POLISH JOURNAL OF ECOLOGY 48 4 327-338 2000 (Pol. J. Ecol.) BIOMANIPULATION OF MACROARTHROPODS- EFFECT ON FOOD WEB Lucyna W ASILEWSKA Institute of Ecology, Polish Academy of Sciences, Dziekan6w Lesny, 05-092 Lomianki, Poland, fax: (48 22) 75 I 3 I 00; e-mail: [email protected] THE EFFECT OF MACROARTHROPODS PATROLLING SOIL SURFACE ON SOIL NEMATODES: A FIELD EXPERIMENT IN A MOWN MEADOW ABSTRACT: A field experiment \vas desig­ predation can affect the rate oforganic matter ned to estimate the effect of soil surface patrolling mineralization(Coleman eta/. 1984,Kajak by n1acroarthropods on organic matter content in 1995). The hypothesis is that predatory mac­ soi I. One of the con1ponents of this experiment was the soil nematode community - density, trophic and roarthropods can change proportions be­ dominance structure, the diversity and maturity in­ tween bacteria and fungi by decreasing the dices. These parameters were compared bet\veen density of fungivorous mesofauna, and, con­ t\VO types of mesocosn1s: accessible and inaccessib­ sequently, they can contribute to the carbon le to tnacroarthropods. The experiment was perfor­ storage in the soil. Nonpredatory macroar­ n1cd under natural environmental conditions and did thropods influence decomposition by com­ not reduce the diversity of the biota characteristic of the ecosystem . Most parameters of nematodes did minution of plant material, by microbial not vary significantly bet\veen mesocosms. Diffe­ grazing and by faeces ejection. rences bet\vecn mesocosms observed over the The relationship between decomposition S-n1onth period of each of the two experiments ( 1992 and 1993) concerned mainly, bacteri vorous processes and structures of heterotrophic nematodes and. within this trophic group, coloni­ communities in the litter and soil was already Lers. The densities of the taxon Rhabditis s.l. \Vere analysed by Kajak (1997), Kajak et al. statistically higher in the mesocosms accessible to (1998),andKajak eta!. (2000). tnacroarthropods. and the proportion of colonizers (r-strategists s.l.) among bacterivorous nematodes This paper analyses a part of the satne \Vas al so higher. problem with reference to soil-inhabiting KEY WORDS: soil nematodes. bacterivores. nematodes. Soil nematodes are useful.. indices macroarthropods. Rhabditis s.l. of soil processes, habitat quality, and of all kinds of management effects (Ward le et al. 19 9 5, F erri s et a!. 199 6, N eher and 1. INTRODUCTION Campbell 1996, Wasilewska 1997, Yeates and King 1997, Yeates et al. Predation by large, motile arthropods on 1997a, Yeates et al. 1997b, Alphei 1998, saprophages in terrestrial ecosystems is rela­ Porazinska et al. 1998). Thus, the vari­ tively little known. It is known, however, that ables compared here comprise the density of 328 Lucyna Wasilewska nematodes, composition of taxa, trophic per trap per day in 1993, and it was over 100 structures, and maturity indices in variants times higher than in the closed mesocosms. accessible to macroarthropods and in the con­ The penetration of the open mesocosms by trol, not accessible to macrofauna. A special nonpredatory animals was only ten times that attention will be paid to bacterivorous nema­ in the closed mesocosms (2.4 and 3.9 mg dry todes, that increase in numbers in response to wt per trap per day in 1992 and 1993, respec­ the addition offaeces (or dung) to the habitat tively). (Bardgett eta/. 1998, Wasilewska 1998). Mesocosms contained soil cores in isola­ On the other hand, however, the role ofmac­ tors (bags) made up of a steelon screen with roarthropods as regulatory forces in the de­ 0.24 mm meshes. The difference between the composer food-webs (fungivorous and open (0) and closed (C) mesocosms was that predatory macroarthropods feed upon soil the for111er had holes cut at the soil interface, nematodes and compete for similar re­ so that even the largest invertebrates search­ sources) should not be neglected (Wardle ing the soil surface could pass through. Soil and Yeates 1993, Hyvonen andPersson cores were taken from a meadow with a cy­ 1996). lindrical1OO-cm2 sampler, 15 cm deep. They were immediately put into isolators and re­ turned to the same pits from which they were 2. EXPERIMENTAL DESIGN taken. To estimate nematodes, 100 meso­ cosms were established in 1992 (Experiment 2.1. STUDY AREA I), and 60 mesocosms in 1993 (Experiment II). Experiment I was run from June 1992 un­ The experiment was conducted in a per­ til April 1993, whereas experiment II from manent, mown meadow situated near the vil­ April 1993 until May 1994. In each year lage of Lomna at the peripheries of the mesocosms were established separately. Kampinos Forest, central Poland. The vege­ A part of mesocosms was used to determine tation was of the order of Arrhenatheretalia, numbers of micro flora and mesofauna in the the soil was gleyed black earth (8% C in the soil, also to detettnine the content of carbon sod layer, 1.85% in A 1 layer), with pH = 4.5, and humic acids, and the rate of litter decom­ exchange capacity in A 1 = 12 cmol per 1 kg position and colonization by biota (K a j a k dry wt of soil. The soil was derived from et al. 2000). loamy sand underlain by loose sand. A detailed description ofthe experiment, 2.3. ESTIMATION OF SOIL its assumptions and parameters are presented NEMATODE DENSITY AND in Kajak (1997), Kajak (2000) and Kajak COMMUNITY STRUCTURE et al. (2000). This paper presents a shortened description concerning the estimation of soil Samples of soil nematodes were taken nematode density and community structure. from the soil ofopen mesocosms (0), closed mesocosms (C), and from surrounding 2.2. EXPERIMENTAL TREATMENTS meadow soil on the following dates: 21 May Two types of mesocosms were used in 1992, 4 June 1992, 2 July 1992, 2 September the experiment, one accessible (open) and the 1992, 20 October 1992 (Exp. I), and 10 May other one not accessible (closed) to macro­ 1993, 21 June 1993, and 27 September 1993 fauna moving on the soil surface. The inten­ (Exp. II). On each sampling occasion, one sity of the penetration of the open soil core 1.8 cm in diameter and 10 cm deep mesocosms by macroarthropods (Fotnlici­ was taken from 10 mesocosms in each vari­ dae, Carabidae, Araneae) was 6.9 mg dry wt ant. After being mixed together, these soil per trap per day in 1992, and 3.6 mg dry wt cores formed a single mixed sample. Identi- The effect of macroarthropods on soil nematodes 329 cal 10 soil cores were taken from surround­ strategists s.l.). These are the following indi­ ings ofthe mesocosms. ces: Nematodes were extracted from three 1) Maturity Index- MI, based solely on subsamples of25 ml ofsoil by using a modi­ free-living taxa of nematodes i.e. omitting fied Baerrnann method. They were identified herbivores, and monitoring habitat coloniza­ to the genus level or to the genus s.l. level, tion and succession, like in the earlier paper (Wasilewska 1979). 2) Maturity Index for total nematodes - The year 1992 was very dry, whereas I MI, calculated for all taxa in a sample. It 1993 was rainy. In the period from May serves the same purpose as MI and responds through October 1992, precipitation sums in the same way, but a slightly different re­ were lower than the long-term mean by at sponse can be expected when natural ecosys­ least 20%. In the period from May through tems are analysed, September 1993, they were higher than on 3) Plant Parasite Index - PPI, con­ average by 40%, even up to 400%. structed using phytoparasitic nematodes, The following parameters were esti­ seems to be positively cotTelated with pri­ mated: density, composition of taxa in the mary production, community, trophic structure (bacterivores­ B, fungivores - F, obligate plant feeders - 4) The MINO Maturity Index - MINO OPF, facultative plant feeders (partially fun­ MI, for free-living nematodes, but excluding givores)- FPF, omnivores - Om, predators ­ opportunists (c -p = I), P, and parasites of insects - PI). Nematodes 5) The I MINO Maturity Index - were assigned to trophic groups after Wasi­ IMINO MI, for free-living nematodes, ex­ lewska ( 1971) with reference to the classifi­ cludes opportunists and includes plant para­ cation by Yeates et al. (1993). Also the sitic nematodes. The last two indices, which relations between trophic groups were con­ exclude opportunists, record rather long-term sidered: B/F, (B+F+FPF)/OPF, and changes, B+F/(OPF+FPF). The difference between the last two ratios is that the group FPF is consid­ 6) Maturity Index for bacterivores - Ba ered as mycophilous in one case and as plant MI, indicates the life strategies within this feeders in the other case. These ratios are in­ trophic group. It may be expected that its dicative of differences in the contribution of lower value points to enhanced microbial ac­ nematodes to the mineralization occurring in tivity when nitrogen supply is increased the detritus food web and grazing food web (Wasilewska 1998). (Wasilewska 1997). Also the number of taxa and the Shannon-Weaver H' index were 2.4. STATISTICS estimated, along with several maturity indi­ ces developed by Bongers (1990) and de­ Two-way ANOVA was used to estimate scribed in more detail by Bongers et al. differences in the density of taxa and in bio­ (1995), Bongers and Bongers (1998), and coenotic parameters of the nematode com­ Wasilewska (1997). Maturity indices are munity between particular sampling dates based on the allocation of taxa according to and between open and closed mesocosms. life strategy. These indices are based on the Also nonparametric Friedman test was used proportions of taxa (genera) with different for analysing differences between open and life strategy in the community, from coloniz­ closed systems.