaltered cuticle or functionaldefence mechanisms (GESSNER et al., 1991).

In this study significant differences for TOC and for TN between streams were found(Table 3). Among many internal factors that produce differences in leaf taxa processing instreams (i.e. nutrients, fiber content, and chemical inhibitors), nitrogen is the one thought tohave the most effect on breakdown rates. KAUSHIK and HYNES (1971) have shown that treeleaves with higher initial nitrogen concentrations break down faster than leaves with lownitrogen content. The initial nitrogen content of Fraxinus excelsior was low (7 mg/g DW),comparing published data on other leaf species. In contrast to our study, PEREIRA et al.(1998) reported higher initial nitrogen content for Alnus (46.8 mg/g), Eucalyptus (20.9), andPopulus (19.7) from southern Europe. The general pattern of nitrogen dynamics was simi-lar for both, streams/zones and bag types. The trend was observed that leaf nitrogen contentincreased during the early phase of decomposition, with maximum values during the mid-dle phase and later decreased during the last phase. Similar observations were made for otherleaf species in Mediterranean ecosystems (PEREIRA et al., 1998).

In conclusion, the comparison of two stream ecosystems and two biotopes showed dis-tinct differences in ash leaf breakdown and nutrient concentration. To what extent theseparameters reflect concepts of functioning of organic matter processing in stream ecosys-tems remains subject to testing as well as to further discussions. The further studies are need-ed to evaluate the breakdown of different other leaf species and all biotopes considered asa mosaic of ecosystems.

6. Acknowledgements

Water chemical procedures were carried out by T. KYSELA and A. BIRGER (Cracow) and chemicalanalyses of leaves by W. FAHRNER (Lunz). This bilateral project (No 9A-1999) was funded partially bythe State Committee for Scientific Research in Warsaw and the Austrian Academic Exchange Servicein Vienna. The authors thank G. BRETSCHKO (the Biological Station Lunz) and J. STARMACH (Karol Star-mach Institute of Freshwater Biology in Cracow) for logistic support.

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Ash Tree Leaf Litter (Fraxinus excelsior L.) Breakdown in Two Different Biotopes and Streams