Abundance Of Oribatida Research Articles

Oribatid mites in different Mediterranean crop rotations fertilized with animal droppings.

Unsustainable soil management is one of the drivers of soil degradation, but impact assessment requires the development of indicators. Oribatids might be considered as early indicators of disturbances due to the stability of their community. The aim of this study was to investigate the feasibility of oribatids as bioindicators of sustainable agricultural practices. Under a dry Mediterranean climate, three fertilization experiments - two under a two-crop rotation system and one under maize monoculture and established 12 years earlier - were sampled 3× for oribatid identification during the last annual cropping cycle. The hypothesis was that different nutrient and crop managements affect the number of oribatid species and individuals present, and these parameters could be used as indicators of soil degradation. In total, 18 oribatid species were identified, and 1974 adult individuals were recovered. Maximum abundance was found prior to sowing. Pig slurry (PS) vs. control, and dairy cattle manure (CM) vs. mineral fertilization increased oribatid abundance. This increase was evident when the average applied rates with PS were ca. 2 Mg of organic matter (OM) ha- 1 yr- 1, or higher than ca. 4 Mg OM ha- 1 yr- 1 for CM. When the preceding crop was wheat and PS or CM were used, Oribatula (Zygoribatula) excavata (which reproduces sexually) predominated. In maize monoculture fertilized with CM, Tectocepheus sarekensis and Acrotritia ardua americana (which can reproduce through parthenogenesis) prevailed vs. Oribatula, which indicated a heavily disturbed soil. Under this specific Mediterranean environment, the predominance of certain parthenogenic oribatid species and the number of individuals provide advanced warning on soil degradation.

Predominant climate control on green leaf decomposition across subtropical rain and dry forests following hurricane disturbances

Hurricanes defoliate canopy and break tree branches and stems, generating large amount of plant debris in forest ecosystems. Forest recovery after hurricane disturbances relies heavily on the decomposition of these plant debris. Here we addressed the “tropical hierarchy of factors” hypothesis that substrate quality replaces climate as the predominant control on plant litter decomposition in tropical forests. We compared leaf decomposition between subtropical rain and dry forests on the island of Puerto Rico by reciprocally transplanting green-leaf litter between rain (Eugenia borinquensis leaves with higher C/N) and dry (Bucida buceras leaves with lower C/N) forests following hurricanes Irma and Maria. We show that leaf decomposed substantially faster in subtropical rain than dry forests, and for high-than low-quality substrates. Over a period of 536 days of field incubation, loss of leaf ash-free dry mass was 51.8% for B. buceras and 26.6% for E. borinquensis in the rainforest, 15.7% for B. buceras and near zero for E. borinquensis in the dry forest. We also found that soil arthropod density was more than 10-folds greater in the rainforest than in the dry forest and was only more than 2-folds greater in the low C/N litterbags than the high C/N litterbags. Analyses of structural equation model revealed that leaf decomposition rate correlated positively with total arthropod abundance in the rainforest and only with Oribatida abundance in the dry forest. The number of effective linkages among leaf C/N, precipitation and arthropods was greater in the subtropical rainforest (19) than in the dry forest (4), but did not vary between B. buceras (12) and E. borinquensis (11) substrates in the rainforest. We conclude that climate, rather than substrate quality, remains to be the predominant control on leaf decomposition across subtropical rain and dry forests following hurricane disturbances, and the controls of substrate quality on leaf decomposition is inferior and climate dependent.

Cushion plants act as facilitators for soil microarthropods in high alpine Sweden

Cushion plants can have positive impacts on plant richness in severe environments and possibly across trophic levels on arthropods, an under-studied topic. This study examined whether soil communities under cushions have higher richness and abundance of soil microarthropods than adjacent non-cushion vegetation, and whether differences in collembolan and mite abundance and species richness between cushions and adjacent vegetation increase with elevation. Paired soil samples were taken under cushions of Silene acaulis along the elevation gradient (1000, 1100, 1200, 1300, 1400 m a.s.l.), under cushions of Diapensia lapponica on the exposed ridge above the treeline (1000 m a.s.l.), and under adjacent non-cushion plant vegetation. In total, 5853 individuals of collembolans (n = 1705) and mites (n = 4148) were obtained from soil samples and identified to order/species level. S. acaulis cushions had a positive effect on species richness and abundance of collembolans, with richness effects from 1100 m a.s.l. upwards. Oribatid mite richness and abundance were also higher under cushions compared with adjacent vegetation. Species richness of collembolans and oribatids declined with increasing elevation from 1200 m a.s.l. Collembolan abundance peaked at mid-elevation (1200 m a.s.l.) under cushions and adjacent vegetation, while oribatid mite abundance peaked at 1300 m a.s.l. under both vegetation types. D. lapponica cushions on the exposed ridge had significant positive effects on species richness, abundance and diversity index of collembolans, and abundance of oribatids. Cushion plants play an important role in supporting the biodiversity of soil fauna in severe alpine environments, with the positive effects of cushion plants increasing with environmental severity.

Soil microarthropods respond differently to simulated drought in organic and conventional farming systems.

In Central Europe, summer droughts are increasing in frequency which threatens production and biodiversity in agroecosystems. The potential of different farming systems to mitigate detrimental drought effects on soil animals is largely unknown. We investigated the effects of simulated drought on the abundance and community composition of soil microarthropods (Collembola and Oribatida and Meso‐, Pro‐, and Astigmata) in winter wheat fields under long‐term conventional and organic farming in the DOK trial, Switzerland. We simulated drought by excluding 65% of the ambient precipitation during the wheat‐growing season from March to June 2017. The abundance of Collembola and Oribatida declined more consistently in conventionally managed fields compared to organically managed fields under simulated drought. The abundance of Collembola as well as Meso‐, Pro‐ and Astigmata, but not the abundance of Oribatida, increased in deeper soil layers due to simulated drought, suggesting vertical migration as a drought avoidance strategy. The species composition of Oribatida communities, but not of Collembola communities, differed significantly between drought treatments and between farming systems. Soil carbon content was a major factor structuring Oribatida communities. Our results suggest that organic farming buffers negative effects of drought on soil microarthropods, presumably due to higher soil carbon content and associated higher soil moisture and improved soil structure. This potential of organic farming systems to mitigate consequences of future droughts on soil biodiversity is promising and needs further exploration across larger climatic and spatial scales and should be extended to other groups of soil biota.

Soil mesofauna participating in driving home-field advantage differ between litter mass loss and nutrient release

Soil organisms play an important role in litter mass loss and nutrient release. Although soil mesofauna participating in driving home-field advantage (HFA) differ between litter mass loss and nutrient release, this has rarely been investigated. A reciprocal transplant experiment was conducted using litterbags with two sizes of mesh (0.01 mm and 1 mm) in Pinus koraiensis Sieb. & Zucc. and Larix olgensis Henry plantations. We found that P. koraiensis and L. olgensis litter had a significantly higher soil mesofaunal abundance at home habitat after 7 and 9 months, respectively. The P. koraiensis and L. olgensis litter were associated with a significantly higher abundance of Oribatida and Tomoceridae at home habitat after 7 and 9 months, respectively. Soil mesofauna enhanced the positive effect on HFA for litter mass loss and carbon release in P. koraiensis and L. olgensis litter that could be observed at months 7 and 9 of the experiment. Nevertheless, the soil mesofauna significantly contributed to the negative effect on HFA for nitrogen and sulphur release for both litter types after 12 months. Our findings suggest that soil mesofaunal specialization could promote HFA effect for litter mass loss and carbon release, but that their effect was only apparent during specific stages of litter decomposition. Soil mesofaunal specialization dynamics are correlated with microclimate conditions and litter quality. Soil mesofauna significantly contributed to the negative effect on HFA for nitrogen and sulphur release, due to the change in the litter quality and imbalance of soil mesofauna between the home and away from home habitats.

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.

Seasonal dynamics of mites (Acari) in pastures and meadows in Poland, with species analysis of Oribatida

The study involved three pastures, grazed by geese, goats and fallow deer, and three nearby meadows (control plots) situated in north-central Poland. Samples of 150 cm3 each (6 cm of soil and 3 cm of lower parts of plants) were collected in spring, summer and autumn 2016 and 2017 in 10 replications, 360 samples in total. This material included 22.561 mites, among which Oribatida accounted for 69%, Mesostigmata for 21%, and other mites for 10%. At most study sites, both pastures and meadows, no significant seasonal differences in the abundance of Oribatida and Mesostigmata were seen. Such differences were only observed for the third category of other mites that were the most abundant in spring and usually the least abundant in autumn. Also species diversity of Oribatida differed between the seasons – in all pastures it was the highest in summer and the lowest in spring, while in all meadows it was the highest in spring and decreased towards autumn. Oribatid species were more affected by the habitats than by seasons, as some species were strongly associated with pastures (Platynothrus peltifer), other with meadows (Achipteria coleoptrata, Liebstadia similis, Metabelba pulverosa, Scheloribates laevigatus and Sellnickochthonius immaculatus), and some (Eupelops occultus and Tectocepheus velatus) were abundant in both habitats. Although the effect of seasonality was weaker than that of the habitat, it was still perceptible. Platynothrus peltifer was most associated with autumn, T. velatus with spring, E. occultus with spring and summer and L. similis with summer.

The effect of grazing by geese, goats, and fallow deer on soil mites (Acari)

The study investigated the effects of grazing by geese, goats, and fallow deer on soil mites. It included a total of 360 samples collected in the spring, summer, and autumn of 2016 and 2017 in north-central Poland. Study plots were situated in three pastures grazed by geese, goats, and fallow deer, and three meadows near the pastures served as controls. All study plots were fenced. In total 22,561 mites Acari were obtained, including 15,641 Oribatida 69.3% , 4926 Mesostigmata 21.8% , and 1994 other mites 8.9% . Only the abundance of Oribatida therefore, also total Acari differed significantly in pastures grazed by different animal species. The abundance of Oribatida in the pasture vs. the corresponding meadow was higher in the case of geese, similar for fallow deer, and lower for goats. We identified a total of 21 oribatid species. The number of species did not differ significantly between the pastures and the corresponding mowed meadows, indicating that they are similarly disturbed biotopes. Eurytopic species characteristic of grasslands predominated in the study plots. The most abundant species were Platynothrus peltifer C. L. Koch, 1839 , Tectocepheus velatus Michael, 1880 , and Eupelops occultus C. L. Koch, 1835 . Platynothrus peltifer and T. velatus preferred pastures to meadows and were most abundant in th goose pasture, while Liebstadia similis Michael, 1888 and Sellnickochthonius immaculatus Forsslund, 1942 were more abundant in meadows.

Edaphic variables conditioning the habitat of oribatid mites in Luvic Phaeozems under forest plantations (Buenos Aires, Argentina)

The soil is a complex three-dimensional habitat and any changes in its structure and porosity are likely to affect the type and abundance of soil biota. Oribatid mites play an important role in the decomposition and mineralization of soil organic matter and their abundance depends on diverse soil parameters, including soil texture, organic matter content, pH, moisture, and the pore system. The aim of the present work is to analyze some of the edaphic variables that condition the habitat of oribatid mites in Luvic Phaeozems under <em>Pinus radiata </em>(site P) and <em>Eucalyptus globulus </em>(site E) plantations, in the Southeast of Buenos Aires, Argentina. Bulk density, penetration resistance, pH, moisture, pore system parameters, and oribatid abundance and species composition were analyzed. Site E had a greater total porosity than site P. The high tortuosity of the pores in both sites generates a complex habitat architecture for the development of oribatid mites. In both sites, oribatids of 70-400 μm in size predominated and were more abundant in site E. A positive correlation between the abundance of oribatids and the pore size in both sites was observed. In site E this correlation was lower for 70-600 µm (R = 0.13) or negative for 70-400 µm (R = -0.78). Therefore, the oribatid abundance could be explained by a greater complexity of the structure of the organic horizon, lower bulk density and lower penetration resistance. These conditions favor the mineralization of organic matter, and therefore food availability. On the other hand, in site P, oribatid abundance is mainly influenced by the porous system, which conditions the access to food, competition between organisms and refuge from predators. Two new species were registered for Argentina: <em>Mesotritia elegantula </em>and<em> Acrogalumna longipluma.

Legacy effects of experimental environmental change on soil micro‐arthropod communities

AbstractGlobal change experiments such as experimental warming and nutrient addition strongly affect the structure and functioning of high latitude and altitude ecosystems. However, it is often unknown to what extend such effects are permanent or whether changes persist after environmental conditions return to pre‐treatment levels. In this study, we assess the legacy effects of temperature manipulation and nutrient addition experiments on alpine soil micro‐arthropod (i.e., Collembola and Oribatida) communities nine years after the treatments were discontinued. Treatment effects on the vegetation were still detectable six years after cessation, although grazing increased the recovery rate. Because micro‐arthropods are often closely associated with vegetation, we expected to find that treatment effects on Collembola and Oribatida abundance and species composition persisted to date, reflecting plant community dynamics. Also, we expected large‐bodied, drought‐resistant Collembola species that live on top of the soil to show less strong legacy effects. We did not find legacy effects of environmental treatments on Collembola and Mesostigmata in terms of abundance. However, we found persistent changes in community composition of Collembola and Oribatida, suggesting treatment effects persist to date. The generalistFolsomia quadrioculatawas the most responsive Collembola species to initial treatments, most likely due to its variable life‐history strategy. Although its abundance recovered,F. quadrioculataremained dominant in Collembola communities after cessation of the treatments. Grazing affected community composition of both Collembola and Oribatida, but we did not find grazing to reduce legacy effects on micro‐arthropod as it did for vegetation. We therefore conclude that the environmental treatments had only temporary effects on micro‐arthropods in terms of overall abundance, but that effects on individual species and therefore species composition may be long‐lasting and less predictable.

Effect of Soil Fauna on Home-Field Advantages of Litter Mass Loss and Nutrient Release in Different Temperate Broad-Leaved Forests

The home-field advantage (HFA) of litter decomposition dynamics has been investigated intensively in different ecosystems with a wide variety of plant types. HFA mainly occurs due to the specialization of a soil organism. However, for the HFA, the linkages between litter mass loss, nutrient release, and soil faunal community are not fully understood. Thus, in this study, we performed a reciprocal litter transplant experiment using coarse and fine mesh litterbags in a Quercus mongolica Fisch. ex Ledeb. forest dominated by Q. mongolica (QM) and Acer pseudosieboldianum (Pax) Komarov (AP) and miscellaneous wood forests dominated by Juglans mandshurica Maxim. (JM) and Ulmus laciniata (Trautv.) Mayr. (UL). Results showed that the A. pseudosieboldianum litter displayed a significantly higher total abundance of Oribatida, Tomoceridae, and Entomobryidae at home than away from home after 7 months. However, all litters showed no significant difference in the HFA between the coarse mesh and fine mesh sizes during the 12-month experiment. A. pseudosieboldianum and J. mandshurica litters showed a significantly higher positive HFA for the C release in the coarse mesh than in the fine mesh litterbags after 7 months. Q. mongolica and J. mandshurica litters showed a significantly higher positive HFA for N release in the coarse mesh than in the fine mesh litterbags after 7 months. The A. pseudosieboldianum litter showed a significantly higher positive HFA for N release in the coarse mesh than in the fine mesh litterbags after 12 months. Q. mongolica and A. pseudosieboldianum litters showed a significantly higher positive HFA for S release in the coarse mesh than in the fine mesh litterbags after 7 and 12 months, respectively. However, A. pseudosieboldianum and Q. mongolica litters showed a significantly higher negative HFA for S release in the coarse mesh than in the fine mesh litterbags after 7 and 12 months, respectively. Our results illustrated that soil faunal specialization was found in the A. pseudosieboldianum litter only at home after 7 months. Soil fauna had a weak effect on the HFA of the litter mass losses during the 12-month experiment. Soil fauna drove the positive HFA for the N release of both the high- and low-quality litters. Soil fauna have a positive and negative HFA for S release in the low-quality litter.

Trees in trimmed hedgerows but not tree health increase diversity of oribatid mite communities in intensively managed agricultural land

Hedgerows structure agricultural landscape worldwide but little is known on their soil communities. In the intensively managed agricultural landscapes of Ireland and the UK, hedgerows protect soil from degradation and are thought to provide a reservoir of soil biodiversity for the farmed fields. But hedgerows are currently threatened by emergent tree diseases spread with rising volumes of trade in plants. This study analysed the effect of the most dominant hedgerow tree species on the composition and diversity of soil communities, which we estimated with oribatid mites in the context of an imminent ash dieback outbreak in Northern Ireland. We hypothesised that the environmental heterogeneity created by different tree species and good tree health are beneficial to the abundance and diversity of these soil communities. We found that communities differ, both in terms of species composition and relative abundances, between different trees in the trimmed hedgerows, and between untrimmed and trimmed hedgerows. The presence of trees was associated with more variable species composition. The analysis of phospholipid fatty acids (PLFA) showed that pasture and adjacent hedgerows were dominated by bacteria but there was no clear relationship between bacterial biomass and oribatid abundance or richness. However, changes in bacterial PLFAs were correlated positively with changes in oribatid community composition. Soil under ash trees which were diseased supported a higher species richness and greater abundance of oribatids than healthy trees. We conclude that the presence of different tree species in hedgerows adds to the overall diversity of soil hedgerow communities and hypothesise that the structural heterogeneity created by tree canopy drives increased diversity. Ill health in ash trees is currently positively affecting oribatid communities, possibly due to the temporarily increase in organic matter in soil. The epidemic of ash dieback, however, is expected to kill and remove trees in the medium term and so reduce soil community diversity in the long term.

The impacts of forest clear felling on the oribatid mite fauna inhabiting Formica aquilonia nest mounds

The ubiquitous soil-dwelling oribatid mites have long been investigated as potential bioindicator agents for environmental changes, such as those resulting from forest management. However, the oribatid community composition often lacks detectable changes, mainly due to the difficulties of finding homogenous microhabitats from the landscape for investigation purposes. Red wood ant nest mounds in boreal forests, however, form uniform, moisture, and temperature regulated, microhabitats of which are also inhabited by a rather characteristic oribatid fauna. With this standardized microhabitat—the red wood ant Formica aquilonia nest mounds in Finland—we studied the impacts of forest clear felling on the oribatid mites inhabiting those nests. We compared the oribatid assemblages of altogether 41 ant mounds, located in three separate clear fell areas and in adjacent mature coniferous forest. A total of 16,499 specimens, representing 67 oribatid species, were observed. The ten most abundant species represented 90.9% of the total abundance. The oribatid species richness was significantly lower in clear fell mounds and was positively related to the surface moisture content of the mounds. Oribatid abundance or community composition did not markedly differ between clear fell and forest mounds. Despite the attempt to standardize the microhabitat of oribatid fauna, the use of oribatid mites as biological indicators of harvesting disturbance was limited with this study design due the lack of changes in community composition. Then again, the oribatid species richness of this characteristic microhabitat may provide useable quality measures about the harms of forest clear felling.

Oribatida (Acari) communities in arable soils formed under waterlogged conditions: the influence of a soil moisture gradient

Oribatid mites make up a dominant group of soil mesofauna. These microarthropods are quite rarely researched in heavy clay soils, and their seasonal dynamics has never been studied thoroughly during the year in such an environment. The research was conducted in 1994–1995 at three sites along a small-scale moisture gradient, with the aim of describing the influence of different moisture conditions on this soil mesofaunal group and evaluating their seasonal dynamics regarding temperature and soil humidity fluctuations. The study area was characterized by a land depression in a field with clay soil, where waterlogged periods occurred, in the Eastern Slovak Lowland (Slovakia). The investigations were based on 24,890 oribatid adults from 72 species. The mean abundance and total species richness of Oribatida increased with increasing soil moisture towards the lower part of the land depression. The abundance and number of species reached a maximum at the bottom site (ca. 8000 ind.m−2 and 59 species) and was two-fold greater than at the summit site. The mean oribatid abundance and the mean species richness between the sites were compared, and significant differences were found on almost all sampling occasions, but the patterns of changes along the moisture gradient differed between study years. The seasonal fluctuations of oribatid abundance within the sites showed a pattern with spring and autumn maxima and a summer minimum only at moist depression bottom. Seasonal changes in the oribatid community composition were more pronounced at sites with lower soil moisture. Specific communities consisting of hygrophilous or eurytopic species and located at the bottom and slope sites of the depression clearly differed from those of the summit site, where xerotolerant species predominated. Ordination analysis confirmed the influence of temperature and precipitation on the species community composition. The bottom and slope site communities were dominated by the species combination of hygrophilous Microppia minus, Oxyoppia europaea and hygrotolerant Oppiella nova, while at the summit site these mites were replaced by more xerotolerant species: Ramusella insculpta, Oppiella obsoleta and Tectocepheus velatus.

Study of Oribatids population on three types of land use at PT Nusantara VIII Plantation, Cisarua Sub-district, Bogor, West Java

Most of the forest area of PT Perkebunan Nusantara VIII have been converted to the plantation (tea, cacao, coffee) and agriculture, such as crops (intercropping of oranges and pineapple) areas. The forest conversion will affect soil biodiversity, which will reduce soil mesofauna population, such as the Oribatids group. Oribatids is one of the soil mesofauna which has a very important role in the soil as a decomposer. Because of its important role and their huge numbers in the soil, Oribatids can be used as a bioindicator of soil fertility. This study aimed to elucidate the abundance and diversity of Oribatids and the relationship between soil properties and population of Oribatids in three types of land use at PT Perkebunan Nusantara VIII. Soil and litter samples were taken in three different types of land use (tea gardens, intercropping, and secondary forests) using a simple random sampling method with a distance of each of the 15 sampling points of 100 m at a soil depth of 0-5 cm. Soil and litter samples were extracted using Berlese Funnel Heat Extractor. Oribatids identification was carried out until the family level, and the Oribatids diversity index were determined according to Shannon's diversity index. The identification results obtained in the three types of land use amounted to 24 families from 172 families found previously. The highest abundance of Oribatids was found in secondary forests both in the soil and litter layer (169.85 and 428.87 individuals/m², respectively), the lowest abundance of Oribatids was found in intercropping both in the soil and litter layer (89.17 and 229.30 individuals/m², respectively). According to Shannon Wiener (H'), the diversity index value ranges from 1.48-1.85 or it was categorized as a low-medium diversity value. The results of this study indicated that there was a positive correlation coefficient value from several families of Oribatids with soil pH, organic C, total N, C/N ratio, water content, and soil temperature.

Hydrology-driven environmental variability determines abiotic characteristics and Oribatida diversity patterns in a Sphagnum peatland system.

We investigated oribatid mite communities in a Sphagnum-dominated boreal peatland system characterised by a mosaic of oligotrophic and meso-eutrophic areas. We aimed to determine the relative importance of environmental factors (pH, Sphagnum nutrient content, water table level, diversity of vascular plants and bryophytes in the surrounding plant community) and spatial variation in influencing abundance, diversity and community composition of aquatic and terrestrial oribatid mites. Among environmental variables, water table level (micro-topography), pH, and K in Sphagnum tissues were the main predictors of Oribatida community structure. Aquatic species were associated with pools; two terrestrial species-Hoplophthiracarus illinoisensis and Nothrus pratensis-were associated with oligotrophic hummocks; the rest of terrestrial species were associated with dryer mesotrophic and eutrophic habitats. Low water table depth (hummocks), high local plant diversity, and high P in Sphagnum tissues were predictors of high abundance of terrestrial Oribatida. Species richness of terrestrial Oribatida was linked with low water table and high plant diversity. For aquatic Oribatida abundance, water table depth was the single most important predictor variable. Plot trophic class (its status on the peatland poor-rich gradient assigned based on plant indicator species) was also a significant predictor of terrestrial Oribatida abundance, richness, and community structure. Spatial structuring was important for terrestrial Oribatida community composition, weak (P < 0.10) for terrestrial Oribatida abundance and richness, and not significant for aquatic Oribatida.

Impact of macro vegetation and edaphic variables on the distribution and diversity of Oribatida (Acari) in Northern Tripura, India

In this communication results of an ecological study of soil Oribatida from Northern Tripura, India have been incorporated. Soil samples were collected fortnightly from two sites over a period of one year (July 2016 to June 2017). An attempt has been made to determine the extent to which macro vegetation, edaphic variables and local microclimatic conditions influence the community structure of Oribatida. Among the 14 species under 12 genera identified, species of the genera Scheloribates, Protoribates and Galumna were the major contributors representing 34.27%, 16.93% and 7.58% of the total population, respectively. Species of Scheloribates and Protoribates were common and dominated in both sites. The oribatid abundance exhibited an irregular and significant trend of fluctuation with a maximum in winter and a minimum in the monsoon period. Out of four edaphic variables analyzed, only the organic matter content and pH showed a positive and significant correlation with oribatid abundance, while temperature and moisture revealed a significant negative correlation. It was interesting to note that although the study sites were close to each other and were more or less similar in topological, edaphological and climatological conditions, with a little variation in distance and vegetation cover they exhibited variations in both oribatid species abundance and diversity. The reason behind the seasonal variation and differences in abundance and species diversity in the studied sites was highlighted. Further extensive and comprehensive research on oribatids is needed in the region of Tripura.

Root chemistry and soil fauna, but not soil abiotic conditions explain the effects of plant diversity on root decomposition.

Plant diversity influences many ecosystem functions including root decomposition. However, due to the presence of multiple pathways via which plant diversity may affect root decomposition, our mechanistic understanding of their relationships is limited. In a grassland biodiversity experiment, we simultaneously assessed the effects of three pathways-root litter quality, soil biota, and soil abiotic conditions-on the relationships between plant diversity (in terms of species richness and the presence/absence of grasses and legumes) and root decomposition using structural equation modeling. Our final structural equation model explained 70% of the variation in root mass loss. However, different measures of plant diversity included in our model operated via different pathways to alter root mass loss. Plant species richness had a negative effect on root mass loss. This was partially due to increased Oribatida abundance, but was weakened by enhanced root potassium (K) concentration in more diverse mixtures. Equally, grass presence negatively affected root mass loss. This effect of grasses was mostly mediated via increased root lignin concentration and supported via increased Oribatida abundance and decreased root K concentration. In contrast, legume presence showed a net positive effect on root mass loss via decreased root lignin concentration and increased root magnesium concentration, both of which led to enhanced root mass loss. Overall, the different measures of plant diversity had contrasting effects on root decomposition. Furthermore, we found that root chemistry and soil biota but not root morphology or soil abiotic conditions mediated these effects of plant diversity on root decomposition.

Patterns of soil mite diversity in Lamto savannah (Côte d’Ivoire) submitted at different fire regimes

In this study, we evaluated the impact of different fire regimes (early, mid-season, or late fire) on soil mite abundance and diversity in three study sites (Salty marigot, Plateau and North piste) of the Lamto shrub savannah at 160 km northwest of Abidjan, Côte d’Ivoire. On each site, three adjacent plots of 100 m x 50 m were delimited, to which a given fire regime was applied. At each site, soil cores were taken at 0-10 cm soil depth three days before the fire application, the day after and one month after the fire (10 soil cores x 3 sampling periods x 3 fire regimes or plots x 3 sites = 270 soil cores). Soil mites were then extracted from these cores. 108 soil cores were sampled at two upper layers (0-5 and 5-10 cm) for estimation of the bulk density and water content. After data analysis, four groups of mite were observed (Actinedida, Gamasida, Oribatida and Acaridida). Gamasida and Oribatida were dominant groups (early fire: Gamasida 35%, Oribatida 55%; mid-season fire: Gamasida 16%, Oribatida 70%; late fire: Gamasida 16%, Oribatida 74%). In total, 70 species were observed, with 29, 44 and 31 species recorded respectively during the early, mid-season and late fires. Mite density and species richness varied significantly along the three fire regimes and decreased substantially after fire application. Except for the mid-season fire, Simpson index from all mites differed significantly across sampling periods. Lower Oribatida represented 25% of the total Oribatida. Whatever the fire regimes, brachypyline Oribatida abundance increased the day after fire application. Overall, fire intensity reduced drastically soil mite abundance and diversity.

Relative importance of local habitat complexity and regional factors for assemblages of oribatid mites (Acari: Oribatida) in Sphagnum peat bogs.

We investigated communities of oribatid mites in five peat bogs in the north-west of the East European plain. We aimed to determine the extent to which geographic factors (latitude, separation distance), local environment (Sphagnum moss species, ground water level, biogeochemistry) and local habitat complexity (diversity of vascular plants and bryophytes in the surrounding plant community) influence diversity and community composition of Oribatida. There was a significant north-to-south increase in Oribatida abundance. In the variance partitioning, spatial factors explained 33.1% of variability in abundance across samples; none of the environmental factors were significant. Across all bogs, Oribatida species richness and community composition were similar in Sphagnum rubellum and Sphagnum magellanicum, but significantly different and less diverse in Sphagnum cuspidatum. Sphagnum microhabitat explained 52.2% of variability in Oribatida species richness, whereas spatial variables explained only 8.7%. There was no distance decay in community similarity between bogs with increased geographical distance. The environmental variables explained 34.9% of the variance in community structure, with vascular plants diversity, bryophytes diversity, and ground water level all contributing significantly; spatial variables explained 15.1% of the total variance. Overall, only 50% of the Oribatida community variance was explained by the spatial structure and environmental variables. We discuss relative importance of spatial and local environmental factors, and make general inferences about the formation of fauna in Sphagnum bogs.