Dynamics of litter carbon turnover and microbial abundance in a rye detritusphere

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Soil Biology & Biochemistry 40 (2008) 1306–1321

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Dynamics of litter carbon turnover and microbialabundance in a rye detritusphere

Christian Polla,�, Sven Marhana, Joachim Ingwersenb, Ellen Kandelera

aInstitute of Soil Science and Land Evaluation, Soil Biology Section, University of Hohenheim, Emil-Wolff-StraX e 27, 70599 Stuttgart, GermanybInstitute of Soil Science and Land Evaluation, Biogeophysics Section, University of Hohenheim, Emil-Wolff-StraX e 27, 70599 Stuttgart, Germany

Received 30 October 2006; received in revised form 2 April 2007; accepted 6 April 2007

Available online 7 May 2007

Abstract

Factors determining C turnover and microbial succession at the small scale are crucial for understanding C cycling in soils. We

performed a microcosm experiment to study how soil moisture affects temporal patterns of C turnover in the detritusphere. Four

treatments were applied to small soil cores with two different water contents (matric potential of �0.0063 and �0.0316MPa) and with or

without addition of 13C labelled rye residues (d13C ¼ 299%), which were placed on top. Microcosms were sampled after 3, 7, 14, 28, 56

and 84 days and soil cores were separated into layers with increasing distance to the litter. Gradients in soil organic carbon, dissolved

organic carbon, extracellular enzyme activity and microbial biomass were detected over a distance of 3mm from the litter layer. At the

end of the incubation, 35.6% of litter C remained on the surface of soils at �0.0063MPa, whereas 41.7% remained on soils at

�0.0316MPa. Most of the lost litter C was mineralised to CO2, with 47.9% and 43.4% at �0.0063 and �0.0316MPa, respectively. In

both treatments about 6% were detected as newly formed soil organic carbon. During the initial phase of litter decomposition, bacteria

dominated the mineralisation of easily available litter substrates. After 14 days fungi depolymerised more complex litter compounds,

thereby producing new soluble substrates, which diffused into the soil. This pattern of differential substrate usage was paralleled by a lag

phase of 3 days and a subsequent increase in enzyme activities. Increased soil water content accelerated the transport of soluble

substrates, which influenced the temporal patterns of microbial growth and activity. Our results underline the importance of considering

the interaction of soil microorganisms and physical processes at the small scale for the understanding of C cycling in soils.

r 2007 Elsevier Ltd. All rights reserved.

Keywords: Small scale; Decomposition; Litter; Soil–litter interface; Microbial succession; r strategists; K strategists; Temporal pattern; Water content; Soil

enzymes; MUF

1. Introduction

Plant biomass is the major source of soil organic carbon(SOC), with an annual net primary production in terrestrialecosystems worldwide of about 60 PgC yr�1 (IPCC, 2001).This important substrate for soil microorganisms isheterogeneously distributed in the soil matrix. For exam-ple, van Noordwijk et al. (1993) estimated that only 5% ofthe soil was in contact with freshly introduced organicmatter in an agricultural soil. The mineralisation of plantcompounds by a succession of microorganisms as well as

e front matter r 2007 Elsevier Ltd. All rights reserved.

ilbio.2007.04.002

ing author. Tel.: +49711/459 22614;

9 23117.

ess: [email protected] (C. Poll).

leaching of soluble compounds into the soil are controlledby biotic and abiotic factors (Couteaux et al., 1995). Thesevary at different scales from millimetres to metres or evenlarger (Ettema and Wardle, 2002). Therefore, the interac-tion of plant litter distribution and varying soil propertiesat the small scale is very important for understanding thesoil carbon cycle. The microhabitat in which this interac-tion takes place is the detritusphere; this layer includes thelitter and the soil influenced by the litter. In the detritu-sphere, plant residues offer new sites for microorganisms,whereas soluble substrates are transported into theadjacent soil (Gaillard et al., 1999; Kandeler et al., 1999).The consequence is enhanced microbial activity and carbonturnover next to the litter layer. Gaillard et al. (1999)found increased dehydrogenase activity and transport of

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Days

Microbial biomassTransport of C

Enzyme activity

3 7 14 28 56 84

r strategistsK strategists

Time

Fig. 1. (a) Schematic illustration of the temporal pattern of C transport,

microbial biomass and enzyme activity as hypothesised before the

experiment. (b) A concept for the interaction between C transport, r

and K strategists and extracellular enzyme activity in the detritusphere

based on the results of the present study.

C. Poll et al. / Soil Biology & Biochemistry 40 (2008) 1306–1321 1307

litter-derived C within a distance of 3–4mm from the litterlayer. In a similar study, Kandeler et al. (1999) reportedincreased protease, xylanase and invertase activity over adistance of 1.1–1.3mm. The importance of the soil layer inthe detritusphere for litter mineralisation was shown byGaillard et al. (2003): depending on the litter quality,23–33% of the mineralisation occurred after litter C wastransported into the soil.

However, the influence of many factors such as soiltexture or soil water content on the C turnover in thedetritusphere remain unclear. The influence of soil moist-ure on litter decomposition has been shown by Virzo deSanto et al. (1993) and Schimel et al. (1999). The transportof soluble C is affected by the soil water content, which isimportant for C turnover at the small scale. For example,the diffusion rate in a loamy soil was reduced by 50% at amatric potential of �0.1MPa compared to saturation(Griffin, 1981). This might influence the transport andturnover of litter C in the detritusphere and therefore theresponse of the soil microbial community to litter addition.

Measuring the phospholipid fatty acids (PLFA) afteradding ryegrass, McMahon et al. (2005) observed asuccession of bacteria and fungi over 80 days at fieldcapacity. The effect of soil water content on the microbialsuccession during litter decomposition, however, hasapparently never been studied at a small scale.We recently found evidence for a changed temporal

pattern of C transport and microbial activity underdiffering soil moisture regimes (Poll et al., 2006). After 2weeks, an elevated water content reduced microbialbiomass but increased enzyme activity. This was explainedby a faster litter C transport in the wetter soil, allowingmicrobial biomass to peak early. At the end of theexperiment, the microbial biomass was already decayingin this soil, thereby releasing extracellular enzymes.The present study identifies temporal patterns of litter C

turnover in the detritusphere. We expect transport ofsoluble litter C to peak early in the incubation, followed bypeaks in microbial biomass and extracellular enzymeactivity (Fig. 1a). A second objective was to analyse themodification of these temporal patterns by soil moistureregime. To test these hypotheses, we performed a micro-cosm experiment that simulates the soil–litter interface attwo different water contents over 84 days. Highly 13Clabelled rye litter was used to trace litter C turnover at sixsampling dates. Activity of extracellular enzymes wasanalysed to detect gradients and temporal patterns ofmicrobial activity; ergosterol content and microbial bio-mass carbon were measured to test the response of fungiand total microbial biomass to litter addition.

2. Materials and methods

2.1. Soil and plant residues

Soil was sampled from the long-term field experiment inRotthalmunster (Germany, 481210N, 131120E) near theDanube River in September 2002. Samples were takenfrom the clay-loamy topsoil of a Stagnic Luvisol (WRB)(pH (CaCl2) 5.5, total C content 12.6 g kg�1, total Ncontent 1.6 g kg�1). Wheat has been cultivated at the site inmonoculture for the last 36 years with NPK fertilisation(171 kg Nha�1). The d13C value of the SOC was �25.5%,which indicates that the SOC was derived from C3 plants.After sampling, the soil was sieved (o2mm) and stored at�20 1C to minimise disturbance by soil faunal activityduring the experiments. For the incubation, labelled ryeresidues with a d13C value of 299% (at% 13C ¼ 1.43) and aC/N ratio of 40 were chosen. Information on the labellingprocedure is given in Butenschoen et al. (2007). Ryeresidues were stored air-dried until the start of theexperiment.

2.2. Experimental design

The experiment consisted of four treatments with twodifferent matric potentials and without or with litter

ARTICLE IN PRESSC. Poll et al. / Soil Biology & Biochemistry 40 (2008) 1306–13211308

addition: (i) �0.0316MPa without litter (control),(ii) �0.0316MPa with litter addition, (iii) �0.0063MPawithout litter (control) and (iv) �0.0063MPa with litteraddition. Each treatment was replicated three times. Forthe sake of simplicity, soils at �0.0316 and �0.0063MPawill be considered below as dry and wet, respectively.

After thawing, the soil was homogenised and filled intocylinders (PVC, diameter ¼ 5.6 cm, height ¼ 3 cm). Thesoil cores had a height of 1.5 cm and were compacted to abulk density of 1.2 g cm�3. Subsequently, soil cores weresaturated with 0.01M CaCl2 solution, placed on ceramicplates and adjusted to the respective matric potentials. Thisprocedure took 13 days. After placing each soil core into anair-tight glass container (microcosm, 750ml), the soil coreswere preincubated for 3 days, which enabled acclimatisa-tion to incubation conditions. After 3, 7, 14, 28, 56 and 84days, six microcosms of each treatment were sampleddestructively. During the experiment, loss of water wasminimal.

For each cylinder, 0.3 g of rye residues was rewetted with2ml of 0.01M CaCl2, 1 day before the start of theexperiment. The rye litter was placed on top of thecylinders and slightly pressed onto the soil cores to ensureadequate contact between soil and litter. The microcosmswere incubated at 10 1C.

2.3. Sample preparation

After incubation, the litter was removed from the soilcores, which were immediately frozen at �20 1C. Subse-quently, the soil cores were sliced on a cryostat microtome(HM 500M, MICROM International GmbH, Walldorf,Germany) in 0–1, 1–2 and 2–3, 3–5 and 5–10mm slices insequence from the top of the core. The respective slices oftwo of the six sampled soil cores were pooled to obtain asufficient amount of soil for analyses. This yielded threereplicates for each treatment.

Analyses of enzyme activities were performed for alllayers to obtain the complete gradient of microbial activity.The measurements of SOC, dissolved organic carbon(DOC), microbial biomass and ergosterol were made forthe three top layers (0–1, 1–2, 2–3mm) because formerstudies indicated a detritusphere thickness of about 3mm(Poll et al., 2006).

2.4. Respiration

CO2-C production was measured at regular intervalsduring the incubation. Evolved CO2 was trapped in 1ml(control) and 2ml (litter treatment) of 1M NaOH solution,which were added to small vessels fixed in the microcosms.An aliquot of 0.5ml was taken from three replicates of eachtreatment, and trapped CO2 was measured titrimetricallyafter precipitation of carbonate with 0.5ml 1M BaCl2solution using 0.1M HCl.

For determining the d13C value of the CO2-C, NaOHwas removed from the other three replicates of each

treatment. The trapped CO2 was precipitated as BaCO3

with 1M BaCl2 in the ratio of 1:1 (v:v) and the precipitatewas washed with 40ml air-free deionised water andcentrifuged at 2500 revmin�1 for 10min. The supernatantwas discarded and washing was repeated three times. TheBaCO3 pellets were dried at 60 1C for 24 h. A mass of0.3–0.5mg of BaCO3 was weighed into tin foils andanalysed by an elemental analyser (EA, Euro EA 3000,EuroVector, Milan, Italy) coupled with an isotope ratiomass spectrometer (IRMS, Delta Plus, Thermo Finnigan,Waltham, USA).

2.5. Litter

Litter was removed from the microcosms, dried at 60 1Cand weighed. The litter was ground and subsamples of0.1mg were weighed into tin capsules for isotopicmeasurement as described above.

2.6. Soil organic carbon

In order to measure the amount and isotopic composi-tion of the SOC, 0.3 g of soil was dried at 60 1C for 3 daysand subsequently ground. Subsamples of 15mg wereweighed into tin capsules and measured for their d13Cvalue of SOC as described above.

2.7. Microbial biomass and DOC

Microbial biomass was determined using the chloro-form-fumigation–extraction (CFE) method (Vance et al.,1987). One gram of soil was fumigated with ethanol-freechloroform for 24 h at room temperature in a desiccator.After the incubation, chloroform was removed. Fumigatedand unfumigated samples were dispersed in 10ml of0.025M K2SO4 and extracted on a horizontal shaker at250 revmin�1 for 30min. Then, samples were centrifugedat 4560 revmin�1 for 30min and the supernatant wastransferred into a flask and analysed for DOC with aDIMATOC 100 (Dimatec GmbH, Essen, Germany). TheDOC contents of the unfumigated samples were used bothas controls for the CFE analysis and as estimates for theDOC content of the soils. Microbial biomass wascalculated from the DOC values using a kEC factor of0.45 (Joergensen, 1996). The d13C values of microbial C(Cmic) and DOC were determined by evaporating extractsusing a rotation vacuum evaporator (RVC 2–25, MartinChrist GmbH, Osterode, Germany). Subsamples of10–15mg of the remaining salt were weighed into tincapsules and analysed as described above (Potthoff et al.,2003).

2.8. Ergosterol

Ergosterol was extracted using the method ofDjajakirana et al. (1996). Briefly, 0.5 g of soil was weighed,dispersed in 25ml ethanol and extracted on a horizontal

ARTICLE IN PRESSC. Poll et al. / Soil Biology & Biochemistry 40 (2008) 1306–1321 1309

shaker at 250 revmin�1 for 30min. Subsequently, sampleswere centrifuged at 4560 revmin�1 for 30min. An aliquotof 20ml was transferred into centrifugation tubes andconcentrated to dryness using an RVC 2–25, (MartinChrist GmbH, Osterode, Germany). To remove ergosterolfrom the tube wall, 3ml ethanol was added and evapo-rated. The residue was dissolved in 1ml methanol andtransferred into 2ml brown glass HPLC vials using 0.45 mmcellulose-acetate filters. Ergosterol was quantitativelydetermined by HPLC analysis (Beckmann Coulter, SystemGold 125, Fullerton, USA) using a 250� 4.6mm2 Spher-isorb ODS II 5 mm column with a mobile phase of puremethanol, a flow rate of 1mlmin�1 and a detectionwavelength of 282 nm (Beckmann Coulter, System Gold166 UV-detector, Fullerton, USA). The standard (Sigma-Aldrich, St. Louis, USA) was dissolved in ethanol anddiluted to give final concentrations of 0, 0.1, 0.2, 0.5, 1 and2 mg ergosterolml�1.

2.9. Enzymatic analyses

The activities of the following enzymes were measuredaccording to Marx et al. (2001): a-D-glucosidase (EC3.2.1.20), b-D-glucosidase (EC 3.2.1.21), xylosidase (EC3.2.1.37), N-acetyl-glucosaminidase (EC 3.2.1.52), phospha-tase (EC 3.1.3.1) and leucine peptidase (EC 3.4.11.1). Sigma-Aldrich (St. Louis, USA) provided substrates containing thefluorescent compounds 4-methylumbelliferone (4-MUF) and7-amino-4-methyl coumarin (7-AMC), standards and buffer(MES-buffer 2-[N-morpholino]ethanesulphonic acid, Trizmabuffer (mixture of a, a, a-Tris-(hydroxymethyl)-methylaminand Tris-(hydroxymethyl)-aminomethane hydrochloride)).

MES buffer (pH 6.1) and Trizma buffer (pH 7.8) had aconcentration of 0.1 and 0.05M, respectively. Substrateswere dissolved in 300 ml dimethyl sulphoxide and made upto 10ml with autoclaved water to obtain a 10mM stocksolution. Working solutions (1mM) were prepared withautoclaved buffer (MES buffer for MUF substrates,Trizma buffer for AMC substrates). Standards weredissolved in methanol and water (v:v; 1/1) to a concentra-tion of 5mM and subsequently diluted to a finalconcentration of 10 mM. After preparation of the solutions,0.5 g fresh soil of each sample was dispersed in 50ml ofautoclaved deionised water by an ultrasonic disaggregator(50 J s�1 for 120 s). Fifty microlitres of soil suspension wasadded into microplate wells (PP microplate, black 96 well,Greiner Bio-one GmbH, Frickenhausen, Germany), fol-lowed by 50 ml autoclaved buffer and 100 ml substratesolution. Standards were mixed with soil suspension andbuffer to give final concentrations of 0, 0.5, 1, 2.5, 4 and6 mM. Wells without soil suspension served as a control forautocleavage of substrates. The microplates were incubatedat 30 1C. Fluorescence was measured after 30, 60, 120 and180min by a microplate reader (excitation at 360 nm,emission at 460 nm, FLX 800, Microplate FluorescenceReader, Bio-Tek Instruments Inc., Winooski, USA).

2.10. Carbon balance

The isotopic ratios of the litter C, CO2-C, SOC, DOCand microbial biomass are reported in the d notationrelative to the Pee Dee Belemnite (PDB) standard:

d13Cð%Þ ¼ ½ðRsam=RstdÞ � 1�n1000, (1)

where Rsam is the 13C/12C ratio of the sample and Rstd is the13C/12C ratio of the standard (PDB).To calculate the C balance we had to account for

heterogeneous labelling of the plant residues. Plantlabelling had started after the second leaf stage(Butenschoen et al., 2007). During the following 5-weeklabelling period, plants were sprayed with a solution ofcontinuously increasing 13C urea concentration. As aconsequence, the carbon assimilated during the last daysof the labelling period probably had the greatest d13Cvalues, whereas the C assimilated before labelling with 13Curea contained no excess 13C. Therefore, the pool ofsoluble litter C with most of the freshly assimilated Cprobably showed the highest labelling. In contrast, com-plex plant compounds were assimilated during the initialphase of the labelling or even before, resulting in a lowerlabelling. We therefore calculated the labelling of the C(AT%r/t) respired from or transported out of the litterlayer between sampling date t ¼ i and the followingsampling date t ¼ i+1 as follows:

AT%r=t ¼ ðCinAT%i � Ciþ1nAT%iþ1Þ=ðCi � Ciþ1Þ, (2)

where Ci and Ci+1 stand for the amount of litter C, AT%i

and AT%i+1 for the atom% of 13C of the litter C at thesampling dates t ¼ i and t ¼ i+1, respectively. Atom% of13C was than converted to d13C values according to Eq. (1).These d13C values of the mineralised or transported litter Cwere taken to calculate the proportion of litter-derived C(%litter C) in CO2-C and SOC at t ¼ i+1:

%LitterC ¼ ðdsample � dcontrolÞ=ðdlitter � dcontrolÞn100, (3)

where dsample stands for the d13C of the sample, dcontrol for

the d13C of the control treatments and dlitter for the litter Crespired from or transported out of the litter layer. Tocalculate the portion of litter C in SOC at t ¼ i+1, we usedthe mean d13C values of the litter treatment at t ¼ i insteadof dcontrol. This accounts for the continuous accumulationof litter C during the incubation, which resulted inincreasing d13C values of SOC during this time.

2.11. Statistics

The results were calculated on the basis of oven-driedsoil. Soil water content was determined by weighing 0.3 g offresh soil into vessels and drying at 60 1C for 72 h.Results of CO2 production were tested for significant

differences by one-way ANOVA. Litter mass loss and d13Cvalues of remaining litter were compared by Student’st-test. For the results of SOC, DOC, microbial biomass,ergosterol content and d13C values of SOC and DOC, the


litter treatments were compared by two-way ANOVA withthe fixed factors time and matric potential; controltreatments served as a baseline. Due to heterogeneity ofvariances, d13C values of the microbial biomass were testedwith the Mann–Whitney U-test and the Kruskal–WallisH-test for the effects of matric potential and time,respectively. Statistical analyses were performed usingSPSS for Windows (12.0, SPSS Inc., Chicago, USA).

3. Results

3.1. Respiration

Litter addition increased the cumulative CO2-C produc-tion by a factor of seven (Fig. 2a). Matric potential(F1,12 ¼ 87.0, Po0.001) as well as presence of litter(F1,12 ¼ 14623.6, Po0.001) significantly affected CO2-Cproduction. Furthermore, the interaction between matricpotential and litter addition significantly affected respira-tion (F1,12 ¼ 41.6, Po0.001), with greatest CO2-C produc-tion in the samples with litter and a matric potential of�0.0063MPa. Respiration peaked after 14 days, with a15-times greater respiration rate for the litter treatmentsthan for the control soils; it then declined until theend of the incubation, when respiration rates were twofoldgreater in litter treatments versus control soils (data notshown).

The d13C values of the CO2-C of the control soilsremained at a constant level of about �21.2% during theincubation (Fig. 2b). In the litter treatments, the values atthe first sampling date sharply increased to 570% and505%, followed by a strong decline to 88% and 99% forwet and dry soils, respectively. The decline was mostpronounced during the initial 20 days of incubation.Differences between wet and dry soils were not significant.

Fig. 2. Cumulative CO2-C production after 84 days incubation (a) and d13C va

show standard deviation. Different letters in (a) indicate statistically different

3.2. Litter

Litter mass gradually decreased over the experiment,with the drop being most pronounced during the first 28days (Fig. 3a). In dry soils, 42.5% of the litter remainedafter 84 days, which was significantly more than the 37.7%in wet soils (t-test, Po0.01). Litter mass loss correlatedwell with the cumulative CO2 production (correlationcoefficient r ¼ 0.98, Po0.001).The temporal pattern of d13C values of the litter carbon

was similar to the d13C values of the produced CO2-C: astrong decrease from the initial 299% to 231% and 234%after 84 days for wet and dry soils, respectively (Fig. 3b).These data were used to calculate the d13C values of the Clost from the litter by diffusion or respiration (Fig. 3c).During the first 3 days, C with a d13C of 1090% and 1327%was decomposed or diffused from the litter at �0.0063 and�0.0316MPa, respectively. Averaged over the whole84-day period, the lost litter C had a d13C value of about335%.

3.3. Soil organic carbon

The SOC content increased due to litter addition after 3days of incubation. This was most pronounced for the0–1mm layer (Figs. 4a and b). In all three layers, SOCcontent declined between days 3 and 7 and then increasedagain until the end of the experiment, particularly in thetop layer. This effect of time on SOC content wassignificant in the 0–1 and 2–3mm layers, whereas matricpotential had no significant influence (Table 1).In all three layers, d13C values were elevated from day 3

until the end of the incubation (Figs. 4c and d), with asignificantly greater increase in wet than in dry soils(Table 1). After being nearly constant during the first 7

lues of respired CO2-C (b). Values are means of three replicates, error bars

groups (Tukey-B, Po0.05).

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Fig. 3. Mass loss (a) and d13C (b) of rye residues over 84 days. (c) d13C value of the removed litter C from the start of the incubation until the sampling.

Values are means of six replicates, error bars show standard deviation. Asterisks indicate statistical difference between treatments (t-test, *Po0.05,**Po0.01).


days of the experiment, d13C values increased again, mostpronouncedly between days 7 and 28. The magnitude ofthis rise was greatest in the 0–1mm layer and declined withdepth.

3.4. K2SO4 extractable carbon

The K2SO4 extractable C, as an indicator of DOC,remained at a constant level in the control soils andincreased after litter addition (Figs. 4e and f). This effectwas greatest for the 0–1mm layer and diminished withdepth. Both matric potential and time had significanteffects on the DOC content (Table 1). At the first twosamplings, no differences between soils with differentmatric potential were detectable, whereas at the followingsamplings wet soils generally contained more DOC thandry soils. The temporal pattern showed an increase in DOCcontent at day 3, followed by a drop and a second increase

at days 28 and 56, depending on the distance to the litterlayer (Figs. 4e and f).The d13C values of DOC in the litter treatments strongly

increased compared to the control soils, showing greatestvalues in all three layers at days 3 and 28 (Figs. 4g and h).Only time affected d13C of DOC significantly; matricpotential showed no effect (Table 1).

3.5. Microbial biomass

During the initial phase of the experiment (days 3 and 7),microbial biomass slightly but significantly increased dueto litter addition in all three layers (two-way ANOVA withlitter and depth as fixed factors, F1,69 ¼ 78.3, Po0.001;Figs. 5a and b). In the 0–1mm layer, microbial biomassincreased after 14 days until the end of the experiment. Thisincrease was also detected in the other layers, but was lessclear and had a delay of 14 and 70 days in the 1–2 and2–3mm layers, respectively. Two-way ANOVA with time

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Fig. 4. Content and d13C of soil organic C and of K2SO4 extractable C in the three top layers (0–1, 1–2 and 2–3mm). Values are means of three replicates,

error bars show standard deviation.

C. Poll et al. / Soil Biology & Biochemistry 40 (2008) 1306–13211312

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Table 1

ANOVA table of F values for the effects of the factors time (3, 7, 14, 28, 56 and 84 days) and matric potential (�0.0063 and �0.0316MPa) on the DOC

content, d13C of DOC, Corg content, d13Corg, microbial biomass and ergosterol content in three layers (0–1, 1–2, 2–3mm) of the litter treatments

0–1mm 1–2mm 2–3mm

df F value df F value df F value

Corg Time 5,36 16.0�� 5,36 0.8 n.s. 5,36 12.4��

Matric potential 1,36 0.4 n.s. 1,36 0.8 n.s. 1,36 1.2 n.s.

Time�matric potential 5,36 1.8 n.s. 5,36 1.2 n.s. 5,36 3.1�

d13Corg Time 5,36 74.2�� 5,36 24.3�� 5,36 29.4��

Matric potential 1,36 5.7� 1,36 4.9� 1,36 15.4��

Time�matric potential 5,36 0.7 n.s. 5,36 1.4 n.s. 5,36 1.9 n.s.

DOCa Time 5,36 10.8�� 5,36 24.9�� 5,36 17.8��

Matric potential 1,36 12.3�� 1,36 13.3�� 1,36 13.5��

Time�matric potential 5,36 1.6 n.s. 5,36 1.9 n.s. 5,36 3.6�

d13C DOC Time 3,24 39.8�� 3,24 7.9�� 3,24 29.9��


Time�matric potential 3,24 0.3 n.s. 3,24 0.9 n.s. 3,24 2.3 n.s.

Microbial biomass Time 5,33 23.3�� 5,36 26.0��,a 5,36 6.5��

Matric potential 1,33 0.2 n.s. 1,36 6.6�,a 1,36 0.1 n.s.

Time�matric potential 5,33 3.0� 5,36 0.9 n.s.a 5,36 0.6 n.s.

Ergosterol Time 5,35 136.1�� 5,36 52.4�� 5,36 35.1��


Time�matric potential 5,35 8.8�� 5,36 4.0�� 5,36 2.0 n.s.

n.s. ¼ not significant.�Po0.05.��Po0.01.��Po0.001.aStatistic performed with ln transformed data.


and matric potential as fixed factors revealed a significanteffect of time, but no effect of matric potential in the 0–1and 1–2mm layers (Table 1). There was, however, asignificant interaction between time and matric potentialfor the top layer.

Three days after litter addition, d13Cmic values rangedfrom 119.0% and 133.8% in the 2–3mm layer to 195.8%and 184.1% in the top layer of wet and dry soils,respectively (Figs. 5c and d). The values remained constantduring the experiment and were not statistically different,except for the 2–3mm layer, which showed a decrease atday 7.

3.6. Ergosterol

The ergosterol content in litter treatments was initiallyslightly less than in control soils, whereas it stronglyincreased between the samplings at days 14 and 28 in littertreatments (Figs. 5e and f). In all layers, time showed asignificant effect on ergosterol content, whereas matricpotential had no effect (Table 1). In the 0–1 and 1–2mmlayers, however, the interaction of time and matric potentialwas also significant, which indicates that matric potentialhad a time-dependent influence on ergosterol, with greatervalues at days 28 and 56 in wet than in dry soils.

3.7. Carbon balance

The d13C values of the litter C, CO2-C, SOC, DOC andCmic were used to calculate a C balance of the detritusphere(Table 2). The recovery rate of litter C in remaininglitter, CO2-C and SOC was approximately 90%. More Cremained in the litter layer of wet than of dry soils,with values of 41.7% and 35.6% after 84 days, respectively.Accordingly, more litter C was found in CO2-C whensoils were wet, except at day 28. After incubation, 47.9%and 43.4% of litter C was mineralised to CO2-C inwet and dry soils, respectively. Compared to the CO2-Cproduction of the control soils, a greater amount —approximately 6.2mg (�0.0063MPa) and 5mg(�0.0316MPa) — of soil-derived CO2-C was respiredin the litter treatments after 84 days. This differencewas mainly built up after day 14. After 3 days, similaramounts of litter C were respired or transported intothe soil, with slightly greater values for wet soils. Duringthe initial phase (days 3 and 7), the proportion of litter C inSOC was almost constant. This was followed by acontinuous accumulation of litter-derived C in SOC untilthe end of the incubation. From days 28 to 84, dry soilscontained more litter C (6.1%) than wet soils (5.8%) after84 days.

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Fig. 5. Microbial biomass (Cmic), d13C of the microbial biomass and ergosterol content in the three top layers (0–1, 1–2 and 2–3mm). Values are means of

three replicates, error bars show standard deviation.


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Table 2

Litter C balance of the detritusphere at two different matric potentials over a period of 84 days

Matric potential Day Litter

mg litter C (%)

CO2

mg litter C (%)

SOC

mg litter C (%)

Recovery (%)

�0.0063MPa 3 142.7 (95.2) 1.5 (1.0) 1.5 (1.0) 97.1

7 135.2 (90.1) 8.9 (5.9) 1.6 (1.1) 97.1

14 101.8 (67.9) 25.9 (17.3) 3.8 (2.5) 87.7

28 78.8 (52.5) 48.5 (32.3) 5.6 (3.7) 88.6

56 65.4 (43.6) 66.0 (44.0) 7.8 (5.2) 92.8

84 53.4 (35.6) 71.8 (47.9) 8.7 (5.8) 89.3

�0.0316MPa 3 145.9 (97.2) 0.9 (0.6) 1.1 (0.7) 98.6

7 138.2 (92.2) 6.5 (4.3) 1.1 (0.7) 97.6

14 107.1 (71.4) 23.2 (15.4) 2.6 (1.8) 88.6

28 82.4 (54.9) 49.2 (32.8) 8.2 (5.4) 93.1

56 67.5 (45.0) 60.7 (40.5) 8.7 (5.8) 91.3

84 62.6 (41.7) 65.1 (43.4) 9.2 (6.1) 91.2

Numbers in parentheses give the percentage of the litter C (150mg) found in the different pools. Values of SOC and DOC are the sum of the upper 3mm of

the soil cores. The recovery of litter C in remaining litter, CO2 and SOC is given in percent.


3.8. Enzymes

Litter addition increased b-D-glucosidase activity within2–3mm from the litter layer after a 3-day lag phase(Figs. 6a and b). The activities of a-D-glucosidase,xylosidase, N-acetyl-glucosaminidase, phosphatase andleucine peptidase showed the same pattern (see Appendix A).To analyse the temporal pattern, we considered the enzymeactivities at 0–1mm. In the deeper layers, differencesbetween litter treatments and control soils were only minor.The activities of a-D-glucosidase, xylosidase, and leucinepeptidase showed a similar lag phase of 3 days asb-D-glucosidase, whereas phosphatase and N-acetyl-gluco-saminidase (Fig. 6c) activity increased 14 and 28 daysafter litter addition, respectively. After the lag phase,b-D-glucosidase activity increased in the 0–1mm layerduring the first 2 weeks of the experiment (Fig. 6d). Thisincrease was more pronounced for wet than for dry soils.For the latter, the increase in enzyme activity lasted untilday 28 and remained constant until the end, whereas theactivity in wet soils slightly decreased after 14 days. Theactivity of a-D-glucosidase, xylosidase, phosphatase andleucine peptidase showed a similar temporal pattern (seeAppendix A). For these five enzymes the activity in wet soilsdeclined below those in dry soils between days 14 and 56. Incontrast to the other enzyme activities, N-acetyl-glucosami-nidase activity jumped between days 14 and 28 and thenincreased slightly until the end of the experiment (Fig. 6c).The activity of this enzyme tended to be greater in wet soils.The N-acetyl-glucosaminidase activity was positively corre-lated with the ergosterol content (r ¼ 0.85, Po0.001).

4. Discussion

4.1. Temporal pattern

In the present experiment, we followed the dynamics ofC turnover and microbial abundance in the detritusphere

of rye residues over a period of 84 days. The observedtemporal pattern of litter mass loss fits well with theproposed concept of Berg and Matzner (1997). Theyascribed the first decline in litter mass to the decompositionof soluble substrates and nonlignified carbohydrates. Afterthis initial decomposition phase, more complex substratessuch as lignified cellulose were mineralised. In ourexperiment, contents and d13C values of SOC and DOCpeaked after 3 days, followed by a decrease between days 3and 7. We suggest that this early effect of litter addition onSOC and DOC is caused by diffusion of soluble C from thelitter (Fig. 1b). This pool is exhausted after the first daysdue to mineralisation and transport. A second increasefollowed after 14 days, probably reflecting the depolymer-isation of more complex litter components like nonlignifiedcellulose and subsequent transport of freshly producedsolutes. Our results are in accordance with Gaillard et al.(1999), who in a similar experiment found that litter Cdiffused 3–4mm into the adjacent soil from added wheatstraw. Carbon accumulation was most pronounced duringthe first 5 days, whereas after 30 days no significantaccumulation occurred.The supposed separation of C turnover in the detritu-

sphere into an initial and a later phase is supported by theresults of the total microbial and the fungal biomassmeasurements. We hypothesised that microbial biomasswill increase due to transport of soluble litter C and start todecay after this transport drops (Fig. 1a). Our experimentrevealed no such decline in microbial biomass. A possibleexplanation is the different response of r and K strategiststo litter addition and C transport. The mineralisation ofcomplex litter compounds requires the presence of suffi-cient decomposer organisms. For example, Tester (1988)showed that wheat straw was colonised with microorgan-isms capable of decomposing easily available substratesduring the initial phase of decomposition. After 30 days,wheat straw mineralisation increased due to contact withsoil, which was correlated with the development of soil

ARTICLE IN PRESS

Fig. 6. Enzyme activities in soil layers of increasing distance to the litter (a and b) and in relation to the time (c and d). (a, b) b-D-glucosidase activity after3 and 14 days incubation, respectively. (c, d) temporal pattern of N-acetyl-glucosaminidase and b-D-glucosidase activity of the 0–1mm layer. Values are

means of three replicates, error bars show standard deviation.


basidiomycetes. We analysed ergosterol content andN-acetyl-glucosaminidase activity, which are both consid-ered as indicators for fungal biomass (Miller et al., 1998).Ergosterol content as well as N-acetyl-glucosaminidaseactivity increased rapidly between days 14 and 28, which isin accordance with McMahon et al. (2005), who observedthat fungal PLFA 18:2o6,9 increased 15 days after addingryegrass to soil. In the present study, however, the totalmicrobial biomass already increased after 3 days, probablydue to growth of bacteria using the soluble fraction of litterC. McMahon et al. (2005) observed a peak in bacterialPLFAs in ryegrass after 0.6 days, which was not detectablein leached ryegrass. Fungi are considered as the maindecomposers of polymerised substrates (Swift et al., 1979);the increase in fungal biomass after 14 days thereforeestablished sufficient decomposers to substantially miner-

alise complex substrates. Consequently, more soluble litterC was produced, which was partly transported into theadjacent soil. This agrees with Lang et al. (2000), whofound a greater DOC production and transport into theadjacent soil after inoculating straw with white rot fungi.The succession of bacteria and fungi agrees with thefindings of Henriksen and Breland (1999), who observed anearly peak in bacterial biomass followed by an increase infungal biomass in soil after adding wheat straw. We suggestthat the initial decomposition phase in our experiment wasdominated by bacterial r strategists, whereas the laterphase was dominated by fungal K strategists (Fig. 1b). Thelatter assumption is further supported by the observedpositive priming effect. Fontaine et al. (2003) hypothesisedthat stimulating r strategists by providing quickly availablesubstrates yields no positive priming effect, whereas


stimulating SOC-feeding K strategists with polymeric litterC will enhance SOC mineralisation.

In the detritusphere, we detected gradients in enzymeactivity after 7 days. This supports our hypothesis thatenzyme activities will increase later than microbial biomass(Fig. 1a). During the first days of the experiment, solublelitter C provided easily available substrates for soilmicroorganisms; these substrates were allocated more togrowth than to enzyme production (Allison, 2005). Thisexplains the initial microbial growth and the lag phase ofenzyme activities. After soluble substrates were exhausted,more complex substrates were degraded with time, requir-ing production of extracellular enzymes. This is inaccordance with our finding that, after 7 days, enzymeactivities increased over a distance of 2–3mm, which is inthe same range as observed in previous studies (Gaillardet al., 1999; Kandeler et al., 1999; Poll et al., 2006).Moreover, decaying r strategists might have contributed tothe increasing enzyme activity by releasing intracellularenzymes. We hypothesised reduced enzyme activity at theend of the incubation (Fig. 1a), but did not detect this tothe expected extent. A possible reason is the ongoingmineralisation of the litter with the concomitant need forextracellular enzymes.

4.2. Water content

Water content significantly affected litter decomposition(Figs. 1 and 2). Both respiration and litter mass loss resultsindicated a greater mineralisation activity in wet versus drysoils. This agrees with Thomsen et al. (1999), who showedthat decomposition of native SOC and labelled ryegrasswas highly correlated with the volumetric water content.Studying the effect of water content on litter decomposi-tion, Scott et al. (1996) observed that significantly moresurface litter was mineralised in soils at �0.0120MPa thanat �0.0330MPa. In a similar experiment, 73.8% of oilseedrape residues remained on the soil surface after 9 weeks(Coppens et al., 2006) compared to 43.6–45% in ourexperiment. However, Coppens et al. (2006) leached theresidues by rain prior to incubation, potentially reducingthe decomposition rate by removing the soluble C fraction.We hypothesised that the water content not only influencesthe total decomposition of litter, but also the temporalpattern of litter C turnover at the microscale. During thefirst 2 weeks, more litter C was respired as CO2 and moresoluble substrates were transported into the adjacent soil at�0.0063 than at �0.0316MPa. Moreover, soil moisturehad a significant effect on the DOC content and the d13Cvalues of the SOC and tended to increase microbialbiomass. We explain this by an accelerated transport rateat great water content. These results agreed with ourprevious finding that water content modifies the transportrate of soluble substrates in the detritusphere (Poll et al.,2006). Beside the transport rate, water content affects themicrobial activity, with greater activity at increased watercontents (Griffin, 1981). In our study, enzyme activities

increased more during the initial incubation phase in thosetreatments with elevated water content. Additionally, morelitter C in the SOC and DOC of wet soils provided agreater substrate concentration. Since extracellular en-zymes are inducible (Allison and Vitousek, 2005), thiscould have induced a greater enzyme activity. After 14days, however, microbial biomass was lower in wet versusdry soils, which was followed by less litter C and lowerenzyme activities after 28 days. We suggest that the greaterinitial microbial activity in wet soils boosted mineralisationof litter-derived C; this interpretation is supported by thegreater amount of litter C found in the microbial biomassin these soils (data not shown). This process reduced theavailable substrates for microbial growth and enzymeactivity in wet soils during the later phase of litterdecomposition.Based on the d13C values of the litter, CO2-C and SOC,

we calculated a balance for the litter C. The heterogeneouslabelling of the litter complicated this calculation. In thebeginning, the respired and transported litter C had a d13Cvalue of up to 1400%, the bulk litter 299%. Despite thedisadvantage of the heterogeneously labelled litter, therecovery rate (�90%) and our calculated amounts of litterC in different pools are in the same range as those observedby Gaillard et al. (1999), although we found highermineralisation rates. The recovery rate indicates that wefound most of the litter C and that the general trends areconsistent: increased water content induced a greater littermass loss. This mainly resulted in more CO2 productionand, only temporarily, in more litter C in SOC. Some of themissing C might be located more than 3mm from the litterlayer.

5. Conclusions

The study of the detritusphere in a microcosm experi-ment clearly revealed an interaction between substratequality, microbial succession and soil moisture regime. Theinitial phase of litter decomposition was dominated bymineralisation and diffusion of easily available and solublelitter compounds, which were mainly used by bacterial r

strategists. Release of soluble substrates by depolymerisa-tion of complex litter compounds through fungal K

strategists started after the initially soluble litter C wasexhausted. The freshly produced soluble substrates diffusedinto the adjacent soil, where SOC and microbial biomassincreased. Based on our results, we developed a two-phaseconceptual model of litter C turnover and microbialresponse in the detritusphere (Fig. 1b). Soil water contentmodified C transport, microbial activity and thereforemineralisation of litter. An increased water content inducedfaster transport of soluble substrates, which resulted ingreater initial microbial biomass and activity. This processreduced the availability of substrates for microbial growthand activity after the initial phase. Our results underline theimportance of studying microbial succession in the contextof C turnover in soils.


Acknowledgement

We thank Erhard Strohm and Nicole Schmid for theirexcellent technical assistance. Funding was provided by theDeutsche Forschungsgemeinschaft (DFG) priorityprogram SPP 1090: ‘‘Boden als Quelle und Senke fur

Table A1

Enzyme activities in soil layers of increasing distance to the litter (means, 7

Depth Treatment 3 days 7 days

b-D-glucosidase (nmol g�1 h�1)

0–1mm �0.0063MPa control 396715.2 531781.9

�0.0063MPa litter 443738.5 685760.0

�0.0316MPa control 400746.8 515796.0

�0.0316MPa litter 439763.4 667745.3

1–2mm �0.0063MPa control 295717.6 462739.0

�0.0063MPa litter 358757.6 530731.3

�0.0316MPa control 364717.5 464749.7

�0.0316MPa litter 345710.1 455731.4

2–3mm �0.0063MPa control 311728.6 422711.2

�0.0063MPa litter 371721.7 544740.2

�0.0316MPa control 354720.7 460743.8

�0.0316MPa litter 396717.2 433736.2

3–5mm �0.0063MPa control 298740.7 498724.6

�0.0063MPa litter 350781.0 441714.8

�0.0316MPa control 398735.3 453714.3

�0.0316MPa litter 364732.0 466753.6

5–10mm �0.0063MPa control 332713.7 482764.5

�0.0063MPa litter 367719.8 48179.9

�0.0316MPa control 369728.1 48574.9

�0.0316MPa litter 377714.4 475712.9

a-D-glucosidase (nmol g�1 h�1)

0–1mm �0.0063MPa control 29679.0 165718.6

�0.0063MPa litter 334736.9 192725.4

�0.0316MPa control 364746.3 15170.8

�0.0316MPa litter 347750.0 186712.1

1–2mm �0.0063MPa control 24872.12 143724.6

�0.0063MPa litter 288757.3 140715.6

�0.0316MPa control 344711.2 144724.5

�0.0316MPa litter 333719.7 14177.6

2–3mm �0.0063MPa control 263719.4 13873.6

�0.0063MPa litter 307746.2 142719.0

�0.0316MPa control 353718.2 141714.0

�0.0316MPa litter 343723.4 13472.8

3–5mm �0.0063MPa control 257717.1 140711.5

�0.0063MPa litter 325765.6 133710.1

�0.0316MPa control 383719.6 14379.6

�0.0316MPa litter 352729.8 140716.4

5–10mm �0.0063MPa control 312730.5 147715.1

�0.0063MPa litter 290732.5 154716.4

�0.0316MPa control 332721.0 15376.2

�0.0316MPa litter 322725.3 168712.9

Xylosidase (nmol g�1 h�1)

0–1mm �0.0063MPa control 64711.0 94711.3

�0.0063MPa litter 6579.4 120717.7

�0.0316MPa control 7175.0 8773.5

�0.0316MPa litter 7972.0 10975.2

CO2- Mechanismen und Regulation der Stabilisierungorganischer Substanz in Boden’’.

Appendix A

For the enzyme data see Table A1.

standard deviation)

14 days 28 days 56 days 84 days

5527114.2 477729.0 5837131.9 531775.9

9207127.9 842795.7 727791.9 7587105.3

5637115.8 496790.4 5147102.4 506768.0

825766.7 9097105.3 8057237.9 872762.1

540746.6 506736.4 563726.3 553742.8

611739.1 596727.3 547780.1 586787.4

476753.8 4777130.2 451783.8 549756.8

614710.3 703715.3 618745.5 5937125.5

465746.1 468778.3 523788.1 547745.7

535749.6 495768.7 530751.3 5777104.4

427746.6 429710.3 483756.3 534763.6

575784.9 6107104.6 540742.0 608710.8

495793.0 497735.2 488745.1 5187126.4

503717.0 499739.0 437785.9 538744.7

430746.8 458736.0 443760.1 489781.3

497787.2 5547122.7 4527103.6 514745.2

468718.6 438727.3 447728.4 495723.6

477728.8 449750.8 468735.6 44978.8

480766.5 455758.8 487777.6 454787.1

472762.2 518718.3 441748.3 5857106.3

162721.6 160716.9 15376.3 166711.2

222717.1 235728.4 198714.0 199723.6

151723.0 140716.2 133714.7 155716.3

204721.3 221715.3 207742.6 219724.6

164731.5 169713.3 135714.3 17574.7

15979.1 16777.5 174711.0 170721.0

14179.6 146718.9 131716.5 14873.9

165712.8 199714.7 17171.3 190726.9

15375.6 149718.5 161713.4 167713.7

15178.0 145718.1 165726.2 16878.1

13477.8 14177.4 140716.6 159718.0

154720.6 164721.5 168721.0 18979.2

163731.6 142710.9 145721.1 160739.3

142710.6 141716.2 144718.5 16973.8

15379.0 12971.4 125728.4 150731.2

143720.1 153724.7 135725.3 164715.6

142716.1 147719.2 147723.0 16277.8

14778.1 143720.9 152724.6 13772.0

14177.7 13478.1 148720.1 146725.3

13973.4 15875.9 133715.8 180717.5

95712.0 9073.6 94712.3 101710.8

171724.0 131724.6 113715.0 125718.8

90.0723.5 8176.1 90714.6 108718.6

151716.5 170717.5 151736.2 15479.0

ARTICLE IN PRESS

Table A1 (continued )

Depth Treatment 3 days 7 days 14 days 28 days 56 days 84 days

1–2mm �0.0063MPa control 5175.0 81715.0 95710.7 8974.7 9070.7 9674.0

�0.0063MPa litter 62713.5 9678.0 11178.8 10075.4 10277.3 103712.1

�0.0316MPa control 7472.2 9476.8 85710.9 8678.6 8475.3 9574.6

�0.0316MPa litter 6774.4 8071.7 117714.4 130714.7 12078.8 134722.4

2–3mm �0.0063MPa control 5774.4 7873.8 8373.6 83711.6 9872.7 11174.3

�0.0063MPa litter 63712.6 8373.0 10278.8 85713.9 9377.3 10271.0

�0.0316MPa control 7476.3 8275.7 7571.5 8879.5 8576.2 95713.5

�0.0316MPa litter 7274.5 8372.1 99717.2 119721.1 10878.5 11177.7

3–5mm �0.0063MPa control 5575.7 8572.1 89713.0 8771.4 90710.5 98730.6

�0.0063MPa litter 62713.2 7879.8 8678.4 9079.3 79714.0 98715.7

�0.0316MPa control 7775.6 8774.3 8677.9 79712.0 8477.3 102730.5

�0.0316MPa litter 7273.2 7474.2 89713.9 10079.7 86721.8 106711.5

5–10mm �0.0063MPa control 6273.1 8473.4 91720.4 8671.3 84714.9 9876.2

�0.0063MPa litter 7273.7 87714.7 8772.6 8079.0 85715.7 8071.8

�0.0316MPa control 7777.9 8273.9 87710.2 8074.3 86713.3 80715.2

�0.0316MPa litter 73712.8 8677.4 8978.7 97716.1 80711.9 10279.4

N-acetyl-glucosaminidase (nmol g�1 h�1)

0–1mm �0.0063MPa control 9578.7 137732.3 145721.7 154713.6 142716.7 13874.2

�0.0063MPa litter 9577.5 152722.3 193720.4 6387237.1 7027144.3 778798.9

�0.0316MPa control 10074.3 11377.3 130724.6 145740.5 100714.6 127714.3

�0.0316MPa litter 102724.4 175721.3 174734.9 562783.3 5767126.2 7517137.6

1–2mm �0.0063MPa control 82711.0 138726.0 13773.3 13578.4 139729.3 149713.0

�0.0063MPa litter 95719.3 128726.0 124712.4 296775.6 342756.7 400724.9

�0.0316MPa control 11776.5 154724.1 11377.4 11577.3 112710.3 12678.4

�0.0316MPa litter 10177.8 125726.2 12975.9 307741.6 277745.6 423786.2

2–3mm �0.0063MPa control 7679.5 124716.3 164757.3 123717.3 133717.8 14779.3

�0.0063MPa litter 96719.3 118711.0 14172.3 192713.0 228735.0 261740.1

�0.0316MPa control 117710.1 12271.70 108711.0 122714.6 121715.1 14373.6

�0.0316MPa litter 121727.3 10871.2 125714.2 201720.7 273710.6 314739.4

3–5mm �0.0063MPa control 82711.3 128715.6 146730.8 12179.0 148720.9 13179.8

�0.0063MPa litter 101725.8 115717.5 130725.9 167745.9 158728.1 201729.3

�0.0316MPa control 10679.5 13573.4 12674.4 117718.5 99718.9 12579.1

�0.0316MPa litter 100716.2 140736.2 115726.0 161727.7 157719.7 218727.9

5–10mm �0.0063MPa control 91713.7 120711.4 151711.7 138718.5 145740.2 137717.4

�0.0063MPa litter 114711.0 126711.8 136722.6 134714.2 141726.2 13676.2

�0.0316MPa control 10375.8 12174.9 122711.3 112710.1 126724.3 108722.2

�0.0316MPa litter 10275.1 132719.3 12578.2 129712.6 135715.3 16376.9

Phosphatase (nmol g�1 h�1)

0–1mm �0.0063MPa control 429727.6 692780.4 7277108.9 686745.9 716736.8 750728.1

�0.0063MPa litter 457761.0 698750.2 911777.9 9517126.4 873726.8 9017101.5

�0.0316MPa control 500741.7 656739.1 7177127.4 674783.0 661788.2 7707116.3

�0.0316MPa litter 520745.7 731776.5 775762.2 906770.2 8667132.6 894793.4

1–2mm �0.0063MPa control 38074.7 668769.0 674756.8 737778.7 673757.2 781767.1

�0.0063MPa litter 4377108.2 652747.5 678726.8 773743.4 819766.7 7587120.2

�0.0316MPa control 52676.3 659761.5 663772.1 673769.0 623748.1 726727.2

�0.0316MPa litter 468729.1 646737.2 690717.4 864721.1 766749.1 934781.3

2–3mm �0.0063MPa control 39973.1 639741.4 665759.6 659765.1 714775.4 764743.7

�0.0063MPa litter 481758.8 661744.1 670741.0 670746.9 760782.9 767770.4

�0.0316MPa control 528729.9 61177.9 63673.4 64979.7 658780.8 732784.9

�0.0316MPa litter 536728.7 620740.0 713749.6 767768.8 803763.5 875748.6

3–5mm �0.0063MPa control 399732.0 679752.7 721765.6 667736.4 675774.3 7467106.5

�0.0063MPa litter 4667101.0 610718.4 679757.7 672741.1 646796.7 764749.7

�0.0316MPa control 557749.1 648726.9 655727.1 628746.1 6137122.9 716786.6

�0.0316MPa litter 524718.4 643713.9 6777121.9 7107102.2 6477162.2 791729.5


ARTICLE IN PRESS

Table A1 (continued )

Depth Treatment 3 days 7 days 14 days 28 days 56 days 84 days

5–10mm �0.0063MPa control 470734.7 650755.1 67078.4 687740.8 653754.5 740761.2

�0.0063MPa litter 477728.2 636724.1 675719.7 655775.7 650766.5 672712.8

�0.0316MPa control 499727.3 653725.5 643734.7 638758.7 684764.7 6807118.2

�0.0316MPa litter 533729.5 710749.5 670731.5 723751.1 6487134.1 7947127.2

Leucine peptidase (nmol g�1 h�1)

0–1mm �0.0063MPa control 115721.2 233762.1 227761.9 176730.4 16073.9 15274.5

�0.0063MPa litter 199760.8 272750.7 332731.5 385792.0 33173.5 325729.7

�0.0316MPa control 165747.1 213740.9 221738.1 174738.7 141718.8 13973.2

�0.0316MPa litter 221741.3 295746.2 311738.8 352786.6 331785.4 366765.3

1–2mm �0.0063MPa control 107718.1 215758.7 198725.2 194756.7 144710.9 177736.6

�0.0063MPa litter 180764.2 224789.8 220723.8 222761.9 206725.5 223727.1

�0.0316MPa control 158745.5 195744.3 20272.5 179763.6 13676.4 161730.7

�0.0316MPa litter 203765.0 209740.0 236721.9 246741.3 215718.1 225721.0

2–3mm �0.0063MPa control 108711.8 183766.0 194746.8 153727.2 163737.5 159722.9

�0.0063MPa litter 168751.1 207749.4 195745.9 191755.0 192719.3 186718.2

�0.0316MPa control 165744.2 202733.5 188719.9 170716.9 159721.3 146720.0

�0.0316MPa litter 188732.8 216739.3 21375.5 205732.1 200733.3 196714.9

3–5mm �0.0063MPa control 123732.2 197755.1 231760.6 166750.7 151744.1 133733.0

�0.0063MPa litter 182768.3 208727.0 197743.4 175738.4 148732.4 155717.4

�0.0316MPa control 174738.7 205747.9 192718.8 176740.4 130716.8 144710.5

�0.0316MPa litter 179740.2 198734.2 191717.2 203758.6 165763.2 165713.7

5–10mm �0.0063MPa control 170730.1 221749.4 180711.4 196759.9 140727.4 142718.1

�0.0063MPa litter 202766.3 214770.9 179716.4 188747.5 151738.5 12974.8

�0.0316MPa control 176755.6 221760.1 195723.0 204777.6 154734.2 143717.4

�0.0316MPa litter 173727.0 229740.1 197729.2 203757.9 166738.6 165715.5


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Documents

Dynamics of litter carbon turnover and microbial abundance in a rye detritusphere