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1. Residence Time Structures Microbial Communities Through Niche Partitioning

   https://doi.org/10.1111/ele.70093  

   Mueller, Emmi_A; Lennon, Jay_T (February 2025, Ecology Letters)

   ABSTRACT Much of life on Earth is at the mercy of currents and flow. Residence time (τ) estimates how long organisms and resources remain in a system based on the ratio of volume (V) to flow rate (Q). Shortτshould promote immigration but limit species establishment, while longτshould favour species that survive on limited resources. Theory suggests these opposing forces shape the abundance, diversity and function of flowing systems. We experimentally tested how residence time affects a lake microbial community by exposing chemostats to aτgradient spanning seven orders of magnitude. Microbial abundance, richness and evenness increased non‐linearly withτ, while functions like productivity and resource consumption declined. Taxa formed distinct clusters of short‐ and long‐τspecialists consistent with niche partitioning. Our findings demonstrate that residence time drives biodiversity and community function in flowing habitats that are commonly found in environmental, engineered and host‐associated ecosystems. 

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2. Predicting benthic macroalgal abundance in shallow coastal lagoons from geomorphology and hydrologic flow patterns

   https://doi.org/10.1002/lno.11592  

   Besterman, Alice F.; McGlathery, Karen J.; Reidenbach, Matthew A.; Wiberg, Patricia L.; Pace, Michael L. (September 2020, Limnology and Oceanography)

   Abstract Macroalgae structure coastal ecosystems affecting metabolism, nutrient dynamics, and food webs. Spatially explicit prediction of macroalgal abundance is critical for understanding coastal ecosystems and trajectories. However, models of macroalgal distribution tend to be mechanistic and generalize poorly, or biogeographic and too coarse to use over spatial scales most appropriate to ecosystem research and management (1–100 km²). Our objective was to develop spatial distribution models for benthic macroalgae in soft‐sediment environments. We compared macroalgal abundance quantified as percent cover, with environmental drivers on 1 ha intertidal flats in a > 900 km²lagoon system along the Atlantic Coast of Virginia, U.S.A. Physical drivers of macroalgae (e.g., depth‐mediated light availability, exposure to waves) are related to bed morphology. We developed a novel topographic index (τ) to determine whether bed morphology predicts macroalgal abundance. This topographic index described variation in elevation occurring over spatial scales relevant to macroalgae, ranging from smooth to hummocky (τ= 0.01–1.07). Models testedτalong with mean elevation, fetch, and water residence time as predictors of macroalgal abundance.τ, and the interaction with water residence time, were most strongly related to macroalgal abundance. Hummocky flats accumulated less macroalgae than smoother flats, but exceptions occurred with short residence times. Model error (root mean square error) was low, varying between 8% and 18% across models. These models, based on readily measured physical features, are a useful approach for assessing macroalgal abundance in relation to shoreline hardening, species invasions, sea‐level rise, and changing sedimentation affecting coastal ecosystems. 

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3. Hydrogeology of desert springs in the Panamint Range, California, USA : Geologic controls on the geochemical kinetics, flowpaths, and mean residence times of springs

   https://doi.org/10.1002/hyp.13776  

   Gleason, Carolyn_L; Frisbee, Marty_D; Rademacher, Laura_K; Sada, Donald_W; Meyers, Zachary_P; Knott, Jeffrey_R; Hedlund, Brian_P (May 2020, Hydrological Processes)

   Abstract Over 180 springs emerge in the Panamint Range near Death Valley National Park, CA, yet, these springs have received very little hydrogeological attention despite their cultural, historical, and ecological importance. Here, we address the following questions: (1) which rock units support groundwater flow to springs in the Panamint Range, (2) what are the geochemical kinetics of these aquifers, and (3) and what are the residence times of these springs? All springs are at least partly supported by recharge in and flow through dolomitic units, namely, the Noonday Dolomite, Kingston Peak Formation, and Johnnie Formation. Thus, the geochemical composition of springs can largely be explained by dedolomitization: the dissolution of dolomite and gypsum with concurrent precipitation of calcite. However, interactions with hydrothermal deposits have likely influenced the geochemical composition of Thorndike Spring, Uppermost Spring, Hanaupah Canyon springs, and Trail Canyon springs. Faults are important controls on spring emergence. Seventeen of twenty‐one sampled springs emerge at faults (13 emerge at low‐angle detachment faults). On the eastern side of the Panamint Range, springs emerge where low‐angle faults intersect nearly vertical Late Proterozoic, Cambrian, and Ordovician sedimentary units. These geologic units are not present on the western side of the Panamint Range. Instead, springs on the west side emerge where low‐angle faults intersect Cenozoic breccias and fanglomerates. Mean residence times of springs range from 33 (±30) to 1,829 (±613) years. A total of 11 springs have relatively short mean residence times less than 500 years, whereas seven springs have mean residence times greater than 1,000 years. We infer that the Panamint Range springs are extremely vulnerable to climate change due to their dependence on local recharge, disconnection from regional groundwater flow (Death Valley Regional Flow System ‐ DVRFS), and relatively short mean residence times as compared with springs that are supported by the DVRFS (e.g., springs in Ash Meadows National Wildlife Refuge). In fact, four springs were not flowing during this campaign, yet they were flowing in the 1990s and 2000s. 

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4. Resources do not limit compensatory response of a tallgrass prairie plant community to the loss of a dominant species

   https://doi.org/10.1111/1365-2745.13741  

   Chaves, Francis A.; Smith, Melinda D. (August 2021, Journal of Ecology)

   Abstract The effect of species loss on ecosystem productivity is determined by both the functional contribution of the species lost, and the response of the remaining species in the community. According to the mass ratio hypothesis, the loss of a dominant plant species, which has a larger proportionate contribution to productivity, is expected to exert an overwhelming effect on this important ecosystem function. However, via competitive release, loss of a dominant species can provide the opportunity for other plant species to establish, thrive and become abundant in the community, potentially compensating for the function lost. Furthermore, if resource limitation is removed, then the compensatory response of function to the loss of a dominant species should be greater and more rapid than if resources are more limiting.To evaluate how resources may limit compensation of above‐ground productivity to the loss of a dominant plant species, we experimentally removed the C₄perennial tallgrass,Andropogon gerardii, from intact plant communities. We added water for 4 years, as well as nitrogen in the fourth year, to test the effect of resource limitation on the compensatory response.Overall, above‐ground biomass production increased in the remaining community with both water and nitrogen addition. However, this increase in biomass production was not sufficient to fully compensate for the loss ofA. gerardii, indicating water and nitrogen were not limiting short‐term compensation in this community.Following the removal of the dominant species, there was reordering of species abundances in the community, rather than changes in species richness. The C₄grassBouteloua curtipendulawas the most responsive species, increasing by 57.9% in abundance with water addition and 91.0% with both water and nitrogen addition. Despite this dramatic increase in abundance, its short stature and lower per capita biomass production prevented this species from compensating for the loss ofA. gerardii.Synthesis. Short‐term compensation after the loss of a dominant plant species can be hastened by increased resource availability, but ultimately full compensation appears to be limited by the presence and abundance of species in the remaining community that possess traits that allow them compensate for the species lost. 

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5. Organic and inorganic fertilizers modulate the response of the soil microbiome to salinity stress

   https://doi.org/10.3389/fmicb.2025.1551586  

   Malal, Halima; Garcia, Joshua A; Marrs, Anna; Ait_Hamza, Mohamed; Emerson, Courtney; Nocco, Mallika; Lakhtar, Hicham; Lazcano, Cristina (June 2025, Frontiers in Microbiology)

   Salinity stress threatens soil microbiomes, a key driver of soil multifunctionality and health. This study employed high-throughput sequencing of 16S rRNA, PLFAs, multifunctionality index, and co-occurrence networks to gain a comprehensive understanding of the dynamic responses of soil microbiomes to salinity stress gradient (0, 0.4 and 1 mol NaCl). Additionally, we investigated how these responses are shaped by the addition of vermicompost and NPK fertilizer during short-term (2-h) and long-term (70-day) incubation periods. Salinity stress reduced bacterial and fungal phospholipid fatty acids (PLFA) concentrations in the short-term. Over the long-term, the microbial community evolved into a new pattern under salt stress, favoring the presence ofBacteriodota, a salt-tolerant phylum, while decreasing the relative abundance ofAcidobacteriotaandPlanctomycetota, which are more salt-sensitive. Furthermore, salinity decreased species richness by 11.33% and soil multifunctionality by 21.48% but increased microbial network complexity while decreasing its stability. Incorporating vermicompost increased bacterial and fungal PLFAs, enhanced bacterial diversity by 2.33%, promoted salt-tolerant bacteria, and increased the complexity and stability of the bacterial network. Conversely, the application of NPK fertilizer reduced bacterial richness, alpha diversity and soil multifunctionality by 14.52, 5.83, and 12.34%, respectively, further disrupting the microbial community and making resilience to salinity stress more challenging. Furthermore, NPK fertilization increased bacterial network complexity but decreased its stability. This study underscores the significance of employing vermicompost to improve the health of saline soils. Furthermore, it emphasizes the negative impacts of NPK fertilizer on soil microbial structure and function and hinder its recovery from salinity’s impacts. 

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