Leaf-litter breakdown in 3 streams in temperate, Mediterranean, and tropical Cerrado climates

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Leaf-litter breakdown in 3 streams in temperate Mediterranean and tropicalCerrado climatesAuthor(s) Joseacute F Gonccedilalves Jr Manuel A S Graccedila Marcos CallistoSource Journal of the North American Benthological Society 25(2)344-355 2006Published By The Society for Freshwater ScienceDOI httpdxdoiorg1018990887-3593(2006)25[344LBISIT]20CO2URL httpwwwbiooneorgdoifull1018990887-359328200629255B3443ALBISIT5D20CO3B2

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J N Am Benthol Soc 2006 25(2)344ndash355 2006 by The North American Benthological Society

Leaf-litter breakdown in 3 streams in temperate Mediterraneanand tropical Cerrado climates

Jose F Goncalves Jr1

Laboratorio de Ecologia de Bentos Departamento de Biologia Geral Instituto de Ciencias BiologicasUniversidade Federal de Minas Gerais CP 486 CEP 30161-970 Belo Horizonte Minas Gerais Brazil

Manuel A S Graca2

Instituto do Mar IMAR - Dep de Zoologia Universidade de Coimbra 3004-517 Coimbra Portugal

Marcos Callisto3


Abstract The objectives of our study were to assess leaf-litter breakdown in 3 streams in 3 climates and todetermine the contributions of associated microbial and invertebrate communities to the process Weincubated leaves of Alnus glutinosa in 1 stream in each of 3 climate zones temperate (mountains of CentralPortugal) Mediterranean (South Portugal) and tropical Cerrado (Minas Gerais Brazil) Leaf-litterbreakdown rates (d) were faster in temperate (k frac14 0023ndash0017) than in tropical (k frac14 0014) orMediterranean (kfrac14 0014ndash0009) streams Leaf-litter breakdown rates (degree day) also were higher in thetemperate stream (k frac14 00018ndash00032) and similar between the other 2 streams (k frac14 0008ndash00012)Colonization of leaves by aquatic hyphomycetes was faster in the temperate stream (maximum frac14 421 lgergosterolg of leaf by day 24) than in the tropical Cerrado or Mediterranean streams However peakergosterol content was highest in the tropical Cerrado stream (573 lgg on day 75) Ergosterol content waslowest in the Mediterranean stream (maximumfrac14 341 lgg on day 7) Total microbial biomass (as ATP) washigher in the tropical Cerrado stream (maximum frac14 531 nmolesg on day 75) than in the Mediterranean(maximumfrac14 108 nmolesg on day 92) and temperate (maximumfrac14 93 nmolesg on day 7) streams Theseresults suggest either that not all microorganisms associated with leaves were involved in leaf-litterbreakdown or that other less efficient microorganisms than fungi were involved in leaf-litter breakdown inthe tropical stream Leaves exposed to invertebrates (coarse-mesh bags) decomposed significantly fasterthan leaves protected from invertebrate feeding (fine-mesh bags) only in the temperate stream This resultsuggests that invertebrates were important mediators of leaf-litter breakdown only in the temperate streamA larger proportion of invertebrates recovered from decomposing leaves were shredders in the temperatestream (nearly 5) than in the Mediterranean (1) and tropical Cerrado (0) streams Leaf-litter processingrates increased with discharge and NO3 concentration in the water Our results suggest that the positiveeffect of temperature on breakdown rates of allochthonous organic matter in streams can be overridden bynutrient content in the water and the presence of invertebrate shredders

Key words Savannah stream Cerrado aquatic hyphomycetes litter breakdown decomposition leaflitter

Food webs in forested headwater streams aresustained by organic matter from the riparian zoneTherefore litter decomposition is a key process linkingnutrient cycling energy transfer and trophic inter-

actions (Benfield 1997 Wallace et al 1997 Rosemondet al 2002) In general leaf-litter breakdown includesleaching of soluble compounds microbial decomposi-tion and conditioning and feeding by aquatic inver-tebrates The relative importance of microbes andinvertebrates in leaf-litter breakdown seems to varyacross systems (Eggert and Wallace 2003 reviews byGraca 2001 Abelho 2001)

1 E-mail addresses jfjunioricbufmgbr2 mgracaciucpt3 callistoicbufmgbr

344

Among microorganisms aquatic hyphomycetes arethe most important decomposers in terms of biomassand activity (Baldy and Gessner 1997 Pascoal andCassio 2004) Microbial communities enhance thequality of litter for invertebrate consumers becausethey have the capacity to break down structuralcompounds such as cellulose and lignin They alsotake nutrients from the water column and incorporatethem into the biofilm thereby increasing leaf nutrientcontent especially N and P (Graca 1993 Gessner et al1999 Haapala et al 2001) Litter consumption byinvertebrates is affected by intrinsic characteristics ofleaves and by microbial colonization of leaves (Rob-inson et al 1998 Graca 2001)

Most studies on leaf processing have been done intemperate deciduous forests (eg reviews by Abelho2001 Graca 2001) but the few studies in tropicalstreams have shown that litter breakdown also can beaffected by land use (Mathuriau and Chauvet 2002Chara 2003) and nutrient availability (Pearson andConnolly 2000 Rosemond et al 2002) The significanceof invertebrates and microbial communities in detritalprocessing in the tropics remains unclear Some studiessuggest that an important difference between temper-ate and tropical systems is the low abundance ofshredders in the tropics (eg Irons et al 1994 Wantzenet al 2002 Goncalves et al 2004 Wantzen and Wagner2006 and references therein) whereas others havesuggested that the apparent lack of shredders intropical studies reflects sampling deficiencies thatcause very large consumers particularly crabs (Want-zen et al 2002 Dobson 2004 Crowl et al 2006) to beundersampled or missed altogether Several recentstudies have shown that invertebrate shredders havean important role in litter processing in some tropicalsystems (eg Crowl et al 2001 2006 Cheshire et al2005) and that tropical invertebrate shredders areselective feeders (Rincon and Martınez 2006)

Tropical savannah (Cerrado) covers 1783200 km2 incentral Brazil Cerrado is the 2nd-largest biome inBrazil (after the tropical rain forest) and accounts for21 of the area of Brazil but it is under agriculturalpressure (Sano and Almeida 1998) Cerrado has apronounced dry season and it supports a unique arrayof 10000 drought- and fire-adapted species of plantsincluding 4400 endemics (Giulietti 1997) Streams arefrequently bordered by riparian trees but studies oforganic-matter dynamics in Cerrado systems areextremely scarce (but see Ciglasch et al 2004)Wantzen and Wagner (2006) showed that litter inputin Cerrado streams is comparable to input in thetemperate zone but shredders are scarce Streams inthe Cerrado generally have extremely low conductiv-ity and buffering capacity (Wantzen 2003)

The Mediterranean climate is characterized by drysummers and mild winters Many streams and rivershave surface flow only in winter after the first rainsbecause of the precipitation regime and topography Insummer streams can be reduced to perennial poolsand some stream sections dry completely Leaf-litterbreakdown studies are scarce in Mediterranean-climatestreams but studies carried out in South Europe andNorth Africa (eg Casas and Gessner 1999 Cherguiand Pattee 1991a) have shown that some shredderstypical of temperate zones are absent in Mediterraneanzones although their trophic niche may be occupied byother consumers such as gastropods

Thus the role of aquatic invertebrate consumers inleaf-litter processing is unclear outside temperatesystems The goal of our study was to compare leaf-litter breakdown and the roles of microorganisms andinvertebrates in 3 streams located in different climatezones temperate Mediterranean and tropical CerradoWe tested 2 hypotheses 1) Leaf-litter breakdown ratesshould be fastest in the tropical stream and slowest inthe temperate stream because decomposition is largelya biotic process and temperature is a major factoraffecting metabolism 2) Streams from the 3 geographicareas do not differ in terms of shredder contribution toleaf-litter breakdown This null hypothesis was testedbecause the data regarding the importance of shreddersin litter processing is controversial

Study Area

The temperate stream was Sao Joao located in theLousa Mountains central Portugal (lat 40860N long88140W) at 230 m asl The experimental stretch was in a4th-order stream (4 m wide 15 cm deep) and wasshaded by a diverse canopy of riparian trees includingCastanea sativa Miller Quercus spp Pinus pinaster AitonAcacia dealbata Link and Eucalyptus globulus Labill

The Mediterranean stream was Oeiras located insouthern Portugal 5 km above the town of Almodovar(lat 378280N long 8810W) at 270 m asl The experimentalstretch was in a 4th-order intermittent stream (6 m wide50 cm maximum depth in pools) with no flow duringsummer The riparian vegetation was sparse andmainly composed of shrubs of Nerium oleander L

The tropical Cerrado stream was Indaia located inthe Serra do Cipo National Park south of theEspinhaco Cordillera State of Minas Gerais Brazil(lat 1981640S long 4383120W) at 1450 m asl Theexperimental reach was in a 3rd-order stream (25 mwide 30 cm deep) The stream is in the high Cerradowhich is dominated by grasses and shrubs Thevegetation in the riparian zone is dense and mainlyconsists of Augusta longifolia (Spreng) Erythroxylum

2006] 345EFFECT OF CLIMATE ON LEAF-LITTER BREAKDOWN

pelleterianum St Hil Miconia chartacea Triana Miconiacyathanthera Triana Myrcia guyanensis (Aubl) DCOcotea lacifolia (Schott) Mez and Protium brasiliense(Spreng) Engl Rains occur from October to April

Methods

Leaf-litter breakdown experiments

The fine- and coarse-mesh-bags approach was usedto assess the role of invertebrates and microbes in leafprocessing This method can be criticized as unnaturaland some invertebrates are not prevented from enter-ing fine-mesh bags (eg Boulton and Boon 1991) butit is a standard widely accepted method used todifferentiate microbial from invertebrate litter process-ing Leaves of alder (Alnus glutinosa) were usedbecause information about decomposition of thisspecies in the Northern Hemisphere is readily avail-able and its breakdown is fast (Abelho 2001) Freshlyfallen leaves were collected from the ground under agroup of trees near Coimbra Portugal in autumn 2002and stored dry in boxes Air-dried leaves wereweighed into 30 6 01 g sets and enclosed in 20 3

20-cm bags (10-mm [coarse] and 05-mm [fine] mesh)Leaf-litter breakdown experiments ran from No-

vember to December 2002 in the temperate stream(incubation periods of 1 7 24 and 35 d) from October2002 to January 2003 in the Mediterranean stream(incubation periods of 1 7 15 30 51 and 92 d) andfrom May to July 2003 in the Cerrado stream(incubation periods of 1 7 15 30 45 and 75 d) Dateswere selected to coincide with the period of peak litterfall in all zones and the experiments were adjusted torun until 75 of the initial leaf mass was lost

Three leaf bags were retrieved from each stream oneach sampling date Leaf bags were transferred toplastic zip-lock bags and transported to the laboratoryin ice chests In the laboratory the bags weredisassembled and the leaves were washed gentlywith running tap water over a sieve (120-lm mesh) toremove debris and invertebrates The invertebratesretained on the sieve were preserved in alcohol forlater identification and classification into functionalfeeding groups according to Merritt and Cummins(1996) and Tachet et al (1987)

Three sets of 5 leaf disks were cut from the leaves ineach bag with a cork borer (7-mm diameter) The discswere obtained from contiguous areas of the leavesavoiding the main ribs One set of disks was used fordetermination of fungal biomass (mass of ergosterolsee below) the 2nd was used for determination of ATPcontent (see below) and the 3rd was used formeasurement of ash-free dry mass (AFDM oven driedat 608C to constant mass weighed burned at 5008C for

4 h and reweighed) Leaf material remaining afterremoval of the disks was dried weighed burned in amuffle furnace and weighed again to determineAFDM The mass of the disks which was estimatedby multiplying the AFDM of the 3rd set of disks 3 3was added to the mass of leaf material remaining afterremoval of the disks

The breakdown rate coefficient (k) was determinedusing the exponential decay model Wtfrac14W0endashkt whereWt is the final mass of leaf material W0 is the initialmass of leaf material and t is time (d) Calculationsalso were made using time expressed as degree days(dd computed from values of mean water temper-atures)

Microorganisms

Fungal biomassmdashFungal biomass was evaluated byergosterol content Sets of disks were preserved in 10mL of methanol and stored in the dark at 48CErgosterol was extracted by lipid extraction andsaponification at 808C for 30 min followed bypurification of the crude extract by solid-phaseextraction The extracted lipids including ergosterolwere partitioned into a nonpolar phase evaporated todryness resuspended in methanol and filteredErgosterol was quantified with HPLC (DIONEXSummit P580) and values were expressed as lgergosterolg leaf litter AFDM (Gessner 2005)

Microbial biomassmdashATP content was used as anindicator of total microbial biomass ATP was ex-tracted from sets of disks with 5 mL of 12 N H2SO4

containing 8 gL oxalic acid and 5 mL HEPES bufferThe sample was homogenized centrifuged neutral-ized with NaOH and stored frozen ATP wasquantified by the firefly bioluminescence methodaccording to Abelho (2005)

Environmental variables

Temperature pH conductivity and dissolved O2

(DO) were measured with field meters at the begin-ning middle and end of each experiment Currentvelocity (Braystoke BFM002 current meter ValeportTotnes UK) was measured at a uniform section of thesite and discharge was calculated from velocitystream width and depth measurements Water (1 L)was collected from the temperate and Mediterraneansites in clean plastic bottles and transported to thelaboratory in an ice chest In the laboratory the waterwas filtered (048-lm glass-fiber filter) and used fordetermination of alkalinity (titration to pH 45 APHA1998) and NO3 and PO4 content (Dionext ion analyzerSunnyvale California) Data for the tropical Cerradostream were taken from Callisto et al (2004)

346 [Volume 25J F GONCALVES ET AL

Data analysis

Analysis of covariance (ANCOVA) was used to testfor differences in leaf-litter breakdown rates betweencoarse- and fine-mesh bags and among the 3 streamsTukeyrsquos tests were used to compare slopes amongtreatments The assumption was made that invertebratecolonization increased linearly with time ANCOVAwas used to compare the rate of colonization of leaf bagsin the 3 streams after testing for normality (Komogor-ovndashSmirnov) and log(x thorn1) transformation of inverte-brate densities Ergosterol and ATP data were used asdependent variables to compare microbial colonizationamong streams and between litter-bag mesh sizes Eachvariable was log transformed and independentlysubjected to a mixed within-block ANOVA usingstream and mesh size as between-block factors andsampling time as the within-block factor (Zar 1996)

Results

Leaf-litter breakdown

Leaf-litter breakdown rates were faster in thetemperate (k frac14 0030ndash0017) than in the tropicalCerrado (k frac14 0014) or Mediterranean (k frac14 0014ndash0009) streams in both coarse- and fine-mesh bags(ANCOVA Ffrac14 866 pfrac14 00001 Table 1 Fig 1A) Leaf-litter breakdown rates differed between coarse- andfine-mesh bags in the temperate stream but not in theMediterranean or tropical Cerrado streams (Tukeyrsquostest p 005) When leaf-litter breakdown rates werecorrected for temperature (ie calculated using dd)leaf-litter breakdown rates were faster in the temperatestream than in the Mediterranean stream and faster inthe Mediterranean stream than in the tropical Cerradostream (ANCOVA F frac14 480 p frac14 00006 Tukeyrsquos testp 005 Table 1 Fig 1B)

Microorganisms

Fungal biomassmdashLeaves had initial values of 12 lgergosterolg suggesting some microbial colonizationbefore incubation in the streams Ergosterol contentdid not differ between leaves incubated in fine- andcoarse-mesh bags (ANOVA Ffrac14 036 pfrac14 055) so datafrom both bags were pooled Colonization of leaves byaquatic hyphomycetes (evaluated by ergosterol con-tent) was fastest in the temperate stream andergosterol content reached 421 lgg on the 24th dayof incubation (Fig 2) In the Mediterranean streamergosterol content reached 341 lgg by day 7 butdecreased afterwards In the tropical Cerrado streamergosterol content increased slowly and consistentlyand reached 573 lgg by day 75 Ergosterol contentdiffered significantly among streams (ANOVA F frac14

832 p frac14 0001) and ergosterol content was higher inthe temperate stream than in the Mediterranean ortropical Cerrado streams (Tukeyrsquos test p 005)

Microbial biomassmdashATP content of leaves (an in-dicator of total microbial biomass) did not differbetween leaves incubated in fine- and coarse-meshbags (ANOVA F frac14 021 p frac14 065) so data from bothbags were pooled ATP content was highest in thetropical Cerrado stream (531 nmolesg by day 75Fig 3) In the Mediterranean and temperate streamsmaximum values were 108 nmolesg (on day 92) and93 nmolesg (on day 7) respectively ATP contentdiffered significantly among streams (ANOVA F frac142610 p frac14 00001) and was higher in the tropicalCerrado stream than in the temperate or Mediterra-nean streams (Tukeyrsquos test p 005)

Invertebrates

Fine-mesh bags did not prevent invertebrates fromcolonizing leaves However invertebrates colonizingfine-mesh bags (mainly Chironomidae and Oligochae-ta) were very small (Table 2) Colonization of leaves byinvertebrates was greater in the temperate stream thanin the Mediterranean and tropical Cerrado streams(ANCOVA Ffrac14 881 pfrac14 000033 Fig 4) Chironomidswere the most abundant invertebrates colonizingleaves in all 3 streams Shredders made up 5 ofthe taxa in the temperate stream (NemouridaeLepidostomatidae Leuctridae) 1 in the Mediterra-nean stream (Leuctridae Nemouridae [within Otherscategory]) and they were absent from the tropicalCerrado stream (Table 2)


Streams were similar in terms of width but theydiffered markedly in chemical characteristics anddischarge (Table 3) The pH of temperate and

TABLE 1 Leaf-litter breakdown rates (k) and correlationcoefficients (R2) for Alnus glutinosa leaves in coarse- (10 mm)and fine- (05 mm) mesh bags in the temperate Mediterra-nean and tropical Cerrado streams Exponential regressionswere calculated for leaf mass loss relative to time expressedas days or degree days (dd)

Time (d) Time (dd)

Location Mesh k R2 k R2

Temperate Coarse 00295 0976 00032 0998Fine 00166 0974 00018 0975

Mediterranean Coarse 00137 0791 00012 0704Fine 00093 0812 00008 0905

Tropical Cerrado Coarse 00136 0960 00009 0960Fine 00143 0906 00009 0919


Mediterranean streams was neutral whereas the pH ofthe tropical Cerrado stream was low The alkalinities ofthe tropical Cerrado and Mediterranean streams weresimilar whereas the alkalinity of the temperate streamwas comparatively low The conductivities of thetropical Cerrado and temperate streams were similar(6ndash39 lScm) but the conductivity of the Mediterra-nean stream was much higher (401 lScm) NO3

content of the temperate stream was higher than thatof the tropical Cerrado stream (070 vs 005 mgL N-NO3) whereas PO4 content of the tropical Cerradostream was higher than that of the temperate stream(001 vs 250 lgL P-PO4 Table 3) Discharge valuesreflected the seasonality of the systems (range 0001 to418 m3s across streams) The experiment coincidedwith the period of high precipitation in the temperate

FIG 1 Mean (61 SE) mass loss relative to time expressed as days (A) and degree days (dd B) of Alnus glutinosa leaves duringleaf-litter breakdown experiments in 3 streams from temperate Mediterranean and tropical Cerrado climates


and Mediterranean streams and with the period of lowprecipitation in the tropical Cerrado stream

Discussion

Leaf-litter breakdown rates

Values of k in the temperate stream were similar tothose previously obtained with A glutinosa in the sametemperate stream (our study k frac14 00166 in fine-meshbags Canhoto and Graca 1996 kfrac14 00161 in fine-meshbags) Values of k obtained in the Mediterranean andtropical Cerrado streams (00093 to 00143) were in thelower range of values reported for this species in

temperate regions (k frac14 00123 see review by Abelho2001) In contrast to our results Irons et al (1994)reported higher decomposition rates of Alnus crispa instreams in Costa Rica than in Alaska and Michigan Inthe Colombian Andes Mathuriau and Chauvet (2002)reported very high leaf-litter breakdown rates for 2tropical leaf species (k frac14 00235 to 00651 mean watertemperature frac14 198C) Similar to our results Chara(2003) reported low decay rates for leaves of somenative species (eg k frac14 00008 to 00645) in streams inthe Colombian Andes (1500 m asl)

However leaf-litter breakdown rates are stronglydependent on leaf chemistry and physical properties

FIG 2 Mean (61 SE) ergosterol content of Alnus glutinosa leaves during leaf-litter breakdown experiments in 3 streams fromtemperate Mediterranean and tropical Cerrado climates (values from fine- and coarse-mesh bags pooled nfrac14 6) AFDMfrac14 ash-freedry mass

FIG 3 Mean (61 SE) ATP content of Alnus glutinosa leaves during leaf-litter breakdown experiments in 3 streams fromtemperate Mediterranean and tropical Cerrado climates (values from fine- and coarse-mesh bags pooled nfrac14 6) AFDMfrac14 ash-freedry mass


(eg Ostrofsky 1997) so comparison of rates amongstudies using different leaf types should be interpretedwith caution We were able to isolate the effects ofclimate (or geography) by comparing breakdown ratesof the same leaf species using the same methods acrossstreams in different climates (locations) If temperaturewere the main factor determining leaf-litter break-down rates then we would expect leaf-litter break-down rates to be fastest in the tropical Cerrado andslowest in the temperate stream Contrary to our initialhypothesis the fastest leaf-litter breakdown rates forA glutinosa were obtained in the temperate streamand lower rates were obtained in the Mediterraneanand the tropical Cerrado streams Similar results werereported by Chergui and Pattee (1991b) who foundthat leaves of Salix sp did not decompose faster in aMediterranean stream (water temperaturefrac14208C) thanstreams in more temperate climates The temperatureeffect apparently was overridden by other factors inour 3 streams We suggest that 2 of these factors couldhave been 1) microbial colonization constrained by

flow-related conditions and water chemistry and 2)invertebrate feeding activities constrained by biogeo-graphical factors

Microbial colonization

Fungal colonization judged by ergosterol contentwas very fast in the temperate stream (24 d) Fungalcolonization was too slow in the tropical Cerradostream to reach levels comparable to those on leaves inthe temperate stream within 45 d although ergosterolvalues measured at the end of the experiment in thetropical Cerrado stream were higher than thoseobtained for the temperate stream Leaf-litter break-down rates were fast in the temperate stream slowerin the tropical Cerrado stream and slowest in theMediterranean stream where leaf ergosterol contentalso was lowest The observation that the only streamwhere fungi accumulated quickly (the temperatestream) also was the stream with fast leaf-litterbreakdown rates is consistent with the notion that

TABLE 2 Mean densities and relative abundances of invertebrates colonizing leaves of Alnus glutinosa in coarse- (10 mm) andfine- (5 mm) mesh bags in 3 streams in temperate Mediterranean and tropical Cerrado climates Shrfrac14 shredder AFDMfrac14 ash-freedry mass

Location Mesh Taxon Density (nog leaf AFDM) Relative abundance ()

Temperate Coarse Chironomidae 320 79Baetidae 13 3

Empididae 9 2Hydropsychidae 9 2

Nemouridae (Shr) 9 2Lepidostomatidae (Shr) 5 1

Leuctridae (Shr) 4 1Others 271 10

Fine Chironomidae 141 74Oligochaeta 14 7

Acarina 14 7Baetidae 6 3


Others 13 7Mediterranean Coarse Chironomidae 333 58

Oligochaeta 175 30Elmidae 28 5Others 37 7

Fine Chironomidae 81 40Oligochaeta 61 30Copepoda 26 13Ostracoda 13 6

Others 23 11Tropical Cerrado Coarse Chironomidae 209 88

Copepoda 18 7Cladocera 7 3

Others 4 2Fine Chironomidae 386 96

Cladocera 12 3Others 5 1


aquatic hyphomycetes are the microorganisms thatplay a key role in the breakdown of leaves in streams

If total microbial biomass estimated from ATPcontent increases with no equivalent increase inergosterol the implication is that microorganismsother than fungi are accumulating biomass in decom-posing leaves Bacteria could be an important compo-nent of the microbiota but their role in the initialstages of leaf-litter breakdown is controversial (egBaldy and Gessner 1997 McArthur and Tuckfield1997 Hieber and Gessner 2002 Pascoal and Cassio2004) at least in temperate streams High ATP alsocould be attributed to other microorganisms such asOomycetes (lacking ergosterol) and protozoans buttheir participation in leaf decomposition is unclear (butsee Ribblett et al 2005) Total microbial biomass wasgreatest on leaves in the tropical Cerrado stream but

the microorganisms involved seem to have had limitedcapabilities to decompose alder leaves because leaf-litter breakdown was slow in this stream In a similarexperiment in another Cerrado stream and also usingleaves of A glutinosa Wantzen and Wagner (2006)reported breakdown rates three times faster (kfrac14 0035)than in our experiment They also found that break-down rates were 4x faster in the Cerrado than in atemperate stream in Germany We do not know whythe 2 studies differed but the differences could partlybe explained by differences in temperature (lower inour study) and water chemistry particularly N (nodata provided by Wantzen and Wagner 2006)

Flow-related conditionsmdashOverall microbial coloniza-tion (ATP and ergosterol content) was low in theMediterranean stream consistent with the low leaf-litter breakdown rates obtained However aquatic

TABLE 3 Mean (range) values of environmental variables in 3 streams in temperate Mediterranean and tropical Cerradoclimates

Variables Temperate Mediterranean Tropical

pH 70 71 53(67ndash74) (114ndash128) (46ndash60)

Dissolved O2 (mgL) 121 107 86(114ndash128) (78ndash136) ndash

Alkalinity (lg CaCO3L) 41 344 216ndash (269ndash419) ndash

Conductivity (lScm) 395 401 6(39ndash40) (398ndash404) (5ndash7)

Temperature (8C) 106 133 155(124ndash75) (65ndash200) (145ndash165)

PO4-P (lgL) 001 012 250NO3-N (mgL) 0702 0240 0050Discharge (m3s) 27 11 01

(117ndash418) (013ndash272) (0001ndash018)

FIG 4 Mean (61 SE) density of invertebrates in Alnus glutinosa leaves during leaf-litter breakdown experiments in 3 streamsfrom temperate Mediterranean and tropical Cerrado climates AFDM frac14 ash-free dry mass


hyphomycetes colonized leaves in other Mediterra-nean streams (eg Chergui 1990 Chergui and Pattee1990 1991a b Maamri et al 1998) Leaf-litter break-down rates in North African streams are slower inintermittent than in permanent sites and they areslower during the drought period than the wet period(Maamri et al 2001) Moreover microbial respiration islower in intermittent than in permanent stream sites inNorth Africa (Maamri et al 1999) and the activity anddiversity of aquatic hyphomycetes decreases duringthe summer (Maamri et al 1998) Absence of flow isnot favorable to aquatic hyphomycetes which needturbulence for reproduction (Chergui and Pattee 1990Suberkropp 1998) Our experiment took place at thebeginning of autumn when leaves had started fallingbut rain was still rare The study section of the streamhad only temporary flow and therefore the currentwas very slow Thus it is plausible that the low rate ofmicrobial colonization in the Mediterranean streamwas related to the timing of our experiment

Environmental factorsmdashThree environmental factors(DO NO3 and discharge) varied across the 3 streamsin a manner consistent with leaf-litter breakdownrates Low DO slows decomposition of leaf litter (egPascoal and Cassio 2004) However DO probably didnot affect leaf-litter breakdown rates in our experi-ments because differences among streams were cer-tainly related to differences in temperature whichaffected the solubility of O2 in the water Aquatichyphomycete growth decomposition activity andsporulation rates are stimulated by turbulence orwater motion (Chergui and Pattee 1990 Suberkropp1998) and nutrients are important in controllinggrowth biomass and decomposition by aquatichyphomycetes (Suberkropp and Chauvet 1995 Rose-mond et al 2002 Chadwick and Huryn 2003) NO3

content and discharge were both high in the temperatestream and could have acted synergistically topromote high leaf-litter breakdown rates NO3 contentwas low in the tropical Cerrado stream and dischargewas extremely low in the Mediterranean stream andthese factors may have constrained microbial coloni-zation Our results suggest that N was a moreimportant factor than P in controlling leaf-litter break-down rates but manipulative experiments will beneeded to address the relative importance of eachnutrient in the experimental streams (eg Gulis andSuberkropp 2003)

Differences in flow also could have caused differ-ences in rates of physical fragmentation of leaves Wecan not rule out this factor but Ferreira et al (2006)reported that current velocities up to 12 ms have aminor role in litter fragmentation in laboratory

channels and in temperate streams probably becauseleaves are protected inside the coarse-mesh bags

Invertebrate feeding activities

The influence of shredders on leaf-litter breakdownis well-known in temperate zones (eg Graca 2001Haapala et al 2001 Hieber and Gessner 2002) butpoorly documented in other areas The proportion ofshredders in the coarse-mesh bags in the temperatestream was low (our study 5 Graca et al 2001 in thesame stream 20ndash24 Fleituch 2001 in a differenttemperate stream 22ndash45) but shredders still weresignificantly more abundant in the temperate streamthan in the Mediterranean and tropical Cerradostreams The results were consistent with the lowproportion of shredders and high proportion ofpredators observed in another Cerrado stream (Want-zen and Wagner 2006)

In our study leaf-litter breakdown was faster incoarse- than in fine-mesh bags in the temperate streambut leaf-litter breakdown rates did not differ betweencoarse- and fine-mesh bags in the Mediterranean andtropical Cerrado stream Our results indicate thatinvertebrates played a role in leaf-litter breakdown inthe temperate stream but not in the Mediterranean ortropical Cerrado streams Irons et al (1994) suggestedthat the role of microbes in decomposition shouldincrease at lower latitudes and the paucity of shreddersin the Mediterranean and tropical Cerrado systemsindicates that the microbial community was mainlyresponsible for leaf-litter breakdown in these systems

Some chironomids the most abundant group ofinvertebrates in the 3 geographic zones feed on leavesand may contribute to decomposition (Grubbs et al1995 Wantzen and Wagner 2006) Leaf-litter break-down rates did not differ between coarse- and fine-mesh bags in the tropical Cerrado stream in our studyso chironomid activities appear to have been unim-portant for leaf-litter breakdown

Biogeographical factorsmdashShredders often are rare orabsent in Mediterranean systems (Essafi et al 1994Maamri et al 1997 but see Chergui and Pattee 1991ab) Other studies in southern Portugal have reportedthe same paucity of shredders that we observed in theMediterranean stream (eg Graca et al 2004) Thisgeneral lack of shredders could be related to theextreme variations in flow conditions found in thesestreams In many Mediterranean areas precipitationoccurs only in winter and during most of the year thestreams are reduced to disconnected pools Theseconditions are not favorable to Plecoptera and manyTrichoptera rheophilic groups containing a largenumber of shredders


Shredders also are often rare or absent in sometropical systems (Mathuriau and Chauvet 2002Mouton and Magalhaes 2003 but see Cheshire et al2005) The low number of shredders in the tropicalCerrado stream in our study is consistent with reportsby Wantzen (2003) for other streams in the tropicalCerrado However Wantzen and Wagner (2006)reported that mining chironomids were able toconsume alder leaves quickly in another Cerradostream and speculated that shredders could eitheroccur briefly in a habitat when food is available or belocalized in small areas of the stream where leaves canpersist Unlike in other tropical systems (eg Covich etal 2003 Crowl et al 2006) crabs shrimps and fishesfeeding on litter were absent from the tropical Cerradostream in our study (Callisto et al 2001) Thus it isunlikely that our conclusion that shredders were notimportant to leaf-litter breakdown in the tropicalCerrado stream was a methods problem caused bycoarse-mesh bags excluding consumers of largedetritus (as suggested by Dobson 2004)

In summary rates of leaf-litter breakdown and therelative importance of organisms involved in decom-position differed among the 3 climategeographicalregions In the tropical Cerrado stream litter break-down was low presumably because of lack ofnutrients and invertebrate shredders In the Mediter-ranean stream decomposition also was slow probablybecause of slow water movement and an absence ofinvertebrate shredders Water temperature was lowerin the temperate stream but breakdown of leavesproceeded faster in the temperate stream than in theother 2 climates The temperate stream had compara-tively high nutrient content faster water movementand invertebrate shredders The contrasting resultsbetween our study and Wantzen and Wagner (2006)suggest that local environmental conditions could beas important as large geographic factors in determin-ing litter breakdown rates

Acknowledgements

JFG received scholarships from Conselho Nacionalde Desenvolvimento Cientıfico e Tecnologico (CNPq ndashBrazil) Coordenacao de Aperfeicoamento de Pessoalde Nivel Superior (CAPES ndash Brazil) and Instituto doMar (IMAR ndash Portugal) We thank the followinginstitutions for financial support CNPq (Proc47232801-8) Fundacao de Amparo a Pesquisa deMinas Gerais (FAPEMIG - Proc 108503) PADI-ProjectAWARE Foundation and the Portuguese ScienceFoundation (FCT - POCTI1999BSE32389) InstitutoBrasileiro do Meio Ambiente e dos Recursos NaturaisRenovaveis (IBAMA) and the US Fish and Wildlife

Service provided some logistical support We thankEric Pattee Christopher Swan Andrew BoultonPamela Silver and an anonymous referee for theircomments on earlier versions of the manuscriptClaudia Mieiro Joana DrsquoArc de Paula Jose PauloJuliana Franca Nuno Coimbra and Veronica Ferreiraassisted us in the field and laboratory

Literature Cited

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ABELHO M 2005 Extraction and quantification of ATP as ameasure of microbial biomass Pages 223ndash229 in M A SGraca F Barlocher and M O Gessner (editors)

Methods to study litter decomposition A practicalguide Springer Dordrecht The Netherlands

APHA (AMERICAN PUBLIC HEALTH ASSOCIATION) 1998 Standardmethods for the examination of water and wastewater20th edition American Public Health AssociationAmerican Waterworks Associationand Water Environ-

ment Federation Washington DC

BALDY V AND M O GESSNER 1997 Towards a budget of leaflitter decomposition in a first order woodland streamLife Sciences 320747ndash758

BENFIELD E F 1997 Comparison of litterfall input to streamsPages 104ndash108 in J R Webster and J L Meyer (editors)

Stream organic matter budgets Journal of the NorthAmerican Benthological Society 16

BOULTON A J AND P I BOON 1991 A review of methodologyused to measure leaf litter decomposition in loticenvironments time to turn over an old leaf AustralianJournal of Marine and Freshwater Research 421ndash43

CALLISTO M M GOULART A O MEDEIROS P MORENO AND CA ROSA 2004 Diversity assessment of benthic macro-invertebrates yeasts and microbiological indicatorsalong a longitudinal gradient in Serra do Cipo BrazilBrazilian Journal of Biology 641ndash12

CALLISTO M P MORENO AND F A R BARBOSA 2001 Habitat

diversity and benthic functional trophic groups at Serrado Cipo Revista Brasileira de Biologia 61259ndash266

CANHOTO C AND M A S GRACA 1996 Decomposition ofEucalyptus globulus leaves and 3 native leaf species (Alnusglutinosa Castanea sativa and Quercus faginea) in aPortuguese low order stream Hydrobiologia 33379ndash85

CASAS J J AND M O GESSNER 1999 Leaf litter breakdown ina mediterranean stream characterised by travertineprecipitation Freshwater Biology 41781ndash793

CHADWICK M A AND A D HURYN 2003 Effects of a whole-catchment N addition on stream detritus processingJournal of the North American Benthological Society 22

194ndash206

CHARA J D 2003 Interaction between biodiversity and landuse in low order stream catchments of the ColombianAndes PhD Thesis University of Stirling StirlingScotland

CHERGUI H 1990 The dynamics of aquatic hyphomycetes in


an eastern Moroccan stream Archiv fur Hydrobiologie118341ndash352

CHERGUI H AND E PATTEE 1990 The processing of leaves oftrees and aquatic macrophytes in the network of theRiver Rhone Internationale Revue der gesamten Hydro-biologie 75281ndash302

CHERGUI H AND E PATTEE 1991a An experimental study ofthe breakdown of submerged leaves by hyphomycetesand invertebrates in Morocco Freshwater Biology 2697ndash110

CHERGUI H AND E PATTEE 1991b Breakdown of allochtho-nous leaves in the catchment of the lower MoulouyaRiver in Morocco Acta Oecologica 12543ndash560

CHESHIRE K L BOYERO AND R C PEARSON 2005 Food websin tropical Australian streams shredders are not scarceFreshwater Biology 50748ndash769

CIGLASCH H J LILIENFEIN K KAISER AND W WITAKE 2004Dissolved organic matter under native cerrado and Pinuscaribaea plantation in Brazilian savannah Biochemistry67157ndash182

COVICH A P T A CROWL AND F N SCATENA 2003 Effects ofextreme low flows on freshwater shrimps in a perennialtropical stream Freshwater Biology 481199ndash1206

CROWL T A W H MCDOWELL A P COVICH AND S LJOHNSON 2001 Freshwater shrimp effects on detritalprocessing and nutrients in a tropical headwater streamEcology 82775ndash783

CROWL T A V WELSH T HEARTSILL-SCALLEY AND A PCOVICH 2006 Effects of different types of conditioning onrates of leaf-litter shredding by Xiphocaris elongata aNeotropical freshwater shrimp Journal of the NorthAmerican Benthological Society 25198ndash208

DOBSON M 2004 Freshwater crabs in Africa FreshwaterForum 213ndash26

EGGERT S L AND J B WALLACE 2003 Litter breakdown andinvertebrate detritivores in a resource-depleted Appala-chian stream Archiv fur Hydrobiologie 156315ndash338

ESSAFI K H CHERGUI E PATTEE AND J MATHIEU 1994 Thebreakdown of dead leaves buried in the sediment of apermanent stream in Morocco Archiv fur Hydrobiologie130105ndash112

FERREIRA V J L M A S GRACA J P LIMA AND R GOMES2006 Role of physical fragmentation and invertebrateactivity in the breakdown of leaves Archiv fur Hydro-biologie (in press)

FLEITUCH T 2001 Beech leaf breakdown and POM storagealong an altitudinal stream gradient International Re-view of Hydrobiology 86515ndash525

GESSNER M O 2005 Ergosterol as a measure of fungalbiomass Pages 189ndash195 in M A S Graca F Barlocherand M O Gessner (editors) Methods to study litterdecomposition A practical guide Springer DordrechtThe Netherlands

GESSNER M O E CHAUVET AND M DOBSON 1999 Aperspective on leaf litter breakdown in stream Oikos85377ndash384

GIULIETTI A M 1997 Flora diversidade distribuicao geo-grafica e endemismo Pages 84ndash100 in G W Fernandes

(editor) Serra do Cipo ecologia e evolucao EdicaoVozes Rio de Janeiro Brazil

GONCALVES J F A M SANTOS AND F A ESTEVES 2004 Theinfluence of the chemical composition of Typha domi-ngensis and Nymphaea ampla detritus on invertebratecolonization during decomposition in a Brazilian coastallagoon Hydrobiologia 527125ndash137

GRACA M A S 1993 Patterns and processes in detritus-based stream systems Limnologica 23107ndash114

GRACA M A S 2001 The role of invertebrates on leaf litterdecomposition in streams ndash a review InternationalReview of Hydrobiology 86383ndash393

GRACA M A S R C F FERREIRA AND C N COIMBRA 2001Litter processing along a stream gradient the role ofinvertebrates and decomposers Journal of the NorthAmerican Benthological Society 20408ndash420

GRACA M A S P PINTO R CORTES N COIMBRA S OLIVEIRAM MORAIS M J CARVALHO AND J MALO 2004 Factorsaffecting macroinvertebrate richness and diversity inPortuguese streams a two-scale analysis InternationalReview of Hydrobiology 89151ndash164

GRUBBS S A R E JACOBSEN AND K W CUMMINS 1995Colonization by Chironomidae (Insecta Diptera) on 3distinct leaf substrates in an Appalachian mountainstream Annales de Limnologie 31105ndash118

GULIS V AND K SUBERKROPP 2003 Interactions betweenstream fungi and bacteria associated with decomposingleaf litter and different levels of nutrient availabilityAquatic Microbial Ecology 30149ndash157

HAAPALA A T MUOTKA AND A MARKKOLA 2001 Breakdownand macroinvertebrate and fungal colonization of alderbirch and willow leaves in a boreal forest streamJournal of the North American Benthological Society 20395ndash407

HIEBER M AND M O GESSNER 2002 Contribution of streamdetritivores fungi and bacteria to leaf breakdown basedon biomass estimates Ecology 831026ndash1038

IRONS J G M W OSWOOD R J STOUT AND C M PRINGLE1994 Latitudinal patterns in leaf litter breakdown istemperature really important Freshwater Biology 32401ndash411

MAAMRI A F BARLOCHER E PATTEE AND H CHERGUI 2001Fungal and bacterial colonisation of Salix pedicellataleaves decaying in permanent and intermittent streamsin eastern Morocco International Review of Hydro-biology 86337ndash348

MAAMRI A E CHAUVET H CHERGUI F GOURBIERE AND EPATTEE 1998 Microbial dynamics on decaying leaves in atemporary Moroccan river I Fungi Archiv fur Hydro-biologie 14441ndash59

MAAMRI A H CHERGUI AND E PATTEE 1997 Leaf litterprocessing in a temporary northeasten Moroccan riverArchiv fur Hydrobiologie 140513ndash531

MAAMRI A E PATTEE X GAYTE AND H CHERGUI 1999Microbial dynamics on decaying leaves in a temporaryMoroccan river II Bacteria Archiv fur Hydrobiologie144157ndash175

MATHURIAU C AND E CHAUVET 2002 Breakdown of leaf litter


in a neotropical stream Journal of the North AmericanBenthological Society 21384ndash396

MCARTHUR J V AND R C TUCKFIELD 1997 Informationlength spatial and temporal parameters among streambacterial assemblages Journal of the North AmericanBenthological Society 16347ndash357

MERRITT R W AND K W CUMMINS (EDITORS) 1996 Anintroduction to the aquatic insects of North America 3rd

edition KendallHunt Dubuque IowaMOULTON T P AND S A P MAGALHAES 2003 Responses of

leaf processing to impacts in streams in Atlantic rainforest Rio de Janeiro Brazil ndash a test of the biodiversityecosystem functioning relationship Brazilian Journal ofBiology 6387ndash95

OSTROFSKY M L 1997 Relationship between chemicalcharacteristics of autumn-shed leaves and aquaticprocessing rates Journal of the North American Bentho-logical Society 16750ndash759

PASCOAL C AND F CASSIO 2004 Contribution of fungi andbacteria to leaf litter decomposition in a polluted riverApplied and Environmental Microbiology 701ndash8

PEARSON R G AND N M CONNOLLY 2000 Nutrient enhance-ment food quality and community dynamics in a tropicalrainforest stream Freshwater Biology 4331ndash42

RIBBLETT S G M A PALMER AND D W COATS 2005 Theimportance of bacterivorous protists in the decom-position of stream leaf litter Freshwater Biology 50516ndash526

RINCON J AND I MARTINEZ 2006 Food quality and feedingpreferences of Phylloicus sp (TrichopteraCalamocerati-dae) Journal of the North American BenthologicalSociety 25208ndash215

ROBINSON C T M O GESSNER AND J V WARD 1998 Leafbreakdown and associated macroinvertebrates in alpineglacial streams Freshwater Biology 40215ndash228

ROSEMOND A D C M PRINGLE A RAMIREZ M J PAUL AND

J L MEYER 2002 Landscape variation in phosphorusconcentration and effects on detritus-based tropicalstreams Limnology and Oceanography 47278ndash289

SANO S M AND S P ALMEIDA (EDITORS) 1998 Cerradoambiente e flora EMBRAPA (Empresa Brasileira dePesquisa Agropecuaria)-CPAC Planaltina Distrito Fed-eral Brazil

SUBERKROPP K 1998 Microorganisms and organic matterdecomposition Pages 120ndash143 in R J Naiman and R EBilby (editors) River ecology and management lessonsfrom the Pacific Coastal ecoregion SpringerndashVerlagNew York

SUBERKROPP K AND E CHAUVET 1995 Regulation of leafbreakdown by fungi in streams influences of waterchemistry Ecology 761433ndash1445

TACHET H M BOURNAUD AND P RICHOUX (EDITORS) 1987Introduction a Lrsquoetude des macroinvertebres des eauxdouces (Systematique elementaire et apercu ecologique)Universite Lyon Lyon France

WALLACE J B S L EGGERT J L MEYER AND J R WEBSTER1997 Multiple trophic levels of a forest stream linked toterrestrial litter inputs Science 277102ndash104

WANTZEN K M 2003 Cerrado streams ndash characteristics of athreatened freshwater ecosystem type on the tertiaryshields of Central South America Amazonia Limnologiaet Oecologia Regionalis Systemae Fluminis Amazonas17481ndash502

WANTZEN K M AND R WAGNER 2006 Detritus processing byinvertebrate shredders a Neotrophicaltemperate com-parison Journal of the North American BenthologicalSociety 25216ndash233

WANTZEN K M R WAGNER R SUTFELD AND W J JUNK2002 How do plant-herbivore interactions of treesinfluence coarse detritus processing by shredders inaquatic ecosystems of different latitudes Verhandlun-gen der Internationalen Vereinigung fur theoretischeund angewandte Limnologie 28815ndash821

ZAR J H 1996 Biostatistical analysis 3rd edition PrenticendashHall Upper Saddle River New Jersey

Received 3 February 2005Accepted 27 January 2006


J N Am Benthol Soc 2006 25(2)344ndash355 2006 by The North American Benthological Society

Leaf-litter breakdown in 3 streams in temperate Mediterraneanand tropical Cerrado climates

Jose F Goncalves Jr1


Manuel A S Graca2

Instituto do Mar IMAR - Dep de Zoologia Universidade de Coimbra 3004-517 Coimbra Portugal

Marcos Callisto3


Abstract The objectives of our study were to assess leaf-litter breakdown in 3 streams in 3 climates and todetermine the contributions of associated microbial and invertebrate communities to the process Weincubated leaves of Alnus glutinosa in 1 stream in each of 3 climate zones temperate (mountains of CentralPortugal) Mediterranean (South Portugal) and tropical Cerrado (Minas Gerais Brazil) Leaf-litterbreakdown rates (d) were faster in temperate (k frac14 0023ndash0017) than in tropical (k frac14 0014) orMediterranean (kfrac14 0014ndash0009) streams Leaf-litter breakdown rates (degree day) also were higher in thetemperate stream (k frac14 00018ndash00032) and similar between the other 2 streams (k frac14 0008ndash00012)Colonization of leaves by aquatic hyphomycetes was faster in the temperate stream (maximum frac14 421 lgergosterolg of leaf by day 24) than in the tropical Cerrado or Mediterranean streams However peakergosterol content was highest in the tropical Cerrado stream (573 lgg on day 75) Ergosterol content waslowest in the Mediterranean stream (maximumfrac14 341 lgg on day 7) Total microbial biomass (as ATP) washigher in the tropical Cerrado stream (maximum frac14 531 nmolesg on day 75) than in the Mediterranean(maximumfrac14 108 nmolesg on day 92) and temperate (maximumfrac14 93 nmolesg on day 7) streams Theseresults suggest either that not all microorganisms associated with leaves were involved in leaf-litterbreakdown or that other less efficient microorganisms than fungi were involved in leaf-litter breakdown inthe tropical stream Leaves exposed to invertebrates (coarse-mesh bags) decomposed significantly fasterthan leaves protected from invertebrate feeding (fine-mesh bags) only in the temperate stream This resultsuggests that invertebrates were important mediators of leaf-litter breakdown only in the temperate streamA larger proportion of invertebrates recovered from decomposing leaves were shredders in the temperatestream (nearly 5) than in the Mediterranean (1) and tropical Cerrado (0) streams Leaf-litter processingrates increased with discharge and NO3 concentration in the water Our results suggest that the positiveeffect of temperature on breakdown rates of allochthonous organic matter in streams can be overridden bynutrient content in the water and the presence of invertebrate shredders

Key words Savannah stream Cerrado aquatic hyphomycetes litter breakdown decomposition leaflitter

Food webs in forested headwater streams aresustained by organic matter from the riparian zoneTherefore litter decomposition is a key process linkingnutrient cycling energy transfer and trophic inter-

actions (Benfield 1997 Wallace et al 1997 Rosemondet al 2002) In general leaf-litter breakdown includesleaching of soluble compounds microbial decomposi-tion and conditioning and feeding by aquatic inver-tebrates The relative importance of microbes andinvertebrates in leaf-litter breakdown seems to varyacross systems (Eggert and Wallace 2003 reviews byGraca 2001 Abelho 2001)

1 E-mail addresses jfjunioricbufmgbr2 mgracaciucpt3 callistoicbufmgbr

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Documents

Leaf-litter breakdown in 3 streams in temperate, Mediterranean, and tropical Cerrado climates