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1. Tree mycorrhizal type predicts within‐site variability in the storage and distribution of soil organic matter

   https://doi.org/10.1111/gcb.14132  

   Craig, Matthew E. ; Turner, Benjamin L. ; Liang, Chao ; Clay, Keith ; Johnson, Daniel J. ; Phillips, Richard P. ( April 2018 , Global Change Biology)

   Forest soils store large amounts of carbon (C) and nitrogen (N), yet how predicted shifts in forest composition will impact long‐term C and N persistence remains poorly understood. A recent hypothesis predicts that soils under trees associated with arbuscular mycorrhizas (AM) store less C than soils dominated by trees associated with ectomycorrhizas (ECM), due to slower decomposition inECM‐dominated forests. However, an incipient hypothesis predicts that systems with rapid decomposition—e.g. mostAM‐dominated forests—enhance soil organic matter (SOM) stabilization by accelerating the production of microbial residues. To address these contrasting predictions, we quantified soil C and N to 1 m depth across gradients ofECM‐dominance in three temperate forests. By focusing on sites whereAM‐ andECM‐plants co‐occur, our analysis controls for climatic factors that covary with mycorrhizal dominance across broad scales. We found that whileECMstands contain moreSOMin topsoil,AMstands contain moreSOMwhen subsoil to 1 m depth is included. Biomarkers and soil fractionations reveal that these patterns are driven by an accumulation of microbial residues inAM‐dominated soils. Collectively, our results support emerging theory onSOMformation, demonstrate the importance of subsurface soils in mediating plant effects on soil C and N, and indicate that shifts inmore »the mycorrhizal composition of temperate forests may alter the stabilization ofSOM.

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2. Soil depth and grassland origin cooperatively shape microbial community co‐occurrence and function

   https://doi.org/10.1002/ecs2.2973  

   Upton, Racheal N. ; Checinska Sielaff, Aleksandra ; Hofmockel, Kirsten S. ; Xu, Xia ; Polley, H. Wayne ; Wilsey, Brian J. ( January 2020 , Ecosphere)

   Many soils are deep, yet soil below 20 cm remains largely unexplored. Exotic plants can have shallower roots than native species, so their impact on microorganisms is anticipated to change with depth. Using environmentalDNAand extracellular enzymatic activities, we studied fungal and bacterial community composition, diversity, function, and co‐occurrence networks between native and exotic grasslands at soil depths up to 1 m. We hypothesized (1) the composition and network structure of both fungal and bacterial communities will change with increasing depth, and diversity and enzymatic function will decrease; (2) microbial enzymatic function and network connectedness will be lower in exotic grasslands; and (3) irrigation will alter microbial networks, increasing the overall connectedness. Microbial diversity decreased with depth, and community composition wasdistinctly differentbetween shallow and deeper soil depths with higher numbers of unknown taxa in lower soil depths. Fungal communities differed between native and exotic plant communities. Microbial community networks were strongly shaped by biotic and abiotic factors concurrently and were the only microbial measurement affected by irrigation. In general, fungal communities were more connected in native plant communities than exotic, especially below 10 cm. Fungal networks were also more connected at lower soil depths albeit with fewer nodes. Bacterial communities demonstrated highermore »complexity, and greater connectedness and nodes, at lower soil depths for native plant communities. Exotic plant communities’ bacterial network connectedness altered at lower soil depths dependent on irrigation treatments. Microbial extracellular enzyme activity for carbon cycling enzymes significantly declined with soil depth, but enzymes associated with nitrogen and phosphorus cycling continued to have similar activities up to 1 m deep. Our results indicate that native and exotic grasslands have significantly different fungal communities in depths up to 1 m and that both fungal and bacterial networks are strongly shaped jointly by plant communities and abiotic factors. Soil depth is independently a major determinant of both fungal and bacterial community structures, functions, and co‐occurrence networks and demonstrates further the importance of including soil itself when investigating plant–microbe interactions.

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3. Effects of Formica podzolica ant colonies on soil moisture, nitrogen, and plant communities near nests

   https://doi.org/10.1111/een.12677  

   Sankovitz, Madison A. ; Breed, Michael D. ; McCreery, Helen F. ( October 2018 , Ecological Entomology)

   1. Ants are widely regarded as ‘ecosystem engineers’ because their nest construction and contributions to nutrient cycling change the biological, chemical, and physical properties of the soil around their nests. Despite increasing attention to ant manipulation of soil ecosystems, the extent to which many common species influence soil properties, as well as nutrient uptake and community composition of plants near nests, is still unknown.

   2. This study tested hypotheses that activities of a common subalpine ant,Formica podzolica, alter soil moisture and pH, redistribute nitrogen around nests, and affect plant species abundance and ground cover.

   3. A combination of field sampling techniques showed that distance from a nest had a positive relationship with soil moisture and a negative relationship with plant abundance next to and downhill from nests. Slope aspect also affected plant communities, with downhill transects having higher plant cover and above‐ground biomass than uphill transects. A stable isotope analysis did not reveal that plants near nests had enriched¹⁵N, but there were substantial differences in¹⁵N among sites.

   4. Overall, this study uncovers significant impacts ofF. podzolicaon the subalpine microhabitats directly surrounding their nests.
4. The Sarracenia alata pitcher plant system and obligate arthropod inquilines should be considered an evolutionary community

   https://doi.org/10.1111/jbi.13498  

   Satler, Jordan D. ; Carstens, Bryan C. ( January 2019 , Journal of Biogeography)

   TheSarracenia alatapitcher plant and inquiline species comprise an ecological community. These inquilines span the continuum in their ecological association with the host pitcher plant, from species that contain little‐to‐no interaction with the plant to species that are completely dependent on the plant for their entire life cycle. We are interested in testing if degree of ecological dependence is positively correlated with a shared evolutionary history, and in identifying members of this community that display concordant phylogeographic structure.

   Southeastern United States.

   We collected genome‐wide sequence data from a set of arthropods that are ecologically associated with the plant to estimate comparative phylogeographic patterns among the species. We estimated species tree distributions from biallelic unlinkedSNPdata and used phylogeographic concordance factors (PCFs) to test degree of phylogeographic concordance among community members. In addition, for each species we conducted an analysis of molecular variance and calculatedF_STvalues to identify population genetic structure across the landscape, and compared these traditional values to the tree‐based approach.

   Obligate members of the pitcher plant community display concordant phylogeographic patterns, suggesting their ecological dependence has manifested itself into a shared evolutionary history. In contrast, two spider species do not contain significant population genetic structure or similar phylogeographicmore »histories, highlighting their loose association with the host pitcher plant.

   TheS. alatapitcher plant system should be considered an evolutionary community, where multiple members sharing strong ecological interactions also display concordant phylogeographic structure. This work demonstrates thatPCFs provide an important quantitative measure into assessing community structure and illustrates how simulations can be used to assess significance of shared patterns of phylogeographic structure across the landscape.

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5. Suilloid fungi as global drivers of pine invasions

   https://doi.org/10.1111/nph.15660  

   Policelli, Nahuel ; Bruns, Thomas D. ; Vilgalys, Rytas ; Nuñez, Martin A. ( January 2019 , New Phytologist)

   Belowground biota can deeply influence plant invasion. The presence of appropriate soil mutualists can act as a driver to enable plants to colonize new ranges. We reviewed the species of ectomycorrhizal fungi (EMF) that facilitate pine establishment in both native and non‐native ranges, and that are associated with their invasion into nonforest settings. We found that one particular group ofEMF, suilloid fungi, uniquely drive pine invasion in the absence of otherEMF. Although the association with otherEMFis variable, suilloidEMFare always associated with invasive pines, particularly at early invasion, when invasive trees are most vulnerable. We identified five main ecological traits of suilloid fungi that may explain their key role at pine invasions: their long‐distance dispersal capacity, the establishment of positive biotic interactions with mammals, their capacity to generate a resistant spore bank, their rapid colonization of roots and their long‐distance exploration type. These results suggest that the identity of mycorrhizal fungi and their ecological interactions, rather than simply the presence of compatible fungi, are key to the understanding of plant invasion processes and their success or failure. Particularly for pines, their specific association with suilloid fungi determines their invasion success in previously uninvaded ecosystems.