Differences in leaf and root litter decomposition in tropical montane rainforests are mediated by soil microorganisms not by decomposer microarthropods.

Background: Plant litter decomposition is a key process in carbon and nutrient cycling. Among the factors determining litter decomposition rates, the role of soil biota in the decomposition of different plant litter types and its modification by variations in climatic conditions is not well understood. Methods: In this study, we used litterbags with different mesh sizes (45 µm, 1 mm and 4 mm) to investigate the effect of microorganisms and decomposer microarthropods on leaf and root litter decomposition along an altitudinal gradient of tropical montane rainforests in Ecuador. We examined decomposition rates, litter C and N concentrations, microbial biomass and activity, as well as decomposer microarthropod abundance over one year of exposure at three different altitudes (1,000, 2,000 and 3,000 m). Results: Leaf litter mass loss did not differ between the 1,000 and 2,000 m sites, while root litter mass loss decreased with increasing altitude. Changes in microbial biomass and activity paralleled the changes in litter decomposition rates. Access of microarthropods to litterbags only increased root litter mass loss significantly at 3,000 m. The results suggest that the impacts of climatic conditions differentially affect the decomposition of leaf and root litter, and these modifications are modulated by the quality of the local litter material. The findings also highlight litter quality as the dominant force structuring detritivore communities. Overall, the results support the view that microorganisms mostly drive decomposition processes in tropical montane rainforests with soil microarthropods playing a more important role in decomposing low-quality litter material.

Leaf litter identity rather than diversity shapes microbial functions and microarthropod abundance in tropical montane rainforests.

In tropical forest ecosystems leaf litter from a large variety of species enters the decomposer system, however, the impact of leaf litter diversity on the abundance and activity of soil organisms during decomposition is little known. We investigated the effect of leaf litter diversity and identity on microbial functions and the abundance of microarthropods in Ecuadorian tropical montane rainforests. We used litterbags filled with leaves of six native tree species (Cecropia andina, Dictyocaryum lamarckianum, Myrcia pubescens, Cavendishia zamorensis, Graffenrieda emarginata, and Clusia spp.) and incubated monocultures and all possible two- and four-species combinations in the field for 6 and 12 months. Mass loss, microbial biomass, basal respiration, metabolic quotient, and the slope of microbial growth after glucose addition, as well as the abundance of microarthropods (Acari and Collembola), were measured at both sampling dates. Leaf litter diversity significantly increased mass loss after 6 months of exposure, but reduced microbial biomass after 12 months of exposure. Leaf litter species identity significantly changed both microbial activity and microarthropod abundance with species of high quality (low C-to-N ratio), such as C. andina, improving resource quality as indicated by lower metabolic quotient and higher abundance of microarthropods. Nonetheless, species of low quality, such as Clusia spp., also increased the abundance of Oribatida suggesting that leaf litter chemical composition alone is insufficient to explain variation in the abundances of soil microarthropods. Overall, the results provide evidence that decomposition and microbial biomass in litter respond to leaf litter diversity as well as litter identity (chemical and physical characteristics), while microarthropods respond only to litter identity but not litter diversity.

Leaf and root litter decomposition is discontinued at high altitude tropical montane rainforests contributing to carbon sequestration.

We investigated how altitude affects the decomposition of leaf and root litter in the Andean tropical montane rainforest of southern Ecuador, that is, through changes in the litter quality between altitudes or other site-specific differences in microenvironmental conditions. Leaf litter from three abundant tree species and roots of different diameter from sites at 1,000, 2,000, and 3,000 m were placed in litterbags and incubated for 6, 12, 24, 36, and 48 months. Environmental conditions at the three altitudes and the sampling time were the main factors driving litter decomposition, while origin, and therefore quality of the litter, was of minor importance. At 2,000 and 3,000 m decomposition of litter declined for 12 months reaching a limit value of ~50% of initial and not decomposing further for about 24 months. After 36 months, decomposition commenced at low rates resulting in an average of 37.9% and 44.4% of initial remaining after 48 months. In contrast, at 1,000 m decomposition continued for 48 months until only 10.9% of the initial litter mass remained. Changes in decomposition rates were paralleled by changes in microorganisms with microbial biomass decreasing after 24 months at 2,000 and 3,000 m, while varying little at 1,000 m. The results show that, irrespective of litter origin (1,000, 2,000, 3,000 m) and type (leaves, roots), unfavorable microenvironmental conditions at high altitudes inhibit decomposition processes resulting in the sequestration of carbon in thick organic layers.

Leaf Litter Chemistry Drives the Structure and Composition of Soil Testate Amoeba Communities in a Tropical Montane Rainforest of the Ecuadorian Andes.

We investigated the role of leaf litter chemistry and richness in affecting testate amoeba communities of tropical rainforest in the Ecuadorian Andes. Litterbags containing leaf litter from four dominating tree species (Clusia sp., Myrcia pubescens, Graffenrieda emarginata, and Cecropia andina) with richness 1, 2, and 4 species were established and exposed in the field for 12 months at 2000 m a.s.l. Chemical elements and compounds of leaf litter were analyzed before exposure. At the end of exposure, microbial biomass and litter mass loss were measured, and living testate amoeba species number, density, biomass, and community composition were determined. In total, 125 testate amoeba species colonized the litter in litterbags. The results suggest that high litter nitrogen and low lignin concentrations are indicators of high litter quality for testate amoebae density and species richness. Their species number and density significantly declined in the order 1 > 4 > 2 leaf litter species and varied with leaf litter chemistry being at a maximum in high-quality single leaf litter species and low in low-quality leaf litter. Further, the addition of litter of high-quality to low-quality litter increased testate amoebae biomass and density; however, the values did not exceed the ones in single high-quality litter treatments. Moreover, the structure of testate amoeba communities varied with litter chemistry, with Fe, Na, lignin, and litter C-to-N ratio being of major importance, and indicating that litter chemistry reflects habitat quality for testate amoebae. Overall, the data show that leaf litter chemistry overrides leaf litter richness in structuring testate amoeba communities.

New and little known species of oribatid mites of the family Haplozetidae (Acari, Oribatida) from Ecuador.

We described two new species, Haplozetes paraminimicoma sp. n. and Protoribates ecuadoriensis sp. n. from Ecuador. Additionally, a detailed supplementary description of Trachyoribates (Rostrozetes) glaber (Beck, 1965) is given on the basis of Ecuadorian specimens, which was known previously only from Peru. An annotated checklist of all identified taxa of Haplozetidae from Ecuador is presented.

Two new species of oribatid mites of the genus Truncozetes (Acari, Oribatida, Epactozetidae) from Ecuador.

Two new oribatid mite species of the genus Truncozetes (Oribatida, Epactozetidae), Truncozetes ecuadoriensis sp. n. and Truncozetes monodactylus sp. n., are described from the Ecuadorian soils. The morphology of the gnathosoma and the legs is presented in detail for the first time for the species of Truncozetes. An identification key to all known species of the family Epactozetidae is given.

Three new species of the genus Sternoppia (Acari: Oribatida: Sternoppiidae) from Ecuador.

Three new oppioid mite species of the genus Sternoppia, S. paraincisa sp. nov., S. paramirabilis sp. nov. and S. fissurata sp. nov., are described. Sternoppia paraincisa sp. nov. is most similar morphologically to Sternoppia incisa Balogh & Mahunka, 1977 from Bolivia, however, it differs from the latter by smaller body size, presence of notogastral setae c, location of lyrifissures ia, presence of granules on anal plates, and setiform sensilli. Sternoppia paramirabilis sp. nov. is most similar morphologically to Sternoppia mirabilis Balogh & Mahunka, 1968 from Argentina, however it differs from the latter by larger body size, presence of two or three sensillar branches only, and long interlamellar setae. Sternoppia fissurata sp. nov. differs from all species of the genus by the nine pairs of notogastral setae, location of lyrifissures iad in inverse apoanal position, and the presence of large tectum on anterior part of ventral plate. Sternoppia brasiliensis is for the first time recorded in Ecuador. An identification key to all known species of Sternoppia is provided.

New taxa and new records of oribatid mites of the family Galumnidae (Acari: Oribatida) from Ecuador.

The new genus Neoctenogalumna gen. nov. with Ctenogalumna moresonensis Engelbrecht, 1972 as a type species and the new subgenus Neoctenogalumna (Paractenogalumna) subgen. nov. with Neoctenogalumna (Paractenogalumna) longiciliata sp. nov. as a type species are proposed. Four new species Allogalumna ampla sp. nov., Galumna miniporosa sp. nov., Pergalumna ornamenta sp. nov. and Neoctenogalumna (Paractenogalumna) longiciliata sp. nov. are described from Ecuadorian soils. Neoctenogalumna moresonensis (Engelbrecht, 1972) comb. nov. and N. congoensis (Starý, 2005) comb. nov. are transferred in the genus Neoctenogalumna gen. nov. from Ctenogalumna. An identification key to known species of Neoctenogalumna gen. nov. is provided. An annotated checklist of identified Ecuadorian Galumnidae is presented. Four species Allogalumna borhidii Balogh & Mahunka, 1979, A. cubana Balogh & Mahunka, 1979, Pergalumna australis Pérez-Íñigo & Baggio, 1980, Galumna laselvae Balogh, 1997--are recorded for the first time from Ecuador. One genus and one species Trichogalumna Balogh, 1960 and Trichogalumna nipponica (Aoki, 1966) are recorded for the first time from the Neotropical region.