Amounts and degradability of dissolved organic carbon from foliar litter at different decomposition stages
Axel Don *,Karsten Kalbitz
Department of Soil Ecology,Bayreuth Institute for Terrestrial Ecosystem Rearch (BITO
¨K),University of Bayreuth,D-95440Bayreuth,Germany Received 18October 2004;received in revid form 18February 2005;accepted 29March 2005
Abstract
Litter is one of the main sources of dissolved organic carbon (DOC)in forest soils and litter decomposition is an important control of
carbon storage and DOC dynamics.The aim of our study was to evaluate (i)effects of tree species on DOC production and (ii)relationships between litter decomposition and the amount and quality of DOC.Five different types of leaves and needles were expod in litterbags at two neighboring forest sites.Within 12months we sampled the litterbags five times and leached aliquots of field moist litter in the laboratory.In the collected litter percolates we measured DOC concentrations and recorded UV a
nd fluorescence spectra in order to estimate the aromaticity and complexity of the organic molecules.Furthermore,we investigated the biodegradability of DOC from fresh and decompod litter during 6weeks incubations.Fresh sycamore maple litter relead the largest amounts of DOC reaching about 6.2%of litter C after applying precipitation of 94mm.We leached 3.9,1.6,1.0and 3.3%carbon from fresh mountain ash,beech,spruce and pine litter,respectively.In the initial pha of litter decomposition significantly decreasing DOC amounts were relead with increasing litter mass loss.However,after mass loss exceeds 20%DOC production from needle litter tended to increa.UV and fluorescence spectra of percolates from pine and spruce litter indicated an increasing degree of aromaticity and complexity with increasing mass loss as often described for decomposing litter.However,for deciduous litter the relationship was less obvious.We assume that during litter decomposition the source of produced DOC in coniferous litter tended toward a larger contribution from lignin-derived compounds.Biodegradability of DOC from fresh litter was very high,ranging from 30to 95%mineralized C.DOC from degraded litter was on average 34%less mineralizable than DOC from fresh litter.Taking into account the large DOC production from decompod needles we can assume there is an important role for DOC in the accumulation of organic matter in soils during litter decomposition particularly in coniferous forests.q 2005Elvier Ltd.All rights rerved.
Keywords:Dissolved organic carbon;Litter decomposition;Biodegradability;Fluorescence spectroscopy
1.Introduction
Foliar litter is the main input of organic carbon into forest soils and litter decomposition is one of the most important process determining the amount of organic C remaining in the forest floor (Berg et al.,2001).During litter decompo-sition parts are leached from the litter layer and percolate as dissolved organic carbon (DOC)into the mineral soil (Qualls and Haines,1991;Kalbitz et al.,2000).In some studies,the litter horizon is considered to be the most
important source of DOC in soils (Qualls and Haines,1991;Michalzik and Matzner,1999).During litter decomposition the specific surface area and the permeability of the litter will increas,leading to incread DOC leaching.DOC plays an important role in transport,mineralisation and stabilization of C in soils (Kalbitz et al.,2000).
There is a lack of knowledge concerning the effect of different tree species on the amount and quality of leached DOC from litter.In the laboratory,Kuiters and Mulder (1993)found the highest amounts of DOC leached from deciduous litter,whereas Strobel et al.(2001)extracted highest DOC a
mounts from spruce forest floor compared to beech,oak and grand fir.Michalzik et al.(2001)did not find a general trend comparing DOC concentrations and fluxes of coniferous and deciduous temperate forests.Besides tree species,the decomposition degree of litter should affect the amount and quality of DOC.Fresh litter releas
highly
Soil Biology &Biochemistry 37(2005)2171–2179
/locate/soilbio
0038-0717/$-e front matter q 2005Elvier Ltd.All rights rerved.doi:10.1016/j.soilbio.2005.03.019
*Corresponding author.Address:Max-Planck-Institute for Biogeochem-istry,P.O.Box 100164,D-07701Jena,Germany.Tel.:C 493641576184;fax:C 493641577863.
英语作文建议信E-mail address:adon@bgc-jena.mpg.de (A.Don).
soluble and readily degradable organic compounds(Norden and Berg,1990).In turn,the relative enrichment of lignin-derived compounds during litter decomposition(Norden and Berg,1990;Baldock et al.,1992)should result in DOC of a more aromatic character.The expected changes in DOC composition should affect its microbial stability becau lignin-derived compounds are the stable ones (Kalbitz et al.,2003a).However,effects of litter decompo-sition on DOC composition have not yet been studied becau soil water sampled in situ contains a mixture of DOC derived from organic matter with different decompo-sition stages.Therefore,the effect of the litter decompo-sition on DOC could not be distinguished.
In our study we combinedfield and laboratory-experi-ments.Litter was decompod in-situ in litterbags,and was leached in the laboratory to relea DOC.The aim of our study was to examine the effect of decomposition offive different types of litter on the amount and spectroscopic properties of DOC and its microbial degradability.
2.Material and methods
2.1.Field-exposure of litter
Air-dried leaves and needles from sycamore maple(Acer pudoplatanus L.),European beech(Fagus sylvatica L.), mountain ash(Sorbus aucuparia L.),Norway spruce(Picea abies(L.)Karst.)and Scots pine(Pinus sylvestris L.)were incubated in litterbags at two neighboring forest sites for up to12months.The sites were located at Coulisnhieb in the Fichtelgebirge mountains in North-East Bavaria(775m a.s.l.,5080803500N,1185201000E).One site was a160y old spruce stand,the other site a neighboring3y old clear-cutting(Kalbitz et al.,2004).The climate in this area is characterized by high precipitation(1100mm yr K1),an annual mean temperature of around58C and a persistent snow cover during winter ason(site descriptions are available by Gerstberger et al.,2004).Senescent litter samples collected by meshes were derived from trees adjacent to the study site except for the p
ine litter.Pine litter originated from the nutrient poor Ja¨rdaa˚s-site in central Sweden(site descriptions by Axelsson and Bra˚kenhielm, 1980).In previous studies on litter decomposition the same pine litter was ud as model litter(Couˆteaux et al.,1998; Berg,2000).We did not cut or grind the litter samples except for maple leaves,which were cut into small pieces (2–4!2–4cm2)tofit into the litter bags.
Each litterbag(mesh size0.5!1mm2)contained two parate parts.Thefirst part wasfilled with2g of litter from one tree species to determine the mass loss and the cond part,with10g for DOC-extraction.The bias of the decomposition process due to the exclusion of soil fauna in litterbags can be expected to be relatively small becau the decomposing community of acidic coniferous ecosys-tems,like the Coulisnhieb site consists mainly of microorganisms,generally lacking a meso-and macrofauna (e.g.Wallwork,1976).
吊瓜子的功效与作用
In total24spatial replications(12at each site)were installed to cope with the high variability of the decompo-sition process.Thefield-exposure started in June2001.After 1,3,5,9and12months120litterbags were always harvested (five litter species in12replications at both sites)and the litter was cleaned manually to remove fungi hyphae,roots, sprouts and small animals.The mass loss of the litter was determined as the difference between initial and actual dry weight(48h drying at808C).The water content of the litter was determined as difference betweenfield
moist and dried litter weight.Four samples of the12replicates with similar mass loss were mixed each time to three composite samples for each litter species.Thus,the variability of the mineralisation process is maintained for further investigation and not evened out as it is done with randomized pooling. Part of the litter samples were ground and the C-and N-content was determined(CHN-O Rapid,Heraeus Ele-mentar).Additionally,the content of heavy metals and macro-nutrients was measured in the fresh undecompod litter(hot HNO3-extraction,ICP-AES,GCP Electronics).
伫倚危楼风细细2.2.DOC extraction and characterization
A sub sample of5.5gfield moist litter(dry matter ba) was expod to an extraction scheme with ultrapure water at 58C,the mean annual temperature of the study site.Content and properties of DOC are affected by ason with mostly larger concentrations in the growing ason(Kalbitz et al., 2000,2004).Furthermore,after dry periods DOC concen-trations are increasing with increasing portions of microbial products(Zsolnay et al.,1999;Kair et al.,2001).We wanted to reveal effects of litter decomposition and tree species but we were not interested in asonal effects on DOC concentrations and composition.Therefore,we considered ourfirst extraction step as a pre-extraction in order to equalize asonal differences at least in the water content of the samples.For this pre-extraction the litter samples were soaked in250ml ultra pure water in beakers for24h.Thereafter,the li
tter samples were spread out evenly in Buchner funnels(12.8cm dia.).The solution pha of the pre-extraction was obtained and analyzed as described below.After allowing the litter7d to acclimatize at58C,it was extracted3d via sprinkler irrigation.During each of the3d,320ml of ultra pure water was sprayed over the sample using a time of20h.The solutions were filtered through a pre-washed0.45m m cellulo acetate membranefilter and the DOC concentration(high TOC Elementar)was measured.The remainders of samples from thefirst irrigation day were immediately frozen for further analys of spectroscopic properties and biodegradability. We considered that concentrations and composition of DOC in thefirst percolates after the pre-extraction and the1-week conditioning period reprented best the effect of different litter species and stages of litter decomposition with minor
A.Don,K.Kalbitz/Soil Biology&Biochemistry37(2005)2171–2179 2172
reflection of asonal effects.However,we also calculated the cumulative amounts of relead DOC including pre-extraction and the three irrigation steps(Table1).The cumulative amount of water(1210ml)was equivalent to 94mm precipitation.
Spectroscopic properties of DOC as UV radiation absorbance andfluorescence spectra are powerful
tools to characterize high numbers of samples(Kalbitz et al.,1999). UV absorbance is a successful predictor for the aromaticity of DOC(Chin et al.,1994;Kalbitz et al.,2003b)whereas fluorescence spectra give some additional information about the complexity and condensation of the organic molecules (Zsolnay et al.,1999;McKnight et al.,2001).For each of the samples UV absorbance at l Z280nm(UVIKON930, BIO-TEK Instrument)andfluorescence spectra using emission mode were recorded(BIO-TEK Instrument; Kalbitz et al.,2003a,b).Humification indices were deduced from thefluorescence spectra as an indicator of the complexity of the molecules.The humification index deduced from emission spectra(HIX)is defined as the area in the upper quarter(S435–480nm)of the usable emission spectra divided by the area in the lower usable quarter(S300–345nm)(Zsolnay et al.,1999).Measure-ments and calculations followed the methods described by Zsolnay et al.(1999),Kalbitz and Geyer(2001).
2.3.Incubation of DOC to measure biodegradability
To quantify the potential biodegradability of DOC, samples extracted from allfive species of fresh and decompod litter from the forest stand site(5months of field exposure,samples from thefirst irrigation)were incubated in120ml aledflasks at208C for6weeks with six to nine replications.The samples with higher concen-trations than10mg C l K1were diluted to10mg C l K1to avoid excessive
microbial growth(Hongve et al.,2000)and effects of different concentrations on DOC mineralization (Zsolnay,2003).The C/N/P ratio was adjusted to100/10/1 by adding NH4NO3and K2HPO4,which was clo to the nutrient concentrations measured in soil solution at the given site(Kalbitz,data unpublished).绒毛活检
To facilitate equivalent start conditions for the microbial community within the litter percolates,a mixed inoculum was added to everyflask.We ud0.5g of litter from each litter species,added6–7ml of ultrapure water and aerobically incubated at208C for12d to reactivate the microorganisms.Thereafter the litter was extracted twice with a4mM CaCl2solution(litter:solution1:5)and pasd through a5m m membranefilter to remove grazing microfauna(Jandl and Sollins,1997).The inoculum was added to the sample in a sample/inoculum volume ratio of 100:1.The chon method aimed to quantify the potential biodegradable DOC.The mineralization dynamic was quantified by daily CO2measurements in the head space during thefirst week,and afterwards at increasing intervals (up to once per week).The CO2concentration was measured with a gas chromatography system(HP6890, Hewlett Packard,thermal conductivity detector).The CO2 evolution by mineralization of the inoculum C was determined in a control sample(ultra pure water,inoculum and nutrients)and subtracted from the other samples.
A double exponential model wasfitted to the data ts estimating an easily degradable(labile)and a more stable pool(Kalbitz et al.,2003b;Wang et al.,2004): mineralized Cð%of total CÞ
Z aÃð1K e K k1ÃtÞCð100K aÞÃð1K e K k2ÃtÞ
a Z size of the labile pool[%of total C],k1,k2Z mineralization rate of the labile and stable pool.
季冠霖个人资料Half life(t1/2)and the size of the labile and stable pool were calculated.Biodegradability of the samples was defined as C-mineralization after6weeks of incubation. 2.4.Data treatment and statistics
Effects of litter species on litter decomposition were tested to be significant for each sampling date with ANOVA procedure and the Fisher-LSD test(P!0.05).For the tests all of the12replicates per site,litter species and sampling day were ud.Differences between the two sites were tested to be significant using t-test(P!0.05).Properties of
Table1
Total extractable amounts of DOC(mg g C K1)cumulative from four extraction steps(94mm)after0to12months offield incubation of the litter in a forest stand(s)and a clear-cut site(c)
Fresh1month3months5months9months12months
Maple(s)62.4(4.34)15.3(0.40)11.5(1.69)10.7(1.35) 6.5(0.22) 6.8(1.42)
Maple(c)28.3(2.46)17.9(2.43)11.6(0.82)7.1(1.25)10.1(1.11) Mountain ash(s)39.3(2.45)13.5(1.46) 6.2(0.97) 5.0(0.56) 4.8(0.71) 5.2(0.85) Mountain ash(c)19.0(5.34)9.5(1.00) 4.5(0.33) 4.4(0.12) 4.6(0.30) Europ.beech(s)16.0(0.07) 4.4(0.21) 3.1(0.49) 2.7(0.57) 4.2(0.56) 4.1(0.46) Europ.beech(c)9.0(0.94) 6.2(1.14) 4.3(0.32) 3.5(0.76) 5.4(0.82) Norway spruce(s)9.5(0.21) 6.2(0.75) 3.6(0.18) 5.5(1.53) 5.9(0.63)11.2(5.17) Norway spruce(c) 4.8(0.45) 5.0(0.55) 4.7(0.75) 2.6(0.42) 5.9(3.21)
Scots pine(s)33.3(0.45)8.0(0.64) 3.7(0.41) 4.4(1.40) 5.5(0.47)9.4(4.07)
Scots pine(c)10.1(0.63) 4.2(0.26) 4.3(1.11) 3.8(0.89) 3.3(0.51) Standard deviation in brackets;n Z3.
A.Don,K.Kalbitz/Soil Biology&Biochemistry37(2005)2171–21792173
dissolved organic matter (UV,humification indices,biode-gradability)were tested to be statistically different as described above using the six replicates (both sites)for each litter species and sampling
day (P !0.05).Furthermore,we calculated linear regressions between different DOC proper-ties and the mass loss of the litter.
3.Results
3.1.Litter decomposition
After 12months of litter decomposition mountain ash had significantly the largest mass loss of all litter types (40.8G 4.0%,mean and standard deviation of all replicates from both sites;Table 2).At the other end of the scale beech litter lost only 8.3%G 4.3%of its mass.Coniferous litter from pine,spruce and maple leaves had a mass loss of between 26.2and 29.4%with no statistically significant differences between the three species.There was a slightly decread decomposition rate during the winter ason compared to the summer ason for all litter species.
The forest site where the litter was expod (forest stand vs.clear-cut site)partly affected the rate of litter decompo-sition.Spruce litter in the forest stand showed significant higher mass loss at four out of five sampling dates.Pine and maple litter decomposition was also faster (P !0.05)in the forest stand during the first 3and first 5months,respectively.The decomposition of the litter species emed to decline at the clear-cut site especially during summer.In contrast beech litter degraded ge
nerally faster at the clear-cut site (three out of five sampling dates were significant)but with an overall very low mass loss (Table 2).There was no significant difference between the two field sites in the mass loss of mountain ash leaves at any time of sampling.3.2.Leaching of DOC from litter
DOC concentrations were largest in solutions obtained by the pre-extraction and declined during the three irrigation steps出棋制胜
(Fig.1).However,DOC amounts of the pre-extraction and the three irrigation steps were obtained in similar proportions to each other for different sampling dates.Therefore,we have to state that the applied pre-extraction was not necessary or not fully successful to equalize for asonal effects on DOC relea.That also means,it does not matter whether we are using DOC concentrations from one of the extractions or the cumulative amounts of relead DOC to discuss effects of litter decomposition on DOC dynamics.For future studies we recommend to skip the complicated extraction and irrigation scheme and u just the single batch extraction.
Fresh leaves relead the largest amounts of DOC with the highest values for maple and mountain ash litter reaching 62.4and 39.3mg g C K 1,respectively (Table 1).DOC relea decread during the first months of litter decomposition for all five species.However,DOC especially from needles tended
to increa reaching up to 11.2mg g C K 1for spruce after exceeding a mass loss of 20%which was even larger than DOC relea from fresh spruce litter.Extractable DOC from spruce and pine almost doubled from the fourth to the fifth sampling dates.In contrast,DOC relea barely altered with increasing decomposition of maple and mountain ash litter.After 5months of field exposure,DOC relea from needles
Table 2
Mass loss (%)of five litter species at five sampling dates incubated in a forest stand (s)and an adjacent clear-cut site (c)Time of harvesting Summer 2001Autumn 2001Autumn 2001Spring 2002Summer 2002Months after start of the experiment 1month 3months 5months 9months 12months Maple (s) 5.6(1.5)16.4(2.9)23.5(2.8)25.2(3.9)28.9(6.1)Maple (c)
2.7(1.4)11.5(2.4)19.9(2.5)22.7(
3.4)29.9(7.4)Mountain ash (s)12.2(
4.3)29.3(4.4)37.1(3.8)36.2(4.4)40.3(2.5)Mountain ash (c)9.0(4.5)26.1(3.9)3
5.0(4.3)3
6.4(3.6)41.2(5.2)Europ.beech (s)K 0.1(1.4) 2.5(1.0)8.6(1.1)8.6(2.5) 5.1(2.0)Europ.beech (c)K 0.1(0.9) 5.2(2.6)10.1(1.7)10.6(1.5)11.5(3.6)Norway spruce (s) 5.8(1.1)15.0(1.6)22.3(2.0)23.2(1.4)29.3(2.9)Norway spruce (c) 3.7(0.6)9.9(1.1)18.0(1.5)22.5(6.2)23.0(2.0)Scots pine (s) 4.8(1.0)13.6(1.7)22.7(6.1)25.0(3.9)28.9(3.6)Scots pine (c)
2.5(0.7)
8.5(0.9)
19.5
22.5
25.1(6.7)蜓字怎么组词
Standard deviation in brackets;n Z
12.
Fig.1.Extractable DOC amounts of maple and pine litter after 3months of field incubation.Four extraction steps-one pre-extraction with 250ml (batch,19mm)and three irrigation with 25mm deionid water;n Z 6(litter from both sites).
A.Don,K.Kalbitz /Soil Biology &Biochemistry 37(2005)2171–2179
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乡镇妇联工作总结in the forest site was more than from the clear-cut site.Concurrently,needle litter in the forest stand had a larger mass loss than in the clear-cut site (Table 2).In contrast to needle litter,the generally larger extracted amounts of DOC from leaves incubated at the clear-cut site compared to the forest stand were not accompanied by larger mass loss.3.3.Spectroscopic properties of DOC
Our experiments showed that specific UV absorbance at l Z 280nm and humification indices (HIX)deduced from fluorescence emission spectra of litter percolates were distinctive for tree species and the decomposition stage of the litter.UV absorbance and HIX showed on average the same tendencies;therefore,only HIX data are prented.They indicated the largest aromaticity and complexity of DOC from maple litter.At the other end of the scale very small values were measured for DOC from pine litter.This was especially the ca for fresh needles (Fig.2).
For percolates of all litter species we measured increasing values of the spectroscopic properties with increasing decomposition time.Percolates from the two coniferous species showed especially steadily increasing UV absorbance and HIX with increasing mass loss of litter or decomposition time (Fig.2).For mountain ash percolates there was no significant trend toward higher HIX with increasing
mass loss of the litter.Due to low mass loss of beech litter the correlation between the HIX and the mass loss was also not significant.3.4.DOC mineralisation
As obrved for spectroscopic properties,the biodegrad-ability of the litter percolates depended strongly on litter species.DOC from the fresh coniferous samples showed the highest biodegradability.About 95%DOC of pine litter and 77%of spruce litter was mineralized within 42d.In contrast only 33%of maple DOC was converted to CO 2(Fig.3
).
Fig.2.Humification indices deduced from fluorescence emission spectra of coniferous (A)and deciduous (B)litter percolates from the first irrigation step.DOC extracts from fresh litter and five sampling dates.No significant trend for mountain ash and
beech.
Fig.3.Mineralisation dynamic of DOC from fresh litter measured as CO 2-production fitted with a double exponential model.Three percolates from each litter species were incubated in three replicates.
A.Don,K.Kalbitz /Soil Biology &Biochemistry 37(2005)2171–21792175
