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Carnivorous plants obtain nutrients from arthropod prey (carnivory) and their environment. However, little is known about the seasonal diet shifts between carnivory versus environment nutrient acquisition among co‐occurring carnivorous plant species. Although studies reporting captured prey species for carnivorous plants are abundant, studies investigating the composition of assimilated prey species are scarce. Here, we report spatiotemporal dynamics in carnivory versus environmental nutrient acquisition and compositional analysis of assimilated prey species for carnivorous plants of New England (USA).We measured the natural abundance stable isotope ratios of aquatic Utricularia inflata (Lentibulariaceae), terrestrial Sarracenia purpurea (Sarraceniaceae) and Drosera intermedia (Droseraceae) and their nutrient sources during their growing season in two oligotrophic ponds in New England (USA). MixSIAR, a Bayesian stable isotope mixing model, was used to estimate the extent of carnivory for each plant species and the composition of prey species assimilated in terrestrial carnivorous plants.Aquatic U. inflata acquired more nutrients from carnivory (c. 70%–100%) than terrestrial species (c. 30–60%). Sarracenia purpurea acquired nutrients mainly from Formicidae. The nutrient sources for D. intermedia varied spatiotemporally between arthropod species.The large contribution of carnivory to the nutrient budget of U. inflata could be due to its lack of roots and high metabolism. Sarracenia purpurea and D. intermedia could benefit from dissolved organic nitrogen in the environment. Our findings on prey compositions can be used as the first available prior information for the Bayesian approach in future studies. Understanding the sources of nutrients in carnivorous plants provides invaluable insight into their ecophysiology and may inform the conservation of their fragile wetland ecosystems. [ABSTRACT FROM AUTHOR]

Background and Aims Freshwater nitrogen inputs are increasing globally, altering the structure and function of wetland ecosystems adapted to low nutrient conditions. Carnivorous wetland plants of the genus Utricularia are hypothesized to reduce their reliance on carnivory and increase their assimilation of environmental nutrients when the supply of ambient nutrients increases. Despite success in using stable isotope approaches to quantify carnivory of terrestrial carnivorous plants, quantifying carnivory of aquatic Utricularia requires improvement. Methods We developed stable isotope mixing models to quantify aquatic plant carnivory and used these models to measure dietary changes of three Utricularia species, Utricularia australis , U. gibba and U. uliginosa , in 11 wetlands across a 794-km gradient in eastern Australia. Diet was assessed using multiple models that compared variations in the natural-abundance nitrogen isotope composition (δ15N) of Utricularia spp. with that of non-carnivorous plants, and environmental and carnivorous nitrogen sources. Key Results Carnivory supplied 40–100 % of plant nitrogen. The lowest carnivory rates coincided with the highest availability of ammonium and dissolved organic carbon. Conclusions Our findings suggest that Utricularia populations may adapt to high nutrient environments by shifting away from energetically costly carnivory. This has implications for species conservation as anthropogenic impacts continue to affect global wetland ecosystems. [ABSTRACT FROM AUTHOR]

This study uses dual‐labeled (13C and 15N) stable isotope applications to examine microbial uptake and short‐term processing of carbon (C) and nitrogen (N) from organic and inorganic compounds in subtropical intertidal sediment. Four treatment applications were applied: (1) algal dissolved organic matter (DOM), (2) amino acid mixture, (3) glucose and NH4+, and (4) NaHCO3 and NH4+ to assess bioavailability effects on processing (1 vs. 2) and short‐term processing for OM fixed via microphytobenthos only (pennate diatom dominated) (4) vs. material taken up by the entire microbial community (3) across 24 h. 13C from algal‐DOM was preferentially used by the microbial community vs. 15N. At 24 h more 13C from algal‐DOM remained in microbial biomass indicating use of labeled precursor molecules to form biomass. Conversely, 13C from the amino acid treatment was not incorporated into biomass and was either rapidly respired to DIC or discarded as the in situ microbial community preferentially used and retained 15N from amino acids. Short‐term export of 13C as CO2 from glucose was lower than from microphytobenthos‐C, while retention of 15N from NH4+ was similar between treatments (3 and 4) despite doubling the application N concentration, suggesting potentially higher glucose‐stimulated 15N export via nitrification–denitrification that was not confirmed via flux measurements in this study. Despite careful site selection for similar tidal exposure and sediment types among the three estuaries, the uptake and processing of labeled substrate varied substantially between replicates and sites which challenged traditional statistical analysis. Disproportionate processing of substrates occurring in sediment hotspots of microbial activity can cause variability spanning orders of magnitude which was found to be widespread through comparison of our results against 19 previous studies in intertidal settings. Development of robust analytical techniques to handle variability from abiotic and biotic factors will allow greater clarity surrounding in situ biogeochemical processing in intertidal environments. [ABSTRACT FROM AUTHOR]

The composition and production of carbohydrates (mannose, rhamnose, fucose, galactose, glucose, and xylose) and their transfer among sediment compartments (microphytobenthos [MPB], bacteria, and detritus) was investigated through in situ labeling with [sup.13]C-bicarbonate. After 60 h, [sup.13]C was found in all sediment compartments, demonstrating rapid transfer of fixed carbon from autotrophs to heterotrophs. Carbohydrates were a major carbon reservoir, accounting for 30% (day 0) to 15% (day 30) of the [sup.13]C within sediments, and probably played a role in this transfer. Carbohydrate fractions were highly reactive (65-87%), less reactive (7-18%), and nonreactive (6-23%) over the experimental period. The rate of loss of the less reactive fraction (0.01-0.05 [d.sup.-1]) was at least an order of magnitude lower than that for the highly reactive fraction (0.8-4.4 [d.sup.-1]). Patterns of diagenesis estimated from label uptake and loss matched the carbohydrate composition observed in the sediment (glucose > galactose > rhamnose > fucose > xylose > mannose) and were similar to patterns reported previously. C : N ratios and [delta][sup.13]C of sediment organic matter indicated an algal origin (MPB and phytoplankton). Although carbon was rapidly processed, loss from sediments was not immediate, and there was evidence of recycling into MPB and bacteria. Rapid transfer of carbon to and from carbohydrates has been found in various environments, including temperate, muddy, and intertidal sediments, and this study demonstrates the important role of carbohydrates in supporting heterotrophic production over extended periods (> 30 d) in subtropical shallow subtidal sands. doi: 10.4319/lo.2010.55.5.2126

Estuaries make a disproportionately large contribution of dissolved organic carbon (DOC) to the global carbon cycle, but it is unknown how this will change under a future climate. As such, the response of DOC fluxes from microbially dominated unvegetated sediments to individual and combined future climate stressors of warming (from Δ-3 °C to Δ+5 °C on ambient mean temperatures) and ocean acidification (OA, ~2 times the current partial pressure of CO2, pCO2) was investigated ex situ. Warming alone increased sediment heterotrophy, resulting in a proportional increase in sediment DOC uptake, with sediments becoming net sinks of DOC (3.5 to 8.8 mmol-C m-2 d-1) at warmer temperatures (Δ+3 °C and Δ+5 °C, respectively). This temperature response changed under OA conditions, with sediments becoming more autotrophic and a greater sink of DOC (1 to 4 times greater than under current-pCO2). This response was attributed to the stimulation of heterotrophic bacteria with the autochthonous production of labile organic matter by microphytobenthos. Extrapolating these results to the global area of unvegetated subtidal estuarine sediments, the future climate of warming (Δ+3 °C) and OA may decrease the estuarine export of DOC by ~80 % (~150 Tg-C yr-1) and have a disproportionately large impact on the global DOC budget. [ABSTRACT FROM AUTHOR]

Shallow coastal waters in many regions are subject to nutrient enrichment. Microphytobenthos (MPB) can account for much of the carbon (C) fixation in these environments, depending on the depth of the water column, but the effect of enhanced nutrient availability on the processing and fate of MPB-derived C (MPB-C) is relatively unknown. In this study, MPB was labeled (stable isotope enrichment) in situ using 13C-sodium bicarbonate. The processing and fate of the newly fixed MPB-C was then traced using ex situ incubations over 3.5 days under different concentrations of nutrients (NH+ 4 and PO3- 4 : ambient, 2× ambient, 5× ambient, and 10× ambient). After 3.5 days, sediments incubated with increased nutrient concentrations (amended treatments) had increased loss of 13C from sediment organic matter (OM) as a portion of initial uptake (95% remaining in ambient vs. 79-93%for amended treatments) and less 13C in MPB (52% ambient, 26-49% amended), most likely reflecting increased turnover of MPB-derived C supporting increased production of extracellular enzymes and storage products. Loss of MPBderived C to the water column via dissolved organic C (DOC) was minimal regardless of treatment (0.4-0.6 %). Loss due to respiration was more substantial, with effluxes of dissolved inorganic C (DIC) increasing with additional nutrient availability (4% ambient, 6.6-19.8% amended). These shifts resulted in a decreased turnover time for algal C (419 days ambient, 134-199 days amended). This suggests that nutrient enrichment of estuaries may ultimately lead to decreased retention of carbon within MPB-dominated sediments. [ABSTRACT FROM AUTHOR]

Shallow coastal waters in many regions are subject to nutrient over-enrichment. Microphytobenthos (MPB) can account for much of the carbon (C) fixation in these environments, depending on the depth of the water column, but the effect of enhanced nutrient availability on the processing and fate of MPB-derived C is relatively unknown. In this study, MPB were labeled (stable isotope enrichment) in situ using 13C-sodium bicarbonate. The processing and fate of the newly-fixed MPB-C was then traced using ex situ incubations over 3.5 d under different concentrations of nutrients (NH4+ and PO43-: ambient, 2× ambient, 5× ambient, and 10× ambient). After 3.5 d, sediments incubated with increased nutrient concentrations (amended treatments) had increased loss of 13C from sediment organic matter as a portion of initial uptake (95 % remaining in ambient vs 79-93 % for amended treatments) and less 13C in MPB (52 % ambient, 26-49 % amended), most likely reflecting increased turnover of MPB-derived C supporting increased production of extracellular enzymes and storage products. Loss of MPB-derived C to the water column via dissolved organic C was minimal regardless of treatment (0.4-0.6 %). Loss due to respiration was more substantial, with effluxes of dissolved inorganic C increasing with additional nutrient availability (4 % ambient, 6.6-19.8 % amended). These shifts resulted in a decreased turnover time for algal C (419 d ambient, 134-199 d amended). This suggests that nutrient enrichment of estuaries may ultimately lead to decreased retention of carbon within MPB-dominated sediments. [ABSTRACT FROM AUTHOR]

Microphytobenthos (MPB) are an important nitrogen (N) sink in coastal systems, but little is known about the fate of this N after it has been assimilated. We used an in situ 15N pulse-chase experiment in subtidal sands to follow the assimilation, trophic transfer, transformation, and flux pathways of MPB-N over 33 d. Throughout the study MPB dominated 15N uptake, on average representing only 18.1% of the biomass but 63.9% of the 15N within 0-2 cm sediment. Following assimilation, 15N was rapidly transferred to deeper sediment, with 32.1% below 2 cm and 16.5% below 5 cm after 60 h. In contrast to MPB, bacteria represented 39.5% of sediment biomass but accounted for only up to 27.3% of assimilated 15N. Foraminifera accumulated and stored 15N more than bacteria; their contribution to the 15N remaining in 0-2 cm sediment at the end of the study was more than double their biomass contribution. Thirty-three days after the 15N was assimilated by MPB 27% remained in the sediment, 16.5% had been effluxed as [ABSTRACT FROM AUTHOR]