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.

Review of the mite genus Krantzolaspina Datta & Bhattacharjee (Mesostigmata, Parholaspididae) with re-description of K. angustatus comb. nov. (Ishikawa) from Indonesia.

Herein, we update the diagnosis and description of the genus Krantzolaspina Datta & Bhattacharjee and provide a list of the three valid species including new combinations and synonyms, as follows: 1) Krantzolaspina angustatus (Ishikawa, 1987) comb. nov. (= Indutolaelaps jiroftensisHajizadeh et al., 2017syn. nov.), 2) K. rebatii Datta & Bhattacharjee, 1989 and 3) K. solimani (Metwali, 1983) comb. nov. Finally, we re-describe K. angustatus (Ishikawa, 1987) comb. nov. based on the holotype from Japan, voucher specimens from Iran and additional females that we found in soil samples from oil palm plantations in Sumatra, Indonesia.

New and interesting species of sacculonotic Haplozetidae (Acari, Oribatida, Haplozetidae) from Indonesia.

Two new species of haplozetid oribatid mites (Oribatida, Haplozetidae) are described on the basis of adult specimens sampled from litter and soil in Sumatra, Indonesia: Haplozetes bayartogtokhi sp. nov. differs from Haplozetes biheterodactylus Ermilov Tolstikov, 2015 by the presence of minute interlamellar setae, foveolate anterior part of the notogaster, five pairs of genital setae and the localization of adanal lyrifissures in preanal position; Magyaria leonilae sp. nov. differs from Magyaria annobonica Pérez-Íñigo, 1981 and Magyaria ornata Balogh, 1963 by the presence of bidactylous legs, pointed rostrum and reticulate prodorsum. The species Indoribates hauseri (Mahunka, 1997) comb. nov. (Haplozetidae) is recorded in Indonesia for the first time. A supplementary description for this species is given in detail on the basis of adult specimens from Indonesia and its main morphological traits are summarized. The taxonomic status of the genus Bolkiah Mahunka, 1997 is discussed, resulting in the following new taxonomic proposals: Indoribates (=Bolkiah syn. nov.).

Shift in trophic niches of soil microarthropods with conversion of tropical rainforest into plantations as indicated by stable isotopes (15N, 13C).

Land-use change is threatening biodiversity worldwide, affecting above and below ground animal communities by altering their trophic niches. However, shifts in trophic niches with changes in land use are little studied and this applies in particular to belowground animals. Oribatid mites are among the most abundant soil animals, involved in decomposition processes and nutrient cycling. We analyzed shifts in trophic niches of six soil-living oribatid mite species with the conversion of lowland secondary rainforest into plantation systems of different land-use intensity (jungle rubber, rubber and oil palm monoculture plantation) in two regions of southwest Sumatra, Indonesia. We measured stable isotope ratios (13C/12C and 15N/14N) of single oribatid mite individuals and calculated shifts in stable isotope niches with changes in land use. Significant changes in stable isotope ratios in three of the six studied oribatid mite species indicated that these species shift their trophic niches with changes in land use. The trophic shift was either due to changes in trophic level (δ15N values), to changes in the use of basal resources (δ13C values) or to changes in both. The trophic shift generally was most pronounced between more natural systems (rainforest and jungle rubber) on one side and monoculture plantations systems (rubber and oil palm plantations) on the other, reflecting that the shifts were related to land-use intensity. Although trophic niches of the other three studied species did not differ significantly between land-use systems they followed a similar trend. Overall, the results suggest that colonization of very different ecosystems such as rainforest and intensively managed monoculture plantations by oribatid mite species likely is related to their ability to shift their trophic niches, i.e. to trophic plasticity.

Review of the mite genus Ololaelaps (Acari, Laelapidae) and redescription of O.formidabilis Berlese.

A species of laelapid mite, Ololaelapsformidabilis, is redescribed based on male and female adults from soil in Sumatra, Indonesia. This species is distinguished from other Ololaelaps species by its metapodal platelet narrowly fused with the parapodal plate and by its hologastric shield having two inverted-V-like ridges. The genus is redescribed based on a review of the literature and examination of specimens of some species. Valid species of Ololaelaps are listed and accompanied by notes on morphological characters to assist future revision of the genus.

Linking size spectrum, energy flux and trophic multifunctionality in soil food webs of tropical land-use systems.

Many ecosystem functions depend on the structure of food webs, which heavily relies on the body size spectrum of the community. Despite that, little is known on how the size spectrum of soil animals responds to agricultural practices in tropical land-use systems and how these responses affect ecosystem functioning. We studied land-use-induced changes in below-ground communities in tropical lowland ecosystems in Sumatra (Jambi province, Indonesia), a hot spot of tropical rainforest conversion into rubber and oil palm plantations. The study included ca. 30,000 measured individuals from 33 high-order taxa of meso- and macrofauna spanning eight orders of magnitude in body mass. Using individual body masses, we calculated the metabolism of trophic guilds and used food web models to calculate energy fluxes and infer ecosystem functions, such as decomposition, herbivory, primary and intraguild predation. Land-use change was associated with reduced abundance and taxonomic diversity of soil invertebrates, but strong increase in total biomass and moderate changes in total energy flux. These changes were due to increased biomass of large-sized decomposers in soil, in particular earthworms, with their share in community metabolism increasing from 11% in rainforest to 59%-76% in jungle rubber, and rubber and oil palm plantations. Decomposition, that is the energy flux to decomposers, stayed unchanged, but herbivory, primary and intraguild predation decreased by an order of magnitude in plantation systems. Intraguild predation was very important, being responsible for 38% of the energy flux in rainforest according to our model. Conversion of rainforest into monoculture plantations is associated by an uneven loss of size classes and trophic levels of soil invertebrates resulting in sequestration of energy in large-sized primary consumers and restricted flux of energy to higher trophic levels. Pronounced differences between rainforest and jungle rubber reflect sensitivity of rainforest soil animal communities to moderate land-use changes. Soil communities in plantation systems sustained high total energy flux despite reduced biodiversity. The high energy flux into large decomposers but low energy fluxes into other trophic guilds suggests that trophic multifunctionality of below-ground communities is compromised in plantation systems.

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.

Contributions to the knowledge of oribatid mites of Indonesia. 1. The genus Allogalumna (Galumnidae) with descriptions of two new species (Acari, Oribatida).

Two new species of oribatid mites of the genus Allogalumna (Oribatida, Galumnidae) are described from litter and soil materials of Sumatra, Indonesia. Allogalumna indonesiensis sp. n. is morphologically most similar to Allogalumna borhidii Balogh & Mahunka, 1979, Allogalumna quadrimaculata (Mahunka, 1988), Allogalumna rotundiceps Aoki, 1996 and Allogalumna plowmanae Balogh & Balogh, 1983; however, the new species differs by having densely ciliate bothridial heads, larger body size and absence of a median pore. Allogalumna paranovazealandica sp. n. is morphologically most similar to Allogalumna novazealandica Hammer, 1968; however, the new species differs by the shorter body length and barbed and curving postero-laterad bothridial setae. The genus Allogalumna is recorded for the first time in the Indonesian fauna.

Contributions to the knowledge of oribatid mites of Indonesia. 2. The genus Pergalumna (Galumnidae) with description of a new species and key to known species in the Oriental region (Acari, Oribatida).

A new species of oribatid mite of the genus Pergalumna (Oribatida, Galumnidae) is described from litter and soil materials in Sumatra, Indonesia. Pergalumna paraindistincta sp. n. is morphologically most similar to Pergalumna indistincta Ermilov & Anichkin, 2011, Pergalumna pertrichosa Mahunka, 1995 and Pergalumna sura Balogh, 1997; however, the new species differs from Pergalumna indistincta by the smaller body size, presence of long adanal setae ad 1, and large, single median pore in females and males; from Pergalumna pertrichosa by the smaller body size, presence of three pairs of notogastral porose areas, elongated A1 and minute anal setae; from Pergalumna sura by the presence of strong adanal setae ad 1, large, single median pore in females and males, and shorter bothridial setae. Furthermore, Pergalumna hawaiiensis hawaiiensis (Jacot, 1934) and Pergalumna panayensis Ermilov & Corpuz-Raros, 2015 are recorded for the first time in the Indonesian fauna. An identification key to the known species of Pergalumna in the Oriental region is given.

Contributions to the knowledge of oribatid mites (Acari, Oribatida) of Indonesia. 3. The genus Galumna (Galumnidae) with description of a new subgenus and seven new species.

Seven new species of oribatid mites of the genus Galumna are described from litter and soil materials of Sumatra, Indonesia. A new subgenus, Galumna (Atypicogalumna) subgen. n., is proposed; it differs from all galumnid genera and subgenera by the simultaneous presence of porose areas and sacculi on the notogaster (vs. either porose areas or sacculi present). Galumna (Galumna) calva Starý, 1997 is recorded for the first time in the Oriental region, and Galumna (Galumna) sabahna Mahunka, 1995 is recorded for the first time in the Indonesian fauna.

Moderate changes in nutrient input alter tropical microbial and protist communities and belowground linkages.

We investigated the response of soil microbial communities in tropical ecosystems to increased nutrient deposition, such as predicted by anthropogenic change scenarios. Moderate amounts of nitrogen and phosphorus and their combination were added along an altitudinal transect. We expected microorganisms and microbial grazers (testate amoebae) to significantly respond to nutrient additions with the effect increasing with increasing altitude and with duration of nutrient additions. Further, we expected nutrients to alter grazer-prey interrelationships. Indeed, nutrient additions strongly altered microbial biomass (MB) and community structure as well as the community structure of testate amoebae. The response of microorganisms varied with both altitude and duration of nutrient addition. The results indicate that microorganisms are generally limited by N, but saprotrophic fungi also by P. Also, arbuscular mycorrhizal fungi benefited from N and/or P addition. Parallel to MB, testate amoebae benefited from the addition of N but were detrimentally affected by P, with the addition of P negating the positive effect of N. Our data suggests that testate amoeba communities are predominantly structured by abiotic factors and by antagonistic interactions with other microorganisms, in particular mycorrhizal fungi, rather than by the availability of prey. Overall, the results suggest that the decomposer system of tropical montane rainforests significantly responds to even moderate changes in nutrient inputs with the potential to cause major ramifications of the whole ecosystem including litter decomposition and plant growth.

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.

Tropical Andean forests are highly susceptible to nutrient inputs--rapid effects of experimental N and P addition to an Ecuadorian montane forest.

Tropical regions are facing increasing atmospheric inputs of nutrients, which will have unknown consequences for the structure and functioning of these systems. Here, we show that Neotropical montane rainforests respond rapidly to moderate additions of N (50 kg ha(-1) yr(-1)) and P (10 kg ha(-1) yr(-1)). Monitoring of nutrient fluxes demonstrated that the majority of added nutrients remained in the system, in either soil or vegetation. N and P additions led to not only an increase in foliar N and P concentrations, but also altered soil microbial biomass, standing fine root biomass, stem growth, and litterfall. The different effects suggest that trees are primarily limited by P, whereas some processes-notably aboveground productivity--are limited by both N and P. Highly variable and partly contrasting responses of different tree species suggest marked changes in species composition and diversity of these forests by nutrient inputs in the long term. The unexpectedly fast response of the ecosystem to moderate nutrient additions suggests high vulnerability of tropical montane forests to the expected increase in nutrient inputs.

Consequences of exclusion of precipitation on microorganisms and microbial consumers in montane tropical rainforests.

The structure and functioning of decomposer systems heavily relies on soil moisture. However, this has been primarily studied in temperate ecosystems; little is known about how soil moisture affects the microfaunal food web in tropical regions. This lack of knowledge is surprising, since the microfaunal food web controls major ecosystem processes. To evaluate the role of precipitation in the structure of soil food web components (i.e., microorganisms and testate amoebae), we excluded water input by rain in montane rainforests at different altitudes in Ecuador. Rain exclusion strongly reduced microbial biomass and respiration by about 50 %, and fungal biomass by 23 %. In testate amoebae, rain exclusion decreased the density of live cells by 91 % and caused a shift in species composition at each of the altitudes studied, with ergosterol concentrations, microbial biomass, and water content explaining 25 % of the variation in species data. The results document that reduced precipitation negatively affects soil microorganisms, but that the response of testate amoebae markedly exceeds that of bacteria and fungi. This suggests that, in addition to food, low precipitation directly affects the community structure of testate amoebae, with the effect being more pronounced at lower altitudes. Overall, the results show that microorganisms and testate amoebae rapidly respond to a reduction in precipitation, with testate amoebae-representatives of higher trophic levels-being more sensitive. The results imply that precipitation and soil moisture in tropical rainforests are the main factors regulating decomposition and nutrient turnover.