Limnology and Oceanography最新文献

{"title":"Gross oxygen production and microbial community respiration in the oligotrophic ocean","authors":"Sara Ferrón, Karin M. Björkman, Matthew J. Church, David M. Karl","doi":"10.1002/lno.70023","DOIUrl":"https://doi.org/10.1002/lno.70023","url":null,"abstract":"Uncertainties in the temporal and spatial patterns of marine primary production and respiration limit our understanding of the ocean carbon (C) cycle and our ability to predict its response to environmental changes. Here we present a comprehensive time‐series analysis of plankton metabolism at the Hawaii Ocean Time‐series program site, Station ALOHA, in the North Pacific Subtropical Gyre. Vertical profiles of gross oxygen production (GOP) and community respiration (CR) were quantified using the <jats:sup>18</jats:sup>O‐labeled water method together with net changes in O<jats:sub>2</jats:sub> to Ar ratios during dawn to dusk in situ incubations. Rates of <jats:sup>14</jats:sup>C‐bicarbonate assimilation (<jats:sup>14</jats:sup>C‐based primary production [<jats:sup>14</jats:sup>C‐PP]) were also determined concurrently. During the observational period (April 2015 to July 2020), euphotic zone depth‐integrated (0–125 m) GOP and <jats:sup>14</jats:sup>C‐PP ranged from 35 to 134 mmol O<jats:sub>2</jats:sub> m<jats:sup>−2</jats:sup> d<jats:sup>−1</jats:sup> and 18 to 75 mmol C m<jats:sup>−2</jats:sup> d<jats:sup>−1</jats:sup>, respectively, while CR ranged from 37 to 187 mmol O<jats:sub>2</jats:sub> m<jats:sup>−2</jats:sup> d<jats:sup>−1</jats:sup>. All biological rates varied with depth and season, with seasonality most pronounced in the lower portion of the euphotic zone (75–125 m). The mean annual ratio of GOP to <jats:sup>14</jats:sup>C‐PP was 1.7 ± 0.1 mol O<jats:sub>2</jats:sub> (mol C)<jats:sup>−1</jats:sup>. While previous studies have reported convergence of GOP and <jats:sup>14</jats:sup>C‐PP with depth, we find a less pronounced vertical decline in the GOP to <jats:sup>14</jats:sup>C‐PP ratios, with GOP exceeding <jats:sup>14</jats:sup>C‐PP by 50% or more in the lower euphotic zone. Variability in CR was higher than for GOP, driving most of the variability in the balance between the two.","PeriodicalId":18143,"journal":{"name":"Limnology and Oceanography","volume":"24 1","pages":""},"PeriodicalIF":4.5,"publicationDate":"2025-03-14","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143627459","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Cyclical prey abundance drives interannual variation in predator diel vertical movement","authors":"Jonathan B. Armstrong, Mark W. Buktenica, Scott F. Girdner, Eric J. Ward","doi":"10.1002/lno.70022","DOIUrl":"https://doi.org/10.1002/lno.70022","url":null,"abstract":"Diel vertical movement (DVM) is a widespread behavior in aquatic ecosystems, occurring across a variety of taxa and water bodies. The factors hypothesized to drive DVM can vary tremendously through time, yet little is known about how DVM changes at interannual timescales. Here we explore how cyclical prey abundance affects predator DVM. Higher consumption levels increase the optimal temperatures for growth in fishes. Thus, annual variation in prey abundance should generate corresponding variation in the depths and temperatures selected during predator DVM. In Crater Lake, one of the deepest and most oligotrophic lakes in the world, <jats:italic>Daphnia</jats:italic> zooplankton exhibit cyclical patterns of abundance. We compiled data spanning four distinct pulses of <jats:italic>Daphnia</jats:italic> and analyzed the response of their predator, kokanee salmon (<jats:italic>Oncorhynchus nerka</jats:italic>). Our data spanned 36 yr for <jats:italic>Daphnia</jats:italic> abundance and kokanee body condition, and 24 yr for kokanee DVM (measured by hydroacoustic surveys). Kokanee exhibited four pulses in body weight and condition that corresponded to the four <jats:italic>Daphnia</jats:italic> pulses, suggesting a strong bottom‐up response. Kokanee altered their DVM in years with <jats:italic>Daphnia</jats:italic> by occurring deeper during the day, where <jats:italic>Daphnia</jats:italic> were concentrated, and shallower at night, where temperatures were &gt; 5°C warmer. By selecting warmer habitat in years with <jats:italic>Daphnia</jats:italic>, kokanee increased their estimated overnight digestion by ~ 25%. Understanding how predators alter DVM and other patterns of cyclical habitat use in response to variation in prey abundance has important implications for understanding predator–prey dynamics, which are highly sensitive to prey encounter rates and maximum consumption rates.","PeriodicalId":18143,"journal":{"name":"Limnology and Oceanography","volume":"14 1","pages":""},"PeriodicalIF":4.5,"publicationDate":"2025-03-14","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143627458","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Daily Sun-induced chlorophyll fluorescence vs. irradiance curves reflect the photoadaptation of phytoplankton in surface waters","authors":"Yannick Huot,&nbsp;David Antoine,&nbsp;Vincenzo Vellucci","doi":"10.1002/lno.70001","DOIUrl":"10.1002/lno.70001","url":null,"abstract":"<p>Phytoplankton chlorophyll Sun-induced fluorescence is observable in the upwelling light field of the ocean. This allows its observation by radiometers in situ or on satellite sensors. Since it is influenced by both biomass and physiology it can potentially provide information about both. Since fluorescence yield is complementary to photosynthesis and heat in photosystem II, its observation throughout the day provides information on the response of phytoplankton to diel light cycles. Here we use a time series collected in the northwestern Mediterranean Sea (BOUSSOLE site) to extract photophysiological parameters of phytoplankton using the Sun-induced fluorescence and as well as with an active chlorophyll fluorometer. The daily resolved patterns are consistent with photoacclimation and photoadaptation processes and reflect seasonal variations of the mixed-layer average irradiance. We also show that fluorescence yields derived from satellite measurements (MODIS) at the same location are not correlated to these patterns, confirming the limited influence of photoacclimation and photoadaptation on the satellite-derived chlorophyll fluorescence yield near solar noon.</p>","PeriodicalId":18143,"journal":{"name":"Limnology and Oceanography","volume":"70 4","pages":"1001-1015"},"PeriodicalIF":3.8,"publicationDate":"2025-03-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://onlinelibrary.wiley.com/doi/epdf/10.1002/lno.70001","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143618453","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Responses of microbial communities and greenhouse gas production to land use change in mangrove wetland sediments","authors":"Xianbiao Lin, Bingqian Zhu, Yongyi Peng, Genmei Lin, Dongyao Sun, Wangwang Ye","doi":"10.1002/lno.70028","DOIUrl":"https://doi.org/10.1002/lno.70028","url":null,"abstract":"Tidal wetland reclamation is a worldwide issue that profoundly alters ecological functions and ecosystem service provisions; however, its impacts on sediment microbial communities and functions remain poorly understood. Here, we investigated the spatial and seasonal patterns of greenhouse gas (GHG) production in response to land use change in mangrove wetlands and elucidated the underlying mechanisms by integrating environmental parameters and microbial community characteristics. In the time period studied, land use change substantially reduced the sediment organic matter content, microbial community richness and diversity, and CO<jats:sub>2</jats:sub> production rates. Converting mangroves to drier land cover types, namely orchard and vegetable field, significantly diminished reducing substrates (sulfide, Fe<jats:sup>2+</jats:sup>, and NH<jats:sub>4</jats:sub><jats:sup>+</jats:sup>), microbial network complexity and stability, and CH<jats:sub>4</jats:sub> production rates, while increasing N<jats:sub>2</jats:sub>O production rates. In contrast, these parameters showed the opposite trend following the conversion of mangroves to flooded aquaculture pond. Overall GHG production rate in mangrove wetlands was 399.8 mg CO<jats:sub>2</jats:sub>e kg<jats:sup>−1</jats:sup> d<jats:sup>−1</jats:sup>, which respectively decreased by 68.83%, 69.86%, and 30.84% in orchard, vegetable field, and aquaculture pond. Microbial community richness and network complexity and stability were strongly related to the production rates of CH<jats:sub>4</jats:sub> and N<jats:sub>2</jats:sub>O, rather than CO<jats:sub>2</jats:sub>, which can be better indicators of specialized functions (CH<jats:sub>4</jats:sub> and N<jats:sub>2</jats:sub>O production). Therefore, preserving microbial “interaction” could be important to mitigate the negative effects of microbial community richness and diversity loss caused by human activities in aquatic environments. Future research should consider environmental conditions and microbial community diversity, composition, interactions, and activities to gain a comprehensive understanding of ecosystem functions.","PeriodicalId":18143,"journal":{"name":"Limnology and Oceanography","volume":"183 1","pages":""},"PeriodicalIF":4.5,"publicationDate":"2025-03-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143618452","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Autonomous observations enhance our ability to observe the biological carbon pump across diverse carbon export regimes","authors":"Shawnee Traylor, David P. Nicholson, Samantha J. Clevenger, Ken O. Buesseler, Eric D'Asaro, Craig M. Lee","doi":"10.1002/lno.70002","DOIUrl":"https://doi.org/10.1002/lno.70002","url":null,"abstract":"The expansion of autonomous observation platforms offers vast opportunities for analyzing ocean ecosystems and their role in carbon export. As part of the EXport Processes in the Ocean from RemoTe Sensing campaign, we autonomously measured the productivity regimes in two contrasting end‐member ecosystem states. The first campaign occurred in the subpolar North Pacific near Ocean Station Papa (Site 1), characterized by iron limitation and a highly regenerative regime. The second captured a springtime bloom in the North Atlantic (Site 2), which typically drives efficient export of productivity. Using a combination of floats and gliders carrying biogeochemical sensors, we quantified gross primary productivity, net community production, and organic carbon export potential (<jats:italic>f</jats:italic>C<jats:sub>org</jats:sub>) to assess biological carbon pump strength. Site 2 demonstrated higher cruise‐period productivity, with roughly 5× the gross primary productivity and 13× the euphotic zone net community production seen at Site 1. Greater export efficiency at Site 2 was reflected in numerous indices, such as the ratio of new production to net primary productivity (<jats:italic>ef</jats:italic>‐ratio; Site 1: 0.33; Site 2: 0.73), the ratio of sinking particulate organic carbon to net primary productivity (<jats:italic>ez</jats:italic>‐ratio; Site 1: 0.24; Site 2: 0.69), and mean daily <jats:italic>f</jats:italic>C<jats:sub>org</jats:sub> (Site 1: 3.4 ± 0.7; Site 2: 20.3 ± 2.3 mmol C m<jats:sup>−2</jats:sup> d<jats:sup>−1</jats:sup>). Together with particulate organic carbon flux derived from thorium‐234 measurements, we infer that observed low net community production was almost entirely routed to sinking particulate organic carbon at Site 1, while the much higher net community production at Site 2 resulted in near‐equal proportions routed to dissolved organic carbon production and sinking particulate organic carbon.","PeriodicalId":18143,"journal":{"name":"Limnology and Oceanography","volume":"11 1","pages":""},"PeriodicalIF":4.5,"publicationDate":"2025-03-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143607807","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Global satellite observations of marine phytoplankton pigments over the past two decades","authors":"Deyong Sun, Yuhang Chen, Zhenghao Li, Shengqiang Wang, Peng Chen, Yu Huan","doi":"10.1002/lno.70017","DOIUrl":"https://doi.org/10.1002/lno.70017","url":null,"abstract":"Documenting the variations of phytoplankton pigments is essential for understanding phytoplankton assemblages' dynamics and physiological characteristics in the global oceans. Advanced chlorophyll <jats:italic>a</jats:italic> satellite product has provided an overview of global phytoplankton biomass, yet deeper taxonomic biomass monitoring demands more detailed pigment information. In this study, we have collected 1562 in situ measured sea surface samples (depth &lt; 10 m) from 1997 to 2017 covering the global ocean, where the in situ dataset consists of pigment concentration and phytoplankton absorption coefficient (<jats:italic>a</jats:italic><jats:sub>ph</jats:sub>). A global semi‐analytical pigment model was developed using the Gaussian decomposition method and was evaluated by the leave‐one‐out cross validation method. Model accuracy verification based on in situ measurement (e.g., mean absolute percentage errors below ~ 67% for most pigments) and satellite synchronization dataset (e.g., most pigments have mean absolute percentage errors below ~ 70%) showed the reliable performance of the pigment model in the global oceans. We reconstructed the global hyperspectral phytoplankton absorption by the three‐component absorption model of the phytoplankton size class, enabling satellite application of the pigment model and obtaining the nearly 20‐yr spatiotemporal variations of 14 phytoplankton pigments. Global pigment concentrations exhibited a generally relatively unchanging pattern at the beginning of the 21<jats:sup>st</jats:sup> century, as evidenced by stable geographic distribution and temporal trends, while local environmental disturbances created anomalies in 1‐yr period. Our findings provide an effective model to detect global pigment concentration and essential satellite products for further analysis of phytoplankton assemblages.","PeriodicalId":18143,"journal":{"name":"Limnology and Oceanography","volume":"16 1","pages":""},"PeriodicalIF":4.5,"publicationDate":"2025-03-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143608179","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Algal food identity affects morphological anti‐predatory defense in Daphnia pulex","authors":"Carlos Sánchez Arcos, Yannick Hill, Sandra Klintworth, Eric von Elert","doi":"10.1002/lno.70018","DOIUrl":"https://doi.org/10.1002/lno.70018","url":null,"abstract":"Microcrustaceans of the genus <jats:italic>Daphnia</jats:italic> have evolved various inducible anti‐predator defenses; however, it is largely underexplored how the bottom‐up factor food quality may affect the extent of these defenses. A well‐studied example of an inducible defense is the deployment of neckteeth in <jats:italic>Daphnia pulex</jats:italic> in response to infochemicals from predatory larvae of <jats:italic>Chaoborus</jats:italic>, which prey on juvenile instars of <jats:italic>Daphnia</jats:italic>. In general, vulnerability depends on the body size in the respective juvenile <jats:italic>Daphnia</jats:italic> instars in relation to the mouth gape diameter of <jats:italic>Chaoborus</jats:italic> larvae. We hypothesized that algae that prolong the time in which juvenile animals remain in the vulnerable size also increase the predation risk and therefore increase the extent of induced neckteeth. To test this, we supplied three <jats:italic>D. pulex</jats:italic> genotypes with three food algae and quantified somatic growth rates, time in vulnerable instars, and neckteeth in response to <jats:italic>Chaoborus</jats:italic> infochemicals. Food algal identity affected the extent of induced neckteeth by up to 66%. However, this effect was not positively related to the time spent in vulnerable instars, indicating that the time that juveniles remain in a vulnerable size is not used to assess predation risk. We demonstrate that food identity may significantly affect the extent of induced neckteeth in <jats:italic>D. pulex</jats:italic> in a genotype‐dependent way. This strongly suggests that in nature, changing phytoplankton composition may affect the degree of morphological defense and thus constitutes a bottom‐up control of chemical predator–prey communication. This is another example of how environmental factors modulate the temporal dynamics of phenotypic plasticity.","PeriodicalId":18143,"journal":{"name":"Limnology and Oceanography","volume":"11 1","pages":""},"PeriodicalIF":4.5,"publicationDate":"2025-03-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143599350","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Multi‐trait responses in two marine diatoms to pH and irradiance reveal interactive effect of light and acidification, mediated by silicification","authors":"Billy FitzGerald‐Lowry, Daniel Aagren Nielsen, Rebecca Julianne Duncan, Alyson May Theseira, Georgia Thompson, Katherina Petrou","doi":"10.1002/lno.70014","DOIUrl":"https://doi.org/10.1002/lno.70014","url":null,"abstract":"Ocean ecosystem shifts in response to anthropogenic climate change are impacting marine organisms, including phytoplankton. Ocean acidification and warming represent two key threats to marine phytoplankton, causing significant changes to the upper mixed layer of the ocean, reshuffling their distribution, and reorganizing their physiology and metabolism. In this study, we investigated changes in biomolecular composition and silicification rates of the two “model” diatom species <jats:italic>Phaeodactylum tricornutum</jats:italic> and <jats:italic>Thalassiosira weissflogii</jats:italic> under low (~ 350) and projected future (~ 800) <jats:italic>p</jats:italic>CO<jats:sub>2</jats:sub> concentrations with low (20 <jats:italic>μ</jats:italic>mol photons m<jats:sup>−2</jats:sup> s<jats:sup>−1</jats:sup>) and high (200 <jats:italic>μ</jats:italic>mol photons m<jats:sup>−2</jats:sup> s<jats:sup>−1</jats:sup>) light, simulating expected climate change‐induced impacts of ocean shoaling and acidification. Specifically, our study conditions elicited changes in lipid and protein content in both species. We also found a negative effect of <jats:italic>p</jats:italic>CO<jats:sub>2</jats:sub> on silica production under high light in <jats:italic>T. weissflogii</jats:italic> that was linked to improved photochemical efficiency. This interactive effect between light and <jats:italic>p</jats:italic>CO<jats:sub>2</jats:sub> with silica production suggests a potential controlling role of the frustule in diatom photosynthesis and photoprotection (energy balance). Based on these data, ocean shoaling and acidification have the potential to influence the nutritional value and biogeochemical role of diatoms through its effect on diatom frustule synthesis and photobiology.","PeriodicalId":18143,"journal":{"name":"Limnology and Oceanography","volume":"86 1","pages":""},"PeriodicalIF":4.5,"publicationDate":"2025-03-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143599352","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Predicting river ecosystem metabolism across large environmental gradients: Drivers and temporal dependencies in the Iberian Peninsula","authors":"Amaia A. Rodeles, Francisco J. Peñas, Maite Arroita, José Barquín","doi":"10.1002/lno.70019","DOIUrl":"https://doi.org/10.1002/lno.70019","url":null,"abstract":"River ecosystem metabolism plays a significant role in the global carbon cycle. However, the limited spatial or temporal scale of most river metabolism studies hinders our ability to draw general patterns, identify common drivers, and make reliable global predictions. We developed Random Forest models for predicting daily metabolism rates using a large database of more than 100 river reaches across the Iberian Peninsula covering a large environmental gradient. As potential drivers, we included static variables (e.g., catchment area, distance to the sea), anthropogenic factors (e.g., land uses), and short‐term dynamic variables (e.g., light, water temperature, discharge) averaged over different periods (from 0 to 40 d) to explore the role of shorter vs. longer‐term environmental control on daily river metabolism rates. Both daily gross primary production and ecosystem respiration rates responded more strongly to average environmental conditions over the previous 40 d than to daily values. The 40‐d average random forest models explained up to 77% of gross primary production and 82% of ecosystem respiration variance. The most important drivers of GPP were stage (depth), distance to the sea, and light, while the main predictors of ER were stage and GPP. Dynamic variables were generally the most important drivers of daily metabolic rates, although static ones such as distance to the sea also played a role. Our results indicate that temporal patterns in river metabolism are influenced by a combination of environmental conditions integrated over several weeks, seasonal timing, and to a lesser extent, topology.","PeriodicalId":18143,"journal":{"name":"Limnology and Oceanography","volume":"36 1","pages":""},"PeriodicalIF":4.5,"publicationDate":"2025-03-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143599551","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Molecular activity mediates the composition and assembly of dissolved organic matter in lake sediments","authors":"Shuailong Wen, Ang Hu, Francisco Dini‐Andreote, Lei Han, Shuyu Jiang, Kyoung‐Soon Jang, Jianjun Wang","doi":"10.1002/lno.70015","DOIUrl":"https://doi.org/10.1002/lno.70015","url":null,"abstract":"Lake sediments are hotspots for carbon transformation and burial, where the turnover of dissolved organic matter (DOM), influenced by molecular activity, regulates global carbon cycling. However, the composition of sediment DOM and how its assembly mechanisms are related to molecular activity remain poorly understood. Here, 63 freshwater sediments were collected from tropical to cold temperate climatic zones in China. We explored the molecular composition and assembly of sediment DOM and the underlying mechanisms driven by climate, physicochemical factors, and microbes along the gradient of molecular activity, indicated by the number of potential biochemical transformations in which a molecule is involved. Sediment DOM was dominated by lipid‐ (35%) and lignin‐like compounds (33%), and the latter were enriched as the molecular activity of DOM increased. Besides, the DOM assemblage with higher potential biochemical transformations had greater compositional similarity across different climatic zones and tended to assemble deterministically. Specifically, as the average number of potential biochemical transformations of molecules increased from 0.4 to 14, the assembly of these molecules was structured by a shift from stochastic to deterministic processes, with the latter accounting for ≥ 75% thereafter. Overall, DOM assemblages were primarily structured by physicochemical factors, including sediment total organic carbon and electrical conductivity. As molecular activity increased, however, assemblages were increasingly affected by climate and bacterial communities, consistent with the enhanced complexity of bacterial–molecular networks. Collectively, our study highlights that the turnover of DOM regulated by biotic and abiotic factors is further constrained by the intrinsic molecular activity.","PeriodicalId":18143,"journal":{"name":"Limnology and Oceanography","volume":"20 1","pages":""},"PeriodicalIF":4.5,"publicationDate":"2025-03-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143599349","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}