Humic acid (HA) and phosphate interactions play a vital role in the biogeochemical cycle of carbo... more Humic acid (HA) and phosphate interactions play a vital role in the biogeochemical cycle of carbon and nutrients and thus the trophic state of a lake. The adsorption behavior of HAs to sediments in the absence and presence of phosphate was investigated in this study. Three types of HAs were used, AHA from algae-dominated lake sediments, MHA from macrophyte-dominated lake sediments, and a reference HA (RHA) with terrestrial sources. The adsorption capacity of lake sediments was highest for AHA, which can be explained by that AHA contained more carboxyl-containing molecules, proteinaceous compounds and polysaccharides that were preferentially adsorbed by minerals. Phosphate showed a stronger inhibitory effect on MHA adsorption than on AHA adsorption, suggesting that AHA can more effectively replace phosphate adsorbed to sediments. Our findings show that the functional groups of organic compounds control not only their fractionation and burial but also their ability to replace phosphate in sediments. We propose a novel mechanism to explain the legacy effect of lake eutrophication. That is, as lakes shift from a macrophyte-dominated state to more eutrophic, algae-dominated state, increasing algae-derived organic compounds can promote the release of phosphate from sediments, forming a positive feedback loop that sustains internal phosphorus loading and hence lake eutrophication.
Lakes are hotspots of dissolved organic matter (DOM) degradation and play an active role in carbo... more Lakes are hotspots of dissolved organic matter (DOM) degradation and play an active role in carbon cycles. Alpine lakes are under the most immediate impacts of climate change and act as sentinels of alpine ecosystem’s response to global warming, yet the primary environmental drivers of DOM variability in alpine lakes remain unidentified. Here, we sampled and analyzed DOM from 25 alpine lakes (>4,000 m above mean sea level) across the Tibetan Plateau. We found that the water residence time (WRT) of lakes and mean annual temperature (MAT) accounted for 30%–59% of the variance in the abundance of chromophoric DOM (CDOM) and fluorescent DOM (FDOM). Both CDOM and FDOM decreased with increasing WRT and MAT. Molecular‐level analysis of selected DOM samples showed that a higher WRT corresponded to DOM with lower molecular intensities, lower proportions of aromatics, lower oxidized compounds, and higher proportions of reduced and nitrogen‐containing compounds. These results indicate that in‐lake DOM processing dominated the regional variability of CDOM and FDOM. Under the scenario of climate warming and lake enlargement due to increasing precipitation and glacier melting, increased amount of DOM could be processed and removed from Tibetan lakes. Our findings are the first that identified WRT as a significant predictor of the amount of various DOM pools in Tibetan lakes and this observation may be broadly applicable to alpine lakes since they share similar DOM source‐sink characteristics. The simple empirical models (DOM vs. WRT + MAT) established here can be integrated into more sophisticated numerical models in predicting changes in the carbon cycle of alpine lakes.
Dysregulation of the developmental gene anterior gradient protein 2 (AGR2) has been associated wi... more Dysregulation of the developmental gene anterior gradient protein 2 (AGR2) has been associated with a metastatic phenotype, but its mechanism of action and control in prostate cancers is unknown. In this study, we show that overexpression of AGR2 promotes the motility and invasiveness of nonmetastatic LNCaP tumor cells, whereas silencing of AGR2 in the metastatic derivative C4-2B blocks invasive behavior. ErbB3 binding protein 1 (EBP1), a putative repressor of AGR2, is attenuated in prostate cancer. We show that the anti-invasive effect of EBP1 occurs, at least in part, through its ability to inhibit AGR2 expression. Mechanistic investigations indicate that EBP1 downregulates Foxa1- and Foxa2-stimulated AGR2 transcription and decreases metastatic behavior. In contrast, EBP1 ablation upregulates AGR2 via Foxa1- and Foxa2-stimulated AGR2 promoter activity and increases metastatic behavior. In both prostate cell lines and primary tumors, we documented an inverse correlation between EBP...
The Frasnian–Famennian (F–F) boundary is characterized by worldwide depositions of organic-rich s... more The Frasnian–Famennian (F–F) boundary is characterized by worldwide depositions of organic-rich strata, a series of marine anoxia events and one of the biggest five mass extinction events of the Phanerozoic. Due to the enhanced burial of organic matter, a coeval positive carbon isotope (δ 13 C) excursion occurred around the F–F boundary, raising questions about carbon cycle feedbacks during the mass extinction. In this study, we test the hypothesis that enhanced burial organic carbon during the F–F mass extinction led to the rise of paleo-wildfire occurrences. Here, we reconstructed paleo-wildfire changes across the F–F boundary via analyzing fossil charcoal (inertinites) and pyrogenic polycyclic aromatic hydrocarbons (PAHs) from an Upper Devonian Chattanooga Shale in the southern Appalachian Basin. Our data show low abundances of inertinites and pyrogenic PAHs before the F–F transition and an increasing trend during the F–F transition, followed by a sustained enhancement through th...
AbstractNitrate-nitrogen (nitrate) pollution remains one of the most common causes of surface wat... more AbstractNitrate-nitrogen (nitrate) pollution remains one of the most common causes of surface water quality degradation. Previous studies explored the fractal scaling behavior of controlling factor...
Streams in the southeastern United States Coastal Plains serve as an essential source of energy a... more Streams in the southeastern United States Coastal Plains serve as an essential source of energy and nutrients for important estuarine ecosystems, and dissolved organic matter (DOM) exported from these streams can have profound impacts on the biogeochemical and ecological functions of fluvial networks. Here, we examined hydrological and temperature controls of DOM during low-flow periods from a forested stream located within the Coastal Plain physiographic region of Alabama, USA. We analyzed DOM via combining dissolved organic carbon (DOC) analysis, fluorescence excitation–emission matrix combined with parallel factor analysis (EEM-PARAFAC), and microbial degradation experiments. Four fluorescence components were identified: terrestrial humic-like DOM, microbial humic-like DOM, tyrosine-like DOM, and tryptophan-like DOM. Humic-like DOM accounted for ~70% of total fluorescence, and biodegradation experiments showed that it was less bioreactive than protein-like DOM that accounted for ...
Biogeochemical cycling has often been characterized by physical and microbial processes, yet anim... more Biogeochemical cycling has often been characterized by physical and microbial processes, yet animals can be essential mediators of energy and nutrients in ecosystems. Excretion by aggregated animals can be an important local source of inorganic nutrients in green food webs, however, whether animals are a source of dissolved energy that can support brown food webs is understudied. We tested whether animal aggregations are a substantial flux of bioavailable dissolved organic matter (DOM) by studying spatially stable, biogeochemical hotspots formed by filter-feeding freshwater mussels. We used parallel-factor analysis to quantify DOM fluorescent components composition of mussel excretion and expected digestive breakdown of particulate food sources would lead to excretion of labile DOM. Next, we combined measured excretion rates of DOM, ammonium (NH4+, N), and phosphorous (SRP; P) for 22 species with biomass estimates for 14 aggregations to quantify contributions of DOM, N, and P to local availability. Because mussels occupy distinct stoichiometric niches, we anticipated that differences in species biomass and assemblage structure would elicit different flux and stoichiometries of aggregate excretion. Aggregate dissolved organic carbon (DOC) excretion was minor (1-11%) compared to N (12-2860%) and P (1-97%), yet generalities across assemblages emerged regarding organic matter transformation by mussels towards labile protein-like compounds compared to abundant aromatic, humic compounds in ambient water. Aggregate excretion of labile DOM was a substantial pool of bioavailable energy, contributing 2 – 114% of local labile DOM. Spatial differences in assemblage structure led to strong differences in aggregate flux and stoichiometry driven by biomass and stoichiometric trait expression of species with contrasting dominance patterns. Under the nutrient conditions of our study (high C:nutrient), biogeochemical hotspots associated with low-trophic position animal biomass may indirectly control energy flow to the brown food w [...]
Humic acid (HA) and phosphate interactions play a vital role in the biogeochemical cycle of carbo... more Humic acid (HA) and phosphate interactions play a vital role in the biogeochemical cycle of carbon and nutrients and thus the trophic state of a lake. The adsorption behavior of HAs to sediments in the absence and presence of phosphate was investigated in this study. Three types of HAs were used, AHA from algae-dominated lake sediments, MHA from macrophyte-dominated lake sediments, and a reference HA (RHA) with terrestrial sources. The adsorption capacity of lake sediments was highest for AHA, which can be explained by that AHA contained more carboxyl-containing molecules, proteinaceous compounds and polysaccharides that were preferentially adsorbed by minerals. Phosphate showed a stronger inhibitory effect on MHA adsorption than on AHA adsorption, suggesting that AHA can more effectively replace phosphate adsorbed to sediments. Our findings show that the functional groups of organic compounds control not only their fractionation and burial but also their ability to replace phosphate in sediments. We propose a novel mechanism to explain the legacy effect of lake eutrophication. That is, as lakes shift from a macrophyte-dominated state to more eutrophic, algae-dominated state, increasing algae-derived organic compounds can promote the release of phosphate from sediments, forming a positive feedback loop that sustains internal phosphorus loading and hence lake eutrophication.
Lakes are hotspots of dissolved organic matter (DOM) degradation and play an active role in carbo... more Lakes are hotspots of dissolved organic matter (DOM) degradation and play an active role in carbon cycles. Alpine lakes are under the most immediate impacts of climate change and act as sentinels of alpine ecosystem’s response to global warming, yet the primary environmental drivers of DOM variability in alpine lakes remain unidentified. Here, we sampled and analyzed DOM from 25 alpine lakes (>4,000 m above mean sea level) across the Tibetan Plateau. We found that the water residence time (WRT) of lakes and mean annual temperature (MAT) accounted for 30%–59% of the variance in the abundance of chromophoric DOM (CDOM) and fluorescent DOM (FDOM). Both CDOM and FDOM decreased with increasing WRT and MAT. Molecular‐level analysis of selected DOM samples showed that a higher WRT corresponded to DOM with lower molecular intensities, lower proportions of aromatics, lower oxidized compounds, and higher proportions of reduced and nitrogen‐containing compounds. These results indicate that in‐lake DOM processing dominated the regional variability of CDOM and FDOM. Under the scenario of climate warming and lake enlargement due to increasing precipitation and glacier melting, increased amount of DOM could be processed and removed from Tibetan lakes. Our findings are the first that identified WRT as a significant predictor of the amount of various DOM pools in Tibetan lakes and this observation may be broadly applicable to alpine lakes since they share similar DOM source‐sink characteristics. The simple empirical models (DOM vs. WRT + MAT) established here can be integrated into more sophisticated numerical models in predicting changes in the carbon cycle of alpine lakes.
Dysregulation of the developmental gene anterior gradient protein 2 (AGR2) has been associated wi... more Dysregulation of the developmental gene anterior gradient protein 2 (AGR2) has been associated with a metastatic phenotype, but its mechanism of action and control in prostate cancers is unknown. In this study, we show that overexpression of AGR2 promotes the motility and invasiveness of nonmetastatic LNCaP tumor cells, whereas silencing of AGR2 in the metastatic derivative C4-2B blocks invasive behavior. ErbB3 binding protein 1 (EBP1), a putative repressor of AGR2, is attenuated in prostate cancer. We show that the anti-invasive effect of EBP1 occurs, at least in part, through its ability to inhibit AGR2 expression. Mechanistic investigations indicate that EBP1 downregulates Foxa1- and Foxa2-stimulated AGR2 transcription and decreases metastatic behavior. In contrast, EBP1 ablation upregulates AGR2 via Foxa1- and Foxa2-stimulated AGR2 promoter activity and increases metastatic behavior. In both prostate cell lines and primary tumors, we documented an inverse correlation between EBP...
The Frasnian–Famennian (F–F) boundary is characterized by worldwide depositions of organic-rich s... more The Frasnian–Famennian (F–F) boundary is characterized by worldwide depositions of organic-rich strata, a series of marine anoxia events and one of the biggest five mass extinction events of the Phanerozoic. Due to the enhanced burial of organic matter, a coeval positive carbon isotope (δ 13 C) excursion occurred around the F–F boundary, raising questions about carbon cycle feedbacks during the mass extinction. In this study, we test the hypothesis that enhanced burial organic carbon during the F–F mass extinction led to the rise of paleo-wildfire occurrences. Here, we reconstructed paleo-wildfire changes across the F–F boundary via analyzing fossil charcoal (inertinites) and pyrogenic polycyclic aromatic hydrocarbons (PAHs) from an Upper Devonian Chattanooga Shale in the southern Appalachian Basin. Our data show low abundances of inertinites and pyrogenic PAHs before the F–F transition and an increasing trend during the F–F transition, followed by a sustained enhancement through th...
AbstractNitrate-nitrogen (nitrate) pollution remains one of the most common causes of surface wat... more AbstractNitrate-nitrogen (nitrate) pollution remains one of the most common causes of surface water quality degradation. Previous studies explored the fractal scaling behavior of controlling factor...
Streams in the southeastern United States Coastal Plains serve as an essential source of energy a... more Streams in the southeastern United States Coastal Plains serve as an essential source of energy and nutrients for important estuarine ecosystems, and dissolved organic matter (DOM) exported from these streams can have profound impacts on the biogeochemical and ecological functions of fluvial networks. Here, we examined hydrological and temperature controls of DOM during low-flow periods from a forested stream located within the Coastal Plain physiographic region of Alabama, USA. We analyzed DOM via combining dissolved organic carbon (DOC) analysis, fluorescence excitation–emission matrix combined with parallel factor analysis (EEM-PARAFAC), and microbial degradation experiments. Four fluorescence components were identified: terrestrial humic-like DOM, microbial humic-like DOM, tyrosine-like DOM, and tryptophan-like DOM. Humic-like DOM accounted for ~70% of total fluorescence, and biodegradation experiments showed that it was less bioreactive than protein-like DOM that accounted for ...
Biogeochemical cycling has often been characterized by physical and microbial processes, yet anim... more Biogeochemical cycling has often been characterized by physical and microbial processes, yet animals can be essential mediators of energy and nutrients in ecosystems. Excretion by aggregated animals can be an important local source of inorganic nutrients in green food webs, however, whether animals are a source of dissolved energy that can support brown food webs is understudied. We tested whether animal aggregations are a substantial flux of bioavailable dissolved organic matter (DOM) by studying spatially stable, biogeochemical hotspots formed by filter-feeding freshwater mussels. We used parallel-factor analysis to quantify DOM fluorescent components composition of mussel excretion and expected digestive breakdown of particulate food sources would lead to excretion of labile DOM. Next, we combined measured excretion rates of DOM, ammonium (NH4+, N), and phosphorous (SRP; P) for 22 species with biomass estimates for 14 aggregations to quantify contributions of DOM, N, and P to local availability. Because mussels occupy distinct stoichiometric niches, we anticipated that differences in species biomass and assemblage structure would elicit different flux and stoichiometries of aggregate excretion. Aggregate dissolved organic carbon (DOC) excretion was minor (1-11%) compared to N (12-2860%) and P (1-97%), yet generalities across assemblages emerged regarding organic matter transformation by mussels towards labile protein-like compounds compared to abundant aromatic, humic compounds in ambient water. Aggregate excretion of labile DOM was a substantial pool of bioavailable energy, contributing 2 – 114% of local labile DOM. Spatial differences in assemblage structure led to strong differences in aggregate flux and stoichiometry driven by biomass and stoichiometric trait expression of species with contrasting dominance patterns. Under the nutrient conditions of our study (high C:nutrient), biogeochemical hotspots associated with low-trophic position animal biomass may indirectly control energy flow to the brown food w [...]
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