Landscape characteristics shape surface soil microbiomes in the Chihuahuan Desert.

Introduction: Soil microbial communities, including biological soil crust microbiomes, play key roles in water, carbon and nitrogen cycling, biological weathering, and other nutrient releasing processes of desert ecosystems. However, our knowledge of microbial distribution patterns and ecological drivers is still poor, especially so for the Chihuahuan Desert. Methods: This project investigated the effects of trampling disturbance on surface soil microbiomes, explored community composition and structure, and related patterns to abiotic and biotic landscape characteristics within the Chihuahuan Desert biome. Composite soil samples were collected in disturbed and undisturbed areas of 15 long-term ecological research plots in the Jornada Basin, New Mexico. Microbial diversity of cross-domain microbial groups (total Bacteria, Cyanobacteria, Archaea, and Fungi) was obtained via DNA amplicon metabarcode sequencing. Sequence data were related to landscape characteristics including vegetation type, landforms, ecological site and state as well as soil properties including gravel content, soil texture, pH, and electrical conductivity. Results: Filamentous Cyanobacteria dominated the photoautotrophic community while Proteobacteria and Actinobacteria dominated among the heterotrophic bacteria. Thaumarchaeota were the most abundant Archaea and drought adapted taxa in Dothideomycetes and Agaricomycetes were most abundant fungi in the soil surface microbiomes. Apart from richness within Archaea (p = 0.0124), disturbed samples did not differ from undisturbed samples with respect to alpha diversity and community composition (p ≥ 0.05), possibly due to a lack of frequent or impactful disturbance. Vegetation type and landform showed differences in richness of Bacteria, Archaea, and Cyanobacteria but not in Fungi. Richness lacked strong relationships with soil variables. Landscape features including parent material, vegetation type, landform type, and ecological sites and states, exhibited stronger influence on relative abundances and microbial community composition than on alpha diversity, especially for Cyanobacteria and Fungi. Soil texture, moisture, pH, electrical conductivity, lichen cover, and perennial plant biomass correlated strongly with microbial community gradients detected in NMDS ordinations. Discussion: Our study provides first comprehensive insights into the relationships between landscape characteristics, associated soil properties, and cross-domain soil microbiomes in the Chihuahuan Desert. Our findings will inform land management and restoration efforts and aid in the understanding of processes such as desertification and state transitioning, which represent urgent ecological and economical challenges in drylands around the world.

Evaluating the performance of DNA metabarcoding for assessment of zooplankton communities in Western Lake Superior using multiple markers.

For DNA metabarcoding to attain its potential as a community assessment tool, we need to better understand its performance versus traditional morphological identification and work to address any remaining performance gaps in incorporating DNA metabarcoding into community assessments. Using fragments of the 18S nuclear and 16S mitochondrial rRNA genes and two fragments of the mitochondrial COI marker, we examined the use of DNA metabarcoding and traditional morphological identification for understanding the diversity and composition of crustacean zooplankton at 42 sites across western Lake Superior. We identified 51 zooplankton taxa (genus or species, depending on the finest resolution of the taxon across all identification methods), of which 17 were identified using only morphological traits, 13 using only DNA and 21 using both methods. The taxa found using only DNA metabarcoding included four species and one genus-level identification not previously known to occur in Lake Superior, the presence of which still needs to be confirmed. A substantial portion of taxa that were identified to genus or species by morphological identification, but not identified using DNA metabarcoding, had zero ("no record") or ≤ 2 ("underrepresented records") reference barcodes in the BOLD or NCBI databases (63% for COI, 80% for 16S, 74% for 18S). The two COI marker fragments identified the most genus- and species-level taxa, whereas 18S was the only marker whose family-level percent sequence abundance patterns showed high correlation to composition patterns from morphological identification, based on a NMDS analysis of Bray-Curtis similarities. Multiple replicates were collected at a subset of sites and an occupancy analysis was performed, which indicated that rare taxa were more likely to be detected using DNA metabarcoding than traditional morphology. Our results support that DNA metabarcoding can augment morphological identification for estimating zooplankton diversity and composition of zooplankton over space and time, but may require use of multiple markers. Further addition of taxa to reference DNA databases will improve our ability to use DNA metabarcoding to identify zooplankton and other invertebrates in aquatic surveys.

Comparison of Larval Fish Detections Using Morphology-Based Taxonomy versus High-Throughput Sequencing for Invasive Species Early Detection.

When first introduced, invasive species typically evade detection; DNA barcoding coupled with high-throughput sequencing (HTS) may be more sensitive and accurate than morphology-based taxonomy, and thereby improve invasive (or rare) species detection. We quantified the relative error of species detection between morphology-based and HTS-based taxonomic identification of ichthyoplankton collections from the Port of Duluth, Minnesota, an aquatic non-native species introduction 'hot-spot' in the Laurentian Great Lakes. We found HTS-based taxonomy identified 28 species and morphology-based taxonomy 30 species, of which 27 were common to both. Among samples, 76% of family-level taxonomic assignments agreed; however, only 42% of species assignments agreed. Most errors were attributed to morphology-based taxonomy, whereas HTS-based taxonomy error was low. For this study system, for most non-native fishes, the detection probability by randomized survey for larvae was similar to that by a survey that is optimized for non-native species early detection of juveniles and adults. We conclude that classifying taxonomic errors by comparing HTS results against morphology-based taxonomy is an important step toward incorporating HTS-based taxonomy into biodiversity surveys.

Dreissena veligers in western Lake Superior - inference from new low-density detection.

The notion that Lake Superior proper is inhospitable to dreissenid mussel survival has been challenged by recent finds on shipwrecks and rocky reefs in the Apostle Islands region. Motivated by concerns surrounding these finds, we conducted an intensive sampling campaign of Apostle Islands waters in 2017 to understand Dreissena prevalence and distribution. The 100-site effort combined random and targeted sites and collected zooplankton, benthos, video, environmental DNA, and supporting water quality data. We did not find settled Dreissena in any video footage or benthos samples, and quantitative PCR applied to eDNA samples was negative for Dreissena. Dreissena veligers were found in almost half the zooplankton samples but at orders of magnitude lower densities than reported from other Laurentian Great Lakes. Veligers were most prevalent around the western islands and associated with shallower depths and slightly higher phosphorus and chlorophyll, but did not spatially match known (still very localized) settled Dreissena colonies. This is the first study to conduct veliger-targeted sampling in western Lake Superior and the first to report consistent detection of veligers there. We speculate that these Apostle Islands veligers are not a new locally-spawned component of the zooplankton community, but instead are transported from an established population in the St. Louis River estuary (~100 km away) by longshore currents; i.e., low-density propagule pressure that may have been present for years. Small-mesh zooplankton data collected along a gradient from the Apostle Islands to the St. Louis River estuary and enumerated with thorough veliger searching would help elucidate these alternatives.

Resolving taxonomic ambiguities: effects on rarity, projected richness, and indices in macroinvertebrate datasets.

Biodiversity information is an important basis for ecological research and environmental assessment, and can be impacted by choices made in the manipulation and analysis of taxonomic data. Such choices include methods for resolving multiple redundant levels of taxonomic resolution, as typically arise with morphological identification of damaged or immature aquatic macro-invertebrates. In particular, the effects of these processing choices on number of rare taxa are poorly understood yet potentially significant to the estimation of projected taxa richness and related evaluations such as biodiversity conservation value and survey sufficiency. Using aquatic macroinvertebrate data collected for two nearshore areas of Lake Superior, we determined how multiple methods of resolving taxonomic redundancies influence two commonly-used estimates of projected richness, Chao1 and Chao2, which hinge on the ratio of taxa that are singletons to doubletons (i.e., just one versus two individuals found) or uniques versus duplicates (i.e., just one versus two occurrences). We also determined how choice of ambiguous taxa method, including some modified specifically to retain rare taxa and others taken from the literature, influenced effort to reach 95% of projected richness, site-level richness and abundance, and representative invertebrate IBI scores. We found that Chao1 was more sensitive to method choice than Chao2, because singleton and doubleton status was more frequently affected when taxa were deleted, merged, or re-assigned in the process of resolving taxonomic redundancies than was unique and duplicate status. Methods that eliminated redundant taxa at the site scale but not the study-area scale tended to overinflate study area and projected richness, and resulted in a significant loss of abundance. The method that aggregated or deleted redundant taxa depending on abundance resulted in a decrease in site and study area richness, abundance, and an underestimation of projected richness. Methods which re-assigned parents to common children retained a majority of richness and abundance information and a more realistic estimate of projected taxa richness; however, the identity of poorly-identified parents was imputed. All methods resulted in little effect to typical IBI scores. Overall, no one method is fully capable of removing spurious richness at the study-area scale while preserving all taxa occurrence, abundance and rarity patterns. Therefore, the most appropriate method for making comparisons among sites may be different than the most appropriate method for comparing among surveys or among study areas, or if a goal is to estimate projected taxa richness or retain rare taxa information.

Effects of nitrate on embryos of three amphibian species.

Embryos of three aquatic breeding amphibian species, Ambystoma mexicanum, Hyla chrysoscelis, and Rana clamitans, were exposed to increasing levels (0, 5, 10, 30, 60, 100, 300, and 500 mg/L) of nitrate-N (NO(3)-) in laboratory, static-renewal experiments. Lethal effects were recorded from Gosner stage 2 (H. chrysoscelis and R. clamitans) or Harrison stage 2 (A. mexicanum) to time of hatching. Date of hatching and length at hatching were also compared between treatments for A. mexicanum. No significant differences in mortality between treatments were found between the three species. A. mexicanum in the 300 and 500 mg/L treatments hatched significantly earlier than individuals in the other treatment groups and, consequently, were significantly shorter in length at hatching. However, no effect on length was detected when days until hatching was considered as a covariate in the analysis. This study supports other recent research showing little to no effect of NO(3)- on amphibian embryos. The lack of effect at such high nitrate concentrations raises questions about the specific mechanisms responsible for protecting amphibians from NO(3)- during embryonic development, especially when compared to other chemicals that have shown more deleterious effects.