Popul Ecol (2013) 55:69–76 DOI 10.1007/s10144-012-0342-5 ORIGINAL ARTICLE Home-field advantage in decomposition of leaf litter and insect frass Hideki Kagata • Takayuki Ohgushi Received: 8 February 2012 / Accepted: 2 September 2012 / Published online: 2 October 2012 Ó The Society of Population Ecology and Springer 2012 Abstract Home-field advantage (HFA) hypothesis Introduction regarding litter decomposition states that litter is decom- posed more rapidly in the habitat from which it is derived Leaf litter inputs are major sources of energy and nutrients (i.e., home) than in other habitat (i.e., away) due to local for the decomposition process in forests (Cebrian 1999; adaptation of soil decomposers. We tested the HFA Wardle et al. 2002). Leaf litter from different tree species hypothesis regarding decomposition of leaf litter, insect generally differs in physical and chemical characteristics, frass, and their mixtures, using laboratory incubation of which can determine the community structure of soil leaf litter from an evergreen (Pinus densiflora) and a decomposers and litter decomposition rate (Negrete- deciduous (Quercus acutissima) tree species, frass excreted Yankelevich et al. 2008; St. John et al. 2011). One can by two insect herbivores (Dendrolimus spectabilis and expect that soil decomposers may be specialized to Lymantria dispar) fed on one of the two trees, and soil decompose leaf litter derived from trees above them (Ayres collected underneath the two trees. We found evidence that et al. 2009). Hence, it has been suggested that leaf litter decomposers in each soil were specialized to decompose may be decomposed faster in the habitat from which it is the litter derived from the tree species above them, indi- derived (i.e., home) than in other habitat (i.e., away), which cating that the HFA occurred in litter decomposition. In is called the home-field advantage (HFA) hypothesis for contrast, the HFA was not detected in the decomposition of litter decomposition (Gholz et al. 2000). Several studies insect frass or litter-frass mixtures. Mixing with D. spect- have tested this hypothesis using litter-bag experiments abilis frass non-additively decelerated, while mixing with with litter transplantation between home and away envi- L. dispar frass non-additively accelerated, decomposition ronments, and found that litter was decomposed faster in its of the mixtures, independent of soil and litter types. These home than in away environments (e.g., Negrete-Yankele- indicate that the presence of insect herbivores may make it vich et al. 2008; Vivanco and Austin 2008, but see St. John difficult to form and maintain a decomposer community et al. 2011). Moreover, Ayres et al. (2009) conducted a specialized to a certain leaf litter, and that it may conse- meta-analysis to test the HFA hypothesis based on pub- quently cancel or weaken HFA in litter decomposition. lished data of litter decomposition in forests. They showed that HFA commonly occurs in forest ecosystems, and that Keywords Insect outbreaks Á Insect-plant interaction Á the litter decomposition rate was approximately 8% greater Non-additive effect Á Soil-litter interaction in home than in away environments. In addition to leaf litter, excrements of insect herbivores (i.e., frass and honeydew) are also important as energy and nutrient sources for the decomposition process in forests when insects occur at high density (Hunter 2001). It is generally thought that insect excrement represents a minor & H. Kagata ( ) Á T. Ohgushi fraction of energy and nutrients in terrestrial ecosystems Center for Ecological Research, Kyoto University, 509-3 Hirano 2-chome, Otsu, Shiga 520-2113, Japan because of the low herbivory rate, i.e., less than 20 % (Cyr e-mail: [email protected] and Pace 1993; Cebrian and Lartigue 2004). However, a 123 70 Popul Ecol (2013) 55:69–76 wide range of insect herbivores in forests sometimes show in temperate forests in Japan. The soil was collected outbreaks and reach to extremely high density (Schowalter underneath (\5 cm in depth) five P. densiflora and five 2000; Kamata 2002), at which the amount of insect Q. acutissima trees in late November 2010. It was air-dried excrement can reach a critical level of energy and nutrient for 1 month and passed though a 2 mm sieve. Although the inputs affecting the decomposition process (Hunter 2001; soil was used as the source of microbial decomposers in the Lovett et al. 2002; Clark et al. 2010). There is increasing present study, we noted that the microbial communities appreciation that frass of insect herbivores has significant may have been, to some extent, affected by the drying. impacts on decomposition and soil nutrient availability After samples were isolated from the soil for CN analysis, (Hunter 2001; Lovett et al. 2002). Insect frass contains the remaining soil was pooled for each tree species. They higher concentrations of nitrogen (N) and labile carbon were stored at 5 °C until the incubation experiment or CN (C) than does leaf litter (Lovett and Ruesink 1995; Mad- analysis. We also collected leaf litter underneath 10 trees of ritch et al. 2007). It can enhance microbial growth (Frost each tree species in late November 2010. Similarly to the and Hunter 2004), which in turn accelerates the decom- soil, the litter was air-dried for 1 month, and stored at 5 °C. position rate (Zimmer and Topp 2002), N mineralization, The pine caterpillar, Dendrolimus spectabilis Bulter and N immobilization (Lovett and Ruesink 1995; Frost and (Lepidoptera: Lasiocampidae), and gypsy moth, Lymantria Hunter 2007). The chemical characteristics of insect frass, dispar (Linnaeus) (Lepidoptera: Lymantriidae), are impor- such as C:N ratio and tannins, are largely dependent on tant insect pests for coniferous and broad-leaved forests, those of the host plant leaves (Madritch et al. 2007; Kagata respectively, and several outbreaks of these two insects and Ohgushi 2011), and influence the decomposition pro- have been recorded in Japan (Kamata 2002). Dendrolimus cess of the frass (Madritch et al. 2007; Kagata and Ohgushi spectabilis is generally univoltine, but partly bivoltine, in 2012a). Therefore, similarly to leaf litter decomposition, central Japan, and overwinters as larvae. Overwintered insect frass may also be decomposed faster underneath the larvae start to feed on the host plants in March and pupate tree species on which the insect fed than underneath other in June to July in this area, although there is a large phe- tree species. However, to our knowledge there have been nological variation among individuals (Habu 1969). Larvae no studies exploring whether the HFA hypothesis is of D. spectabilis exclusively feed on Pinaceae species applicable to insect frass decomposition. Elucidating the (Kamata 2002). We collected 3rd- to 5th-instar larvae from decomposition features of insect frass should contribute several P. densiflora trees in November 2009. The larvae importantly to further understanding how insect outbreaks were placed in 3-l plastic containers with P. densiflora influence litter decomposition and nutrient cycling in ter- leaves in dark and temperature-uncontrolled (i.e., without restrial ecosystems. heater) rooms until the end of March 2010. Approximately Here, we tested the HFA hypothesis for decomposition 50 individuals of D. spectabilis successfully overwintered. of leaf litter, insect frass, and their mixtures, using labo- In April, the overwintered larvae were transferred to 3-l ratory incubation of leaf litter from an evergreen and a containers, with a maximum of five individuals per con- deciduous tree species, frass excreted by two insect her- tainer, in an environmental chamber at 25 °C with a LD bivores fed on one of the two trees, and soil collected 16:8 h cycle. One-year leaves of P. densiflora collected underneath the two trees. from ten randomly selected trees were provided as food and replaced with new ones every day. When the larvae reached the final instar (mostly 8th-instar larvae), 15 larvae Materials and methods were randomly transferred individually to a 500-ml plastic cup with leaves of P. densiflora. The frass was collected for Collection of soil, leaf litter, and insect frass 3 days. Thereafter, the larvae were kept for 24 h without food to allow them to excrete the frass in their gut. These Soil, leaf litter, and insect herbivores were collected in and frass and larvae were used for CN analysis. The one-year around an experimental field of the Center for Ecological leaves of P. densiflora from the ten trees were also col- Research (forest of CER; 34°970N, 135°960E), Kyoto lected for CN analysis. The frass, larvae, and leaves were University, in Shiga prefecture, central Japan. The sec- oven-dried at 60 °C for 1 week, and stored at 5 °C until ondary forest includes more than 50 tree species occurring CN analysis. The remaining larvae (more than 30 indi- naturally and artificially. We selected two tree species for viduals) continued to be reared in the 3-l containers, and the present study: Japanese red pine, Pinus densiflora the frass was collected every day until pupation for the Siebold. & Zucca. (Pinaceae) and sawtooth oak, Quercus incubation experiment. Collected frass was pooled, oven- acutissima Carruth. (Fagaceae). Pinus densiflora and dried, and stored at 5 °C until the experiment. Q. acutissima are evergreen coniferous and deciduous Lymantria dispar is univoltine and overwinters as eggs. broad-leaved trees, respectively. They are commonly co-occur Larvae generally hatch in March to April and pupate in 123 Popul Ecol (2013) 55:69–76 71 June in central Japan. They are highly polyphagous and can the substrates. These substrates made an approximately feed on over 500 plant species, including many deciduous 5-mm layer at the bottom of the vial. We established 18 broad-leaved trees such as Betulaceae, Fagaceae, Salica- treatments consisting of various combinations of soil, litter, ceae, and Tiliaceae (Barbosa and Krischik 1987; Liebhold and frass, including home and away environments et al.