The Effect of Litter Type and Macrofauna Community on Litter

Biologia 63/2: 249—253, 2008 Section Zoology DOI: 10.2478/s11756-008-0031-1

The eﬀect of litter type and macrofauna community on litter decomposition and organic matter accumulation in post-mining sites

Jan Frouz

Institute of Soil Biology, Biological Center, Academy of Sciences of the Czech Republic, Na Sádkách 7,CZ-37005 České Budějovice, Czech Republic; e-mail: [email protected]

Abstract: Field microcosms consisting of mineral soil (spoil substrate) and two types of litter taken either from an unreclaimed site with spontaneously developed vegetation (mostly Salix caprea) or from an alder plantation (a mixture of Alnus glutinosa and A. incana) were exposed in spontaneously developed or reclaimed sites at a post-mining heap near Sokolov (Czech Republic) for one year. The litter types diﬀered remarkably in C:N ratio which was 29 for spontaneous litter and 14 for alder litter. The two microcosm types were either accessible or not accessible to soil macrofauna. The eﬀect of macrofauna exclusion on soil mixing was complex and depended on litter quality and the site that determined soil fauna composition. In reclaimed sites where macrofauna was dominated by saprophags, mainly earthworms, the macrofauna access increased soil mixing. In sites where predators dominated, the macrofauna exclusion probably suppressed fragmentation and mixing activity of the mesofauna. Key words: soil formation; reclamation; succession; litter type; macrofauna

Introduction al. 2007). Consequently, enhanced soil mixing in post mining sites may indirectly be affected by the compo- Restoration of soil is crucial for ecosystem restoration sition and abundance of soil macrofauna. in post-mining sites (Bradshaw 1997). Accumulation of The aim of this study was to separate the effects soil organic matter (SOM) is an important part of the of litter quality, presence of soil macrofauna and local soil forming process. This is particularly true in post- site conditions (microclimate) on litter decomposition mining sites since spoil substrates in tailing heaps usu- and incorporation of soil organic matter in mineral soil. ally come from layers deep below the surface and sub- The study was performed in two post-mining sites near soil horizons and do not contain recent organic matter Sokolov (Czech Republic); the first site was covered (Schafer et al. 1979). The shift of organic matter from by an alder plantation and the second by spontaneous above-ground to below-ground pools represents an im- woody vegetation dominated by Salix caprea and Pop- portant succession trend in post-mining sites (Schafer ulus tremula. Field microcosms consisting of litter and et al. 1979). SOM accumulation in mineral soil affects mineral (tertiary clay from a pioneer site) layers were soil structure, water retention and the sorption of nu- positioned in both sites. During the study, both types trients (Allison 1973; Lavelle & Spain 2001). of microcosms containing alder and willow litter were Plant communities affect litter decomposition and either accessible or non-accessible to soil macrofauna. soil organic matter content either directly by litter quality or indirectly due to their effects on local microclimate and the structure of decomposers communi- Material and methods ties (Lavele et al. 1997; Lavelle & Spain 2001). Pre- The study was conducted at Velká podkrušnohorská heap, in vious field experiments indicated that in unreclaimed the Sokolov coal mining area in North Bohemia (50◦1421 sites the incorporation of carbon (C) in mineral soil N, 12◦3924 E). The average altitude of the study area was much slower than in reclaimed alder plantations is 600 m a.s.l., the mean annual precipitation is 650 mm ◦ (Frouz et al. 2006). This can be due to litter quality and the mean annual temperature is 6.8 C(fordetailssee as spontaneous sites are supplied with litter with high Frouz et al. 2001a). The two selected study sites were lo- C:N ratio while alder litter has low C:N ration (Frouz cated about 1 km apart; both were located on clay spoil et al. 2007). Moreover, alder plantations support the of the so-called cypris formation, the most common type of heap spoil substrate in the area (Kříbek et al. 1998). The development of more abundant macrofauna communi- first site was reclaimed by alder planting (a mixture of Alnus ties than spontaneous sites. Previous laboratory experi- glutinosa and A. incana) 30 years ago. The second site was ments and observations of soil microstructure indicated heaped about 20 years ago and no reclamation was applied. that soil macrofauna played a crucial role in soil mixing It is covered by vegetation, which has developed by natu- (Frouz et al. 2001a; Frouz & Nováková 2005; Frouz et ral colonization and is dominated by willow shrubs (Salix

c 2008 Institute of Zoology, Slovak Academy of Sciences 250 J. Frouz caprea). No levelling was applied in unreclaimed sites and to the litter layer and that below the net to the mineral longitudinal rows of depressions and elevations formed by layer. Fresh weights of both litter and mineral layers were the heaping process remained there. Further characteristics measured separately. A sample representing about half of of the unreclaimed site refer to the depression where micro- each layer was separated, weighed, dried to establish the cosms were exposed. A ca. 2 cm fermentation layer and a dry matter content and then used for C content analysis ca. 4 cm humus layer developed on the reclaimed site. In (Jackson 1958). the unreclaimed site, a 4–6 cm deep fermentation layer was The undried part of the mineral layer was homogenized present, while the humus layer was missing. The density of separately and about 10 g were used to measure microbial soil saprophagous macrofauna was much higher in the re- respiration. Microbial respiration was measured based on claimed than in the unreclaimed site (Frouz et al. 2001a, CO2 production, by trapping CO2 with NaOH in an air- ◦ b). In the places where microcosms were exposed, Lumbri- tight vial (for two days at 20 C) and subsequent titration −2 cidae density was 152 ± 35 (mean ± SD) individuals m in of NaOH by HCl after adding BaCl2. the reclaimed site and 11 ± 16 ind. m−2 in the unreclaimed The total amount of C in individual layers was calcu- site. The density of dipteran larvae was 127 ± 75 and 44 ± lated as the dry weight (dw) of the layer × the C content. 27 ind. m−2 and the density of millipedes was 15 ± 6and The amount of C removed from the litter layer was calcu- 4 ± 4 ind. m−2 in the reclaimed and the unreclaimed site, lated as the amount of C added to the litter layer at the respectively (Frouz et al. 2004). Both sites differred in litter beginning and during the experiment, minus the amount quality: C and N content in alder litter was 46.6 ± 0.97 and of C in the litter layer at the end of the experiment. The 3.26 ± 0.19, while in unreclaimed site litter C and N content amount of C accumulated in the mineral layer was calcu- was 45.01 ± 0.49 and 1.57 ± 0.13, respectively (Frouz et al. lated as the amount of C in the mineral layer at the end 2007). Thus C:N ratio was much higher in spontaneous (29) of the experiment minus the amount of C in the mineral than in alder litter (14). layer at the start of the experiment. Finally, the loss of C Two types of microcosms, accessible and non-accessible from the system (carbon mineralization) was calculated as for macrofauna, were prepared (for details see Frouz 2002 the difference between C removal from the litter layer and and Frouz et al. 2006). The microcosms were prepared in C accumulation in the mineral layer. Values in macrofauna- plastic boxes of 18 × 25 × 5 cm with twelve openings (1 accessible and non-accessible treatments were compared by cm in diameter), covered with a 0.2 mm nylon net on the a t-test. A three-way ANOVA (Sokal & Rohlf 1981) was top and bottom surfaces. In macrofauna-accessible boxes, used to compare the effects of fauna, site and litter on mea- six horizontal openings (4 × 30 mm) were located in each sured parameters; as there were only two treatments for longer lateral side; no openings were made in boxes that each factor, no post hoc test was applied. Data processing were not accessible for macrofauna. Each box contained a was performed using Microsoft Excel 7 and the three-way mineral layer (20 g of clay spoil) and a litter layer (ca. 25 ANOVA was conducted with SPSS 10.0. g of dry weight equivalent). A 2 mm nylon mesh with 8 large (1 cm diameter) openings separated the layers. This Results net was pervious to all size groups of soil macrofauna and served only to mark the original border between the litter Both carbon content and carbon accumulation in the and the mineral layer. The spoil used in the mineral layer mineral layer were significantly affected by the site came from a pioneer site (ca. 10 years old) where vegetation where the boxes were exposed and by the litter used was almost absent, from a depth of 3–10 cm. The clay was sieved through a 5 mm screen and homogenized. The litter in the boxes; higher values of both parameters were was hand-sorted, cut into pieces of ca. 1 × 3 cm and homog- measured in the alder site and in boxes filled by alder enized. Both litter and clay were defaunated by deep freez- litter (Table 1). ing at −40 ◦C for 12 hours. The materials were placed into The box accessibility to macrofauna did not affect the microcosms at natural moisture content and separate the carbon content or the amount of carbon that accu- samples were taken from each microcosm to determine the mulated in the mineral layer (Table 1). Significant in- moisture and carbon content. Moisture was measured gravi- ◦ teractions were found between the sites and the effects metrically after drying the material at 90 C for 24 hours. In of macrofauna on carbon content in the mineral layer both sites, both types of litter were exposed, i.e., litter orig- and the translocation of organic matter into the min- inating from the alder plantation or the willow dominated eral layer (Table 1). In the reclaimed site, macrofauna litter originating from spontaneous unreclaimed sites. Both litter types were either accessible or non accessible to soil stimulated the translocation of organic matter to the macrofauna as described above (eight treatments in total: mineral layer, while an opposite effect was observed in two sites × two types of litter, each either accessible or not the spontaneous site. Micromorphological observations accessible to macrofauna). indicated that earthworms were responsible for mixing The microcosms were exposed in the field for one year, of the substrate in reclaimed sites while enchtreids dom- from September 2004 to September 2005, with three repli- inated at the spontaneous site (Fig. 2). cates for each treatment. The microcosms were partly buried Macrofauna exclusion did not affect overall min- in the fermentation and humus layers in a way that about eralization. Both mineralization and the loss of carbon half of the large openings on the sides of the macrofauna- from the litter layer were significantly affected by litter accessible microcosms were buried and half were positioned quality, with a significant interaction of litter quality partly above the surface. About 100 ml of the fermentation layerwereplacedonthetopmeshofthemicrocosmsto and site; the alder litter tended to decompose faster accelerate box inoculation by mesofauna and other smaller than the willow litter, which was more pronounced in members of the soil biota. the alder litter at the spontaneous site (Table 1). The litter and the mineral layers were separated after Microbial respiration in the mineral layer of the en- exposure. The material above the net was assumed to belong closures was significantly affected by the site, litter and Litter and fauna in post-mining soil formations 251

Table 1. Carbon content in the mineral layer and changes of carbon stock in the litter and mineral layers (mean ± SD) of ﬁeld microcosms exposed for one year either in the alder plantation (A) or in sites covered by spontaneous succession (S) supplied either with alder litter or litter from a spontaneous site (the ﬁrst letter marks the exposition site, the second letter marks the litter used in microcosms), which were either accessible (+) or non accessible (–) to soil macrocauna.

C content C stock increase C stock loss Total C loss in mineral layer in mineral layer from litter layer (%) (g box−1)(gbox−1)(gbox−1)

AA+ 4.49 ± 0.98 0.47 ± 0.11* 6.83 ± 1.62 6.36 ± 1.67 AA- 3.16 ± 0.19 0.24 ± 0.04* 6.16 ± 1.34 5.92 ± 1.37 AS+ 3.46 ± 0.10 0.30 ± 0.04 6.44 ± 0.39 6.15 ± 0.41 AS- 3.10 ± 0.47 0.23 ± 0.11 6.09 ± 0.60 5.86 ± 0.60 SA+ 2.40 ± 0.36* 0.13 ± 0.10 7.27 ± 0.56 7.14 ± 0.46 SA- 3.24 ± 0.12* 0.24 ± 0.03 7.99 ± 0.26 7.75 ± 0.29 SS+ 2.47 ± 0.21 0.09 ± 0.00* 4.34 ± 1.28 4.25 ± 1.28 SS- 2.11 ± 0.16 0.03 ± 0.02* 4.50 ± 0.52 4.47 ± 0.54

Three-way ANOVA FPF P FPFP

Site 19.68 0.0005 24.70 0.0002 0.53 0.4791 0.11 0.7399 Litter 5.76 0.0299 8.88 0.0093 12.56 0.0029 10.65 0.0052 Macrofauna 1.78 0.2024 2.59 0.1281 0.01 0.9425 0.00 0.9609 Site x litter 0.00 0.9710 0.16 0.6908 9.45 0.0077 8.97 0.0091 Site x macrofauna 5.79 0.0294 5.67 0.0310 0.96 0.3418 0.62 0.4441 Litter x macrofauna 0.07 0.7934 0.01 0.9371 0.02 0.9031 0.01 0.9093 All factors Interaction 5.86 0.0286 4.95 0.0419 0.20 0.6600 0.07 0.7883

Explanations: * Indicates a significant difference between fauna accessible and non accessible treatment (t- test, P < 0.05). The bottom of the table summarises F (the first column for each parameter) and P (the second column) values of three-way ANOVA for individual factors and their interactions, n = 24.

Fig. 1. Microbial respiration in the mineral layer (mean ± SD) of field microcosms exposed for one year in alder plantation (A) or in sites covered by spontaneous succession (S), supplied either with alder litter or litter from a spontaneous site (the first letter marks the exposition site, the second letter marks the litter used in microcosms) which were either accessible or non accessible to soil macrocauna. ** and *** indicate significant difference at P < 0.01 and 0.001, respectively, between treatments accessible and non-accessible to fauna (t-test). The table summarises F and P values of three-way ANOVA for individual factors and their interactions.

presence of fauna. Enclosures exposed in the alder plantation and those supplied by alder litter showed, on av- Fig. 2. Thin soil sections from the surface of the mineral layer erage, higher respiration. This pattern was strongly af- of field microcosms that were exposed for one year. A – Treat- fected by fauna accessibility; treatments not-accessible ment supplied with alder litter, exposed at the alder plantation to fauna did not differ significantly between the sites and accessible for soil macro fauna; it was completely filled with earthworm cast. B – Treatment exposed in the spontaneous site or the litter supplied (two-way ANOVA). Treatments and unaccessible to soil macrofauna. Enchytraeid and mesofauna accessible to fauna showed significantly higher respira- excrements are marked by the arrow. Scale 1 mm. 252 J. Frouz tion than the non-accessible ones (three-way ANOVA, in the mineral layer, namely in microcosms supplied Fig. 1). This difference was particularly pronounced for by alder litter. This may be due to the low density of alder litter (t-test, Fig. 1). macrofauna in spontaneous sites; macrofauna in these The micro morphological analyses indicated that sites consists mostly of groups living in the litter and earthworm excrements ranged among the most impor- fermentation layers of soil (Frouz et al. 2001b, 2002). tant biogenic structures in the macrofauna accessible Moreover, the analysis of thin soil sections in this site treatments in the alder plantation (Fig. 2A), while ex- indicated no effect of soil macrofauna on organic mate- crements of Enchytraeidae, followed by excrements of rial mixing in the mineral layer but showed an intensive Collembolla, belonged to the most important structures effect of macrofauna on litter fragmentation (Frouz & in enclosures that were not accessible for soil macro- Nováková 2005). The finding that this phenomenon is fauna in spontaneous sites (Fig. 2B) more pronounced in alder litter may correspond with lower C:N ratio in alder litter and thus its higher at- Discussion tractivity to soil macrofauna (Lavelle & Spain 2001). Macrofauna access significantly increased micro- In agreement with previous studies (Frouz 2002; Frouz bial respiration in the mineral layer. This effect was et al. 2006), it was ascertained that the accessibility of more pronounced in alder sites. Litter fragmentation soil fauna did not affect the overall carbon loss from enhanced by soil macrofauna may increase the leach- microcosms, while the mixing of organic matter be- ing of easily available substances into the mineral soil, tween the litter and mineral layers did. This seems to be which may support microbial respiration either directly caused by the low assimilation efficiency of soil fauna. or indirectly by a priming effect that enhances the Consequently, the majority of litter consumed by soil decomposition of fossil organic matter abundant in macrofauna is deposited in the form of excrements (Irm- Sokolov tertiary clays (Kříbek et al. 1998). Preliminar- ler 1995). The decomposition of macrofauna excrements ily laboratory experiments indicated that the process- can be in the long term slower than the decomposition ing of alder litter by soil macrofauna increased micro- of intact litter (Lavelle & Martin 1992). bial respiration more than spontaneous litter processing The effect of soil macrofauna on the mixing of or- (Frouz et al. 2007). ganic mater in mineral soil depends on the site; the In conclusion, the effect of macrofauna exclusion mixing is generally more pronounced in reclaimed sites. on soil mixing is complex and depends on litter quality Micro-morphological observations indicated that mix- and soil fauna composition. In sites where macrofauna ing in this site was mainly caused by earthworm ac- was dominated by saprophags, mainly earthworms, the tivity which corresponded with a well-developed earth- macrofauna increased soil mixing. In sites where preda- worm population that reached a much higher density tors dominated, soil macrofauna exclusion may support in reclaimed sites than in unreclaimed sites (Frouz et fragmentation and mixing activity of mesofauna. Modi- al. 2001a, b, 2002; Pižl 2001). fication of reclamation technologies in a way that would In unreclaimed sites, macrofauna access decreased support site colonisation by saprophagous soil macro- significantly the carbon content in the mineral layer. fauna might enhance soil mixing and carbon storage in Micro-morphological observations showed that in the mineral sites. unreclaimed site the incorporation of organic matter into soil was enhanced by litter fragmentation activity Acknowledgements of the mesofauna, namely Enchytraeidae and Collem- bola. The fragmented litter can be washed down by wa- This study was supported by grants of the Czech Academy ter. Exclusion of macrofauna most probably eliminated of Sciences No. S600660505, Czech Science Foundation Nos the access of predators (centipedes, predatory beetles), 526/01/1055, 526/03/1259, 526/06/0728, Czech Ministry of which may normally reduce the mesofauna population, Education No. LC06066 and by the Sokolovská uhelná min- and this way it indirectly supported mesofauna-driven ing company. Two anonymous referees are thanked for their critical and helpful comments. litter fragmentation and mixing (Kajak 1996; Kajak et al. 2000; Frouz et al. 2006). In microcosms supplied with spontaneous litter in spontaneous sites, the macro- References fauna significantly increased carbon mixing. The reason of this difference is not clear, however, mixing in these Allison F.E. 1973. Soil Organic Matter and its Role in Crop Pro- duction. Elsevier, Amsterdam and New York, 637 pp. treatments was one order of magnitude lower than in Bradshaw A. 1997. 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