Journal of Geophysical Research: Biogeosciences

Snow algae are major biological drivers of snow darkening in polar and high-alpine environments. However, the direct contribution of algal pigmentation to snow reflectance has remained difficult to quantify because field observations cannot disentangle the effects of pigmentation from variation in biomass, species composition, and snow physical properties. Here, we characterized the optical effects of pigmentation using hyperspectral spectroradiometry to compare green, orange, and red cyst-like cells of a snow-derived Haematococcus isolate while controlling for developmental stage and cell abundance. Cysts became more red with increasing astaxanthin concentrations while chlorophyll-a concentrations remained relatively constant. Relative to green cysts, mean reflectance decreased by approximately 30% in orange cysts and 40% in red cysts. Integrated reflectance across the visible spectrum (350-800 nm) was negatively correlated with astaxanthin concentration. These results provide direct experimental evidence that algal pigmentation alone substantially reduces reflectance after controlling for cell abundance and developmental stage, and indicate that differences in snow physical properties may partly obscure this effect under natural field conditions. Our findings identify astaxanthin accumulation as an intrinsic driver of biological snow darkening and suggest that algal pigmentation, which may vary with species identity and physiological state, should be considered alongside biomass when predicting the radiative effects of snow algal blooms.

Rainfall and vapor pressure deficit (VPD) are well-studied hydrological variables that largely determine aboveground net primary production (ANPP) in most ecosystems. Meanwhile, the impacts of another important part of the hydrologic cycle, non-rainfall water from fog and dew, remain poorly understood at the ecosystem level. To fill this gap, we used meteorological variables measured at weather stations along with satellite-derived vegetation greenness data from surrounding areas to examine how fog and dew frequency affect summer plant growth across the contiguous United States. Our analysis shows that, even after accounting for precipitation, VPD, and land-cover type, fog and, more so, dew enhanced vegetation productivity in water-limited regions. In contrast, non-rainfall water had a neutral or negative impact on plant growth in humid regions, with fog showing the strongest and most widespread negative effects. Taken together, our findings reveal that summertime non-rainfall water has differential effects on vegetation that are largely determined by ecosystem-level water availability. These aridity-dependent effects of fog and dew should be considered in future ecological and agricultural studies and in assessments of projected climate impacts on vegetation.

The Arctic is warming rapidly, causing permafrost thaw and accelerating the release of greenhouse gases. Rapid thaw features such as retrogressive thaw slumps are increasing in frequency and severity across the Arctic; however, their associated greenhouse gas emissions are poorly constrained. Current estimates of emissions from retrogressive thaw slumps rely largely on laboratory incubations and carbon stock estimates rather than in-situ field measurements. Here we directly quantify methane and carbon dioxide fluxes from the exposed headwall of an active retrogressive thaw slump. We show that thaw immediately releases biogenic methane and carbon dioxide, originating from gases trapped within the frozen soil matrix. Microbial transcription of methyl-coenzyme M reductase suggests archaea carrying out methanogenesis at subzero temperatures are the source of trapped methane. Carbon emissions varied by an order of magnitude among cryostratigraphic units, reflecting differences in geomorphologic history, organic carbon and nitrogen content, and microbial community composition. Carbon emissions were highest from organic-rich paleo cryosols from the Late Holocene that contained abundant methanogenic archaea. We estimate that [~]300 kg C (CO2 equivalents) is emitted annually from the headwall of this small thaw slump (surface area of [~]1200 m2). Considering the thousands of active slumps and extensive coastal permafrost erosion across the northern continuous permafrost zone, such features may represent a growing natural source of GHG emissions. These findings indicate that current permafrost carbon feedback models underestimate GHG release by omitting the direct release of trapped gases stored in permafrost.

A direct empirical relationship between gross primary productivity (GPP) estimated by the eddy covariance method and satellite vegetation indices (VIs) has been widely observed across diverse ecosystems globally. Building on this observed covariation, VIs are frequently utilized as critical parameters - such as the fraction of absorbed photosynthetically active radiation (fPAR) - within light use efficiency (LUE) and greenness-based models for carbon cycle monitoring. However, actual canopy carbon assimilation is jointly governed by slowly evolving structural parameters and highly dynamic functional traits, such as physiological efficiency. The extent to which the macro-scale VI-GPP covariance is driven by structural scaffolding, and how this structural signal decouples from physiological function under environmental stress, remains to be systematically quantified. Here, we synthesized half-hourly eddy covariance measurements from 328 globally distributed sites and paired them with a rigorously angle-normalized Enhanced Vegetation Index (nadir view and fixed solar zenith angle at 30 degrees, EVI_SZA30). By applying a nonlinear light-response curve model across 54,720 high-frequency temporal windows, we mechanistically disentangled observed actual GPP (GPP_EC) into baseline photosynthetic capacity (P_c) and intrinsic quantum yield (alpha). Our results demonstrate that the macroscopic covariance between EVI_SZA30 and GPP_EC (R^2=0.554) is primarily driven by the index's robust ability to track structural capacity (P_c, R^2=0.538). In contrast, EVI_SZA30 exhibits limited sensitivity to high-frequency variations in functional traits like physiological efficiency (alpha, R^2=0.038). Particularly in water-limited biomes (e.g., open shrublands and woody savannas), intense environmental stress triggers rapid stomatal regulation while the physical canopy structure remains relatively stable. Consequently, the correlation between EVI and P_c becomes notably stronger than its correlation with actual GPP_EC, highlighting a pronounced structural-physiological decoupling. Because discrete overpasses by sun-synchronous polar-orbiting satellites face intrinsic temporal constraints in capturing sub-daily physiological down-regulation (e.g., midday photosynthetic depression), future monitoring paradigms could greatly benefit from the continuous, high-frequency observations provided by next-generation geostationary (GEO) satellites to bridge the gap between structural parameters and transient ecosystem function.

A substantial fraction of marine sediments experience elevated temperatures due to burial or hydrothermal activity. These conditions can fundamentally reshape both microbial activity and the chemical nature of sedimentary organic matter (OM). Laboratory incubations have demonstrated that moderate heating of marine sediments can lead to the production of labile organic compounds such as acetate, however, it remains unclear whether heating alters the bioavailability of the remaining OM pool. In this study, we experimentally tested the effect of temperature on the bioavailability of OM through a series of bioreactor experiments using deeply buried sediment collected from Guaymas Basin (Gulf of California). We measured acetate concentrations in sterilized Guaymas Basin sediments before and after artificial heating (70{degrees}C for 7 days) to quantify abiotic acetate generation. We then conducted incubations of a model marine bacterium with sterilized, artificially heated sediment and tracked respired CO2 production and its associated 13C and 14C signatures. Our study revealed that sediment depth and hydrothermal history strongly control abiotic acetate production, with higher acetate yields from shallower, cooler sediments. Respiration rates in control and heated sediment incubations were nearly identical, indicating that heating does not measurably alter the bioavailability of bulk sedimentary OM. Moreover, the {delta}13C values of respired CO2 were indistinguishable between control and heated sediment incubations while the {Delta}14C values were more depleted in the first 24 hours in incubations with heated sediment. This transient offset suggests that low-temperature heating mobilizes a small pool of older material due to desorption of mineral-bound OM without altering overall bioavailability. Our findings shed light on the role of thermal alteration in shaping carbon cycling in marine sediments by influencing how OM is made available to sedimentary microorganisms.

The present-day martian surface is generally considered inhospitable to life because of low atmospheric pressure, intense surface radiation, global desiccation, and oxidizing chemistry which has been increasing since the late Noachian. However, shallow martian subsurface regions where mineralogy has shown groundwater movement may include localized hypersaline environments capable of retaining liquid water and supporting microbial metabolism. Haloferax volcanii, a model halophilic archaeon, has previously been shown to survive under low-pressure martian conditions (24 mbar) and to grow anaerobically supported by the Mars-relevant oxyanions nitrate and perchlorate under high-salinity conditions. Here, we investigated whether H. volcanii could actively grow under a combination of environmental and chemical conditions relevant to potentially habitable shallow subsurface martian lacustrine settings. Cultures were incubated for 160 days under anoxic, CO2-enriched, low-pressure conditions (24 mbar) in hypersaline liquid media supplemented with nitrate or perchlorate. Growth was observed in all low-pressure treatments and was confirmed by increases in optical density and biological reduction of nitrate and perchlorate. Scanning electron microscopy revealed extensive biofilm formation in low-pressure cultures, and Raman spectroscopy demonstrated the persistence of carotenoid biosignatures after prolonged incubation under martian conditions. Water loss remained below 4% across all treatments, indicating long-term stability of hypersaline brines throughout the experiment. These results demonstrate for the first time that a halophilic archaeon is capable of active growth and metabolism under a Mars-relevant combination of low pressure, high salinity, anoxia, and oxidizing chemistry, providing experimental support for the potential habitability of localized shallow subsurface martian environments. ImportanceThe search for cellular life is a major objective of future Mars exploration. While many studies have examined whether microorganisms can survive under martian conditions, far fewer have demonstrated active growth and metabolism. Here, we document Haloferax volcanii as the first halophilic archaeon capable of active growth under a defined combination of Mars-relevant low atmospheric pressure, high salinity, anoxia, and oxidizing chemical conditions. These findings expand the current understanding of the environmental limits of microbial growth and provide experimental evidence that localized brine environments in the shallow martian subsurface could support active microbial metabolism, if suitable organics and liquid water are present. In addition, this study establishes a practical framework for cultivating halophilic microorganisms under low-pressure martian conditions and may help guide future efforts to detect, cultivate, and characterize potential extant life on Mars.

Forest soils are an important source of volatile organic compounds (VOCs), yet little is known about how different tree species influence soil VOC emissions and the role of rhizosphere processes in mediating VOC release form roots. We analysed soil VOC emissions from the soil surface and bulk soil as well as from roots with intact rhizosphere and washed roots of Picea abies and Fagus sylvatica. Tree saplings were grown on natural forest soil, and VOC emissions and gas exchange of soils and roots were measured under controlled conditions using online gas analysers integrated into an automated system. To assess the contribution of rhizosphere soil and microbial communities to root VOC emissions, roots were analysed (a) without washing, preserving the rhizosphere, (b) water-washed, and (c) ethanol-washed (70 vol%) to minimize microbial contributions. Species-specific VOC emission patterns were observed in both soils and roots. P. abies showed higher total emission rates and a more diverse, terpenoid-rich VOC profile dominated by -pinene, {beta}-pinene, {beta}-myrcene, and -phellandrene than F. sylvatica. Notably, these differences were evident not only at the soil surface but also in root and litter free bulk soil. Root washing further revealed that the rhizosphere is a hotspot of terpenoid production in P. abies, with significantly higher monoterpenoid emissions from unwashed roots than from water or ethanol-washed roots. This study demonstrates how tree species shape net soil VOC emissions, potentially leading to cascading effects on atmospheric VOC concentrations, and highlights the importance of the rhizosphere in regulating belowground VOC production.

Microbial communities living on and in rocks operate at the microscale, where interactions with minerals fundamentally shape community structure and function. Yet the relationship between micron scale mineralogical configurations and microbial distributions remains poorly understood. We tested the hypothesis that microbial biomass spatially correlates with areas of heightened mineralogical heterogeneity by applying Raman microspectroscopy to rock samples from three geologically distinct substrates: authigenic carbonates from a marine methane seep, volcanic basalt from Iceland, and polymetallic nodules from the abyssal seafloor. Using spectral decomposition and multiple complementary metrics of compositional heterogeneity, we evaluated intra-pixel and inter-pixel heterogeneity patterns in relation to biomass distribution. Our analyses reveal three patterns across all sample types. 1) When spectra are deconstructed into their constituent components, biomass zones are disproportionately dominated by the biomass spectral component compared with primary mineral components in zones of different minerals. 2) Biomass spectra have more homogeneous compositional profiles than mineral spectra. 3) Biomass is surrounded by more heterogeneous microhabitats than mineral pixels. These findings demonstrate that biomass exerts a distinctive and consistent influence on Raman spectral signatures, both within and between pixels, in ways that mineral components do not. Our results establish generalizable principles linking microscale mineralogical properties to microbial biogeography; these properties could be used as a potential biosignature and may provide a standardized workflow applicable to diverse rock systems and astrobiological exploration strategies.

Mangrove forests are major blue carbon ecosystems but are often characterized by low surface methane (CH4) emissions. Such low emissions, however, do not necessarily indicate weak methanogenesis, because CH4 production may be offset by internal CH4 consumption before reaching the atmosphere. Although previous community, genomic, and transcriptomic studies have implicated methylotrophic methanogenesis in mangrove sediments, direct taxon-resolved evidence linking methylated carbon assimilation to potentially active methanogens remains limited. Here, we combined methanogenic activity assays, DNA stable isotope probing (DNA-SIP), mcrA and 16S rRNA gene analyses, and phylogenetic comparisons to identify potentially active methanogens across saline-influenced mangrove soils. The results showed that CH4 production potentials were consistently dominated by methylotrophic pathways (1.86-2.78 g CH4 g-1 soil hr-1) across all sites. DNA-SIP, together with consistent community patterns in fresh soils, indicated the potential activity of methylotrophic and mixotrophic methanogens under saline conditions. Methanolobus-affiliated methanogens were associated with salinity, Na+, Cl-, and NH4+, whereas Methanosarcina and unclassified Methanosarcinaceae were linked to soil soluble organic carbon availability and water content, indicating niche differentiation among active methanogenic groups. Phylogenetic analyses incorporating reference sequences from diverse environments further showed that potentially active mangrove methanogens were dominated by saline-associated lineages. Together with our previous methanotrophic evidence from the same sites, these findings suggest that low CH4 emissions from mangrove blue carbon ecosystems can mask substantial internal CH4 cycling sustained by active methanogenesis and CH4 consumption.

Current planetary protection approaches rely heavily on spore-based tests developed for Mars missions and may not adequately assess contamination risks for icy ocean worlds such as Europa. We developed a genome-based framework combining deep shotgun metagenomics and supervised machine learning to predict survival-relevant microbial traits in ESA JUICE launch-site cleanrooms. From 183 genome bins, 25 representative genomes were analyzed for traits including cryotolerance, desiccation tolerance, salt resilience, anaerobic metabolism, autotrophy, and sporulation. Several skin-associated microbes carried multiple relevant traits, and some appeared actively replicating. A broader meta-analysis of 1,868 genomes showed that trait profiles vary strongly within taxa, demonstrating that taxonomy alone is insufficient for risk assessment. This framework complements current planetary protection assays, helps to predict how microbes would survive in a new biotope, and supports functional, risk-informed contamination monitoring for future space missions.

O_LIDrought and warming can disrupt soil microbial processes and ecosystem functioning. Although soil microorganisms can exhibit physiological adjustments to drought, it remains unclear how they allocate resources between extracellular resource acquisition, potential oxidative metabolism, and carbon storage during drought and recovery, particularly under constant warming and/or heat waves. C_LIO_LIHere, we tested the effects of drought on microbial resource allocation strategies across warming regimes during the resistance and recovery phases. We performed a full-factorial outdoor mesocosm experiment combining drought with constant warming and periodic heat waves, applied individually and in combination. We measured the potential activities of extracellular enzymes as proxy for the acquisition of microbial resources, the activity of dehydrogenase as a proxy for the potential active oxidative metabolism, and microbial glycogen pools as a proxy for carbon storage. We also quantified drought legacy effects by measuring microbial functioning before the new drought treatments, capturing the influence of the drought imposed in the previous year. C_LIO_LIDuring the resistance phase, dehydrogenase activity and glycogen pools remained stable, despite reduced extracellular enzyme production, while enzyme allocation shifted towards oxidative enzymes associated with acquisition of recalcitrant C in warming regimes. One month after rewetting, all microbial proxies no longer differed from the control soil moisture conditions. Drought legacy effects were observed in extracellular enzymes, dehydrogenase activity, and glycogen pools, with glycogen exhibiting the strongest legacy effect. C_LIO_LIWe conclude that the asymmetrical responses of extracellular resource acquisition and internal C storage to drought and warming may function as strategies for microbial survival in increasingly variable climates. C_LI

Biochar amendments are increasingly applied to improve soil physical functioning and support carbon dioxide removal, but their effects on intrinsic soil thermal properties remain poorly characterised. We conducted the first global systematic meta-analysis of 19 independent studies, 231 control-biochar comparisons, and 529 property-specific effect sizes to test how biochar changes soil heat transfer and storage. Biochar reduced thermal conductivity by 17.6% (95% CI, -22.7 to -12.2), thermal diffusivity by 11.0% (-14.5 to -7.3), and volumetric heat capacity by 8.3% (-12.3 to -4.1). Gravimetric heat capacity showed no significant overall response (+3.3%; -7.6 to 15.4) but was supported by fewer studies. Negative responses were directionally consistent for thermal conductivity, diffusivity, and volumetric heat capacity. Moderator analyses showed that responses were most consistently associated with post-application bulk density and changes in bulk density, while application rate modulated response magnitude and soil texture constrained context dependence. Co-variation among thermal conductivity, thermal diffusivity, and volumetric heat capacity matched expected physical dependencies, indicating coordinated structural reorganisation rather than independent shifts in isolated parameters. These estimates describe intrinsic conductive and storage properties; field-scale soil temperature responses may also be modified by albedo, evaporation, vegetation, and surface energy balance. Improved integration of soil thermal measurements with moisture dynamics, structural changes, and carbon cycling is essential to accurately represent biochar effects in soil and land-surface models.

Tropical dryland ecosystems are highly biodiverse and fragmented and are experiencing significant anthropogenic and climatic changes. With increasing extremes in temperature and precipitation, coupled with significant alteration, these ecosystems are at greater risk of increased exposure and vulnerability to climatic change; however, little work has quantified the climatic shifts occurring within these ecosystems globally. Here, we aim to fill this gap by using the ERA-5 reanalysis and CHIRPS precipitation data to quantify changes in essential climatic variables in tropical drylands since 2000. Overall, we find that regional pressures differ, with tropical dry forests, savannas, and shrublands becoming hotter and drier in the Neotropics and parts of the Afrotropics and Australasia. By contrast, the tropical dry forests in the Indomalayan, Oceania, and Nearctic are experiencing hotter and wetter conditions. Globally, though, these ecosystems are experiencing more change than the global average, suggesting they may be approaching tipping points in their resilience, ultimately shrinking the area where they can survive.

Antarctica represents a significant, unresolved, and unstable source of methane to the atmosphere. To advance our understanding of the biological filter of methane in Antarctica, here we identify the taxa and functional genes present during methane oxidation in an Antarctic Methane Seep. Methane oxidation was present in all sediments, including in a non seep control site. Using 16S rRNA analysis alongside metagenomics, we found that ANaerobic MEthane oxidizing (ANME) archaea coupled to Sulfate-Reducing Bacteria (SRB), documented as the most important marine methane sink in other locations, were not present. Instead, we observed the presence of denitrification-dependent methane oxidizers, including the anaerobic genus Candidatus Methylomirabilis, alongside the nitrate reducing archaea Candidatus Methanoperedens through short-read metagenomic classification. In addition, we note the presence of multiple aerobic methanotrophs, with a particularly high abundance of the Methylobacter, Methylomonas, and Methyloprofundus genera. Our results support denitrification-mediated methane oxidation and aerobic methanotrophy as the primary potential methane sinks in the Ross Sea. The widespread methane oxidation, including in control sediment, combined with the possibility of anaerobic methane oxidation linked to denitrification rather than sulfate reduction highlights the ubiquity and uniqueness of the Antarctic methane cycle.

John Raven pioneered the field of algae ecophysiology, advancing our understanding of cellular resource economics, carbon acquisition, and energy allocation. His work laid the foundation for investigating integrative physiology, linking growth-survival trade-offs across diverse environments. The sea ice habitat provides an excellent framework to continue the research John championed. With steep temperature-salinity gradients, algae survival requires a shift in physiology that we are only beginning to understand. We developed two small scale, reproducible icecosms to investigate physiological changes associated with incorporation into sea ice and survival potential post-melt. Fragilariopsis cylindrus and Nitzschia frigida, known for their association with the ice environment, and Porosira glacialis, known for its association with the ice edge, were used to mechanistically link physical properties with algal physiology and post-melt survival. We observe incorporation into the ice of F. cylindrus and N. frigida alongside vertical photophysiological profiles of F. cylindrus revealing inhospitable conditions in the top compared to the bottom layers of ice. N. frigida and P. glacialis remain viable within the ice and retain the capacity to seed populations following melt. Our results establish icecosms as experimental framework to investigate ecophysiological responses of sea ice algae and provide a foundation toward ecological and evolutionary questions.

The perennial grass Miscanthus x giganteus (miscanthus) offers a sustainable alternative to traditional biomass feedstocks while improving key soil health parameters, including aggregation. Aggregate stability results from dynamic soil-plant-microbe interactions, yet the relative importance of each factor remains an active research question. Building on previous observations that miscanthus alters soil structure to improve water-holding capacity and aggregate stability, we characterized the communities of soil bacteria and arbuscular mycorrhizal fungi (AMF) across three sites in Iowa, USA, comparing miscanthus to annual maize (Zea mays L.) and non-cropped perennial turfgrass (Poa spp.). We examined whether microbiomes co-varied with soil aggregation and, if so, whether plant cover identity or life history categorization better explained the observed patterns. Bacterial and AMF communities varied across sites and plant types, with signals that life history and plant cover identity both mattered. Aggregate stability aligned with a perennial-annual divergence in microbial beta diversity, while finer-scale differences in community composition and network structure were plant-specific. Soils under perennial plants were enriched in microbial groups positively correlated with aggregate stability; we identified 61 bacterial and 8 AMF "architect" taxa for future study. Within- and cross-kingdom co-occurrence network analysis revealed greater complexity under perennial plants: 1.9-fold more network links in miscanthus bacteria-bacteria networks than in maize, and 1.7-fold more in turfgrass AMF-AMF networks. Miscanthus fundamentally shapes microbial interactions, particularly among bacteria, relating to improved soil physical structure. Understanding these soil-plant-microbe feedbacks advances the development of biomass feedstocks with a portfolio of soil health benefits for next-generation biofuels and bioproducts. IMPORTANCEPerennial bioenergy crops can provide the raw material for biofuels and bioproducts while simultaneously improving soil health. Miscanthus x giganteus (miscanthus) efficiently stabilizes soil aggregates, potentially leading to higher water retention and erosion resistance. Understanding the microbial contributions to these outcomes is key to building resilient, sustainable bioenergy systems. This study highlights the connections between communities of soil microbes--bacteria and arbuscular mycorrhizal fungi--across three sites and three plant covers, including miscanthus, maize, and turfgrass. We identify a guild of potential "microbial architects" linked to soil aggregation and show more interconnected microbial networks under the perennial plant covers compared to annual maize. These insights shed light on the interactions between soil biological communities and soil physical and chemical properties. More broadly, the results may inform efforts to harness plant-associated microbiomes for sustainable biomass production.

Soil microbial communities have a variety of mechanisms to deal with emerging drought stress. One well-documented mechanism is increased microbial production of extracellular polymeric substances (EPS), which can potentially change the soil density and water holding capacity. Yet little is known about how microbial diversity influences the functional capacity of EPS formation and the resulting outcomes in water dynamics. To understand more about communal microbiome EPS production, we set up sterile mesocosms where we examined the effects of microbial diversity (high or low treatments) and nutrient input (supplement or deficient treatments) on these processes. To capture the microhydrology of the mesocosms, we measured water holding (WH), infiltration, evaporation, and soil properties we believe microbes are altering (EPS, soil aggregation). Our hypothesis stated that if diversity was artificially manipulated, then soil-water properties will be altered via production of EPS. We predicted that low diversity systems would have lower functional diversity, leading to less EPS production, moisture storage, and minimal changes from inert soil media. As predicted, we found that the high-diversity systems had a higher water retention and lower rates of water loss over time than low-diversity systems. This trend was magnified in the nutrient-supplemented treatment, suggesting that EPS production and subsequent water-holding traits are emergent features of the microbiome. Unexpectedly, we observed a correlation between the amount of water retained and the quantity of lipid EPS produced. This suggests that EPS composition, rather than quantity, is determinative of a biofilms function. In conclusion, it appears that microbial diversity influences soil properties that are important to moisture retention within these systems. To date, the role that microbes and their diversity play in soil hydrology has been severely understudied, so this work aims to build ecological understandings of these systems. These findings are valuable, for if we learn how microbes manipulate soil moisture, we can apply these functions to advance sustainable agricultural practices and enhance ecosystem resilience to water scarcity in arid regions. Open Research StatementUpon publication data, and code will be made available through Zenodo. Sequencing data will be uploaded to NCBI SRA.

Primary production in the Southern Ocean (SO) plays a critical role in regulating the global carbon cycle, yet the physiological mechanisms governing phytoplankton responses to iron (Fe) limitation and variable light remain poorly constrained. Using a custom made incubation system that simulated natural diel solar variability, we examined the interactive effects of Fe availability, light intensity, and photoperiod (continuous vs. variable) on three ecologically important SO phytoplankton: Fragilariopsis cylindrus, Phaeocystis antarctica, and Thalassiosira antarctica. Physiological, photophysiological, and proteomic measurements revealed that Fe availability was the dominant factor regulating growth, carbon production, photosynthetic performance and protein expression across all species. Distinct acclimation strategies emerged: F. cylindrus exhibited marked trade-offs between productivity and photoprotection under Fe stress, consistent with adaptation to stable, low-light, Fe-poor environments; P. antarctica maintained growth by flexibly modulating photoprotective and photosynthetic capacity, reflecting high plasticity suited to dynamic, open-ocean conditions; and T. antarctica expressed a balanced strategy, sustaining productivity and photoprotection simultaneously, characteristic of coastal bloom formers with higher Fe demand. Dynamic light regimes produced smaller, species-specific effects, influencing chlorophyll content and carbon storage primarily in T. antarctica. Correlation and z-score analyses demonstrated that Fe-rich photosynthetic proteins co-varied with biomass production, whereas photoprotective traits clustered independently, underscoring divergent energy-allocation strategies. Together, these results reveal how SO phytoplankton partition resources between productivity and photoprotection under shifting Fe-light regimes, providing mechanistic insight into their ecological niches.

Modern agriculture is characterized by substantial fertilizer nitrogen (N) losses from soils, resulting in low crop N-use efficiency. Biological nitrification inhibitors (BNIs) are studied as a strategy to improve N retention in soils by suppressing nitrification. However, the impacts of applying exogenous BNIs to crops with unknown intrinsic BNI capacity remain poorly understood. In this study, we evaluated the impacts of adding three BNIs (methyl 3-(4-hydroxyphenyl) acrylate [MHPA], 6-methoxy-2(3H)-benzoxazolone [MBOA], and limonene), their mixture, and the synthetic nitrification inhibitor 3,4-dimethylpyrazole phosphate (DMPP) on barley (Hordeum vulgare L.) growth, plant and soil N dynamics, and soil microbial communities. Using a rhizobox system with planted and bare-soil compartments, combined with 15N isotope tracing and molecular microbial community analyses, we assessed the spatio-temporal dynamics of N transformations, losses, plant N uptake, and microbial community responses in an alkaline agricultural soil. Independent of inhibitor application, the applied fertilizer N was lost primarily through NO- leaching (3-9% of the applied N). In contrast, N2O emissions represented only 0.001-0.028% of the applied N and varied with inhibitor type. MHPA increased dissolved inorganic N soil pools without affecting plant biomass or 15N uptake or strongly shifting microbial community composition. MBOA reduced NO3- concentrations in soil pore water without influencing plant growth or N uptake but shifted soil microbial community composition. In contrast, limonene reduced plant growth and 15N uptake and most significantly altered microbial community composition, without significantly changing N availability. Applying a BNI mixture, as well as limonene alone, was detrimental to plant growth and 15N uptake. DMPP showed only minor effects on N pools, plant growth, plant N uptake and microbial community composition. Overall, our results reveal both the potential and limitations of exogenous BNI application for improving N retention in crop systems.

Nutrient limitation is an important control on heterotrophic microbial activity that helps to stabilize the massive stocks of organic carbon held in ombrotrophic peatlands. Minerals contained in atmospheric dusts are critical nutrient sources for peatlands, yet the role of dust in supporting the below-ground microbial processes that underpin primary productivity is largely unknown. We investigated how mineral dust generated from mining waste rock (<20 {micro}m) influences element bioavailability and subsurface microbial functioning using flow-through soil mesocosms. The bioavailability of base cations (Ca, Mg, K), transition metals (Fe, Al, Ni, Cu), Al, and P was tracked over two months at three soil depths (0-6, 6-12, and 12-18 cm) using an extended sequential extraction method. We also analyzed microbial community composition (16S rRNA and ITS amplicon sequencing) and mineralization capacity (exoenzyme assays and carbon substrate incubations). After two months, the concentration of metals in the peat increased substantially after dust application, but the mobility and bioavailability varied by element. Responses of microbial communities to dust application were highly dependent on depth from the surface. Carbon substrate incubations revealed enhanced mineralization capabilities in soil from the surface zone (0-6 cm), but a relatively low stimulation of exoenzymes. Soil pH and phosphorus mobility were also impacted near the site of dust application, while acid phosphatase activity was lower throughout the column. In the middle zone (6-12 cm), the activities of {beta}-glucosidase, {beta}-xylosidase, and NAGase were higher with dust exposure. Measured microbial activity mostly remained unchanged in the lowest depth (12-18 cm). We observed increases in the relative abundances of putative saprotrophic fungi throughout the mesocosm profile. Results from this experiment show that the deposition and weathering of mineral dust can induce a complex set of changes to the capacity and nature of microbial carbon mineralization within a shallow layer of peat.