L6DNet: Light 6 DoF Network for Robust and Precise Object Pose Estimation with Small Datasets

Estimating the 3D pose of an object is a challenging task that can be considered within augmented reality or robotic applications. In this paper, we propose a novel approach to perform 6 DoF object pose estimation from a single RGB-D image. We adopt a hybrid pipeline in two stages: data-driven and geometric respectively. The data-driven step consists of a classification CNN to estimate the object 2D location in the image from local patches, followed by a regression CNN trained to predict the 3D location of a set of keypoints in the camera coordinate system. To extract the pose information, the geometric step consists in aligning the 3D points in the camera coordinate system with the corresponding 3D points in world coordinate system by minimizing a registration error, thus computing the pose. Our experiments on the standard dataset LineMod show that our approach is more robust and accurate than state-of-the-art methods. The approach is also validated to achieve a 6 DoF positioning task by visual servoing.Comment: This work has been accepted at IEEE Robotics and Automation Letter

Responses of soil hexapod communities to increasing nitrogen in a subarctic grassland

Altres ajuts: acords transformatius de la UABThe warming of boreal ecosystems accelerates decomposition and increases nitrogen (N) availability. The impact of increased N on subarctic soil fauna communities, however, remains poorly understood. We investigated the response of soil hexapods to a N addition experiment in a subarctic grassland. We characterized the soil hexapod communities using environmental DNA metabarcoding and analyzed the levels of dissolved organic carbon (DOC), dissolved organic nitrogen (DON), microbial carbon (Cmic), and microbial nitrogen (Nmic). N addition increased DON and Nmic, while DOC and Cmic pools remained unchanged. Furthermore, N addition caused shifts in soil hexapod community compositional diversity between control and N plots in herbivore and microbivore taxa. The levels of DON and Nmic strongly correlated with these shifts, explaining 54% and 45% of the compositional variability, respectively. This study demonstrates a clear link between N availability and shifts in soil hexapod communities, associated to changes in microbial and dissolved N pools in subarctic grasslands

Responses of soil hexapod communities to warming are mediated by microbial carbon and nitrogen in a subarctic grassland

Altres ajuts: acords transformatius de la UABWarming in subarctic ecosystems will be two-fold higher compared to lower latitudes under current climate change projections. While the effects of warming in northern ecosystems on plants and microorganisms have been extensively studied, the responses of soil fauna have received much less attention, despite their important role in regulating key soil processes. We analyzed the response of soil hexapod communities in a subarctic grassland exposed to a natural geothermal gradient in Iceland with increases of +3 and + 6 °C above ambient temperature. We characterized hexapod communities using environmental DNA (eDNA) metabarcoding. We analyzed the amounts of microbial carbon (Cmic), microbial N (Nmic), dissolved organic C (DOC) and dissolved organic N (DON) and then assessed whether these variables could help to account for the compositional dissimilarity of ground hexapod communities across temperatures. The increases in soil temperature did lead to changes in the composition of hexapod communities. The compositional differences caused by +6 °C plots were correlated with a decrease in Cmic and Nmic, soil DOC and DON. Our results highlight the response of soil hexapods to warming, and their interaction with microbial biomass ultimately correlated with changes in the availabilities of soil C and N

Decay of similarity across tropical forest communities : integrating spatial distance with soil nutrients

Altres ajuts: Acord transformatiu CRUE-CSICUnderstanding the mechanisms that drive the change of biotic assemblages over space and time is the main quest of community ecology. Assessing the relative importance of dispersal and environmental species selection in a range of organismic sizes and motilities has been a fruitful strategy. A consensus for whether spatial and environmental distances operate similarly across spatial scales and taxa, however, has yet to emerge. We used censuses of four major groups of organisms (soil bacteria, fungi, ground insects, and trees) at two observation scales (1-m sampling point vs. 2,500-m plots) in a topographically standardized sampling design replicated in two tropical rainforests with contrasting relationships between spatial distance and nutrient availability. We modeled the decay of assemblage similarity for each taxon set and site to assess the relative contributions of spatial distance and nutrient availability distance. Then, we evaluated the potentially structuring effect of tree composition over all other taxa. The similarity of nutrient content in the litter and topsoil had a stronger and more consistent selective effect than did dispersal limitation, particularly for bacteria, fungi, and trees at the plot level. Ground insects, the only group assessed with the capacity of active dispersal, had the highest species turnover and the flattest nonsignificant distance−decay relationship, suggesting that neither dispersal limitation nor nutrient availability were fundamental drivers of their community assembly at this scale of analysis. Only the fungal communities at one of our study sites were clearly coordinated with tree composition. The spatial distance at the smallest scale was more important than nutrient selection for the bacteria, fungi, and insects. The lower initial similarity and the moderate variation in composition identified by these distance-decay models, however, suggested that the effects of stochastic sampling were important at this smaller spatial scale. Our results highlight the importance of nutrients as one of the main environmental drivers of rainforest communities irrespective of organismic or propagule size and how the overriding effect of the analytical scale influences the interpretation, leading to the perception of greater importance of dispersal limitation and ecological drift over selection associated with environmental niches at decreasing observation scales

Responses of soil hexapod communities to increasing nitrogen in a subarctic grassland

Abstract: The warming of boreal ecosystems accelerates decomposition and increases nitrogen (N) availability. The impact of increased N on subarctic soil fauna communities, however, remains poorly understood. We investigated the response of soil hexapods to a N addition experiment in a subarctic grassland. We characterized the soil hexapod communities using environmental DNA metabarcoding and analyzed the levels of dissolved organic carbon (DOC), dissolved organic nitrogen (DON), microbial carbon (Cmic), and microbial nitrogen (Nmic). N addition increased DON and Nmic, while DOC and Cmic pools remained unchanged. Furthermore, N addition caused shifts in soil hexapod community compositional diversity between control and N plots in herbivore and microbivore taxa. The levels of DON and Nmic strongly correlated with these shifts, explaining 54% and 45% of the compositional variability, respectively. This study demonstrates a clear link between N availability and shifts in soil hexapod communities, associated to changes in microbial and dissolved N pools in subarctic grasslands

ferrinetal_c&nmediatewarmingimpactonsoilhexapods

This study was conducted at the ForHot research site in Iceland (Sigurdsson et al., 2016) between August 2017 and June 2018 (64°0′N, 21°11′W). Soil type was a Brown Andosol (Arnalds, 2015). Mean annual temperature at the site was 5.1 °C. The coldest and warmest temperatures in the neighboring village of Eyrarbakki in 2016 were -12.3 °C and 21.6 °C, respectively. Average annual precipitation for the same year was 1153 mm (Icelandic Meteorological Office, 2016). The vegetation was an unmanaged grassland dominated by Agrostis capillaris L., Galium boreale L. and Anthoxantum odoratum L. Vascular plants cover 46% of the area over a moss mat which covers up to 88% of the ground. This grassland has been geothermally warmed since 29 May 2008, when an earthquake transferred geothermal energy from hot groundwater to previously unheated soils (Sigurdsson et al., 2016). Belowground temperatures at 10 cm depth now display a permanent warming gradient reaching +10 °C, with a discreet increase in aboveground temperature of +0.2 °C. The warming has only been mildly disruptive, with seasonality remaining unchanged. Soil humidity was only marginally affected, with volumetric water content changing from 40% to 38%, and water pH increased from 5.6 in unheated soil to up to 6.3 after warming. Geothermal groundwater has remained in the bedrock and has not reached the root zone, thus avoiding direct eco-toxicological effects (Sigurdsson et al., 2016). The resulting stable conditions and lack of artifacts provide a realistic natural belowground experiment on soil warming under climate change. Natural N deposition in the area is 1.3 ± 0.1kg N ha-1 y-1 (Leblans et al., 2014). Five transects were established, each one consisting of three 2 x 2 m plots, and each plot at different temperature: an unheated control, a low warming level of ca. +3 °C and a higher warming level of ca. +6 °C above the ambient reference in the control (henceforth referred as “+3 °C” and “+6 °C”). Soil cores were collected using an auger to a depth of ~10 cm, excluding the O horizon. Soil cores were sampled seasonally four times: August 2017, corresponding to late growing season; November 2017, at start of winter and initial soil freezing; April 2018, with the first soil thaw in un-warmed soils, and June 2018, in the early part of the growing season. We thus collected a total of 20 core samples for each warming treatment (5 replicates in 4 seasons for 3 temperature levels = 60 samples). All samples were immediately sieved to remove roots and stones larger than 2 mm. Fifteen grams of each sample were then frozen in plastic bags in liquid N in the field to immediately stop all biological processes. All frozen samples were freeze-dried in the laboratory. eDNA was extracted from 15 g soil samples belonging to DNA remains (i.e. no alive fauna) as previously described (Taberlet et al., 2012; Zinger et al., 2016). The soil hexapod communities were genetically characterized based on Molecular Operational Taxonomic Units (MOTUs) using the retrieved eDNA and applying a metabarcoding approach. We amplified the 16S mitochondrial rDNA region using the Ins16S_l primer pair (Ins16S_1-F: 5′-TRRGACGAGAAGACCCTATA-3′; Ins16_1-R: 5′-TCTTAATCCAACATCGAGGTC-3′; Clarke et al. 2014). This primer pair, specifically designed for hexapod metabarcoding, introduces a very limited taxonomic bias and performs very well for identifications at the species level throughout the Hexapoda subphylum (e.g. Kocher et al., 2017; Talaga et al., 2017). PCR amplification was performed in triplicate in 20-μL mixtures consisting of 10 μL of AmpliTaq Gold Master Mix (Life Technologies, Carlsbad, USA), 5.84 μL of nuclease-free Ambion water (Thermo Fisher Scientific, Waltham, USA), 0.25 μM each primer, 3.2 μg of bovine serum albumin (Roche Diagnostic, Basel, Switzerland) and 2 μl of DNA template that was diluted 10-fold to reduce PCR inhibition by humic substances. The thermal profile of the PCR amplification was 40 cycles of denaturation at 95 °C (30 s), annealing at 49 °C (30 s) and elongation at 72 °C (60 s), with a final elongation step at 72 °C for 7 min. Tags had at least five differences between them to minimize ambiguities (Coissac et al., 2012). The sequenced multiplexes comprised extractions/PCR blank controls, unused tag combinations and positive controls (Kocher et al., 2017). The PCR products were then sequenced using the MiSeq platform (Illumina Inc., San Diego, USA), with the expected sequencing depth set at 400 000 reads per sample. The sequences were processed using OBITOOLS software (Boyer et al., 2016). Low-quality sequences (containing Ns, alignment scores 320 bp and singletons) were excluded. The remaining sequences were clustered into MOTUs using SUMACLUST (Mercier et al., 2013) at a threshold of sequence similarity of 97%. The hexapod MOTUs were taxonomically assigned using Blast. MOTUs showing <80% similarity with either the local or the EMBL reference databases were removed, leading to 219 MOTUs. These retained MOTUs included taxa from classes Insecta and Entognatha, which both belong to the subphylum Hexapoda. We then applied a post-processing pipeline (Zinger et al., 2021) to minimize PCR and sequencing errors, contaminations and false-positive sequences, and by detailed curation of ecologically incongruent assignments (i.e. taxa with distributions outside the palearctic and neartic ecozones). This conservative approach retained a total of 33 identified species. We then used checklists of Icelandic hexapod species and information from previous studies at the same study site (Fjellberg, 2007; Holmstrup et al., 2018) to assess the performance of our eDNA metabarcoding protocol to properly describe the hexapod communities in the soil.Peer reviewe

Decay of similarity across tropical forest communities: integrating spatial distance with soil nutrients

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