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Soil Biology & Biochemistry 41 (2009) 176–178

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Soil Biology & Biochemistry

journal homepage: www.elsevier .com/locate/soi lb io

Short Communication

Particle size alters litter diversity effects on decomposition

Alexei V. Tiunov*

Institute of Ecology and Evolution RAS, Leninsky Prospect 33, 119071 Moscow, Russian Federation

a r t i c l e i n f o

Article history:Received 27 March 2008Received in revised form 9 September 2008Accepted 22 September 2008Available online 20 October 2008

Keywords:Litter diversityDiversity-functioningSaprophagous animalsRespirationDecompositionComminutionFungiNutrient translocationMycelial transport

* Corresponding author. Tel.: þ7 495 958 1449; faxE-mail address: a_tiunov@mail.ru

0038-0717/$ – see front matter � 2008 Elsevier Ltd.doi:10.1016/j.soilbio.2008.09.017

a b s t r a c t

Nutrient transfer between decomposing leaves may explain non-additive species diversity effects ondecomposition. The influence of the diversity of litter species on decomposition was compared inmixtures composed of large (>200 mm2) or small (<9 mm2) litter fragments. The increase in the numberof species (aspen, oak, alder and pine, from monocultures to four species in all possible combinations)initially (at day 43) suppressed respiration, but eventually (after 142 days) did not affect the mass loss ofthe mixtures of small litter fragments. In contrast, the decomposition of litter in large fragmentsincreased with increased diversity, and 93% of all mixtures decomposed faster than would be predictedfrom monocultures. The results suggest that the active transport of nutrients by fungal hyphae, ratherthan passive diffusion, drives positive effect of the litter species diversity on decomposition.

� 2008 Elsevier Ltd. All rights reserved.

The increase in species diversity of decomposing litter oftenleads to significant and sometimes relatively strong changes indecomposition rates (Gartner and Cardon, 2004; Hattenschwileret al., 2005). The nutrient exchange between different litter speciesis often regarded as one of the most important mechanisms of non-additive effects observed in litter mixtures (Wardle et al., 1997;Salamanca et al., 1998). This exchange can be achieved by twodifferent processes: a passive diffusion (Schimel and Hat-tenschwiler, 2007) and an active transport by fungal hyphae(Briones and Ineson, 1996; McTiernan et al., 1997). With diffusionnutrients that stimulate microbial activity as well as inhibitorycompounds, such as phenolics, might be translocated (Gartner andCardon, 2004). Therefore, the decomposition of a litter species canbe stimulated, retarded or not affected by the presence of otherlitter species. In the case of fungal translocation, the inhibitorycompounds are not transported, and the microbial activity anddecomposition rates of litter mixtures are more likely to increase.

The relative importance of passive and active nutrient exchangeshould depend on the physical state of the litter. Though ina majority of litter decomposition experiments the activity of largesoil invertebrates was not taken into account (Prescott, 2005), inmany natural habitats a large part of leaf litter is processed by soil

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invertebrates. Saprotrophic animals, such as earthworms or diplo-pods, have limited digestive capabilities, and a major part of theconsumed litter returns into soil in an altered physical form. Inparticular, the litter is finely comminuted with a strongly reducedparticle size (e.g. Schulmann and Tiunov, 1999).

The pattern of nutrient exchange should be different in frag-mented litter of different sizes. If finely fragmented litter is mixed,passive diffusion of nutrients and/or inhibitors would be facilitated.In the mixture of large litter fragments, active mycelial transportwould be of greater importance, leading to a more pronouncedpositive diversity effect on decomposition. Here I report a labora-tory experiment in which the effect of the litter species diversity ondecomposition was compared in mixtures of differently frag-mented litter.

Freshly fallen leaves of aspen (Populus tremula L.), alder (Alnusglutinosa (L.) Gaertn.) and oak (Quercus robur L.) were collected inOctober near Malinky biological station (Moscow region, 55�450 N,37�230 E). Each litter species was collected under 5–8 individualtrees. Senescent needles were gathered from 10 Scotch pine (Pinussylvestris L.) trees. Leaves and needles were dried at 60 �C toa constant weight. In addition, a small amount of litter of eachspecies was collected from the soil surface, mixed and subsequentlyused to inoculate experimental microcosms with native microor-ganisms. To obtain ‘‘large’’ litter fragments, the dried litter was cutwith scissors into relatively large pieces (from 200 to 400 mm2, ca.20 mm in length for needles). To obtain ‘‘small’’ fragments, the

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Fig. 1. Respiration rates at day 43 (A) and mass loss after 142 days (B) of litter monocultures of different fragment size (meanþ SE). A. g. – Alnus glutinosa, P. t. – Populus tremula,P. s. – Pinus sylvestris, Q. r. – Quercus robur. Bars sharing the same letter are not significantly different (Tukey’s HSD test, P< 0.05, n¼ 5–6).

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Fig. 2. Changes in respiration with litter species richness (day 43 of the experiment).A – small fragments, B – large fragments. Solid line represents linear regression,dashed line shows mean expected values for litter mixtures, data points representindividual microcosms. Mixtures included all possible combinations of the litter ofA. glutinosa, P. tremula, P. sylvestris and Q. robur.

A.V. Tiunov / Soil Biology & Biochemistry 41 (2009) 176–178 177

dried litter was minced with a kitchen meat processor (GOST 4025-78). The minced litter was sieved through a series of sieves toremove very small (<0.5 mm) and large (>3 mm) particles.

The experiment was performed in 70-ml plastic vessels.Each microcosm received 900 mg of oven-dry litter either in largeor in small fragments. To produce multispecies mixtures, litterspecies were mixed proportionally (2� 450 mg, 3� 300 mg, or4� 225 mg). Thus, all possible combinations of four litter species(four monocultures, six 2-species, four 3-species and one 4-speciesmixture) for each fragment size were produced. There were sixreplicates of each mixture, except for the 4-species mixtures thatwere replicated ten times. A few replicates (six microcosms in total)were lost due to technical problems. Communities of native littermicroorganisms and microfauna were re-inoculated by adding toeach microcosm 2.5 ml of twice 40-mm filtered water suspension offresh litter. The initial moisture content was 74% of wet weight in alltreatments. The vessels were covered by air-permeable lids andkept in water-saturated atmosphere at 18 (�2) �C.

The respiration of litter was measured 43, 98 and 142 days afterthe start of experiment by the alkali trapping method (Alef, 1995).One milliliter 1 N KOH in a test tube was placed inside eachmicrocosm. Alkali was exposed for 24 h with microcosms closedairtight, and then titrated with 0.1 N HCl. Results were expressed asmg CO2-C g�1 litter day�1. After 142 days, remaining litter was driedat 60 �C and weighed. The mass loss was expressed as percentage ofinitial litter mass. To estimate the composition of the fungalcommunity in the microcosms, three small particles of litter (ca.0.5 mm2) were taken before drying from three microcosms in eachtreatment and placed on malt-extract agar.

A linear regression was used to assess the overall effect ofspecies richness on the rate of litter decomposition. Two-wayanalysis of variance was used to analyse the effects of litter frag-ment size and species richness on the deviations of observedrespiration or mass loss of litter mixtures from expected values.Expected values were calculated as the average of componentspecies respiration or mass loss observed in monocultures (Wardleet al., 1997). Tukey’s HSD test was used for comparison of means.Calculations were made in Statistica 6.0 (StatSoft Inc., Tulsa).

The litter species differed significantly (P< 0.001) in decompo-sition rates. The fragmentation of litter led to an immediateincrease in respiration (data not shown), but after 43 days (or after98 days for alder litter, data not shown) the respiration of finelyfragmented litter was lower than of litter in large fragments(Fig. 1A). Consequently, in each species the finely fragmented litter

lost significantly (P< 0.05) less weight than the litter in largefragments (Fig. 1B).

The mixing of finely fragmented litter of different species didnot increase litter decomposition, both in terms of respiration andtotal mass loss. In fact, at day 43 the respiration of mixtures of smalllitter fragments decreased significantly (P< 0.0001, n¼ 92) withincreased species diversity (Fig. 2A). However, the species diversitydid not affect respiration at days 98 and 142, and the overall weightloss of the mixtures of finely fragmented litters (23.0%, SE 0.5) didnot differ from expected values (23.2%, Fig. 3).

In contrast, the respiration of the litter in large fragments hada tendency to increase with increased species diversity (Fig. 2B).Though this increase in respiration was not significant (day 43:P¼ 0.119), the overall weight loss correlated significantly with the

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Fig. 3. Observed mass loss of litter mixtures as a function of the expected mass loss.Expected mass loss was calculated as the average of component species mass lossobserved in monocultures. Data points represent individual microcosms containinglitter either in small (solid triangles) or large (open circles) fragments. Along the 1:1line expected and observed values are equal; 93% of litter mixtures composed of largeand 47% of mixtures composed of small litter fragments lost more mass than expected.

A.V. Tiunov / Soil Biology & Biochemistry 41 (2009) 176–178178

diversity of litter (r¼ 0.209, P¼ 0.042, n¼ 93). Ninety-threepercent of all litter mixtures lost more weight than expected(average mass loss 31.9% (SE 0.5) and 28.8% (SE 1.4) in mixtures andmonocultures, respectively; Fig. 3). The two-way ANOVA confirmedthe strong interaction between the effects of litter fragment sizeand litter diversity (F3,177¼ 9.9, P< 0.001 for respiration at day 43;F3,176¼ 6.7, P< 0.001 for total mass loss).

Thus, the diversity of litter species differently affected decom-position depending on the size of litter fragments. The mixing offinely fragmented litter initially decreased microbial respiration,but eventually did not affect litter mass loss. Presumably, the closecontact between small litter fragments ensured easy diffusion ofnutrients, but also inhibitory compounds. In mixtures of large litterfragments the passive exchange of nutrients and inhibitorsbetween different litter types was more difficult. The litter inmicrocosms was inhabited by a diverse community of saprotrophicfungi. The most abundant species in all experimental treatmentswere very common and ubiquitous species Trichoderma koningii,Acremonium furcatum, Fusarium sambucinum, Botrytis cinerea,Penicillium aurantiogriseum and Penicillium brevicompactum. Themicromycetes produced dense networks of hyphae that connected

litter fragments and presumably translocated nutrients across littertypes.

Results of this study highlight the importance of the selectivetranslocation of nutrients by the network of fungal mycelium in soiland litter. The potential significance of this mechanism is wellknown, but its role in regulating litter decomposition is onlyscarcely studied (Frey et al., 2000, 2003). Also, these results suggestthat the activity of large soil invertebrates can modify and controllitter diversity effects on decomposition not only through selectiveconsumption (Schadler and Brandl, 2005; Hattenschwiler andGasser, 2005), but also through reducing particle size of the litter.

Acknowledgements

This study was sponsored by the Russian Foundation for BasicResearch. I thank A. Polyakova (MPSU) and N. Chigineva (MSU) forthe help in performing experiment.

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